Friday, March 28, 2008

The Electron

The Electron is an elementary particle found in the atom.  It is a lepton, and is stable, although it is possible that an electron may decay in 10^26 years (average).  The electron is the basis for the study of orbitals and atomic bonding.  Electrons are so small that their exact location is never determined and, like other particles have a wave form.  The electron has a negative charge (note 4). 


Electromagnetism is a force that effects anything with an electrical charge.  Also, electrically charged objects produce an electromagnetic field.  Like gravity, an electromagnetic field weakens with distance.  Electromagnetism is the force we observe most often and explains most phenomena seen by humans (with the exception of gravity, of course).  Atomic bonding, molecular interaction, and even some particle interactions all are caused by the electromagnetic force.  This force is carried by the photon.

The Neutron

The Neutron is an elementary particle found in the nucleus of the atom with the proton.  Its neutral charge is caused by the quark composition (udd or up, down, down) because the charges of the quarks add (up=2/3 + down=-1/3 + down=-1/3 = 0) to zero.  Bound inside the nucleus neutrons are stable, but the free neutron (synthetic) is unstable, having a half-life of about 885 seconds (approx. 15 minutes).  It interacts with all four forces and through beta decay, it becomes a proton.  The neutron is the heaviest particle in the atom.

Wednesday, March 26, 2008

The Proton


Monday, March 24, 2008

Strong Nuclear Force

The Strong Nuclear Force (Strong Interaction) is the most powerful force in our Universe.  Up until recently, it was thought that this was the force holding atomic nuclei together against repelling protons.  But this was found only to be an effect of the real Strong Nuclear Force (once the real force was discovered this effect was named the Residual Strong Nuclear Force).  The real force holds hadrons, but primarily protons and neutrons (collectively called nucleons) together.  This force is carried by gluons (named for glue) which connect quarks.

Wednesday, March 19, 2008

Weak Nuclear Force

The Weak Nuclear Force (also called the Weak Interaction) is a process that causes beta decay. This process involves a neutron turning into a proton. To do this, a neutron must not only lose in mass, but one of its quarks has to change from a down to a up quark. To do this it must eject a W boson which separates into a electron and an electron antinutrino. This decay happens in the proton-proton chain discussed here. Leptons can also emit W bosons and become corresponding nutrinos. Also, quarks can absorb or emit a Z boson. W and Z bosons are the particles that carry the Weak Nuclear force.

Tuesday, March 18, 2008

Black Hole Evaporation

An important question about Black Holes. Do they die? Hawking proposed Black hole evaporation, a theory in which Black Holes lose mass due to the separation of particle-antiparticle pairs. Vacuum fluctuations cause one particle to escape while its partner falls in. The negative particle falls in so the end equation is the Black Hole losing one particle. A massive Black Hole absorbs more Cosmic Background Radiation than it loses in mass because of Hawking Radiation. Because of this, until the Universe expands further and the Cosmic Radiation fades, a massive Black Hole will live forever. Eventually though, all Black Holes will evaporate. At the end of its life, a Black hole explodes with a temperature of over one quadrillion (1,000,000,000,000,000) degrees Fahrenheit with the force of over one billion atomic bombs.

Monday, March 17, 2008

Heavier Fusion

After a star exhausts its Hydrogen fuel, it either stops shining, or if it is massive enough, continues on to heavier elements. A red giant star, beyond its Hydrogen rations begins to fuse Helium. Helium, through the triple alpha process (a process where two Helium atoms fuse to form Beryllium, and then another alpha particle joins, forming Carbon) can produce Carbon, which produces Neon, Oxygen, Silicon, Nickel, and as alpha particles (note 3) are added to these heavier elements, forming Nickel, and finally iron. If a star reaches an iron core it explodes in a supernova, explained here. Only massive stars can obtain iron cores, with temperatures in the center soaring to 90 trillion degrees.

Sunday, March 16, 2008

Burning Hydrogen

All stars, including our Sun, begin their lives burning Hydrogen. For stars the mass of our sun or less, the process of burning is the proton-proton chain. Two Hydrogen atoms fuse to form a deuterium atom. This is the longest step because it takes a while for a proton to release energy and become a neutron. Then another Hydrogen atom fuses in forming Helium 3, a light isotope. Then this atom fuses with another He3 atom and releases two protons to become Helium 4, the regular isotope. This process takes over 10^9 years to complete (over a billion years), and that's why the sun is still shining.

The most common production of Helium in stars heavier than our sun is done in a cycle called the Carbon-Nitrogen-Oxygen Cycle (CNO cycle for short). The most common CNO cycle begins with a Carbon 12 atom (this atom is given because today's stars have a small metallic content). Then a Hydrogen atom fuses in, creating Nitrogen 13. Then as a positron departs a C13 is left. Then another Hydrogen fuses in creating N14. Then another H creating Oxygen 15. Then another positron leaves forming N15 (note that in all the steps metioned so far about the CNO cycle energy is released). Then, as a last Hydrogen atom fuses in, a Helium 4 atom is ejected leaving a C12 atom to restart the process again. A star like our sun burns its Hydrogen in 10 billion years, while more massive stars only burn it for less than 10 million years.

Gravity and Its Effects

Gravity, one or the four fundamental forces of the Universe has a devastating effect on our world. It is the force that created the stars and galaxies, and the force that destroys them. Gravity causes moons to orbit planets, that orbit stars, the orbit galaxy centers, that orbit in clusters, which orbit in superclusters. Also, it holds other types of groups like star clusters together. Examples of its effects can be seen in the end of stars' lives. A star such as our sun will expand into a red giant and shed its outer layers into space. The core the star would be left to collapse under its own gravity until its atoms are packed so tightly that a match box of material from its would weigh as much as a full-grown elephant. This remnant is called a white dwarf.

For a star whose core is more massive than 1.4 the sun's weight, a supernova occurs. This happens when a giant star runs out of hydrogen fuel. The star fuses heavier and heavier elements until the core is iron. Stellar fusion is discussed here and here. When the star attempts to fuse iron, however energy is taken in rather than released, upsetting the balance between contracting gravity and out flowing energy. Matter bounces off the core as it contracts and powered by tiny neutrinos the star rips apart. After a supernova, there are two possibilities for the star's core. One is to become a neutron star (also called a pulsar). The core collapses and atoms break under the extreme pressure. Protons and electrons combine to form neutrons and the particles are packed as tight as possible, forming a neutron star. Over a solar mass of matter is packed into a sphere only about 15 miles across. A pinhead of material from this star would weigh more than the Titanic. For the first million years of its existence, the neutron star's magnetic field is so strong (thousands of times as strong as Earth) that intense radiation beams are shot from its poles. If the beam passes Earth, a pulse is recorded earning it the name pulsar.

The other possibility for a star's core after a supernova, one weighing more than four suns, is that it collapses further to become a black hole. A black hole is gravity's greatest victory. It sucks matter in, and since its escape velocity exceeds the speed of light, no radiation is emitted, making it "black". More on Black holes can be found here, here, here and here. Everything in our Universe (almost) is orbiting another body because of gravitational pull. The Moon is orbiting the Earth, which in turn is orbiting the Sun, which is orbiting the center of the galaxy, which is orbiting the Local Cluster, orbiting the Local Supercluster. For a spherical body, the strength of the gravitational field at any point is proportional to the body's mass and inversely proportional to the square of the distance of the object. Another star interaction caused by gravity is called a nova. This is when one star of a binary system turns into a black hole. It sucks in mass from its companion, disturbing the energy-gravity balance. The star becomes unstable and eventually explodes. In other words, gravity is the force that rules our Universe.

Wednesday, March 12, 2008

Cosmic Inflation

When the Universe was very young, many scientists believe it went through a period of exponential expansion (note that expansion is exponential because that space seems to actually "grow" between two objects, rather than them moving apart). Evidence for this theory includes characteristics of the Universe today. A rapid expansion would flatten the Universe, which is reflected in the current Universe's structure.  The Universe is also roughly homogeneous, which means that a period of quick expansion may have delayed interactions between particles.  Also, based on the current information, the geometry of the Universe is the same in all directions which means its also isotropic, also a sign of rapid inflation.  Scientists have yet to explain this theory, but they have suggested the existence of an inflaton, a particle or field used to explain inflation.  But the real cause of this expansion, or proof that it even happened is currently out of reach. 

Black Holes and Universe Budding?

Some people believe that the Universe itself is a giant Black hole, expanding and eventually contracting in a Big Crunch. Then a chain of universes follow from successive Big Crunches and Big Bangs. But if a Black hole can form a Universe, what about Black holes formed by collapsed giant stars? This opens an idea called Universal Budding. It states that a Black hole in our Universe can begin a baby universe. It would then expand into another dimension and set separate laws of physics. Thousands of universes could bud from ours.

Tuesday, March 11, 2008

The Big Bang

Before the quark epoch of the Universe (10^-12 to 10^-6 seconds after the Big Bang), theories were less accurate and more speculative.  This is due to the massive energy needed to duplicate the reactions.   Among these early epochs are the Planck epoch, the grand unification epoch, the inflationary epoch, and the electroweak epoch.  The first and most unknown period of the Universe was the Planck epoch (up to 10^-43 seconds after the Big Bang).  This epoch (named after Max Planck) happened before the first unit of Planck time was over.  Due to the fact that this is supposed to be the smallest unit of time possible, the happenings during that time would defy all laws of physics.  During the Planck epoch, all four of the forces were of equal strength, and therefore unified.  Scientists think that the development of the Quantum Gravity theory will shed light on the secrets of this epoch.  The second of the Universe's epochs was the grand unification epoch (10^-43 to 10^-36 seconds).  During this epoch gravity separated from the other three forces.   The inflationary epoch (10^-36 to 10^-32 seconds) was an epoch of extremely fast expansion.  The conditions of the Universe had not settled enough for quarks or anti-quarks to form.  This epoch is discussed more specifically in another article.

 The electroweak epoch (10^-36 to 10^-12 seconds) was the last of these early epochs.  This period was cool enough to separate the electromagnetic and the weak nuclear force (combined) from the strong nuclear force.  The beginning of this epoch allowed the formation of W, Z and Higgs bosons.  Also, the rapid, exponential expansion that occurred during the inflationary epoch had slowed to allow particles such as quarks and neutrinos, to form.  No matter what happened in the early Universe, the actual Big Bang and its causes may never be fully understood.  The best theory about the cause is the Big Bounce theory (discussed briefly in the Big Crunch article).  But this subject is mainly a topic of imagination.

Hadron and Lepton Epochs

Before these eras, the early Universe was dominated by quark-gluon plasma. Th first of the two, the Hadron epoch, began .000001 seconds after the Big Bang. In this epoch, quarks became stable enough to bind together and form hadrons such as protons and neutrons. At 1 second after the Big Bang most hadrons and anti-hadrons annihilated each other leaving a residue that would later form atomic nuclei in a process called Big Bang Nucleosynthesis. The lepton epoch lasted from 1 to 3 seconds after the Big Bang. In that time leptons, including electrons, and anti-leptons were formed. At the end of the epoch, these pairs were annihilated as well, leaving another small residue. After these epochs the Universe was dominated by photons until about 380,000 years after the Big Bang.

Monday, March 10, 2008

Big Bang Nucleosynthesis


The Formation of Stars and Galaxies in the Universe

For a while after the Big Bang the Universe had almost no structure.  The Universe was a void filled with sparse amounts of Hydrogen, Helium (formed by early fusing of Hydrogen under high pressure), dark matter, and dark energy.  Then, as the Universe cooled, dark matter clumped together.  Gravity attracted gases and more dark matter to add to the clump.  A proto-galaxy had formed.  Within a proto-galaxy, pressurized gases formed the first stars.  It is believed that these stars had no metal content.  As the Universe continued to expand more galaxies formed, the very galaxies we look at today were created.  Developing proto-galaxies have been seen through telescopes about 13.2 billion light years away, making the age of the Universe there about 500 million years.

Sunday, March 9, 2008

Geometry of the Universe


The Big Rip

The Big Rip is yet another theory describing the possible fate of the Universe.  In this theory, the expansion of the Universe reaches infinite speed (due to to balance between Dark Energy and Dark Matter), and everything in it, even atoms, are ripped apart.  According to the theory, 60 million years before the end of the Universe, every galaxy but the Milky Way  would be out of visible range from the Earth.  Right before the end, the galaxy and the solar system (if the solar system still exists) would be gravitationally unbound.  A split second before the end, everything down to atoms would be ripped apart as the expansion speed of the Universe reaches infinity.  If this theory is correct, the Big Rip will happen in approximately 50 billion years.

The Big Crunch

If the amount of Dark Energy in the Universe was reduced to lower than the amount of Dark Matter a phenomena called the Big Crunch will occur.  The Universe would slow down its accelerated expansion and reverse.  Black holes would engulf stars and eventually entire galaxies as everything contracted.  As the shrinking increased in speed, black holes would swallow each other and the universe would end as an almost indefinitely tiny singularity, all matter squeezed into a small speck at the center of a black hole.  A variation of this theory is called the Big Bounce.  It includes the possibility that a Big Crunch would lead to another Big Bang, therefore creating a  second universe.  This theory opens up another important question.  Are we the first, five hundredth, or the one trillionth universe?  This question is explored in another article.

The Big Freeze

Of all the Ultimate fates of the Universe the Big Freeze is the most supported. This theory proposes that the Universe reaches a temperature too cold to sustain life. This would happen because as the Universe expands, the Cosmic Background Radiation (formed immediately after the Big Bang) would fade away completely causing the temperature of the Universe to drop. Once a star dies its gases used to create another star wouldn't group together and begin fusion because extreme cold means no moving particles. The Universe's temperature would reach absolute zero (-459.67 Fahrenheit) and stay that way forever.