Conservation of energy in GR and symmetry

In summary, the conversation discusses how general relativity is built on principles of symmetry but it may not conserve energy. The energy of redshifted photons from distant galaxies goes into the increasing potential energy gained by the universe in its expansion. However, dark energy, which is constant throughout the universe, does not affect this mechanism. The potential energy created by gluons in holding the proton or neutron together can also contribute to the mass of the nucleon. There is a debate on whether energy is conserved in GR, and it is noted that GR has too much symmetry for its own good.
  • #1
kurious
641
0
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?
 
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  • #2
How is mass-energy not conserved in GR?

- Warren
 
  • #3
I was referring to the energy of redshifted photons from distant galaxies.
.
 
  • #4
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
 
  • #5
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 enrgy of redshifted photons
get put into gravitational force carriers?
And if it does why is there no blurring as photons lose momentum?
 
  • #6
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
 
  • #7
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.
 
  • #8
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
 
  • #9
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).
 
  • #10
Gravitons are not electrically charged, and thus do not interact with photons.

- Warren
 
  • #11
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.
 
  • #12
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
 
  • #13
kurious said:
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
 
Last edited by a moderator:

1. What is the Conservation of Energy in General Relativity (GR)?

The Conservation of Energy in General Relativity (GR) is a fundamental law in physics that states energy cannot be created or destroyed, only transformed from one form to another. It is a key principle in understanding the behavior of matter and energy in the universe.

2. How does the Conservation of Energy apply to General Relativity?

In General Relativity, the Conservation of Energy is closely related to the concept of symmetry. This means that the laws of physics remain the same regardless of the position, orientation, or motion of an object. This symmetry ensures that energy is conserved in all physical processes.

3. What are the implications of the Conservation of Energy in GR?

The Conservation of Energy in GR has far-reaching implications for our understanding of the universe. It allows us to make predictions and calculations about the behavior of matter and energy, and is an essential component of many theories and models in physics.

4. Is the Conservation of Energy absolute in GR?

No, the Conservation of Energy is not absolute in GR. This is because GR allows for the concept of spacetime curvature, which means that energy can be transferred from one form to another without being conserved. However, in most cases, the Conservation of Energy still holds true.

5. How does the Conservation of Energy impact our daily lives?

The Conservation of Energy impacts our daily lives in various ways, from the energy we use to power our homes and vehicles to the behavior of light and matter in our surroundings. It also plays a crucial role in understanding the functioning of the universe and its evolution over time.

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