Questions regarding "infinite" universe

[Pukka]

Alright, this has been in my head for quite awhile and ive never heard anyone talking about it before.

Big Bang theory. Began with one point of mass etc etc. If that is expanding, can you not reach the beginning of that mass (or end of the universe) if you traveled fast enough?

 

[vogon13]

If you could travel fast enough but you can't.

Not that important, anyhow, we can just simulate it on a computer.

 

[DrRocket]

Alright, this has been in my head for quite awhile and ive never heard anyone talking about it before.

Big Bang theory. Began with one point of mass etc etc. If that is expanding, can you not reach the beginning of that mass (or end of the universe) if you traveled fast enough?

You need to formulate this question more clearly.

How would you reach the Big Bang ? Time travel into the past ?

What do you mean by the "end of the universe"? Are you assuming that at some point expansion stops and contraction begins, with the universe ending in the so-called "Big Crunch" ? In that case to get there, just wait long enough. (It will be a LONG wait,)

 

[Pukka]

Im saying could you "catch up" to the expansion of the universe?

Maybe this will help me question.

 

[Mee_n_Mac]

Im saying could you "catch up" to the expansion of the universe?

Vogon had your answer ... it's no. You're limited to less than C and that's not fast enough.

 

[DrRocket]

Im saying could you "catch up" to the expansion of the universe?

Maybe this will help me question.

That picture helps a lot.

You have misconstrued the Big Bang completely. The picture is all wrong.

That picture show matter expanding outward in space from the point in space that is the origin of the Big Bang. That picture represents a common misconception.

The Big Bang, and the subsequent expansion since then are in fact expansions of space and time itself. It is not an expansion of something within space, but an expansion of space-time itself. You can't "chase" the expansion because there is nothing to chase.

Where did the Big Bang start ? EVERYWHERE. I can quite honestly say that the origin point of the Big Bang is right here on my keyboard, at the top of the "I". That is literally true. It is also try of EVERY OTHER point in the universe. There is nothing to chase.

Further, given that some points in the universe, distant points, are receding superluminallly, you cannot,even in principle, ravel fast enough to reach them, because of the special relativity limitation against traveling THROUGH space at any speed faster than light. It you were at some of those distant locations, what you would see, at least if the cosmological principle is correct, is the same thing that you see from here. The universe is thought to be homogeneous and isotropic -- it is the same everywhere and the same in every direction. So even f your reached whatever it is that you thing there might be on the circle in your diagram, it would look the same as it does right here.

 

[Pukka]

Well that explains alot. Seems that my knowledge of the Big bang theory has been skewed.

 

[michaelmozina]

That picture helps a lot.

You have misconstrued the Big Bang completely. The picture is all wrong.

That picture show matter expanding outward in space from the point in space that is the origin of the Big Bang. That picture represents a common misconception.

The Big Bang, and the subsequent expansion since then are in fact expansions of space and time itself. It is not an expansion of something within space, but an expansion of space-time itself. You can't "chase" the expansion because there is nothing to chase.

That response is a bit misleading IMO. "Spacetime" can expand as the objects that make up space time separate and spread out over time as that drawing suggests. The BB however relies upon "space" (not spacetime) expansion, and that issue is still hotly debated. "Space" expansion cannot be physically demonstrated in a controlled test here on Earth, and the redshift phenomenon is evidently not dependent upon any type of "space" expansion.

http://arxiv.org/abs/astro-ph/0601171

Where did the Big Bang start ? EVERYWHERE.

Whatever that means.....

There is absolutely no possibility that the universe is "infinite" in size if it has a "finite" age.

 

[SpeedFreek]

There is absolutely no possibility that the universe is "infinite" in size if it has a "finite" age.

Really? Are you sure you aren't simply referring to the observable universe here? :|

The question as to whether it is a good idea to say that "space is expanding" is, as you said, currently a hot topic in cosmology. Nobody denies that the notion lends itself well to helping people understand the concepts, but there is the question as to whether it also introduces misconceptions - i.e. attributing "space" with intrinsic qualities it may not actually possess.

The links below are all the recent papers relating to this issue, in chronological order. You may have seen some of them already, the one you linked is 4th in the list. (My notes in italics)

Inflation and the Cosmic Microwave Background See how space seems to expand in these 2 papers
Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe
Misconceptions about the Big-Bang and here is the easy version of the above paper
Is space really expanding? A counterexample Are you sure that "space" expands?
A direct consequence of the expansion of space? Expanding "space" is not a physical reality, it is a matter of philosophy
Eppur si espande Well it's definitely not due to the kinematic motion of galaxies
Expanding Space: the Root of all Evil? Maybe not, but General Relativity doesn't need "space itself" to expand.
Coordinate Confusion in Conformal Cosmology Oh yes it does!
Cosmological Radar Ranging in an Expanding Universe Oh no it doesn't!
A short answer to critics of our article "Eppur si espande" Yes it does! We were right and here's why!
Eppur si muove No it doesn't, you are using the wrong metric.. I will soon show you why.

This is where we are at, right now.

For anyone who is wondering, all of these papers completely and utterly agree with the expansion of the universe, they are just arguing about whether it is the "space" that is expanding.

 

[origin]

That response is a bit misleading IMO. "Spacetime" can expand as the objects that make up space time separate and spread out over time as that drawing suggests. The BB however relies upon "space" (not spacetime) expansion, and that issue is still hotly debated.

The answer may be misleading 'in your opinion', but it is not misleading as an accurate representation of the BB theory. The issue is not 'hotly debated', unless you cruise the fringe theories on the internet. :roll:

 

[michaelmozina]

There is absolutely no possibility that the universe is "infinite" in size if it has a "finite" age.

Really? Are you sure you aren't simply referring to the observable universe here? :|

Until we are sure what might actually be expanding or dilating, I can hardly be sure of anything.

The question as to whether it is a good idea to say that "space is expanding" is, as you said, currently a hot topic in cosmology. Nobody denies that the notion lends itself well to helping people understand the concepts, but there is the question as to whether it also introduces misconceptions - i.e. attributing "space" with intrinsic qualities it may not actually possess.

I guess I'm attracted to this specific question at the bottom of his abstract:

Let us finish with a question resembling a Buddhism-Zen `koan': in an empty universe, what is expanding?

The links below are all the recent papers relating to this issue, in chronological order. You may have seen some of them already, the one you linked is 4th in the list. (My notes in italics)

Way cool. Thank you. It will take me awhile to go though that list, but I will do so as I get time. Bear with me a bit, it's pretty busy at work so it probably won't be today. I do however appreciate the links.

For anyone who is wondering, all of these papers completely and utterly agree with the expansion of the universe, they are just arguing about whether it is the "space" that is expanding.

The paper I cited suggests the expansion need not necessarily be "superluminal", and the redshift is more of a feature of "time dilation" related to the expansion process. Both "solutions" seem viable, and time dilation "explanations" seem not to require any breaking of the universal speed limit of matter. That seems like a "plus" in my book.

 

[michaelmozina]

The answer may be misleading 'in your opinion', but it is not misleading as an accurate representation of the BB theory. The issue is not 'hotly debated', unless you cruise the fringe theories on the internet. :roll:

Inflation and the Cosmic Microwave Background See how space seems to expand in these 2 papers
Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe
Misconceptions about the Big-Bang and here is the easy version of the above paper
Is space really expanding? A counterexample Are you sure that "space" expands?
A direct consequence of the expansion of space? Expanding "space" is not a physical reality, it is a matter of philosophy
Eppur si espande Well it's definitely not due to the kinematic motion of galaxies
Expanding Space: the Root of all Evil? Maybe not, but General Relativity doesn't need "space itself" to expand.
Coordinate Confusion in Conformal Cosmology Oh yes it does!
Cosmological Radar Ranging in an Expanding Universe Oh no it doesn't!
A short answer to critics of our article "Eppur si espande" Yes it does! We were right and here's why!
Eppur si muove No it doesn't, you are using the wrong metric.. I will soon show you why.

Speedfreeks list looks pretty extensive to me, and I know for a fact that the paper I cited and the author I cited back up their claims with that "math" thing that you folks profess to like so much. I don't suppose that you personally actually found a flaw in his work?

 

[SpeedFreek]

The paper I cited suggests the expansion need not necessarily be "superluminal", and the redshift is more of a feature of "time dilation" related to the expansion process. Both "solutions" seem viable, and time dilation "explanations" seem not to require any breaking of the universal speed limit of matter. That seems like a "plus" in my book.

As you will see, as you work your way down that list, it is shown that the expansion cannot be kinematic, so the speed limit of SR does not apply. It is then shown that you can have apparently superluminal recession speeds in GR, without needing "space" to expand in order for that to happen...

The universe is expanding. It is how it expands that is the question.

 

[michaelmozina]

The paper I cited suggests the expansion need not necessarily be "superluminal", and the redshift is more of a feature of "time dilation" related to the expansion process. Both "solutions" seem viable, and time dilation "explanations" seem not to require any breaking of the universal speed limit of matter. That seems like a "plus" in my book.

As you will see, as you work your way down that list, it is shown that the expansion cannot be kinematic, so the speed limit of SR does not apply. It is then shown that you can have apparently superluminal recession speeds in GR, without needing "space" to expand in order for that to happen.

I suppose I'll have to work my way down the list then.

Is there a "readers digest" explanation of why it cannot be kinematic in nature that you could share with us?

FYI, I grant you that we are likely only describing and observing the events of a small "visible" sliver of a potentially much larger physical entity that may or may not exhibit all the same physical properties universally in all areas of the whole universe.

 

[michaelmozina]

Eppur si espande Well it's definitely not due to the kinematic motion of galaxies

From the abstract of that paper:

Thus it is impossible to mimic the true cosmological redshift by a Doppler effect caused by motion of galaxies in a non-expanding 3D-space, flat or curved.

This seems like a red herring from my perspective since the paper I cited assumed an expanding "spacetime", just not one that achieved superluminal speeds, or any sort of expansion of "space" (whatever that is).

The authors question is viable. What exactly might "expand" in empty space?

 

[SpeedFreek]

Nope.. I tried, but failed, to come up with a "readers digest" explanation! The risk is too high that I might introduce a potential straw man.

I might suggest you familiarise yourself with the Milne model, if you don't know it already.

 

[SpeedFreek]

What exactly might "expand" in empty space?

I can think of a few potential candidates involving higgs-like fields such as the inflaton field of cosmic inflation, dark energy, or the cosmological constant by any other name. These are of course meaningless in an empty universe, but our universe is not empty!

 

[DrRocket]

That response is a bit misleading IMO. "Spacetime" can expand as the objects that make up space time separate and spread out over time as that drawing suggests. The BB however relies upon "space" (not spacetime) expansion, and that issue is still hotly debated. "Space" expansion cannot be physically demonstrated in a controlled test here on Earth, and the redshift phenomenon is evidently not dependent upon any type of "space" expansion.

http://arxiv.org/abs/astro-ph/0601171

No Michael, as usual you are skewing things toward the lunatic fringe. It is not hotly debated among the competent.
These fringe ideas are not based on science and should be confined to The Unexplained where they belong.

What is "expanding" are space-like slices of space-tiime, or in reasonable terminology is it SPACE ITSELF that is expanding as measured by the Riemannian metric that the space-like slices inherit from the Lorentzian metric of space-time. This notion is based on a realization of space-time as a foliation by a one-parameter family of space-like slices and that foliation is enabled by the assumption, called the cosmological principle, that the universe is homogeneous and isotropic on the largest scales. Yes it is space that is expanding, and it most certainly is that expansion that accounts for redshift.

The inability to measure the expansion of space in an earth-bound laboratory is totally irrelevant. The effects of the expansion are predicted by models of the universe based on general relativity (yes, Einstein's general relativity as practiced by he man himself), and the expansion is supported by a mountain of EMPIRICAL observational data. Even Hannes Alfven himself recognized the value of a need for careful in situ observational measurements and knoew tha tnot all experiments can take place in an earth-bound laboratory. Your position to the contrary is neither rational nor scientific.

I am quite aware that you will dispute all of this . We have been here before. But I also recognize that you have no idea what you are talking about and that your are pushing your personal agenda. Unfortunately that agenda has the potential to do harm to people like the OP who are trying to actually learn something about science.

That is why it has been made quite clear in the past that the only place where your agenda should be discussed is in The Unexplained. Please keep it there.

]Where did the Big Bang start ? EVERYWHERE.

Whatever that means.....
There is absolutely no possibility that the universe is "infinite" in size if it has a "finite" age.

1) It means exactly what it says. I know that you don't understand that point. We have talked about it before. I know that I cannot educate you, and that you have no wish to learn and be educated in any case.

2) Rubbish. The universe can be either finite or infinite (in proper terminology closed or open) in a finite time. In fact it is quite easy to describe a smooth transition from a point to a full Euclidean space in 0 time, and I have given you the equations previously -- it is what mathematicians call a strong deformation retract to a point. Here it is one more time
f(X,t) = tx. As one can easily see f(X,0)=o for any x and the image of f(x.t) is all of whatever dimensional space you start with for any t other than zero. While this does NOT describe the dynamics of the Big Bang it does quite clearly ow why your contention has no merit whatever.

Your inability to comprehend general relativity and mathematics does not invalidate the hard science that supports the Big Bang.

 

[SpeedFreek]

I don't think the author of that paper is denying that space expands as described by the current mainstream model. The question has taken on a more subtle aspect.

If it is "space" that is expanding, and that expansion is causing the redshift we see for distant galaxies, is the light being redshifted continuously as it travels, as if some property of the expanding space is acting upon that light, or is the redshift only measured at the detector, due to the difference in the reference frame of the emitter in relation to the observer.

This is the difference between the two points of view in those recent papers I listed. Here is one view:

The key is to make it clear that cosmological redshift is not, as is often implied, a gradual process caused by the stretching of the space a photon is travelling through. Rather cosmological redshift is caused by the photon being observed in a different frame to that which it is emitted. In this way it is not as dissimilar to a Doppler shift as is often implied. The difference between frames relates to a changing background metric rather than a differing velocity. Page 367 of Hobson, Efstathiou, & Lasenby (2005) as well as innumerable other texts shows how redshift can be derived very simply by considering the change in the orthonormal basis of observers with different scale factors in their background metrics. This process is discreet, occurring at the point of reception of the photon, rather than being continuous, which would require an integral. If we consider a series of comoving observers, then they effectively see the wave as being stretched with the scale factor.

 

[xXTheOneRavenXx]

lol, now I of course have to ask a question. I am aware that through popular theories, red shift, etc... the universe & space-time expands in volume with a given area as any volume measurement would. but like all volume measurements, there is something it expands into (ie. a flask, a box, etc...) whatever the case may be. Volume is measured by how full something is, which leads me to believe there is an actual border somewhere to the universe. Whether another form of space-time, a void, or the sandbox of a giant baby alien exists containing the universe or housing it's enormous bubble from the beyond. Wouldn't the conception of volume require a containment area to be measured within? or is it merely the estimated distance to which we believe the Big bang occurred the only method we use for measuring the area in which the volume is measured? (make sense?) Also, if the universe is expanding by volume in a given area, and a planet existed close to the edge of this area, could they theoretically see beyond the edge of the universe with powerful telescopes as we can see +13.7 Billion ly's from our current location?

 

[SpeedFreek]

Have a look at this wiki page, it answers all your questions.

Metric expansion of space

 

[michaelmozina]

The universe is expanding. It is how it expands that is the question.

I assume that this debate ultimately comes back to the question of "physical cause". In other words, I have no doubt it may "expand", but there must be a physical "cause" and and effect relationship that drives such a process. Objects can and certainly do "expand", and the distance between objects can increase. That is "spacetime" expansion. The belief that "space" expands however is not a given, and based on what I've read, there still seems to be some debate as to whether or not "space" expansion is even required to explain these observations. I'm still slugging my way through some of the papers you cited so my opinions may change as I wade though the other papers, but thus far I've not read anything that seems particularly convincing to me one way or the other.

 

[michaelmozina]

Have a look at this wiki page, it answers all your questions.

Metric expansion of space

It doesn't seem to offer a "demonstration of concept" in any sort of "controlled experiment". While it may have a mathematical foundation, it lacks physical empirical support. In the lab, objects in motion stay in motion, and the "distance" between objects changes, but the "space" between them does not change one iota.

 

[SpeedFreek]

Have a look at this wiki page, it answers all your questions.

Metric expansion of space

It doesn't seem to offer a "demonstration of concept" in any sort of "controlled experiment". While it may have a mathematical foundation, it lacks physical empirical support. In the lab, objects in motion stay in motion, and the "distance" between objects changes, but the "space" between them does not change one iota.

That wiki link was meant to be a reply to xXTheOneRavenXx, by the way.

 

[SpeedFreek]

The universe is expanding. It is how it expands that is the question.

I assume that this debate ultimately comes back to the question of "physical cause". In other words, I have no doubt it may "expand", but there must be a physical "cause" and and effect relationship that drives such a process. Objects can and certainly do "expand", and the distance between objects can increase. That is "spacetime" expansion. The belief that "space" expands however is not a given, and based on what I've read, there still seems to be some debate as to whether or not "space" expansion is even required to explain these observations. I'm still slugging my way through some of the papers you cited so my opinions may change as I wade though the other papers, but thus far I've not read anything that seems particularly convincing to me one way or the other.

I think that the prevailing view is coming around to Chodorowski's way of thinking, i.e. the light is not redshifted en-route, but is caused by the difference in the scale factor for the background metric between emitter and detector.