| From: Phil | 29/06/99
15:16:21 |
| Subject: Does space end? | post id:
20859 |
| Look I'm sure this has been gone
over again and again. But for those of us who slept through it...... How
can space end?? If it does what is after it? There can't be nothing. As
far as I know there is no such thing as nothing. I was thinking that if
space does not end then it is all likely that there could be a so called
parallel universe of type. The world as we know it is made up of a
relatively small number of elements that can only bind together in a
relatively small number of configurations (on the grand scheme of things).
If the universe was infinite, wouldn't these binding combinations
eventually reach a point where they had to repeat those that have already
been made?? Just a thought that's all. | |
| From: Daryn Voss | 29/06/99
15:29:54 |
| Subject: re: Does space end? | post id:
20864 |
| There are a number of different
models in existence. Here is a quick and simplistic explanation of one of
them. The universe could be finite as a self contained bubble of three dimensional space plus time. It wouldn't need to have an "edge" beyond which nothing existed, because it would loop back around (presumably in some higher order space) like the surface of a bubble. To use an old parallel: suppose there is a train on a circular track. Things are arranged so that the people on the train can only see forward or backward. Their universe is finite, because there is only a certain length of track, but they will never come to an "edge" of the universe, because it is nicely curled up in a closed loop. Like I say, this is only one model. There is no real evidence that the universe is like this, but it does fit in with some cosmologists theories. It is important to remember that sometimes the commonsense notions that work well when we are dealing with medium sized objects don't always apply when we are talking about very small things (like electrons) or very big things (like the universe). I hope this has helped. 8^) | |
| From: Chris (Avatar) | 29/06/99
16:03:17 |
| Subject: re: Does space end? | post id:
20882 |
Like I say, this is only one model. There is no real evidence that the universe is like this, but it does fit in with some cosmologists theories. If you're saying there is no real evidence that space-time is curved - that's not quite right. If you're saying there is no real evidence for any space-time models - that's not quite right either. If you're talking about a specific model having finite closed curvature (eg Friedmann-Lemaître) then you're right - evidence is mounting up against such a curvature. We won't ever be able to step back into a fifth dimension to view a 4D manifold of space-time, so we will have to look for other means of determining which model best describes the universe in which we live. But this doesn't mean this "other" evidence is any less compelling! Chris | |
| From: Phil | 29/06/99
16:04:20 |
| Subject: re: Does space end? | post id:
20883 |
| Hm. interesting but I still come
back to the fact that what is outside "the bubble". And what do you think of my parallel universe theory? | |
| From: James Richmond (Avatar) | 29/06/99
16:11:37 |
| Subject: re: Does space end? | post id:
20885 |
| Look I'm
sure this has been gone over again and again. But for those of us who
slept through it...... How can space end?? If it does what is after it?
There can't be nothing. As far as I know there is no such thing as
nothing. It is possible that the universe is infinite in size, and that it will keep expanding forever. If this is the case, then space has no boundary. Another possibility is that the universe is finite in size. However, even if this is the case, it need not have a boundary, since space could "wrap around", as Daryn has explained. The universe is everything, by definition. There is not even nothing outside the universe, since there is no outside to speak of. The world as we know it is made up of a relatively small number of elements that can only bind together in a relatively small number of configurations (on the grand scheme of things). The number of atoms in the universe is estimated to be somewhere around 1080 (that's 1 followed by 80 zeros!). Although there are only around 100 naturally occurring types of atoms, the number of possible configurations of individual atoms is a humungous number (to use a technical term). If the universe was infinite, wouldn't these binding combinations eventually reach a point where they had to repeat those that have already been made?? Just a thought that's all. Because of the huge number of possible combinations, the "cycle time" before a repeat could occur would also be immense. And it possible that such a repeat would not occur anyway. If the universe keeps expanding forever, eventually all the useful energy will be converted to heat. The universe will be at a uniform temperature, with nothing forming new combinations. In other words, a steady state will be reached where nothing interesting ever happens. On the other hand, if the universe is finite, it will probably eventually recollapse to a "big crunch", which will happen long before the "cycle time" for repeating combinations rolls around. JR | |
| From: Daryn Voss | 29/06/99
16:14:25 |
| Subject: re: Does space end? | post id:
20888 |
| I was talking specifically about
the universe being a closed T1S3 bubble in a higher order
space. | |
| From: Daryn Voss | 29/06/99
16:25:47 |
| Subject: re: Does space end? | post id:
20891 |
| About evidence for the wraparound
universe model: Suppose we placed four pieces of equipment in a prefect
square. Suppose these things have instruments for sending and receiving
laser signals, and for timing. Suppose we use this stuff to measure the
distance between the objects (sides and diagonals.) If space is not curved, we would expect the diagonals to be exactly sqrt(2) times the sides. If space is curved, we would expect the diagonals to be a bit longer than than. Obviously, we would need this square to be very large for this to work (around a billion light years across), so we wouldn't want to be in any big hurry for the results, but would this be a theoretically sound means of determining whether or not there was a broad scale curvature into the spooky fifth dimension (without having to actually step into the fifth dimension to take a peak), or are there theoretical reasons why this would not work? 8^) | |
| From: Chris (Avatar) | 29/06/99
17:36:01 |
| Subject: re: Does space end? | post id:
20903 |
You only need to fire two light beams along parallel paths. In a flat einstein space (which is still S3T1 as you use it) the beams will remain parallel. In any curved manifold they will diverge or converge. Light unfailingly follows the local space-time geometry, and the path it takes (called a "geodesic") tells us a lot about the manifold it is tracing. Hope this helps! Chris | |
| From: MichaelT | 29/06/99
18:50:25 |
| Subject: re: Does space end? | post id:
20908 |
| > Hm. interesting but I still
come back to the >fact that what is outside "the bubble". The hardest bit about understanding this expanding universe thing is the above question. The answer is 'nothing'. There is no matter. There is no vacuum. There is no time even. Just plain undiluted nothing. We cannot get out there and experience it, because it doesn't exist. Once your brain stops fighting against this notion and you just accept it, it all becomes much easier to understand. :) Well, that's the way my Laborador explained it to me when we went for a run in the park... And I trust her, after all, she was right about the Telstra shares... Regards, MichaelT | |