4 ms·

"We find that falling bodies in gravity are subject to random fluctuations (“noise”) whose characteristics depend on the quantum state of the gravitational fiel

by Qw3r7 5y ago

"We find that falling bodies in gravity are subject to random fluctuations (“noise”) whose characteristics depend on the quantum state of the gravitational field. " So I read this, and I have not touched up on physics in awhile, but can someone explain to me the difference between their postulozation and the lumeniferous aether?

bradrn 5y ago
I’m not sure I see any similarities. Could you elaborate on why you think this is similar to the aether theory?
OGMcOW2 5y ago
My very superficial understanding is that the aether was a fictional - fluid and solid - physical medium that was supposed to model behavior but created more problems. Quantum fields are mathematical representations that model physical behavior (including the probabilities inherent in quantum mechanics). Aether, in my interpretation, was a "thing", and quantum fields are just values that describe properties of things. Depending on how crazy you wanna go, that does of course also make them things, and you could also look at the aether as a mathematical abstraction, but afaik, quantum fields work ridiculously well and are a solid theory, while aether - despite maybe being cutting edge at its time - is more one of the homeopathies of physics. That said, I'm sure if looked over by someone who actually studied QT/QM/QFT/GR/SR, they'd find what I wrote to be comically primitive and inaccurate :) edit: punctuation
whatshisface 5y ago
Although aether and fields share a couple similarities, that they're both conceptualized as filling space, and both are wave media, they have a big difference, which is that fields behave the same no matter how fast you are going, whereas aether is like air or water in that you move "though" it. Removing the concept of through-moving from space was one of the big changes that relativity made to scientific thinking. The big consequence of through-moving was that if you send out a wave, and then move through its medium in the direction of the emission, you will "chase after" the wave front and it will escape from you more slowly than if you sat still after sending it. It turns out that this does not happen in real life when the waves involved are light or gravity. Instead, they escape you just as quickly no matter how fast you chase after them. This was discovered in the Michelson-Morley experiment where an attempt was made to detect the motion of the earth through the universe but instead no evidence of moving through the medium that bore light was found. Edit: By the way, I think the downvotes the parent comment received are completely unfair, they are asking for an explanation, not claiming there are no differences.
- jerf 5y ago
  To put it another way, with aether, the zeroth derivative of position may be relative ("above me" may be "below you"), but the first derivative (in principle) had a universally agreeable absolute value as the velocity of something against the universal aether. In current physics, it is only the second derivative that is absolute. We can universally agree how much acceleration something is undergoing, but neither position nor velocity have a method for absolutely measuring them. This can be a difficult distinction to express in English but with this math terminology it should be clear how very significant the difference is.
  - whatshisface 5y ago
    >We can universally agree how much acceleration something is undergoing, You can't tell the difference between acceleration and gravitation. That's the principle of equivalence from general relativity. [0] [0] https://www.physicsoftheuniverse.com/topics_relativity_gravity.html https://www.physicsoftheuniverse.com/topics_relativity_gravi...
    - raattgift 5y ago
      Pretty sure you know this, but for the benefit of other readers, extracting from the SEP we might more properly put this as, "no-one can tell the difference between uniform acceleration and being at rest while immersed in a uniform gravitational field". A uniform gravitational field is not a feature of our universe, and especially not around our planet. More concretely, a necessary condition for a spacetime equipped with a uniform gravitational field is a constant https://en.wikipedia.org/wiki/Scalar_curvature https://en.wikipedia.org/wiki/Scalar_curvature . In sufficiently small (compared to galaxy clusters) patches of our universe we can get an excellent (corrections in less than parts per billion) local approximation of the SEP, however, as tested by human-built space probes like MESSENGER ( https://pgda.gsfc.nasa.gov/products/66 https://pgda.gsfc.nasa.gov/products/66 ) and observations of natural systems like Archibald et al.'s work on the PSR J0337+1715 triple ( https://astrobites.org/2019/03/25/testing-einsteins-equivalence-principle-by-timing-a-pulsar-in-a-stellar-triple-system/ https://astrobites.org/2019/03/25/testing-einsteins-equivale... and to save clicks, here are the linked-to the pre-referreed version https://arxiv.org/abs/1807.02059 https://arxiv.org/abs/1807.02059 and the pretty animation at https://vimeo.com/83397123 https://vimeo.com/83397123 ). Additionally, in our universe one can only accelerate uniformly for a finite time, whereas in a universe equipped with a uniform gravitational field, one can be at rest eternally. The SEP (strong equivalence principle) imposes deep requirements on the mathematical structure of any general (as in insensitive to initial conditions) theory of gravitation that is compatible with it to such high precision and on the mechanisms that generate stress-energy (that is, the non-gravitational behaviour of matter).
kkylin 5y ago
Wilczek himself has been writing / speaking about ether. A couple things I could dig up on short notice: - https://www.quantamagazine.org/why-feynman-diagrams-are-so-important-20160705/ https://www.quantamagazine.org/why-feynman-diagrams-are-so-i... - https://news.asu.edu/20170208-finding-nothing-conversation-frank-wilczek https://news.asu.edu/20170208-finding-nothing-conversation-f... I'm sure there's more, including in Wilczek's book.
- kkylin 5y ago
  Addendum: I was looking for this short article from Physics Today (https://physicstoday.scitation.org/doi/10.1063/1.882562 https://physicstoday.scitation.org/doi/10.1063/1.882562) but page 2 is behind a paywall. Then there's the book (https://www.amazon.com/Lightness-Being-Ether-Unification-Forces-ebook/dp/B007ZDEH0E/ref=sr_1_3?dchild=1&keywords=wilczek&qid=1629514320&sr=8-3 https://www.amazon.com/Lightness-Being-Ether-Unification-For...) which appears to expand on the theme (I've not read it).
steve76 5y ago
- This one has a universal speed limit. Emission theory does not. Huge galaxies blow up. Black holes suck them in and whip them around. Big bang blows everything up. Remnants such as CMB and red shift are measured. Still nothing faster than the universal speed limit. Go any faster nature gobbles you up. - This one has energy quanta. Newton's law of cooling does not. Things need heat before they change their outsides. Poke a hole in oven with something glowing inside. Refract the light. The bands of refracted light don't budge even though temperature goes up. Whatever is glowing radiate lights per packets of heat, or energy, externally transferred. That's not what happens with convective mediums where it's continuous. - Insides can be a medium of interaction. - Outsides do not need to be spatially localized. - Things can exist without any structural insides. That oven's temperature, with its discrete start and end, is a particle in itself. Describing gravity without special relativity, internal clocks ticking differently, is counter-intuitive but can be done. This uses Einstein-Hilbert action. Instead of a distinct space and time properties, it's nature has no mind and does what the surroundings dictate. - Fields can be explained without requiring any mystic interaction in between. Gravity is due to properties of the two objects. There's an extended region around them due to their internals. I found once you get down to it, although it does change the world, the concept is very narrow. The Maxwell equations uses the mean value theorem and Gibb's vector analysis to model the electrical medium of nothing, and pegs it to the observed speed of light, the latency of electromagnetics and telescopes, because they didn't have any observed knowledge to explain it. It speaks to the very high standards and the amount of proven work that's been done before: >As the field interacts with the detector, its quantum state changes because the detector generically both absorbs and emits gravitons through spontaneous and stimulated emission; the final field state jfi is a priori unknown. >The default “classical” treatment of gravitational radiation, which corresponds to coherent states, is appropriate when the sources are governed by approximately deterministic dynamics involving weak linear coupling to the gravitational field. >During the late stages of black hole mergers, the approximation of treating gravitational radiation as a weak linear perturbation is not appropriate, despite the deterministic nature of the dynamics. Here one can expect to encounter effects we might call molding of the quantum radiation state, which go beyond (quadratic) squeezing. Unless you can predict the future, only call me if you're going to blow up two black holes. When you do, it bends a little. Other than that, use the math I already gave you. You can still do a lot. Instruments inside the sun. Matter waves in orbit. Pair production. Nature won't see you coming.

by Qw3r7 5y ago

bradrn 5y ago

I’m not sure I see any similarities. Could you elaborate on why you think this is similar to the aether theory?

OGMcOW2 5y ago

My very superficial understanding is that the aether was a fictional - fluid and solid - physical medium that was supposed to model behavior but created more problems. Quantum fields are mathematical representations that model physical behavior (including the probabilities inherent in quantum mechanics). Aether, in my interpretation, was a "thing", and quantum fields are just values that describe properties of things. Depending on how crazy you wanna go, that does of course also make them things, and you could also look at the aether as a mathematical abstraction, but afaik, quantum fields work ridiculously well and are a solid theory, while aether - despite maybe being cutting edge at its time - is more one of the homeopathies of physics. That said, I'm sure if looked over by someone who actually studied QT/QM/QFT/GR/SR, they'd find what I wrote to be comically primitive and inaccurate :) edit: punctuation

whatshisface 5y ago

Although aether and fields share a couple similarities, that they're both conceptualized as filling space, and both are wave media, they have a big difference, which is that fields behave the same no matter how fast you are going, whereas aether is like air or water in that you move "though" it. Removing the concept of through-moving from space was one of the big changes that relativity made to scientific thinking. The big consequence of through-moving was that if you send out a wave, and then move through its medium in the direction of the emission, you will "chase after" the wave front and it will escape from you more slowly than if you sat still after sending it. It turns out that this does not happen in real life when the waves involved are light or gravity. Instead, they escape you just as quickly no matter how fast you chase after them. This was discovered in the Michelson-Morley experiment where an attempt was made to detect the motion of the earth through the universe but instead no evidence of moving through the medium that bore light was found. Edit: By the way, I think the downvotes the parent comment received are completely unfair, they are asking for an explanation, not claiming there are no differences.

jerf 5y ago
To put it another way, with aether, the zeroth derivative of position may be relative ("above me" may be "below you"), but the first derivative (in principle) had a universally agreeable absolute value as the velocity of something against the universal aether. In current physics, it is only the second derivative that is absolute. We can universally agree how much acceleration something is undergoing, but neither position nor velocity have a method for absolutely measuring them. This can be a difficult distinction to express in English but with this math terminology it should be clear how very significant the difference is.
- whatshisface 5y ago
  >We can universally agree how much acceleration something is undergoing, You can't tell the difference between acceleration and gravitation. That's the principle of equivalence from general relativity. [0] [0] https://www.physicsoftheuniverse.com/topics_relativity_gravity.html https://www.physicsoftheuniverse.com/topics_relativity_gravi...
  - raattgift 5y ago
    Pretty sure you know this, but for the benefit of other readers, extracting from the SEP we might more properly put this as, "no-one can tell the difference between uniform acceleration and being at rest while immersed in a uniform gravitational field". A uniform gravitational field is not a feature of our universe, and especially not around our planet. More concretely, a necessary condition for a spacetime equipped with a uniform gravitational field is a constant https://en.wikipedia.org/wiki/Scalar_curvature https://en.wikipedia.org/wiki/Scalar_curvature . In sufficiently small (compared to galaxy clusters) patches of our universe we can get an excellent (corrections in less than parts per billion) local approximation of the SEP, however, as tested by human-built space probes like MESSENGER ( https://pgda.gsfc.nasa.gov/products/66 https://pgda.gsfc.nasa.gov/products/66 ) and observations of natural systems like Archibald et al.'s work on the PSR J0337+1715 triple ( https://astrobites.org/2019/03/25/testing-einsteins-equivalence-principle-by-timing-a-pulsar-in-a-stellar-triple-system/ https://astrobites.org/2019/03/25/testing-einsteins-equivale... and to save clicks, here are the linked-to the pre-referreed version https://arxiv.org/abs/1807.02059 https://arxiv.org/abs/1807.02059 and the pretty animation at https://vimeo.com/83397123 https://vimeo.com/83397123 ). Additionally, in our universe one can only accelerate uniformly for a finite time, whereas in a universe equipped with a uniform gravitational field, one can be at rest eternally. The SEP (strong equivalence principle) imposes deep requirements on the mathematical structure of any general (as in insensitive to initial conditions) theory of gravitation that is compatible with it to such high precision and on the mechanisms that generate stress-energy (that is, the non-gravitational behaviour of matter).

kkylin 5y ago

Wilczek himself has been writing / speaking about ether. A couple things I could dig up on short notice: - https://www.quantamagazine.org/why-feynman-diagrams-are-so-important-20160705/ https://www.quantamagazine.org/why-feynman-diagrams-are-so-i... - https://news.asu.edu/20170208-finding-nothing-conversation-frank-wilczek https://news.asu.edu/20170208-finding-nothing-conversation-f... I'm sure there's more, including in Wilczek's book.

kkylin 5y ago
Addendum: I was looking for this short article from Physics Today (https://physicstoday.scitation.org/doi/10.1063/1.882562 https://physicstoday.scitation.org/doi/10.1063/1.882562) but page 2 is behind a paywall. Then there's the book (https://www.amazon.com/Lightness-Being-Ether-Unification-Forces-ebook/dp/B007ZDEH0E/ref=sr_1_3?dchild=1&keywords=wilczek&qid=1629514320&sr=8-3 https://www.amazon.com/Lightness-Being-Ether-Unification-For...) which appears to expand on the theme (I've not read it).

steve76 5y ago

- This one has a universal speed limit. Emission theory does not. Huge galaxies blow up. Black holes suck them in and whip them around. Big bang blows everything up. Remnants such as CMB and red shift are measured. Still nothing faster than the universal speed limit. Go any faster nature gobbles you up. - This one has energy quanta. Newton's law of cooling does not. Things need heat before they change their outsides. Poke a hole in oven with something glowing inside. Refract the light. The bands of refracted light don't budge even though temperature goes up. Whatever is glowing radiate lights per packets of heat, or energy, externally transferred. That's not what happens with convective mediums where it's continuous. - Insides can be a medium of interaction. - Outsides do not need to be spatially localized. - Things can exist without any structural insides. That oven's temperature, with its discrete start and end, is a particle in itself. Describing gravity without special relativity, internal clocks ticking differently, is counter-intuitive but can be done. This uses Einstein-Hilbert action. Instead of a distinct space and time properties, it's nature has no mind and does what the surroundings dictate. - Fields can be explained without requiring any mystic interaction in between. Gravity is due to properties of the two objects. There's an extended region around them due to their internals. I found once you get down to it, although it does change the world, the concept is very narrow. The Maxwell equations uses the mean value theorem and Gibb's vector analysis to model the electrical medium of nothing, and pegs it to the observed speed of light, the latency of electromagnetics and telescopes, because they didn't have any observed knowledge to explain it. It speaks to the very high standards and the amount of proven work that's been done before: >As the field interacts with the detector, its quantum state changes because the detector generically both absorbs and emits gravitons through spontaneous and stimulated emission; the final field state jfi is a priori unknown. >The default “classical” treatment of gravitational radiation, which corresponds to coherent states, is appropriate when the sources are governed by approximately deterministic dynamics involving weak linear coupling to the gravitational field. >During the late stages of black hole mergers, the approximation of treating gravitational radiation as a weak linear perturbation is not appropriate, despite the deterministic nature of the dynamics. Here one can expect to encounter effects we might call molding of the quantum radiation state, which go beyond (quadratic) squeezing. Unless you can predict the future, only call me if you're going to blow up two black holes. When you do, it bends a little. Other than that, use the math I already gave you. You can still do a lot. Instruments inside the sun. Matter waves in orbit. Pair production. Nature won't see you coming.