Big Bang - Where's the hole?

Originally posted by Aim64C
reply to post by wirehead

 

Okay. We can write the metric of space as ds^2 = -c^2 dt + a(t)^2 * (dr^2 + S(r)^2 do^2)
where a(t) is a variable scale factor, S is a curve parameterization (0 for flat space, +1 for positive curvature, -1 for negative curvature, depending on your model.)
dt, dr and do are the differentials of time, distance and angular size, respectively, which contribute to the distance measure ds.

You act like you're telling me something I don't know.

The problem is that this doesn't actually work to explain volumetric expansion of space. Applying special relativity, I can argue that a ball thrown into the air is experiencing the effects of volumetric expansion brought about by a dark energy as opposed to a physical force.

You can? Please do! I'd love to see you start with Einstein's field equations and work this out! I am waiting with bated breath, and in no way anticipate that you will totally fail to do this on account of it being total nonsense.

Originally posted by ImaFungi
and this is the basis in the question of the OP..,,.,.., you seem to think of time and the universe as traveling one way all together.,.,., as in the central starting point is back in the arrow of time,.,..,,.. but if the universe had a starting point,.,.,,. and matter and energy spread outward in all directions,,,,, this is what i was curious about as well,,,,, wouldnt that starting point have expanded,,,, as the energy and matter would be traveling in all directions,.,.,.,not just one direction away from a starting point,,.,.,. but all directions surrounding a starting point,,,, meaning if we are over here,,,,,, the direction the galaxies near us are expanding outwardly are expanding in the exact opposite direction outwardly on the other side of that starting point.,

edit on 8-7-2012 by ImaFungi because: (no reason given)

Whether you're over here or over there, you see everything else expanding away from you. So yes, while there will be one point which is the center of mass of the universe, it's nothing special. Everything looks to be expanding away from there, just as everything looks to be expanding away from us from our vantage point on earth.

This is equivalent to saying, wind the clock back to find that "center point" from which everything expands. When you get there, so does every other point in the universe- so how are any of them different?

Originally posted by SpittinTruth
Ok...let's PRETEND...a bang did actually occur. How did EVERYTHING fall PERFECTLY into place? How is it that Earth has it's own features, and Saturn has it's own. What keeps EVERYTHING floating in space? Also, how do you explain where LIFE came from??? Why is there life on this planet...and nothing on the rest of them?

Too many questions...not enough answers!

Let's say everything didn't fall perfectly into place. Now there's five planets in our solar system instead of eight, saturn doesn't have rings, etc.

We're on some planet not called earth but urth.

And you'd be there, asking, "how did EVERYTHING fall PERFECTLY into place? Why doesn't sutarn have rings? Why do we perfectly have five planets and not some other crazy number like eight?"

reply to post by wirehead


"but I do know that Einstein rejected this model on the basis of Mach's principle. "

so einstein believed that the universe and the "space" within the physical universe was all that existed,,,, and it was finite,,, yet "infinite" in the fact that it is expanding and does not "end",,,,, for we are in the middle of a process with no way of telling when it will end and when and where it started,,, it is infinite,,,, but finite in the fact that it is a contained system and can only be and do so much?

Originally posted by Moduli

You can? Please do! I'd love to see you start with Einstein's field equations and work this out! I am waiting with bated breath, and in no way anticipate that you will totally fail to do this on account of it being total nonsense.

edit on 8-7-2012 by Moduli because: (no reason given)

Remember, he said special relativity, so somehow he'd have to start from the lorentz boost and come up with a notion of dark energy...

reply to post by wirehead

Modified gravity theories fail dramatically in reproducing the observed density fluctuations of the early universe.

Now you're really getting circular.

All "observations" of the early universe are implicit and indirect. (This is also why I call you out on treating the theory as fact - you're using the theory's postulates of a beginning and expansion of the universe in an attempt to validate current models predicting origin from cosmic expansion).

edit: and of course, the observed gravitational lensing of, e.g. the bullet cluster merger.

That's a fly in everybody's soup.

en.wikipedia.org...

Mordehai Milgrom, the original proposer of MOND (Modified Newtonian Dynamics), has posted on-line a refutation[15] of claims that the Bullet Cluster proves the existence of dark matter. Milgrom claims that MOND correctly accounts for the dynamics of galaxies outside of galaxy clusters, and even in clusters such as the Bullet Cluster it removes the need for most dark matter, leaving only a factor of two which Milgrom expects to be simply unseen ordinary matter (non-luminous baryonic matter) rather than cold dark matter. Without MOND, or some similar theory, the matter discrepancy in galaxy clusters is a factor of 10, i.e. MOND reduces this discrepancy five-fold to a factor of 2. Whilst another study in 2006[16] cautions against "simple interpretations of the analysis of weak lensing in the bullet cluster", leaving it open that even in the non-symmetrical case of the Bullet Cluster, MOND, or rather its relativistic version TeVeS (Tensor–vector–scalar gravity), could account for the observed gravitational lensing.

However, NASA also has this to say:

www.nasa.gov...

"This result is a puzzle," said astronomer James Jee of the University of California in Davis, lead author of paper about the results available online in The Astrophysical Journal. "Dark matter is not behaving as predicted, and it's not obviously clear what is going on. It is difficult to explain this Hubble observation with the current theories of galaxy formation and dark matter."

Initial detections of dark matter in the cluster, made in 2007, were so unusual that astronomers shrugged them off as unreal, because of poor data. New results from NASA's Hubble Space Telescope confirm that dark matter and galaxies separated in Abell 520.

It's not evidence -for- dark matter so much as it is evidence that we still don't know what the # is going on.

What exactly is the problem? Einstein's equations describe how space behaves based on its mass-energy content.

It doesn't define space as anything. Space is a result of energy states between two objects. The energy held in a gravitational relationship is conserved. That is all the field equations have to say about space - the more potential between two objects, the greater the space between them must be.

space is thus an arbitrary concept that cannot be expanded without explaining the entrance of energy into the existing system.

CLPrime was able to correctly respond to the challenge by presenting a theoretical model for how this induction of energy could occur (though I do plan to challenge this theory - it's no fun to debate as a consensus unless you're a highschool student).

You seem to take issue with GR for some reason. Perhaps you could just explicitly lay this out for us.

You really don't understand what you're working with or who you're talking to.

General Relativity predicts behavior. It does not necessarily provide its mechanics (what is the propagator of gravity? How does mass and velocity result in a slowing of perceived time? What interaction on the subatomic scale causes this?).

Ohm's law predicts the behavior of current and thermal dissipation within a circuit. It doesn't explain a transistor.

Every predictive theory survives only so long as the mechanics are restricted to the elements used to construct it. Upon the discovery of new constituents, it will soon be presented with scenarios it cannot predict or does not provide an adequate description to predict or postulate on those mechanics.

E.g. if that were the effect of dark energy, you'd expect to see its effects on everything else in the universe, not just the ball.

Irrelevant. Special Relativity excludes preferential reference frames.

Further, this principle can easily be extrapolated to the larger problem. "Prove to me space is expanding and all the galaxies are simply not just moving away from each other."

Field equations cannot differentiate between the two processes that are, computationally, equivalent.

You can't infer cause from the field equations - only a relationship.

Originally posted by ImaFungi
reply to post by wirehead

 

"but I do know that Einstein rejected this model on the basis of Mach's principle. "

so einstein believed that the universe and the "space" within the physical universe was all that existed,,,, and it was finite,,, yet "infinite" in the fact that it is expanding and does not "end",,,,, for we are in the middle of a process with no way of telling when it will end and when and where it started,,, it is infinite,,,, but finite in the fact that it is a contained system and can only be and do so much?

Well, the question of whether it's infinite or not isn't easy to answer... It's an open question. The "big bang" may not even have been the start, some have argued for an infinite sequence of "big bounces," for instance. Not many subscribe to the "big bounce" but it's still an open question.

Things can be finite but unbounded: you can travel forever in any direction on the surface of the earth and never come across an end. Our space could be the same way: finite, but without a boundary.

But Einstein did believe that that the physical universe and the space it occupies were all that existed. His argument (via Mach) was something to the effect of "infinite empty space outside of this stuff doesn't make sense, physically." I'm butchering the argument though so please don't take this as literal.

Originally posted by wirehead

Originally posted by ImaFungi
and this is the basis in the question of the OP..,,.,.., you seem to think of time and the universe as traveling one way all together.,.,., as in the central starting point is back in the arrow of time,.,..,,.. but if the universe had a starting point,.,.,,. and matter and energy spread outward in all directions,,,,, this is what i was curious about as well,,,,, wouldnt that starting point have expanded,,,, as the energy and matter would be traveling in all directions,.,.,.,not just one direction away from a starting point,,.,.,. but all directions surrounding a starting point,,,, meaning if we are over here,,,,,, the direction the galaxies near us are expanding outwardly are expanding in the exact opposite direction outwardly on the other side of that starting point.,

edit on 8-7-2012 by ImaFungi because: (no reason given)

Whether you're over here or over there, you see everything else expanding away from you. So yes, while there will be one point which is the center of mass of the universe, it's nothing special. Everything looks to be expanding away from there, just as everything looks to be expanding away from us from our vantage point on earth.

This is equivalent to saying, wind the clock back to find that "center point" from which everything expands. When you get there, so does every other point in the universe- so how are any of them different?

it is different and "special" because since the universe has been expanding for such a long time,,,,, that starting point would be a very large and vast void like the inside of a balloon compared to the surface which is where our galaxies are by now in time..


,

Originally posted by Aim64C
General Relativity predicts behavior. It does not necessarily provide its mechanics (what is the propagator of gravity? How does mass and velocity result in a slowing of perceived time? What interaction on the subatomic scale causes this?).

Yes exactly, and its predictions have been completely correct in every test to date.

Which is why I don't really understand your point. You want me to define space? You won't accept GR without a definition of space for some reason? There's no need. Nobody has yet gotten to that point. We can probably truthfully say that we don't know what space is.

So are you proposing some definition of space? If so, we can discuss it. Are you demanding a definition of space? If so, I don't have one. "Space is what we measure with rulers."

Are you taking issue with GR because it doesn't define space? You don't need to get into what space is, just whether or not GR's predictions are correct.

Originally posted by ImaFungi
it is different and "special" because since the universe has been expanding for such a long time,,,,, that starting point would be a very large and vast void like the inside of a balloon compared to the surface which is where our galaxies are by now in time..

Nope, this is a misconception. Things aren't moving outward and away from one another- if that were the case, the only possible explanation for the redshift we observe would be that we are in the one exact center of the entire universe.

reply to post by wirehead


what your saying is imagine a perfectly round lake with a circumference of 100 yards,.,.,.,. and we are plankton in that lake that can not move on our own,.,.,,. and we all started out in the exact center,,.,.,,. and there were millions of us,.,.,. and a bowling bowl was dropped in the exact middle of us,,.,.,. and for past ten years we have been drifting towards the edges of the lake,..,.,.,., all the plankton near us in our group is moving away from us..,., and all the plankton we can see is moving away from us,,, whatever whatever,..,.,, im saying,,, where the bowling ball fell in would be a large chasm,,,,, and im saying.,,.,. that the same thing that is going on in our local area of unilake,,,, would be going on,, on the other side of where the bowling ball landed,,, but in the opposite direction,.,.,.

reply to post by Moduli

You can? Please do! I'd love to see you start with Einstein's field equations and work this out! I am waiting with bated breath, and in no way anticipate that you will totally fail to do this on account of it being total nonsense.

It's called the transient property.

You learned about it in algebra.

The equation cannot determine cause. The space between two objects will always be representative of the energy potential between them (mass being a factor, as well - but since that isn't going to change - it's a mute component to the argument). Increasing the distance between two objects increases the energy potential while increasing the energy potential requires increasing the distance.

Please - I have respect for trained individuals - but you're really not grasping the issue at hand - which has to do with the mechanics of the system as opposed to mathematics that predict it.

Simple mathematics can determine the maximum speed of a vehicle. Mechanics explain the exchange of energy that bring about the behavior predicted by more simple mathematical equations.

Field equations fail to provide mechanics that allow for space to expand - and since space is only defined as the distance between two arbitrary points (presumably with relevance to the propagation of light - but that's not always necessary) - the difference between volumetric expansion and classical motion is null.

Which means a prediction of spatial expansion is no more valid than a prediction of classical acceleration - perhaps even less so, since there currently exist so few mechanics that lend themselves to describing spatial expansion.

Originally posted by ImaFungi
reply to post by wirehead

 

what your saying is imagine a perfectly round lake with a circumference of 100 yards,.,.,.,. and we are plankton in that lake that can not move on our own,.,.,,. and we all started out in the exact center,,.,.,,. and there were millions of us,.,.,. and a bowling bowl was dropped in the exact middle of us,,.,.,. and for past ten years we have been drifting towards the edges of the lake,..,.,.,., all the plankton near us in our group is moving away from us..,., and all the plankton we can see is moving away from us,,, whatever whatever,..,.,,

That's not at all what I'm saying. That's a misconception of the model, and this is why you think there must be a hole in the big bang model.

Go back to the balloon analogy. You're a 2D person constrained to living on the 2D surface of the balloon. It's inflating. Where's the hole?

Originally posted by Aim64C
You really don't understand what you're working with or who you're talking to.

I don't think he's the one who doesn't know who he's talking to .

General Relativity predicts behavior. It does not necessarily provide its mechanics (what is the propagator of gravity?

What an ironic choice of words, considering I know how to write down the low-energy graviton propagator in quantum field theory! Although that's not hard, it's been known for many decades...

MOND, incidentally, is something taken seriously by precisely zero theoretical physicists. I know many of the world's experts in this kinda stuff, and they all think it's hilariously dumb.

But hey, that just proves you're right, though, doesn't it? After all, science is never interested in making progress. It's not like we give prizes out for that kind of thing, or anything. And it's not like every grad student in theoretical physics thinks carefully about gravity and tries to see if he can make any cool discoveries about it. Not at all.

Originally posted by wirehead
Well, the question of whether it's infinite or not isn't easy to answer... It's an open question. The "big bang" may not even have been the start, some have argued for an infinite sequence of "big bounces," for instance. Not many subscribe to the "big bounce" but it's still an open question.

Actually, those models aren't very reasonable. They all rely on violating the second law of thermodynamics somehow, and there aren't any compelling reasons to think these models have any better features that make them worth considering despite this.

Of course, the entopy of the universe being finite means that it can only have a finite age, because eventually you'd have to run into a point in the past where the universe had zero entropy, and then there's no point before to go back to.

We can also determine that the entropy of the early universe must have been very small. So you'd need a way to "reset" the entropy each bounce, and there isn't really a reasonable way to do this. So the models are amusing, but not by any means compelling.

Originally posted by Aim64C
Field equations fail to provide mechanics that allow for space to expand - and since space is only defined as the distance between two arbitrary points (presumably with relevance to the propagation of light - but that's not always necessary) - the difference between volumetric expansion and classical motion is null.

So you want Einstein to have explained how space can expand? That would have been nice, but I'm sure he didn't know. He did know, however, how to write down a theory which lays out the precise implications that space curvature would have, and how they must relate to mass in order to reduce to Newtonian gravity.

From there, every major prediction of the theory was verified: gravitational lensing, gravitational waves, the anomalous precession of mercury, etc. etc.

So no, there's no explanation of how matter curves space. There is none that I'm aware of.

Which means a prediction of spatial expansion is no more valid than a prediction of classical acceleration - perhaps even less so, since there currently exist so few mechanics that lend themselves to describing spatial expansion.

Absolutely not true. Spatial curvature has implications for many things beyond simply reproducing the acceleration of matter. For instance, the curving of geodesics results in gravitational lensing. The wave solution allows the propagation of gravity waves, which can transport energy out of a rotating system. Torsion of space allows for frame dragging. All of these things have been observed and can not be explained with Newtonian gravity or special relativity.

Originally posted by Moduli
Actually, those models aren't very reasonable. They all rely on violating the second law of thermodynamics somehow, and there aren't any compelling reasons to think these models have any better features that make them worth considering despite this.

Of course, the entopy of the universe being finite means that it can only have a finite age, because eventually you'd have to run into a point in the past where the universe had zero entropy, and then there's no point before to go back to.

We can also determine that the entropy of the early universe must have been very small. So you'd need a way to "reset" the entropy each bounce, and there isn't really a reasonable way to do this. So the models are amusing, but not by any means compelling.

Yes good points, and why I said not many take the "big bounce" seriously.

reply to post by wirehead

Yes exactly, and its predictions have been completely correct in every test to date.

Hence the creation of both dark energy and dark matter.

Which is why I don't really understand your point. You want me to define space? You won't accept GR without a definition of space for some reason? There's no need. Nobody has yet gotten to that point. We can probably truthfully say that we don't know what space is.

CLPrime understands it. He may disagree with it - but I get the impression from his explanations and from his intrinsic lack of fielding the debate that he gets it.

He knows that the debate really has no answer as my point is that the theories are not nearly as well established as you would like to think.

Humans have the instinctive desire to tell a story. If they walk in mid-story, they want to know the beginning (and will often attempt to use present content and contexts to infer a beginning).

Scientists need to be wary of this instinct.

So are you proposing some definition of space? If so, we can discuss it. Are you demanding a definition of space? If so, I don't have one. "Space is what we measure with rulers."

If you can't define space then you can't really make the claim that it's expanding, particularly when your only tool of predicting that is incapable of determining spatial expansion from classical motion with the choice to support spatial expansion done out of convenience.

Are you taking issue with GR because it doesn't define space? You don't need to get into what space is, just whether or not GR's predictions are correct.

Except there is a very, very, large difference between the expansion of metric space and expansion via classical motion. GR's predictions are moot on the difference between the two. However, metric expansion of space would ultimately predict an end to the universe (left unchecked, of course). The "big rip" theory - if you will. Something that would not happen if space is only apparently expanding due to classical motion of its gravitational constituents (and the inability of current measurement methods to distinguish between the two).

It's not enough for GR's predictions to be "correct" - the mechanical process of their correct (or incorrect)-ness is essential to formulating an understanding of the universe.

Originally posted by wirehead

Originally posted by ImaFungi
reply to post by wirehead

 

what your saying is imagine a perfectly round lake with a circumference of 100 yards,.,.,.,. and we are plankton in that lake that can not move on our own,.,.,,. and we all started out in the exact center,,.,.,,. and there were millions of us,.,.,. and a bowling bowl was dropped in the exact middle of us,,.,.,. and for past ten years we have been drifting towards the edges of the lake,..,.,.,., all the plankton near us in our group is moving away from us..,., and all the plankton we can see is moving away from us,,, whatever whatever,..,.,,

That's not at all what I'm saying. That's a misconception of the model, and this is why you think there must be a hole in the big bang model.

Go back to the balloon analogy. You're a 2D person constrained to living on the 2D surface of the balloon. It's inflating. Where's the hole?

so in reality all galaxies are exactly the same distance from each other,, since space expanded equally,,,, and accelerated equally? the universe is a perfect even grid of galaxies equal distances apart from each other,,and the universe is infinite for it has no edges, and it exists everywhere and takes up all space,,, and every point is the exact center of everything ,.,,,,.. every point is the exact same distance from the furthest object away from it,,,,,,, as every other point,,,, this is what your saying?

in my analogy I only meant to say what you were saying about locally,,, everything is moving away from us,.,.,. thats the only example.,.,.,.,., im saying,..,.,,. if this concept of locally moving away started at a point in space,.,.,. and everything that now exists away from everything else started to move away from everything else at this point,.,., it all moved away from that point,.,.,.,. and that activity would have created the opposite of a dense mass where that point was,,,, a large vast space,,,..,

Originally posted by Aim64C

Hence the creation of both dark energy and dark matter.

This is more a failing of our current understanding of cosmology, and not with general relativity.

Originally posted by Aim64C

Except there is a very, very, large difference between the expansion of metric space and expansion via classical motion. GR's predictions are moot on the difference between the two. However, metric expansion of space would ultimately predict an end to the universe (left unchecked, of course). The "big rip" theory - if you will. Something that would not happen if space is only apparently expanding due to classical motion of its gravitational constituents (and the inability of current measurement methods to distinguish between the two).

You're right, there's a huge, glaring difference. In order for the redshifts we observe to be the result of classical motion, then we must be in the exact center of the universe, and everything is moving away from us specifically.

It's not enough for GR's predictions to be "correct" - the mechanical process of their correct (or incorrect)-ness is essential to formulating an understanding of the universe.

Why? If GR has made correct predictions (and it has made, many, many correct predictions) then it is a good model to use.

Why do you insist on this extra understanding of "mechanism" which GR doesn't even propose to provide? I understand that such a mechanism would be a great leap forward in our understanding, but not having it doesn't invalidate GR.

reply to post by Moduli


"Of course, the entopy of the universe being finite means that it can only have a finite age, because eventually you'd have to run into a point in the past where the universe had zero entropy, and then there's no point before to go back to.

We can also determine that the entropy of the early universe must have been very small. So you'd need a way to "reset" the entropy each bounce, and there isn't really a reasonable way to do this. So the models are amusing, but not by any means compelling. "

when the universe expends and exhausts all of its potential and finite energy,,, wouldnt the same potential energy exist in the universe that always has?

also doesnt the big bang violate the law of thermodynamics,,, was all of the energy of the universe created during the big bang?