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Asaf Pe'er

Physics for all



Where is the centre of the universe? Is there light in a black hole?

According to what we know, the universe has no center. Rather, since the "big bang" it expands the same way in all directions. The expansion of the universe is different than "normal" expansion, since regular expansion (e.g., inflation of a balloon), occurs into an already pre-existing space. Contrary to that, the expansion of the universe is an expansion of space itself. An analogy I like is that of "copy machine", in which the zoom function is used. If one begins with an infinite paper and use the zoom option, the result would also be infinite... but still sparser than the original. A somewhat similar analogue is good for the universe as a whole. Initially it was extremely dense; though we can't say it was "small", since it could still be infinitely big... (if you go back close enough to the exact time of the big bang, the known laws of physics break, and thus nobody really knows what happened then).

About light in black holes: of course there is !. There is no problem for light - or anything, such as astronauts, to get into a black hole. It is the getting out that is impossible... thus, if you happen to be inside a black hole, you would still see light coming from the stars above you... though you could never reach them. The sky will look "funny", as light will be distorted. A nice vision of travel into a black hole can be found here:
http://jila.colorado.edu/~ajsh/insidebh/schw.html

In fact, once you enter a black hole, you can't stay there forever; gravity will pull you further into the "center" - the singularity, in which space and time shrinks to zero. Thus, you don't have too much time to enjoy the "funny looking" stars...

Interesting site with similar idea:
http://math.ucr.edu/home/baez/physics/index.html

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