| From: Steven McLaren | 25/03/99
10:37:30 |
| Subject: The Expanding Universe | post id:
4784 |
| Hi there Karl and other Science
Fans .... Could you please answer a question that a colleague and I cannot answer, or have been unable to receive an answer from folks more learned in Space, Time 'n Science. We have been of the understanding that the universe is indeed expanding, or rather inflating. The laymans analogy given to us was the well used "inflating balloon". As this inflation is at a constant rate (an increasing constant we now know, but a constant none the less ), we see no reason why we couldn't calculate the point of the Big Bang !!! Furthermore, would this then help in determining the 5th mysterious Constant of Nature explaining the accelerating inflation of the galaxies ??? Thanks for your help Steve | |
| From: James Richmond (Avatar) | 25/03/99
14:47:35 |
| Subject: re: The Expanding Universe | post id:
4857 |
| The inflating balloon analogy
provides a visualisable mental image of the universe's expansion by
dropping one dimension from the real situation. Imagine that the balloon's surface is the universe. If we draw dots on it which represent galaxies, then as we blow up the balloon the dots move further apart. The important point to realise is that the "real" space in this picture is the SURFACE of the balloon. People living in the galaxies (on the dots) can only look along the surface of the balloon. They can't look through the balloon's inside, since the inside is not part of the perceivable universe. Any distances the inhabitants of the balloon universe measure must be measured along the surface. From the point of view of a person on any individual dot, all the other dots appear to be receding, and the further they are away from the original dot, the faster they appear to go. Where is the centre of expansion in the balloon picture? It is, of course, the centre of the balloon. But the centre of the balloon is not part of the perceivable universe, so to a balloon surface-dweller, the expansion has no centre (or at least, not one that they can point to, since they are only allowed to point along the surface). Another way to say this is that the balloon picture involves a 2D universe (the surface of the balloon) embedded in an unobservable 3D external space. The balloon picture is an ANALOGY with one less dimension than our real universe. Our universe is a 3D observable one embedded in a 4D external space. We, like the people living on the balloon's surface, see galaxies moving away from us with speeds proportional to their distances, in all 3D directions. The Big Bang expansion had a centre, but only in the external 4D space, which we can't observe, so in our 3D universe there is no identifiable point where the big bang occurred (i.e. we can't point in the direction of the centre of expansion since we're restricted to pointing in only 3 of the 4 dimensions). Recent data seems to suggest that the universe is expanding at a faster rate as time goes by. One possible explanation for this is that there is some type of anti-gravity force operating on large distance scales, causing the expansion to accelerate. I'm not sure what you mean by the "5th mysterious constant of nature". What are the first 4 mysterious constants? JR | |
| From: Chris (Avatar) | 28/03/99
13:11:23 |
| Subject: re: The Expanding Universe | post id:
5034 |
James I think the "5th mysterious constant" is a pop-sci bastardisation. You get it by taking the 4 fundamental interactions, adding cosmological anti-gravity as a 5th interaction, and then someone somewhere mentions that einstein's original GR field equations contained a cosmological constant which might account for it (which it doesn't - the constant was einstein's attempt to maintain a steady state universe in accordance with current beliefs). So you mix it up, call them all constants instead of interactions. Then you toss in the word mysterious for the fifth one, partly because it will fire up the public imagination, partly because you don't really get it. Presto! 5th mysterious constant. For the public - the observations which suggest that there might be a linear decrease in the recession velocities of galaxies with increased distance (hence in increase in velocity over time) are still being debated. The implications, if the observations are born out, will be somewhat astounding but are far from defined as yet. Hope this helps! Chris | |