Big Bang Theory

Big Bang

The Big Bang model of the universe's birth is the most widely accepted model that has ever been conceived for the scientific origin of everything. No other model can predict as much with as high accuracy as the Big Bang model can.

A common question that people ask is "What happened before the Big Bang?" The phrase "in the beginning" is used here to refer to the birth of our universe with the Big Bang. In the creation of the universe, everything was compressed into an infinitesimally small point in which all physical laws that we know of do not apply. No information from any "previous" stuff could have remained intact. Therefore, for all intents and purposes, the Big Bang is considered thebeginning of everything, for we can never know if there was anything before it.

The Big Bang model had its beginnings with Edwin Hubble's discovery in 1929 that, on large scales, everything in the universe is moving away from everything else. The only explanation for this was that the universe was expanding in every direction, and it was taking galaxies along with it. This is known as "Hubble's Law."

The next step towards the Big Bang model was to take this process in reverse - that is, to go back in time. If the universe is "blowing up" like a balloon as time progresses, then what would happen if you were to run the timeline backwards? What was the universe like in the past?

If the universe is currently growing, then the universe was smaller in the past. There must have been some point in time when the universe was half its current size. Then there must have been a time when it was half that size. If you continue to run time backwards, there must have been a time when the universe was an infinitesimally small point*.

This is the basic idea behind the Big Bang. All matter and energy existed in an infinitely small point of infinite density a long time ago, and has since been expanding as our universe. One important note here is that the Big Bang was not an explosion in the universe, but rather it is an explosion of the universe. Therefore, there is no "center" of the universe from where the Big Bang started.

*In calculus, this is an adaptation of "Zeno's Paradox." Through this process, Zeno presented the paradox that a runner could never actually complete a race: They go half way, then three-quarters, then seven-eighths, and so on, but never do they get to finish the race. In calculus this is paradox is solved theoretically with limits, but with the Big Bang, it can be used to show that the universe was not ever "nothing," but must have existed in an extremely tiny space at some time in the past.

The Big Bang is the leading theory that almost all astrophysicists believe explains the origin of the universe. This is because all observations so far made support the Big Bang theory; there are four main lines of evidence that are most-often used.

The first was discussed above: The expansion of the universe. The universe is expanding now, so in the past it must have been smaller. If it were smaller in the past, then there probably was a time when it was infinitesimally small. One could ask why don't we think that it might be expanding now but it could have been shrinking before and we just don't know about it. The answer is that there is simply no mechanism that we know about that could accomplish this transition on a universal scale.

The second line of evidence is the Cosmic Microwave Background Radiation (CMB) that was discovered in 1965 by Arno Penzias and Robert Wilson from Bell Labs. They were working with a microwave receiver used to communicate with the Telstar satellite, but were getting noise from every direction they pointed the receiver. It was coming from all over the sky at what seemed to be exactly the same frequency. This was the first evidence for the CMB, and they later shared a Nobel Prize for this discovery.

WMAP CMB Picture The CMB is an "echo" left over from when the universe was approximately 300,000 years old, as predicted by the Big Bang model. As something becomes compressed, as matter was when the universe was young, it becomes hot. The actual "heat" comes from particles' movements - the faster they move, the more energetic they are, and so the more heat we see. The universe was so hot before it was 300,000 years old that atoms could not form. Because of this, photons - particles of light - could not move around, for they kept reacting with electrons - the negatively charged parts of atoms.

Therefore, during this period, the universe was effectively opaque. Once the universe had reached 300,000 years old, atoms could form, and electrons were now bound to a nucleus. Once this happened, photons could move about freely. This "first light" is the CMB, and its existence is a very strong indication that the Big Bang occurred.

The third major pillar of the Big Bang theory lies in the abundance of the different elements of the universe. The theory predicts that certain amounts of hydrogen (~72%), helium (~28%), and other elements should be made. Observations have shown almost exactly the amounts that are predicted.

The fourth piece is that the Big Bang theory is the only one that comprehensively lays down a framework for the eventual evolution of the universe as we observe it today.