Time Before Big Bang: Is Time Eternal?

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In summary, there is no scientific evidence that proves the impossibility of something existing before the Big Bang. However, our current standard model is limited and cannot look beyond the Big Bang. Other models, such as the no-boundary and tunneling proposals, do not break down before the Big Bang but require a topological trick to discuss "before". Additionally, the concept of time itself is an emergent property of gravity, and some quantum interpretations suggest that classical physics is also emergent. There are various models that propose different explanations for the beginning of time, such as Loop Quantum Cosmology, Conformal Cyclic Cosmology, and Eternal Inflation. Ultimately, we do not know for certain what happened before the Big Bang and should
  • #1
revo74
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You often hear that it makes no sense to talk about time before the Big Bang because time itself did not exist, however, isn't it possible and perhaps even likely that only the time that is an inherent property of our Universe did not exists before the BB, but time in another physical realm may have? Aren't we making an unwarranted assumption when we say time (in general) did not exist before the BB?
 
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  • #2
The other time-like dimension would have to come into being somehow, and then what happened before that time-like dimension came into being?
We cannot talk about a meta-time before the meta-time dimension ... but maybe there is a meta-meta time and so on ad infinitum?

Even if this meta-time did not need to come into existence (it is eternal say) there are still no space dimensions for stuff to happen in that would make having the meta-time useful.

Most of the current cosmogonies try to avoid this sort of thing:
https://www.physicsforums.com/showthread.php?p=3605530
 
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  • #3
There is nothing in science that says it is impossible that something existed prior to the Big Bang. It is simply that our standard model cannot look beyond that. There are other models that don't break down past that point, they simply don't have enough evidence to be accepted yet.
 
  • #4
OP explicitly assumes a model of the big bang where time does not exist beforehand and then speculates about how one may talk about "before" when there is no time to have a "before" in - for instance, if there were another time-like dimension.

I doubt the assumption [no time before the big bang] is scientifically "unwarranted".
However, I also suspect that "big bang" may be a tad imprecise a term for this discussion. It is commonly takes as the beginning of the Universe - with nothing "before", though others may use it to mean the particular period of rapid expansion in the early Universe.

The no-boundary and tunneling proposals don't break down - but the concept of "before" requires a topological trick. Usually these models are worked out in configuration space rather than space-time right?
 
  • #5
Under GR, time and space are emergent properties of the gravitational field. If you could turn off gravity, time and space would cease to exist. See http://www.astronomycafe.net/gravity/gravity.html for discussion. The is no evidence of gravity prior to the BB
 
  • #6
Or the other way around - GR treats gravity as curvature in space-time but it is mathematically ambiguous which gives rise to what.

Some non-copenhagen quantum interpretations treat classical physics, like gravity, as emergent behavior rather than an average behavior.

Ive found an accessible lecture, from Hawking as it happens, describing his kind of ideas about the beginning of time:
http://www.hawking.org.uk/index.php/lectures/62 [Broken]

I've been looking for a similar level talk about the tunneling model.
 
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  • #7
As I understand it,the evidence is clear that the universe was in a very hot dense 13.7 billion years. If you assume GR can describe the universe at the smallest scales then time may stop around this time.
NOW THE CAVEATS:
We have to assume GR is good to these tiny scales. Gr has never been tested down to these tiny scales and so one might argue there is no good evidence for the conclusion of no time before the big bang.

Other quanutm gravity models for example, Loop quanutm cosmology predict there was time before the big bang. see for example http://arxiv.org/abs/0812.4703

Another assumption one has to make is inflation is not eternal, accoprding to Guth most models of inflation imply its eternal, which implies our big bang is only one of many and there's no reason to think ours is the first. See:http://arxiv.org/abs/hep-th/0702178

Its also possible to construct models that have no inflation and no quantum gravity corrections that still imply our big bang is one of many eg Penropse CCC: http://en.wikipedia.org/wiki/Conformal_Cyclic_Cosmology

There are many other models too frequent to mention to be honest.

Bottom line: the idea that time began at the big bang is one conjecture out of many, at the moment we don't know if it or alternate models such as quanutm bounce, CCC, eternal inflation, ekprotic etc are correct. So we should keep an open mind.
 
  • #8
The 'we do not know' card is always in play. That is the nature of science. We can apply what we do know to make reasonable conclusions. I'm not saying we shouldn't keep an open mind, merely keeping the discussion focused on physics as we currently understand it.
 
  • #9
Agreed, all science has doubt. But there are certian things in physics that are reasonably well understood and there are others which are not . The behaviour of the universe at the so called sinugularity is without doubt one of the things that is not well understood and I think many times the public is often misled into thinking that it is.
 

1. What is the Big Bang theory and how does it relate to the concept of time before the Big Bang?

The Big Bang theory is a scientific model that explains the origin and evolution of the universe. It states that about 13.8 billion years ago, all matter and energy in the universe was compressed into an incredibly dense and hot singularity, and then rapidly expanded and cooled, resulting in the formation of the universe as we know it. According to this theory, time, space, and matter all came into existence at the moment of the Big Bang, so there was no time before it.

2. Is time eternal, or did it also have a beginning with the Big Bang?

According to the Big Bang theory, time did not exist before the Big Bang. The concept of time is a fundamental aspect of our universe, and it is believed to have come into existence along with space and matter at the moment of the Big Bang. While some theories propose the idea of a cyclical universe where time may be eternal, there is currently no scientific evidence to support this.

3. If time did not exist before the Big Bang, how can we even talk about the "time" before it?

It is important to understand that the concept of time as we know it is based on the laws of physics that govern our universe. However, these laws did not exist before the Big Bang, so the concept of time itself may not be applicable in the same way. Some theories suggest that time may have emerged as a result of the expansion of the universe, but it is still a topic of ongoing research and debate among scientists.

4. Can we ever know what happened before the Big Bang?

Since the Big Bang is considered to be the beginning of the universe, it is not possible to know what happened before it with our current understanding of physics. The laws of physics as we know them break down at the singularity of the Big Bang, so any events or conditions before that moment are currently beyond our ability to observe or comprehend.

5. Are there any theories about what existed before the Big Bang?

There are various theories and hypotheses that attempt to explain what may have existed before the Big Bang. Some propose the idea of a multiverse, where our universe is just one of many parallel universes. Others suggest the concept of a pre-Big Bang era where time and space may have existed in a different form. However, these theories are still speculative and are not currently supported by scientific evidence.

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