title: Spider-Man in film

text: Michael Keaton reprises his "Spider-Man: Homecoming" role as Adrian Toomes / Vulture during the post-credits scenes in "Morbius". Following the casting of Doctor Strange's second spell permanently erasing the world's knowledge of Peter Parker's civilian identity, Toomes is accidentally transported from the MCU to the SSU, ending up in a vacated prison cell in the latter universe. Upon being released immediately due to lacking a criminal record in the new universe, Toomes begins to surmise Spider-Man's involvement in his displacement. He soon constructs a new Vulture suit and arranges to meet Dr. Michael Morbius, to whom he proposes they form a team.


title: Spider-Man in film

text: On May 31, 2010, an animated 4D film, titled "Marvel Super Heroes 4D", was launched at Madame Tussauds London, featuring Spider-Man and Iron Man leading the Avengers against Doctor Doom. On April 26, 2012, an updated version of the film with a different plot, featuring Spider-Man in a diminished capacity, was opened at Madame Tussauds New York. The film features Tom Kenny as the voice of Peter Parker / Spider-Man.


title: Spider-Man in film

text: At Comic-Con 2013, Dan Buckley, president of Marvel Worldwide, Inc announced the development of a crossover television film of the animated series "Phineas and Ferb", that would feature characters from Marvel Entertainment. The film aired between August 16–25, 2013 on Disney Channel and Disney XD, featuring Drake Bell reprising his role from "Ultimate Spider-Man" and "Avengers Assemble" as Peter Parker / Spider-Man, alongside Danny Trejo as Venom.


title: Spider-Man in film

text: Stan Lee, one of the co-creators of Spider-Man, appeared in varied cameos in all films from the Raimi-trilogy to "Into the Spider-Verse". Bruce Campbell, a long-time colleague of Sam Raimi, appeared in all three of his films. In "Spider-Man", he was the announcer at the wrestling ring Peter was in and gave him the name "Spider-Man", instead of the "Human Spider" (the name with which Peter wanted to be introduced). In "Spider-Man 2", he was an usher who refuses to let Peter enter the theatre for Mary Jane's play when arriving late. In "Spider-Man 3", Campbell appears as a French maître d'. In the ultimately unmade "Spider-Man 4", Campbell's character would have been revealed as Quentin Beck / Mysterio. Mysterio would later appear in "" (2019) played by Jake Gyllenhaal.


title: Spider-Man in film

text: The Sam Raimi trilogy was released on DVD, the first two being released exclusively as two-disc sets and on VHS, with the third film being released in both single and two-disc editions. All three films were later packaged in a "Motion Picture DVD Trilogy" box set.


title: Spider-Man in film

text: "Spider-Man 3" was initially the only "Spider-Man" film to be released individually on the high-definition Blu-ray format. The first two films were made available on Blu-ray, but only as part of a boxed set with the third film, called "Spider-Man: The High-Definition Trilogy". The first two films lacked the bonus features from the DVDs, although "Spider-Man 2" did contain both cuts of the film.


title: Spider-Man in film

text: Sony re-released the three films on June 12, 2012. The DVDs of the first two films reinstated a selection of the bonus features missing from the earlier Blu-ray releases, although the "Spider-Man 3" reissue did not include the bonus disc of additional special features that appeared on earlier Blu-ray releases.


title: Spider-Man in film

text: "The Amazing Spider-Man 2" became the first Spider-Man movie released on Ultra HD Blu-ray on March 1, 2016. Sony released the home video release of "Homecoming" on UHD and other home video formats on October 17, 2017, as well as sets featuring all of their other Spider-Man movies on UHD. This included "Spider-Man": Limited Edition Collection, which includes all three Raimi films, and "The Amazing Spider-Man": Limited Edition Collection, which includes both Webb films.


title: Spider-Man in film

text: All three films of the Raimi-trilogy set opening day records in North America. The "Spider-Man" films are among the top of North American rankings of , with "Spider-Man: No Way Home" ranking 2nd, "Spider-Man" ranking 10th, "Spider-Man: Far From Home" ranking 11th, "Spider-Man 2" ranking 13th, "Spider-Man 3" ranking 15th, and "Spider-Man: Homecoming" ranking 16th. In North America, "Spider-Man: No Way Home", "Spider-Man", "Spider-Man: Far From Home", "Spider-Man 2", "Spider-Man 3" and "Spider-Man: Homecoming" are ranked 2nd, 14th, 15th, 17th, 19th, and 22nd for all superhero films. Worldwide, "Spider-Man: No Way Home", "Spider-Man: Far From Home", "Spider-Man 3", and "Spider-Man: Homecoming" are ranked 3rd, 11th, 16th, and 17th for all superhero films. The Raimi-trilogy and the MCU films ("Homecoming", "Far From Home", and "No Way Home") are six of the seven most successful films produced by Sony/Columbia Pictures in North America, with "No Way Home" becoming Sony's highest-grossing film both in North America and worldwide.


title: Spider-Man in film

text: David Ansen of "Newsweek" enjoyed "Spider-Man" as a fun film to watch, though he considered "Spider-Man 2" to be "a little too self-important for its own good." Ansen saw "Spider-Man 3" as a return to form, finding it "the most grandiose chapter and the nuttiest." Tom Charity of CNN appreciated the films' "solidly redemptive moral convictions", also noting the vast improvement of the visual effects from the first film to the third. While he saw the second film's Doc Ock as the "most engaging" villain, he applauded the third film's Sandman as "a triumph of CGI wizardry." Richard Corliss of "Time" enjoyed the action of the films and thought that they did better than most action movies by "rethinking the characters, the franchise and the genre."


title: Spider-Man in film

text: Colin Covert of the "Star Tribune" praised "Spider-Man" as a "superb debut" of the superhero as well as "Spider-Man 2" as a "superior sequel" for filmgoers who are fans "of spectacle and of story." Covert expressed disappointment in "Spider-Man 3" as too ambitious with the multiple storylines leaving one "feeling overstuffed yet shortchanged." Manohla Dargis of "The New York Times" enjoyed the humor of the first two films, but found it missing in the third installment. Dargis also noted, "The bittersweet paradox of this franchise is that while the stories have grown progressively less interesting the special effects have improved tremendously." Robert Denerstein of the "Rocky Mountain News" ranked the films from his favorite to his least favorite: "Spider-Man 2", "Spider-Man", and "Spider-Man 3". While Denerstein missed the presence of Alfred Molina as Doctor Octopus from the second film, he found the third film – despite being "bigger, though not necessarily better" – to have a "satisfying conclusion."


Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by excessive amounts of inattention, hyperactivity, and impulsivity that are pervasive, impairing in multiple contexts, and otherwise age-inappropriate.


title: Attention deficit hyperactivity disorder

text: ADHD symptoms arise from executive dysfunction, and emotional dysregulation is often considered a core symptom. In children, problems paying attention may result in poor school performance. ADHD is associated with other neurodevelopmental and mental disorders as well as some non-psychiatric disorders, which can cause additional impairment, especially in modern society. Although people with ADHD struggle to focus on tasks they are not particularly interested in completing, they are often able to maintain an unusually prolonged and intense level of attention for tasks they do find interesting or rewarding; this is known as hyperfocus.


text: The precise causes of ADHD are unknown in the majority of cases. Genetic factors play an important role; ADHD tends to run in families and has a heritability rate of 74%. Toxins and infections during pregnancy and brain damage may be environmental risks.


text: It affects about 5–7% of children when diagnosed via the DSM-IV criteria, and 1–2% when diagnosed via the ICD-10 criteria. Rates are similar between countries and differences in rates depend mostly on how it is diagnosed. ADHD is diagnosed approximately twice as often in boys than in girls, and 1.6 times more often in men than in women, although the disorder is overlooked in girls or diagnosed in later life because their symptoms sometimes differ from diagnostic criteria. About 30–50% of people diagnosed in childhood continue to have ADHD in adulthood, with 2.58% of adults estimated to have ADHD which began in childhood. In adults, hyperactivity is usually replaced by inner restlessness, and adults often develop coping skills to compensate for their impairments. The condition can be difficult to tell apart from other conditions, as well as from high levels of activity within the range of normal behavior. ADHD has a negative impact on patients' health related quality of life and that this may be further exacerbated by, or may increase the risk of, other psychiatric conditions such as anxiety and depression.


text: ADHD management recommendations vary and usually involve some combination of medications, counseling, and lifestyle changes. The British guideline emphasises environmental modifications and education for individuals and carers about ADHD as the first response. If symptoms persist, parent-training, medication, or psychotherapy (especially cognitive behavioral therapy) can be recommended based on age. Canadian and American guidelines recommend medications and behavioral therapy together, except in preschool-aged children for whom the first-line treatment is behavioral therapy alone. Stimulant medications are the most effective pharmaceutical treatment, although there may be side effects and any improvements will be reverted if medication is ceased.


text: ADHD, its diagnosis, and its treatment have been considered controversial since the 1970s. These controversies have involved doctors, teachers, policymakers, parents, and the media. Topics have included causes of ADHD and the use of stimulant medications in its treatment. ADHD is now a well-validated clinical diagnosis in children and adults, and the debate in the scientific community mainly centers on how it is diagnosed and treated. ADHD was officially known as attention deficit disorder (ADD) from 1980 to 1987; prior to the 1980s, it was known as hyperkinetic reaction of childhood. Symptoms similar to those of ADHD have been described in medical literature dating back to the 18th century.


text: Inattention, hyperactivity (restlessness in adults), disruptive behavior, and impulsivity are common in ADHD. Academic difficulties are frequent as are problems with relationships. The symptoms can be difficult to define, as it is hard to draw a line at where normal levels of inattention, hyperactivity, and impulsivity end and significant levels requiring interventions begin.


text: According to the fifth edition of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-5) and its text revision (DSM-5-TR), symptoms must be present for six months or more to a degree that is much greater than others of the same age. This requires at least six symptoms of either inattention or hyperactivity/impulsivity for those under 17 and at least five symptoms for those 17 years or older. The symptoms must be present in at least two settings (e.g., social, school, work, or home), and must directly interfere with or reduce quality of functioning. Additionally, several symptoms must have been present before age twelve.


text: The table "Symptoms" lists the symptoms for ADHD-I and ADHD-HI from two major classification systems. Symptoms which can be better explained by another psychiatric or medical condition which an individual has are not considered to be a symptom of ADHD for that person.


text: Girls and women with ADHD tend to display fewer hyperactivity and impulsivity symptoms but more symptoms of inattention and distractibility.


text: Symptoms are expressed differently and more subtly as the individual ages. Hyperactivity tends to become less overt with age and turns into inner restlessness, difficulty relaxing or remaining still, talkativeness or constant mental activity in teens and adults with ADHD. Impulsivity in adulthood may appear as thoughtless behaviour, impatience, irresponsible spending and sensation-seeking behaviours, while inattention may appear as becoming easily bored, difficulty with organization, remaining on task and making decisions, and sensitivity to stress.


text: Although not listed as an official symptom for this condition, emotional dysregulation or mood lability is generally understood to be a common symptom of ADHD. People with ADHD of all ages are more likely to have problems with social skills, such as social interaction and forming and maintaining friendships. This is true for all presentations. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. People with attention deficits are prone to having difficulty processing verbal and nonverbal language which can negatively affect social interaction. They also may drift off during conversations, miss social cues, and have trouble learning social skills.


text: Difficulties managing anger are more common in children with ADHD as are delays in speech, language and motor development. Poorer handwriting is more common in children with ADHD. Poor handwriting in many situations can be a side effect of ADHD in itself due to decreased attentiveness but when it's a constant problem it may also be in part due to both Dyslexic and Dysgraphic individuals having higher rates of ADHD than the general population, with 3 in 10 people who have dyslexia also having ADHD. Although it causes significant difficulty, many children with ADHD have an attention span equal to or greater than that of other children for tasks and subjects they find interesting.


text: Other neurodevelopmental conditions are common comorbidities. Autism spectrum disorder (ASD), co-occurring at a rate of 21% in those with ADHD, affects social skills, ability to communicate, behaviour, and interests. Both ADHD and ASD can be diagnosed in the same person. Learning disabilities have been found to occur in about 20–30% of children with ADHD. Learning disabilities can include developmental speech and language disorders, and academic skills disorders. ADHD, however, is not considered a learning disability, but it very frequently causes academic difficulties. Intellectual disabilities and Tourette's syndrome are also common.


text: ADHD is often comorbid with disruptive, impulse control, and conduct disorders. Oppositional defiant disorder (ODD) occurs in about 25% of children with an inattentive presentation and 50% of those with a combined presentation. It is characterised by angry or irritable mood, argumentative or defiant behavior and vindictiveness which are age-inappropriate. Conduct disorder (CD) occurs in about 25% of adolescents with ADHD. It is characterised by aggression, destruction of property, deceitfulness, theft and violations of rules. Adolescents with ADHD who also have CD are more likely to develop antisocial personality disorder in adulthood. Brain imaging supports that CD and ADHD are separate conditions, wherein conduct disorder was shown to reduce the size of one's temporal lobe and limbic system, and increase the size of one's orbitofrontal cortex, whereas ADHD was shown to reduce connections in the cerebellum and prefrontal cortex more broadly. Conduct disorder involves more impairment in motivation control than ADHD. Intermittent explosive disorder is characterised by sudden and disproportionate outbursts of anger and co-occurs in individuals with ADHD more frequently than in the general population.


text: Anxiety and mood disorders are frequent comorbidities. Anxiety disorders have been found to occur more commonly in the ADHD population, as have mood disorders (especially bipolar disorder and major depressive disorder). Boys diagnosed with the combined ADHD subtype are more likely to have a mood disorder. Adults and children with ADHD sometimes also have bipolar disorder, which requires careful assessment to accurately diagnose and treat both conditions.


text: Sleep disorders and ADHD commonly co-exist. They can also occur as a side effect of medications used to treat ADHD. In children with ADHD, insomnia is the most common sleep disorder with behavioral therapy being the preferred treatment. Problems with sleep initiation are common among individuals with ADHD but often they will be deep sleepers and have significant difficulty getting up in the morning. Melatonin is sometimes used in children who have sleep onset insomnia. Specifically, the sleep disorder restless legs syndrome has been found to be more common in those with ADHD and is often due to iron deficiency anemia. However, restless legs can simply be a part of ADHD and requires careful assessment to differentiate between the two disorders. Delayed sleep phase disorder is also a common comorbidity of those with ADHD.


text: There are other psychiatric conditions which are often co-morbid with ADHD, such as substance use disorders. Individuals with ADHD are at increased risk of substance abuse. This is most commonly seen with alcohol or cannabis. The reason for this may be an altered reward pathway in the brains of ADHD individuals, self-treatment and increased psychosocial risk factors. This makes the evaluation and treatment of ADHD more difficult, with serious substance misuse problems usually treated first due to their greater risks. Other psychiatric conditions include reactive attachment disorder, characterised by a severe inability to appropriately relate socially, and sluggish cognitive tempo, a cluster of symptoms that potentially comprises another attention disorder and may occur in 30–50% of ADHD cases, regardless of the subtype. Individuals with ADHD are 4x more likely to develop and be diagnosed with an eating disorder (Anorexia, Bulimia, Binge Eating, ARFID) compared to those without ADHD. Individuals with diagnosed eating disorders are 2.6x more likely to have ADHD than those without eating disorders, though these numbers are likely much lower than actual rates, due to limitations with screening and diagnosis in marginalized populations.


text: ADHD, trauma, and Adverse Childhood Experiences are also comorbid, which could in part be potentially explained by the similarity in presentation between different diagnoses. The symptoms of ADHD and PTSD can have significant behavioral overlap with ADHD—in particular, motor restlessness, difficulty concentrating, distractibility, irritability/anger, emotional constriction or dysregulation, poor impulse control, and forgetfulness are common in both. This could result in trauma-related disorders or ADHD being mis-identified as the other. Additionally, traumatic events in childhood are a risk factor for ADHD - it can lead to structural brain changes and the development of ADHD behaviors. Finally, the behavioral consequences of ADHD symptoms cause a higher chance of the individual experiencing trauma (and therefore ADHD leads to a concrete diagnosis of a trauma-related disorder).


text: Some non-psychiatric conditions are also comorbidities of ADHD. This includes epilepsy, a neurological condition characterised by recurrent seizures. There are well established associations between ADHD and obesity, asthma and sleep disorders, and an association with celiac disease. Children with ADHD have a higher risk for migraine headaches, but have no increased risk of tension-type headaches. In addition, children with ADHD may also experience headaches as a result of medication.


text: A 2021 review reported that several neurometabolic disorders caused by inborn errors of metabolism converge on common neurochemical mechanisms that interfere with biological mechanisms also considered central in ADHD pathophysiology and treatment. This highlights the importance of close collaboration between health services to avoid clinical overshadowing.


text: Systematic reviews conducted in 2017 and 2020 found strong evidence that ADHD is associated with increased suicide risk across all age groups, as well as growing evidence that an ADHD diagnosis in childhood or adolescence represents a significant future suicidal risk factor. Potential causes include ADHD's association with functional impairment, negative social, educational and occupational outcomes, and financial distress. A 2019 meta-analysis indicated a significant association between ADHD and suicidal spectrum behaviors (suicidal attempts, ideations, plans, and completed suicides); across the studies examined, the prevalence of suicide attempts in individuals with ADHD was 18.9%, compared to 9.3% in individuals without ADHD, and the findings were substantially replicated among studies which adjusted for other variables. However, the relationship between ADHD and suicidal spectrum behaviors remains unclear due to mixed findings across individual studies and the complicating impact of comorbid psychiatric disorders. There is no clear data on whether there is a direct relationship between ADHD and suicidality, or whether ADHD increases suicide risk through comorbidities.


text: Certain studies have found that people with ADHD tend to have lower scores on intelligence quotient (IQ) tests. The significance of this is controversial due to the differences between people with ADHD and the difficulty determining the influence of symptoms, such as distractibility, on lower scores rather than intellectual capacity. In studies of ADHD, higher IQs may be over-represented because many studies exclude individuals who have lower IQs despite those with ADHD scoring on average nine points lower on standardized intelligence measures. In individuals with high intelligence, there is increased risk of a missed ADHD diagnosis, possibly because of compensatory strategies in highly intelligent individuals.


text: Studies of adults suggest that negative differences in intelligence are not meaningful and may be explained by associated health problems.


text: ADHD is generally claimed to be the result of neurological dysfunction in processes associated with the production or use of dopamine and norepinephrine in various brain structures, but there are no confirmed causes. It may involve interactions between genetics and the environment.


text: ADHD has a high heritability of 74%, meaning that 74% of the presence of ADHD in the population is due to genetic factors. There are multiple gene variants which each slightly increase the likelihood of a person having ADHD; it is polygenic and arises through the combination of many gene variants which each have a small effect. The siblings of children with ADHD are three to four times more likely to develop the disorder than siblings of children without the disorder.


text: Arousal is related to dopaminergic functioning, and ADHD presents with low dopaminergic functioning. Typically, a number of genes are involved, many of which directly affect dopamine neurotransmission. Those involved with dopamine include DAT, DRD4, DRD5, TAAR1, MAOA, COMT, and DBH. Other genes associated with ADHD include SERT, HTR1B, SNAP25, GRIN2A, ADRA2A, TPH2, and BDNF. A common variant of a gene called latrophilin 3 is estimated to be responsible for about 9% of cases and when this variant is present, people are particularly responsive to stimulant medication. The 7 repeat variant of dopamine receptor D4 (DRD4–7R) causes increased inhibitory effects induced by dopamine and is associated with ADHD. The DRD4 receptor is a G protein-coupled receptor that inhibits adenylyl cyclase. The DRD4–7R mutation results in a wide range of behavioral phenotypes, including ADHD symptoms reflecting split attention. The DRD4 gene is both linked to novelty seeking and ADHD. The genes GFOD1 and CDH13 show strong genetic associations with ADHD. CHD13's association with ASD, schizophrenia, bipolar disorder, and depression make it an interesting candidate causative gene. Another candidate causative gene that has been identified is ADGRL3. In zebrafish, knockout of this gene causes a loss of dopaminergic function in the ventral diencephalon and the fish display a hyperactive/impulsive phenotype.


text: For genetic variation to be used as a tool for diagnosis, more validating studies need to be performed. However, smaller studies have shown that genetic polymorphisms in genes related to catecholaminergic neurotransmission or the SNARE complex of the synapse can reliably predict a person's response to stimulant medication. Rare genetic variants show more relevant clinical significance as their penetrance (the chance of developing the disorder) tends to be much higher. However their usefulness as tools for diagnosis is limited as no single gene predicts ADHD. ASD shows genetic overlap with ADHD at both common and rare levels of genetic variation.


text: In addition to genetics, some environmental factors might play a role in causing ADHD. Alcohol intake during pregnancy can cause fetal alcohol spectrum disorders which can include ADHD or symptoms like it. Children exposed to certain toxic substances, such as lead or polychlorinated biphenyls, may develop problems which resemble ADHD. Exposure to the organophosphate insecticides chlorpyrifos and dialkyl phosphate is associated with an increased risk; however, the evidence is not conclusive. Exposure to tobacco smoke during pregnancy can cause problems with central nervous system development and can increase the risk of ADHD. Nicotine exposure during pregnancy may be an environmental risk.


text: Extreme premature birth, very low birth weight, and extreme neglect, abuse, or social deprivation also increase the risk as do certain infections during pregnancy, at birth, and in early childhood. These infections include, among others, various viruses (measles, varicella zoster encephalitis, rubella, enterovirus 71). At least 30% of children with a traumatic brain injury later develop ADHD and about 5% of cases are due to brain damage.


text: Some studies suggest that in a small number of children, artificial food dyes or preservatives may be associated with an increased prevalence of ADHD or ADHD-like symptoms, but the evidence is weak and may only apply to children with food sensitivities. The European Union has put in place regulatory measures based on these concerns. In a minority of children, intolerances or allergies to certain foods may worsen ADHD symptoms.


text: Individuals with hypokalemic sensory overstimulation are sometimes diagnosed as having attention deficit hyperactivity disorder (ADHD), raising the possibility that a subtype of ADHD has a cause that can be understood mechanistically and treated in a novel way. The sensory overload is treatable with oral potassium gluconate.


text: Research does not support popular beliefs that ADHD is caused by eating too much refined sugar, watching too much television, parenting, poverty or family chaos; however, they might worsen ADHD symptoms in certain people.


text: The youngest children in a class have been found to be more likely to be diagnosed as having ADHD, possibly due to them being developmentally behind their older classmates. They also appear to use ADHD medications at nearly twice the rate of their peers.


text: In some cases, an inappropriate diagnosis of ADHD may reflect a dysfunctional family or a poor educational system, rather than any true presence of ADHD in the individual. In other cases, it may be explained by increasing academic expectations, with a diagnosis being a method for parents in some countries to get extra financial and educational support for their child. Behaviors typical of ADHD occur more commonly in children who have experienced violence and emotional abuse.


text: Current models of ADHD suggest that it is associated with functional impairments in some of the brain's neurotransmitter systems, particularly those involving dopamine and norepinephrine. The dopamine and norepinephrine pathways that originate in the ventral tegmental area and locus coeruleus project to diverse regions of the brain and govern a variety of cognitive processes. The dopamine pathways and norepinephrine pathways which project to the prefrontal cortex and striatum are directly responsible for modulating executive function (cognitive control of behavior), motivation, reward perception, and motor function; these pathways are known to play a central role in the pathophysiology of ADHD. Larger models of ADHD with additional pathways have been proposed.


text: In children with ADHD, there is a general reduction of volume in certain brain structures, with a proportionally greater decrease in the volume in the left-sided prefrontal cortex. The posterior parietal cortex also shows thinning in individuals with ADHD compared to controls. Other brain structures in the prefrontal-striatal-cerebellar and prefrontal-striatal-thalamic circuits have also been found to differ between people with and without ADHD.


text: The subcortical volumes of the accumbens, amygdala, caudate, hippocampus, and putamen appears smaller in individuals with ADHD compared with controls. Structural MRI studies have also revealed differences in white matter, with marked differences in inter-hemispheric asymmetry between ADHD and typically developing youths.


text: Functional MRI fMRI studies have revealed a number of differences between ADHD and control brains. Independent component analysis performed on resting-state fMRI data have revealed that individuals with the inattentive type of ADHD have significantly more independent components are required to describe the variance of this data.


text: Previously, it had been suggested that the elevated number of dopamine transporters in people with ADHD was part of the pathophysiology, but it appears the elevated numbers may be due to adaptation following exposure to stimulant medication. Current models involve the mesocorticolimbic dopamine pathway and the locus coeruleus-noradrenergic system. ADHD psychostimulants possess treatment efficacy because they increase neurotransmitter activity in these systems. There may additionally be abnormalities in serotonergic, glutamatergic, or cholinergic pathways.


text: The symptoms of ADHD arise from a deficiency in certain executive functions (e.g., attentional control, inhibitory control, and working memory). Executive functions are a set of cognitive processes that are required to successfully select and monitor behaviors that facilitate the attainment of one's chosen goals. The executive function impairments that occur in ADHD individuals result in problems with staying organised, time keeping, excessive procrastination, maintaining concentration, paying attention, ignoring distractions, regulating emotions, and remembering details. People with ADHD appear to have unimpaired long-term memory, and deficits in long-term recall appear to be attributed to impairments in working memory. Due to the rates of brain maturation and the increasing demands for executive control as a person gets older, ADHD impairments may not fully manifest themselves until adolescence or even early adulthood.


text: ADHD has also been associated with motivational deficits in children. Children with ADHD often find it difficult to focus on long-term over short-term rewards, and exhibit impulsive behavior for short-term rewards.


text: Another sign of the structurally altered signal processing in the central nervous system in this group of people is the conspicuously common Paradoxical reaction ( of patients). These are unexpected reactions in the opposite direction as with a normal effect, or otherwise significant different reactions. These are reactions to neuroactive substances such as local anesthetic at the dentist, sedative, caffeine, antihistamine, weak neuroleptics and central and peripheral painkillers. Since the causes of "paradoxical reactions" are at least partly genetic, it may be useful in critical situations, for example before operations, to ask whether such abnormalities may also exist in family members.


text: ADHD is diagnosed by an assessment of a person's behavioral and mental development, including ruling out the effects of drugs, medications, and other medical or psychiatric problems as explanations for the symptoms. ADHD diagnosis often takes into account feedback from parents and teachers with most diagnoses begun after a teacher raises concerns. It may be viewed as the extreme end of one or more continuous human traits found in all people. Imaging studies of the brain do not give consistent results between individuals; thus, they are only used for research purposes and not a diagnosis.


text: In North America and Australia, DSM-5 criteria are used for diagnosis, while European countries usually use the ICD-10. The DSM-IV criteria for diagnosis of ADHD is more likely to diagnose ADHD than is the ICD-10 criteria. ADHD is alternately classified as neurodevelopmental disorder or a disruptive behavior disorder along with ODD, CD, and antisocial personality disorder. A diagnosis does not imply a neurological disorder.


text: Associated conditions that should be screened for include anxiety, depression, ODD, CD, and learning and language disorders. Other conditions that should be considered are other neurodevelopmental disorders, tics, and sleep apnea.


text: Self-rating scales, such as the ADHD rating scale and the Vanderbilt ADHD diagnostic rating scale, are used in the screening and evaluation of ADHD. Electroencephalography is not accurate enough to make an ADHD diagnosis.


text: As with many other psychiatric disorders, a formal diagnosis should be made by a qualified professional based on a set number of criteria. In the United States, these criteria are defined by the American Psychiatric Association in the DSM. Based on the DSM-5 criteria published in 2013 and the DSM-5-TR criteria published in 2022, there are three presentations of ADHD:


text: This subdivision is based on presence of at least six (in children) or five (in older teenagers and adults) out of nine long-term (lasting at least six months) symptoms of inattention, hyperactivity–impulsivity, or both. To be considered, several symptoms must have appeared by the age of six to twelve and occur in more than one environment (e.g. at home and at school or work). The symptoms must be inappropriate for a child of that age and there must be clear evidence that they are causing social, school or work related problems.


text: The DSM-5 and the DSM-5-TR also provide two diagnoses for individuals who have symptoms of ADHD but do not entirely meet the requirements. "Other Specified ADHD" allows the clinician to describe why the individual does not meet the criteria, whereas "Unspecified ADHD" is used where the clinician chooses not to describe the reason.


text: In the eleventh revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) by the World Health Organization, the disorder is classified as Attention deficit hyperactivity disorder (with the code 6A05). The defined subtypes are similar to those of the DSM-5: "predominantly inattentive presentation" (6A05.0); "predominantly hyperactive-impulsive presentation"(6A05.1); "combined presentation" (6A05.2). However, the ICD-11 includes two residual categories for individuals who do not entirely match any of the defined subtypes: "other specified presentation" (6A05.Y) where the clinician includes detail on the individual's presentation; and "presentation unspecified" (6A05.Z) where the clinician does not provide detail.


text: In the tenth revision (ICD-10), the symptoms of "hyperkinetic disorder" were analogous to ADHD in the ICD-11. When a conduct disorder (as defined by ICD-10) is present, the condition was referred to as "hyperkinetic conduct disorder". Otherwise, the disorder was classified as "disturbance of activity and attention", "other hyperkinetic disorders" or "hyperkinetic disorders, unspecified". The latter was sometimes referred to as "hyperkinetic syndrome".


text: The social construct theory of ADHD suggests that, because the boundaries between normal and abnormal behavior are socially constructed (i.e. jointly created and validated by all members of society, and in particular by physicians, parents, teachers, and others), it then follows that subjective valuations and judgements determine which diagnostic criteria are used and thus, the number of people affected. This difference means using DSM-IV criteria could diagnose ADHD at rates three to four times higher than ICD-10 criteria. Thomas Szasz, a supporter of this theory, has argued that ADHD was "invented and then given a name".


text: Adults with ADHD are diagnosed under the same criteria, including that their signs must have been present by the age of six to twelve. The individual is the best source for information in diagnosis, however others may provide useful information about the individual's symptoms currently and in childhood; a family history of ADHD also adds weight to a diagnosis. While the core symptoms of ADHD are similar in children and adults, they often present differently in adults than in children: for example, excessive physical activity seen in children may present as feelings of restlessness and constant mental activity in adults.


text: Worldwide, it is estimated that 2.58% of adults have persistent ADHD (where the individual currently meets the criteria and there is evidence of childhood onset), and 6.76% of adults have symptomatic ADHD (meaning that they currently meet the criteria for ADHD, regardless of childhood onset). In 2020, this was 139.84 million and 366.33 million affected adults respectively. Around 15% of children with ADHD continue to meet full DSM-IV-TR criteria at 25 years of age, and 50% still experience some symptoms. , most adults remain untreated. Many adults with ADHD without diagnosis and treatment have a disorganised life, and some use non-prescribed drugs or alcohol as a coping mechanism. Other problems may include relationship and job difficulties, and an increased risk of criminal activities. Associated mental health problems include depression, anxiety disorders, and learning disabilities.


text: Some ADHD symptoms in adults differ from those seen in children. While children with ADHD may climb and run about excessively, adults may experience an inability to relax, or may talk excessively in social situations. Adults with ADHD may start relationships impulsively, display sensation-seeking behavior, and be short-tempered. Addictive behavior such as substance abuse and gambling are common. This led to those who presented differently as they aged having outgrown the DSM-IV criteria. The DSM-5 criteria does specifically deal with adults unlike that of DSM-IV, which does not fully take into account the differences in impairments seen in adulthood compared to childhood.


text: For diagnosis in an adult, having symptoms since childhood is required. Nevertheless, a proportion of adults who meet the criteria for ADHD in adulthood would not have been diagnosed with ADHD as children. Most cases of late-onset ADHD develop the disorder between the ages of 12-16 and may therefore be considered early adult or adolescent-onset ADHD.


text: The DSM provides potential differential diagnoses - potential alternate explanations for specific symptoms. Assessment and investigation of clinical history determines which is the most appropriate diagnosis. The DSM-5 suggests ODD, intermittent explosive disorder, and other neurodevelopmental disorders (such as stereotypic movement disorder and Tourette's disorder), in addition to specific learning disorder, intellectual developmental disorder, ASD, reactive attachment disorder, anxiety disorders, depressive disorders, bipolar disorder, disruptive mood dysregulation disorder, substance use disorder, personality disorders, psychotic disorders, medication-induced symptoms, and neurocognitive disorders. Many but not all of these are also common comorbidities of ADHD. The DSM-5-TR also suggests post-traumatic stress disorder.


text: Symptoms of ADHD, such as low mood and poor self-image, mood swings, and irritability, can be confused with dysthymia, cyclothymia or bipolar disorder as well as with borderline personality disorder. Some symptoms that are due to anxiety disorders, personality disorder, developmental disabilities or intellectual disability or the effects of substance abuse such as intoxication and withdrawal can overlap with ADHD. These disorders can also sometimes occur along with ADHD. Medical conditions which can cause ADHD-type symptoms include: hyperthyroidism, seizure disorder, lead toxicity, hearing deficits, hepatic disease, sleep apnea, drug interactions, untreated celiac disease, and head injury.


text: Primary sleep disorders may affect attention and behavior and the symptoms of ADHD may affect sleep. It is thus recommended that children with ADHD be regularly assessed for sleep problems. Sleepiness in children may result in symptoms ranging from the classic ones of yawning and rubbing the eyes, to hyperactivity and inattentiveness. Obstructive sleep apnea can also cause ADHD-type symptoms.


text: The management of ADHD typically involves counseling or medications, either alone or in combination. While treatment may improve long-term outcomes, it does not get rid of negative outcomes entirely. Medications used include stimulants, atomoxetine, alpha-2 adrenergic receptor agonists, and sometimes antidepressants. In those who have trouble focusing on long-term rewards, a large amount of positive reinforcement improves task performance. ADHD stimulants also improve persistence and task performance in children with ADHD. "Recent evidence from observational and registry studies indicates that pharmacological treatment of ADHD is associated with increased achievement and decreased absenteeism at school, a reduced risk of trauma-related emergency hospital visits, reduced risks of suicide and attempted suicide, and decreased rates of substance abuse and criminality".


text: There is good evidence for the use of behavioral therapies in ADHD. They are the recommended first-line treatment in those who have mild symptoms or who are preschool-aged. Psychological therapies used include: psychoeducational input, behavior therapy, cognitive behavioral therapy, interpersonal psychotherapy, family therapy, school-based interventions, social skills training, behavioral peer intervention, organization training, and parent management training. Neurofeedback has greater treatment effects than non-active controls for up to 6 months and possibly a year following treatment, and may have treatment effects comparable to active controls (controls proven to have a clinical effect) over that time period. Despite efficacy in research, there is insufficient regulation of neurofeedback practice, leading to ineffective applications and false claims regarding innovations. Parent training may improve a number of behavioral problems including oppositional and non-compliant behaviors.


text: There is little high-quality research on the effectiveness of family therapy for ADHD—but the existing evidence shows that it is similar to community care, and better than placebo. ADHD-specific support groups can provide information and may help families cope with ADHD.


text: Social skills training, behavioral modification, and medication may have some limited beneficial effects in peer relationships. Stable, high-quality friendships with non-deviant peers protect against later psychological problems.


text: Methylphenidate and amphetamine or its derivatives are first-line treatments for ADHD as they are considered the most effective pharmaceutical treatments. About 70 percent respond to the first stimulant tried and as few as 10 percent respond to neither amphetamines nor methylphenidate. Stimulants may also reduce the risk of unintentional injuries in children with ADHD. Magnetic resonance imaging studies suggest that long-term treatment with amphetamine or methylphenidate decreases abnormalities in brain structure and function found in subjects with ADHD. A 2018 review found the greatest short-term benefit with methylphenidate in children, and amphetamines in adults.


text: The likelihood of developing insomnia for ADHD patients taking stimulants has been measured at between 11 and 45 percent for different medications, and may be a main reason for discontinuation. Other side effects, such as tics, decreased appetite and weight loss, or emotional lability, may also lead to discontinuation. Stimulant psychosis and mania are rare at therapeutic doses, appearing to occur in approximately 0.1% of individuals, within the first several weeks after starting amphetamine therapy. The safety of these medications in pregnancy is unclear. Symptom improvement is not sustained if medication is ceased.


text: The long-term effects of ADHD medication have yet to be fully determined, although stimulants are generally beneficial and safe for up to two years for children and adolescents.


text: Regular monitoring has been recommended in those on long-term treatment. There are indications suggesting that stimulant therapy for children and adolescents should be stopped periodically to assess continuing need for medication, decrease possible growth delay, and reduce tolerance. Although potentially addictive at high doses, stimulants used to treat ADHD have low potential for abuse. Treatment with stimulants is either protective against substance abuse or has no effect.


text: The majority of studies on nicotine and other nicotinic agonists as treatments for ADHD have shown favorable results; however, no nicotinic drug has been approved for ADHD treatment. Caffeine was formerly used as a second-line treatment for ADHD. It is considered less effective than methylphenidate or amphetamine but more so than placebo for children with ADHD. Pseudoephedrine and ephedrine do not affect ADHD symptoms.


text: Modafinil has shown some efficacy in reducing the severity of ADHD in children and adolescents. It may be prescribed off-label to treat ADHD.


text: There are a number of non-stimulant medications, such as Viloxazine, atomoxetine, bupropion, guanfacine, amantadine (effective in children and adolescents but still not been seen for adults), and clonidine, that may be used as alternatives, or added to stimulant therapy. There are no good studies comparing the various medications; however, they appear more or less equal with respect to side effects. For children, stimulants appear to improve academic performance while atomoxetine does not.


text: Atomoxetine, due to its lack of addiction liability, may be preferred in those who are at risk of recreational or compulsive stimulant use, although evidence is lacking to support its use over stimulants for this reason. Evidence supports its ability to improve symptoms when compared to placebo.


text: Amantadine was shown to induce similar improvements in children treated methylphenidate, with less frequent side effects. A 2021 retrospective study showed showed that amantadine may serve as an effective adjunct to stimulants for ADHD–related symptoms and appears to be a safer alternative to second- or third-generation antipsychotics.


text: There is little evidence on the effects of medication on social behaviors. Antipsychotics may also be used to treat aggression in ADHD.


text: Guidelines on when to use medications vary by country. The United Kingdom's National Institute for Health and Care Excellence recommends use for children only in severe cases, though for adults medication is a first-line treatment. Conversely, most United States guidelines recommend medications in most age groups. Medications are especially not recommended for preschool children. Underdosing of stimulants can occur, and can result in a lack of response or later loss of effectiveness. This is particularly common in adolescents and adults as approved dosing is based on school-aged children, causing some practitioners to use weight-based or benefit-based off-label dosing instead.


text: Regular physical exercise, particularly aerobic exercise, is an effective add-on treatment for ADHD in children and adults, particularly when combined with stimulant medication (although the best intensity and type of aerobic exercise for improving symptoms are not currently known). The long-term effects of regular aerobic exercise in ADHD individuals include better behavior and motor abilities, improved executive functions (including attention, inhibitory control, and planning, among other cognitive domains), faster information processing speed, and better memory. Parent-teacher ratings of behavioral and socio-emotional outcomes in response to regular aerobic exercise include: better overall function, reduced ADHD symptoms, better self-esteem, reduced levels of anxiety and depression, fewer somatic complaints, better academic and classroom behavior, and improved social behavior. Exercising while on stimulant medication augments the effect of stimulant medication on executive function. It is believed that these short-term effects of exercise are mediated by an increased abundance of synaptic dopamine and norepinephrine in the brain.


text: Dietary modifications are not recommended by the American Academy of Pediatrics, the National Institute for Health and Care Excellence, or the Agency for Healthcare Research and Quality due to insufficient evidence.


text: A 2013 meta-analysis found less than a third of children with ADHD see some improvement in symptoms with free fatty acid supplementation or decreased eating of artificial food coloring. These benefits may be limited to children with food sensitivities or those who are simultaneously being treated with ADHD medications. This review also found that evidence does not support removing other foods from the diet to treat ADHD. A 2014 review found that an elimination diet results in a small overall benefit in a minority of children, such as those with allergies. A 2016 review stated that the use of a gluten-free diet as standard ADHD treatment is not advised. A 2017 review showed that a few-foods elimination diet may help children too young to be medicated or not responding to medication, while free fatty acid supplementation or decreased eating of artificial food coloring as standard ADHD treatment is not advised. Chronic deficiencies of iron, magnesium and iodine may have a negative impact on ADHD symptoms. There is a small amount of evidence that lower tissue zinc levels may be associated with ADHD. In the absence of a demonstrated zinc deficiency (which is rare outside of developing countries), zinc supplementation is not recommended as treatment for ADHD. However, zinc supplementation may reduce the minimum effective dose of amphetamine when it is used with amphetamine for the treatment of ADHD.


text: ADHD persists into adulthood in about 30–50% of cases. Those affected are likely to develop coping mechanisms as they mature, thus compensating to some extent for their previous symptoms. Children with ADHD have a higher risk of unintentional injuries. Effects of medication on functional impairment and quality of life (e.g. reduced risk of accidents) have been found across multiple domains. Rates of smoking among those with ADHD are higher than in the general population at about 40%.


text: Individuals with ADHD are significantly overrepresented in prison populations. Although there is no generally accepted estimate of ADHD prevalence among inmates, a 2015 meta-analysis estimated a prevalence of 25.5%, and a larger 2018 meta-analysis estimated the frequency to be 26.2%. ADHD is more common among longer-term inmates; a 2010 study at Norrtälje Prison, a high-security prison in Sweden, found an estimated ADHD prevalence of 40%.


text: ADHD is estimated to affect about 6–7% of people aged 18 and under when diagnosed via the DSM-IV criteria. When diagnosed via the ICD-10 criteria, rates in this age group are estimated around 1–2%. Children in North America appear to have a higher rate of ADHD than children in Africa and the Middle East; this is believed to be due to differing methods of diagnosis rather than a difference in underlying frequency. it was estimated to affect 84.7 million people globally. If the same diagnostic methods are used, the rates are similar between countries. ADHD is diagnosed approximately three times more often in boys than in girls. This may reflect either a true difference in underlying rate, or that women and girls with ADHD are less likely to be diagnosed.


text: Rates of diagnosis and treatment have increased in both the United Kingdom and the United States since the 1970s. Prior to 1970, it was rare for children to be diagnosed with ADHD, while in the 1970s rates were about 1%. This is believed to be primarily due to changes in how the condition is diagnosed and how readily people are willing to treat it with medications rather than a true change in how common the condition is. It was believed changes to the diagnostic criteria in 2013 with the release of the DSM-5 would increase the percentage of people diagnosed with ADHD, especially among adults.


text: Due to disparities in the treatment and understanding of ADHD between caucasian and non-caucasian populations, many non-caucasian children go undiagnosed and unmedicated. It was found that within the US that there was often a disparity between caucasian and non-caucasian understandings of ADHD. This led to a difference in the classification of the symptoms of ADHD, and therefore, its misdiagnosis. It was also found that it was common in non-caucasian families and teachers to understand the symptoms of ADHD as behavioral issues, rather than mental illness.


text: Crosscultural differences in diagnosis of ADHD can also be attributed to the long-lasting effects of harmful, racially targeted medical practices. Medical pseudosciences, particularly those that targeted African American populations during the period of slavery in the US, lead to a distrust of medical practices within certain communities. The combination of ADHD symptoms often being regarded as misbehavior rather than as a psychiatric condition, and the use of drugs to regulate ADHD, result in a hesitancy to trust a diagnosis of ADHD. Cases of misdiagnosis in ADHD can also occur due to stereotyping of non-caucasian individuals. Due to ADHD's subjectively determined symptoms, medical professionals may diagnose individuals based on stereotyped behavior or misdiagnose due to differences in symptom presentation between Caucasian and non-Caucasian individuals.


text: Hyperactivity has long been part of the human condition. Sir Alexander Crichton describes "mental restlessness" in his book "An inquiry into the nature and origin of mental derangement" written in 1798. He made observations about children showing signs of being inattentive and having the "fidgets". The first clear description of ADHD is credited to George Still in 1902 during a series of lectures he gave to the Royal College of Physicians of London. He noted both nature and nurture could be influencing this disorder.


text: Alfred Tredgold proposed an association between brain damage and behavioral or learning problems which was able to be validated by the encephalitis lethargica epidemic from 1917 through 1928.


text: The terminology used to describe the condition has changed over time and has included: "minimal brain dysfunction" in the DSM-I (1952), "hyperkinetic reaction of childhood" in the DSM-II (1968), and "attention-deficit disorder with or without hyperactivity" in the DSM-III (1980). In 1987, this was changed to ADHD in the DSM-III-R, and in 1994 the DSM-IV in split the diagnosis into three subtypes: ADHD inattentive type, ADHD hyperactive-impulsive type, and ADHD combined type. These terms were kept in the DSM-5 in 2013 and in the DSM-5-TR in 2022. Prior to the DSM, terms included "minimal brain damage" in the 1930s.


text: In 1934, Benzedrine became the first amphetamine medication approved for use in the United States. Methylphenidate was introduced in the 1950s, and enantiopure dextroamphetamine in the 1970s. The use of stimulants to treat ADHD was first described in 1937. Charles Bradley gave the children with behavioral disorders Benzedrine and found it improved academic performance and behavior.


text: Once neuroimaging studies were possible, studies conducted in the 1990s provided support for the pre-existing theory that neurological differences - particularly in the frontal lobes - were involved in ADHD. During this same period, a genetic component was identified and ADHD was acknowledged to be a persistent, long-term disorder which lasted from childhood into adulthood.


text: ADHD was split into the current three sub-types because of a field trial completed by Lahey and colleagues.


text: ADHD, its diagnosis, and its treatment have been controversial since the 1970s. The controversies involve clinicians, teachers, policymakers, parents, and the media. Positions range from the view that ADHD is within the normal range of behavior to the hypothesis that ADHD is a genetic condition. Other areas of controversy include the use of stimulant medications in children, the method of diagnosis, and the possibility of overdiagnosis. In 2009, the National Institute for Health and Care Excellence, while acknowledging the controversy, states that the current treatments and methods of diagnosis are based on the dominant view of the academic literature. In 2014, Keith Conners, one of the early advocates for recognition of the disorder, spoke out against overdiagnosis in a "The New York Times" article. In contrast, a 2014 peer-reviewed medical literature review indicated that ADHD is underdiagnosed in adults.


text: With widely differing rates of diagnosis across countries, states within countries, races, and ethnicities, some suspect factors other than the presence of the symptoms of ADHD are playing a role in diagnosis, such as cultural norms. Some sociologists consider ADHD to be an example of the medicalization of deviant behavior, that is, the turning of the previously issue of school performance into a medical one. Most healthcare providers accept ADHD as a genuine disorder, at least in the small number of people with severe symptoms. Among healthcare providers the debate mainly centers on diagnosis and treatment in the much greater number of people with mild symptoms.


text: The nature and range of desirable endpoints of ADHD treatment vary among diagnostic standards for ADHD. In most studies, the efficacy of treatment is determined by reductions in ADHD symptoms. However, some studies have included subjective ratings from teachers and parents as part of their assessment of ADHD treatment efficacies. By contrast, the subjective ratings of children undergoing ADHD treatment are seldom included in studies evaluating the efficacy of ADHD treatments.


text: There have been notable differences in the diagnosis patterns of birthdays in school-age children. Those born relatively younger to the school starting age than others in a classroom environment are shown to be more likely diagnosed with ADHD. Boys who were born in December in which the school age cut-off was December 31 were shown to be 30% more likely to be diagnosed and 41% to be treated than others born in January. Girls born in December had a diagnosis percentage of 70% and 77% treatment more than ones born the following month. Children who were born at the last 3 days of a calendar year were reported to have significantly higher levels of diagnosis and treatment for ADHD than children born at the first 3 days of a calendar year. The studies suggest that ADHD diagnosis is prone to subjective analysis.


text: A 2020 review found that creativity may be associated with ADHD symptoms, particularly divergent thinking and quantity of creative achievements, but not with the disorder of ADHD itself – i.e. it has not been found to be increased in people diagnosed with the disorder, only in people with subclinical symptoms or those that possess traits associated with the disorder. Divergent thinking is the ability to produce creative solutions which differ significantly from each other and consider the issue from multiple perspectives. Those with ADHD symptoms could be advantaged in this form of creativity as they tend to have diffuse attention, allowing rapid switching between aspects of the task under consideration; flexible associative memory, allowing them to remember and use more distantly-related ideas which is associated with creativity; and impulsivity, which causes people with ADHD symptoms to consider ideas which others may not have. However, people with ADHD may struggle with convergent thinking, which is a cognitive process through which a set of obviously relevant knowledge is utilized in a focused effort to arrive at a single perceived best solution to a problem.


text: A 2020 article suggested that historical documentation supported Leonardo da Vinci's difficulties with procrastination and time management as characteristic of ADHD and that he was constantly on the go, but often jumping from task to task.


text: Reviews of ADHD biomarkers have noted that platelet monoamine oxidase expression, urinary norepinephrine, urinary MHPG, and urinary phenethylamine levels consistently differ between ADHD individuals and non-ADHD controls. These measurements could potentially serve as diagnostic biomarkers for ADHD, but more research is needed to establish their diagnostic utility. Urinary and blood plasma phenethylamine concentrations are lower in ADHD individuals relative to controls and the two most commonly prescribed drugs for ADHD, amphetamine and methylphenidate, increase phenethylamine biosynthesis in treatment-responsive individuals with ADHD. Lower urinary phenethylamine concentrations are also associated with symptoms of inattentiveness in ADHD individuals.


title: Big Bang

text: The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The overall uniformity of the Universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. However, physics currently lacks a widely accepted theory of quantum gravity that can successfully model the earliest conditions of the Big Bang.


title: Big Bang

text: Crucially, these models are compatible with the Hubble–Lemaître law—the observation that the farther away a galaxy is, the faster it is moving away from Earth. Extrapolating this cosmic expansion backwards in time using the known laws of physics, the models describe an increasingly concentrated cosmos preceded by a singularity in which space and time lose meaning (typically named "the Big Bang singularity"). In 1964 the CMB was discovered, which convinced many cosmologists that the competing steady-state model of cosmic evolution was falsified, since the Big Bang models predict a uniform background radiation caused by high temperatures and densities in the distant past. A wide range of empirical evidence strongly favors the Big Bang event, which is now essentially universally accepted. Detailed measurements of the expansion rate of the universe place the Big Bang singularity at an estimated  billion years ago, which is considered the age of the universe.


title: Big Bang

text: There remain aspects of the observed universe that are not yet adequately explained by the Big Bang models. After its initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later atoms. The unequal abundances of matter and antimatter that allowed this to occur is an unexplained effect known as baryon asymmetry. These primordial elements—mostly hydrogen, with some helium and lithium—later coalesced through gravity, forming early stars and galaxies. Astronomers observe the gravitational effects of an unknown dark matter surrounding galaxies. Most of the gravitational potential in the universe seems to be in this form, and the Big Bang models and various observations indicate that this excess gravitational potential is not created by baryonic matter, such as normal atoms. Measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation attributed to an unexplained phenomenon known as dark energy.


title: Big Bang

text: The Big Bang models offer a comprehensive explanation for a broad range of observed phenomena, including the abundances of the light elements, the CMB, large-scale structure, and Hubble's law. The models depend on two major assumptions: the universality of physical laws and the cosmological principle. The universality of physical laws is one of the underlying principles of the theory of relativity. The cosmological principle states that on large scales the universe is homogeneous and isotropic—appearing the same in all directions regardless of location.


title: Big Bang

text: These ideas were initially taken as postulates, but later efforts were made to test each of them. For example, the first assumption has been tested by observations showing that largest possible deviation of the fine-structure constant over much of the age of the universe is of order 10. Also, general relativity has passed stringent tests on the scale of the Solar System and binary stars.


title: Big Bang

text: The large-scale universe appears isotropic as viewed from Earth. If it is indeed isotropic, the cosmological principle can be derived from the simpler Copernican principle, which states that there is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10 via observations of the temperature of the CMB. At the scale of the CMB horizon, the universe has been measured to be homogeneous with an upper bound on the order of 10% inhomogeneity, as of 1995.


title: Big Bang

text: The expansion of the Universe was inferred from early twentieth century astronomical observations and is an essential ingredient of the Big Bang models. Mathematically, general relativity describes spacetime by a metric, which determines the distances that separate nearby points. The points, which can be relative to galaxies, stars, or other objects, are specified using a coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. This metric contains a scale factor, which describes how the size of the universe changes with time. This enables a convenient choice of a coordinate system to be made, called comoving coordinates. In this coordinate system, the grid expands along with the universe, and objects that are moving only because of the expansion of the universe remain at fixed points on the grid. While their "coordinate" distance (comoving distance) remains constant, the "physical" distance between two such co-moving points expands proportionally with the scale factor of the universe.


title: Big Bang

text: The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distances between comoving points. In other words, the Big Bang is not an explosion "in space", but rather an expansion "of space". Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our universe only on large scales—local concentrations of matter such as our galaxy do not necessarily expand with the same speed as the whole Universe.


title: Big Bang

text: An important feature of the Big Bang spacetime is the presence of particle horizons. Since the universe has a finite age, and light travels at a finite speed, there may be events in the past whose light has not yet had time to reach us. This places a limit or a "past horizon" on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never "catch up" to very distant objects. This defines a "future horizon", which limits the events in the future that we will be able to influence. The presence of either type of horizon depends on the details of the FLRW model that describes our universe.


title: Big Bang

text: Our understanding of the universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well.


title: Big Bang

text: Some processes in the early universe occurred too slowly, compared to the expansion rate of the universe, to reach approximate thermodynamic equilibrium. Others were fast enough to reach thermalization. The parameter usually used to find out whether a process in the very early universe has reached thermal equilibrium is the ratio between the rate of the process (usually rate of collisions between particles) and the Hubble parameter. The larger the ratio, the more time particles had to thermalize before they were too far away from each other.


title: Big Bang

text: According to the Big Bang models, the universe at the beginning was very hot and very compact, and since then it has been expanding and cooling down.


title: Big Bang

text: Extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This irregular behavior, known as the gravitational singularity, indicates that general relativity is not an adequate description of the laws of physics in this regime. Models based on general relativity alone cannot fully extrapolate toward the singularity.


title: Big Bang

text: This primordial singularity is itself sometimes called "the Big Bang", but the term can also refer to a more generic early hot, dense phase of the universe. In either case, "the Big Bang" as an event is also colloquially referred to as the "birth" of our universe since it represents the point in history where the universe can be verified to have entered into a regime where the laws of physics as we understand them (specifically general relativity and the Standard Model of particle physics) work. Based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background, the time that has passed since that event—known as the "age of the universe"—is 13.8 billion years.


title: Big Bang

text: Despite being extremely dense at this time—far denser than is usually required to form a black hole—the universe did not re-collapse into a singularity. Commonly used calculations and limits for explaining gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not apply to rapidly expanding space such as the Big Bang. Since the early universe did not immediately collapse into a multitude of black holes, matter at that time must have been very evenly distributed with a negligible density gradient.


title: Big Bang

text: The earliest phases of the Big Bang are subject to much speculation, since astronomical data about them are not available. In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures, and was very rapidly expanding and cooling. The period from 0 to 10 seconds into the expansion, the Planck epoch, was a phase in which the four fundamental forces — the electromagnetic force, the strong nuclear force, the weak nuclear force, and the gravitational force, were unified as one. In this stage, the characteristic scale length of the universe was the Planck length, , and consequently had a temperature of approximately 10 degrees Celsius. Even the very concept of a particle breaks down in these conditions. A proper understanding of this period awaits the development of a theory of quantum gravity. The Planck epoch was succeeded by the grand unification epoch beginning at 10 seconds, where gravitation separated from the other forces as the universe's temperature fell.


title: Big Bang

text: At approximately 10 seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially, unconstrained by the light speed invariance, and temperatures dropped by a factor of 100,000. This concept is motivated by the flatness problem, where the density of matter and energy is very close to the critical density needed to produce a flat universe. That is, the shape of the universe has no overall geometric curvature due to gravitational influence. Microscopic quantum fluctuations that occurred because of Heisenberg's uncertainty principle were "frozen in" by inflation, becoming amplified into the seeds that would later form the large-scale structure of the universe. At a time around 10 seconds, the electroweak epoch begins when the strong nuclear force separates from the other forces, with only the electromagnetic force and weak nuclear force remaining unified.


title: Big Bang

text: Inflation stopped at around the 10 to 10 seconds mark, with the universe's volume having increased by a factor of at least 10. Reheating occurred until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles. Temperatures were so high that the random motions of particles were at relativistic speeds, and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions. At some point, an unknown reaction called baryogenesis violated the conservation of baryon number, leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in the predominance of matter over antimatter in the present universe.


title: Big Bang

text: The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry-breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form, with the electromagnetic force and weak nuclear force separating at about 10 seconds. After about 10 seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in particle accelerators. At about 10 seconds, quarks and gluons combined to form baryons such as protons and neutrons. The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was no longer high enough to create either new proton–antiproton or neutron–antineutron pairs. A mass annihilation immediately followed, leaving just one in 10 of the original matter particles and none of their antiparticles. A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by photons (with a minor contribution from neutrinos).


title: Big Bang

text: A few minutes into the expansion, when the temperature was about a billion kelvin and the density of matter in the universe was comparable to the current density of Earth's atmosphere, neutrons combined with protons to form the universe's deuterium and helium nuclei in a process called Big Bang nucleosynthesis (BBN). Most protons remained uncombined as hydrogen nuclei.


title: Big Bang

text: As the universe cooled, the rest energy density of matter came to gravitationally dominate that of the photon radiation. After about 379,000 years, the electrons and nuclei combined into atoms (mostly hydrogen), which were able to emit radiation. This relic radiation, which continued through space largely unimpeded, is known as the cosmic microwave background.


title: Big Bang

text: Over a long period of time, the slightly denser regions of the uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today. The details of this process depend on the amount and type of matter in the universe. The four possible types of matter are known as cold dark matter (CDM), warm dark matter, hot dark matter, and baryonic matter. The best measurements available, from the Wilkinson Microwave Anisotropy Probe (WMAP), show that the data is well-fit by a Lambda-CDM model in which dark matter is assumed to be cold. (Warm dark matter is ruled out by early reionization.) This CDM is estimated to make up about 23% of the matter/energy of the universe, while baryonic matter makes up about 4.6%.


title: Big Bang

text: In an "extended model" which includes hot dark matter in the form of neutrinos, then the "physical baryon density" formula_1 is estimated at 0.023. (This is different from the 'baryon density' formula_2 expressed as a fraction of the total matter/energy density, which is about 0.046.) The corresponding cold dark matter density formula_3 is about 0.11, and the corresponding neutrino density formula_4 is estimated to be less than 0.0062.


title: Big Bang

text: Independent lines of evidence from Type Ia supernovae and the CMB imply that the universe today is dominated by a mysterious form of energy known as dark energy, which appears to homogeneously permeate all of space. Observations suggest that 73% of the total energy density of the present day universe is in this form. When the universe was very young it was likely infused with dark energy, but with everything closer together gravity predominated, braking the expansion. Eventually, after billions of years of expansion, the declining density of matter relative to the density of dark energy allowed the expansion of the universe to begin to accelerate.


title: Big Bang

text: Dark energy in its simplest formulation is modeled by a cosmological constant term in Einstein field equations of general relativity, but its composition and mechanism are unknown. More generally, the details of its equation of state and relationship with the Standard Model of particle physics continue to be investigated both through observation and theory.


title: Big Bang

text: All of this cosmic evolution after the inflationary epoch can be rigorously described and modeled by the lambda-CDM model of cosmology, which uses the independent frameworks of quantum mechanics and general relativity. There are no easily testable models that would describe the situation prior to approximately 10 seconds. Understanding this earliest of eras in the history of the universe is currently one of the greatest unsolved problems in physics.


title: Big Bang

text: English astronomer Fred Hoyle is credited with coining the term "Big Bang" during a talk for a March 1949 BBC Radio broadcast, saying: "These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." However, it did not catch on until the 1970s.


title: Big Bang

text: It is popularly reported that Hoyle, who favored an alternative "steady-state" cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models. Helge Kragh writes that the evidence for the claim that it was meant as a pejorative is "unconvincing", and mentions a number of indications that it was not a pejorative.


title: Big Bang

text: The term itself is a misnomer as it implies the occurrence of an explosion. However, an explosion implies expansion from a center point out into the surrounding space. Rather than expanding "into" space, the Big Bang was the expansion/stretching "of" space itself, everywhere simultaneously (not from a single point), causing the universe to cool down and the density to be lowered. Another issue pointed out by Santhosh Mathew is that bang implies sound, which would require a vibrating particle and medium through which it travels. Since this is the beginning of anything we can imagine, there is no basis for any sound, and thus the Big Bang was likely silent. An attempt to find a more suitable alternative was not successful.


title: Big Bang

text: The Big Bang models developed from observations of the structure of the universe and from theoretical considerations. In 1912, Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way. Ten years later, Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann equations from the Einstein field equations, showing that the universe might be expanding in contrast to the static universe model advocated by Albert Einstein at that time.


title: Big Bang

text: In 1924, American astronomer Edwin Hubble's measurement of the great distance to the nearest spiral nebulae showed that these systems were indeed other galaxies. Starting that same year, Hubble painstakingly developed a series of distance indicators, the forerunner of the cosmic distance ladder, using the Hooker telescope at Mount Wilson Observatory. This allowed him to estimate distances to galaxies whose redshifts had already been measured, mostly by Slipher. In 1929, Hubble discovered a correlation between distance and recessional velocity—now known as Hubble's law.


title: Big Bang

text: Independently deriving Friedmann's equations in 1927, Georges Lemaître, a Belgian physicist and Roman Catholic priest, proposed that the recession of the nebulae was due to the expansion of the universe. He inferred the relation that Hubble would later observe, given the cosmological principle. In 1931, Lemaître went further and suggested that the evident expansion of the universe, if projected back in time, meant that the further in the past the smaller the universe was, until at some finite time in the past all the mass of the universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and space came into existence.


title: Big Bang

text: In the 1920s and 1930s, almost every major cosmologist preferred an eternal steady-state universe, and several complained that the beginning of time implied by the Big Bang imported religious concepts into physics; this objection was later repeated by supporters of the steady-state theory. This perception was enhanced by the fact that the originator of the Big Bang concept, Lemaître, was a Roman Catholic priest. Arthur Eddington agreed with Aristotle that the universe did not have a beginning in time, "viz"., that matter is eternal. A beginning in time was "repugnant" to him. Lemaître, however, disagreed:


title: Big Bang

text: During the 1930s, other ideas were proposed as non-standard cosmologies to explain Hubble's observations, including the Milne model, the oscillatory universe (originally suggested by Friedmann, but advocated by Albert Einstein and Richard C. Tolman) and Fritz Zwicky's tired light hypothesis.


title: Big Bang

text: After World War II, two distinct possibilities emerged. One was Fred Hoyle's steady-state model, whereby new matter would be created as the universe seemed to expand. In this model the universe is roughly the same at any point in time. The other was Lemaître's Big Bang theory, advocated and developed by George Gamow, who introduced BBN and whose associates, Ralph Alpher and Robert Herman, predicted the CMB. Ironically, it was Hoyle who coined the phrase that came to be applied to Lemaître's theory, referring to it as "this "big bang" idea" during a BBC Radio broadcast in March 1949. For a while, support was split between these two theories. Eventually, the observational evidence, most notably from radio source counts, began to favor Big Bang over steady state. The discovery and confirmation of the CMB in 1964 secured the Big Bang as the best theory of the origin and evolution of the universe.


title: Big Bang

text: In 1968 and 1970, Roger Penrose, Stephen Hawking, and George F. R. Ellis published papers where they showed that mathematical singularities were an inevitable initial condition of relativistic models of the Big Bang. Then, from the 1970s to the 1990s, cosmologists worked on characterizing the features of the Big Bang universe and resolving outstanding problems. In 1981, Alan Guth made a breakthrough in theoretical work on resolving certain outstanding theoretical problems in the Big Bang models with the introduction of an epoch of rapid expansion in the early universe he called "inflation". Meanwhile, during these decades, two questions in observational cosmology that generated much discussion and disagreement were over the precise values of the Hubble Constant and the matter-density of the universe (before the discovery of dark energy, thought to be the key predictor for the eventual fate of the universe).


title: Big Bang

text: In the mid-1990s, observations of certain globular clusters appeared to indicate that they were about 15 billion years old, which conflicted with most then-current estimates of the age of the universe (and indeed with the age measured today). This issue was later resolved when new computer simulations, which included the effects of mass loss due to stellar winds, indicated a much younger age for globular clusters.


title: Big Bang

text: Significant progress in Big Bang cosmology has been made since the late 1990s as a result of advances in telescope technology as well as the analysis of data from satellites such as the Cosmic Background Explorer (COBE), the Hubble Space Telescope and WMAP. Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the universe appears to be accelerating.


title: Big Bang

text: The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang nucleosynthesis (BBN). More recent evidence includes observations of galaxy formation and evolution, and the distribution of large-scale cosmic structures, These are sometimes called the "four pillars" of the Big Bang models.


title: Big Bang

text: Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, dark matter is currently the subject of most active laboratory investigations. Remaining issues include the cuspy halo problem and the dwarf galaxy problem of cold dark matter. Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible. Inflation and baryogenesis remain more speculative features of current Big Bang models. Viable, quantitative explanations for such phenomena are still being sought. These are currently unsolved problems in physics.


title: Big Bang

text: Observations of distant galaxies and quasars show that these objects are redshifted: the light emitted from them has been shifted to longer wavelengths. This can be seen by taking a frequency spectrum of an object and matching the spectroscopic pattern of emission or absorption lines corresponding to atoms of the chemical elements interacting with the light. These redshifts are uniformly isotropic, distributed evenly among the observed objects in all directions. If the redshift is interpreted as a Doppler shift, the recessional velocity of the object can be calculated. For some galaxies, it is possible to estimate distances via the cosmic distance ladder. When the recessional velocities are plotted against these distances, a linear relationship known as Hubble's law is observed:


title: Big Bang

text: Hubble's law has two possible explanations. Either we are at the center of an explosion of galaxies—which is untenable under the assumption of the Copernican principle—or the universe is uniformly expanding everywhere. This universal expansion was predicted from general relativity by Friedmann in 1922 and Lemaître in 1927, well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang model as developed by Friedmann, Lemaître, Robertson, and Walker.


title: Big Bang

text: The theory requires the relation formula_9 to hold at all times, where formula_7 is the proper distance, "v" is the recessional velocity, and formula_6, formula_12, and formula_7 vary as the universe expands (hence we write formula_8 to denote the present-day Hubble "constant"). For distances much smaller than the size of the observable universe, the Hubble redshift can be thought of as the Doppler shift corresponding to the recession velocity formula_6. However, the redshift is not a true Doppler shift, but rather the result of the expansion of the universe between the time the light was emitted and the time that it was detected.


title: Big Bang

text: That space is undergoing metric expansion is shown by direct observational evidence of the cosmological principle and the Copernican principle, which together with Hubble's law have no other explanation. Astronomical redshifts are extremely isotropic and homogeneous, supporting the cosmological principle that the universe looks the same in all directions, along with much other evidence. If the redshifts were the result of an explosion from a center distant from us, they would not be so similar in different directions.


title: Big Bang

text: Measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems in 2000 proved the Copernican principle, that, on a cosmological scale, the Earth is not in a central position. Radiation from the Big Bang was demonstrably warmer at earlier times throughout the universe. Uniform cooling of the CMB over billions of years is explainable only if the universe is experiencing a metric expansion, and excludes the possibility that we are near the unique center of an explosion.


title: Big Bang

text: In 1964, Arno Penzias and Robert Wilson serendipitously discovered the cosmic background radiation, an omnidirectional signal in the microwave band. Their discovery provided substantial confirmation of the big-bang predictions by Alpher, Herman and Gamow around 1950. Through the 1970s, the radiation was found to be approximately consistent with a blackbody spectrum in all directions; this spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. This tipped the balance of evidence in favor of the Big Bang model, and Penzias and Wilson were awarded the 1978 Nobel Prize in Physics.


title: Big Bang

text: The "surface of last scattering" corresponding to emission of the CMB occurs shortly after "recombination", the epoch when neutral hydrogen becomes stable. Prior to this, the universe comprised a hot dense photon-baryon plasma sea where photons were quickly scattered from free charged particles. Peaking at around , the mean free path for a photon becomes long enough to reach the present day and the universe becomes transparent.


title: Big Bang

text: In 1989, NASA launched COBE, which made two major advances: in 1990, high-precision spectrum measurements showed that the CMB frequency spectrum is an almost perfect blackbody with no deviations at a level of 1 part in 10, and measured a residual temperature of 2.726 K (more recent measurements have revised this figure down slightly to 2.7255 K); then in 1992, further COBE measurements discovered tiny fluctuations (anisotropies) in the CMB temperature across the sky, at a level of about one part in 10. John C. Mather and George Smoot were awarded the 2006 Nobel Prize in Physics for their leadership in these results.


title: Big Bang

text: During the following decade, CMB anisotropies were further investigated by a large number of ground-based and balloon experiments. In 2000–2001, several experiments, most notably BOOMERanG, found the shape of the universe to be spatially almost flat by measuring the typical angular size (the size on the sky) of the anisotropies.


title: Big Bang

text: In early 2003, the first results of the Wilkinson Microwave Anisotropy Probe were released, yielding what were at the time the most accurate values for some of the cosmological parameters. The results disproved several specific cosmic inflation models, but are consistent with the inflation theory in general. The "Planck" space probe was launched in May 2009. Other ground and balloon-based cosmic microwave background experiments are ongoing.


title: Big Bang

text: Using the Big Bang model, it is possible to calculate the concentration of the isotopes helium-4 (He), helium-3 (He), deuterium (H), and lithium-7 (Li) in the universe as ratios to the amount of ordinary hydrogen. The relative abundances depend on a single parameter, the ratio of photons to baryons. This value can be calculated independently from the detailed structure of CMB fluctuations. The ratios predicted (by mass, not by abundance) are about 0.25 for He:H, about 10 for H:H, about 10 for He:H, and about 10 for Li:H.


title: Big Bang

text: The measured abundances all agree at least roughly with those predicted from a single value of the baryon-to-photon ratio. The agreement is excellent for deuterium, close but formally discrepant for He, and off by a factor of two for Li (this anomaly is known as the cosmological lithium problem); in the latter two cases, there are substantial systematic uncertainties. Nonetheless, the general consistency with abundances predicted by BBN is strong evidence for the Big Bang, as the theory is the only known explanation for the relative abundances of light elements, and it is virtually impossible to "tune" the Big Bang to produce much more or less than 20–30% helium. Indeed, there is no obvious reason outside of the Big Bang that, for example, the young universe before star formation, as determined by studying matter supposedly free of stellar nucleosynthesis products, should have more helium than deuterium or more deuterium than He, and in constant ratios, too.


title: Big Bang

text: Detailed observations of the morphology and distribution of galaxies and quasars are in agreement with the current state of the Big Bang models. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the Big Bang, and since then, larger structures have been forming, such as galaxy clusters and superclusters.


title: Big Bang

text: Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early universe) appear very different from nearby galaxies (observed in a more recent state). Moreover, galaxies that formed relatively recently, appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions and larger structures, agree well with Big Bang simulations of the formation of structure in the universe, and are helping to complete details of the theory.


title: Big Bang

text: In 2011, astronomers found what they believe to be pristine clouds of primordial gas by analyzing absorption lines in the spectra of distant quasars. Before this discovery, all other astronomical objects have been observed to contain heavy elements that are formed in stars. Despite being sensitive to carbon, oxygen, and silicon, these three elements were not detected in these two clouds. Since the clouds of gas have no detectable levels of heavy elements, they likely formed in the first few minutes after the Big Bang, during BBN.


title: Big Bang

text: The age of the universe as estimated from the Hubble expansion and the CMB is now in good agreement with other estimates using the ages of the oldest stars, both as measured by applying the theory of stellar evolution to globular clusters and through radiometric dating of individual Population II stars. It is also in good agreement with age estimates based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background. The agreement of independent measurements of this age supports the Lambda-CDM (ΛCDM) model, since the model is used to relate some of the measurements to an age estimate, and all estimates turn out to agree. Still, some observations of objects from the relatively early universe (in particular quasar APM 08279+5255) raise concern as to whether these objects had enough time to form so early in the ΛCDM model.


title: Big Bang

text: The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift. This prediction also implies that the amplitude of the Sunyaev–Zel'dovich effect in clusters of galaxies does not depend directly on redshift. Observations have found this to be roughly true, but this effect depends on cluster properties that do change with cosmic time, making precise measurements difficult.


title: Big Bang

text: Future gravitational-wave observatories might be able to detect primordial gravitational waves, relics of the early universe, up to less than a second after the Big Bang.