Location of Big Bang?

[Cadmus]

Reference please?

You can get oriented at http://wwwphy.princeton.edu/~steinh/.

[Cadmus]

Space and time are joined. They have to either both be finite, or both be infinite.

If you consider only the time since the big bang, as it typically the case, then I agree with you. This joining is known as space-time.

 

And explain how you think space is finite, because I don't see how that could be possible.

Unlike time, space was born in the big bang, or perhaps just before the big bang. Space will die in the big crunch, only to be reborn in the next cycle.

 

Therefore, time is infinite, and continues thorugh each cycle of existence of the universe, but space if born and dies in each cycle of big bang and big crunch.

[Macroscopic]

Originally posted by Cadmus

Unlike time, space was born in the big bang, or perhaps just before the big bang.

 

1. Space existed before the Big Bang. If space hadn't existed, neither could that original concentration of matter that made the BB.

 

2. Time cannot exist while space does not. Time can only exist where space does. If space had ends at the big crunch, it would be impossible for there to be another big bang. If space ends at the big crunch, then so does time. Then a big bang couldn't happen because an event would have to take place outside of time.

 

Time can not be infinite while space is not.

[Cadmus]

1. Space existed before the Big Bang.

I agree that space existed immediately before the big bang, but not indefinitely before.

 

2. Time cannot exist while space does not. Time can only exist where space does.

Why must this be so, in your opinion? I agree that post big bang this must be so, as spce and time combine as space-time. However, why must it be so prior to the big bang?

 

Time can not be infinite while space is not.

Please explain why this must be so.

[Severian]

You can get oriented at http://wwwphy.princeton.edu/~steinh/[/url'].

 

OK, I am familiar with these 'ekpyrotic' models, and they are quite a nice idea. My only objection to this model would be that the shape of the potential is rather unmotivated apart from the desire to explain cosmological data. You need to constrain the slope of the curve in a particular region (region 'a' I think it is usually called) to make the universe flat and isotropic. Why the potential has this shape is unexplained. To a certain extent this is an unfair comment since the inflation potential is also unmoticated as yet (although there are candidate models). (Incidentaly I met Neil Turok in Cambridge recently and he seems a very smart guy.)

 

However, the use of the term 'Big Crunch' is not really very accurate since the Ekpyrotic model has no Big Crunch in the traditional sense. It is an oscillitory model, so the contraction is stopped before a Big Crunch can happen.

[Severian]

Why must this be so' date=' in your opinion? I agree that post big bang this must be so, as spce and time combine as space-time. However, why must it be so prior to the big bang?

 

Please explain why this must be so.[/quote']

 

You can transform space and time into one another by a Lorentz transformation. So if you have an arbitarily large space coordinate, I can map it into an arbitrarily large time coordinate. Therefore if space is infinite, time must be too.

 

(That is not to say that the universe couldn't be cut off in some particlular direction. It could be, even though that would break Lorentz invariance. But whether this was a cut in time or a cut in space would be a frame dependent statement.)

[Johnny5]

Can I ask you guys what you think the odds are of there having been a big bang?

 

I'm quite interested.

 

either P=1 or P=0

[Johnny5]

probability = 1 (approximately)

 

Probably

 

If you think about it, the whole point of this thread is that the issue isn't one of probability. The original post suggests that we can infer from the current relative positions/velocity/acceleration of galaxies, that the material found there was concentrated near some single point in the past, so that we can draw the inference that probability = 1. That is the poster's whole point. That we can triangulate that position in space even now, thus properly inferring that the big bang occurred. The inference would be based upon experimental evidence, so that the truth of the premises of a short and simple argument would be empirically verifiable. I think this is a wonderful thread.

[Johnny5]

Space and time are joined.

 

 

They are not joined literally' date=' mathematically they are in a certain theory, but not literally. When I say joined mathematically, I am referring to the spacetime metric of relativity:

 

[math'] dS = \sqrt{ x^2+y^2+z^2+(ict)^2} [/math]

 

The presence of the square root of negative one in that formula is a cause for concern.

 

Regards

[Johnny5]

Unlike time' date=' space was born in the big bang, or perhaps just before the big bang. Space will die in the big crunch, only to be reborn in the next cycle.

[/quote']

 

Space was not created in the big bang, space isn't something which can be created.

 

Therefore' date=' time is infinite

[/quote']

 

I think unbounded is a better word. What you mean is that for any moment in time A, there is a moment in time B, such that A before B.

[Johnny5]

1. Space existed before the Big Bang. If space hadn't existed' date=' neither could that original concentration of matter that made the BB.

 

[/quote']

 

This is right. Space is a container, a vacuum, which material bodies move in. If there was ever a moment in time when there was no space, then there was no material at that moment in time. Then to say that later there was material, leads to something from nothing... creation ex nihilo i think it's called. <--and that is a violation of conservation of energy. You might object by saying that energy conservation happens all the time, it's part of QFT, virtual photon's violate it, but there are other conservation laws, and something from nothing surely violates them all.

 

 

 

2. Time cannot exist while space does not. Time can only exist where space does.

 

Time can not be infinite while space is not.

 

 

To exist means to be in the current moment in time. It is logically improper to say that "time exists" because then time is a thing inside of itself... ding an sich(thing in itself).

 

You are obviously using the word 'exist' in some other sense, but what sense that is I have no clue. I only understand its temporal connotation. When you say "time exists" what do you mean by time?

 

Regards

[BlackHole]

The way i see it, time and space are mathematical entities. It's just a part of abstract mathematical thinking.

 

In general relativity spacetime is the alternate name that physicists have given the gravitational field of the universe. There is no mathematical difference between the thing that we call 'spacetime' and the other thing that we call the gravitational field. Spacetime is the manifold and the curvature is the metric tensor. Because gravitational fields that act like the ones we know about cannot exist in more than four dimensions, this also means that spacetimes that lead to our kind of world cannot exist in other than four dimensions. Basically nothing moves in spacetime.

[Johnny5]

Basically nothing moves in spacetime[/url'].

 

Say what?

[BlackHole]

Say what?

 

Space and time are just parts of abstract mathematical thinking.

[Cadmus]

You can transform space and time into one another by a Lorentz transformation. So if you have an arbitarily large space coordinate, I can map it into an arbitrarily large time coordinate. Therefore if space is infinite, time must be too.

Your explanation attempts to convert space into time. This is valid as long as there is space-time. However, the question was in post 53 was not limited to post big bang space-time. Does your post take this into account?

[Cadmus]

They are not joined literally, mathematically they are in a certain theory, but not literally.

Please provide an example of some particle or other entity of space that is not bound up inextricably with time.

[Cadmus]

Space was not created in the big bang,

I agree. Space-time was created in the big bang.

 

space isn't something which can be created.

I disagree. On what basis do you make this statement?

 

I think unbounded is a better word. What you mean is that for any moment in time A, there is a moment in time B, such that A before B.

Thank you for telling me what I mean, but I think that I will stick with the wording that I used.

[Cadmus]

Space is a container, a vacuum, which material bodies move in.

I think that this is called the ether theory. I contend that space is not a container, and furthermore that space has no meaning at all in the context that you are using it. Post big bang, there is only space-time. Space-time is not a container for material objects, but rather it is the objects themselves.

[Cadmus]

Space and time are just parts of abstract mathematical thinking.

I have only one objection to your statement, and that is the word just. You are free to use these words in this manner, but you are greatly limiting their value with the word just.

[swansont]

If you think about it, the whole point of this thread is that the issue isn't one of probability. The original post suggests that we can infer from the current relative positions/velocity/acceleration of galaxies, that the material found there was concentrated near some single point in the past, so that we can draw the inference that probability = 1. That is the poster's whole point. That we can triangulate that position in space even now, thus properly inferring that the big bang occurred. The inference would be based upon experimental evidence, so that the truth of the premises of a short and simple argument would be empirically verifiable. I think this is a wonderful thread.

 

I agree that the inference of the expansion is that there was a big bang, but when you say that all the matter was concentrated at one point, note that the BB says that was the only point in existence at the time.

[Johnny5]

Please provide an example of some particle or other entity of space that is not bound up inextricably with time.

 

You cannot 'connect' space to time. You can connect your trailer to your car using a trailer hitch, but you cannot join space and time, and that's all I meant.

 

As for macroscopic objects... they move relative to one another. I think if I devoted enough time to it, I could formulate the laws of physics without any reference to time whatsoever. Things move... we can measure 'amounts of time,' as I stated in another thread in which I briefly discussed pendulums. Time isn't a phyiscal thing that you can connect to space... in fact space isn't matter so you can't join anything to it either.

 

A body of matter isn't joined to the vacuum, it moves through the vacuum.

 

I guess the basic fact which proves this, is that the vacuum does not impede the foward motion of a body. If you apply a force to some object in the vacuum, you and the object will move away from your common CM forever, you will never come to rest, because the vacuum doesn't decelerate you in the CM frame. Gravity might decelerate you, but not the vacuum. So unless you are going to tell me that gravity is vacuum inertial impedence (which would rule out gravitons), I don't think you are going to hold my attention.

[Johnny5]

I agree that the inference of the expansion is that there was a big bang, but when you say that all the matter was concentrated at one point, note that the BB says that was the only point in existence at the time.

 

I didn't mean all matter was located at one point in space simultaneously, that was/is impossible. BB theory may say that, but that's wrong.

 

I think I said, near one point, and what I mean is only this... That all the material, wherever it is now, used to form a single body.

 

If the BB model says that there was a moment in time, at which all of space was just one point, well then that's false.

 

I have repeatedly stated that space isn't something which was created. Tom and I debated this in another thread, where I said that if you could create points in space, then points in a single frame could move relative to one another, so that you could have two points at one point simultaneously, and then 2=1. He had a problem with the reasoning, and then we discussed mappings, specifically one in which space could stretch, and I pointed out that such a mapping led to a contradiction. I never heard a word from him again about it.

[Cadmus]

You cannot 'connect' space to time. You can connect your trailer to your car using a trailer hitch' date=' but you cannot join space and time, and that's all I meant.

 

So unless you are going to tell me that gravity is vacuum inertial impedence, I don't think you are going to hold my attention.[/quote']

Well, I think that you and I have extremely different notions of what time is and what space is. Since I am not going to tell you that gravity is ..., I guess that I am not going to hold your attention.

[Johnny5]

Well, I think that you and I have extremely different notions of what time is and what space is. Since I am not going to tell you that gravity is ..., I guess that I am not going to hold your attention.

 

It is highly unlikely that our thoughts would be identical, but now I feel bad. Ok what is space, and what is time?

[Cadmus]

It is highly unlikely that our thoughts would be identical, but now I feel bad. Ok what is space, and what is time?

Post big bang, the words space and time are artifical subdivisions of what is actually integrated into space-time. Everything in the universe that we are aware of is space-time. Everything with mass is space, and all particles or objects of space are always in motion, where such motion is motion through time. I think that space is not a container for objects, the objects are the space. Furthermore, there are no objects in space that can ever be without motion, which requires time. For example, it is meaningless to discuss a subatomic particle as an object frozen in time, where all of its rotation, let alone motion through space, has stilled.