I was wondering last night: are any of the fundamental forces "blocked" by an intervening object? I assume not, since there is nothing like that in the equations. But that is kind of interesting, since sometimes you hear talk of hypothetical particles like gravitons.
From the article: "The result does not unite quantum mechanics and gravity, nor does it show that gravity itself is quantum".
I must say, it's actually quite refreshing to read an article about a science topic that conveys the caveats and limitations of the study. Far too many of these studies get filtered through the news outlet hype-machine
The article says that this proves that Einstein's equivalence principle (resulting in relativity) holds in this test of a falling quantum particle (where gravity results in a phase shift in the quantum state).
It doesn't show/prove how general relativity and quantum mechanics interact.
NOTE: The Dirac equation and Quantum Electro Dynamics (QED) unify quantum mechanics and special relativity (non-accelerating frames of reference).
So the remaining piece is either to extend QED/QCD to accelerating frames of reference or to quantize general relativity. That would likely predict the phase shift observed in this experiment.
> The Dirac equation and Quantum Electro Dynamics (QED) unify quantum mechanics and special relativity
And more generally the Standard Model, which includes the weak and strong interactions. The SM is a quantum field theory, which, as you say, unifies QM and SR.
> (non-accelerating frames of reference).
No, SR and QFT are not limited to non-accelerating frames. They are limited to small enough regions of spacetime that spacetime curvature is negligible. This experiment is an illustration of that: it compares an accelerated atom with a free-falling atom to show the phase shift between them, and the lab frame in which it is done is accelerated--but the SM and SR work just fine. But the experiment does not show any effects of spacetime curvature.
> the remaining piece is either to extend QED/QCD to accelerating frames of reference
No, that's already done. See above.
> or to quantize general relativity.
That's the big missing piece, yes. We know how to write the QFT of a massless spin-2 field (which is our naive expectation of what a QFT for gravity would look like), and we know that the classical limit of that QFT is the classical GR we have now. But we know that QFT has to be just an effective theory, just like the Standard Model; it can't be the final answer.
> That would likely predict the phase shift observed in this experiment.
The theories we already have (Standard Model + the equivalence principle are all we actually need) are sufficient to predict that. Of course any more comprehensive theory will have to reproduce that prediction, yes.
> the remaining piece is either to extend QED/QCD to accelerating frames of reference or to quantize general relativity
Quantum field theory in accelerating frames of reference is old hat; poster children like the Unruh effect [1] and Hawking radiation [2] are from the 1970s.
Unfounded speculation, but is it possible that every particle could have a different individual light speed, and the one we know is just the average speed that they have to drop or speed up to, the way a car needs to travel at the same speed as the highway?
By "every particle" do you mean like, every type of particle?
If you mean individual particles, fundamental particles don't really have distinct individual identities (as shown by fermi and bose statistics).
As for types of particles: Well, photons surely move at the speed photons move at.
Special relativity is derived from the assumption/observation that light travels at the same speed in all inertial reference frames, and generally that the laws of physics work the same in any inertial reference frame.
What you are proposing sounds pretty vague and unclear to me, but, is what you are trying to say compatible with this?
I was wondering last night: are any of the fundamental forces "blocked" by an intervening object? I assume not, since there is nothing like that in the equations. But that is kind of interesting, since sometimes you hear talk of hypothetical particles like gravitons.
There is a GREAT, accessible video about this experiment here:
https://www.youtube.com/watch?v=CfjnTJos_no
Thanks! We'll put that link in the toptext as well.
So do we finally have one unified theory or are we still none the wiser?
From the article: "The result does not unite quantum mechanics and gravity, nor does it show that gravity itself is quantum".
I must say, it's actually quite refreshing to read an article about a science topic that conveys the caveats and limitations of the study. Far too many of these studies get filtered through the news outlet hype-machine
If you'd learn about a proposed experiment to test the quantum nature of gravity, this is a cool video:
https://www.youtube.com/watch?v=Uey_mUy1vN0
Hopefully we'll see a result in the next decade
The article says that this proves that Einstein's equivalence principle (resulting in relativity) holds in this test of a falling quantum particle (where gravity results in a phase shift in the quantum state).
It doesn't show/prove how general relativity and quantum mechanics interact.
NOTE: The Dirac equation and Quantum Electro Dynamics (QED) unify quantum mechanics and special relativity (non-accelerating frames of reference).
So the remaining piece is either to extend QED/QCD to accelerating frames of reference or to quantize general relativity. That would likely predict the phase shift observed in this experiment.
> The Dirac equation and Quantum Electro Dynamics (QED) unify quantum mechanics and special relativity
And more generally the Standard Model, which includes the weak and strong interactions. The SM is a quantum field theory, which, as you say, unifies QM and SR.
> (non-accelerating frames of reference).
No, SR and QFT are not limited to non-accelerating frames. They are limited to small enough regions of spacetime that spacetime curvature is negligible. This experiment is an illustration of that: it compares an accelerated atom with a free-falling atom to show the phase shift between them, and the lab frame in which it is done is accelerated--but the SM and SR work just fine. But the experiment does not show any effects of spacetime curvature.
> the remaining piece is either to extend QED/QCD to accelerating frames of reference
No, that's already done. See above.
> or to quantize general relativity.
That's the big missing piece, yes. We know how to write the QFT of a massless spin-2 field (which is our naive expectation of what a QFT for gravity would look like), and we know that the classical limit of that QFT is the classical GR we have now. But we know that QFT has to be just an effective theory, just like the Standard Model; it can't be the final answer.
> That would likely predict the phase shift observed in this experiment.
The theories we already have (Standard Model + the equivalence principle are all we actually need) are sufficient to predict that. Of course any more comprehensive theory will have to reproduce that prediction, yes.
Can one really derive classical GR completely from a QFT of a spin-2 field? Or only a linear approximation?
> the remaining piece is either to extend QED/QCD to accelerating frames of reference or to quantize general relativity
Quantum field theory in accelerating frames of reference is old hat; poster children like the Unruh effect [1] and Hawking radiation [2] are from the 1970s.
[1] https://en.wikipedia.org/wiki/Unruh_effect
[2] https://en.wikipedia.org/wiki/Hawking_radiation
so many great PBS Space Time on this concept
* https://www.youtube.com/@pbsspacetime/search?query=graviton
Unfounded speculation, but is it possible that every particle could have a different individual light speed, and the one we know is just the average speed that they have to drop or speed up to, the way a car needs to travel at the same speed as the highway?
By "every particle" do you mean like, every type of particle?
If you mean individual particles, fundamental particles don't really have distinct individual identities (as shown by fermi and bose statistics).
As for types of particles: Well, photons surely move at the speed photons move at.
Special relativity is derived from the assumption/observation that light travels at the same speed in all inertial reference frames, and generally that the laws of physics work the same in any inertial reference frame.
What you are proposing sounds pretty vague and unclear to me, but, is what you are trying to say compatible with this?
Probably no, because according to quantum mechanics, photons are indistinguishable in a way that affects experiments.
What measurable predictions does this hypothesis make that would differ from the existing models?
Well, yeah. Perhaps if this experiment was expanded for a chain or a filter of cause and effect then it could be shown that one event affects another.
I'm sorry for me , for Einstein and for you but i can t read this article because is written in the occupy Land of فلسطين
There will be no science studies without humans. What do you think of Human Zoo Safari?
Free Palestine
> Please don't use Hacker News for political or ideological battle. It tramples curiosity.
https://news.ycombinator.com/newsguidelines.html