The Naked Scientists

The Naked Scientists Forum

Author Topic: Why does the universe have to be expanding?  (Read 1321 times)

Offline acecharly

  • Sr. Member
  • ****
  • Posts: 171
    • View Profile
Why does the universe have to be expanding?
« on: 25/12/2015 14:31:13 »
Is it possible that the universe is already at a set size and that everything is just expanding out to its edge instead of the universe coming from a point at the big bang? If the edge had mass would this not explain how the matter in the universe is accelerating? as the gravitational effect grew as it gets closer.
« Last Edit: 25/12/2015 14:35:00 by acecharly »


 

Offline Ethos_

  • Neilep Level Member
  • ******
  • Posts: 1277
  • Thanked: 14 times
    • View Profile
Re: Why does the universe have to be expanding?
« Reply #1 on: 25/12/2015 17:06:19 »
Is it possible that the universe is already at a set size
In relation to what standard? To speak of our universe having a set size doesn't really make much sense unless we have something else to compare that size to. And understanding that we are limited to information contained within this universe, we have nothing else to gauge that size against.

Quote from: acecharly


 and that everything is just expanding out to its edge instead
Theorists speculate that our universe has no edge so talking about an edge is of no consequence.

Quote from: acecharly

 If the edge had mass would this not explain how the matter in the universe is accelerating? as the gravitational effect grew as it gets closer.

Since speaking about an edge has no meaning, suggesting that  this "edge" is responsible for universal expansion is also out of the question. Theorists are not completely sure what the reason for expansion is, however, some have suggested that the so-called "Dark Energy" may be the culprit.
 

Offline Space Flow

  • Sr. Member
  • ****
  • Posts: 400
  • Thanked: 31 times
    • View Profile
Re: Why does the universe have to be expanding?
« Reply #2 on: 25/12/2015 22:45:13 »
If the edge had mass would this not explain how the matter in the universe is accelerating? as the gravitational effect grew as it gets closer.
This runs into several large obstacles;
For this to be true we would have to accept there there is a stupendous amount of Mass, pilled up just out of reach of all our instruments in all directions globally. Because what we see looks the same in all directions.

Because we see everything moving away from US, this would also have to mean that we really are the only physical centre of the entire Universe. How amazing would that be? And how unlikely?

Anyway according to your hypothesis;
We are the only centre of the Universe, and in all directions there is enough Mass just out of detectable range to pull the rest of the Universe away from us. Maybe we smell bad or something?

I'll be the first to say "Everything is possible", but this seems far too complicated a situation to have any probability of approaching any kind of truth.
The questions it raises are both more and harder than the expanding Universe model, which I understand raises a few big  questions of it's own.
What is necessary is a simpler solution to the whole question, not a more complicated one.

Hope this helps.

 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3916
  • Thanked: 53 times
  • The graviton sucks
    • View Profile
Re: Why does the universe have to be expanding?
« Reply #3 on: 26/12/2015 18:59:26 »
The universe doesn't have to be doing anything. We record observations of what we see the universe doing and then try to fit a theory to the observations. The theory works if it makes predictions that are then borne out through experiment or further observation. The idea of dark energy could be exactly right, completely wrong or somewhere in between. If it is right then we may need to deal with the concept of negative energy.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4109
  • Thanked: 245 times
    • View Profile
Re: Why does the universe have to be expanding?
« Reply #4 on: 27/12/2015 02:28:13 »
Quote from: Title
Why does the universe have to be expanding?
It doesn't have to be expanding.

When Einstein developed his general theory of relativity in 1915 (centenary this year!), he discovered that, due to gravity, the natural state of the universe is to collapse.

The astronomers of the time just assumed the universe was unchanging. Einstein's equations showed that the universe could be expanding, or it could be collapsing, but one thing it could not do (for very long) was to stay the same.

So Einstein inserted a "fudge factor" into his equation that would exactly counteract the gravitational collapse. When Lemaitre(1927) and Hubble (1929) later showed that the universe was actually expanding, Einstein felt very foolish, and removed his "cosmological constant".

More recent studies have shown that the the rate of expansion is actually increasing, while Einstein suggests that the rate of expansion should be slowing (due to gravity). This recently discovered effect is dubbed "Dark Energy", and is a factor that Einstein could not possibly have known, or included in his theory.
 

Offline puppypower

  • Hero Member
  • *****
  • Posts: 555
  • Thanked: 43 times
    • View Profile
Re: Why does the universe have to be expanding?
« Reply #5 on: 27/12/2015 12:51:20 »
Let me address the expanding universe with a thought experiment.

Say we have two space-time references, A and B. Reference A is earlier and B is later in the expansion. In each reference, we have identical factories that make gears. Each factory uses X watts of energy per hour (energy) and each makes one defective gear per hour (entropy). Since time is moving faster in reference B, compared to the reference A, in a side by side comparison, the rate of energy usage and the rate of entropy in B, will appear to be faster than in reference A.

This is similar to the twin paradox, where the twin in the slower reference (earth) ages faster than the twin in the faster/moving reference where time has slowed. The younger moving twin uses less metabolic energy, while also exhibiting less entropy of aging. When they meet energy and entropy are different.

If the universe is expanding, via an expansion of space-time, is rate of entropy and the rate of energy usage faster today, than any time in the past? Is this experimentally observed?

 
« Last Edit: 27/12/2015 12:53:13 by puppypower »
 

The Naked Scientists Forum

Re: Why does the universe have to be expanding?
« Reply #5 on: 27/12/2015 12:51:20 »

 

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