Within the theoretical regime of the big bang origin of the universe, the big bang defines the beginning of the time. You can call it the time, t = 0. In this formulation, the space and time originated at big bang. You can not conceptualize anything before this kind of a beginning that can be physically verified within the frame work of the laws of Physics. Anything that can not be verified need not exist.

Within the theoretical regime of the big bang origin of the universe, the big bang defines the beginning of the time. You can call it the time, t = 0. In this formulation, the space and time originated at big bang. You can not conceptualize anything before this kind of a beginning that can be physically verified within the frame work of the laws of Physics. Anything that can not be verified need not exist.

The entire universe was NOT originated from a single point after the Big Bang.

Is their any possibility for negative time or can we consider the time before big bang is negative time.

@J.-Fernando Pascual-Sánchez ,Where did the universe was originated.

"Why don't we consider ..... Unquote.

It depends who is meant by 'we', but e.g. Martin Bojowald, Roger Penrose, and a number of other stellar physicists are certainly not part of this 'we' set .....

Under Bojowald's QLT calculations, for instance, the pre-existence of Time is a necessary precondition for a BB to happen. This result can also be found independently under other scenarios than QLG. It ultimately comes down to the nature of Time itself ....

In the standard classical perturbed FLLRW models, all the universe, i.e., the spacetime, was originated from the singularity at once.

Simple answer

before the Planck Time (or the beginning of the "big bang: if you want)

the equivalent coordinates/units for mass, length and time are just not known

given our present day physical theories. So, we don't even know how

to correctly ask this question of "... what was before ..."

We cannot. The big bang's condition cannot be described as such by our physical laws and all information, if you would go backward in time, about anything in time - if it even existed before big bang - is lost because everything, all energy had been concentrated in one point, a singularity. There is no way we can learn anything before the big bang.

I asked similar question posted in RG: " What was before Big-Bang?" !

Since we do not know the nature of " time" and lack of current physics in Big-Bang, opposite of others, I say we do not know what happened just at the t=0 and before creation of spacetime, there is no reason not to have TIME.

In summary, if space and time are independent according to Gallilian transform then it would possible that TIME exists independent of space. Conversely, based on Lorentz transform, time and space may be dependent to each other. According to Einstein's spacetime, TIME and SPACE coexist. However, at the onset of Big-Bang, Galllilian or Loerntz trasforms do not hold and we can not apply these concept at the initiation time. I conclude that TIME may have existed before Big-Bang. In this case Big-Bang may take place at a definite instant and not at t=0, because there is no initiation TIME.

The string theory may contribute to clarify this, where higher dimensions squeeze to 4 dimentions (t,x,y,z).

@Parviz: As you said yourself, the big bang is the creation of space-time as we know/ understand it. Therefore there is no way of saying what has been before, it is possible that there has been something similar before or not, but there is no way of telling as we cannot access information before that.

Volker

Big-Bang is an event just before the cration of spacetime. In fact, Big-Bang created the spacetime a little bit after occurence. Since then, the univense started expanding.

Hey, I am physiologist (neurosciene/biomechanics) so I am not an expert (far from it). However, this interests me a lot. What I can make out of it is:

-The big bag created time and space and from thereon entropy increases so the universe expands etc. etc. (I actually like to believe that the big bang created an increase in entropy gradient which stretches space and time, anyway) ...

- Is it possible that other events (occurring maybe in the other dimensions that I don't really comprehend, since i really don't understand the math behind it) are omnipresent regardless of the presence of space and time and can might generate from 'time to time' a big bang?

(I hope what I say makes sense)

There is another theory of cyclic expansion and contraction of universe in oppposite of Big-Bang ever expandiing universe. No one can prove which one is correct?!

@Parviz Parvin: What you mean is the "Big crunch", but it is not a theory, it is a hypothesis (theory is not hypothetical, it has been proven and there is a lot of proof for the big bang, e.g. the background radiation). And it also does not contradict the Big Bang. It just says that it is possible that the universe returns to this state in the future. However this would be a contradiction to the law of entropy as we understand it now and also measurements show that expansion is not slowing but accelerating, so a big crunch is unlikely, although not impossible. Due to the nature of the big bang origin (i.e. in a singularity) it is impossible for us to determine if there was a big crunch before or not...

Its a bit difficult. Time is relative, against what would we measure it?

Volker

Big-Bang means the initiation (creation) of the universe suddenly. It is not resonable since it can be iferred the likelihood of a sudden annihilaiation too. Since such annihiliation has not happened so far then I believe the continuity of universe opposite of a sudden singularity.

The evidences of Big-Bang such as accelerating universe may be due to vaccum energy and dark matter ... because the galaxies afar is relatively faster than ours. It does not arise from Big-Bang. The background radiation may be due to conitinual cosmic ray activation. How do you correlate the background radiation with the Big-Bang??

Entropy does not necessarily originate from the expansion, in thermodynamics, if you compress, the gas would still increase. The entropy always increases according to second law and is not dependent of expansion as an irreversible process.

You may visit my similar question posted in RG too.

I am aware of the things you mentioned and in fact, just from gut feeling, I think a "pulsing" universe is far more natural. But you state things like "does not arise from Big-Bang" with too much certainty.

The Background radiation has been postulated by the Big Bang theory and later measured. So apparently it matches. It is the remaining radiation of the early universe. Initially the universe was filled with a glowing plasma, expansion cooled the plasma and associated radiation to a point where recombination of protons and neutrons was possible - forming hydrogen atoms. Those atoms could not absorb the radiation, like the plasma did and thus the universe became transparent, which allowed photons to travel freely. And these are the photons we still see today, cooled down a lot due to the immense expansion of the universe.

I am aware that the acceleration of the universe's expansion is not an indicator of big bang, this is not what I meant. I am just saying that the current accelerated expansion, makes it unlikely that eventually the expansion will actual SLOW down to zero and then accelerate in negative direction (collaps).

Also if you think of a collapsing universe, i.e. mass becomes more and more concentrated, atoms rearrange, reform and eventually are compressed in one tiny spot. How does this order not decrease entropy? A cristal has a smaller entropy than a space nebula... Entropy is also directly linked to the volume, so if the volume decreases, so does the entropy. So how do you see that this can be solved?

Volker

Thank you for your lucid and interesting comments.

The gas during expansion and compression ( in non-adiabatic irreversible process) undergoes entropy rise. It is basis of second law. Therefore , to my knowledge if you decrease the volume (by exerting pressure), the entropy would increase (unless it is done adiabatically then no change in entropy happens but it does not reduce). Look at carnot cycle, at adiabatic ideal termodynamical paths, the entropy increases(T-S) only at isothermal heating (and a volume rise simultaneously ,P-V) ) and decreases(T-S) due to isothermal cooling (and a volume drop too, P-V). On the other hand, two other paths are adiabatic ones with no entropy change while the volume may rise or drop. In fact , entropy is not directly dependent of volume as I expressed above. Expanding universe and collapsing universe show entropy rise as it happens in nature because of second law violation.

If a space nebula compresses, then the colission rate enhances leading to nebula heating and consequently entropy increases. I have no comment regarding crystal because the likelihood of the formation in this case based on such contraction (pulsing universe) is very low.

Carno Cycle,T-S Diagram:

Carnot Cycle, P-V Diagram:

because in this model, big bang is the moment when time started existing, so before it time was not existing