The Big Bang Theory

[StringJunky]

2 hours 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."

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?

 

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.

You'd never get to this point in time because it is at the other end of the infinite past, therefore an infinite past composed of linear time as we know it is not logical... Captain.

Edited December 24, 2018 by StringJunky

[Strange]

2 hours ago, J.C.MacSwell said:

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.

And yet ... I can count from 10 to 20.

 

[J.C.MacSwell]

Just now, Strange said:

And yet ... I can count from 10 to 20.

 

In the context given...ya gotta lotta work to do first!

[Carrock]

1 hour ago, J.C.MacSwell said:

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.

You're comparing a finite future time with an infinite past time.

I

3 hours ago, Carrock said:

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.

 

1 hour ago, StringJunky said:

You'd never get to this point in time because it is at the other end of the infinite past, therefore an infinite past composed of linear time as we know it is not logical... Captain.

You'd never get to 10 seconds ago because it is in the past, therefore a finite past composed of linear time as we know it is not logical... Spock.

I think both of these statements are not logical. If you think your statement but not mine is logical, please explain.

 

J.C.MacSwell and StringJunky :

You both seem to think certain times cannot exist because you can't reach them. This problem doesn't seem to exist for you if the universe is spatially infinite i.e. mostly unreachable.

[Strange]

33 minutes ago, J.C.MacSwell said:

In the context given...ya gotta lotta work to do first!

Apparently not. 

We are here now, and the universe could be infinitely old.

And ... 10,11,12,13,14,15,16,17,18,19,20

[J.C.MacSwell]

13 minutes ago, Strange said:

Apparently not. 

We are here now, and the universe could be infinitely old.

And ... 10,11,12,13,14,15,16,17,18,19,20

Apparently you suggest it is infinitely old and time works as we intuitively perceive it.

You counting to 20 from 10 doesn't change my argument any more than you breathing.

If we got to this point in time...time is not infinitely old and/or it doesn't work as we perceive it.

Edited December 24, 2018 by J.C.MacSwell

[Strange]

Just now, J.C.MacSwell said:

If we got to this point in time...time is not infinitely old or it doesn't work as we perceive it.

I’m afraid that just makes zero sense. 

[J.C.MacSwell]

48 minutes ago, Carrock said:

You're comparing a finite future time with an infinite past time.

I

 

You'd never get to 10 seconds ago because it is in the past, therefore a finite past composed of linear time as we know it is not logical... Spock.

I think both of these statements are not logical. If you think your statement but not mine is logical, please explain.

 

J.C.MacSwell and StringJunky :

You both seem to think certain times cannot exist because you can't reach them. This problem doesn't seem to exist for you if the universe is spatially infinite i.e. mostly unreachable.

I'm pretty sure we have reached this point in time.

5 minutes ago, Strange said:

I’m afraid that just makes zero sense. 

Something about the lack of obligation of the Universe...(for me also)

I think Stringy understands my line of thinking...time cannot be infinite in the past and as we are describing/attempting to describe...the fact we are here now rules out at least one.

 

I really have no problem with the suggestion that time is infinite in the past, as long as you don't combine it with time as we intuitively perceive it, with the past expiring before any future can be reached.

[StringJunky]

1 hour ago, Strange said:

Apparently not. 

We are here now, and the universe could be infinitely old.

And ... 10,11,12,13,14,15,16,17,18,19,20

We are in an epoch of the universe where the clock ticks as we know it and you can count as you do.

Edited December 25, 2018 by StringJunky

[Strange]

7 hours ago, J.C.MacSwell said:

I really have no problem with the suggestion that time is infinite in the past, as long as you don't combine it with time as we intuitively perceive it, with the past expiring before any future can be reached.

Well, I guess that’s OK, as GR doesn’t use that model of time. (I still don’t understand your objection, but it doesn't matter.)

[StringJunky]

1 hour ago, Strange said:

Well, I guess that’s OK, as GR doesn’t use that model of time. (I still don’t understand your objection, but it doesn't matter.)

We  were just mildly  speculating with a concept that doesn't involve infinite regression or infinities, buy hey, this is in "Physics" and we shouldn't, so I'll shut up.

[taeto]

Approaching the question from the mathematical side (and being somewhat naive about the physics), the question isn't necessarily so much about the finiteness of time, but rather whether time has an actual "beginning". Assuming that time will proceed forever after (I have not seen anybody opposed to that assumption), there could be three distinct possibilities:

(1)  time progresses as \(t \in (-\infty,\infty)\), or

(2) as \( t \in (0,\infty)\), or

(3) as \( t \in [0,\infty],\)

where \(0\) is a 'starting point' for the existence of time.

Possibilities (1) and (2) are homeomorphic, in particular, for every time, there was a time prior to it. The only difference being that the progression of time would appear faster in (2) as in (1). 

Possibility (3) would be similar to the familiar picture of BB in a spacetime with only one space dimension, where BB represents the North Pole of the globe and the time represents moving south along laterals such that space is represented by ever increasing circles. It also means that there were times for which there was no time that was 1 second previously. Does this seem the most reasonable idea of the 'beginning' of time?

Oh, and if my intuition is worth much, then I do not see much chance of making any determination of either possibility by physical measurement. But feel free to disagree.

Edited December 25, 2018 by taeto

[J.C.MacSwell]

17 hours ago, Strange said:

Well, I guess that’s OK, as GR doesn’t use that model of time. (I still don’t understand your objection, but it doesn't matter.)

Agree.

Now just to try a different tack:

Say I proposed a BB model with time starting abruptly and going forever forward infinitely...followed by a reversal with time going backward to the starting point.

Would this make sense? Would the reversal actually get to happen in this model, assuming it would have to wait for the completion and expiration of the first part?

[MigL]

All this number/counting theory is fine, but is it applicable ?

As you examine smaller and smaller features, you eventually get to Planck scale.
Past this point, space-time has been described as 'quantum foam' by J A Wheeler.
This quantum foam has lost all aspects of geometry; the three spatial and one time dimension are no longer existent.
events are 'everywhere' and 'anytime'.

The journey back towards t=0 is similar.
You shrink space-time to a dimensionless point at t=0.
But we don't necessarily have to go back that far. At some time before reaching that dimensionless point, we again lose all geometry, and the universe is a quantum foam where time and space has no meaning.

IOW before the emergence of the geometry ( at around the Planck scale ) that makes our universe measurable, time had no meaning, and we cannot say anything about the duration of that era and state.

 

Of course you can mathematically get around this.
See Moontanman's post in Science News about the possibility of time existing prior to the Big Bang.

Edited December 26, 2018 by MigL

[beecee]

On 12/24/2018 at 4:58 PM, Siyatanush said:

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

As others have said, we really do not have any theory of the moment of, or more correctly, the incident of any BB. The BB is actually a theory about the evolution and expansion of space and time [as we know them] from t+10-43 seconds. From that point, and with the current knowledge that we have observed with particle accelerators etc, we can reasonably logically deduce how the observable universe evolved to what we see today. 

[MigL]

In direct reply to the OP...

If there is a discontinuity in time prior to t+10^-43 sec then, since the law of energy conservation is due to the Lagrangian being symmetric under continuous translation in time ( Noether ), our conservation laws fall apart at this point.

So, yes, there is a good possibility that conservation laws ( as we know them ) do not apply to the BB event

[Martyred Goat]

On 12/26/2018 at 12:57 AM, J.C.MacSwell said:

Agree.

Now just to try a different tack:

Say I proposed a BB model with time starting abruptly and going forever forward infinitely...followed by a reversal with time going backward to the starting point.

Would this make sense? Would the reversal actually get to happen in this model, assuming it would have to wait for the completion and expiration of the first part?

You can run time forwards and backwards as much as you like, you can rewind and restart as many times as you like.. and its as if you never did. The billionth reverse and restart would be identical to the first, because it is the first. 

Unless you have something (Anti time thing) that the time reversal does not effect... then there is no way of knowing/telling. If you have something like that, then you have another type of time, one which stays forwards for this (anti time thing) even when you reverse normal time.... but you can just propose reversing this "greater time" and the same issue happens... now your anti time thing... which told you if time had been restarted doesn't work....  Damn... i would love one of them anti time doodahs

[J.C.MacSwell]

18 minutes ago, Martyred Goat said:

You can run time forwards and backwards as much as you like, you can rewind and restart as many times as you like..

Not based on the assumption I included.

 

On 12/25/2018 at 8:57 PM, J.C.MacSwell said:

Agree.

Now just to try a different tack:

Say I proposed a BB model with time starting abruptly and going forever forward infinitely...followed by a reversal with time going backward to the starting point.

Would this make sense? Would the reversal actually get to happen in this model, assuming it would have to wait for the completion and expiration of the first part?

 

[Martyred Goat]

5 minutes ago, J.C.MacSwell said:

Not based on the assumption I included.

 

 

Urm.... 

It doesn't matter how much you mess with time.... forwards or backwards.... All things within time would remain relative. For it to change anything, be measurable/knowable or for it to contradict any theory.... you would also need something that is not effected by the reversal. 

Edited January 24, 2019 by Martyred Goat