<p>This is a difficult question to answer. Physics really starts after the big bang. Scientist don't know about the laws, if any, before the first instance after the big bang. The time before and during the big bang is really the province of philosophy.</p>

CC BY-SA 4.0
2020-10-05T14:46:07.357Z
2020-10-05T14:46:07.357Z
Natsfan
<p>There are theories which suggest that the universe is like a giant spring, constantly expanding and collapsing. Its possible that pre-big-bang, there was another universe which collapsed, only to re-expand into the universe we know now.</p>
<p>But in reality we have no idea</p>

CC BY-SA 4.0
2020-10-06T08:34:49.660Z
Hello and welcome! Do you have any links to sources that present these theories, in case someone wanted to learn more?
usernumber
CC BY-SA 4.0
2020-10-06T12:58:20.173Z
@usernumber this is a nice little exerpt about it. it explains that its not a very well accepted theory but it is still viable. https://www.universetoday.com/38195/oscillating-universe-theory/    And this one is a little more advanced: https://www.researchgate.net/publication/287711668_Oscillating_Theory_of_the_Universe
jrima12
CC BY-SA 4.0
2020-10-05T18:14:36.680Z
2020-10-05T18:14:36.680Z
jrima12
<p>According to the <a href="https://en.m.wikipedia.org/wiki/First_law_of_thermodynamics" rel="nofollow noreferrer">first law of thermodynamics</a>, law of conservation of energy states,</p>
<blockquote>
<p>The total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.</p>
</blockquote>
<p>Question is where was the energy that triggered the big bang at the first place? What are the popular hypotheses?</p>

CC BY-SA 4.0
2020-10-05T06:07:09.980Z
Big bang is surely out of the coverage of thermodynamics. Your question is lecit but you don't need the law of thermodynamics to arrive at it. Also, not sure if energy conservation holds at cosmological scale. Just think of dark energy.
Alchimista
CC BY-SA 4.0
2020-10-05T21:21:38.907Z
Energy conservation is only true for a system which is time symmetric, as formulated through [Noether's theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem). The Universe is not time symmetric, so we can't expect its energy to be conserved. In fact, it isn't — due to the expansion of the Universe, radiation is constantly redshifted and hence loses energy. On the other hand, as @Alchimista says energy is also created though dark energy (and no, these two processes don't equal out, as they have nothing to do with each other).
pela
CC BY-SA 4.0
2020-10-05T21:29:50.930Z
@pela so we can say that the law is not applicable for our universe. Is it because the precondition of the law, an isolated system?
Sazzad Hissain Khan
CC BY-SA 4.0
2020-10-05T21:37:00.553Z
Yes, the law is only applicable for an isolated system, i.e. energy doesn't leave or enter the system. But that's not a sufficient condition: it is also important that the system is _time symmetric_, i.e. if you repeat an experiment tomorrow, you should get the same result as today. This is of course true for the Universe in most cases, on sufficiently small time scales, but only approximately.
pela
<big-bang-theory><cosmological-inflation><high-energy-astrophysics><thermodynamics>
What powered the Big Bang?
Sazzad Hissain Khan
# What powered the Big Bang?

(Asked by: username_0 on 2020-10-04)

According to the [first law of thermodynamics](https://en.m.wikipedia.org/wiki/First_law_of_thermodynamics), law of conservation of energy states,

> The total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.

Question is where was the energy that triggered the big bang at the first place? What are the popular hypotheses?

**Tags:** big-bang-theory, cosmological-inflation, high-energy-astrophysics, thermodynamics

> **Comments:**
> **username_1**: Big bang is surely out of the coverage of thermodynamics. Your question is lecit but you don't need the law of thermodynamics to arrive at it. Also, not sure if energy conservation holds at cosmological scale. Just think of dark energy.  
> **username_2**: Energy conservation is only true for a system which is time symmetric, as formulated through [Noether's theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem). The Universe is not time symmetric, so we can't expect its energy to be conserved. In fact, it isn't — due to the expansion of the Universe, radiation is constantly redshifted and hence loses energy. On the other hand, as @username_1 says energy is also created though dark energy (and no, these two processes don't equal out, as they have nothing to do with each other).  
> **username_0**: @username_2 so we can say that the law is not applicable for our universe. Is it because the precondition of the law, an isolated system?  
> **username_2**: Yes, the law is only applicable for an isolated system, i.e. energy doesn't leave or enter the system. But that's not a sufficient condition: it is also important that the system is _time symmetric_, i.e. if you repeat an experiment tomorrow, you should get the same result as today. This is of course true for the Universe in most cases, on sufficiently small time scales, but only approximately.  

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## 2 answers

### Answer by username_3 on 2020-10-05. Score: 2 | Accepted answer

This is a difficult question to answer. Physics really starts after the big bang. Scientist don't know about the laws, if any, before the first instance after the big bang. The time before and during the big bang is really the province of philosophy.


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### Answer by username_4 on 2020-10-05. Score: 1

There are theories which suggest that the universe is like a giant spring, constantly expanding and collapsing. Its possible that pre-big-bang, there was another universe which collapsed, only to re-expand into the universe we know now.

But in reality we have no idea

> **Comments:**
> **username_5**: Hello and welcome! Do you have any links to sources that present these theories, in case someone wanted to learn more?  
> **username_4**: @username_5 this is a nice little exerpt about it. it explains that its not a very well accepted theory but it is still viable. https://www.universetoday.com/38195/oscillating-universe-theory/    And this one is a little more advanced: https://www.researchgate.net/publication/287711668_Oscillating_Theory_of_the_Universe  

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