Sunday, August 18, 2013

Does it Matter?

I saw a joke the other day: “Never believe atoms. They make up everything.” A fun play on words and basic science. But, is that true? Do atoms make up everything?

The answer is not well understood, but, according to modern science, it is a resounding NO. Since the 90’s we’ve realized that the normal matter made up of atoms in configurations classified as elements do not make up everything. In fact, they only make up about 4% of what we now know as the composition of the universe.

I’ll bet you find that statement a bit unbelievable. After all, the only things we know of here on this earth, or, as far as that goes, in our solar system and even our galaxy, are made up of various combinations of the little more than one hundred known elements and those atoms are all made up of protons, neutrons, and electrons.

Sure, we know about other atomic and sub-atomic particles. We know that protons and neutrons are made up of finer particles called quarks and we know there are other particles that exist such as mesons and neutrinos and a whole zoo of high energy particles. But there is something else out there, at least according to the latest measurements and theories, and we don’t know what this other stuff is.

Matter is a poorly-defined term in science. The term has often been used in reference to a substance or a particle that has rest mass. The rest mass, also called invariant mass, intrinsic mass, proper mass, or simply mass, is a characteristic of the total energy and momentum of an object that is the same in all frames of reference.

Matter is used loosely as a general term for the substance that makes up all observable physical objects. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC). Democritus actually coined the term “atom.” He named the atom after the Greek word “atomos,” which means that which can't be split. The cool part is that he was right, well 90% right.

A few thousand years later, Albert Einstein showed that ultimately all matter is capable of being converted to energy (known as mass-energy equivalence) by the famous formula E = mc2, where E is the energy of a piece of matter of mass m, times c2, the speed of light squared. As the speed of light is 186,282 miles per second or, in metric terms, 299,792,458 meters per second, c2 is a very large number and, therefore, a relatively small amount of matter may be converted to a very large amount of energy. Einstein’s theory was proven by the explosive power of the atom bomb.

Matter should not be confused with mass, as the two are not quite the same in modern physics. For example, mass is a conserved quantity, which means that its value is unchanging through time, within closed systems. However, matter is not conserved in such systems, although this is not obvious in ordinary conditions on Earth, where matter is approximately conserved. Still, special relativity shows that matter may disappear by conversion into energy, even inside closed systems, and it can also be created from energy, within such systems.

Scientifically, the term "mass" is well-defined, but "matter" is not. Sometimes in the field of physics "matter" is simply equated with particles that exhibit rest mass (that is, cannot travel at the speed of light), such as quarks and leptons. However, in both physics and chemistry, matter exhibits both wave-like and particle-like properties, the so-called wave–particle duality. It is difficult to understand the tiny world of atoms and particles, and it doesn't behave quite like things we experience in our life such as tables, chairs, and a glass of water. Our understanding of the makeup of the known matter is limited and mostly consists of sets of equations. But we do know about the matter around us, the kinds of atoms, and how the basic laws affect these objects.

We know a lot about the various elements and have organized them in the Periodic Table that is familiar to all students of chemistry and physics. We've worked out rules for the behavior of matter and energy and can explain common experiences such as why it rains or why the moon doesn't crash into the earth or how to build radios and atomic power plants to provide electricity to light up our lives. We are surrounded by gadgets that demonstrate our ability to manipulate and make matter work for us on an everyday scale in our homes, our highways, and our space ships. But now we think there is something else … out there! Something that doesn't fit the Periodic Table. Something that doesn't obey some of the laws we thought were universal.

Look up at the night sky. Our universe may contain 100 billion galaxies, each with billions of stars, great clouds of gas and dust, and, as recently discovered, there are planets and moons and other little bits of cosmic flotsam revolving around those stars. The stars produce an abundance of energy, from light to radio waves to X-rays, which streak across the universe at the speed of light.

Yet everything that we can see is like the tip of the cosmic iceberg — it accounts for only about four percent of the total mass and energy in the universe. Astronomers have discovered something new that they call "dark matter" while studying the outer regions of our galaxy, the Milky Way.

The Milky Way is shaped like a disk that is about 100,000 light-years across. That is, it would take light 100,000 years to travel across it. The stars in this disk all orbit the center of the galaxy. The laws of gravity say that the stars that are closest to the center of the galaxy — which is also its center of mass — should move faster than those out on the galaxy’s edge. This is based on Newton’s basic laws of motion. Just as a spinning ice skater will spin faster if she pulls in her arms, the inner planets of the solar system orbit the sun faster than the outer planets. The same response to gravity in the solar system should be seen in the revolving Milky Way galaxy.

Yet when astronomers measured stars all across the galaxy, they found that they all orbit the center of the galaxy at about the same speed. This suggests that something outside the galaxy’s disk is tugging at the stars. Since the source of this tugging force or gravity does not show up on our instruments, we call it “dark matter.’

Now large clouds of dust or other particles that do not emit any energy or light might be invisible to our telescopes and other instruments, but radiation and light from other galaxies shines through this dark matter and does not cause it to emit any energy that we can record. The clouds of gas and other particles that we know exist in space would not act this way, so this appears to be a new type of matter exerting a gravitational pull, yet not emitting any radiation or interacting with the radiation that passes through it … “dark matter.”

We know of particles, such as the neutrino, that are not effected by other particles or radiation. But neutrinos have no mass, so they won’t create any gravity. We don’t know of any particles with mass that are not affected or excited by energy passing by them. This dark matter does not behave like anything we know of now.

Calculations show that a vast "halo" of dark matter surrounds the Milky Way. The halo may be 10 times as massive as the bright disk, so it exerts a strong gravitational pull. We can’t “see” it, but we can definitely observe the effect of this dark matter.

The same effect is seen in many other galaxies. And clusters of galaxies show exactly the same thing — their gravity is far stronger than the combined pull of all their visible stars and gas clouds.

Further studies in the last twenty years have found another odd thing in our universe. We know the galaxies in our universe are flying apart. The big bang theory explains this expansion of the universe as the result of the initial velocity from this explosion that literally created our universe. However, the effect of gravity, especially when the dark matter gravity is added in to the calculation, should be slowing down this expansion.

However, it does not appear to be slowing down, but rather increasing in velocity. To explain this phenomenon, scientists have theorized the existence of some unknown repelling force that they have named “dark energy.”

Now don’t get hung up on the name. It does not mean that this stuff, whatever it is, is “dark” or “energy.” It is just a name in contrast to the “dark matter” term. You see, gravity is always attractive. There is no anti-gravity. Dark matter acts like ordinary matter and attracts things. This “dark energy” is just the opposite, it repels matter.

Further, by observing the motions and rotations of the galaxies and bodies in our universe, it is estimated that universe is made up of 4% normal matter, the stuff we experience every day in the laboratory, and 21% dark matter and a whopping 74% dark energy.

All of this is based on very recent discoveries and scientists are scrambling to produce theories to explain this and experiments to verify the theories. There is very little evidence of the existence of both dark matter and dark energy, but there is definitely something going on that doesn’t fit our current understanding.

So the use of the term “dark” for these two unknown substances is quite appropriate. It may be that our theory of gravity needs a major overhaul and that some new theory would explain all this behavior without postulating the existence of these unknown, “dark” substances. We only assume these things exist because the behavior we observe with our telescopes and instruments does not fit our current understanding. It is possible it is just our current understanding that is in error.

We also know that space itself — areas where nothing exists — are actually boiling and teaming regions of the creation and destruction of particles. Our quantum theories include the idea that there is an underlying background energy that exists in space throughout the entire Universe called “vacuum energy.” One contribution to the vacuum energy may be from virtual particles which are thought to be particle pairs that blink into existence and then annihilate in a timespan too short to observe.

They are expected to do this everywhere, throughout the Universe. Their behavior is codified in Heisenberg's energy–time uncertainty principle. Still, the exact effect of such fleeting bits of energy is difficult to quantify. So this is another possible explanation for the observed behavior.

It may be that another “Einstein” is working in some menial job like a patent clerk at this very moment, and he (or she) is about to publish a paper that will bring light to this darkness and revolutionize our understanding exactly like that brilliant young man with the crazy hair did about one hundred years ago.

Now do you understand why I love this physics stuff? The wonder; the excitement; the exploration; the discoveries; it’s out there for us to find and understand. The wonders of creation are so far beyond the understanding of man. That is our great challenge. To try to solve the mysteries of the universe. Don’t worry, there’s plenty more mystery to solve. The universe seems to have an unlimited amount of mystery for us to discover.

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