Big Bang for beginners-6: The evidence

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

Why has the Big Bang theory become the standard model for understanding the origins of the universe? In the 15th century and earlier, most people thought that the Earth was the center of the universe and that the stars were embedded in a celestial sphere beyond the outer planets and that the size of the universe was not much larger than the Solar System. The Copernican revolution (with the publication of his book in 1543) displaced the Earth from the center of the universe. This led to suspicions that the universe could be very large, possibly even infinite, but there were at that time no good theories to explain its origins and structure.

Einstein’s General Theory of Relativity (published in 1915) provided a framework for building more systematic models of the universe and various theories began to be put forth. The initial ones argued for a static universe in which everything had a fixed and unchanging location. But some early data suggested that some galaxies were moving away from us and around 1922 models of an expanding universe were proposed, with some early suggestions that perhaps galaxies were moving away from us at speeds proportional to their distance from us. Soon after, observational data supporting that theory started coming in, most famously that of Edwin Hubble in 1929 that, while somewhat scattered, seemed to support that general idea.

If this steady movement away from us had been the case throughout all of time (a reasonable enough assumption in the absence of contradictory evidence), people inferred that if we looked back in time, then everything must have been closer to each other than they are now. And if we go back in time far enough, everything would have all converged to a single point. Thus was born the idea of a Big Bang, the basic idea of which was floated around as early as 1927 by Georges Lemaitre (a Belgian physicist who was interestingly enough also a Roman Catholic priest) and made concrete by George Gamow in 1948, along with the prediction that if this theory were true, the present temperature of the universe (as measured by the primordial photons left over from that initial state) would be around -268 degrees Celsius (5K).

At around the same time another theory called the Steady State was also proposed. This theory also assumed that the universe was expanding but that new matter was also being produced continuously to keep the density of the universe constant. The underlying idea behind this was something called the Perfect Cosmological Principle which said that the universe should look the same everywhere, in every direction, and at all times. This meant that the density of the universe should not change with time either. The amount of new matter that was needed to keep the density constant as the universe expanded was really small (about one hydrogen atom per cubic meter per billion years) but the key idea that the total matter in the universe was not constant made it radically different from the standard Big Bang model.

In 1964, the temperature of the universe was accidentally measured by scientists who had been looking for something else and was found to be -270 degrees Celsius (2.7K). This gave a huge boost to the Big Bang theory.

Another early prediction of the Big Bang theory was the relative abundance of light nuclei (hydrogen, helium, lithium), all of which depended on just one parameter, the total density of protons and neutrons at the time the nuclei were created. The measured values of the light nuclei are in good agreement with the predictions.

These successes added to the credibility of the Big Bang theory and pretty much eliminated the appeal of any competitors. The theory has since moved from strength to strength as scientists have used this basic model to make new predictions that can be tested. These later evidences include the large-scale structure of the universe and the evolution of galaxies, all of which are in reasonable, though not perfect, agreement with expectations.

There is one item about the evidence that I listed in favor of the Big Bang that might have puzzled some readers. I said that Edwin Hubble’s initial data and those that came later seemed to confirm early speculations that all the objects in the universe are moving away with speeds that are directly proportional to their distance from us. i.e., if galaxy A is moving away from us with some speed, then galaxy B that is twice as far away will be moving with twice that speed.

The question is why are they all moving away from us? Don’t they like us? Oddly enough, such an issue would not have been a problem to someone living in pre-Copernican times when it was thought that the Earth was the center of the cosmos. But with the Copernican revolution, it has become common to think that Earth does not occupy any special place in the universe. So wouldn’t you expect at least a few galaxies to be moving towards us since we are not located at a special place in the universe? How do we explain this?

Then explanation goes back to the crucial idea that it is space that is expanding as a result of the Big Bang. We need to go back to the raisin bread analogy from yesterday. If we view the dough as space and the raisins as the matter that is dragged along with the dough (space), then as the dough expands uniformly everywhere, it is easy to show that every raisin will be moving away from every other raisin and its speed will be proportional to its distance from that raisin. This is true irrespective of which raisin we choose as the vantage point from which to make measurements of velocity and distance.

The idea that no particular point in the universe has any special significance has been extended to what is called the Cosmological Principle, which asserts that when viewed on a large enough scale, the observed universe will look the same irrespective of where the observer might be situated. This implies that the laws of science will also be the same everywhere in the universe and underlies our belief that we can apply the same laws of physics that we have discovered to work so well in our neighborhood of the universe even to the most distant reaches of it.

Next: What about the edge of the universe?

POST SCRIPT: The Galaxy Song

From Monty Python and the Meaning of Life. It captures the sense of wonder at the amazing universe we live in.

Big Bang for beginners-5: Some conceptual challenges

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

Although the story of the Big Bang in its essence is quite simple and straightforward, it contains many fascinating subtleties that are worth exploring further. It is good to get some conceptual hurdles and misconceptions out of the way right now.

When we use the words ‘Big Bang’ it immediately conjure up certain images. We immediately think of familiar explosions, like bombs or firecrackers going off. We envisage a big noise and the exploding pieces hurtling away from the center of the explosion and spreading out into the surrounding space at great speed. This image captures correctly the idea of a hot compressed beginning with a fixed amount of matter spreading out through space and getting cooler and more dilute with time. But there are important ways in which the image is inaccurate.

One simple misconception is to think there was a loud noise at all. The very idea of sound at those huge densities is highly problematic and it is not helpful to think in those terms. But this is a minor misconception. The major misconception that people have is the idea that space always existed and extended all the way to infinity and that the Big Bang occurred in one small region of it and the matter that was created then spread out to fill increasing amounts of that pre-existing space.

What the theory actually says is that the only space that exists is the space occupied by the matter produced in the Big Bang and that, as the matter spread out, it did not fill already existing empty space, but instead it was space itself that was expanding, carrying the matter along with it.

To better understand this difficult idea, a good analogy is raisin bread baking in an oven. The raisins occupy more-or-less fixed positions in the dough. As the bread bakes, the dough expands, carrying the raisins along with it.

The wrong way to interpret this analogy to the Big Bang theory is to think of the dough and raisins as the matter expanding into the pre-existing space of the oven.

The correct way to view the analogy is to think of the bread dough as being space and the raisins as the matter. As the bread bakes, the dough (i.e., space) expands carrying the raisins (i.e., matter) along with it. The hard thing for people to grasp is that there is no space outside of the dough. There is no oven for the dough to expand into. So the ‘explosion’ we speak of is not of matter expanding into space but of space itself expanding.

In addition to the motion associated with the expansion of space, there is also what we call local motion caused by the forces between objects. So for example, Earth and the planets orbit our Sun under the influence of gravity, and our solar system rotates in the spiral arm of our galaxy the Milky Way, again under the influence of gravitational forces. Protons and neutrons in nuclei move under the influence of nuclear forces and electrons in atoms move under the influence of electromagnetic forces. All these motions are due to forces acting locally and not part of the motion caused by the expansion of space itself. Back to our raisin bread analogy, the raisins are not rigidly embedded in the dough. In addition to the raisins being dragged along by the expanding dough, they may also move around slightly in the dough due to (say) air pockets near them. But when we speak of the motion associated with the Big Bang, we are referring to the motion due to the expansion of space and not these local motions.

(It should be borne in mind that the well-known assertion that nothing can travel faster than the speed of light is popularly interpreted a little too broadly. That limit applies to the speed of particles and information flow. But there are things like the collapse of the wave function and the phase velocity of wave packets that occur at speeds greater than the speed of light. As I described yesterday, in the case of the early universe, space expanded at a much faster rate than the speed of light but that too is allowed by the theory of relativity. In other words, the dough can expand faster than the speed of light but the speed of the raisins relative to the dough has to be less than the speed of light.)

One consequence of the view that the Big Bang consists of space itself expanding is that it did not occur at a point ‘in’ space (like a blob of dough in an oven) but occurred everywhere in space simultaneously, and that it is space itself that was initially compressed. So it does not make sense to look for a point in the universe where the Big Bang occurred and treat it as the ‘center’ of the universe. There is also no ‘edge’ or boundary to the universe, so it does not make sense to ask what exists beyond the edge either.

I will come back to these last points later because they are undoubtedly hard to grasp, especially the idea about the absence of a boundary.

POST SCRIPT: Will Ferrell tries out for a part in West Side Story

Big Bang for beginners-4: The speed of cosmic evolution

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

What may surprise people is how rapidly the universe went from a very hot initial state to one in which it was cool enough for atoms and molecules to form. If we push our theories back as far as we dare, bearing in mind that we have stretched them to the limits and that we may well be wrong in some aspects, the earliest time that we can speak of is 10-43 seconds after the Big Bang (called the Planck time). i.e., this is 0.0000… 0001 seconds (43 zeros in all, including the one before the decimal) after the Big Bang. In other words, it is a really tiny time. It is estimated that the temperature of the universe at that time was about 1030 degrees. That is 10 followed by 30 zeros, a really huge number.

It is now believed (according to the inflationary model of the universe), that roughly around 10-36 seconds after the Big Bang, the universe began undergoing an extraordinarily rapid expansion. This expansion lasted for a very short time (a tiny fraction of a second) but it was sufficient to increase the linear size of the universe by a factor of around 1026, which is such a staggeringly rapid expansion that it boggles the mind. After that tiny period of very rapid inflation, the universe settled into the steady and slow expansion that we currently experience.

It took just one millionth of a second for the universe to cool from its extremely hot initial state to a cooler (but still very hot) 1013 degrees, the temperature at which the photons’ energy became low enough that protons and neutrons could form out of quarks and gluons without being immediately blasted apart by them. So quarks and gluons existed in the free state for just about a millionth of a second after the Big Bang and ever since then have been confined in protons and neutrons. At this stage, the universe was now about the size of our Solar System.

About two to three minutes after the Big Bang, its temperature had dropped to about one billion (109) degrees, and now nuclei could also exist without being blown apart by photons. The size of our universe was now about 50 light-years (a light-year is the distance traveled by light in one year which works out to roughly 1014 miles), which is still pretty small when you consider that the radius of just our own Milky Way galaxy is about 50,000 light years.

After about 300,000 years, atoms began forming. The only atoms that could form were the very smallest ones (hydrogen, helium, and lithium) because only their nuclei existed at this time. The temperature of the universe is now about 3,500 degrees.

After about 100 million years all the matter that initially existed as a more or less uniformly spread out gas that occupied the entire universe, start forming into clumps. The atoms in the clumps attract each other because of gravity and they coalesce to form all the galaxies, stars, and planets that the universe now contains. It is estimated that the first stars began to be formed about 150 million years after the Big Bang. Galaxies started forming after about 1 billion years, when the temperature was about 20 K or -253 degrees Celsius. (The temperature scale called Kelvin (K) is used in physics and its value is obtained by adding 273 to the Celsius temperature. For very high temperatures, we can ignore this difference as well as the difference between Celsius and Fahrenheit scales, which is why I have not been too specific about the temperature scale so far.)

The stars that were formed initially consisted of mostly hydrogen and helium. The energy that makes the stars so bright and hot is primarily caused by nuclear reactions in which hydrogen nuclei fuse together to form helium nuclei. It is only within stars that are above a certain size that all the other heavier elements we now have were created. At the end of their lives, these massive stars first collapse and then explode in what we call a supernova, spewing all the heavier elements that they created into space, where they end up in planets like ours. The mass of our own Sun is not large enough to explode in this way. Its life will end with a whimper, not a bang.

So that is the basic story of the Big Bang: Starting with a highly dense, uniform, and hot gas consisting of quarks, gluons, electrons and photons that was compressed into a tiny amount of space that was smaller than a golf ball, it rapidly expanded and cooled to become the vast universe we now have with all the basic elements.

Our universe began 13.7 billion years ago, stars came into being about 150 million years later, galaxies started forming after about one billion years, and our Solar System with the Sun, Earth, and other planets was formed about 4.5 billion years ago.

This graphic gives a summary of the time evolution of the universe.

99-1145D.jpg

If we want to run the clock further to see what happened on Earth alone, bacteria appeared about 3.5 billion years ago, followed by green plants and algae (1.3 billion years ago), the first wormlike animals (600 million years ago), fish (550 million years ago), amphibians (400 million years ago), reptiles (350 million years ago), mammals (250 million years ago), birds (180 million years ago), and humans (6 million years ago), bearing in mind that these numbers are approximate. The New Scientist magazine gives a more detailed timeline for evolution.

In subsequent posts I will examine some subtleties of the Big Bang theory and the evidence in support of it.

POST SCRIPT: Richard Dawkins on Australian TV

Richard Dawkins appeared on an Australian TV panel program called Q/A that takes questions from the audience. It is interesting that Dawkins is the person who most directly answers questions while the others tend to waffle and hedge. Calls for ‘respect for religion’ make their predictable appearance when Dawkins’s points against it hit too close to home. Well worth watching. (Thanks to Pharyngula.)

The program is a little under an hour and can be viewed in six parts. The last two segments deal mostly with a specific Australian issue about how they treat refugees who arrive by boat, an issue that has created a huge controversy in that country.

The very last question gets back to religion with a question about the afterlife. Again compare the wishful thinking of the other panelists with Dawkins’s directness.

Part 1:

(part 2, part 3, part 4, part 5, part 6)

Big Bang for beginners-3: The basic story

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

The starting point of the Big Bang story is a cosmic event that started out small and expanded rapidly (like an explosion). This event brought into being the universe we now inhabit and produced all the matter that our universe is presently composed of, though not in its present form. The time at the beginning is arbitrarily set to zero.

We do not know what happened right at the very beginning (at time zero by our convention) because our known theories are believed to not apply right at the beginning. So our story begins very shortly after the Big Bang occurred. It is believed that what existed then were quarks, gluons, electrons, and photons that were moving freely around in a hot dense gas called a plasma. (There were also a few other exotic particles that I will ignore as they are not central to a basic understanding of the evolution of the universe). As the universe expanded over time, these quarks and gluons and electrons and photons eventually became the ordinary matter that we now have. No new matter was created after the Big Bang, but the form that the matter took did change dramatically.

To understand how this process of evolution occurred, we have to understand two basic relationships.

  1. The ‘temperature’ of the universe is related to the average energy of the photons that the universe contains.
  2. As the universe expands and gets bigger, the same amount of matter now occupies a larger amount of space and so the density of matter gets smaller and the temperature of the universe drops.

So right at the beginning the universe was highly dense because all the matter that now exists in the visible universe was compressed into a region that was smaller than a golf ball, if you can imagine that. As a result, the early universe was extremely hot. Because the density of photons (the number occupying a given region of space) was huge and they were so highly energetic, they could (and did) blast apart every composite object they encountered, so that the only things that could exist in the very early universe were those that could not be further broken up into smaller bits, which is what we think that quarks and gluons and electrons are.

As the universe expanded, it became cooler and the photons became less energetic and after some time their average energy became so low that if some quarks and gluons happened to combine to form protons and neutrons, the photons could not break them apart anymore, so the protons and neutrons remained intact. So now the universe consisted of protons, neutrons, electrons, and (lower energy) photons, with all the quarks and gluons being trapped inside the protons and neutrons and no longer free to move around independently.

As the universe expanded and cooled even more, the photons became even less energetic and they could not break apart any nuclei that happened to be formed by protons and neutrons combining. So now the universe consisted of nuclei as well, along with protons, neutrons, and electrons. The only nuclei that formed during the Big Bang were those of the three lightest atoms: hydrogen, helium, and lithium in decreasing order of abundance, with hydrogen forming about 75%, helium about 25%, and just trace amounts of lithium. (The nuclei of all the hundred or so heavier elements that currently exist were formed in the interior of heavy stars, and so came along much later.)

As time went by, the temperature of the universe became even less, so that the photons could not break apart any atoms that formed by nuclei and electrons combining, so the universe now included atoms as well.

And finally, the temperature of the universe became so low that the photons could not even break apart any molecules that formed.

After that, as the universe expanded and cooled even further, the primordial photons in the universe (i.e., those that were created right at the beginning) had such low energies that they ceased to have any effect on anything else. They became, in effect, disconnected from the rest of the matter in the universe. But these photons still exist, getting steadily cooler, and occupy all of space, surrounding us. They give us important information about the origin of the universe, its evolution, and its eventual fate. It is these photons that are referred to as the ‘cosmic microwave background radiation’.

The term ‘microwave’ is used because the average energy of these primordial photons now is roughly equal to that of the photons produced by your microwave oven. Fortunately for us, the density of these cosmic photons is now extremely low (only about 400 per cubic centimeter) because the universe has become so large. Otherwise we would all be cooked in this cosmic microwave oven. The temperature of the universe at the present time is about -270 degrees Celsius, very close to the absolute minimum temperature that is possible which is -273 degrees Celsius.

Next: How rapidly did this cosmic evolution happen?

POST SCRIPT: Goodbye, Peter Graves

Actor Peter Graves, actor and star of the long running TV series Mission: Impossible, has died at the age of 83. Like Leslie Nielsen, Lloyd Bridges, and Robert Stack, he was better known for serious roles but their deadpan delivery helped make the spoof Airplane! one of the funniest films of all time, one that I watch every few years and it still makes me laugh.

Here is a compilation of the scenes with Graves (as Captain Clarence Oveur), though there was a funny opening segment with the Hare Krishnas that did not make this cut.

And here is the trailer:

Big Bang for beginners-2: The nature of energy

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

In order to understand the Big Bang theory, we also need to have an understanding of the nature of energy in addition to that of matter that was discussed yesterday. The word ‘energy’ has a technical meaning in science but has also entered into the vernacular and thus has been used to mean many things. In everyday language, it usually signifies the source of the ability to do things, such as move objects or break them up or put them together. So gasoline provides the energy to run cars, coal the energy to heat things, and so on.

Energy takes many forms. Some of it comes from the motion of objects that have mass. For example, the energy associated with the motion of a speeding car can be used to break through a fence. Wind energy comes from the motion of air and can be used to power wind turbines. Water waves in the form of tsunamis can carry vast amounts of energy that can wreak widespread destruction. Some energy is stored as chemical energy in certain kinds of matter such as gasoline and coal that are released under certain conditions. Nuclear energy is what is stored in atomic nuclei. All these forms of energy are associated with things that have mass.

But there is a form of energy that is not associated with any mass. Electromagnetic energy refers to energy that is not associated with a tangible object that has mass but still has the ability to do things. In everyday language, we do not use the term electromagnetic but instead refer to this kind of energy according to the source that produces it. Sunlight is one such case. It has no mass but it has energy (what we call solar energy) and can heat objects, as anyone who has been warmed by the Sun can testify. A microwave oven produces a similar massless energy that we use to cook food. X-ray machines also produce massless energy that we can use to see through some things. Radio waves are another form of massless energy.

All these different forms of massless electromagnetic energy differ only in how much energy is carried by a single unit of that energy. The name given to this single unit is the ‘photon’. The energy that can be carried by a photon varies continuously and the popular names we assign, such as microwave, radio, visible light, X-rays, refer to ranges of photon energy that are based on somewhat arbitrary boundaries. So a photon in a radio wave has less energy than a photon produced by a microwave oven, which has on average less energy than a photon of sunlight, which in turn has less average energy than a photon produced by an X-ray machine.

The energy of each photon is tiny but any energy source that has an observable effect in everyday life, such as sunlight and microwave ovens, contains enormous numbers of them.

So to summarize in terms of increasing energy of photons:

radio waves→microwaves→sunlight→X-rays→ …

In scientific research, we often use photons to break matter up into its smaller constituents because photons can be aimed extremely precisely at small targets. In yesterday’s post I described a hierarchy of constituents of matter in order of decreasing size.

molecules→atoms→nuclei/electrons→protons/neutrons/electrons→quarks/gluons/electrons→…

I also said that it takes larger and larger amounts of energy to break up the smaller constituents. If we use photons for this purpose, then we can split a molecule into atoms using a low-energy photon, while we would require a higher energy photon to split up an atom into nuclei and electrons, and yet higher energy photon to break up a nucleus into protons and neutrons. We have not as yet produced in laboratories or accelerators photons that have high enough energy to break up protons and neutrons into free quarks and gluons, assuming that this can be done at all.

As far as we know, there is no upper limit to the energy that a photon can have, just as we do not know if there is a lower limit to the size of the basic constituents of matter. In both cases, our knowledge is limited by our present technology to produce the required energies in the laboratory. There are photons with extremely high energy (many orders of magnitude larger than anything we can produce in the laboratory) that come to us from outer space in what are called cosmic rays but we cannot corral them to use them in controlled experiments.

With these preliminaries out of the way, we can begin to explain the Big Bang theory.

POST SCRIPT: Art films

Monty Python made an art form of parodying BBC-style interviews and in this clip That Mitchell and Webb Look pay homage to them and take on pretentious films and their directors.

Big Bang for beginners-1: The nature of matter

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

I was recently asked by a relative to provide a simple explanation of the Big Bang theory ‘in words of one syllable’, i.e., without using jargon or esoteric scientific concepts and in a way that it could be understood by non-scientists. So here goes my attempt at fulfilling that request. In doing so I have tried to follow a paraphrase of Einstein’s dictum that says that when explaining something we should make things as simple as possible, but not simpler. In other words don’t distort in the search for simplicity. In trying to achieve this goal, I have created a multi-part series. (I promised my relative that my explanation would be simple, not short!)

But it is inevitable that in explaining a sophisticated scientific theory like the Big Bang to non-scientists, in essence telling it in the form of a story, some distortions will creep in, not the least because this is not my area of specialization and so I may simply not be as up-to-date as I should be. An excellent site for more current and authoritative information is one put together by Professor Edward Wright of UCLA. In particular he has put together a tutorial and a valuable FAQ page that enables one to quickly find answers to questions, and I have helped myself from that resource so generously provided.

I will readily acknowledge that I will also consciously introduce some distortions by taking the kind of liberties that film makers do when adapting books to create a screenplay, by omitting those characters that are peripheral to the story in order to maintain focus and brevity. My main omissions will consist of some elementary particles of matter that do not add anything to the basic story. Those who want a highly readable yet more accurate treatment of the basics of the theory are well advised to seek out what I think is still one of the best popular treatments of this subject, and that is Steven Weinberg’s The First Three Minutes (1988). Though it does not have anything about the more recent observations and refinements (such as dark matter, dark energy, and cosmic inflation), the basic paradigm it presents is still valid.

The Big Bang theory seeks to explain how the physical universe that we now inhabit came about. Since it now consists of lots of stuff, one needs to first start by looking at what that stuff (i.e., ordinary matter) consists of. This exercise turns out to be like peeling an onion. As each layer of matter is examined, it reveals another layer below it.

Most everyday stuff (plants, animals, plastics, etc.) is made up of tiny but complex entities called molecules that give them their distinctive properties and which are held together by attractive forces. To separate matter into individual molecules, we need to apply an external force that is sufficient to overcome the force that binds a molecule to its neighbors. Doing so requires us to expend some energy as well.

Each individual molecule is in turn made up of simpler entities that we call atoms, which are also held together by attractive forces. Atoms are the units of matter that distinguish one element from another, and there are a little over a hundred such elements, oxygen, hydrogen, iron, carbon, being a few of the well-known ones. The periodic table lists all of them. A very simple molecule is that of water, which consists of just three atoms, two atoms of hydrogen and one atom of oxygen, held together by attractive forces. Other molecules, like the DNA that exist in the core of our body’s cells and contain our genes, consist of millions of atoms joined together.

Atoms were once considered the most basic units of matter. They were thought to be indivisible but we know now that that is not true and that they too are composite objects, consisting of a tiny central core (called the nucleus) and electrons outside the nucleus, again held together by attractive forces. Electrons do seem to be truly fundamental particles that cannot be broken up into any smaller constituents.

The nucleus of an atom, however, turns out to be yet another composite object that consists of still smaller entities called protons and neutrons.

The protons and neutrons are now known to be composite objects too, consisting of even smaller entities called quarks and gluons.

So to summarize, when we peel off the layers of matter, the component units of which it is made are, in order of decreasing size:
molecules→atoms→nuclei/electrons→protons/neutrons/electrons→quarks/gluons/electrons→…

This is where things stand now.

Are the quarks and gluons (and electrons) the ultimate constituents of matter? We don’t know for sure but given past history with the onion-like nature of matter, we should not be too surprised if searches reveal yet another layer beneath the current one.

Why is it that we do not know if quarks and gluons are the ultimate components of matter? The reason comes down to the fact that it takes force and energy to separate matter into its smaller constituents, and the force and energy required increases rapidly as one moves down the chain of matter. It takes a small amount of energy to separate molecules into atoms. It takes much more energy to separate atoms into nuclei and electrons. (Some electrons can be removed from atoms by just rubbing materials together, which is the source of what we call ‘static’ electricity.) It takes much greater energy to separate nuclei into protons and neutrons, which is why we need huge and expensive accelerators to do so. When it comes to separating protons and neutrons into quarks and gluons we seem to have reached the limits of our ability. We have not actually been able to create quarks and gluons as free objects but instead can only study them while they are still inside nuclei.

The reason that we cannot produce free quarks and gluons is thought to be due to the fact that the forces holding them together in protons and neutrons are like the forces exerted by rubber. When you try to separate two objects that are joined by a piece of elastic, the force you need to apply keeps increasing as the objects move apart. With real rubber bands, the band breaks at some point and the two objects break free of each other. But with the rubber band-like forces holding quarks and gluons together, we have not been able as yet to create forces that can break the bands, leaving us unsure whether they can be broken if only we could to make the forces large enough, or whether they simply cannot be broken, ever.

Next: The nature of energy

POST SCRIPT: Harry Markopolos

In my series on financial frauds, I wrote about the Bernie Madoff scandal and how Harry Markopolos’s repeated warnings that Madoff was running a scam were ignored by the regulatory authorities and the media. He appeared recently on The Daily Show to repeat those charges.

<td style='padding:2px 1px 0px 5px;' colspan='2'Harry Markopolos
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