Evidence now suggest that the expansion of our universe is accelerating this coupled with evidence that we most likely live in an unbound universe suggest that as space continues to expand it will eventually reach a point that matter will not be able to hold itself together. If this is correct it means that all the matter in our universe will eventually be converted back into energy. Is that possible? If it is then what of E=MC2?

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Possible? Yes. Whether it will happen or not? Unknown at this time.
I don't understand your question. E=mc^2 defines how much energy you get from conversion.

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E=MC^2 has always implied a two way relationship between matter and energy anyway so what's the problem?

Maybe not all. I don't think that neutrinos can break down under any circumstances, and they might represent up to 4% of the mass of the universe.

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The end of the universe... Oh boy, something new to worry about!

Our sun Sol is a second generation star. We have and can observe star forming regions. Regeneration of stellar material is on going. Yes at some distant point in the future the expansion rate and the continuing death of stars may, no will end the universe... but thats a very long time away.

Slowly over millions of billions of years the universe will darken and spread so distantly that just seeing another star will be impossible. To sagest that the very fabric of mater will not be able to hold itself together is a little beyond comprehension. Gravity will not die.

The ultimate fate of the universe is as yet unknown. Just because I do not think it will destruct does not rule it out.

What I was wondering by citing Einsteins' equation is that if the matter in the universe is converted back to energy by expanding space then would it be a radical release?or just a gradual return of all the energy produced by the Big Bang?

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"If we crave some cosmic purpose, then let us find ourselves a worthy goal." --Carl Sagan

Antoniseb. Under the rules of conservation of Electron, Muon, and Tauon Family Number...that's true. But that assumes that the massless neutrino is distinguishable from it's massless antineutrino, and from the other family types. If purported neutrino masses are real then the neutrino travels subluminally, and it's identity depends upon the Lorentz frame....making antineutrinos indistinguishable from their partners....and allowing neutrino mixing in a "vacuum". They could then annihilate with no fuss from conservation laws into regular photons. pete

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To paraphrase what I think you are asking:
If the total mass+energy of the universe is constant, and dark energy is making the universe accelerate its expansion, where would it get enough energy to accelerate the expansion significantly beyond where it is today (given that roughly two-thirds the mass+energy of the universe is already in the form of dark energy).

That's a good question to which *I* have no answer... but you can't be certain that the conservation of energy really applies to the entire universe all at once, as it clearly didn't apply when the universe first began.

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Apparently so. But with expansion over so many billion years, think of the resulting energy density, which must become next to nothing after all the black holes evaporate....

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Well, we assume it didn't. We can't be sure where that energy was, what form it was in, or where it came from, if anywhere. Or that "begin" is the applicable term; maybe it just changed form from something else to "expanding, life-supporting Universe."

EDIT: Which brings up the point that the hypothesised "big rip" would technically not be the "end" of the Universe, just the end of the Universe as we know it.

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I personally like this thought. The universe can not now cease to exist it might get dark and cold. some may revert directly into energy and become very difuse...
but it will all still be there.
In order to see this we are going to need to be very cleaver.
Surviving a weekend is one thing, bur for the billions of billions of years we is going to need to be very very prolific.

The end of the universe as we know it, will not be the big rip, will be when the last human dies and we become extinct. Perhaps from old age in a fallout shelter, or in a generation ship, alone in the vastness of space.


In all probablity, there will be nothing of Earth that will be around when the universe ends as we know it.

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LOGIC, n.
The art of thinking and reasoning in strict accordance with the limitations and incapacities of the human misunderstanding.

In the Year 2525.

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If an astronaut doesn't need good grammar, niether does you.

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You know I heard something on the TV about matter not being able to hold itself together as well when the universe has expanded enough.

A few things to remember here:

A "Big Rip" is full blown curvature singularity scenario -- and a singularity that occurs "everywhere" at finite proper comoving time. The universe just "blows up". You can see this as coming from a type of "dark energy" that behaves as an increasing Lambda. Lambda, and the scale factor, just blows up, becomes infinite after some finite time.

In that Rindler/deSitter expanding hyperballoon picture, the proper accleration of the hyperradius would go to infinity. A comover sitting on it and using deSitter static coordinates would see the Cosmological Horizon shrink down on him to a point. The "rip tide" would go to infinity.

So I would say that is indeed an end of the universe, not just as we know it.

And second, energy conservation does not have to hold globally in GR. It will always hold *locally*, but not globally. That's happenning right now in the cosmological picture.

And third, I'm just not exactly kosher with considering "dark energy" as a "regular energy density". You can move Lambda over to the right in the EFE and say, hey, that looks like some sort of source term. Such a thing there is certainly not conservered in any sort of sense as you "make more of it" as space expands.

You can leave it on the left and consider Lambda to be "just geometry" and nothing to do with a source term, which is the regular "stuff" that exists in space-time. So keep in mind the distinction between the energy of "stuff in space-time", matter and fields, vs the "energy of space-time itself". Dark energy is something in the latter category, whatever it may be.

And finally about global energy -- this is one of the most vexing things in GR that the "high priests" have puzzled and worked for a long time, with different approaches and even different pedagogies.

If you space-time is asymptotically flat, an observer there can conserve energy globally, and one can invoke that and say it *is conserved*. And I think the restriction is actually just asymptotically static/stationary and not flat, but I'm not sure.

Our universe meets none of those conditions. Now, you can (try) to define a "gravitational field energy". The Landau Lifshi-tz psuedo (hyphe to avoid the profanity filter kicking in) tensor is a popular way to do it. But it is not invariant, and no such invariant thing can be defined. Note the LL energy has nothing whatsoever to do with gravitational potential energy, or field energy in any EM-like manner. There is no "energy" associated with a static space-time at all. It's only when it's dynamic and seems to be "carrying energy in or away" does the LL thing kick in.

So, by using the LL construction, one can conserver energy in a particular coordinate system by saying the difference of energy is going in or out of the gravitational field. And that is just not invariant. Another observer would say that flow is different.

-Richard

Am I the sol voice that does not understand the post obove...?
I have read it three times and am beginning to lose the will to live...
Would you "Richard"-Publius., Please try and explain without the LL or EFE and Those big words that I have never seen befor...
I am a confused amature, still I want to know what it is you have said.

Well, that's exactly I how I feel sometimes when I read stuff myself. I guess it's all relative, like everything else.

I could try to rephrase everything I wrote above but that might just be more sound and fury. What is it you want me to 'splain better, exactly?

Oh, EFE = Einstein Field Equations. It is the governing equation of General Relativity which describes how the "shape" of space-time depends on the mass-energy (and momentum and how it is all changing, too) content of the space-time.

The Landau-LifDirtyWord energy thingy is not that important.

-Richard

Hi astromark: I don't understand much of this either. More numbers would be helpful such as the 67% dark energy suggested by Antoniseb. If that was 60 percent in 1907, we have reason to worry. If it was 60 percent 13 billion years ago, and linear, we still have perhaps 50 billion more good years. Same for the Hubble constant, I think. If it has gone from 60 to 67 (linear) in the past 13 billion years, we should still have perhaps 50 billion more good years. While our sun likely will last only about 1/10 th that long, a few humans can likely move to the outer solar system, or even to other solar systems, so we don't all have to die when our sun becomes a red giant. Neil

The question seems to have evolved a little into 'what will become of this universe eventually'?

IMHO it will always continue to expand and as doing so will run out of heat (energy) and, be so sparsely spread that thinly that darkness will fall across the universe forevermore....

But rest easy this is going to take a very long time.

Understanding the leakage of energy from the hart of black holes does not for me sagest the end of the universe.
Mater can be made to change its form. If pure energy became mater then could the opposite happen ?
If this were so, would it not sagest that the universe will survive for ever.
We just might not recognize it.