8 ms·

Even the title is wrong, we know for a fact that we are getting gravity wrong. A better article with actual content: https://www.ipmu.jp/en/20190619-symmetry

Even the title is wrong, we know for a fact that we are getting gravity wrong. A better article with actual content: https://www.ipmu.jp/en/20190619-symmetry https://www.ipmu.jp/en/20190619-symmetry

glofish 7y ago
TLDR: [...] the holographic principle allows physicists to study gravitational systems by projecting them on a boundary [...] proved that symmetry is not possible in a gravitational theory if it obeys the holographic principle. [...] meaning that symmetry would not be possible in quantum gravity.
- deleted 7y ago
  [deleted]
- Khaine 7y ago
  PBS Space Time have done a number of episodes on the holographic principle[1] I strongly recommend anyone interested in physics check out the channel [1] https://www.youtube.com/watch?v=klpDHn8viX8 https://www.youtube.com/watch?v=klpDHn8viX8
- RandomBacon 7y ago
  For people on a mobile device: > TLDR: > the holographic principle allows physicists to study gravitational systems by projecting them on a boundary > proved that symmetry is not possible in a gravitational theory if it obeys the holographic principle. > meaning that symmetry would not be possible in quantum gravity.
  - foobar1962 7y ago
    ... if it obeys the holographic principle.
- hinkley 7y ago
  By inference. this means we trust the holographic principle so thoroughly that we don't even consider that it could be the unbalanced part of this equation. Is that true?
  - TheOtherHobbes 7y ago
    AdS/CFT fell out of string theory. It's only holographic in the sense that in some circumstances you can summarise an n=dimensional system using n-1 dimensions - not in the literal sense of using the kind of optical transforms that make visual holography possible, but in the more abstract sense that all of the information in some spaces ends up on a notional surrounding boundary. The AdS universe is basically a mathematical toy for physicists to play with. It doesn't correspond with the physical structure of the real universe. There's a hope that it might correspond to some kind of mathematical meta-structure that defines physical laws. This article suggests that's very unlikely. Personally I wouldn't be surprised if AdS/CFT turned out to be a dead end - probably like supersymmetry - and the real structure of quantum gravity turned out to be completely different and unexpected, and not a Conformal Field Theory at all. But IANAP, so I may well be wrong about that.
austincheney 7y ago
Does this account for the subject of "dark matter", which at this point is absent from all evidence?
- mkl 7y ago
  No one would have come up with a hypothesis like dark matter without evidence pointing in that direction: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
  - austincheney 7y ago
    Dark matter was hypothesized because the universe is expanding faster than our understanding of gravity allows. The problem in that is if the universe is expanding so fast then something else must be holding galaxies together since galaxies are so incredibly vast and yet contain so very little matter. Particle physics is currently defined according to the Standard Model. Dark matter was proposed because it plugs many of the gaps of universal expansion in contrast to the Standard Model, but not all the gaps. It would take far greater effort to invalidate the Standard Model and all of particular physics built upon it. There is also the problem of not having any other model to replace the current one. https://en.m.wikipedia.org/wiki/Standard_Model https://en.m.wikipedia.org/wiki/Standard_Model The expansion of the universe is observed as red shifts and these observations are numerous and largely uniform. Dark matter, on the other hand, has not been directly observed. * https://arstechnica.com/features/2014/07/dark-matter-makes-up-80-of-the-universe-but-where-is-it-all/ https://arstechnica.com/features/2014/07/dark-matter-makes-u... * https://arstechnica.com/science/2019/11/dark-matter-link-to-regular-matters-dominance-fails-to-show-up/ https://arstechnica.com/science/2019/11/dark-matter-link-to-... * https://arstechnica.com/science/2019/02/more-bad-news-for-controversial-20-year-old-claim-of-dark-matter-detection/ https://arstechnica.com/science/2019/02/more-bad-news-for-co... * https://arstechnica.com/science/2019/04/one-night-of-telescope-time-rules-out-black-holedark-matter-idea/ https://arstechnica.com/science/2019/04/one-night-of-telesco... * https://arstechnica.com/science/2017/02/a-history-of-dark-matter/3/ https://arstechnica.com/science/2017/02/a-history-of-dark-ma... * https://arstechnica.com/science/2016/07/dark-matter-still-mia-after-most-exhaustive-search-yet/ https://arstechnica.com/science/2016/07/dark-matter-still-mi...
makach 7y ago
gravity sucks. thanks for the link :)
- dylan604 7y ago
  I always thought gravity was much more attractive.
pdonis 7y ago
> we know for a fact that we are getting gravity wrong This statement is way, way too strong. We have a theory of gravity, General Relativity, which has had its predictions confirmed by countless experiments, in some cases to thirteen or fourteen decimal places. That is not "getting it wrong". Many physicists believe that GR, as well confirmed as it is, can't be the final fundamental theory of gravity because it's not a quantum theory. But nobody has yet found a quantum theory of gravity that (a) is consistent with the rest of quantum mechanics, and (b) makes experimental predictions that have been confirmed. Unless and until both (a) and (b) are done, the claim that we are "getting it wrong", even in the restricted sense of not having a final fundamental theory of gravity, because GR isn't a quantum theory is just speculation and might itself be wrong. It should certainly not be stated with the confidence you are stating it.
- mnl 7y ago
  Now, why am I seeing this factual comment in grey? See here for instance a popsci take on the problem: https://www.scientificamerican.com/article/is-gravity-quantum/ https://www.scientificamerican.com/article/is-gravity-quantu... Everybody expects a quantum theory of gravitation, but if we were drawing it from scratch no one would make it that weak. It is a difficult problem, people work in string theory because you can get Einstein's equations from strings and the alternatives look indeed worse. I don't think that means GR is a wrong take on gravitation, it's more like an amazing one to begin with.
  - opless 7y ago
    It's grey because someone in their infinite wisdom downvoted you. Most likely because they'd rather downvote rather than challenge your statement. It's a worrying trend.
- JackRabbitSlim 7y ago
  GR is no more or less wrong than Newtonian physics.
  - flatline 7y ago
m4r35n357 7y ago
Just because quantum physicists can't get their act together over gravitation doesn't make General Relativity wrong! When the lay person reads headlines like this, they assume you are talking about Einstein's theory.

Even the title is wrong, we know for a fact that we are getting gravity wrong. A better article with actual content: https://www.ipmu.jp/en/20190619-symmetry https://www.ipmu.jp/en/20190619-symmetry

glofish 7y ago

TLDR: [...] the holographic principle allows physicists to study gravitational systems by projecting them on a boundary [...] proved that symmetry is not possible in a gravitational theory if it obeys the holographic principle. [...] meaning that symmetry would not be possible in quantum gravity.

deleted 7y ago
[deleted]
Khaine 7y ago
PBS Space Time have done a number of episodes on the holographic principle[1] I strongly recommend anyone interested in physics check out the channel [1] https://www.youtube.com/watch?v=klpDHn8viX8 https://www.youtube.com/watch?v=klpDHn8viX8
RandomBacon 7y ago
For people on a mobile device: > TLDR: > the holographic principle allows physicists to study gravitational systems by projecting them on a boundary > proved that symmetry is not possible in a gravitational theory if it obeys the holographic principle. > meaning that symmetry would not be possible in quantum gravity.
- foobar1962 7y ago
  ... if it obeys the holographic principle.
hinkley 7y ago
By inference. this means we trust the holographic principle so thoroughly that we don't even consider that it could be the unbalanced part of this equation. Is that true?
- TheOtherHobbes 7y ago
  AdS/CFT fell out of string theory. It's only holographic in the sense that in some circumstances you can summarise an n=dimensional system using n-1 dimensions - not in the literal sense of using the kind of optical transforms that make visual holography possible, but in the more abstract sense that all of the information in some spaces ends up on a notional surrounding boundary. The AdS universe is basically a mathematical toy for physicists to play with. It doesn't correspond with the physical structure of the real universe. There's a hope that it might correspond to some kind of mathematical meta-structure that defines physical laws. This article suggests that's very unlikely. Personally I wouldn't be surprised if AdS/CFT turned out to be a dead end - probably like supersymmetry - and the real structure of quantum gravity turned out to be completely different and unexpected, and not a Conformal Field Theory at all. But IANAP, so I may well be wrong about that.

austincheney 7y ago

Does this account for the subject of "dark matter", which at this point is absent from all evidence?

mkl 7y ago
No one would have come up with a hypothesis like dark matter without evidence pointing in that direction: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
- austincheney 7y ago
  Dark matter was hypothesized because the universe is expanding faster than our understanding of gravity allows. The problem in that is if the universe is expanding so fast then something else must be holding galaxies together since galaxies are so incredibly vast and yet contain so very little matter. Particle physics is currently defined according to the Standard Model. Dark matter was proposed because it plugs many of the gaps of universal expansion in contrast to the Standard Model, but not all the gaps. It would take far greater effort to invalidate the Standard Model and all of particular physics built upon it. There is also the problem of not having any other model to replace the current one. https://en.m.wikipedia.org/wiki/Standard_Model https://en.m.wikipedia.org/wiki/Standard_Model The expansion of the universe is observed as red shifts and these observations are numerous and largely uniform. Dark matter, on the other hand, has not been directly observed. * https://arstechnica.com/features/2014/07/dark-matter-makes-up-80-of-the-universe-but-where-is-it-all/ https://arstechnica.com/features/2014/07/dark-matter-makes-u... * https://arstechnica.com/science/2019/11/dark-matter-link-to-regular-matters-dominance-fails-to-show-up/ https://arstechnica.com/science/2019/11/dark-matter-link-to-... * https://arstechnica.com/science/2019/02/more-bad-news-for-controversial-20-year-old-claim-of-dark-matter-detection/ https://arstechnica.com/science/2019/02/more-bad-news-for-co... * https://arstechnica.com/science/2019/04/one-night-of-telescope-time-rules-out-black-holedark-matter-idea/ https://arstechnica.com/science/2019/04/one-night-of-telesco... * https://arstechnica.com/science/2017/02/a-history-of-dark-matter/3/ https://arstechnica.com/science/2017/02/a-history-of-dark-ma... * https://arstechnica.com/science/2016/07/dark-matter-still-mia-after-most-exhaustive-search-yet/ https://arstechnica.com/science/2016/07/dark-matter-still-mi...

makach 7y ago

gravity sucks. thanks for the link :)

dylan604 7y ago
I always thought gravity was much more attractive.

pdonis 7y ago

> we know for a fact that we are getting gravity wrong This statement is way, way too strong. We have a theory of gravity, General Relativity, which has had its predictions confirmed by countless experiments, in some cases to thirteen or fourteen decimal places. That is not "getting it wrong". Many physicists believe that GR, as well confirmed as it is, can't be the final fundamental theory of gravity because it's not a quantum theory. But nobody has yet found a quantum theory of gravity that (a) is consistent with the rest of quantum mechanics, and (b) makes experimental predictions that have been confirmed. Unless and until both (a) and (b) are done, the claim that we are "getting it wrong", even in the restricted sense of not having a final fundamental theory of gravity, because GR isn't a quantum theory is just speculation and might itself be wrong. It should certainly not be stated with the confidence you are stating it.

mnl 7y ago
Now, why am I seeing this factual comment in grey? See here for instance a popsci take on the problem: https://www.scientificamerican.com/article/is-gravity-quantum/ https://www.scientificamerican.com/article/is-gravity-quantu... Everybody expects a quantum theory of gravitation, but if we were drawing it from scratch no one would make it that weak. It is a difficult problem, people work in string theory because you can get Einstein's equations from strings and the alternatives look indeed worse. I don't think that means GR is a wrong take on gravitation, it's more like an amazing one to begin with.
- opless 7y ago
  It's grey because someone in their infinite wisdom downvoted you. Most likely because they'd rather downvote rather than challenge your statement. It's a worrying trend.
JackRabbitSlim 7y ago
GR is no more or less wrong than Newtonian physics.
- flatline 7y ago

m4r35n357 7y ago

Just because quantum physicists can't get their act together over gravitation doesn't make General Relativity wrong! When the lay person reads headlines like this, they assume you are talking about Einstein's theory.