# The Universal Expansion? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [April 3, 2000, 3:54am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681 "2000-04-03T03:54:00Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [April 3, 2000, 3:54am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/1 "2000-04-03T03:54:00Z")
Here is the original column, by Karen: ["][www.straightdope.com/mailbag/mmissingmatt.html](http://www.straightdope.com/mailbag/mmissingmatt.html)]([http://www.straightdope.com/mailbag/mmissingmatt.html](http://www.straightdope.com/mailbag/mmissingmatt.html)[/url) > [@](#): > > You are right about one thing: our universe is expanding, what with the explosion of the Big Bang flinging everything apart. There are three choices for what happens next: (1) there is enough mass in the universe such that the gravitational forces are strong enough to stop the universe from expanding and cause it to start to shrink back into tight little ball; (2) there is not enough mass in the universe to halt the expansion and the universe expands forever; or (3) there is exactly enough mass in the universe to exactly halt the expansion, but not cause any shrinking. Sure, in scenarios #2 and #3 the universe gets larger and more lonely, but do you really prefer a shrinking universe? Parking spots are already too hard to find. > The mass of the universe is usually expressed as W, the fraction of critical mass. Critical mass is the mass the universe needs in order to get Scenario #3, i.e., W = 1. W \< 1 gives a forever-expanding universe and W \> 1 gives eventual shrinkage. Might there be a “4th” possibility…Doesn’t it make sense that Omega and W = 1. It must have been designed that way. If Omega is greater than or less than one the number (Omega equals) would be an infinite number of possibilities. It seems that it has to be one. And at Omega =1 the laws (physical laws of the universe) would re-orient themselves and result in a collapsing universe. ## …Just a thought Karen --Mike If at first you don’t succeed you’re about average. ---
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [April 3, 2000, 3:56am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/2 "2000-04-03T03:56:00Z")
Whoops! url again. [www.straightdope.com/mailbag/mmissingmatt.html](http://www.straightdope.com/mailbag/mmissingmatt.html) ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [April 3, 2000, 2:20pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/3 "2000-04-03T14:20:00Z")
No offense, silo, but that post has some grammatical problems that make it difficult to understand what you are postulating. Karen offered three choices: W \< 1, W = 1, w\> 1. I am trying to understand how you are creating a fourth possibility, but the sentences: > [@](#): > > “If Omega is greater than or less than one the number (Omega equals) would be an infinite number of possibilities. It seems that it has to be one.” don’t seem to make any sense. Perhaps you could re-write the post to clarify your thought? 🙂 ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 3, 2000, 2:28pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/4 "2000-04-03T14:28:00Z")
> [@](#): > > Whoops! url again. This is why you should leave adding the link to the column to the professionals, like Arnold. 🙂 Even if we are exactly at W = 1, wouldn’t this be unstable? It would seem that quantum mechanical variations, or the uncertainty principle, would tip the balance one way or the other. I would also think that if W=1 for the whole universe, (or even if W is slightly less than 1) there has to be some **huge** subset of the universe where W was greater greater than 1. If you took everywhere in the universe but some void which has less than the average density of the universe, that part would have W\>1. Wouldn’t that part then collapse, leaving just a few wisps of matter to fill the expanding void? I guess you could call it a really big black hole and say it wuld evaporate in 10^ReallyBigNumber years, but is this so different than the case where everything collapses. * * * _It is too clear, and so it is hard to see._ ---
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [April 3, 2000, 6:17pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/5 "2000-04-03T18:17:00Z")
> [@](#): > > 1. there is exactly enough mass in the universe to exactly halt the expansion, but not cause any shrinking. Ok, this is what i’m talking about. Karen says if Omega=1 (3rd case) the expansion will halt and not get any bigger or smaller. I am proposing (a 4th case) that at Omega=1 the universe does halt at which point the laws of the universe reorient themselves. In turn this causes the beginning of the “big crunch.” So at Omega=1 the Universe stops then shrinks. Understand now? * * * If at first you don’t succeed you’re about average. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 3, 2000, 6:39pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/6 "2000-04-03T18:39:00Z")
> [@](#): > > Ok, this is what i’m talking about. Karen says if Omega=1 (3rd case) the expansion will halt and not get any bigger or smaller. With W=1, the expansion doesn’t halt, it asymptotically approaches zero. With W\>1, the expansion stops, then falls back. With W\<1, the expansion approaches a constant rate larger than 0. * * * _It is too clear, and so it is hard to see._ ---
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [April 3, 2000, 6:46pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/7 "2000-04-03T18:46:00Z")
## ZenBeam do you understand what i’m saying? If at first you don’t succeed you’re about average. ---
**Author:** ![WillGolfForFood](https://avatars.discourse-cdn.com/v4/letter/w/82dd89/32.png) [@WillGolfForFood](https://boards.straightdope.com/u/WillGolfForFood)\ **Post date:** [April 3, 2000, 7:03pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/8 "2000-04-03T19:03:00Z")
Silo, I think I know what you’re saying. The problem is that what you’re saying isn’t what happens when W=1. Zenbeam is describing the situation accurately there. The universe is expanding at the moment, and if in fact W is _exactly_ 1 then this expansion will gradually slow down, approaching (but never quite reaching) equilibrium. If W \> 1, then the expansion does in act slow down to the point of equilibrium, reach that point briefly, then begin the big contraction. However, I see no reason for “the laws of the universe [to] reorient themselves” at that inflection point (after all, they don’t reorient themselves when a bouncing ball reaches its highest point and starts falling), and you haven’t given us one. Please tell us why they’d do so at that point. ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [April 3, 2000, 11:36pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/9 "2000-04-03T23:36:00Z")
> [@](#): > > Originally posted by ZenBeam: > \*\* If you took everywhere in the universe but some void which has less than the average density of the universe, that part would have W\>1.\*\* I don’t think it really works that way. Take away a virtually empty section of the universe, and the rest will have a greater mass density, but it will be just as spread out. Just because you are no longer considerig a certain region in your calculations of mass doesn’t mean you can ignore that region as far as distance; since gravity decreases over distance, all that intervening space will diminish gravity. ---
**Author:** ![JLPicard](https://avatars.discourse-cdn.com/v4/letter/j/858c86/32.png) [@JLPicard](https://boards.straightdope.com/u/JLPicard)\ **Post date:** [April 4, 2000, 12:58am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/10 "2000-04-04T00:58:00Z")
Ok I have a stupid question. What would happen if the universe did start to shrink back into a tiny little ball? Let’s say that this was to, hypothetically, happen tomorrow at noon. Yes sir, tomorrow at 11:30 the universe expands as far as it can and at noon it starts to fall back in. (I know I’m exaggerating) what would be the effects on the rest of the universe? Would we be able to even tell? Or would we not know until the edge of the universe squished us into earth dust. * * * Bad spellers of the world… UNTIE ---
**Author:** ![WillGolfForFood](https://avatars.discourse-cdn.com/v4/letter/w/82dd89/32.png) [@WillGolfForFood](https://boards.straightdope.com/u/WillGolfForFood)\ **Post date:** [April 4, 2000, 10:53am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/11 "2000-04-04T10:53:00Z")
We’d definitely be able to detect this. For one thing, the doppler shift would change from a red shift to a blue shift as the galaxies started moving closer to each other rather than farther apart. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [April 4, 2000, 12:46pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/12 "2000-04-04T12:46:00Z")
> [@](#): > > Originally posted by WillGolfForFood: > \*\*We’d definitely be able to detect this. > \*\* But not tomorrow. * * * rocks ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 4, 2000, 4:59pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/13 "2000-04-04T16:59:00Z")
> [@](#): > > ZenBeam do you understand what I’m saying? I think so, and I think WillGolfForFood answered pretty well, but i’ll add my 2 scents also. I think you’re hung up on the original column where it reads > [@](#): > > there is exactly enough mass in the universe to exactly halt the expansion This is correct, but it doesn’t mean the expansion ever actually halts. The universe has just enough energy that if it were infinitely spread out, the rate of expansion would be zero, but it can never get there. It keeps expanding at a rate which gets closer and closer to zero, but never quite makes it. * * * _It is too clear, and so it is hard to see._ ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 5, 2000, 5:13am UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/14 "2000-04-05T05:13:00Z")
> [@](#): > > I don’t think it really works that way. Take away a virtually empty section of the universe, and the rest will have a greater mass density, but it will be just as spread out. Just because you are no longer considerig a certain region in your calculations of mass doesn’t mean you can ignore that region as far as distance; since gravity decreases over distance, all that intervening space will diminish gravity. I was thinking in terms of the analogy often used of a balloon expanding being like a two-dimensional analogue of the universe. All the matter is confined to the surface of the balloon. Assume the density of matter over the balloon is at critical density. If the distribution of matter is not perfectly uniform, there is some region with less than the average density, which might be some spot on the balloon. If you consider the point on the opposite side of the balloon from this empty spot, this is the center of a region whose radius is almost 1/2 the balloon circumference, and which has an average density greater than the critical density. The force of gravity doesn’t have to extend over the empty region, so it isn’t diminished by it. * * * _It is too clear, and so it is hard to see._ ---
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [April 4, 2000, 8:33pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/15 "2000-04-04T20:33:00Z")
Forget I mentioned W (omit it from the OP), it was a mistake. I was up late when I started this topic. I understand that at W=1 the limit of expansion is zero. But I still think when OMEGA=1 the laws reorient and contraction is triggered. I’m busy right now but a better explanation will be forthcoming. * * * If at first you don’t succeed you’re about average. ---
**Author:** ![proulx](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@proulx](https://boards.straightdope.com/u/proulx)\ **Post date:** [April 7, 2000, 1:15pm UTC](https://boards.straightdope.com/t/the-universal-expansion/1681/16 "2000-04-07T13:15:00Z")
Here is a third possibility: David Bartlett, a professor at the University of Colorado at Boulder, has been studying various data from images of galaxies, and has come to the hypothesis (not confirmed, of course) that gravitation acts somewhat differently on very large scales that we might expect. Basically, instead of gravitational potential given by ``` V = Gm/R ``` we have ``` V = (Gm/R)E^(iR/L) ``` where i is the square root of -1, and L is a characteristic length, a constant of nature on the order of 1400 lightyears. Note that the real part of this potential (which we observe, according to Bartlett) oscillates, even though it behaves like normal Newtonian gravity when R \<\< L. The net effect is that extremely large clouds would tend to expand if initially stable. This confirms recent reports that the expansion of the universe is accellerating. Of course, most physicists dismiss this as unaesthetic, but it is nonetheless a very interesting possibility.