Random Thoughts on the Universe

Tuesday, October 04, 2011

2011 Nobel Prize

The Nobel prize people have just announced that the 2011 prize for physics will go to the two teams that inadvertently discovered dark energy (or at least their leaders).

For those who haven't followed this story, here is a brief review.

Back in 1915 Einstein published his General Theory of Relativity which describes the properties of space, time and gravity. One of its predictions was that the size of the Universe is changing - but Einstein didn't like that so he added an extra term called the Cosmological Constant whose sole purpose was to stop the Universe from growing.

A few years later Hubble discovered that the Universe is expanding, and Einstein felt rather foolish.

Now fast forward to the year 1998. Two teams of astronomers are cataloging distant supernovae (exploding stars) and independently discover that the supernovae are travelling faster away from us than expected. More study and they discover that in fact they are accelerating away.

Many explanations were proposed, but ultimately the only one the withstood further experimental data was that the Universe is not only growing as Einstein predicted and Hubble measured, but it is accelerating in size! (In other terms, the larger it gets, the faster it grows)

The only way to explain this is to either alter the laws of gravity which are valid for all other experiments or to add a large amount of mysterious substance called dark energy. In fact other experiments in the mid 2000s have determined that nearly three quarters of the energy in the Universe is in this dark energy form, but no one can explain what it is. (A leading candidate though is Einstein's Cosmological Constant but with the sign reversed).

So here we are 13 years after the discovery, and more evidence mounts for the existence of dark energy but with still no evidence for what it is. A most interesting mystery, and one that certainly warrants a Nobel Prize for its discoverers!

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