Tuesday, March 31, 2015

How Did the Universe Begin?

Discoveries in astronomy and physics show the universe had a beginning 13.7 billion years ago. Prior to that moment, there was perhaps nothing but during and after the moment, our universe came into existence for reasons we still do not understand. The Big Bang theory tries to explain what happened during and after the moment. Astronomers speculate that our universe sprang into existence as "singularity," which are regions of infinite mass density that defy our current understanding of physics. However, no one knows what or where that singularity came from. What we do know is that volume of the universe inflated to huge sizes in the fraction of a second after the "bang" occurred. The temperature of the universe one second after it began was 10 billion degrees Fahrenheit. As the universe continued to expand, it continued to cool down, allowing the formation of fundamental particles like neutrons, electrons, and protons that decayed and/or combined to form the cosmos that we know today.

Although the Big Bang theory is widely accepted as the explanation of what happened after the "bang" that began our universe, it does not offer explanation for "bang" itself. Some theories attempting to explain the cause of the Big Bang include the oscillating universe theory and the chaotic inflation theory. The oscillation theory builds upon the Big Bang theory in that it believes the universe starts with a Big Bang, experiences a Big Crunch and repeats the cycle again with another Big Bang. Therefore, the Big Bang that occurred 13.7 billion years ago was just another step in the continuous cycle. Stanford physicist Andrei Linde also proposed a different possible explanation in the 1980s: chaotic inflation. Linde considered the possibility that the Big Bang may have been "a scattered and irregular inflation" that occurred wherever the right potential energy was available instead of being a single event. The Cosmic Microwave Background findings in the 1990s in fact showed variations of intensity that provided supporting evidence for the chaotic inflation theory.

While predictions from the Big Bang have been supported by observations, one of the main problems with the theory is that the temperature of the universe is nearly uniform. If the Big Bang marked the beginning of the universe, then according to some explanations, there has not been enough for the universe to reach the temperature equilibrium. Instead, the most plausible explanation for that uniformity is that, soon after the beginning of time, some unknown form of energy made the universe inflate at a rate faster than the speed of light so that the temperature in the inflated cosmos would be nearly the same everywhere. Alternative theories to inflation supported by the Big Bang explain this problem. For example, a group of theoretical physicists proposed a new theory that the beginning of the universe could have happened after a four-dimensional star collapsed into a black hole and ejected debris. Their reason to doubt the Big Bang theory is that “the Big Bang was so chaotic, it’s not clear there would have been even a small homogenous patch for inflation to start working on.” Instead, they proposed a theory in which the three-dimensional universe floats as a membrane in a four-dimensional "bulk universe." Since the bulk universe has four-dimensional stars, the stars go through the same life cycles as three-dimensional ones and when the massive ones explode as supernovae, their innermost parts collapse as a black hole and create a three-dimensional membrane surrounding the boundary between the inside and the outside of the four- dimensional black hole, the event horizon. Then, expansion would occur as a result of the three-dimensional membrane's growth. While this is an interesting possibility of the "bang" and the short period after it, the main question that must be asked of this or any other alternative theory is whether it provides testable predictions. It is ultimately only through observations that we know how the universe began.

Sources:

http://www.space.com/25126-big-bang-theory.html
- Alice Zhang
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