Before the Big Bang

[uppi]

What evidence and how were they measuring it? With a clock? That clock wouldnt be at 0 kelvin so it would be in a different frame of reference. I gaurantee if they put that clock in 0 kelvin, it would stop.

So what else do they use to measure time?

They're measuring the frequency of specific electromagnetic transitions. The second is actually defined over the frequency of a hyperfine transition in Cs-133. That can be measured no matter the temperature of the Cs (if you compensate for the doppler shift)

That doesnt sound like a fundemental force of nature. That just sounds like a "tape measure" that mankind made up.

All descriptions of nature are basically concepts that mankind made up. There apparently is a fundamental force of nature that makes a concept of time neccessary. But there is no way to say, whether our concept of time is the only one, or even whether it is right. Maybe in the future someone will come up with something that shows that our concept of time is flawed. But until then we have to work with what we have.

 

[Birdjaguar]

Time-invariance means that under the same initial conditions, the result doesn't depend on when something is started. If I am doing the exact same experiment (of course this is difficult in practice), it doesn't matter, whether I am doing it the first or the millionth time.

All that seems to mean is that outcomes are not dependent upon when you do an experiment and that the laws appropriate to the experiment do not change from one moment to the next. Said another way: time (as a locater) is irrelevant to experimentation.

The way a state behaves if time progresses. In classical quantum mechanics, this basically means the Schödinger equation.

Thanks.

... that the quantum mechanical time evolution does not depend on temperature in any way.

So you seem to be saying that temperature does not affect the passage of time. I would agree since I cannot see any connection between matter and time. Temperature affects matter.

I'll give it a try: Time is a coordinate to order events according to their (potential) causality. That means that all events that could (theoretically) have influenced a certain event get assigned a lesser value, all events that this event could (theoretically) influence get assigned a greater value.

Ok, by this definition, time is a system to assign values, but the values are merely descriptive and do not actually affect any events.

 

[Omni314]

Wouldnt that be dependent on gravity existing? Didnt the big bang create gravity and time?

no gravity didnt just appear it exists there is no "condtion" for it no to.

 

[achilleszero]

no gravity didnt just appear it exists there is no "condtion" for it no to.

Really? Supposedly the big bang created everything including the other 3 fundemental forces (strong, weak force, and electromagnetism).

 

[Mise]

I don't know if anyone answered this yet, but:

But once time starts (say at the Big Bang 13 billion years ago), then that point denotes the end of "timelessness" and unless time has always existed, existence would appear to have two "parts", one timeless and one with time. Prior to 13 billion years ago there was no time, but was there something?

Like Perfy said, there is no "prior to [13.7] bn years ago". Everything that has ever existed and ever will exist came into existence 13.7 bn years ago. Anything else is more north than the north pole.

(usual caveat of "as far as we know" applies.)

 

[AngryZealot]

Really? Supposedly the big bang created everything including the other 3 fundemental forces (strong, weak force, and electromagnetism).

The big bang did not create anything. These forces already existed, presumably as a unified force in higher dimensionality. The big bang began the expansion of the universe, which split the forces apart into what we see today.

 

[achilleszero]

The big bang did not create anything. These forces already existed, presumably as a unified force in higher dimensionality. The big bang began the expansion of the universe, which split the forces apart into what we see today.

I would pose that they didnt exist. What did exist is this grand unified force. None of the forces wouldnt have had the same properties at all being combined with the other 3. Not until they were split apart did they actually exist as what we know them to be.

 

[uppi]

If all forces were unified during the big bang, then they were only unified because of the high energy density during it. Without these high energy densities, there is no unification. Thus it doesn't make sense to talk about an unified force before the big bang, because the big bang was the thing to make this unification possible.

Another thing is that in quantum field theory, the forces work through bosonic particles. Thus for forces to exist, there needs to be something already there. Therefore it doesn't make much sense to talk about forces before the big bang, unless you postulate some sort of predecessor to our universe.

 

[achilleszero]

If all forces were unified during the big bang, then they were only unified because of the high energy density during it. Without these high energy densities, there is no unification. Thus it doesn't make sense to talk about an unified force before the big bang, because the big bang was the thing to make this unification possible.

Another thing is that in quantum field theory, the forces work through bosonic particles. Thus for forces to exist, there needs to be something already there. Therefore it doesn't make much sense to talk about forces before the big bang, unless you postulate some sort of predecessor to our universe.

So that would mean I was right about gravity not existing until after the big bang, just that my reasoning was off?

 

[uppi]

So that would mean I was right about gravity not existing until after the big bang, just that my reasoning was off?

Generally yes, but there are some scenarios in which gravity could exist before. A big bounce (A predecessor universe collapsing and "creating" the big bang) would be one example.

 

[Omni314]

Really? Supposedly the big bang created everything including the other 3 fundemental forces (strong, weak force, and electromagnetism).

It didnt create anything, in fact thinking about it the big bang wasn't even an event since it has no cause

 

[warpus]

It could have a cause. We don't know.

 

[Birdjaguar]

No, because physical matter (as we know it) cannot exist without space, and space cannot exist without time.

Sure. We don't know that the big bang actually created anything. What we call the big bang is the extrapolated start of the expansion of the universe.

Time cannot exist without space.

The big bang did not create anything.

It didnt create anything, in fact thinking about it the big bang wasn't even an event since it has no cause

If the BB didn't create anything, then matter existed prior to it. If matter existed, then time must have also existed.

So are you saying that prior to the BB, all matter (and time) existed in some unknown state that was different from our current universe and then something (we don't know what) happened and our universe began to expand.

String theory and multiple universes are current guesses at an explanation.

 

[achilleszero]

It didnt create anything, in fact thinking about it the big bang wasn't even an event since it has no cause

What?? But before the big bang spewed out everything, nothing as we know it existed in the same form as it is now. Everything was completely combined into one, completely different 'thing', whatever it may have been.

 

[warpus]

If the BB didn't create anything, then matter existed prior to it. If matter existed, then time must have also existed.

There was no "prior to it", though, as far as we know.

 

[Atrebates]

It easy to say "what happened before the Big Bang?" is an invalid question, but that's not the case... It's really hard, sure - but there are theories about whether there was anything before the big bang; it's just currently nigh on impossible to find experimental evidence to decide which theories are possible.

This lack of evidence means that there's no such thing as a leading theory in this field, there are "fashionable" theories at best.

Just to mention one from Sir Roger Penrose that he's started to lecture on, we should look for circular irregularities in the Cosmic Microwave Background (CMB) that would indicate a universe consistent with the big bang being what a black hole looks like from the inside. And this was all to do with 2nd order derivatives of some general relativity equation being continuous across singularities... oh, and if we saw ellipses rather than circles the universe is spinning.

I'm mentioning this to demonstrate that theories about the big bang can be mind-buggeringly hard and very few people who claim to understand to topic have a clue about real research.

Overall the lack of good experimental evidence makes BEFORE the big bang a hard topic to talk about but I think the pre-eminent view is that we cannot see past the big bang (regardless of whether there was anything previously or not) but this view can change if a good theory comes along

 

[warpus]

@Atrebates

The "invalid question" response to "what happened before the big bang?" is a result of the idea that time was created during the big bang, and thus it's impossible for anything to have happened before the event.

 

[Atrebates]

My phrasing is perhaps harsher than it should be, time being created at the big bang is a respected idea, and the majority of theories that don't prescribe to this view (eg. cyclic universes)state that info from before the big bang is not recoverable afterwards. For these theories, there is little to say pre-BB (for the former theory you can consider how the BB occurred, for the latter, prior universes are restricted to a set that corresponds to the cyclic condition).

A member of the public will be told by an academic that pre-BB is not worth thinking about; because the academic knows meaningful discussion will not get very far and give everyone a headache. But serious researchers haven't yet pinned down pre-BB, choosing your theory is pretty much personal preference. Under these circumstances it isn't really fair to say pre-BB is invalid... It's an option, and it could well be correct - but till we're sure I don't mind thinking about the other options

 

[Birdjaguar]

There was no "prior to it", though, as far as we know.

My point was the following:
Some of you have said...
The BB didn't create anything, including matter
Matter requires space and space requires time
So if matter and space (even if quite small) pre-existed the BB (ie wasn't created by it), then time must have pre-existed the BB too and there was a "prior".

 

[Olleus]

Why is there a new thread about this every week or more?

Nobody knows what there was before the big bang or if there even was time before it. Hell, no body has any theories for what happened at the instant of the big bang or in the 10^-40 seconds after is. All known physics breaks down near then so we don't even have any approximations as to what could have happened. General relativity and quantum field theory (which are both applicable during the big bang) both fail. Even if one of them could be twisted to work under those extreme conditions it wouldn't be valid as only a unified theory (which hasn't been created yet) which takes into account both the warping of spacetime and quantum effects would work.
In short not only do we not know what happens, we don't know how in which direction we need to work to know.