Was the Big Bang a quantum mechanical vacuum fluctuation?

[sysprog]

In this context, phinds did mean that energy disappears. All CMB photons redshift everywhere.

He said evaporates. I replied to what he said. Just as water seems to disappear from a dish left in open air, but is in fact somewhere else rather than simply gone, the energy diminution we encounter in our observations of photons should not be presumed to be un-accounted-for in the grand ledger of the universe.

Facts don't care about your sensibilities.

I'm fairly confident that for the most part you're right about that.

If it is "conserved not as such", whatever that means, where, in your opinion, energy of redshifting photons goes?

I suspect that it goes somewhere other than nowhere. We can observe that it doesn't appear to us to continue to inhere in or exhere from the photons we measure. We cannot thereby infer that it is leaked out of the entire universe.

 

[dreens]

Perhaps its useful to think about this photon energy question in a simpler setting. Consider photons emitted from someone speeding away from you. They arrive at a different frequency, which can be calculated based on relativistic doppler formulas.

However, the intensity of the light is also influenced. I think since E gets multiplied by gamma for a lorentz boost, the intensity should be reduced by gamma squared?

Can anyone fill in the dots? I'm interested to see whether photon number is actually conserved- if someone speeding away emits 10^10 photons at a certain wavelength over a finite period of time, does the stationary observer really see that same number? I don't think so. Photon numbers depend on choice of basis for hilbert spaces which can be done differently. This is part of the story behind spontaneous particle creation in Hawking radiation for example.

Related would be to do this for gravitational redshift.

 

[sysprog]

Perhaps its useful to think about this photon energy question in a simpler setting. Consider photons emitted from someone speeding away from you. They arrive at a different frequency, which can be calculated based on relativistic doppler formulas.

However, the intensity of the light is also influenced. I think since E gets multiplied by gamma for a lorentz boost, the intensity should be reduced by gamma squared?

Can anyone fill in the dots? I'm interested to see whether photon number is actually conserved- if someone speeding away emits 10^10 photons at a certain wavelength over a finite period of time, does the stationary observer really see that same number? I don't think so. Photon numbers depend on choice of basis for hilbert spaces which can be done differently. This is part of the story behind spontaneous particle creation in Hawking radiation for example.

Related would be to do this for gravitational redshift.

That meander does not serve to clarify. It's clear that there's an energy loss that is not fully accounted for merely by the accepted paradigms. Although I've stated that I think that the energy must go somewhere rather than nowhere, I confess that I think that I'm as much at a loss to explain exactly where, as are the proponents of nowhere to explain exactly how.

 

[phinds]

That meander does not serve to clarify. It's clear that there's an energy loss that is not fully accounted for merely by the accepted paradigms. Although I've stated that I think that the energy must go somewhere rather than nowhere, I confess that I think that I'm as much at a loss to explain exactly where, as are the proponents of nowhere to explain exactly how.

But there is no NEED to explain "how" since that question only arises if you insist on applying a local principle (conservation of energy) in a domain (large scale cosmological distances) where it does not apply.

 

[sysprog]

But there is no NEED to explain "how" since that question only arises if you insist on applying a local principle (conservation of energy) in a domain (large scale cosmological distances) where it does not apply.

If you insist that energy exits the universe, when all you can show is that it became no longer to you findable, while I insist that it must be somewhere, when all I can show is that historically, energy once reported as missing usually turns up somewhere else, I think it's at least as incumbent upon you to account for how energy leaves the universe, as it is on me to account for where it went.

 

[nikkkom]

If you insist that energy exits the universe, when all you can show is that it became no longer to you findable, while I insist that it must be somewhere, when all I can show is that historically, energy once reported as missing usually turns up somewhere else

It's not a "he said, she said" competition. Energy conservation is a theorem. For time-translation invariant spacetime, energy must be conserved.

Since our local conditions, to a very high precision, are time-translation invariant, we should, and we are, observing that energy is conserved in all processes.

At the same time, on a cosmological scale, we observe that Universe is not time-translation invariant. Therefore, energy conservation on that scale is not required by any theorem.

 

[fresh_42]

I cut off the discussion about energy conservation at this point, because this post summarizes it all:

It's not a "he said, she said" competition. Energy conservation is a theorem. For time-translation invariant spacetime, energy must be conserved.

Since our local conditions, to a very high precision, are time-translation invariant, we should, and we are, observing that energy is conserved in all processes.

At the same time, on a cosmological scale, we observe that Universe is not time-translation invariant. Therefore, energy conservation on that scale is not required by any theorem.

Everything else I've read so far is an argumentation about phrasing it. It is furthermore off topic, resp. will become off topic if we go on with it. So please return to the question, whether the big bang can be considered a quantum fluctuation, on which scale ever, i.e. possibly a real giant one. Otherwise we will be forced to close the thread, as personal debates about wordings won't help anybody to understand what has been going on before inflation.

Thank you.

 

[Deepblu]

To expand on that a bit, conservation of energy is universally true LOCALLY. That is, everywhere in the universe energy is conserved on small scales (~ within glactic clusters) but over cosmological distances it is not.

That is true in General Relativity which is not the full picture .. maybe energy will be conserved in a quantum theory of gravity.

 

[phinds]

That is true in General Relativity which is not the full picture .. maybe energy will be conserved in a quantum theory of gravity.

Nothing about a quantum theory of gravity would change the fact that photons lose energy as they travel in an expanding universe, so no, it would not.

 

[Deepblu]

Nothing about a quantum theory of gravity would change the fact that photons lose energy as they travel in an expanding universe, so no, it would not.

It might explain where that energy goes.

 

[phinds]

It might explain where that energy goes.

That was just one example. Another is that you can't even DEFINE kinetic energy between two objects separated by cosmological distances. You really should read this:

http://math.ucr.edu/home/baez/physic...energy_gr.html

or this:

http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

 

[Deepblu]

That was just one example. Another is that you can't even DEFINE kinetic energy between two objects separated by cosmological distances.

Yes I know that.

My point is that our current theories are not complete.. what appears to us as violation to the law of conservation of energy, and what makes it appear to only work "localy", could be our lack of knowledge on the complete picture.

Thats why we need a more complete theory such as a quantum gravity theory.

 

[haushofer]

Yes I know that.

My point is that our current theories are not complete.. what appears to us as violation to the law of conservation of energy, and what makes it appear to only work "localy", could be our lack of knowledge on the complete picture.

Thats why we need a more complete theory such as a quantum gravity theory.

I think that these "pseudoproblems" are because we try to impose Newtonian concepts (e.g. energy conservation in fixed backgrounds) into general relativistic frameworks. It has nothing to do with a "lack of the complete picture". It's just a matter of oversymplifying, based on Newtonian intuition.

 

[PeroK]

It might explain where that energy goes.

Why do you think energy must be conserved?

 

[Deepblu]

I think that these "pseudoproblems" are because we try to impose Newtonian concepts (e.g. energy conservation in fixed backgrounds) into general relativistic frameworks. It has nothing to do with a "lack of the complete picture". It's just a matter of oversymplifying, based on Newtonian intuition.

Conservation of energy is not Newtonian concept! It is a law of physics.
In my view it is as fundamental as 2nd law of thermodynamics.

 

[PeroK]

Conservation of energy is not Newtonian concept! It is a law of physics.
In my view it is as fundamental as 2nd law of thermodynamics.

Why do you think it's a law of physics?

 

[Deepblu]

Why do you think energy must be conserved?

Why you do not?

 

[fresh_42]

Conservation of energy is not Newtonian concept! It is a law of physics.
In my view it is as fundamental as 2nd law of thermodynamics.

I always thought it is Newtonian and the consequence of Noether's local theorem about invariant Lagrangians. I cannot see a system of differential equations for some particles be extended on the entire universe. That would result in serious problems with the atlas.

 

[PeroK]

Why you do not?

Because I've studied GR.

 

[nikkkom]

Conservation of energy is not Newtonian concept! It is a law of physics. In my view it is as fundamental as 2nd law of thermodynamics.

"Laws of physics" are proposed by people, then tested against experiments. If experiments match, then the corresponding law might be true; if experiments contradict them, they are out. No law is secure against refuting by future developments.

In this case, conservation of energy fell victim to the discovery of expansion of the Universe, especially accelerating one.

Mathematically speaking, conservation of energy is consequence of time translation invariance ("the same experiment tomorrow has the same result as today"). Our local part of Universe on the scale of, say, our Galaxy, is very nearly time translation invariant. That causes conservation of energy to be not violated in our experiments.

As it turns out, most global solutions of GR are not globally time translation invariant. Therefore, globally, no mathematical logic exists for conservation of energy.

 

[Deepblu]

Because I've studied GR.

GR is not complete to describe universe on large scale.. GR is not reality it is a good approximation to reality!

And no energy does not just evaporize into nothing, we are still far from completely understanding how the universe work on cosmological scale, to jump to a definitive conclusion that energy is not conserved.

Btw "no energy conservation" is troublesome, imagine if we lived in a universe that is contracting instead of expanding? We will see as if energy is being created from nothing!

 

[nikkkom]

GR is not complete to describe universe on large scale..

Wrong. GR's problems lie elsewhere. Its description of large-scale Universe works just fine.

 

[Deepblu]

Wrong. GR's problems lie elsewhere. Its description of large-scale Universe works just fine.

I said "it is not complete" i didnt say "is wrong".
The Standard Model is not complete too ..you know that.

Not seeing the full puctures gives the illusion that energy is not conserved.

 

[PeroK]

GR is not complete to describe universe on large scale.. GR is not reality it is a good approximation to reality!

And no energy does not just evaporize into nothing, we are still far from completely understanding how the universe work on cosmological scale, to jump to a definitive conclusion that energy is not conserved.

Btw "no energy conservation" is troublesome, imagine if we lived in a universe that is contracting instead of expanding? We will see as if energy is being created from nothing!

You didn't answer my question, so let me try to answer it for you.

Someone told you once that energy conservation is a law of physics. And, for the physics you were learning at the time, this was true. But, it wasn't true in general and in particular for an expanding universe.

And, because you learned conservation of energy before you heard about GR, you are inclined to reject the latter.

 

[PeroK]

I said "it is not complete" i didnt say "is wrong".
The Standard Model is not complete too ..you know that.

Not seeing the full puctures gives the illusion that energy is not conserved.

And the classical physics that suggested the conservation of energy in the first place is a complete theory?

Conservation of energy arises from theories with less applicability than GR, not more. You may as well argue for Newtonian absolute time and space.

 

[Deepblu]

You didn't answer my question, so let me try to answer it for you.

Someone told you once that energy conservation is a law of physics. And, for the physics you were learning at the time, this was true. But, it wasn't true in general and in particular for an expanding universe.

And, because you learned conservation of energy before you heard about GR, you are inclined to reject the latter.

I don't reject GR! ofcourse not!

GR does not state that energy should or should not be conserved. Our current expansion model suggess that it is not. GR is not even compatible with our expansion model in first place!

 

[PeroK]

I don't reject GR! ofcourse not!

GR does not state that energy should or should not be conserved. Our current expansion model suggess that it is not. GR is not even compatible with our expansion model in first place!

You're the second person today to suggest that. It's an extraordinary idea. Modern cosmology is entirely based on GR!

The Einstein field equations do not naturally admit a steady state solution but imply an expanding universe.

 

[Deepblu]

You're the second person today to suggest that. It's an extraordinary idea. Modern cosmology is entirely based on GR!

The Einstein field equations do not naturally admit a steady state solution but imply an expanding universe.

Correction:
"GR is not even compatible with our accelerating expansion model in first place!"

 

[PeroK]

Correction:
"GR is not even compatible with our accelerating expansion model in first place!"

Not true. Having a non-zero vacuum energy explains that.

Where are you getting your misinformation?

 

[Deepblu]

Not true. Having a non-zero vacuum energy explains that.

Where are you getting your misinformation?

We need dark energy to make GR work for current expansion model, dark energy is theorized but never proven to actually exist. Thats why there are many alternative theories with and without dark energy.

Dark matter is also needed to explain observed galaxies rotation speed that do not match what is predicted by GR, dark matter also has never been observed.

That does not mean GR is wrong, it means that it is not the final ultimate theory.