Does Inflation Theory Exclude the Impact on Temporal Dimension?

[Mayank_Jha]

"In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the exponential expansion of space in the early universe. " -Wikipedia
Since Inflation Theory specifically talks about 'space', does it mean that inflation didn't have any effects on the temporal dimension even though space and time are interwoven?

 

[Drakkith]

Correct. Both inflation and regular expansion involve only the spatial dimensions, not time. Both are the result of changing spatial geometry that leaves time unaffected.

 

[DiracPool]

Correct. Both inflation and regular expansion involve only the spatial dimensions, not time. Both are the result of changing spatial geometry that leaves time unaffected.

Doesn't "change," though, involve time? How can something change, or go from one thing to another, if you don't include a concept/variable of time?

 

[Mayank_Jha]

If we consider the Hartle-Hawking state, did inflation occur before the introduction of time?

 

[DiracPool]

If we consider the Hartle-Hawking state, did inflation occur before the introduction of time?

From: http://en.wikipedia.org/wiki/Inflation_(cosmology )

The inflationary epoch lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds.

By this estimate, it looks as though time was already around during the inflationary epoch. Hartle-Hawking is a speculation dating prior to the Planck epoch. Inflation is thought to have occurred well past this

 

[Drakkith]

Doesn't "change," though, involve time? How can something change, or go from one thing to another, if you don't include a concept/variable of time?

Just because it occurs over time does not mean that it affects time. The spatial geometry changes over time. Time does not change as far as I know.

If we consider the Hartle-Hawking state, did inflation occur before the introduction of time?

In standard cosmological models, inflation takes place around 10^-36 seconds after the big bang. I believe the Hartle-Hawking state is concerned with the universe prior to the big bang.

 

[Mayank_Jha]

If the inflationary epoch would've been longer/shorter, the rate of expansion of space would've been affected, right?
So is there any such 'factor' that might've affected the rate of flow of time? (I know this is a stupid question, but this just occurred to me right now)

 

[Drakkith]

Note that inflation and expansion are both the result of the geometry of space changing. This affects the position of objects relative to one another within space. As far as I know there is no analog for time since it is only one dimensional, but I'm not an expert so I could be wrong.

 

[Mayank_Jha]

Note that inflation and expansion are both the result of the geometry of space changing. This affects the position of objects relative to one another within space. As far as I know there is no analog for time since it is only one dimensional, but I'm not an expert so I could be wrong.

With 142 views on this thread already, I think you're right because nobody said otherwise.

 

[bahamagreen]

Geometry of space or spacetime?
Is it thought that spacetime did not exit prior?
Is it thought that spacetime expanded, not just space?

 

[Mordred]

in this case it amounts to the same thing, the space component of spacetime expands

 

[Mayank_Jha]

Is it thought that spacetime expanded, not just space?

That's exactly what I thought initially, but later when I realized that Wikipedia (and many other sources) specifically talk about 'space' in Inflation Theory, I became doubtful...

 

[phinds]

That's exactly what I thought initially, but later when I realized that Wikipedia (and many other sources) specifically talk about 'space' in Inflation Theory, I became doubtful...

Since inflation (if it did indeed happen, as it very likely did) did not take place instantaneously, it obviously happened over a period of time.

Inflation is stated variously as having occurred during the period from about 10E-35 seconds after the singularity to about 10E-33 seconds after the singularity, which is to say a duration of about 10E-33 seconds.

I've seen the amount of the expansion stated variously as being anything from about 10E40 to about 10E50, which is a range of a FACTOR of 10E10, which implies pretty strongly that the actual amount of expansion is not well known but it was huge.

These numbers (10E-33 seconds and 10E40 factor of expansion) are simply unimaginable in anything like human terms and so the combination of the two is even less imaginable in human terms.

Had either the duration or the expansion been a different amount with the other staying the same then the rate would obviously have been different.

 

[Ich]

Is it thought that spacetime expanded, not just space?

"Expanding spacetime" simply does not make sense. It would mean that you have at one point in time a certain spacetime, and at the next instant a larger one.
There is only one spacetime. You have at one moment in time a certain space, and at the next instant a larger one. All these spaces together build spacetime, just like infinitely many 2d planes together build 3d space.

Caution: "moment in time" and "space" are terms with a rather complicated definition in GR. Don't imagine space as something fundamental that has expansion as one of its fundamental properties. It's a bit more subtle.

 

[Mayank_Jha]

Since inflation (if it did indeed happen, as it very likely did) did not take place instantaneously, it obviously happened over a period of time.

Inflation is stated variously as having occurred during the period from about 10E-35 seconds after the singularity to about 10E-33 seconds after the singularity, which is to say a duration of about 10E-33 seconds.

I've seen the amount of the expansion stated variously as being anything from about 10E40 to about 10E50, which is a range of a FACTOR of 10E10, which implies pretty strongly that the actual amount of expansion is not well known but it was huge.

These numbers (10E-33 seconds and 10E40 factor of expansion) are simply unimaginable in anything like human terms and so the combination of the two is even less imaginable in human terms.

Had either the duration or the expansion been a different amount with the other staying the same then the rate would obviously have been different.

I guess you quoted the wrong thing while saying this.

 

[Mayank_Jha]

"Expanding spacetime" simply does not make sense. It would mean that you have at one point in time a certain spacetime, and at the next instant a larger one.
There is only one spacetime. You have at one moment in time a certain space, and at the next instant a larger one. All these spaces together build spacetime, just like infinitely many 2d planes together build 3d space.

Caution: "moment in time" and "space" are terms with a rather complicated definition in GR. Don't imagine space as something fundamental that has expansion as one of its fundamental properties. It's a bit more subtle.

I wasn't really talking about spacetime as a whole...I was talking about space and time independently...
Although it's understood that inflation didn't have any effects on the temporal dimension, I can't really make sense of the example given...if it's an infinitely finite system made up of different planes, if a few more planes are to stacked to the whole wouldn't it affect the system as a whole anyway?

 

[phinds]

I guess you quoted the wrong thing while saying this.

I have no idea what you are talking about. What do you find incorrect about what I said?

 

[Mayank_Jha]

Since inflation (if it did indeed happen, as it very likely did) did not take place instantaneously, it obviously happened over a period of time.

Inflation is stated variously as having occurred during the period from about 10E-35 seconds after the singularity to about 10E-33 seconds after the singularity, which is to say a duration of about 10E-33 seconds.

I've seen the amount of the expansion stated variously as being anything from about 10E40 to about 10E50, which is a range of a FACTOR of 10E10, which implies pretty strongly that the actual amount of expansion is not well known but it was huge.

These numbers (10E-33 seconds and 10E40 factor of expansion) are simply unimaginable in anything like human terms and so the combination of the two is even less imaginable in human terms.

Had either the duration or the expansion been a different amount with the other staying the same then the rate would obviously have been different.

The above was your reply to this, I guess:

If the inflationary epoch would've been longer/shorter, the rate of expansion of space would've been affected, right?
So is there any such 'factor' that might've affected the rate of flow of time? (I know this is a stupid question, but this just occurred to me right now)

But you quoted this:

That's exactly what I thought initially, but later when I realized that Wikipedia (and many other sources) specifically talk about 'space' in Inflation Theory, I became doubtful...

 

[Ich]

I wasn't really talking about spacetime as a whole...I was talking about space and time independently...

I quoted bahamagreen, not you. But you seemed to agree with him at that time.

I can't really make sense of the example given...if it's an infinitely finite system made up of different planes, if a few more planes are to stacked to the whole wouldn't it affect the system as a whole anyway?

Sorry. Another try: Forget about one dimension and imagine spacetime as some three-dimensional (instead of four-dimensional) thing. Then imagine you slice that thing into infinitely many infinitely thin sheets. This is called a "foliation".
Now every sheet of said foliation represents a "space". The direction orthogonal to all those sheets is "time". And "space expansion" means that every later sheet is - by some measure - larger than the former ones.
That whole "spacetime" thing is absolutely static. "Expansion" is something that denotes a difference of sheets that are separated by a certain distance in the time direction. With this in mind, it absolutely makes no sense to think about an "expansion of the time dimension".

 

[Mayank_Jha]

I quoted bahamagreen, not you. But you seemed to agree with him at that time.
Sorry. Another try: Forget about one dimension and imagine spacetime as some three-dimensional (instead of four-dimensional) thing. Then imagine you slice that thing into infinitely many infinitely thin sheets. This is called a "foliation".
Now every sheet of said foliation represents a "space". The direction orthogonal to all those sheets is "time". And "space expansion" means that every later sheet is - by some measure - larger than the former ones.
That whole "spacetime" thing is absolutely static. "Expansion" is something that denotes a difference of sheets that are separated by a certain distance in the time direction. With this in mind, it absolutely makes no sense to think about an "expansion of the time dimension".

Thank you, I get it now.
I wasn't really talking about expansion per se...I was wondering if there's anything that affected the rate of flow of time...because initially I thought inflation affected the rate of time as well.

 

[timmdeeg]

...because initially I thought inflation affected the rate of time as well.

I think that's not the case per definition. The concept of proper time, the time as measured by a clock, doesn't depend on what happens. In the case of inflation the elapsed proper time is just short.

 

[Ich]

I was wondering if there's anything that affected the rate of flow of time...because initially I thought inflation affected the rate of time as well.

There's no such thing as a "rate of time". As timmdeeg says, proper time flows with 1s per s, per definition.
Time dilation happens when you compare the length of two segments on different world lines and find them different, even when you thought that they ought to represent the same "amount of time" for one reason or another. It's a very subjective, coordinate-dependent concept. And, most importantly, it always applies to a comparison of two different worldlines. There is no way in GR to define the "flow of time" for a single observer, other than said boring 1 second per second, which could not be affected by whatever inflationary or other reason you might come up with.

 

[Mayank_Jha]

GR = General Relativity, right?

 

[phinds]

GR = General Relativity, right?

Yes.