h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I can't explain why, but it disturbs me to think that the Universe will one day go completely dark - forever - once all of the stars lose their fuel.

How do the laws of thermodynamics affect the expansion of the universe? Based on the theory that our Universe is surrounded by emptiness, I assume that the Universe would continue to expand. However, suppose that our "big bang" (and Universe) has occurred amongst an infinite number of neighbouring big bangs, in a much larger Universe than we had ever imagined. In theory, wouldn't the matter from surrounding "big bangs" come into contact with the matter from our big bang, and start clustering into an immense black hole for the makings of a new big bang? I assume that all the "useless" energy that gets sucked in, would under the immense gravitational pressure, lose all entropy and become fuel once again?

Or, what if the blackness of our Universe is actually the backdrop of an immensly enormous black hole that our whole Universe is enveloped in? (I'm just being silly, but what if?)

Anyway, please explain to me as you would a child. I don't really know what I'm talking about, but I still find this stuff fascinating.

Starbuck

gosh - work to do here... and I barely know myself...

The universe isn't surrounded and growing into emptiness - it's just growing - not into anything, just growing. It doesn't have an edge either - if you go far enough in one direction you get back to where you started from...

High entropy (low order) energy doesn't transform to useful energy under high pressure, I'm afraid. The second law holds in all cases. However, in very high temperatures, it is possible that the current laws of the universe break down, so there might be a violation of the first law - and a creation of 'fresh' energy.

Black holes don't look black from the inside. We could be inside one now, and we wouldn't notice until the tidal forces became large enough to affect the solar system...

It's not all bleak - if the universe managed to happen once...

The way I see it is that the expansion is not against anytrhing .. but just into nothingness ... in my own way this is how I think of entropy ... take liquid nitrogen and poor it onto a surface .. it spreads thinner and thinner and thinner until .. its gone .. okay its a bad metaphor I know .. but its gets across the idea ... if there is finite energy, and infinite potential for expansion .. eventually it will spread to thin to do anything. Insert theory of big Crunch here ... it there is nothing to resist gravity ..well .. you get the picture.

There was an Horizon broadcast (BBC in Britain) a few weeks ago that was talking about theories other than the big bang (due to problems that this theory has at around the time it was supposed to happen). One of the other theories that was talked about considered what happened if the speed of light was not constant. When you get to the point that all your energy is spread so thinly that it is no more use to anyone then some mechanism causes the speed of light to reduce and 'hey presto' you get another big bang. This may not be directly relevant, but it gives hope that reincarnation may happen on a very big scale.

Wick

Thanks, that seems to make sense for the most part. But it seems to me that you've suggested that the Universe is finite. If there's no "emptiness" outside the Universe, and if you travel far enough in one direction you will get back to the same starting point, that to me would suggest that the Universe is spherical, surrounded by non-existence. This sounds cool, but what science did you use to come to this conclusion? And how do you know that Black Holes don't look black from inside? Have you been in one? (I'm not trying to be a jerk, I just like to pick things apart).

I understand that time and space can be bent, so it could be plausible that space just raps around and meets itself at some point. In all honesty, this is the best theory I've heard yet (to put infinity into a finite perspective). But, I still don't think we have enough information to know for sure. Secondly, I agree that you probably would see light in a black hole, although, how deep would you have to go? If no light can escape the core, how would you see it? Steven Hawking suggested that there would probably be some point at which the gravitational force in one direction would be equal to the speed of light trying to escape in the other direction, leaving photons suspended in a thin space around the black hole. I dunno if I agree with that either, because I'm guessing that the gravitational fields constantly fluctuate, and wouldn't give anything the chance to "hover" in one place. But then the whole issue of time comes up. If time becomes infinitely slow inside a black hole, would you see the light (from a point further out) in its time-suspended state?

This raises another question for me. If immense objects (such as the core of a galaxy) have a black hole in the centre, wouldn't this dramatically raise our estimated age of the Universe? Scientists have estimated the age of the Universe based on our own perception of time, but if the time around these huge gravitational centres goes much slower, wouldn't that mean that they've been around for a lot longer than we've thought? And wouldn't that also mean that it will take that much longer for the Universe to "burn out"? I realize that this might only affect a celestial body at it's very core, but who knows how large an area could be affected.

Anyway, I'm getting off the topic of thermodynamics, and I apologize. Also, my brain really does hurt right now, so I'll leave all this stuff to the greater minds. I just wish that I could, in my lifetime, find out the answer to the big question. Unfortunately, I don't foresee it ever happening in anyone's lifetime..

LF

The universe is indeed finite (according to A-level physics... ) - there are various arguments for this (like, why don't we see stars in every direction?). On the other hand, I've heard physicists suggest the opposite might be the case - that the universe is infinite (but still expanding).

The reason a black hole is black is because light cannot escape its gravitational pull - the same problem would not effect someone inside a (very large) black hole because they would be falling in towards the center at close to the speed of light (which is why the hole has to be very large - otherwise you'd get to the center before blinking). So it becomes easier, in some bizzare way to see light emanating from near the center. However, I'm a long way from certain about that - ain't in Kansas any more.

You can't see photons except when they come into contact with your eyes... so you'd not see this 'frozen light' until you crossed the event horizon... at which point you'd probably be blinded...

re: time dilation and age of the universe - yeah, that should have an effect, but I'm betting that it's a fairly small effect in most of the universe - only coming into play around black holes and suchlike. I guess this means that some part of the universe are older than others, though - although it's the opposite way round - the stuff around black holes is going to be a lot younger.

Thanks Lucinda. Your guidance is much appreciated!

I'll have to do some more reading on all this stuff. So much to learn...

Starbuck