The Big Bang Theory

[Siyatanush]

Do the laws of Mass and Energy conservation not apply at the time of Big Bang?

[StringJunky]

The BB is only the beginning of a new epoch in the universe's evolution, continuing on from a previous one.

[Strange]

44 minutes ago, Siyatanush said:

Do the laws of Mass and Energy conservation not apply at the time of Big Bang?

We don't really know anything about "the time of the Big Bang". Or even if there was such a thing. There are various speculative ideas about what might have happened early in the universe. The universe could be expanding following the collapse of an earlier universe (the "big bounce"). Or the universe might have come from the energy in a false vacuum ("universe from nothing"). Or the total energy of the universe might be zero ("zero energy universe"). Or the energy might be infinitely old. Or ...

All the science tells us at the moment is that the universe was once hotter and denser than it is now.

 

[Siyatanush]

At the time of the Big Bang, nothing should have been there. No space, no time, nothing. Am I right?

[StringJunky]

9 minutes ago, Siyatanush said:

At the time of the Big Bang, nothing should have been there. No space, no time, nothing. Am I right?

The universe may have manifested in some state before time and space emerged with the BB. It's all guessing but it didn't pop out of nothing. Best to look at the BB as the beginning of a new epoch in its evolution.

[Strange]

1 hour ago, Siyatanush said:

At the time of the Big Bang, nothing should have been there. No space, no time, nothing. Am I right?

We don’t know. There is no evidence and no theories that apply at that time. 

The idea that there was no time or space comes from a naive extrapolation of general relativity. But we are fairly sure that is not valid because it does not take quantum effects into account. 

It is possible the universe is infinitely old. 

[StringJunky]

2 hours ago, Strange said:

It is possible the universe is infinitely old. 

Or possibly  things didn't happen in the temporally linear way that we know pre-BB.

[J.C.MacSwell]

 

 

2 hours ago, StringJunky said:

Or possibly  things didn't happen in the temporally linear way that we know pre-BB.

Agree. If they did, how could we have gotten to this point in time, if an infinite amount of time had to come before?

[taeto]

28 minutes ago, J.C.MacSwell said:

Agree. If they did, how could we have gotten to this point in time, if an infinite amount of time had to come before?

We would get here in a finite amount of time from any previous point in time, there is nothing problematic about that

[StringJunky]

35 minutes ago, J.C.MacSwell said:

 

 

Agree. If they did, how could we have gotten to this point in time, if an infinite amount of time had to come before?

To my way of thinking, and in cosmology generally it seems, infinities are bad and the idea of no time or non-linear time seems to remove that problem. There may be other ways to make them disappear, of course, that I haven't come across yet.

[Siyatanush]

Will the cosmos exist for a finite time?

[StringJunky]

10 minutes ago, taeto said:

We would get here in a finite amount of time from any previous point in time, there is nothing problematic about that

Yes, a finite amount of time from the BB.

[J.C.MacSwell]

43 minutes ago, taeto said:

We would get here in a finite amount of time from any previous point in time, there is nothing problematic about that

Turtles all the way back?

https://en.wikipedia.org/wiki/Turtles_all_the_way_down

Edited December 24, 2018 by J.C.MacSwell

[StringJunky]

32 minutes ago, Siyatanush said:

Will the cosmos exist for a finite time?

What I've read, the universe may eventually go into heat death which means basically everything will decay to the point of there being no more interactions or reactions

[dimreepr]

52 minutes ago, taeto said:

We would get here in a finite amount of time from any previous point in time, there is nothing problematic about that

relative to what?

[taeto]

33 minutes ago, J.C.MacSwell said:

Turtles all the way back?

https://en.wikipedia.org/wiki/Turtles_all_the_way_down

For the turtles to do proper support, there cannot be a bottom turtle, unless it gets provided with something else to stand on.

It doesn't seem that a time measuring device must have a similar property. Either there is a first second (say, after BB), or there isn't one, it doesn't appear to make a big difference to what comes after.

[dimreepr]

7 minutes ago, taeto said:

It doesn't seem that a time measuring device must have a similar property. Either there is a first second (say, after BB), or there isn't one, it doesn't appear to make a big difference to what comes after.

1

 

32 minutes ago, dimreepr said:

relative to what?

 

what does it stand on?

Edited December 24, 2018 by dimreepr

[Carrock]

2 hours ago, J.C.MacSwell said:

Agree. If they did, how could we have gotten to this point in time, if an infinite amount of time had to come before?

Photons have infinite range, so can 'reach' infinity spatially and temporally (past or future) if the laws of physics don't change along their path.

Why is not getting to now from infinite past time a problem for massive particles?

I can't get to here from inside the event horizon of a black hole.

Not being able to reach infinity in space or time is not generally considered to be proof that the universe is finite in space and time.

[dimreepr]

41 minutes ago, Carrock said:

Photons have infinite range, so can 'reach' infinity spatially and temporally (past or future) if the laws of physics don't change along their path.

1

they don't know

[taeto]

1 hour ago, dimreepr said:

what does it stand on?

I am not sure what your "it" stands for. In the turtle picture, a turtle is supposed to stand on a lower turtle. I am trying to suggest that a segment of time does not have to stand on any previous segment of time necessarily. Viewed in isolation it could conceivably be the initial segment of time that exists, or it might have any amount of time preceding it. Which is why I would hesitate to entertain the turtle analogy when it comes to time progression.

If you mean to point to different possible choices of inertial frame of reference, then the question of finiteness of time appears to be frame independent. I.e. if an amount of time is finite in any frame then it would also measure finite as seen from any other frame, even when the precise length of time measures different.   

[dimreepr]

3 minutes ago, taeto said:

if an amount of time is finite in any frame then it would also measure finite as seen from any other frame, even when the precise length of time measures different. 

 

why?

[J.C.MacSwell]

2 hours ago, taeto said:

For the turtles to do proper support, there cannot be a bottom turtle, unless it gets provided with something else to stand on.

It doesn't seem that a time measuring device must have a similar property. Either there is a first second (say, after BB), or there isn't one, it doesn't appear to make a big difference to what comes after.

 

1 hour ago, Carrock said:

Photons have infinite range, so can 'reach' infinity spatially and temporally (past or future) if the laws of physics don't change along their path.

Why is not getting to now from infinite past time a problem for massive particles?

I can't get to here from inside the event horizon of a black hole.

Not being able to reach infinity in space or time is not generally considered to be proof that the universe is finite in space and time.

Keep in mind this all said was with respect to time as we know it. It has a direction, and is linear, with previous time expiring before the present can take place.  If it also was infinite into the past, how could we have reached this point in time? This is not the same as a position in space, nor is it the same problem with respect to time going infinitely into the future.

The point is that we don't have a concept of time for the start of any cosmological model that makes sense in terms of how we perceive time generally.

[zapatos]

51 minutes ago, J.C.MacSwell said:

 

If it also was infinite into the past, how could we have reached this point in time?

Are you saying that it would have taken an infinite amount of time to reach this point?

[Carrock]

54 minutes ago, J.C.MacSwell said:

If it also was infinite into the past, how could we have reached this point in time? This is not the same as a position in space, nor is it the same problem with respect to time going infinitely into the future.

This seems very anthropocentric.

If there are entities in the infinite future, would they say "there's no way we could have got here from the infinite past," (which includes the time humans existed) "therefor the infinite past doesn't exist."

The only way to avoid infinite future time is for time to cease at some finite future time and I'm not aware of (m)any mainstream theories which predict that.

 

An analogy from maths:

You can create 'instantaneously' the infinite set [1,2,3,4....]

It's impossible to count the whole set one by one i.e. there are numbers which cannot be reached in this way..

 

Why is unreachable infinite space or unreachable infinite future time OK but unreachable infinite past time not OK?

 

1 hour ago, J.C.MacSwell said:

The point is that we don't have a concept of time for the start of any cosmological model that makes sense in terms of how we perceive time generally.

e.g. some models of inflation posit an eternal 'base' universe from which inflation started one or more times. Whether time existed 'before' BB is still speculation with AFIK no evidence either way.

[J.C.MacSwell]

1 hour ago, Carrock said:

This seems very anthropocentric.

If there are entities in the infinite future, would they say "there's no way we could have got here from the infinite past," (which includes the time humans existed) "therefor the infinite past doesn't exist."

 

Yes. If they assume an infinite past...and are using the narrow definition of time I described.

Here is the difference between infinite past and infinite future

If you count whole numbers starting from 0 and going forwward, at say 1 per second, you cannot name a single positive whole number that eventually won't be reached.

If you count whole numbers starting from negative infinite, at say 1 per second, you cannot name a single whole number that eventually will be reached.

2 hours ago, zapatos said:

Are you saying that it would have taken an infinite amount of time to reach this point?

Essentially.

7 hours ago, J.C.MacSwell said:

 

 

Agree. If they did, how could we have gotten to this point in time, if an infinite amount of time had to come before?

 

If time had no arrow, infinite future would be no different from infinite past.