VACETS Regular Technical Column

"Science for Everyone"

"Science for Everyone" was a technical column posted regularly on the VACETS forum. The author of the following articles is Dr. Vo Ta Duc. For more publications produced by other VACETS  members, please visit the VACETS Member Publications page or Technical Columns page.

The VACETS Technical Column is contributed by various members , especially those of the VACETS Technical Affairs Committe. Articles are posted regulary on [email protected] forum. Please send questions, comments and suggestions to [email protected]

Mon, 6 Mar 1995

The Big Bang

In the beginning... no, no, no! Before the beginning, there was no space and there was no time. There was nothing and there was God. And God said, "Let there be light". BANG!!! There was light! And there was the universe.

So, how big was the original BANG? Only God knows. However, it is generally believed that it is bigger than the pop of a balloon, the explosion of a dynamite stick or a nuclear bomb, or even a supernova. It is not even akin to the explosions of any kind of matter. In the concept of general relativity, the BIG BANG is an expansion of spacetime itself, filled with incredibly hot matter and radiation. In that titanic cosmic explosion, the universe began an expansion which has never ceased.

"What makes you think there was the big bang before which there was nothing (I mean except God)? Why must there a beginning? And why the beginning is the big bang?"

There are reasons to believed the big bang is the beginning of everything. First, we know that the universe is expanding. This is exactly what we would expect if there had been a big bang at the beginning that had flung out matter and space together. Secondly, the universe is uniformly filled with electromagnetic radiation corresponding to those from a black-body glowing at 2.7 degree Kelvins. This is expected from a big bang at the beginning of time that produced a large amount of radiant energy that subsequently cooled as the universe expanded. Thirdly, the cosmic abundance of certain light elements such as Deuterium, Helium... can only be explained if there was a big bang and those elements were created minutes later.

"What happened right after the big bang?"

No one was around at that time to know for sure exactly what happened. Physicists and astronomers now construct theories attempting to understand the evolution of the universe. According to the grand unified theories (GUT), from the time of 10^-43 seconds to 10^-35 seconds after the big bang (which we may call time zero), the temperature of the universe was so hot (~10^30 K) and only one type of force other than gravity, the grand unified force, was operating. During that time, the universe was expanding and cooling in a regular manner. At about 10^-35 seconds, when the temperature was about 10^28 K, the grand unified force began to separate into 3 distinct forces: strong, weak, and electromagnetic. The universe started to inflate, increasing its size by a factor of 10^20 in a mere 10^-35 seconds. After that, the universe returned to its regular expansion and cooling. The universe at this time was a fireball composing of radiation and elementary particles (electrons, neutrinos, quarks...). At about the time 10^-5 seconds, the secondary particles such as protons, neutrons, and related particles were formed. These particles condensed into light nuclei (deuterons, tritium, helium) seconds later. The temperature was still too hot for atoms to form until approximately half million years after the big bang. Then the atoms combined to form planets, stars, galaxies... and finally we have a beautiful universe as of today.

"You forgot to tell about the time from zero to 10^-43 seconds. What happened then?"

Because of some guy named Werner Heisenberg, we will never know exactly what happened before the time 10^-43 seconds (just kidding). Heisenberg postulated that it is impossible to specify exactly both the position and momentum of a particle. Equivalently, it says that we can never know exactly both the time and energy of a system. It turns out that at the time 10^-43 seconds, called the Planck time, our knowledge of the energy of the universe must have an uncertainty at least equals to the total energy. Any attempt to calculate what happened before the Planck time will produce an error larger than the value itself.

"Alright, so we will never know exactly what happened before 10^-43 seconds. Can we guess what will happen to our universe in a latter time, that is, billion, trillion, zillion,... years from now? And do you know what time is it now?... I mean what is the age of our universe?"

The universe is estimated to be some where between 8 billion and 20 billion years old. Scientist are fighting fiercely over how old the universe is. Look at the latest Time magazine (3/6/95) and you will see. About the future of our universe, we live in an expanding universe and our guess is that the universe may either keep expanding at a fast rate forever (open universe), or gravity may slow down the expansion but can never completely make it come to a stop (flat universe), or the expansion will halt and revert to collapse back into a singular state much like that from which it began in the big bang (close universe).

"That does not mean a thing. Don't we know exactly if the universe is open, flat, or closed?"

It depends. According to the big bang model, the universe is open if the amount of matter in it is less than a certain critical value (~10^-29 grams/cm^3). If the amount of matter exceeds this critical value, the universe is closed. And if it is exact then the universe is flat. The problem is that we have to know the exact amount of matter in the universe. We can estimate the amount of matter by counting and weighing the stars and galaxies. This total seen mass accounts for less than 10% of the critical mass. However, from the motions of stars within galaxies and galaxies within cluster of galaxies, it is found that additional mass must be present in some from that is hidden from our immediate view. Adding these masses, the total mass of the universe will be close to the critical mass. And now we are back to square one: one miligram below critical mass and we have open universe, one miligram above and we have closed universe, and if it is exact then we have flat universe. Can you lend me a three sided coin?

"So the hidden mass accounts for more than 90% of the total matter of the universe. What is the nature of the matter comprising the hidden mass?"

In principle, it could be made of diffuse gas, collapsed stars such as white dwarfs, neutron stars, and black holes, or faint red dwarfs. Some suggest that it is composed of neutrinos and the neutrinos have finite rest masses. Some other suggest the "massive compact halo objects (MACHOs)", the planet-size clumps of ordinary matter, are the carriers of the hidden mass. Other scientists says that the hypothetical "weakly interacting massive particles (WIMPs)" are the carriers. The battles between these scientists and their ideas are continuing. There have been some knock downs but no knock out yet in these hyperheavyweight bouts.

"How big is the universe and where is the center of the universe?"

Physicists, cosmologists, and mathematicians often say things to confuse people outside of their fields like "the universe is finite and unbounded, and its center is nowhere, or its center is everywhere". It's really confusing, isn't it? Actually they have reasons to state something like that. Imaging a two-dimensional universe curving through a third dimension, like, a surface of a sphere. While there is only so much area on the surface of the sphere, there is no edge to this universe. It is finite but unbounded. The center of this universe is not in that universe; it is in the third dimension, inside the sphere which is inaccessible to this universe. Now, if you increase the dimensions of this universe by one and you will have a universe similar to our universe, a three-dimensional universe curving through a fourth dimension. (I can't picture a fourth-dimensional object, can you?)

"Can there be many big bang? And can many universes arise from one big bang?"

If the universe is closed then there can be many big bang. After a big bang, the universe will expand for some time, come to a halt, and then contract. It will collapse back into a singular and then bounce back. Another big bang has begun. Many forms of inflationary theories lead to the likelihood of many universes born out of a single big bang. However, we may not know if any other universe exists due to the noncommunicating nature.

"You can not make something out of nothing. So where in the Heaven did God get the energy from to create the universe?"

You know, God is powerful. Making something out of nothing seems impossible for you, but for God, it may just be a simple thing like a sentence "let there be light". The act of making the universe might not cost God anything. The universe contains matter and radiation which have positive energy. But the matter and the mass equivalence of the radiation acts gravitationally upon itself, and that corresponds to a negative energy. It is a fairly general result from general relativity that these two sources of energy might exactly cancel one another so that the net cost of the universe is zero.

"Is there anything else interesting about the big bang and the universe that I should ask?"

Yes, but I'm running out of time. Ask them another time. Good night...

Duc Ta Vo, Ph.D.
[email protected]

For discussion on this column, join [email protected]

Copyright © 1996 by VACETS and Duc Ta Vo


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