Showing posts with label observable universe. Show all posts
Showing posts with label observable universe. Show all posts

Monday, November 23, 2009

Final chapter: Possability of Time Travel



Is time travel possible? Can we actually move backwards or forwards to different points on time? It is currently unknown whether the laws of physics will allow time travel to pass. In theory, particularly the multiverse theory, it is believed to be possible.

One man, a University of Connecticut professor
Ronald Mallett is challenging this notion by trying to send elementary particles back into time using a laser. His project has received criticism within the physics community, but he nonetheless continues its efforts.

A central problem with time travel to the past is the violation of causality. This phenomenon is relationship between a first event and a second event where the second event is a direct consequence of the first. Thus, should an effect precede its cause, it would give rise to the possibility of temporal paradox. One of the most famous temporal paradoxes is the Grandfather Paradox. In this riddle, a boy travels back in time and kills his grandfather before his grandfather is conceived. This leaves the boy unable to return to his previous state, because in his present world, he now would not exist. Some interpretations of time travel resolve this by accepting the possibility of travel between parallel realities or universes.

I know its sort of exciting to imagine a thing like this happening. But really, according to the laws of physics- you could not travel back in time without somehow affecting the present and the future.

Wednesday, October 14, 2009

The "visible" universe

In Big Bang Cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach us since the beginning of the cosmological expansion. The portion of it that we (humans, from the perspective of planet Earth) are able to observe is determined by whether or not the light and other signals originating from distant objects has had time to arrive at our point of observation (planet Earth).
The edge of the observable universe is now located about 46.5 billion light-years away
Estimates of the matter content of the observable universe indicate that it contains on the order of 1080 (10 to the 80Th) atoms. The vast majority of the energy density is contributed by dark matter and dark energy.