Brian Greene’s The Elegant Universe (I believe that’s it anyway) goes into this. According to M-theory, the universe can be measured as very large or very tiny at the same time depending on how you measure it. The two sizes are the reciprocal of each other in Planck lengths. As one expands, the other condenses. Every big bang, the two sizes switch places. That’s about the limit to which I understand it. Now that my math skills are a little better, maybe I should go back to the appendix of the book and see the math behind it.
These two would also happen with an explosion where you have a range of velocities such as you’d expect from an explosion of gas released into the vacuum.
Here, I’ll draw you a picture. The numbers are the velocity of that part of the gas, in the center of momentum frame. There’s no hole in the middle. Also, if I’m on galaxy 1, I see all the other galaxies moving away from me in just the same way, with the same variation of redshift with distance, as if I were on galaxy 0. This of course assumes I’m close enough to the center that I can’t see the edge of the explosion.
Time X
| -3-2-10123
| -3 -2 -1 0 1 2 3
| -3 -2 -1 0 1 2 3
V -3 -2 -1 0 1 2 3
(Of course, I don’t have an answer for the other two points.)
The part where M-theory is concerned has to do with universal “Supergravity” and the distribution of Gravitons over eleven dimensions. I can’t cite a source as that’s just a succinct explaination based on information I’ve gathered from many varied sources but if you search or wiki it you should find something on it backing this up. again you are looking too closely at the hand grenade metaphore unless you can come up with a better metaphore for describing the universe expang short of saying, “Imagine a universe that is expanding mathematically incongruous with the acceleration of inertia where at first elementary particles are thought to have expanded faster than light and show no signs of slowing at a predictable rate and you’ll be pretty close to the idea of the universe expanding…” can a guy catch a metaphorical break? Also, I know what a googol years is I was just being facetious. Also, while it is true that the tangential velocity of Messier 31 (Andromeda) is only known to within a factor of two it would have to be on the far outside of estimated paths to completely miss the galaxy (and when I say completely miss, if it comes within a thousand lightyears of us it could still strip a large chunk of stars and debris from the milky way causing the galaxy’s equilibrium to be seriously compromised.) Besides this kind of thing is fairly common (M51, NGC4038/9, NGC1097 and NGC520 among others) so I don’t think it so unbeleivable that it will collide or make a disquieting pass 4.5billion years or so in the future.
So you no longer believe that “The universe is, in fact expanding from a central point” (which, again, is really remarkably wrong - one introductory Astro textbook I have, Filippenko’s The Cosmos, has a section actually titled “Expansion without a center”) and we can agree that metric expansion of space is, in fact, possible? Your gripe now is just that there isn’t a convenient metaphor for the real explanation?
Ok, there are plenty of very common popular metaphors used which aren’t fundamentally wrong. I’ve always liked the “ants on a balloon” model which doesn’t claim a center - the universe is an expanding surface; it doesn’t have a center.
Just to be 100% sure our OP doesn’t walk away with a bad understanding. …
The human astronomer Edwin Hubble Edwin Hubble - Wikipedia discovered the expansion of the universe in the 1930s using ground based telescopes.
When NASA orbited their first big optical telescope in 1990, they named it the “Hubble Space Telescope” Hubble Space Telescope - Wikipedia in his honor.
I suppose so and will concede my point and the argument of the expansion comment with as much grace as I am allowed and close the discussion on the topic to the extent of my power to do so.
But the M theory has a nice explaination as to why the universe is expanding which I beleive still holds water.
Supergravity is an imperfect theory, like relativity, that could be a stepping stone to actual progress in determining the genesis of the universe.
thats the wiki link but as a warning it is very technical in an attempt to portray as fact things that have been disproven. If your good at math read it and formulate your own theories.
heh. As one of the earliest employees of the (now Hubble Space Telescope Science Institute, I still feel awkward with the name Hubble, which was tacked on much later. to me, it is still just “Space Telescope”
Reminds me of a crossword I was doing, where the clue was “Successor to HST”, and I was puzzled because “NGST” didn’t fit (this was before the Next Generation Space Telescope was named Webb). Of course, the answer they were looking for was “DDE” (the successor to Harry S Truman).
I’m very sorry to have to ask such a simplistic question. I think I understand that when the constantly expanding Universe was posited people were amazed. But what is it that prevents gravity from kicking in? Is there a tipping point, as in the formation of black holes, or when those two hydrogen atoms someone above mentioned, they say, the hell with this, let’s start attracting again because of gravitational attraction? Is there a name for this tipping point?
Gravity is always in effect. If it weren’t for the cosmological constant, then the expansion would be continually slowing down, and the question would just be whether it’ll ever slow down enough to stop and all fall back together. The cosmological constant (or dark energy or quintessence or whatever the Heaven it is) throws a monkey wrench in all this, since it effectively provides a repulsive force that’s more than enough to overwhelm the attraction at large distances, but gravity is still present (and in fact, the cosmological constant is itself probably some sort of manifestation of gravity).
Thnx. What constitutes a large distance? Am I not being drawn toward some black hole somewhere? Why are galaxies so priveledged?
If this has been asked and answered upthread, let me know and I’ll clam up.
It comes down to gravity versus momentum. There is a minimum speed at which two objects can recede from each other without gravity ever overcoming the momentum and causing them to start approaching each other even though they will perpetually slow down. It’s called escape velocity. It’s a little more complex when you have matter distributed throughout the entire universe, but it’s the same basic concept. If galaxies are moving away from each other fast enough (and it appears most are), then gravity will never overcome their momentum completely, only slow them down. Of course, as was mentioned, the galaxies actually seem to be accelerating away from each other, which would mean they have no chance of ever condensing.
As for why galaxies are privileged, I’m pretty sure the gravitational attraction between them is pretty weak relative to smaller scales due to the immense distances. Also, they tend to be moving apart quite rapidly compared to objects at smaller scales. This makes them more likely to be travelling away from each other at over escape velocity.
Thank you very much.
Leo