Ever Expanding Universe

One fine day, Edwin Hubble noticed a red-shift in the radiations coming from different galaxies. Doppler's Effect made him conclude that other galaxies were moving away from us! The universe was expanding! This was a breathtaking discovery in those times. This has resulted into the creation of various theories on how the universe began.

The discovery of the expanding universe soon abolished the ideas of the steady-universe people previously believed in. Physicists started making models of how the universe might behave. One such person was Alexander Friedmann. He predicted that according to the mass of the universe (which would determine the gravitational attraction) and the rate of expansion, the universe could follow one of the following three models:

One of the models predicts that our universe starts with a Big Bang and keeps expanding. In another model, the universe starts of likely, but the expansion converges towards a finite size. Although the universe tends to that size, it never attains it. In the third model the universe starts contracting after a critical time and ends up at a singularity similar to the Big Bang called the Big Crunch.

Which of the models our real universe follows has been a debatable issue. It would depend on the current rate of expansion as well as the mass-density of our universe.
The density of our universe was estimated. The next thing was to measure the rate at which the expansion was decreasing. But then, the discovery which resulted startled the scientific community! The universe was expanding, nevertheless, instead of decreasing; the rate of expansion was increasing!

To appreciate the mysterious nature of this discovery, we must realize that the force acting at such cosmic level is gravity. Now mass is always positive and hence gravity is always attractive. Then what was this force which made our universe expand? All ready to decide which Friedmann model to take up, we get an all new picture in which some mysterious force favors the expansion! It makes the galaxies accelerate away from each other at an ever increasing rate!

It is herein that the concept of Dark Energy comes it. It is hypothesized that there is another kind of mass (or energy) which has not yet been detected for some reason, which is in a sense negative! For it makes gravity repulsive! A calculation to estimate how much of such energy would be needed for the present rate of expansion showed that 70% of the mass of the universe was this Dark Energy!

Another explanation for this weird expansion is in terms of the cosmological constant. This term follows an interesting history of its own. It was originally in Einstein’s equations for Gravity, to account for the steady universe which was then observed. It made gravity act as a repulsive force for very large distances. When an expanding universe was discovered, Einstein called this ‘the biggest mistake of his life’. However this constant was reintroduced when the rate of expansion was found to be increasing.

Today the Dark Energy explanation is largely accepted by the scientific community. They are just waiting patiently for someone to announce the discovery of this strange form of matter/energy. For more info on Dark Energy, keep reading REALITY QUANTIZED.

~ Twish ~