6 ms·

I'm not sure how it's possible to "never touch" a gravitational field given that they extend throughout the universe and are impossible to be shielded.

wilbdhm 5y ago
criddell 5y ago
They touch on that in the article: > Notably, the particles weren’t in a gravitational field–free zone. Instead, the experiment was designed so that the researchers could filter out the effects of gravitational forces, laying bare the eerie Aharonov-Bohm influence. I'm no physicist, but I think they calculated the expected influence and compared that with a measurement.
- pdonis 5y ago
  The "filter out the effects of gravitational forces" means that the measured particles were in free fall; in free fall there is no gravitational force.
  - kenjackson 5y ago
    Is that the common way you'd express that they were measured in free fall -- that the effects were "filtered" out? That seems like an odd way of saying it, but I'm not a physicist.
    - pdonis 5y ago
      I don't think it's a very good way of expressing that the objects were in free fall, no. Nor, as far as I can tell, does the actual paper (as opposed to the pop science article) use such an expression.
PicassoCTs 5y ago
One, in theory could shield of them, by having the same field apply from the opposing direction and distance. So if one could create such a "mirror" copy of all attractors - one would have a L1 Lagrange point. The forces still interact, but chancel each other out.
- pdonis 5y ago
  While this is of course possible in theory, it's not at all what was being done in this experiment.
Arwill 5y ago
They measured a bigger gravitational effect on the particle, because the superpositional pair of the particle flew closer to a mass than the actually measured particle. Regarding the "never touch", gravity decreases with distance squared, so it diminishes quickly with distance. There is a big difference in being near the mass, as opposed to feeling the dimished effect of it from far.
- pdonis 5y ago
  > They measured a bigger gravitational effect on the particle No, they didn't. They measured a phase shift in the particle's wave function. There is no "gravitational force" in free fall, and the particles were in free fall. > gravity decreases with distance squared The Newtonian gravitational force does, but the Newtonian gravitational force is irrelevant for an experiment conducted in free fall, as this one was. The gravitational potential is the key thing being measured, and it's not the potential due to the Earth, it's the potential due to a 1-kg "source mass". > There is a big difference in being near the mass, as opposed to feeling the dimished effect of it from far. The particles were near the 1-kg source mass.
  - hilbert42 5y ago
    "The gravitational potential is the key thing being measured, and it's not the potential due to the Earth, it's the potential due to a 1-kg "source mass"." Right, it seems that for many the 'potential' worldview is hard to grasp (it was for me too until it drawned on me that it's important). I blame this on poor training and poor textbooks, they don't emphasize the importance of potentials. Also, we seem to grow up with a 'fields' perspective, electric fields and so on. Maxwell was on the 'right' path with his original formulation of his equations where potentials were involved. However, when Heaviside reformulated them to the 'vector' view we quickly lost the 'potential' one. No doubt, Heaviside's formulation is incredibly useful in electrical engineering and eleconics and as you'd know that's how they usually appear in textbooks. Trouble is, outside advanced physics texts the 'potential' view is usually omitted. Educators really need to fix this. Another problem is that the description of a potential is not up to scratch. All too often we seem to be stuck with highschool physics descriptions - those that involve pith balls. The concept that we never measure absolute energy, but only differences often gets lost when describing potentials. You'd reckon that after Feynman's well documented whingeing about the fact he wasn't taught about potentials early enough that you'd think by now educators would have had sufficient time to have rewritten their notes but apparently they've not.
pdonis 5y ago
As is unfortunately common in pop science writeups, the article gives a garbled description of what the Aharonov-Bohm effect actually is. The key point is not that "the field never touches the particles". The key point is that the potential, rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potential) is. However, in QM, the potential itself can have observable effects. That's what's going on here, but with the gravitational potential instead of the EM potential (as in the ordinary Aharonov-Bohm effect). The paper itself is here: https://www.science.org/doi/10.1126/science.abl7152 https://www.science.org/doi/10.1126/science.abl7152 It's paywalled and unfortunately I have not been able to find a preprint on arxiv.org.
- Koshkin 5y ago
  > description Importantly, it's "famed" and "eerie."
- mikewarot 5y ago
  You're right, most descriptions of Aharonov-Bohm fail to mention Electromagnetic Potential, and just describe it as quantum woo. I'd love to have an actual quantum detector, like a SQUID, to do some physics experiments with.
  - hilbert42 5y ago
    You'll recall that Feynman whinged about the lack of potentials when he was trained (there bring too much emphasis on fields and almost nothing on potentials). And I reckon he was right to do so for the same reasons, as it took me a considerable amount of time to shift my thinking around to thinking potentials and not fields. Re SQUIDs, likewise, I could amuse myself for ages if I had several to play with.
- hilbert42 5y ago
  "The key point is that the potential, rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potential) is. However, in QM, the potential itself can have observable effects." That comment is short, succinct and understandable, it's the best summary of the physics involved that I've heard in so few words. It seems to me that we don't put sufficient emphasis into considering potentials. Viewing things from the aspect of potentials I reckon changes one's perspective, and I think the Aharonov-Bohm effect is a case in point, without doing so we easily come aground. However, the Aharonov-Bohm effect still perplexes me more than I'd like - in QM, why exactly does potential have observable effects? Why is it that a phase shift occurs in the wave function of a charged particle in the near vicinity of a solenoid even though both magnetic and electric fields are negligible? (I'm either not convinced by explanations that I've heard to date or thst I don't fully understand them.) Whilst my understanding of the Aharonov-Bohm effect is deficient in this regard, it nevertheless seems to me that if the effect can also be detected in a gravitational field context then we've likely found a profound and deeply relevant connection between EM fields/relatively and gravity. If verified, then we'd have to consider it a breakthrough in our understanding of what up until now has been an intractable problem. The key point is that we've now experimental evidence for such a connection and that's really good news.
wongarsu 5y ago
Changes in the gravitational field are only propagated at the speed of light, so in principle you could say something "never touched" a gravitational field if it just hasn't been reached by it yet.

wilbdhm 5y ago

criddell 5y ago

They touch on that in the article: > Notably, the particles weren’t in a gravitational field–free zone. Instead, the experiment was designed so that the researchers could filter out the effects of gravitational forces, laying bare the eerie Aharonov-Bohm influence. I'm no physicist, but I think they calculated the expected influence and compared that with a measurement.

pdonis 5y ago
The "filter out the effects of gravitational forces" means that the measured particles were in free fall; in free fall there is no gravitational force.
- kenjackson 5y ago
  Is that the common way you'd express that they were measured in free fall -- that the effects were "filtered" out? That seems like an odd way of saying it, but I'm not a physicist.
  - pdonis 5y ago
    I don't think it's a very good way of expressing that the objects were in free fall, no. Nor, as far as I can tell, does the actual paper (as opposed to the pop science article) use such an expression.

PicassoCTs 5y ago

One, in theory could shield of them, by having the same field apply from the opposing direction and distance. So if one could create such a "mirror" copy of all attractors - one would have a L1 Lagrange point. The forces still interact, but chancel each other out.

pdonis 5y ago
While this is of course possible in theory, it's not at all what was being done in this experiment.

Arwill 5y ago

They measured a bigger gravitational effect on the particle, because the superpositional pair of the particle flew closer to a mass than the actually measured particle. Regarding the "never touch", gravity decreases with distance squared, so it diminishes quickly with distance. There is a big difference in being near the mass, as opposed to feeling the dimished effect of it from far.

pdonis 5y ago
> They measured a bigger gravitational effect on the particle No, they didn't. They measured a phase shift in the particle's wave function. There is no "gravitational force" in free fall, and the particles were in free fall. > gravity decreases with distance squared The Newtonian gravitational force does, but the Newtonian gravitational force is irrelevant for an experiment conducted in free fall, as this one was. The gravitational potential is the key thing being measured, and it's not the potential due to the Earth, it's the potential due to a 1-kg "source mass". > There is a big difference in being near the mass, as opposed to feeling the dimished effect of it from far. The particles were near the 1-kg source mass.
- hilbert42 5y ago
  "The gravitational potential is the key thing being measured, and it's not the potential due to the Earth, it's the potential due to a 1-kg "source mass"." Right, it seems that for many the 'potential' worldview is hard to grasp (it was for me too until it drawned on me that it's important). I blame this on poor training and poor textbooks, they don't emphasize the importance of potentials. Also, we seem to grow up with a 'fields' perspective, electric fields and so on. Maxwell was on the 'right' path with his original formulation of his equations where potentials were involved. However, when Heaviside reformulated them to the 'vector' view we quickly lost the 'potential' one. No doubt, Heaviside's formulation is incredibly useful in electrical engineering and eleconics and as you'd know that's how they usually appear in textbooks. Trouble is, outside advanced physics texts the 'potential' view is usually omitted. Educators really need to fix this. Another problem is that the description of a potential is not up to scratch. All too often we seem to be stuck with highschool physics descriptions - those that involve pith balls. The concept that we never measure absolute energy, but only differences often gets lost when describing potentials. You'd reckon that after Feynman's well documented whingeing about the fact he wasn't taught about potentials early enough that you'd think by now educators would have had sufficient time to have rewritten their notes but apparently they've not.

pdonis 5y ago

As is unfortunately common in pop science writeups, the article gives a garbled description of what the Aharonov-Bohm effect actually is. The key point is not that "the field never touches the particles". The key point is that the potential, rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potential) is. However, in QM, the potential itself can have observable effects. That's what's going on here, but with the gravitational potential instead of the EM potential (as in the ordinary Aharonov-Bohm effect). The paper itself is here: https://www.science.org/doi/10.1126/science.abl7152 https://www.science.org/doi/10.1126/science.abl7152 It's paywalled and unfortunately I have not been able to find a preprint on arxiv.org.

Koshkin 5y ago
> description Importantly, it's "famed" and "eerie."
mikewarot 5y ago
You're right, most descriptions of Aharonov-Bohm fail to mention Electromagnetic Potential, and just describe it as quantum woo. I'd love to have an actual quantum detector, like a SQUID, to do some physics experiments with.
- hilbert42 5y ago
  You'll recall that Feynman whinged about the lack of potentials when he was trained (there bring too much emphasis on fields and almost nothing on potentials). And I reckon he was right to do so for the same reasons, as it took me a considerable amount of time to shift my thinking around to thinking potentials and not fields. Re SQUIDs, likewise, I could amuse myself for ages if I had several to play with.
hilbert42 5y ago
"The key point is that the potential, rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potential) is. However, in QM, the potential itself can have observable effects." That comment is short, succinct and understandable, it's the best summary of the physics involved that I've heard in so few words. It seems to me that we don't put sufficient emphasis into considering potentials. Viewing things from the aspect of potentials I reckon changes one's perspective, and I think the Aharonov-Bohm effect is a case in point, without doing so we easily come aground. However, the Aharonov-Bohm effect still perplexes me more than I'd like - in QM, why exactly does potential have observable effects? Why is it that a phase shift occurs in the wave function of a charged particle in the near vicinity of a solenoid even though both magnetic and electric fields are negligible? (I'm either not convinced by explanations that I've heard to date or thst I don't fully understand them.) Whilst my understanding of the Aharonov-Bohm effect is deficient in this regard, it nevertheless seems to me that if the effect can also be detected in a gravitational field context then we've likely found a profound and deeply relevant connection between EM fields/relatively and gravity. If verified, then we'd have to consider it a breakthrough in our understanding of what up until now has been an intractable problem. The key point is that we've now experimental evidence for such a connection and that's really good news.

wongarsu 5y ago

Changes in the gravitational field are only propagated at the speed of light, so in principle you could say something "never touched" a gravitational field if it just hasn't been reached by it yet.