Conservation of energy in GR and symmetry

[kurious]

Experiment shows that many physical quantities are conserved
and that the associated conservation laws can be linked to symmetries.
However it seems strange that general relativity is a theory built from
principles of symmetry and yet energy might not be conserved in general relativity.Surely energy must be conserved in general relativity?

 

[chroot]

How is mass-energy not conserved in GR?

- Warren

 

[kurious]

I was referring to the energy of redshifted photons from distant galaxies.
.

 

[chroot]

GR predicts that mass and energy gravitate, and that the expansion of the universe should slow down due to that gravitation.The energy lost by the redshifted photons goes into the increasing potential energy gained by the universe in its expansion. Analogously, a baseball tossed into the air loses kinetic energy as it gains potential energy.

Dark energy appears to be a non-zero vacuum energy density, but it is constant throughout the universe and thus does not affect this mechanism.

- Warren

 

[kurious]

How does the energy of the photons go into gravitational potential energy?
Gluons give protons potential energy and presumably increasing the number of gluons would increase the potential energy,so does the energy of redshifted photons
get put into gravitational force carriers?
And if it does why is there no blurring as photons lose momentum?

 

[chroot]

You could also argue a complementary viewpoint that the total energy of the universe is fixed, but it continues to expand -- thus its energy density must decrease.

I don't know what you're talking about with the gluons.

- Warren

 

[kurious]

Croot:
I don't know what you're talking about with the gluons.

Kurious:
SELF-ADJOINT said in "Nuclei and particles" with respect to " Mass gap and Yang-Mills
theory" :

Yes the gluons, unlike photons, can and do interact with each other. This is all in aid of holding the proton or neutron together, and it generates a lot of potential energy; the energy keeping the quarks from wandering off. This potential energy is added to the quark mass (also a form of potential energy according to Einstein) to make up the mass of the nucleon.

 

[chroot]

I know what gluons are, kurious. I don't know why you think that gluons inside a nucleus have anything to do with CMBR photons and the expansion of the universe.

- Warren

 

[kurious]

I was referring to the potential energy created by the gluons -
can the potential energy created by gravitational force carriers
come from the energy of redshifted photons?
Tired light theories are criticised because there is no mechanism
that can take energy from photons without changing photon momentum
and causing stars to look blurred.But would the situation be different if
gravitational force carriers took energy from photons - can spin 2 force carriers
take photon energy without changing the direction photons are moving in
( quantum mechanics says that the force carrier for gravity is spin 2 regardless of whether or not that carrier is a graviton).

 

[chroot]

Gravitons are not electrically charged, and thus do not interact with photons.

- Warren

 

[kurious]

But if gravitons and photons have energy can't they both curve spacetime
and affect one another's trajectories.I suppose photons would have to
emit and absorb gravitons for this to be feasible and gravitons would have
to emit gravitons - and be a bit like gluons.
There was a big debate on energy conservation in GR on sci.physics.research
but the issue was not resolved.

 

[chroot]

If your question goes all the way down to how gravitons interact with the gravitation caused by a photon, I'm afraid I cannot help you -- it's beyond my level. Perhaps someone else here can offer a better response.

- Warren

 

[pervect]

Experiment shows that many physical quantities are conserved
and that the associated conservation laws can be linked to symmetries.
However it seems strange that general relativity is a theory built from
principles of symmetry and yet energy might not be conserved in general relativity.Surely energy must be conserved in general relativity?

The problem with GR is that it has too much symmetry for it's own good :-)

http://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html