5 ms·

First off, the author doesn't appear to be a crank. Here's the Wikipedia entry: https://en.wikipedia.org/wiki/Jonathan_Oppenheim https://en.wikipedia.org/wiki/

First off, the author doesn't appear to be a crank. Here's the Wikipedia entry: https://en.wikipedia.org/wiki/Jonathan_Oppenheim https://en.wikipedia.org/wiki/Jonathan_Oppenheim Second, we should note that even Einstein himself cautioned against believing spacetime was actually curved. His writings inform us he didn't believe it. I don't want to appeal to authority, that's just to say smart people, including the main developer of general relativity, didn't believe it. But he didn't believe in the non-local nature of quantum theory either, which we have now, since Einstein's death, proven to be true. Third, the claim that only gravity can be described using geometry is false, which the author himself notes later in this article. The stress-energy-momentum tensor simply makes gravity universal, unlike the other forces. I don't see any reason why that universality confers something special to gravity with regards to interpreting it as geometry. Just because we can model gravity as geometry, doesn't make gravity a result of geometry, and the author notes that modeling gravity that way makes it so we can't unify the forces. Finally, as the old saying goes, if you think gravity isn't a force, drop a brick on your toe! :) I'll also point out that singularities are generally considered to be a sign of issues with a model. GR has singularities. Maybe that should tell us something.

BeetleB 2y ago
> First off, the author doesn't appear to be a crank. Is this the first most people are hearing about this? In the 90's, I had a physics textbook for the layperson (i.e. non-STEM fields). It had a fantastic chapter on general relativity, and it also went with "not a force but a spacetime curvature".
- taylodl 2y ago
  Popular scientists have been saying it for decades and always use the flexible rubber sheet as the learning aid. Serious physicists tended to stay out of the fray, preferring to just "shut up and compute", as they do for quantum mechanics. It's a relatively recent development that physicists have entered the fray and say maybe curved spacetime isn't a model, maybe it's reality. I urge caution to all as we have no evidence that the model of curved spacetime is indeed reality. I think the caution is warranted considering that GR contains singularities, which is a sign the theory has issues.
  - Filligree 2y ago
    GR is a theory of the bulk. It’s like fluid mechanics, which treats fluids as infinitely divisible and doesn’t acknowledge the existence of molecules: There’s no way it’s accurate at small enough scales that molecules matter, which is what would be happening inside a black hole. At larger scales, however, fluid mechanics is extremely reliable.
  - api 2y ago
    What if singularities do in fact exist? What issues does that create? They might not be observable if superextremal black holes don't exist and thus naked singularities do not exist.
    - Filligree 2y ago
      We’d have no way to predict what they do, since the math breaks down. This is fine if you treat the math as only a model, and you’re willing to accept that it can’t predict the behaviour of a thing that can’t affect you anyway, but given your wording — “do in fact exist” — I assume that’s not what you mean. A theory that purports to describe how the universe actually functions, can’t have places where the theory says “and now the universe bluescreens”. At a minimum it would need additional postulates about computational order that allows the inside of the black hole to be NaN without that causing external reality to seize up.
      - taylodl 2y ago
        > “and now the universe bluescreens”. I love it!
      - toast0 2y ago
        > A theory that purports to describe how the universe actually functions, can’t have places where the theory says “and now the universe bluescreens”. A theory that provides useful predictions in some conditions and doesn't provide useful predictions in other conditions is a useful theory if you can determine which conditions are which. My lay understanding is general relativity provides useful predictions as long as mass isn't too dense (black hole) and as long as nothing breaks the speed limit; which is pretty general for everyday use, even if it doesn't cover the whole universe.
Filligree 2y ago
> But he didn't believe in the non-local nature of quantum theory either, which we have now, since Einstein's death, proven to be true. We have not proven quantum theory to be non-local. We’ve only proven that it can’t be both local and contain particles, as opposed to particles being emergent from the wavefunction’s interactions. MWI chooses the latter, and is therefore a local theory. (Alternately, collapse. But collapse theories are largely nonsensical.)
wongarsu 2y ago
> we should note that even Einstein himself cautioned against believing spacetime was actually curved. [...] I don't want to appeal to authority Another example that comes to mind is Max Planck believing that light being absorbed in discrete packets of energy was only a neat mathematical hack he came up with. It took Albert Einstein to say "but what if light is discrete packets". And then as you say Einstein having major reservations against the field of quantum physics that he himself spawned. > if you think gravity isn't a force, drop a brick on your toe By that logic the centrifugal force has to be a force. If you don't believe it, just drive a vehicle around a curve, or whirl a rock on a string.
- marcosdumay 2y ago
  > By that logic the centrifugal force has to be a force. Are you trying to claim it's not?
  - ivansavz 2y ago
    Not the OP, but I think I know what wongarsu is referring to. In order to make an object turn, it needs to experience an centripetal acceleration (towards the centre of rotation). This is the force causing objects to change trajectory. If there is another object inside the turning object (like clothes inside a washer, or a person inside a car) they will "feel" like they are being flug out as if a centrifugal force existed, but actually that is just the effect of Newton's first law: the natural tendency of every moving body is to continue to move in a straight line, so when the containing object is changing direction (due to the centripetal force), Newton's first law tends to push you outwards. All of the above is from the static (world) frame of reference. It is also possible to put a coordinate system on the rotating object, in which case something like a centrifugal force will exit, but we kind of created it by choosing an accelerating reference frame, so it's not real. Sometimes called a pseudoforce.
- cryptonector 2y ago
  "There is no centrifugal force" is often found together with "centrifugal forces appear as a term when using the frame of reference of the object going around", and this implicitly says that some reference frames are more privileged than others which -in a world that accepts the principle of Relativity- is just not acceptable. So of course gravity is a force, and of course centrifugal forces are real. These dogmas serve to do nothing more than to scare away students, and to make the dogmatic seem like geniuses because only they can understand these things.
fxj 2y ago
It is possible to unify the electromagnetic field into a geometric framework via the Kaluza-Klein theory which is just rewriting GR + ED. Then electromagnetic forces are also of geometric origin. How do you interpret this? Is electromagnetism then also not a force? I am not a physicist, so I am asking the experts. https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory
fxj 2y ago
I found this paper which details how a charged particle falling into a black hole radiates. How is this possible when there is no acceleration on the particle? https://adsabs.harvard.edu/full/1971PASP...83..633R https://adsabs.harvard.edu/full/1971PASP...83..633R Title: Radiation from Particles Falling into Black-Holes Authors: Ross, D. K. Journal: Publications of the Astronomical Society of the Pacific, Vol. 83, No. 495, p.633 Bibliographic Code: 1971PASP...83..633R
- cryptonector 2y ago
  I'm going to have to read that one. Thanks for the link!
cryptonector 2y ago
> First off, the author doesn't appear to be a crank. Perhaps, but the author is being dogmatic. See commentary elsewhere in this post.

BeetleB 2y ago

> First off, the author doesn't appear to be a crank. Is this the first most people are hearing about this? In the 90's, I had a physics textbook for the layperson (i.e. non-STEM fields). It had a fantastic chapter on general relativity, and it also went with "not a force but a spacetime curvature".

taylodl 2y ago
Popular scientists have been saying it for decades and always use the flexible rubber sheet as the learning aid. Serious physicists tended to stay out of the fray, preferring to just "shut up and compute", as they do for quantum mechanics. It's a relatively recent development that physicists have entered the fray and say maybe curved spacetime isn't a model, maybe it's reality. I urge caution to all as we have no evidence that the model of curved spacetime is indeed reality. I think the caution is warranted considering that GR contains singularities, which is a sign the theory has issues.
- Filligree 2y ago
  GR is a theory of the bulk. It’s like fluid mechanics, which treats fluids as infinitely divisible and doesn’t acknowledge the existence of molecules: There’s no way it’s accurate at small enough scales that molecules matter, which is what would be happening inside a black hole. At larger scales, however, fluid mechanics is extremely reliable.
- api 2y ago
  What if singularities do in fact exist? What issues does that create? They might not be observable if superextremal black holes don't exist and thus naked singularities do not exist.
  - Filligree 2y ago
    We’d have no way to predict what they do, since the math breaks down. This is fine if you treat the math as only a model, and you’re willing to accept that it can’t predict the behaviour of a thing that can’t affect you anyway, but given your wording — “do in fact exist” — I assume that’s not what you mean. A theory that purports to describe how the universe actually functions, can’t have places where the theory says “and now the universe bluescreens”. At a minimum it would need additional postulates about computational order that allows the inside of the black hole to be NaN without that causing external reality to seize up.
    - taylodl 2y ago
      > “and now the universe bluescreens”. I love it!
    - toast0 2y ago
      > A theory that purports to describe how the universe actually functions, can’t have places where the theory says “and now the universe bluescreens”. A theory that provides useful predictions in some conditions and doesn't provide useful predictions in other conditions is a useful theory if you can determine which conditions are which. My lay understanding is general relativity provides useful predictions as long as mass isn't too dense (black hole) and as long as nothing breaks the speed limit; which is pretty general for everyday use, even if it doesn't cover the whole universe.

Filligree 2y ago

> But he didn't believe in the non-local nature of quantum theory either, which we have now, since Einstein's death, proven to be true. We have not proven quantum theory to be non-local. We’ve only proven that it can’t be both local and contain particles, as opposed to particles being emergent from the wavefunction’s interactions. MWI chooses the latter, and is therefore a local theory. (Alternately, collapse. But collapse theories are largely nonsensical.)

wongarsu 2y ago

> we should note that even Einstein himself cautioned against believing spacetime was actually curved. [...] I don't want to appeal to authority Another example that comes to mind is Max Planck believing that light being absorbed in discrete packets of energy was only a neat mathematical hack he came up with. It took Albert Einstein to say "but what if light is discrete packets". And then as you say Einstein having major reservations against the field of quantum physics that he himself spawned. > if you think gravity isn't a force, drop a brick on your toe By that logic the centrifugal force has to be a force. If you don't believe it, just drive a vehicle around a curve, or whirl a rock on a string.

marcosdumay 2y ago
> By that logic the centrifugal force has to be a force. Are you trying to claim it's not?
- ivansavz 2y ago
  Not the OP, but I think I know what wongarsu is referring to. In order to make an object turn, it needs to experience an centripetal acceleration (towards the centre of rotation). This is the force causing objects to change trajectory. If there is another object inside the turning object (like clothes inside a washer, or a person inside a car) they will "feel" like they are being flug out as if a centrifugal force existed, but actually that is just the effect of Newton's first law: the natural tendency of every moving body is to continue to move in a straight line, so when the containing object is changing direction (due to the centripetal force), Newton's first law tends to push you outwards. All of the above is from the static (world) frame of reference. It is also possible to put a coordinate system on the rotating object, in which case something like a centrifugal force will exit, but we kind of created it by choosing an accelerating reference frame, so it's not real. Sometimes called a pseudoforce.
cryptonector 2y ago
"There is no centrifugal force" is often found together with "centrifugal forces appear as a term when using the frame of reference of the object going around", and this implicitly says that some reference frames are more privileged than others which -in a world that accepts the principle of Relativity- is just not acceptable. So of course gravity is a force, and of course centrifugal forces are real. These dogmas serve to do nothing more than to scare away students, and to make the dogmatic seem like geniuses because only they can understand these things.

fxj 2y ago

It is possible to unify the electromagnetic field into a geometric framework via the Kaluza-Klein theory which is just rewriting GR + ED. Then electromagnetic forces are also of geometric origin. How do you interpret this? Is electromagnetism then also not a force? I am not a physicist, so I am asking the experts. https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory

fxj 2y ago

I found this paper which details how a charged particle falling into a black hole radiates. How is this possible when there is no acceleration on the particle? https://adsabs.harvard.edu/full/1971PASP...83..633R https://adsabs.harvard.edu/full/1971PASP...83..633R Title: Radiation from Particles Falling into Black-Holes Authors: Ross, D. K. Journal: Publications of the Astronomical Society of the Pacific, Vol. 83, No. 495, p.633 Bibliographic Code: 1971PASP...83..633R

cryptonector 2y ago
I'm going to have to read that one. Thanks for the link!

cryptonector 2y ago

> First off, the author doesn't appear to be a crank. Perhaps, but the author is being dogmatic. See commentary elsewhere in this post.