# Black holes effect Reality?

When a star turns into a black hole does it change the movement of the Universe at all? Through a funneling effect?

Chronos
Gold Member
Hi taeth. Welcome to PF. Not sure what you mean by movement of the universe. Things move within the universe relative to each other. The universe as a whole does not move. There is nothing for it to move through, so the short answer is no. Black hole formation has no effect on anything aside from spacetime curvature [increased gravity] in the volume of space previously occupied by the precursor object [star].

K thx sorry I didn't explain myself very good, but a blackhole has more mass than the star who's place it takes... Also do black hole ever die out because they emmit radiation I was just curious if they could run out?

Staff Emeritus
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taeth said:
K thx sorry I didn't explain myself very good, but a blackhole has more mass than the star who's place it takes.
Not initially. The star collapses to the black hole and its mass is conserved. Later inflow may increase the mass.

.. Also do black hole ever die out because they emmit radiation I was just curious if they could run out?

Yes they can. It's called evaporation, and it's a real prediction. Every time a particle escapes the BH because of the Hawking mechanism, the BH loses that particle's mass. But evaporation may take a very, very long time.

Jenab
Might the universe as a whole be rotating? Would it matter if it were?

cepheid
Staff Emeritus
Gold Member
Hmm...all motion is relative. So the question is...rotating relative to what? You're talking about the universe here...the whole of existence. There is nothing else to compare it with.

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Jenab said:
Might the universe as a whole be rotating? Would it matter if it were?

Goedel (yes the famous "incompleteness" Goedel) developed the equations for a rotating version of general relativity. He showed that such a universe contains closed timelike paths, i.e. time travel is possible.

Most physicists have considered Goedel's universe to be unphysical, for exactly the reaon cepheid gave; rotating with respect to what?

rotating with respect to another universe separated by a membrane like bubbles inside of bubbles...

...with black holes maintaining the equilibrium of any particular universe around a fixed expansion point in multiversal time

Does time go slower in a black hole?

tony873004
Gold Member
cepheid said:
Hmm...all motion is relative. So the question is...rotating relative to what? You're talking about the universe here...the whole of existence. There is nothing else to compare it with.
I didn't think that rotational motion needs a reference.

For example, if I put a fly in a jar, attach string to the jar and swing it around in circles, the fly feels an artificial gravity caused by me doing so. A spider, outside the jar watches me do this, but he does not feel the artificial gravity. If all of a sudden, I considered the fly in the jar to be the origin of my coordinate system (ie it is now still), then the spider on the wall outside the jar should begin to feel an artifical gravity caused by the room spinning around the jar. But obviously he will not.

I think its because your direction keeps changing in circular motion. Therefore, circular motion needs no reference point, which opens the door for the universe to rotate.

Or another example, in most physics problems such as dropping a rock, you consider the surface of the Earth to be stationary and not rotating. But in reality, if I were to swing a pendulum, over a few minutes I could note a change in direction, proving that the Earth rotates, but relative to nothing except its own instantainous momentum.

floped perfect said:
Does time go slower in a black hole?

Yes, I pretty sure it does. I think one of my friends told me that time is almost slowed down to 0.

Staff Emeritus
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Interesting property of a Schwartzschild black hole; once you cross the event horizon, time and the radial space direction swap, so that as it were, things inside the horizon "age" toward the singularity at the center, i.e they can't escape going there. This time is not slow, my impression is that it passes at c.

Where time slows down, is close to the horizon, on the outside, and then ONLY for far-away observers. To them, looking through a telescope at something falling into the hole, it seems literally to take forever to do so, although observers falling with the object see time as passing normally. This is due to the warping of spacetime by the huge gravity of the hole.

Janitor