Near a black hole spacetime gets contracted, more and more as we get closer to it. At the event horizon the contraction (pull of spacetime towards the singularity) equals the speed of light, we could say that space is falling into the black hole at precisely the same rate as light trying to travel outwards can catch up. Beyond the event horizon space is falling into the singularity at a rate faster than what light can catch up.(adsbygoogle = window.adsbygoogle || []).push({});

The contracting space seems to be similar to imagining a contracting universe, space(time) falling into a singularity.

In which respects can both situations be likened and in which respects are they fundamentally different?

I can guess that one important difference is that in a black hole, there remains an external spacetime to which the black hole can be said to be relative to, while in the case of a contracting universe the whole of spacetime contracts until becoming a singularity. There is no space beyond the portion which is contracting at a rate equal to the speed of light.

I'm also interested in the question: if the universe started as a singularity, and the laws of physics seem to be time-symmetrical, does the expanding universe have anything equivalent to an event horizon? And if so, what would that be?

And conversely, would a contracting universe have anything equivalent to an event horizon and if so, what would it be? The edge of spacetime itself? or some region defined by the speed of light? (such as when we speak of our current event horizon at our present coordinates in spacetime, which I believe has not much to do with the event horizon of a black hole).

Thanks!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# I Can a black hole be likened to a contracting universe?

Have something to add?

Draft saved
Draft deleted

Loading...

**Physics Forums | Science Articles, Homework Help, Discussion**