Is it possible that the universe could be eternal??...

[Anomalocaris]

Time is part of space-time. Space-time is the gravitational field, which in turn is part of the universe.  So time and the universe are concurrent. If there was a moment with no prior moments, then the universe has experienced a finite duration in time and also has existed for all time.

Just FYI you are replying to a 12-year old post

the thread is apparently eternal.

[LinuxGal]

And what is wrong with matter existing eternally? No specific piece of matter needs to do so, just matter in general.

Per the Heisenberg Uncertainty Principle, how could matter not exist, as matter & energy can be converted one to another.  Zero matter, zero fields and zero energy is a precisely defined state which would violate the HUP.

Per Emmy Noether's theorem making time and energy conjugate variables, if there's energy now, there must have been the same energy then, just not necessarily in the same form.  So there never was nothing.

[Fireball]

Per the Heisenberg Uncertainty Principle, how could matter not exist, as matter & energy can be converted one to another.  Zero matter, zero fields and zero energy is a precisely defined state which would violate the HUP.

Per Emmy Noether's theorem making time and energy conjugate variables, if there's energy now, there must have been the same energy then, just not necessarily in the same form.  So there never was nothing.

Which is a really interesting concept, if one thinks about it. There was never nothing. I don't have an explanation, but I don't credit/blame a god for it. Please point me to a source for Noether's theorem, I know who she is, but it's been a long day and I'm tired Thanks in advance!

[Anomalocaris]

And what is wrong with matter existing eternally? No specific piece of matter needs to do so, just matter in general.

Per the Heisenberg Uncertainty Principle, how could matter not exist, as matter & energy can be converted one to another.  Zero matter, zero fields and zero energy is a precisely defined state which would violate the HUP.

Negative energy and positive energy can cancel out?.   Perhaps global aggregate state is zero but local deviation is possible?

[Jehanne]

Per Emmy Noether's theorem making time and energy conjugate variables, if there's energy now, there must have been the same energy then, just not necessarily in the same form.  So there never was nothing.

Which is a really interesting concept, if one thinks about it. There was never nothing. I don't have an explanation, but I don't credit/blame a god for it. Please point me to a source for Noether's theorem, I know who she is, but it's been a long day and I'm tired Thanks in advance!

Wikipedia -- Noether's theorem

[polymath257]

Per the Heisenberg Uncertainty Principle, how could matter not exist, as matter & energy can be converted one to another.  Zero matter, zero fields and zero energy is a precisely defined state which would violate the HUP.

Per Emmy Noether's theorem making time and energy conjugate variables, if there's energy now, there must have been the same energy then, just not necessarily in the same form.  So there never was nothing.

That is assuming time translation invariance of the physical laws (or at least the Lagrangian). In the context of curved spacetime, that need not be the case.

And, in fact, the conservation of energy is a very delicate thing in general relativity. There is a *local* version, where each interaction at an event conserves energy in all reference frames. But curvature means that it is impossible to even define what the 'total energy of a region' is.

[polymath257]

Per the Heisenberg Uncertainty Principle, how could matter not exist, as matter & energy can be converted one to another.  Zero matter, zero fields and zero energy is a precisely defined state which would violate the HUP.

Negative energy and positive energy can cancel out?.   Perhaps global aggregate state is zero but local deviation is possible?

One problem is how to define the 'energy of curvature', in other words, the energy of gravity. This has to be done in a way that is frame independent.

For compact spacetime (finite, negatively curved), this is possible and gives a 'total energy' of zero. For non-compact space, this is still a problematic thing.

[LinuxGal]

For compact spacetime (finite, negatively curved), this is possible and gives a 'total energy' of zero. For non-compact space, this is still a problematic thing.

The cosmological constant corresponds to a non-zero vacuum energy, which causes an acceleration in the expansion, and the total of this energy is integrated over the (increasing) volume of the universe.  Money for nothing and chicks for free.

[polymath257]

For compact spacetime (finite, negatively curved), this is possible and gives a 'total energy' of zero. For non-compact space, this is still a problematic thing.

The cosmological constant corresponds to a non-zero vacuum energy, which causes an acceleration in the expansion, and the total of this energy is integrated over the (increasing) volume of the universe.  Money for nothing and chicks for free.

Once again, the problem is that energy is NOT a scalar quantity. It is one component of the four-dimensional energy-momentum vector. As such, it simply doesn't have a well-defined value at each point. Even observers moving at different speeds will measure the energy of an event as different. For a flat spacetime, this can be resolved frame-by-frame. When curvature effects are also brought in as well, you can't even make a common frame of reference at different points.

In the case of dark energy (old school, the cosmological constant), the easiest local frame to use is the co-moving frame. And, in that frame, it represents a type of energy density of the vacuum. But that doesn't allow to 'integrate over the volume' to get a meaningful answer.

Sorry. It was a good idea, but the details simply don't work that way.

[LinuxGal]

The cosmological constant corresponds to a non-zero vacuum energy, which causes an acceleration in the expansion, and the total of this energy is integrated over the (increasing) volume of the universe.  Money for nothing and chicks for free.

Once again, the problem is that energy is NOT a scalar quantity. It is one component of the four-dimensional energy-momentum vector. As such, it simply doesn't have a well-defined value at each point. Even observers moving at different speeds will measure the energy of an event as different. For a flat spacetime, this can be resolved frame-by-frame. When curvature effects are also brought in as well, you can't even make a common frame of reference at different points.

In the case of dark energy (old school, the cosmological constant), the easiest local frame to use is the co-moving frame. And, in that frame, it represents a type of energy density of the vacuum. But that doesn't allow to 'integrate over the volume' to get a meaningful answer.

Sorry. It was a good idea, but the details simply don't work that way.

Well, it also fails for perfectly practical reasons: If your source of energy is the lowest energy state of the universe, then you've got nowhere to dump your waste photons and take advantage of the differing quantities of degrees of freedom to do work.   This seems to elude the folks with pi in the sky notions of tapping "zero point energy".