Friday, April 10, 2015

The Big Bulk

The leading theory for the expansion of the universe after the bang is called the Big Bang Theory. Hubble discovered that the universe is expanding and then George Lemaitre used Hubble’s findings to extrapolate that at some point in time there must have been a single point where everything started. This bang was said to have been an explosion of space and time, which then brings the question, what was there before this bang and what is described in the Big Bang Theory? Also what really is this bang and how did it begin?

These questions drove Paul Steinhardt and Neil Turok to try and develop a theory of the events that led up to this bang as a supplement to the ideas of the Big Bang Theory. Their idea begins with a model that looked at the universe as a brane, which is a three-dimensional world that lies within a higher-dimensional space. A good way to visual what a brane is, is to image a sheet of paper flapping in the wind. The paper may be thought of as a two-dimensional object in a three-dimensional world. Both Steinhardt and Turok compared the piece of paper to our universe, except our Universe is three-dimensional inside of a four-dimensional background which they called the “bulk.” With this hypothesis they theorize that there were more than one brane in the bulk, just like there could be more than one piece of paper flying around in the wind.

This is where the Big Bulk theory starts to have similarities with and ties to the Big Bang Theory. If two branes, each holding a massive amount of energy, collided, the result would resemble that of an explosion. The theoretical characteristics of the explosion are actually quite similar to what we think the bang would have been like which is why the most important part of the Big Bulk Theory is how it helps explain what preceded the Big Bang Theory. Years later Steinhardt and Turok discovered something else about their Big Bulk Theory. After the collision, the brane world energy gives rise to matter such as galaxies, stars, and planets like our Earth. After the collision the branes start to expand and keep on expanding until the space between them is nearly empty. What’s interesting is that when that point is reached there are attractive forces that draw the world-sheets back together together, causing a collision that resets our Universe with another bang. The time between cycles would be roughly one trillion years. This idea of a cyclical universe also explains some gaps in the Big Bang Theory. In the Big Bang Theory which theoretically occurred 13.7 billion years ago, we do not know what time was before the bang or even if it existed. At this point in time we still do not know much about time and if it will one day come to an end or expire. The bulk theory could supplement the Big Bang Theory and explain what came before the bang and what eventually will happen to our universe.

- Eric Chow