<p>Yes, everything that happens in the universe depends on the energy delivered by the Big Bang. The very substance of the stars and galaxies was formed from it. Never forget the 1st Law of Thermodynamics: mass/energy can neither be created nor destroyed. If the universe stops expanding it will undergo gravitational collapse, slowly at first but ever faster, to become a blue-shifted, contracting universe. The same energy that caused the expansion will be recaptured in the collapse, to turn the universe into a fireball similar to the one from which it was created. This is called the Big Crunch. One version of what follows says it then disappears into a singularity, only to emerge again as a white hole and continue the cycle ad infinitum.</p>

<p>At present, dark energy has thrown a spanner in the works, and we can't be sure the universe will collapse, but if dark energy turns out to be a reality it must have been there all the time in some form, from the very birth of the universe.</p>

CC BY-SA 4.0
2019-08-07T08:23:57.947Z
Conservation of energy cannot be applied to an entire universe governed by General Relativity.
ProfRob
CC BY-SA 4.0
2019-08-07T08:55:48.837Z
How do you know?
Michael Walsby
CC BY-SA 4.0
2019-08-07T13:29:57.697Z
As space expands, the dark energy density does not decrease, that is, more dark energy is created. See https://medium.com/starts-with-a-bang/the-counterintuitive-reason-why-dark-energy-makes-the-universe-accelerate-3c57f6f31c30
PM 2Ring
CC BY-SA 4.0
2019-08-07T13:57:06.197Z
But that violates the Third Law.. If the 3rd Law can be violated with impunity on a cosmic scale, there is nothing to stop the total energy of the universe from eventually vanishing completely. I think some cosmologists want to banish the 3rd Law on a cosmic scale because it gets in the way of some of their theories. That's not a good enough reason.
Michael Walsby
CC BY-SA 4.0
2019-08-07T23:53:31.907Z
A [physical law](https://en.m.wikipedia.org/wiki/Scientific_law) is simply an empirical statement that seems to hold for a given data set. Theories are usually developed to support the law in its context, and make predictions beyond that data set. There's no reason to expect the thermodynamic laws hold at the cosmological scale when the observations don't support them.
Sir Cumference
CC BY-SA 4.0
2019-08-08T09:27:15.357Z
@Sir Cumference : Cosmological observations don't support the vacuum energy density required by QM,so there is a 40-orders-of magnitude discrepancy between QM and cosmological observations. 40 0rders of magnitude! Yet nobody seems to worry about that. I have noticed that questions which point out awkward facts are rated as bad questions on this site, which speaks volumes about the character deficiencies of the people who drew up the rules and run the site. Same on the physics stack.
Michael Walsby
CC BY-SA 4.0
2019-08-08T17:48:09.040Z
I don't think there is a problem if the facts are well referenced.
Keith McClary
CC BY-SA 4.0
2019-08-07T07:52:16.553Z
2019-08-07T07:52:16.553Z
Michael Walsby
<p>I do have a small question, which may seem a bit stupid but we are all here to learn. Anyways my question is: Is the universe expanding using the energy  it had from the Big Bang? if so what would happen if the universe stops expanding?</p>

CC BY-SA 4.0
2019-08-12T04:56:22.667Z
The most widely accepted cosmological theory holds that the expansion of the universe is currently *accelerating*, and this is primarily due to *dark energy*. What do you think could cause this acceleration to be reversed?
Chappo Hasn't Forgotten
<universe>
Energy to expand
Icey
# Energy to expand

(Asked by: username_0 on 2019-08-07)

I do have a small question, which may seem a bit stupid but we are all here to learn. Anyways my question is: Is the universe expanding using the energy it had from the Big Bang? if so what would happen if the universe stops expanding?

**Tags:** universe
> **Comments:**
> **username_1**: The most widely accepted cosmological theory holds that the expansion of the universe is currently *accelerating*, and this is primarily due to *dark energy*. What do you think could cause this acceleration to be reversed?  

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## 1 answers

### Answer by username_2 on 2019-08-07. Score: -6

Yes, everything that happens in the universe depends on the energy delivered by the Big Bang. The very substance of the stars and galaxies was formed from it. Never forget the 1st Law of Thermodynamics: mass/energy can neither be created nor destroyed. If the universe stops expanding it will undergo gravitational collapse, slowly at first but ever faster, to become a blue-shifted, contracting universe. The same energy that caused the expansion will be recaptured in the collapse, to turn the universe into a fireball similar to the one from which it was created. This is called the Big Crunch. One version of what follows says it then disappears into a singularity, only to emerge again as a white hole and continue the cycle ad infinitum.

At present, dark energy has thrown a spanner in the works, and we can't be sure the universe will collapse, but if dark energy turns out to be a reality it must have been there all the time in some form, from the very birth of the universe.

> **Comments:**
> **username_3**: Conservation of energy cannot be applied to an entire universe governed by General Relativity.  
> **username_2**: How do you know?  
> **username_4**: As space expands, the dark energy density does not decrease, that is, more dark energy is created. See https://medium.com/starts-with-a-bang/the-counterintuitive-reason-why-dark-energy-makes-the-universe-accelerate-3c57f6f31c30  
> **username_2**: But that violates the Third Law.. If the 3rd Law can be violated with impunity on a cosmic scale, there is nothing to stop the total energy of the universe from eventually vanishing completely. I think some cosmologists want to banish the 3rd Law on a cosmic scale because it gets in the way of some of their theories. That's not a good enough reason.  
> **username_5**: A [physical law](https://en.m.wikipedia.org/wiki/Scientific_law) is simply an empirical statement that seems to hold for a given data set. Theories are usually developed to support the law in its context, and make predictions beyond that data set. There's no reason to expect the thermodynamic laws hold at the cosmological scale when the observations don't support them.  
> **username_2**: @Sir Cumference : Cosmological observations don't support the vacuum energy density required by QM,so there is a 40-orders-of magnitude discrepancy between QM and cosmological observations. 40 0rders of magnitude! Yet nobody seems to worry about that. I have noticed that questions which point out awkward facts are rated as bad questions on this site, which speaks volumes about the character deficiencies of the people who drew up the rules and run the site. Same on the physics stack.  
> **username_6**: I don't think there is a problem if the facts are well referenced.  

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