The universe looks identical in whichever direction we look!

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The universe looks identical in whichever direction we look!

Postby babaonet » Fri Sep 09, 2011 7:45 am

In 1922, Friedmann said that the universe looks identical in whichever direction we look, and this would also be true if we were observing the universe from anywhere else(say from other galaxies).
Later, it was proved to be true by Arno Penzias and Robert Wilson of Bell Laboratory.
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Explanation solicited.
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Re: The universe looks identical in whichever direction we l

Postby Markus Schwarz » Fri Sep 09, 2011 1:45 pm

Dear babaonet,

Friedmann and others were searching for solutions to Einstein's new theory of gravitation (general relativity).
Since the equations are quite complicated, Friedmann made the simplifying assumption that the universe is homogenous and isotropic.
These are technical terms, which translate into plain English as the words you highlighted above. So, under this assumption he was able to
find a solution to Einstein's theory.

The question remained whether this solution is actually a good description of the universe we live in. The answer hinges on if we can find evidence or proof of this. In the 40ies, based on Friedmann's solution, Gamow predicted that there would be a "cosmic background radiation" with certain specific properties. It took another 20 years until Penzias and Wilson discovered this radiation. It was the missing proof to show that the universe is homogenous and isotropic. They were awarded the Nobel prize for it.

Hope that helps.
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Re: The universe looks identical in whichever direction we l

Postby Chris Peterson » Fri Sep 09, 2011 1:48 pm

babaonet wrote:In 1922, Friedmann said that the universe looks identical in whichever direction we look, and this would also be true if we were observing the universe from anywhere else(say from other galaxies).
Later, it was proved to be true by Arno Penzias and Robert Wilson of Bell Laboratory.
-
Explanation solicited.

To be clear, "identical" in this context means that the same broad structure is observed, not that you literally see the exact same view from everywhere.

So all this is saying is that the Universe is substantially the same everywhere, and that no large section of the Universe has a different evolutionary history from any other place. That doesn't seem extraordinary at all; indeed, seeing something different is what would be surprising (and with recent measurements, there is a hint of some large scale anisotropies, which suggests something about structures that are outside the observable Universe).
Chris

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