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I wonder if the recent news about the background gravitational hum of the universe has any bearing on this: https://www.sciencealert.com/breaking-news-physicis

by rapjr9 3y ago

I wonder if the recent news about the background gravitational hum of the universe has any bearing on this: https://www.sciencealert.com/breaking-news-physicists-have-detected-the-background-hum-of-the-universe https://www.sciencealert.com/breaking-news-physicists-have-d... It essentially means that gravity is always in flux everywhere, at all frequencies of gravity waves, so there is noise in gravity. This is in addition to the background EM radiation in the universe. Gravitational and EM fields are infinite are they not? Maybe this is the source of gravitational randomness that Oppenheim is looking for. Although he seems to be positing that gravity itself has some inherent randomness.

bdamm 3y ago
Do we actually know that the fields are infinite? I thought it was just the easiest way to model what we know and can observe.
- rapjr9 3y ago
  I think the question would be, what happens at the edge of the universe? If the universe is finite, though expanding, then the waves can not be infinite unless they reflect at the edge, although one definition of the size of the universe might be that it extends as far as gravity and EM waves have traveled since the big bang. In which case I think the answer would be that if waves define fields then fields are not currently infinite nor will they ever be infinite, but they will always define the edge of the universe and keep traveling forever and over infinite time they will keep traveling infinitely. Which means they are essentially infinite, but not actually currently infinite, but that difference might not be much of a difference, even mathematically. It would suggest that EM radiation and gravity become more dilute in any one place over time though, as the universe gets bigger and the waves spread out more. There is also the speed of light problem. If EM radiation and gravity can only travel at the speed of light, then when new fields are created they do not propagate to infinity instantly, it takes time. So there is a kind of localness to EM/gravity but given the age of the universe a huge number of waves have propagated very far, which may be close enough to infinite we can't tell the difference. Matter can be created and destroyed so there can be new gravity fields created? Although I believe current thinking is that energy also exhibits gravity so maybe all the gravity that will ever exist is already here. That would be a difference in the nature of gravity versus EM waves since new EM radiation can be created while perhaps new gravity can not. Is a wave a perturbance that travels at the speed of light in a field that propagates instantly? Or is a field the propagation of a wave that travels at the speed of light? The idea of infinite fields suggests instant propagation, but gravity waves and EM waves certainly do not seem to propagate instantly. Maybe the idea of fields makes no sense and there are only waves?
dawnofdusk 3y ago
Yeah the "gravitational hum" would not seem to be the same as gravity itself having some inherent randomness. On the flipside, in a very real sense if the cosmological history of our universe is such that we exist in a universe with an always present indeterministic hum, then for our intents and purposes this is the same as gravity itself being random... unless we can devise experiments to study gravity in other universes with different cosmological initial conditions.
scrubs 3y ago
The hum is merely the change in the shape of space time by all the gravitational events like block hole creation, mergers, and novae. In that sense it's not random certainly not in the sense of quantum measurement say of position or momentum.

by rapjr9 3y ago

bdamm 3y ago

Do we actually know that the fields are infinite? I thought it was just the easiest way to model what we know and can observe.

rapjr9 3y ago
I think the question would be, what happens at the edge of the universe? If the universe is finite, though expanding, then the waves can not be infinite unless they reflect at the edge, although one definition of the size of the universe might be that it extends as far as gravity and EM waves have traveled since the big bang. In which case I think the answer would be that if waves define fields then fields are not currently infinite nor will they ever be infinite, but they will always define the edge of the universe and keep traveling forever and over infinite time they will keep traveling infinitely. Which means they are essentially infinite, but not actually currently infinite, but that difference might not be much of a difference, even mathematically. It would suggest that EM radiation and gravity become more dilute in any one place over time though, as the universe gets bigger and the waves spread out more. There is also the speed of light problem. If EM radiation and gravity can only travel at the speed of light, then when new fields are created they do not propagate to infinity instantly, it takes time. So there is a kind of localness to EM/gravity but given the age of the universe a huge number of waves have propagated very far, which may be close enough to infinite we can't tell the difference. Matter can be created and destroyed so there can be new gravity fields created? Although I believe current thinking is that energy also exhibits gravity so maybe all the gravity that will ever exist is already here. That would be a difference in the nature of gravity versus EM waves since new EM radiation can be created while perhaps new gravity can not. Is a wave a perturbance that travels at the speed of light in a field that propagates instantly? Or is a field the propagation of a wave that travels at the speed of light? The idea of infinite fields suggests instant propagation, but gravity waves and EM waves certainly do not seem to propagate instantly. Maybe the idea of fields makes no sense and there are only waves?

dawnofdusk 3y ago

Yeah the "gravitational hum" would not seem to be the same as gravity itself having some inherent randomness. On the flipside, in a very real sense if the cosmological history of our universe is such that we exist in a universe with an always present indeterministic hum, then for our intents and purposes this is the same as gravity itself being random... unless we can devise experiments to study gravity in other universes with different cosmological initial conditions.

scrubs 3y ago

The hum is merely the change in the shape of space time by all the gravitational events like block hole creation, mergers, and novae. In that sense it's not random certainly not in the sense of quantum measurement say of position or momentum.