Category Archives: Physics

The Building Blocks

Have you ever wondered what everything is made of? What gives different substances their distinctive properties? Why are substances solids, liquids, or gases? Why are they soft or hard; light or heavy? And if we probed matter at the deepest possible level, how small would it be? Certainly we are not intuitively equipped to interpret the world at the microscopic scale. When it comes to extremely small things, it’s out of sight, out of mind. Our senses operate on a different field altogether. Scientists, however, have somewhat closed the intuitive gap. They have identified the atom as the basic structure of matter—the building blocks of nature. In A Short History of Nearly Everything, Bill Bryson writes:

“The Great Caltech physicist Richard Feynman once observed that if you had to reduce scientific history to one important statement it would be: ‘All things are made of atoms.’ They are everywhere and they constitute everything. Look around you. It is all atoms. Not just the solid things like walls and tables and sofas, but the air in between. And they are there in numbers that you really cannot conceive.”

Although understanding the behavior of atoms is far beyond most of us, the basic components and arrangements that make up the atom are fairly straightforward. The traditional visual model of the atom (although not entirely accurate) consists of a nucleus made up of protons and neutrons, and electrons orbiting on the outside. In reality the atom is mostly empty space; it could never be illustrated to scale on a single sheet of paper or a computer screen. If we drew the atom to scale, with protons and neutrons a centimeter in diameter, it would take more than 30 football fields to draw out its total diameter. Atoms are 99.99 % just empty space. If that is the case, why don’t we walk right through walls or fall through the floor? This is due to the atom’s electrical charges. We don’t fall through the floor because the electrically charged atoms of the floor repel the electrically charged atoms of our feet. When we walk across the floor we are not actually touching the floor, but levitating at a height of a hundred millionth of a centimeter.

Now let’s get back to the structure of the atom. The electrons and quarks are believed to be the irreducible elementary particles that make up the atom. Quarks are grouped together in the nucleus to form protons and neutrons. Electrons whiz around the nucleus, not like orbits as the tradition model portrays, but more like a cloud of electrons that simultaneously occupy every possible location. Protons and electrons carry opposite electrical charges, which are arbitrarily called positive and negative—protons have a positive charge, and electrons have a negative charge.

The number of protons determines an atom’s chemical identity. Hydrogen, which contains only one proton, is the simplest element. Helium has two protons, lithium three protons, and so on. Every time you add a proton, you get a new element, up to about one hundred that are listed in the periodic table. The number of electrons is equal to the number of protons. This means that generally an atom has no net charge, because the positive and negative charges cancel out. However, certain atoms can lose or gain electrons, and acquire a charge—either positive or negative. This is called an ion. Neutrons have no charge, but they contribute to the atom’s mass. The mass of a neutron is equal to the mass of a proton. What’s more, although neutrons share the nucleus with protons, they don’t influence an atom’s chemical identity. Similar to electrons, the number of neutrons is usually the same as protons, but not always. They can vary, either more or less. In a nutshell, that’s the basic structure of the atom.

When two or more atoms are joined in a stable arrangement, you get a molecule. A molecule may consist of atoms of a single chemical element, such as two atoms of oxygen. Or it may also consist of different elements, such as a water molecule (H2O), which is made up of two hydrogen atoms and one oxygen atom. Although everything is made up of atoms, an element is the simplest arrangement, which cannot be split by chemical means. A compound consists of two or more different elements that are held together by chemical bonds. Therefore, water is a compound, composed of two elements, which are hydrogen and oxygen.

Another point worth noting is that there is no fundamental difference from one like subatomic particle to another. Every proton is exactly the same, irrespective of the element it is a part of. A proton in a hydrogen atom is identical to a proton in an oxygen atom or a helium atom. The same is true for neutrons and electrons.

Atoms are extremely small, abundant, durable, versatile and useful. It is difficult to get an idea of the scale of atoms. Numbers alone cannot really convey what’s going on down there, but I will give it a try anyway. Let’s start with size. If you examine the metric scale on an ordinary ruler, you will typically see numbers that mark out thirty centimeters. Each centimeter will also be divided in ten increments (those are millimeters). Take one millimeter and divide it into one thousand equal lengths, and you have microns. Now you are down to the scale of microorganisms, but you have not yet come close to the scale of atoms. To get down to the size of atoms you have to divide a micron into ten thousand equal lengths. Finally, you have reached your destination in inner space—the scale of atoms—one ten-millionth of a millimeter.

From our medium world perspective (somewhere in-between the universe’s large and small scales), this is an unimaginably small scale. Half a million atoms could hide behind the thickness of a human hair. And the size of an atom in relation to a millimeter is comparable to the thickness of a sheet of paper to the height of the Empire State Building. You may think we have reached the end of the line, but remember that atoms are made up of even more elementary particles. The nucleus is ten thousand times smaller than the whole atom, and electrons are at least ten thousand times smaller than the nucleus.

With some kind of idea how small atoms really are, there is virtually no point contemplating the actually number of atoms that exist—there are just too many. Atoms practically last forever; they circulate from place to place, and when something has outlived its usefulness, the atoms will reassemble to become part of something else. The atoms that make up you and me have been part of countless other living and nonliving things. Actually, this process of atomic reassembling is on-going. Even during our lifetime, the atoms in our body are continually being replaced by new ones—that is, new for us. Nevertheless, it all comes down to one basic realization. Everything is made from different arrangements of the same fundamental ingredients. Just take a look at the world around you. Even though things exhibit different properties, whether you are looking at water, air, wood, stone and metals—or plants, animals and people—it’s all made of the same stuff.


References: Bill Bryson, A Short History of Nearly Everything (London: Black Swan, 2004), 175.


The Universe Revealed Through Modern Science



















There seems to be three possibilities:









Electromagnetism and the Modern Age



Fascination and Curiosity





The Insights of Faraday and Maxwell






Fields, Waves and Light






A World Beyond Imagination








In Our Time: Science, Maxwell, Oct 1, 2003


The Physics of Time?




Einstein’s Revision of Newtonian Time






The Laws of Physics, Entropy and The Arrow of Time







The River of Time






Change as The Scorekeeper of  Time











The Anthropic Principle

the astronomerWhy are we here? This is perhaps the most fundamental philosophical question. One can imagine contemplating this question at any time in human history. Many stories have been inspired by this question, usually taking the form of myths, or religious and spiritual traditions. Today, ‘why are we here’ is also a scientific question. The anthropic principle arose as a response to the question of human existence. The idea was first proposed in 1973 by theoretical astrophysicist Brandon Carter. Since then it has been expanded and stated in several forms.

What is the Anthropic Principle?

The word anthropic is defined by the Merriam-Webster online dictionary as: “Of or relating to human beings or the period of their existence on Earth.” That’s a start. For simplicity I will stick close to Brandon Carter’s original formulation, which he expressed as two variants. I will paraphrase based on the description from a few sources:

  1. The Weak Anthropic Principle refers to our special location in the universe (both in time and space), which is conducive to our existence. The fact that we can observe the universe means that planet Earth must have the conditions necessary for our existence.
  2. The Strong Anthropic Principle refers to the fundamental laws of physics, which are precisely set for our existence. The strong principle takes into account the properties of the universe as a whole.

The Burden of Proof

habitable zoneIn a vast universe it is not surprising that a planet, like the Earth, has a special location (usually called a habitable zone or a Goldilocks zone). The specific laws of the universe needed for human life are more difficult to explain (usually called fine tuning). Using a legal metaphor, the strong anthropic principle has a greater burden of proof than the weak anthropic principle. In this case, burden of proof is a figure of speech, because the anthropic principle is as much a philosophical idea as a scientific one. 

In The Grand Design, Stephen Hawking and Leonard Mlodinow describe the weak anthropic principle as an environmental factor. They write:

“Environmental coincidences are easy to understand because ours is only one cosmic habitat among many that exist in the universe, and we obviously must exist in a habitat that supports life”

The strong anthropic principle is all-encompassing and generally more controversial. Hawkings and Mlodinow go on:

“The strong anthropic principle suggests that the fact that we exist imposes constraints not just on our environment but on the possible form and content of the laws of nature themselves”

Stating the Obvious or a Profound Insight

Is the anthropic principle a satisfying explanation? On the surface, it seems like an obvious statement that explains very little. But as I reflect on the idea, I am not so sure. Maybe it is suggesting something profound. Perhaps the answer to why we are here is simple: it could not be otherwise.

Lawrence KraussFor example, Lawrence Krauss provides an anthropic interpretation to one of the universe’s properties. In the book, A Universe from Nothing, he examines the relationship between the energy density of matter and the energy density of empty space. Yes, space has energy and it can be measured. The density of matter in the universe can also be measured. It turns out that now is the only time in cosmic history that both values are comparable. That’s a curious result.

The universe has been expanding since the big bang, and as it expands the density of matter decreases. Matter gets diluted as galaxies get farther apart from each other. Meanwhile the energy in empty space remains constant (there is nothing to dilute or increase in empty space). Therefore at the time galaxies formed the density of matter was greater than the energy in empty space. That’s a good thing, because the gravitational effect of matter was dominant, which allowed matter to come together.

However, if the values for matter and energy had been comparable at the epoch of galaxy formation, galaxies would not have formed. Empty space exerts a repulsive force, which would have canceled out normal attractive gravity. Matter would not have clumped together. Krauss writes in A Universe from Nothing:


It seems highly coincidental that the energy values for matter and space are roughly equal now, but they could not have equalized too much earlier. Otherwise, no one would be here to observe it. Similarly, if one of a number of physical properties were slightly different, we would also not be here. That’s when anthropic reasoning steps in: An observer must observe the conditions of the universe that allows the observer to exist.

astronomersMaybe a change of perspective is needed: Instead of focusing on our present circumstances and looking back, we can look at the evolution of the universe. Life is a latecomer to the process, of which an incalculable series of events occurred. Our existence is the result of all that came before. Although it does appear that the universe was made for us, it is in fact, the universe that made us. We were formed from the conditions that were set long before conscious beings could observe any of it.

Is Physics an Environmental Science?

The traditional approach of physics is to discover and understand the universe we live in. The fundamental laws and the values for the constants of nature are consistent throughout the observable universe. The physical laws discovered on Earth can be applied to the universe as a whole. But there can only be one exact set of laws and history that allow for our existence. That’s unless our universe is not the only one.

For some, recent scientific evidence is suggesting that there are many universes (a multiverse). Others point out that inferring a multiverse is not science; because by definition other universes cannot be observed directly (they would exist outside our observable universe). If we apply the strong anthropic principle to the multiverse theme, it does partly explain the exact parameters of our universe.

If the cosmos is populated with many universes, possibly infinite universes, then the laws of physics could be purely random. They would simply emerge as an environmental consequence. Some physicists have compared the multiverse to a foam of bubbles (each bubble representing a universe). The laws could be different in every bubble of an endless cosmic foam. Some bubble universes could be similar to ours, others vastly different.

Of course, this is a hypothetical argument. Nevertheless, if we could observe every universe in a multiverse, every single one would be finely tuned for its own existence. Anthropic reasoning would state that there is nothing special about our universe. In all the non-life generating universes there is no one to observe them, in ours there is. It’s that simple. Obviously, the anthropic principle (inferring a multiverse or not) is not a proven argument, but it’s one of many possible answers to the question: Why are we here?



Lawrence M. Krauss, A Universe from Nothing (New York: Free Press, 2012).


The Paradox of Wave-Particle Duality

blue light beam The wave-particle duality of light and other subatomic particles, such as electrons, is a central concept in quantum mechanics. The idea that light and elementary particles have both wave-like and particle-like properties is just one of a number of strange quantum realities. The quantum revolution, which began at the turn of the 20th century, has transformed our world from a technological standpoint. A century later the quantum laws underpin our modern technology. But scientists that were probing the atom in the early 1900s were simply trying to understand the nature of reality at the smallest scales. The challenges proved to be immense, mind-boggling and paradoxical. Wave-particle duality is one paradox that is still not completely understood.

The Photoelectric Effect

Albert Einstein is most famously known for the theories of special relativity, general relativity and the equation E=MC². However, in 1905 he won the Nobel Prize for his explanation of the photoelectric effect. Before Einstein, light was generally thought to behave like a wave, similar to a water wave. But there were some unsolved questions regarding properties of different colored light. Specifically, the ability of ultra-violet light to remove an electric charge from a metal plate (a phenomenon not observed with red light).

Photoelectric Effect

Photoelectric Effect

Einstein proposed that light was composed of packets of energy called quanta (later known as photon). These particles of light acted like miniature billiard balls, knocking the electrons off the metal plate. According to Einstein, the particles from the red light carried low energy, because red light has a low-frequency. Conversely, the higher frequency ultra-violet light contains higher energy particles, which were able to dislodge the electrons from the metal plate. With the analogy of the billiard balls, it was like the ultra-violet particles were heavier than the red light particles. Therefore, the heavy particles of light were able to knock off the electrons, while the lite particles could not.

Einstein’s explanation of the photoelectric effect showed that light was made up of individual particles. It opened the doorway to a new branch of physics. Although Einstein played a key role in the foundation of quantum physics, he never accepted the implications that the theory would eventually bear out. The idea that the quantum world was ruled by uncertainty, did not sit well with him. Einstein supported the classical view of physics, where precise predictions and conclusions could be made. Referring to the probabilistic foundation of quantum mechanics, Einstein said: “God does not play dice.”

 The Double-Slit Experiment

The discovery of the wave-particle duality of light was only the beginning of the paradoxes that would later emerge. A simple experiment, known as the double-slit experiment would overthrow any common sense notion of the quantum realm. The experiment worked as follows: An electron gun was set up to fire an electron beam through a barrier with two open slits. A full screen was placed a small distance behind the barrier. One would expect that the electrons that go through the slits would strike the background screen and produce two bands. However, the outcome showed not two, but a number of bands across the length of the screen; a striped pattern emerged.

Double-Slit Experiment

Double-slit Experiment

The electrons were behaving like a wave; the stripes were consistent with an interference pattern. This had already been observed in water waves. For instance, when two ripples in a pond meet they interfere with each other, causing the similar interference pattern that was observed with the electrons. Water is composed of individual molecules and together they combine to form a wave. Similarly, the electrons were exhibiting both wave-like and particle-like properties (this was also observed in light).

If this was not strange enough, the next step of the experiment would reveal a greater paradox. When the electron gun was allowed to fire one electron at a time, the screen in the back would eventually show the same striped pattern. How could single electrons produce an interference pattern? To point out how strange that was: it was like a single electron was passing through both slits at the same time, or like each electron was carrying information from the wave as it was passing through the slits.

Explaining the Impossible

Niels BohrDanish physicist Niels Bohr, one of the founders of quantum mechanics provided a possible explanation. It is known as the Copenhagen Interpretation. According to Bohr, the electrons that travel from the gun to the screen cannot be viewed as single point particles, but rather as a probability wave. In other words, an electron exists only as a spectrum of possibilities when it travels. It carries with it every possible path from the gun to the screen, including passing through the two slits at the same time. Only when it strikes the screen is the electron forced to take an exact position.

In this view, each electron will strike the screen at a different point, however, with a sufficient number of electrons the striped pattern will emerge on the screen. Whether the electrons are traveling in a continuous beam or as single travelers, the outcome will produce an interference pattern. Even if it is not completely understood, wave-particle duality is a fundamental property of the quantum world.

It is safe to say that Einstein and Bohr disagreed as to what is ultimately responsible for quantum uncertainty. For Bohr it was enough to apply a workable mathematical framework (based on probabilities), but for Einstein there must have been an undiscovered classical principle guiding the process. A century after Einstein and Bohr there is still no classical physical principle (one that agrees with common sense) that explains the uncertainty of quantum mechanics. However unsatisfying, it seems that Bohr’s explanation of the double-slit experiment is still as good as we have. Nevertheless, Bohr realized the gap between quantum mechanics and everyday experience, he said: “If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.”

In time, Bohr’s approach would lead to a revolution in technology. Even if exact outcomes cannot be known, physicists can calculate probabilities that will allow electronic devises to work. Similar to the double-slit experiment, even if the path of each individual electron cannot be known, the overall pattern can be predicted. Today, computers, mobile phones and GPS devices operate based on quantum mechanics.


References: The Secrets of Quantum Physics Episode 1 Einstein’s Nightmare BBC Documentary 2014. Published on Feb 28, 2015.

Brainy Quote, 2001-2015.

Brian Greene, The Fabric of the Cosmos.

Nature’s Fine Tuning and the Multiverse

numbersThere are a number of fundamental physical constants of nature, in which their values seem to be finely tuned. Examples of  such constants are: the speed of light, the strength of gravity, the mass of the elementary particles, and the strength of the atomic forces. The fine-tuning angle comes into play when one considers the exact parameters of the constants. Hypothetically, if one were to adjust the values just a little bit, the universe would be vastly different. This fact alone does not present a problem. However, physicists have noted that minor changes to the values of the constants would not allow life to develop. It is as if the universe knew we were coming, or is it?

The values of the physical constants are critical for giving our universe the structure that it has. For example: the precise strength needed to hold the atomic particles together in stable arrangements, and the gravitational force needed to clump matter into stars and planets. If the strength of gravity was slightly weaker, matter in the early universe would have spread apart too quickly; thus preventing stars from forming. Conversely, if the gravitational force was a little stronger, matter would have come together too quickly and everything would have collapsed. It is clear to scientists that gravity, as well as other values, could not be adjusted very much without erasing the possibility for life.

The Most Extreme Fine Tuning

Although the apparent fine tuning of the constants demand an explanation, nothing compares to the level of fine tuning of one particular constant. This is called the cosmological constant (also called dark energy), and it represents the value of the energy in empty space. The cosmological constant is believed to exert an outward force, which is causing the universe to expand at an accelerated rate. In 1998, the value of the cosmological constant was measured by two teams of astronomers. The number they came up with is extremely small, a decimal point followed by 122 zeros and a one (measured in Planck units).

The energy in empty space, represented by the cosmological constant, is only relevant at the largest of scales. As the universe expands the amount of space is also increasing, thus increasing the effect of the dark energy. But in the distant past when the universe was much smaller, the total energy in space would have produced a far lesser effect. And here is the catch. If the outward push of the cosmological constant was slightly larger by a few decimal points, it would have counteracted the pull of gravity too quickly. This would have prevented stars, planets and galaxies from forming. In this scenario life would not exist.

By removing just a few zeros from an already small value, a universe suitable for life would disappear. Physicists are at a loss to explain why the number is so small and so finely tuned for our existence. In addition, the value of the cosmological constant revealed by observations is far less that what theory predicts. That is, the theory of the microscopic realm (quantum mechanics) predicts that the energy in empty space should be much larger. The mismatch between theory and observation does not sit well with physicists, as it shows that there is something missing with this picture.

Possible Solutions

The specific values of the physical constants require an explanation. Some people will look for a metaphysical solution. This will usually imply a creator for the universe who setup the constants for a purpose. The word God is the preferred choice, and it suggests that the universe was planned for our existence. Yet for others, crediting God for designing the universe in a special way is a non-explanation. One would still have to explain where God came from and why he was there in the first place.

Another line of reasoning would be to accept that mere chance accounts for the constants. But given the amount of fine tuning, this seems akin to winning a lottery with an infinite number of combinations. Chance alone is not a very satisfying solution. There is also the possibility that we don’t have enough information to solve the problem. Maybe a deeper understanding of the laws of physics is needed, and someday physicists will find the answer.

 The Multiple Universe Proposal

multiverseThe word universe has traditionally been used to describe all that exists. However, cutting-edge physics is requiring that a change of perspective is needed. Through a variety of physical discoveries the idea of multiple universes is being considered. The words parallel universes, parallel worlds, alternate universes, multiverse and others are being used. In the multiple-universe theme, the word universe has a slightly different meaning. Universe no longer means all there is, but rather means a region of a larger cosmos that is separated from other regions.

Physicist and science writer Brian Greene states, in The Hidden Reality, why the concept of multiple universes is compelling:

” The subject of parallel universes is highly speculative. No experiment or observation has established that any version of the idea is realized in nature… That said, I find it both curious and compelling that numerous developments in physics, if followed sufficiently far, bump into some variation on the parallel-universe theme.”

Although not yet experimentally tested, having large numbers of universes (possibly infinite) could explain the fine tuning of the physical constants. The logic is simple. With many universes, with different possible values for the constants, it is likely that one has the values we observe. Therefore, it is not surprising that we find ourselves in a universe that allows life. In the universes that have conditions that don’t allow life, there is no one to observe them, no one to say that they are not finely tuned for life.

As Brian Greene suggested, there are several theories in physics that imply a multiverse. The reasoning is technical, though I will list a few examples, which point to the possibility of a multiverse:

  • Eternal Cosmological Inflation: The extreme burst of spatial expansion at the early moments of the universe is known as inflation. Inflation is a cosmological principle, which in theory could happen anywhere, thus giving rise to multiple big bangs.
  •  A Spatially Infinite Cosmos: By inferring an infinite expanse of space-time, there is a limit to ways particles of matter can be arranged. Conditions in one location would eventually have to repeat somewhere else, creating parallel universes.
  •  The Extra Dimensions of String Theory: String theory proposes that at the tiniest of scales there exist extra spatial dimensions. It also states that there are many possible shapes for the extra dimensions of space. However, string theory cannot determine which of the shapes corresponds to our universe. If string theory is correct, the different possible shapes for these extra dimensions could be realized in different universes.
  • The Many-Worlds Interpretation of Quantum Mechanics: The atomic/subatomic realm is governed by randomness and understood using probabilities. Interpretations can vary. The many-worlds interpretation states that all the possible outcomes associated with quantum mechanical probabilities really happen, resulting in parallel worlds.

parrallel universeNot all the multiple universe proposals would yield different values for the constants. Some would produce exact replicas of our universe, or very close copies. Hence the term parallel universe. Yet other proposals would allow for different laws of physics or different values for the constants. These could be universes that are totally foreign and barely recognizable to us.

Whether we live in one of multiple universes is anyone’s guess. Presently, there is no known method that could observe them. Nevertheless, there are plenty of cases where physical theories or mathematics have pointed toward a phenomenon in nature, even before it was observed. And then at some later date, observations confirmed the theory. Therefore, if modern physics is suggesting the existence of a multiverse, it provides an interesting argument for the fine tuning of the physical constants of nature.


References: Brian Greene, The Hidden Reality (New York: Alfred A. Knopf, 2011), 8, 9.

Leonard Susskind – Is the Universe Fine-Tuned for Life and Mind? (Closer to Truth), Published on Jan 8, 2013.

 The Fabric of the Cosmos – Universe or Multiverse (Published on July 16, 2014)


The Cosmological Constant: From Einstein to Dark Energy

EinsteinThe cosmological constant has its humble beginnings with Albert Einstein’s theory of gravity. In 1915, after a decade of working on some unsolved issues regarding gravity, Einstein completed the theory of general relativity. Today, this is still the best theory we have for describing how gravity works at large scales. Nevertheless, 2 years later (in 1917) Einstein made a small adjustment to the equations of general relativity. He introduced a term called the cosmological constant, which represented a repulsive force to counteract the attractive force of gravity.

Einstein realized that general relativity would require the universe to either be expanding or contracting, however, the belief at the time was that the universe was essentially static and eternal. Because gravity causes large structures to attract each other, logic would deduce that the universe as a whole should be contracting. But this was neither observed nor part of conventional thinking. The cosmological constant, a repulsive force with just the right value, allowed the universe to remain static. Although the cosmological constant was present in all of space, Einstein provided little details concerning what this mysterious force actually was.

Einstein’s Greatest Blunder

In 1929, Edwin Hubble carefully studied light from distant galaxies. He calculated the distance of the galaxies by examining the luminosity of a specific type of star, known as a Cepheid variable. The light from a Cepheid displayed a distinct pulsating pattern, which could be used as a distant indicator.

Hubble expanded on the work of astronomer Vesto Slipher, who was the first to observe the redshift of distant galaxies (although they were called spiral nebula at the time, because it was not yet known that other galaxies existed beyond our Milky Way). The redshift meant that incoming light waves were stretched, indicating that the observed light was moving away. This provided evidence that the galaxies were moving away from the earth. And even more significant, Hubble found that all galaxies were also moving away from each other.

Hubble’s observations confirmed that the universe was expanding. Upon learning the news, Einstein went back to his equations and removed the cosmological constant, as it was no longer needed to maintain the former belief of a static universe. It has been reported that Einstein called the cosmological constant his “greatest blunder.” Despite Einstein’s claim, the cosmological constant would resurface many decades later, but it came as an unexpected turn of events.

The Universe is Accelerating

galaxyAs of 1998 the expansion rate of the universe over cosmic time was still unknown. Either the universe would continue to expand forever, or the gravitational effects of galaxies would cause the expansion to slow down and perhaps stop. If at some time the expansion did stop, then it would stand to reason that gravity would cause the universe to collapse. This would lead to something like the opposite of a big bang (a big crunch).

The rate of expansion will determine the future fate of the universe. But how can one determine the expansion rates at different time periods? How can we know how the current expansion rate compares with past rates? Fortunately, the universe is extremely large and extremely old. Light from faraway galaxies can take millions and billions of years to reach the earth. This allows astronomers to go back in time and examine galaxies as they were in the past. The light we see now was emitted many years ago; these stars and galaxies appear as they once were.

Two international teams, one lead by Saul Perlmutter, the other by Brian Schmidt, set out to determine the expansion rate over cosmic time. They applied some creative methods based on a specific type of exploding star, called a Type Ia supernova. At the end of their lives these particular stars explode in a consistent pattern, which signal an intrinsic brightness. The astronomers determined a star’s distance from earth using the information from a Type Ia supernova. Then they calculated the redshift of the star’s host galaxy, and made the calculations with a number of galaxies at various times in the past.

Accelerating universeThe two teams eventually arrived at the same conclusion. The galaxies are currently receding faster than they were in the distant past; the universe is accelerating! This was an unexpected result, as it was mostly assumed that the expansion was slowing down over time (due to the attractive force of gravity).

The Return of the Cosmological Constant

If gravity is an attractive force, then what could be causing the universe to speed up. Enter the cosmological constant or its reincarnation, dark energy. Einstein’s hypothesis of a repulsive force that was counteracting gravity may not have been far off base (though his reason for introducing it was misguided). An unknown form of energy in empty space seems to be responsible for the acceleration of the universe. It has been dubbed dark energy because it does not emit light, but it could also be a term that points to the mysterious nature of this type of energy. Dark energy does, however, make up 70% of the total energy of the universe. Remarkably, this has been calculated and it seems to describe the universe we live in.

One more point of note: Since dark energy/cosmological constant is presumed to occupy all of space, its overall influence increases as space expands. Therefore in the distant past, when the universe was more condensed (relatively speaking) attractive gravity was dominant. The expansion of the universe slowed down at some point. However, as space swelled and galaxies moved farther apart, the dark energy caught up and then surpassed gravity as the dominant force. The tables turned, causing the universe to speed up.

Current evidence supports a cosmic story in which the universe will continue to expand practically forever. Galaxy clusters, like our local group, will still be held together by normal gravity, because they contain enough matter. However, in the far future all evidence from beyond our local group will disappear. The universe will be comprised of a bunch of island universes.


References: Mysteries of a Dark Universe: Uploaded on Oct. 31, 2011.



Ludwig Boltzmann: The Master of Disorder

BoltzmannThe principle in physics called entropy has a convoluted history. The genesis of the idea started in the 1800s with the industrial revolution and the advent of steam engines. Although steam power was producing an incredible amount of energy and transforming societies, the fundamental physical laws behind the process was largely unknown. The full story behind solving this question concludes with Austrian physicist, Ludwig Boltzmannand his view of entropy. His insights into the physical reality behind heat and energy were later applied to a much larger scheme, including the whole universe.

The Universe in a Coffee Cup

Why does a hot cup of coffee left on a table get colder over time? The answer to this simple question is at the heart of Boltzmann’s idea. The explanation is due to the behavior of atoms. Today, the existence of atoms is taken for granted, but back in the late 1800s many prominent scientists did not believe in atoms (including Ernst Mach, one of Boltzmann’s adversaries). No one had observed an atom, and it was thought that no one ever would. Nevertheless, Boltzmann peered deeper into the physical world than any of his contemporaries.

cup of coffeeLet’s get back to the hot cup of coffee. The heat from the coffee will disperse to the cup, the table and the surrounding air, until the temperature of the coffee is roughly equal to its environment. The same amount of energy still exists, but now covers a wider area. The flow of energy, left alone, will always flow from a hot source to a cold source. This natural flow of energy was the secret behind the steam engine, as the heat energy was converted to physical work. Boltzmann realized that this phenomenon of heat transferring and dispersing could be explained within the framework of atoms.

In the hot coffee, the atoms are tightly arranged and jostling about. The vibrations of the atoms are responsible for the heat. But as they move they contact the atoms of the cup, and transfer some of their energy. This continual process of bumping eventually distributes the heat energy to a much larger number of atoms. In the hot coffee the atoms are arranged in a unique way, but there are may possible arrangements in which the atoms can spread out. In the language of entropy, the system has moved from low entropy (an ordered state) to high entropy (a disordered state). The natural tendency for systems to move from order to disorder is now understood as a fundamental principle that underpins the entire universe. Loosely speaking, this describes the second law of thermodynamics.

 What is Order and Disorder?

disorderClassical physics, the method of scientific reasoning that held sway since Issac Newton, demanded that precise calculations were made. Physics was about discovering exactly how things moved and interacted. If atoms really existed, the sheer amount of them imposed an almost insurmountable problem. How could they ever be studied? Boltzmann took a different approach. Perhaps his greatest insight was that the motion of atoms could be described mathematically by using statistical probabilities. In addition to studying atoms, probabilities could be used to determine the amount of entropy in any system. This idea leads us to a definition of order and disorder:

  • Disorder means that there are many configurations, if changed, which would go unnoticed.

For example, take the analogy of a deck of playing cards. Dealt at random, there are few arrangements of cards that will line up in numerical order. Conversely, there are many arrangements of cards that will be mixed up. The reason is obvious. The probability is much higher for a disordered configuration than for an ordered configuration. Order is a special and unique condition, while disorder can come about in numerous ways. Therefore, we can conclude that high entropy (disorder) is a more natural state. We can still create order, but we need to intervene in some way. Still, any system left alone will move from order to disorder (or entropy will increase).

Statistical Reasoning

The entropy in a cup of coffee will tend to increase. Someone has to create the order by heating up the water and making the coffee. What would be the likelihood that the heat would naturally occur in the coffee? Of course we know that doesn’t make any sense. Thus by statistical reasoning, it makes perfect sense that disorder is more likely than order. Entropy, and in turn the second law of thermodynamics, is based on the probability of how any physical system will evolve. Eventually, everything dissolves, crumbles, decays, degrades and collapses.

We don’t need to look any further than our own homes, as it is a constant effort to maintain order (the special condition where items are neatly arranged). Disorder happens much more naturally, because there are many more ways in which the home can be disordered. Left unchecked, dirty dishes will accumulate, laundry will build up, and things will get scattered. The condition of the home’s structure will also degrade over time. This is all due to the principle of entropy.

A Story of Triumph and Tragedy

Boltzmann’s theories were highly controversial in his time; many prominent physicists rejected his ideas. And to make matters worse, he suffered from severe bouts of depression (probably due to undiagnosed bipolar disorder). On the positive side, he also went through periods of intense creativity. Aside from describing what entropy actually was, Boltzmann was able to put numbers to his theory. He devised a mathematical formula that could calculate the amount of disorder in a system.

His use of probabilities went against years of certainty behind the theories of classical physics. In the early 20th century, scientists would soon find his method useful in probing the atom. Probabilities would become a fundamental feature of quantum mechanics. The sad part to the story is that Boltzmann’s achievements would only be recognized after his death. In 1906, he committed suicide during one of his episodes of depression. Whether the final blow was delivered by his mental illness or the lack of recognition for his work is unclear. Nevertheless, his lasting legacy is engraved on his tombstone in Vienna: his equation for quantifying entropy, S = K log W.


References: Order and Disorder the ENERGY – HD Documentary, Published on June 24, 2014.


Decoding Light to Unlock the Secrets of the Universe

prism Much of what we know about the large-scale universe is due to decoding signals from light. The light that reaches the earth from faraway galaxies arrives as a wide spectrum, which is much more than visible light (or white light). Light is actually an electromagnetic wave with a range of wavelengths. White light is but a tiny band in the middle of the spectrum of wavelengths. When white light is refracted, such as passing through a prism, we see the colors of the rainbow.

If we move past the red band the wavelengths get longer, from infrared to microwaves to radio waves. Moving towards the opposite side of the spectrum, past the violet band, the wavelengths get shorter, from ultraviolet to x-rays to gamma rays. Even though the large majority of light is invisible to us, scientists have instruments that can detect information from the spectrum. The following list shows 5 things we know about the universe from decoding light.

1) The Contents of the Universe

Exploring the universe started simple with just visible light; ancient astronomers gazed at the night sky with the naked eye. All the twinkling yellow dots basically looked identical. They could not determine the size and distance of objects. The advent of the telescope added detail to the night sky, such as differentiating stars from planets and discovering individual galaxies.

Space telescopes, like Hubble and Kepler, are now placed in the earth’s orbit. From above the atmosphere, these and other instruments are collecting a tremendous amount of details about the universe. For example, the Hubble Space Telescope focused on a dark spot in the sky for a period of 10 days. In this tiny patch (roughly the opening of a drinking straw) an image of 10,000 galaxies was produced.

2) The Existence of Extrasolar Planets

In recent years, over 1,700 planets outside our solar system have been discovered (some of them are earth-like). Most planets orbit stars, therefore planets can be detected by examining changes in starlight, which are caused by existing planets. Astronomers use a number of methods to find planets. The two most effective methods are:

  1. The transit method: By observing a star for a period of time a planet will occasionally pass in front of the star. Viewed from earth, a planet will cause the starlight to dim slightly, thus announcing the planet’s presence.
  2. The Doppler method: As a planet orbits a star it exerts a gravitational effect on the star, which causes the star to wobble slightly. This can be detected by examining variations in the light spectrum as the star moves towards or away from the earth.

3) The Chemical Composition

Light from distant stars and galaxies can be converted into a spectrum of colors. This is achieved with an instrument called a spectroscope, which is attached to a telescope. This is perhaps the most valuable tool for decoding light. As it pertains to the chemical composition of the universe, a particular property of light contains precise information from its source.

When the light spectrum of a star is displayed by a spectroscope, vertical lines (called absorption lines) appear at specific locations, depending on the elements contained in the star. Each element produces a unique pattern of lines, which can be matched with experiments in a laboratory. Even though the information contained in the spectrum will be from a number of elements, the distinct pattern of each element can be sorted out.

Absorption lines

Absorption lines

By studying the information from light, astronomers have found that all the stars in the universe have more or less the same chemistry (including our sun). Thus, knowing that all the elements originate in stars, the chemical composition of the universe is essentially the same everywhere. The elements found here on earth are plentiful in other galaxies as well, leaving us to speculate that other life-sustaining planets may be out there.

4) The Universe is Expanding

There is another valuable piece of information from the spectroscope that has transformed our view of the universes. It is called a redshift. When the spectrum from distant galaxies is examined, the vertical lines are shifted towards the red end. This is due to the Doppler effect or the Doppler shift, and it has to do with the nature of waves. Light is a wave, and similar to sound waves, incoming waves will be stretched when the source is moving away; thus causing the absorption lines to shift towards the red end of the spectrum.



The conclusion from this information is that galaxies are moving away from us. The universe is expanding. The exception to this rule is that nearby galaxies are not expanding, because they are held together by gravitational forces. But for the universe as a whole, galaxies are moving away from each other. In other words, the earth’s location is not unique; the view from any location in the universe would be similar. Incidentally, it is actually the space that is expanding. The galaxies are rushing away because they are being pulled by the swelling of space.

5) The Big Bang

There are 3 ways we can get to a big bang origin of the universe by studying light:

  1. The expansion rate: The universe is expanding at a defined rate (based on the redshift), which is simply stated as: distant galaxies that are twice as far away from us are moving twice as fast, and galaxies that are 3 times as far are moving 3 times as fast. This means that if we reverse the timeline, in the distant past all the galaxies would converge at a point of infinite density. This was the moment of creation.
  2. The cosmic microwave background radiation: The CMBR is the remnant of the intense energy that was created at the big bang. The light from the big bang event has propagated throughout space, and is presently detectable as microwave radiation. Although the radiation is now faint, it is present in all directions of space.
  3. The agreement between prediction and observation: The amount of lighter elements (hydrogen, helium, deuterium and lithium) that are now present in the universe agrees with the predictions of the big bang theory. The quantity of these elements were detected from light coming from old stars and distant galaxies. The amounts are consistent with what the theory predicts would have been created in the early universe.

From an everyday perspective, light illuminates the world and we see things as a consequence. However, when we examine the large-scale universe our eyes alone are not sufficient. It is remarkable that light from very far away contains information from its source. And if not for ingenious techniques in decoding light, figuratively speaking, we would forever remain in the dark.


References: Richard Dawkins, The Magic of Reality

Lawrence M. Krauss, A Universe from Nothing

Stephen Hawking’s Universe -101- Seeing is Believing (June 14, 2013)
The Big Bang: Observational Evidence (June 4, 2012)