general relativity - Entering a black hole, jumping into another universe---with questions

I'm quite familiar with SR, but I have very limited understanding in GR, singularities, and black holes. My friend, which is well-read and is interested in general physics, said that we can "jump" into another universe by entering a black hole.

Suppose that we and our equipments can withstand the tidal forces near black holes. We jumped from our spaceship into a black hole. As we had passed the event horizon, we couldn't send any information to the outside anymore.

1. 
   

   Can this situation be interpreted as that we were in another universe separate from our previous universe?

   
   


2. 
   

   Is there corrections or anything else to be added to above statement?

   
   

Answer

Let me attempt a more "popular science" answer (Ron please be gentle with me!).

In GR a geodesic is the path followed by a freely moving object. There's nothing especially complex about this; if you throw a stone (in a vacuum to avoid air resistance) it follows a geodesic. If the universe is simply connected you'd expect to be able to get anywhere and back by following geodesics.

However in a static black hole, described by the Schwartzchild geometry, something a bit odd happens to the geodesics. Firstly anything following a geodesic through the event horizon can't go back the way it came, and secondly all geodesics passing through the event horizon end at a single point i.e. the singularity at the centre of the black hole.

If you now rotate the black hole, or you add electric charge to it, or both, you can find geodesics that pass through the event horizons (there are now two of them!), miss the singularity and travel back out of the black hole again.

But, and this is where the separate universes idea comes in, you now can't find any geodesics that will take you back to your starting point. So you seem to be back in the normal universe but you're in a region that is disconnected from where you started. Does this mean it's a "separate universe". That's really a matter of terminology, but I would say not. After all you just got there by coasting - you didn't pass through any portals of the type so beloved by SciFi films. And there's no reason to think that physics is any different where you ended than where you started.

If you're interested in pursuing this further I strongly recommend The Cosmic Frontiers of General Relativity by William J. Kaufmann. It claims to be a layman's guide, but few laymen I know could understand it. However if you know SR you shouldn't have any problems with it.