6 ms·

It seems the common expectation is that GR is more likely to be the theory that needs to be modified the most - or more or less tossed out and replaced with a q

by zeven7 4y ago

It seems the common expectation is that GR is more likely to be the theory that needs to be modified the most - or more or less tossed out and replaced with a quantum theory of gravity. Is it possible that GR is just "right" and QM needs to be modified to fit into it?

ISL 4y ago
Whenever we learn more about the connections between GR and the rest of physics, the early corrections are likely to appear as "GR+new stuff" or "QM+new stuff". Both theories have enough predictive power that we'll hang on to them as effective theories for the rest of humanity's existence. That said, the mathematical fundamentals of GR do not directly incorporate notions of the uncertainty principle. That fact alone, I believe, means that GR is an incomplete description of space/time/physics.
- raattgift 4y ago
  Just to cause trouble, since we're straying far far from today's presentations (except arguably UCL's Z. Younsi in the ongoing ESO Q&A panel). :-) Can we write down the uncertainty principle in covariant form? Maybe! There is active theoretical work ongoing (e.g.) <https://arxiv.org/abs/2110.15951v2 https://arxiv.org/abs/2110.15951v2> ("... a geometric formalism for the generalised uncertainty principle which is covariant and connects features of the underlying geometry with the deformation of canonical commutator relations ... [and] an elegant interpretation for the standard dispersion relation p^2=−m^2: it describes flat spacetime in the Milne coordinates, with rest mass m giving the measure of geodesic length from origin").
- brabel 4y ago
  As I understand it, quantum physicis essentially predicts that the randomness of quantum fields effectively disappears at scales of just micrometers, let alone at the scale GR works on. How is the uncertainty principle supposed to affect bodies at the scale of light years?
sillysaurusx 4y ago
The most likely explanation is that we have no clue, just like every other point in history. Science is always new. Everyone is different, but most scientists seek areas where experiment doesn’t match the predictions. It’s the only way we learn. One such instance is the W Boson Anomaly: https://vm.tiktok.com/ZTdpwrmoj/?k=1 https://vm.tiktok.com/ZTdpwrmoj/?k=1 If the equations were right, the experimental error would be zero (modulo uncertainty bars). Instead, we’re quite confident the standard model is wrong (or “incomplete” to phrase it diplomatically). As an aside, this is also a great example of TikTok turning a corner. I now have 184 educational videos saved, along with dozens of science videos. I learn more on TikTok than any other source now, which I didn’t expect. There’s an avid physicist community, and I made friends with someone who works at CERN. https://twitter.com/simoneragoni?s=21&t=xIkxhA--TzKDWA5XN3veMw https://twitter.com/simoneragoni?s=21&t=xIkxhA--TzKDWA5XN3ve... Get ready for TikTok to become the new Wikipedia within a decade.
- deleted 4y ago
  [deleted]
- KineticLensman 4y ago
  > Get ready for TikTok to become the new Wikipedia within a decade. I've also learned a lot from TikTok, where short form content has led to 30 second tutorials that leave 30 minute YouTube equivalents in their dust. My learning topics include smartphone photography, wood working, and knots. I was also surprised at how informative it can be. It'll be interesting to see how TikTok's content moderation compares against Wikipedia. We won't have notability wars, but there is massive scope for disinformation and banal wrongness.
- dahdum 4y ago
  > As an aside, this is also a great example of TikTok turning a corner. I now have 184 educational videos saved, along with dozens of science videos. I learn more on TikTok than any other source now, which I didn’t expect. I too have been surprised with the amount of genuinely educational and interesting material on TikTok. It won't replace Wikipedia but it's a great companion to it.
- babypuncher 4y ago
kloch 4y ago
We can't even measure the gravitational constant to more than about 4.5 significant digits. Most other natural constants are in the 7-12 digit range and improving along with our technology. Measurement of big G hasn't convincingly progressed since the vacuum tube era. We have a lot more to learn about gravity, especially at laboratory scale and smaller.
- ISL 4y ago
  As a laboratory-scale experimentalist, I heartily agree, but must also point out the existence of compelling precision equivalence principle tests. While we can only measure G to ~10 ppm, the equivalence principle has been tested at the 10^{-14} level (and ~10^{-9} at meter-scales). The EP is the property that makes gravity really special and simultaneously the thing that makes gravity hard to test. The core assertion that all things fall the same way is axiomatic to GR and has been very well tested. We have everything left to learn about gravity, but at the same time, GR has held up far better than it "should" have against a battery of really great experiments.

by zeven7 4y ago

ISL 4y ago

Whenever we learn more about the connections between GR and the rest of physics, the early corrections are likely to appear as "GR+new stuff" or "QM+new stuff". Both theories have enough predictive power that we'll hang on to them as effective theories for the rest of humanity's existence. That said, the mathematical fundamentals of GR do not directly incorporate notions of the uncertainty principle. That fact alone, I believe, means that GR is an incomplete description of space/time/physics.

raattgift 4y ago
Just to cause trouble, since we're straying far far from today's presentations (except arguably UCL's Z. Younsi in the ongoing ESO Q&A panel). :-) Can we write down the uncertainty principle in covariant form? Maybe! There is active theoretical work ongoing (e.g.) <https://arxiv.org/abs/2110.15951v2 https://arxiv.org/abs/2110.15951v2> ("... a geometric formalism for the generalised uncertainty principle which is covariant and connects features of the underlying geometry with the deformation of canonical commutator relations ... [and] an elegant interpretation for the standard dispersion relation p^2=−m^2: it describes flat spacetime in the Milne coordinates, with rest mass m giving the measure of geodesic length from origin").
brabel 4y ago
As I understand it, quantum physicis essentially predicts that the randomness of quantum fields effectively disappears at scales of just micrometers, let alone at the scale GR works on. How is the uncertainty principle supposed to affect bodies at the scale of light years?

sillysaurusx 4y ago

The most likely explanation is that we have no clue, just like every other point in history. Science is always new. Everyone is different, but most scientists seek areas where experiment doesn’t match the predictions. It’s the only way we learn. One such instance is the W Boson Anomaly: https://vm.tiktok.com/ZTdpwrmoj/?k=1 https://vm.tiktok.com/ZTdpwrmoj/?k=1 If the equations were right, the experimental error would be zero (modulo uncertainty bars). Instead, we’re quite confident the standard model is wrong (or “incomplete” to phrase it diplomatically). As an aside, this is also a great example of TikTok turning a corner. I now have 184 educational videos saved, along with dozens of science videos. I learn more on TikTok than any other source now, which I didn’t expect. There’s an avid physicist community, and I made friends with someone who works at CERN. https://twitter.com/simoneragoni?s=21&t=xIkxhA--TzKDWA5XN3veMw https://twitter.com/simoneragoni?s=21&t=xIkxhA--TzKDWA5XN3ve... Get ready for TikTok to become the new Wikipedia within a decade.

deleted 4y ago
[deleted]
KineticLensman 4y ago
> Get ready for TikTok to become the new Wikipedia within a decade. I've also learned a lot from TikTok, where short form content has led to 30 second tutorials that leave 30 minute YouTube equivalents in their dust. My learning topics include smartphone photography, wood working, and knots. I was also surprised at how informative it can be. It'll be interesting to see how TikTok's content moderation compares against Wikipedia. We won't have notability wars, but there is massive scope for disinformation and banal wrongness.
dahdum 4y ago
> As an aside, this is also a great example of TikTok turning a corner. I now have 184 educational videos saved, along with dozens of science videos. I learn more on TikTok than any other source now, which I didn’t expect. I too have been surprised with the amount of genuinely educational and interesting material on TikTok. It won't replace Wikipedia but it's a great companion to it.
babypuncher 4y ago

kloch 4y ago

We can't even measure the gravitational constant to more than about 4.5 significant digits. Most other natural constants are in the 7-12 digit range and improving along with our technology. Measurement of big G hasn't convincingly progressed since the vacuum tube era. We have a lot more to learn about gravity, especially at laboratory scale and smaller.

ISL 4y ago
As a laboratory-scale experimentalist, I heartily agree, but must also point out the existence of compelling precision equivalence principle tests. While we can only measure G to ~10 ppm, the equivalence principle has been tested at the 10^{-14} level (and ~10^{-9} at meter-scales). The EP is the property that makes gravity really special and simultaneously the thing that makes gravity hard to test. The core assertion that all things fall the same way is axiomatic to GR and has been very well tested. We have everything left to learn about gravity, but at the same time, GR has held up far better than it "should" have against a battery of really great experiments.