What does Energy Non-Conservation in GR mean?

[Alan Grayson]

Since photons are redshifted as the universe expands, this is offered to support the claim that energy is not conserved in GR. When I asked where the lost energy goes, the answer offered is that it "disappears". I find this answer woefully insufficient for the following reason: if energy in GR is not conserved, it just means that a photon's energy changes as the universe expands. No matter at what time in the evolution of the universe, the photon's energy remains unchanged if it's conserved. That is, conservation of energy means the photon's energy remains unchanged. It doesn't say the lost energy "disappears". So the open question IMO is this; where does the lost energy go, and GR does not answer this question. AG

[Brent Meeker]

Forget GR.  Ask yourself where would it go in an expanding Newtonian universe?

Brent

On 11/9/2025 1:37 AM, Alan Grayson wrote:

Since photons are redshifted as the universe expands, this is offered to support the claim that energy is not conserved in GR. When I asked where the lost energy goes, the answer offered is that it "disappears". I find this answer woefully insufficient for the following reason: if energy in GR is not conserved, it just means that a photon's energy changes as the universe expands. No matter at what time in the evolution of the universe, the photon's energy remains unchanged if it's conserved. That is, conservation of energy means the photon's energy remains unchanged. It doesn't say the lost energy "disappears". So the open question IMO is this; where does the lost energy go, and GR does not answer this question. AG --
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[Alan Grayson]

On Sunday, November 9, 2025 at 2:14:22 PM UTC-7 Brent Meeker wrote:

Forget GR.  Ask yourself where would it go in an expanding Newtonian universe?

Brent

My conjecture is that the lost energy is absorbed into the surrounding space. To claim it "disappears" is to indulge in magic. AG 

[Brent Meeker]

On 11/9/2025 4:04 PM, Alan Grayson wrote:

On Sunday, November 9, 2025 at 2:14:22 PM UTC-7 Brent Meeker wrote:

Forget GR.  Ask yourself where would it go in an expanding Newtonian universe?

Brent

My conjecture is that the lost energy is absorbed into the surrounding space. To claim it "disappears" is to indulge in magic. AG 

You think EM radiation is absorbed into space.  How is this different than "it disappears"; is the space heated up?

Brent

On 11/9/2025 1:37 AM, Alan Grayson wrote:

Since photons are redshifted as the universe expands, this is offered to support the claim that energy is not conserved in GR. When I asked where the lost energy goes, the answer offered is that it "disappears". I find this answer woefully insufficient for the following reason: if energy in GR is not conserved, it just means that a photon's energy changes as the universe expands. No matter at what time in the evolution of the universe, the photon's energy remains unchanged if it's conserved. That is, conservation of energy means the photon's energy remains unchanged. It doesn't say the lost energy "disappears". So the open question IMO is this; where does the lost energy go, and GR does not answer this question. AG --

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[Alan Grayson]

On Sunday, November 9, 2025 at 6:28:13 PM UTC-7 Brent Meeker wrote:

On 11/9/2025 4:04 PM, Alan Grayson wrote:

On Sunday, November 9, 2025 at 2:14:22 PM UTC-7 Brent Meeker wrote:

Forget GR.  Ask yourself where would it go in an expanding Newtonian universe?

Brent

My conjecture is that the lost energy is absorbed into the surrounding space. To claim it "disappears" is to indulge in magic. AG 

You think EM radiation is absorbed into space.  How is this different than "it disappears"; is the space heated up?

Brent

"Disappears" carries the implication of magic; and not worth trying to come up with a mechanism. AG