The Naked Scientists

The Naked Scientists Forum

Author Topic: Should the universe be thought of as becoming less dense?  (Read 2965 times)

Offline Eric A. Taylor

  • Sr. Member
  • ****
  • Posts: 447
  • I before E except after C, unless weird science
    • View Profile
We have been taught that the universe is expanding, but what it's expanding INTO is said to be nothing. "Size" like motion needs a benchmark. A Toyoda car is big when compared to a dog which is big compared to an ant. (I'd hate to meet a dog sized ant)

I've heard is said that the entire universe was once the size of a peanut. This means that everything, every bit of matter/energy was contained in a small space. At this time the universe must have been incredibly dense. Does "size" have any meaning if we look at the universe from the outside. Is there even an "outside" at all?

Today we see the "expansion" of the universe is accelerating. I wonder if we think of the universe becoming less dense, rather than "bigger" if the acceleration could be explained.


 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Should the universe be thought of as becoming less dense?
« Reply #1 on: 26/12/2010 23:28:46 »
I have just found time to get round to this interesting question because it opens the door to some details that many people seem to ignore. When we talk about the "size" of the universe we are always talking about the "size of the piece of the universe that we can see"

because if the universe did end physically at the limit of our visibility and it was empty space beyond it would in effect be non uniform and this non uniformity could be detected  similarly if our visible universe and nothing else was compressed to become very small it would have become a black hole long before it got down to the size of a peanut.  So logically there must be a lot more outside of this limit that we cannot see to stabilise the process.  Therefore it might be better to talk about the amount of the universe that is visible to us is decreasing.
 

Offline QuantumClue

  • Hero Member
  • *****
  • Posts: 613
    • View Profile
Should the universe be thought of as becoming less dense?
« Reply #2 on: 27/12/2010 01:00:18 »
The density may be unchanging, or it can change according to cosmological constant. According to popular belief, it is unchanging.
 

Offline Eric A. Taylor

  • Sr. Member
  • ****
  • Posts: 447
  • I before E except after C, unless weird science
    • View Profile
Should the universe be thought of as becoming less dense?
« Reply #3 on: 27/12/2010 11:23:06 »
I have just found time to get round to this interesting question because it opens the door to some details that many people seem to ignore. When we talk about the "size" of the universe we are always talking about the "size of the piece of the universe that we can see"

because if the universe did end physically at the limit of our visibility and it was empty space beyond it would in effect be non uniform and this non uniformity could be detected  similarly if our visible universe and nothing else was compressed to become very small it would have become a black hole long before it got down to the size of a peanut.  So logically there must be a lot more outside of this limit that we cannot see to stabilise the process.  Therefore it might be better to talk about the amount of the universe that is visible to us is decreasing.

I've read that thinking the universe is composed of three (or four including time) spacial dimensions is incorrect. The analogy often drawn is to imagine a 2-D being on Earth. To that being the Earth would look flat. Indeed he probably would not even be able to imagine a curved Earth, so the idea of "flat" has no real meaning to it.

He could set off on a journey heading west, always following the setting sun, He knows he's not turning left or right but one day he sees a familiar building. Off to the west is his home.

Like the Flatlander, our universe is thought to be curved, so you'd simply come back to were you started (assuming you can out run the expansion, which you can't. Perhaps the objects just beyond the limit of our view to the West are the objects that are just visible to the East? So for a person who lives on OUR horizon would see the Milky Way to his western horizon and the Andromeda Galaxy on his Eastern horizon. He would assume that the two Galaxies were REALLY far apart (opposite sides of the universe.)

Going back to the Flatlander: Let's say, through some strange property of light in the 2-D plain he can see all of Earth's surface except a 50 mile wide swath exactly opposite of where he is. Thinking the Earth was flat He could look to the East, see all of North America and the Atlantic and right on the edge of where He can see, Briton with just a bit of water on the far side. When he looks west he sees all of the Pacific and Asia all the way to the coast of France. He'd assume that the two were very far apart, never realizing that just a few miles of water separates them.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Should the universe be thought of as becoming less dense?
« Reply #4 on: 29/12/2010 00:16:37 »
I agree that it is quite possible and in fact probable that our universe is closed in some way and that there is no edge for this reason.  Several times in my experience of at least 60 years people have thought they have detected evidence of this curvature.  This curvature is however quite small although it may still be that we can see right round our universe in some directions but I feel that this is unlikely.  My statement was purely to say that it is clearly not a flat earth scenario where there is an edge to fall over!
 

Offline yamo

  • Full Member
  • ***
  • Posts: 78
    • View Profile
Should the universe be thought of as becoming less dense?
« Reply #5 on: 30/12/2010 11:17:40 »
am i expanding at the same rate as the universe?...so ...like...it's not my fault...?
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1832
  • Thanked: 12 times
    • View Profile
Should the universe be thought of as becoming less dense?
« Reply #6 on: 30/12/2010 21:36:58 »
Quote from: yamo
am i expanding at the same rate as the universe?

Only if you believe Mark McCutcheon, "The Final Theory". ::)
 

The Naked Scientists Forum

Should the universe be thought of as becoming less dense?
« Reply #6 on: 30/12/2010 21:36:58 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length