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MathMonkeyMan 2 days ago [-]
Here's the [paper][1] on the arxiv.
I found it hard to believe that they accounted for other forces precisely enough that they could attribute the phase change to gravity, but this is beyond me so I trust the result.
At first I thought "they showed that you can measure a particle falling in gravity," which seemed dumb because we already know that particles fall in gravity. But they showed that you can measure a single (aggregate) particle falling in gravity, which is pretty cool because if gravity is quantum then that means that they observed an interaction between the graviton and their rubidium atom.
Their point is measuring gravity's influence on a single particle is not necessarily evidence of the existence of the graviton.
omnicognate 1 days ago [-]
Nobody's claiming it is.
NuclearPM 1 days ago [-]
“ if gravity is quantum then that means that they observed an interaction between the graviton and their rubidium atom.”
jacquesm 24 hours ago [-]
'if'
fizzbuzzbarbazz 24 hours ago [-]
That's pretty pedantic. They were simply addressing one branch of the if, so their statement was relevant.
gps372 1 days ago [-]
Actually, we do need evidence for premises which are not definitions or basic assumptions (axioms). Graviton is still a hypothetical particle and falls under neither of two categories - Definitions or axioms.
simiones 24 hours ago [-]
The statement "if gravity is quantum, this was an interaction with a graviton" is true even if it ultimately turns out that gravity is not quantum. The statement is about the consequences of a premise, and is not falsified if that premise is false.
The only way this statement could be false would be to have quantum gravity but no particle that mediates this interaction - which doesn't seem plausible almost by definition.
gps372 23 hours ago [-]
>> The only way this statement could be false
That's quite an exotic claim! If Sound and Temperature can emerge without a sound particle or temperature particle, why is it not plausible for gravity to exists without graviton?
Though, I get it that mainstream view from physicists is Graviton is the most 'likely' cause, if the gravity is proven to be quantized. But even they would have the humility to accept that this is a theory yet to be proven and observed!
simiones 22 hours ago [-]
Their statement has two possibilities:
A: If gravity is quantum, then (B) there must be some particle-like think that we call a graviton that mediates the interactions, and then seeing a rubidium atom fall must have been an interaction with this particle.
not A: If gravity is not quantum, then they are making no claims about a graviton.
If you think gravity is not quantum, then you go to the "not A" branch, and they make no claims about that branch - so there is no contradiction with their IF.
However, for me to claim that quantum Gravity is only emergent without a particle like graviton's mediation, I would need to present evidence. Just like this claim - quantum gravity is only possible from gravitons.
LoganDark 1 days ago [-]
That doesn't stop us from imagining what something could mean in the context of gravitons if evidence of them ever does turn up.
Yizahi 22 hours ago [-]
This is a global issue with modern particle physics - scientists imagine something and then blink, and two decades and a hundred of books had been published while that something is still not present in any test. It would be fine if that happened rarely, but it seems that it's just par for course nowadays.
LoganDark 17 hours ago [-]
This is literally everything ever, not just particle physics or even physics in general.
TheOtherHobbes 1 days ago [-]
It's a quiet test of Penrose's idea that gravitational interactions cause objective collapse of superposition.
Maybe there's something subtle in the details which explains why it isn't that, but it certainly looks adjacent to it - although maybe not deliberately?
theturtletalks 23 hours ago [-]
Is this the basis of gravitational propulsion engines?
cineticdaffodil 1 days ago [-]
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gaze 2 days ago [-]
Vlatko tends to show up on papers with let's say, big claims. Consider the superconducting qubit/Tardigrade paper https://arxiv.org/abs/2112.07978
MarkusQ 1 days ago [-]
Vlatko Vedral (of Oxford) to be clear.
(He's listed as V. Vedral on the Tardigrade paper you linked, and it's more common to use last names in this context.)
pjungwir 2 days ago [-]
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.
EA-3167 2 days ago [-]
Blocked? No. Greatly attenuated and restricted in what modes can be accommodated? Yes.
More critically though the study gets into how they used a reference wave packet to establish a stationary baseline for the interferometer. Assuming the experiment is sufficiently isolated to reduce noise below the necessary threshold this can work in principle.
> Blocked? No. Greatly attenuated and restricted in what modes can be accommodated? Yes.
Can you give me some examples? I guess I'm thinking lead barriers or a Bose Einstein condensate but curious what you mean here.
AlotOfReading 1 days ago [-]
Your house has walls to attenuate photons.
EA-3167 1 days ago [-]
Casimir plates are a good example, although Faraday cages are probably better known along with Mu-metal.
Ono-Sendai 1 days ago [-]
That's a very deep question. In some sense no, in some sense yes.
I would say on the deepest level, no, they are not blocked.
24 hours ago [-]
hoppp 2 days ago [-]
I am not very well versed in the subject but
if quantum objects can fall and multiple quantum waves can occupy the same space, then why doesn't everything always collapse into a single point?
Why does it only happen in black holes and outside of that quantum waves instead create emergent systems instead of just collapsing together?
Does high gravitational force nullify emergence in space/time?
Might be a stupid question. I don't study this subject much.
hgoel 2 days ago [-]
They can't exactly occupy the same space due to the Pauli exclusion principle. IIRC that's believed to be the final "barrier" that prevents neutron stars from collapsing into black holes. But this is also getting into the tricky parts of wave particle duality, so the precise details are a bit difficult for me too.
limaoscarjuliet 1 days ago [-]
Only cats can violate Pauli's principle. Anybody who had a cat can attest to the fact they can go through walls. Just close a room with a cat inside and - given enough time - the cat will escape.
mettamage 1 days ago [-]
So Schrödinger’s cat has an orthogonal state!
(not inside the box)
codeduck 23 hours ago [-]
Actually, the third possible state is Bloody Furious.
robocat 1 days ago [-]
How could you measure that the cat was inside the room?
zdragnar 23 hours ago [-]
Thermal residue?
GoblinSlayer 1 days ago [-]
If particles were zero size, they would be already black holes. That's the fix introduced by string theory: particles aren't zero size there.
EA-3167 2 days ago [-]
It's not a stupid question at all, here's the answer:
Electrons (as an example) experience Coulomb pressure (charge repulsion), but also a quantum statistical pressure called Fermi Degeneracy pressure related to their kinetic energy, AND ultimately the Pauli Exclusion Principle (Identical Fermions cannot occupy the same state, but higher momentum states take more energy to reach naturally so this creates resistance to collapse). If you want to learn more about this you can get a lot of mileage out of some reading on Fermi-Dirac statistics, the Pauli Exclusion Principle, and degeneracy pressure. Now this is just using electrons as a model, but ultimately all of the above can be overcome by gravity. When it does you still can't have electrons disobeying the rules, but the potential energy barrier to merge electrons and protons into neutrons is overcome. THEN you have neutron degeneracy pressure, and in theory after that you have a black hole (spacetime singularity surrounded by an event horizon.
However... that may not be the case. It is true that observation has confirmed the existence of objects that are so dense and massive they must have an event horizon, but beyond that we have no way of direct observation, right now (even in principle). A lot of people believe this indicates that a singularity doesn't really exist; it's the usual lesson when a singularity appears in your math: your math is wrong. In the end maybe there's another sort of degeneracy pressure from quarks or something even more fundamental like strings that ultimately prevents final collapse to a true singularity.
ed: typos
hoppp 1 days ago [-]
Thanks! Lots of information for me to learn about.
I assumed they can occupy the same space due to superposition principle, as waves could stack and modulate each other, sort of like wave A and wave B occupying the same space could produce a wave A+B
So a singular point would be the sum of all waves occupying the space.
But maybe gravity or spacetime itself is a recursive function and black holes are functions without a base case and there is no singular point, only non-terminating recursion.
Some ideas to funnel into AI so I can entertain myself hah
robochat 1 days ago [-]
The world is made of two types of particle - fermions and bosons. A difference between them is that fermions can not occupy the same quantum state (the Pauli exclusion principle) while bosons can exist as superpositions. Matter is made of electrons, protons and neutrons which are fermions, while the forces are photons, gluons, W , Z and Higgs which are bosons.
In a black hole though … who knows
simiones 23 hours ago [-]
There is a difference between "being in a superposition" and "occupying the same space". The uncertainty principle basically tells you that an electron is never in a defined place - it exists with some probability in many different places (technically it could be at a definite position, but only if it had completely indefinite momentum, and that's not physically meaningful given energy constraints).
Now, say we have an experiment where two different sources each fire one electron in some direction; and say the electrons have the same spin and other properties except for their initial position and momentum. We can meaningfully say that for a certain location between the two sources there is some > 0 probability for either electron to be there, so the amplitude of each electron's wavefunction at that position is > 0. However, that doesn't mean we can ever find both electrons at that same postion at the same time: the individual wavefunctions are just parts of the two-electron system's wavefunction, and, per the Pauli exclusion principle, that one will be 0 for any state of the form "electron A at position x and electron B at position x". So, for any position, you can find either electron there, but never both.
An additional wrinkle is that this only applies for two identical electrons. If the electrons have different spins, then they can actually be found at the same location at the same time. You can have a spin-up and a spin-down electron in the same place at the same time, but not two spin-up electrons. This is the fundamental property of fermions. However, you can have any number of identical photons at the same location - that's the fundamental property of bosons.
hammock 4 days ago [-]
There is a GREAT, accessible video about this experiment here:
Thanks! We'll put that link in the toptext as well.
canadiantim 2 days ago [-]
Any explanation by Roger Penrose is bound to be good
thrance 2 days ago [-]
Except when he's rambling about quantum consciousness or other nonsense, which happens a lot nowadays.
qsera 1 days ago [-]
>quantum consciousness or other nonsense
Can you tell me why it is non-sense?
We, through our senses perceive a world. This world we try to understand using physics. But these perceptions itself stands on top of consciousness. So consciousness is at least, as real as the world that physics conventionally tries to reason about. It could be even more fundamental, because you can have only consciousness in this universe, but still could sense a whole universe with "things" inside it. But without consciousness, and just a universe with "things", there is no "sensing"...
Point is, physics should include study of consciousness...
mr_toad 24 hours ago [-]
> But these perceptions itself stands on top of consciousness.
There’s plenty of evidence for unconscious perception.
qsera 23 hours ago [-]
Sure, but I don't think when a person does a physics experiment, the perceptions involved are unconscious.
yreg 1 days ago [-]
Have you actually hear him talk about it? It is very far from rambling and he will be the first to tell you that he is not sure he is right.
We need physicists to come up with and develop novel ideas to consider no matter how many of them might be entirely wrong.
thrance 1 days ago [-]
There's a difference between making and testing hypotheses, and desperately scrambling to find proof to justify a conclusion made in advance in the face of mounting evidence that said conclusion is false, which is what Penrose is doing regarding quantum consciousness.
Grossly simplifying: he is a dualist, he wants to reconcile his belief in the soul and his physicist's materialist view of biology, so he resorts to putting the source of consciousness in quantum phenomenas, and seeks to prove that they occur in the brain. I disagree that there's an immaterial soul, I disagree that it puppets the material universe through quantum phenomenas, and I disagree that there are important quantum phenomenas in the brain. Most physicists are with me on these.
qsera 1 days ago [-]
>source of consciousness in quantum phenomenas, and seeks to prove that they occur in the brain
I think he should look for consciousness as the source of quantum phenomena. Not the other way around. But as he is a physicist, all nails looks like a physics problem.
It is the same situation where people might have struggled to explain the heavenly observation using an earth centric model. Once you invert the wrong premise that you consider as fundamental, the answer, previously so elusive, becomes trivial...
yreg 1 days ago [-]
I'm with you regarding opinion on consciousness, but do you think it would be 'better' if there were no dualists and no dualist essays and ideas?
Because I hardly think so.
This is not like alternative medicine where there is harm for people who don't follow the mainstream. And I stress again that Penrose (in the interviews I saw) doesn't actually claim that he absolutely has to be right.
thrance 1 days ago [-]
> do you think it would be 'better' if there were no dualists and no dualist essays and ideas?
No of course not, people should be free to discuss and believe in dualism. What I find regrettable, is how often Penrose's name is invoked in an appeal to authority, as if his past (and very valuable) contributions to physics were enough to make him right on everything, including this subject.
Ultimately, I believe dualism is wrong, and I believe I have good reasons to think so. My previous comment was simply my attempt at deconstructing Penrose's argument, participating in the ever-ongoing popular debate.
jacquesm 24 hours ago [-]
> My previous comment was simply my attempt at deconstructing Penrose's argument, participating in the ever-ongoing popular debate.
That may be so, but just the mention of Penrose's name in the context of something else caused you to start a whole subthread that had nothing to do with the subject.
thrance 23 hours ago [-]
It was not "just the mention of Penrose's name", it was this comment specifically:
> "Any explanation by Roger Penrose is bound to be good"
Is something wrong with my original comment?
yreg 1 days ago [-]
Fair enough, I can see that.
GoblinSlayer 1 days ago [-]
If mind was random, people would miscalculate 1+1 with 50% probability. So earth might be flat, but it's unlikely.
yreg 1 days ago [-]
> If mind was random, people would miscalculate 1+1 with 50% probability.
That does not follow at all.
GoblinSlayer 1 days ago [-]
Miscalculation doesn't follow from randomness?
yreg 1 days ago [-]
If you run an LLM (with temp >0) and use a true random generator for seeds, it will still tell you 1+1 is 2.
GoblinSlayer 23 hours ago [-]
You mean mind is deterministic and cancels all noise? Then what quantum physics would do there?
yreg 23 hours ago [-]
You don't need to cancel all the noise to solve 1+1 correctly. The model in the example is non-deterministic.
I don't know Penrose's view deeply enough to defend it further (view which I for the record do not share).
GoblinSlayer 20 hours ago [-]
He's just rambling.
j16sdiz 22 hours ago [-]
Where did the 50% came from?!
Many phenomenon emerge from randomness with very high probability just because the law of large number.
GoblinSlayer 20 hours ago [-]
It's statistics that emerges with very high probability due to the law of large numbers. If you calculate 1+1=2 with 100% probability, then quantum physics doesn't meaningfully participate in your reasoning, not more than brownian motion.
randomImmigrant 1 days ago [-]
You know, I pooh poohed his theories. Still do in sum. But there’s a there there that’s building.
Damn Deepak Chopra and his ilk of idiots for making any conversation of quantum mechanics and biology tinged with pseudoscience. Hopefully we’ll keep getting experimental evidence as we go that it’s not at all absurd to consider quantum effects in biology.
That said, those effects are going to look nothing like sustained coherence for long periods of time.
MarkusQ 1 days ago [-]
They didn't start the fire. Quantum + biology → Woo has been with us since the 1960s at least.
20 hours ago [-]
stared 2 days ago [-]
Is it a subtle effect that cannot be explained by Newtonian gravity (i.e. a different potential affecting, V(z) in the Hamiltonian)?
traes 1 days ago [-]
No. From the paper linked above [0]:
> The phase of free fall is predicted in a purely quantum manner to have a dependence m/6 g^2T^3/ℏ + gmzT on the free-fall time T, where m is the mass of the object, g is the gravitational acceleration relative to the surface of Earth, and z in the spatial coordinate in the direction of gravity. This
prediction follows the calculated phase accumulated by an object accelerating in a linear potential, and has been made starting from almost one hundred years ago by Darwin, Kennard and others.
Apparently the phase shift is derivable from just adding a linear potential term mgz to the Hamiltonian.
So do we finally have one unified theory or are we still none the wiser?
rhdunn 2 days ago [-]
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.
pdonis 2 days ago [-]
> 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.
rhdunn 1 days ago [-]
My understanding is that 1) SR doesn't consider acceleration (it's an extension of Galilean/uniform motion), and that 2) when Einstein considered acceleration as well as gravity via the equivalence principle which lead to GR [1]. The key insight of the equivalence principle was that the force from gravity (e.g. standing on the Earth) is no different to the observer in their frame of reference to them being in a room in a rocket accelerating at the same rate as gravity [1], [2].
Thus, if you extend QED/QCD/SM in a similar way (thinking of QED/QCD/SM extensions in terms of acceleration and curved space with the equivalence principle in mind) that may lead to a quantized theory of gravity. -- Sir Roger Penrose has a similar idea/thinking [3].
One of the key challenges with quantizing gravity is in how the terms in the expressions resulting from analyzing the Feynman diagram interactions behave [4] which prevent them being renormalized. For electromagnetism you can formulate the terms using the fine structure constant (via the coulomb potential, ħ, and c) which results in successive terms decreasing in value and thus stabilizing to a single value.
For gravity using Newton's relationship between two masses in a similar way to deriving the fine structure constant you get Gm^2/ħc. Applying E=mc^2 gives GE^2/ħc^5. Using the Planck energy constant gives (E/E_p)^2 for the energy coupling strength. This means that unlike electromagnetism, the successive terms in the Feynman diagram analysis grows exponentially instead of decreasing to 0. Thus, this approach to quantization doesn't work for gravity.
Note: you can still use this to analyze quantum gravitational effects at small energies by evaluating to a given number of terms.
> One of the key challenges with quantizing gravity is in how the terms in the expressions resulting from analyzing the Feynman diagram interactions behave [4] which prevent them being renormalized.
Not being renormalizable actually isn't a problem in itself if you view the theory as an effective theory, valid only up to some energy scale, not beyond that. You can still use the theory to make some predictions, as long as you're careful. But that does mean that the QFT of a massless spin-2 field can't be a fundamental theory of gravity; it can only be an effective theory, that approximates something deeper.
pdonis 11 hours ago [-]
> SR doesn't consider acceleration
As I said, this is not correct. Early on, in the first years after Einstein published his papers, there were physicists who believed this (and IIRC Einstein was initially one of them), but that was well over a century ago. We've made a lot of progress since then, and part of that progress is understanding that SR can handle acceleration just fine, as long as spacetime is flat.
> when Einstein considered acceleration as well as gravity via the equivalence principle which lead to GR
The equivalence principle as Einstein first came up with it was actually about free fall. What he called "the happiest thought of my life" was "if a person falls freely, they will not feel their own weight". In modern terminology, we would say that, if you are dealing with a small enough piece of spacetime, you can treat it as flat, even if the spacetime globally is curved. And that means you can use all of the physics of SR in that small piece of spacetime. And that turns out to be a key piece of getting to GR, how to handle spacetimes that are globally curved.
> The key insight of the equivalence principle was that the force from gravity (e.g. standing on the Earth) is no different to the observer in their frame of reference to them being in a room in a rocket accelerating at the same rate as gravity
This was a further development of the equivalence principle from the free-fall version I described above. But note what it implies: it implies that, in modern terminology, treating a small enough piece of spacetime as flat works even if we adopt an accelerating reference frame in that small piece. Physics ultimately looks the same whether we adopt the frame of the object freely falling in the elevator/towards the Earth's surface, or the accelerated frame of the elevator/observer standing on the surface of the Earth. SR handles both just fine.
Where SR breaks down is when we need to extend our analysis beyond a small piece of spacetime--when the effects of spacetime curvature start to show up. That's when we need GR.
Again, all these implications were not necessarily clear to physicists a century ago. But they are now, and have been for decades.
uecker 2 days ago [-]
Can one really derive classical GR completely from a QFT of a spin-2 field? Or only a linear approximation?
pdonis 11 hours ago [-]
All of it. The theoretical work that showed this was done in the 1960s and early 1970s by Feynman, Deser, and others. One of the key insights was figuring out how to reformulate the theory so that it did not require an infinite series of terms, whose sum nobody knew how to calculate, in order to derive the exact field equation correct to all orders. IIRC Deser was the one who figured that out, and he published a paper in the early 1970s that summarized the research.
T-A 2 days ago [-]
> 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.
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
Mizza 2 days ago [-]
If you'd learn about a proposed experiment to test the quantum nature of gravity, this is a cool video:
I'm way in over my depth here, but does this maybe that the unification of gravity and quantum physics is further out of reach than we might have hoped? Because it would be easier if gravity disappeared at quantum scales - then it could be understood as an emergent property that emerges out of quantum when you move to bigger scales. But now we have to find something that underlies both.
qsera 1 days ago [-]
I have, but no one takes it seriously. But who cares, one needs to answer ones own questions, and not of the entire world.
rimworld 1 hours ago [-]
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ziomerlojahsay 2 days ago [-]
[flagged]
0x62 2 days ago [-]
> Please don't use Hacker News for political or ideological battle. It tramples curiosity.
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?
drdeca 2 days ago [-]
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?
setopt 2 days ago [-]
Probably no, because according to quantum mechanics, photons are indistinguishable in a way that affects experiments.
exe34 2 days ago [-]
What measurable predictions does this hypothesis make that would differ from the existing models?
hyperhello 2 days ago [-]
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.
exe34 2 days ago [-]
As opposed to current models, where one event does not affect subsequent events?
hyperhello 1 days ago [-]
Good god, sorry I participated in any way. Apparently there’s a quantum physics colloquium I’m disturbing.
exe34 1 days ago [-]
I'm sorry, I thought you knew how scientific ideas were discussed, I didn't know you were just trying to bootstrap a new religion.
ars 1 days ago [-]
Before you figure that out, you will be surprised to discover that it's impossible to tell if the speed of light is the same in both directions, with only the average of a round trip being the speed of light.
Anyway, reading that should help you answer your own question, or at least give you a lot more questions to ask.
irjustin 1 days ago [-]
Criticism: It's not literally impossible.
I hate this one because it's true Einstein said we cannot measure the speed of light in one direction that is independent of the clocks' synchronization technique being used to measure.
And yet, somehow we changed that to "we don't know the speed of light in one direction!!!" Which is bogus - can you imagine if speed of light was different if you were pointing east vs west? In space, what is even a direction vs another?
Did you even read the wiki you linked? We've done one-way speeds, it's down below.
zmgsabst 23 hours ago [-]
How do you synchronize the clocks and compute the measurement, without depending on the conclusion?
You run into a similar problem with Michelson-Morley: because the apparatus and the light both get distorted by any motion, you can’t even in principle detect the aether wind with interferometry. You need a non-comoving dynamic source, eg, LIGO with black hole collisions.
Their one-way experiments seem to require similar, ie, we can observe dynamics but cannot measure a static bias.
2 days ago [-]
dmfdmf 2 days ago [-]
I thought QM and GR were mathematically incompatible. How do you even perform an experiment without accepting one frame or the other? Sus.
traes 1 days ago [-]
Seems like they just added a linear gravitational potential term mgz to their hamiltonian and computed the phase change it would induce. They claim they experimentally confirmed the phase change. I didn't think that worked! They also claim its consistent with some kind of GR derivation, but I haven't looked at that.
I found it hard to believe that they accounted for other forces precisely enough that they could attribute the phase change to gravity, but this is beyond me so I trust the result.
At first I thought "they showed that you can measure a particle falling in gravity," which seemed dumb because we already know that particles fall in gravity. But they showed that you can measure a single (aggregate) particle falling in gravity, which is pretty cool because if gravity is quantum then that means that they observed an interaction between the graviton and their rubidium atom.
[1]: https://arxiv.org/pdf/2502.14535
You don't need evidence to support a premise.
The only way this statement could be false would be to have quantum gravity but no particle that mediates this interaction - which doesn't seem plausible almost by definition.
That's quite an exotic claim! If Sound and Temperature can emerge without a sound particle or temperature particle, why is it not plausible for gravity to exists without graviton?
Though, I get it that mainstream view from physicists is Graviton is the most 'likely' cause, if the gravity is proven to be quantized. But even they would have the humility to accept that this is a theory yet to be proven and observed!
A: If gravity is quantum, then (B) there must be some particle-like think that we call a graviton that mediates the interactions, and then seeing a rubidium atom fall must have been an interaction with this particle.
not A: If gravity is not quantum, then they are making no claims about a graviton.
If you think gravity is not quantum, then you go to the "not A" branch, and they make no claims about that branch - so there is no contradiction with their IF.
However, for me to claim that quantum Gravity is only emergent without a particle like graviton's mediation, I would need to present evidence. Just like this claim - quantum gravity is only possible from gravitons.
Maybe there's something subtle in the details which explains why it isn't that, but it certainly looks adjacent to it - although maybe not deliberately?
(He's listed as V. Vedral on the Tardigrade paper you linked, and it's more common to use last names in this context.)
More critically though the study gets into how they used a reference wave packet to establish a stationary baseline for the interferometer. Assuming the experiment is sufficiently isolated to reduce noise below the necessary threshold this can work in principle.
https://www.science.org/doi/10.1126/sciadv.aec8045
Can you give me some examples? I guess I'm thinking lead barriers or a Bose Einstein condensate but curious what you mean here.
if quantum objects can fall and multiple quantum waves can occupy the same space, then why doesn't everything always collapse into a single point?
Why does it only happen in black holes and outside of that quantum waves instead create emergent systems instead of just collapsing together?
Does high gravitational force nullify emergence in space/time?
Might be a stupid question. I don't study this subject much.
(not inside the box)
Electrons (as an example) experience Coulomb pressure (charge repulsion), but also a quantum statistical pressure called Fermi Degeneracy pressure related to their kinetic energy, AND ultimately the Pauli Exclusion Principle (Identical Fermions cannot occupy the same state, but higher momentum states take more energy to reach naturally so this creates resistance to collapse). If you want to learn more about this you can get a lot of mileage out of some reading on Fermi-Dirac statistics, the Pauli Exclusion Principle, and degeneracy pressure. Now this is just using electrons as a model, but ultimately all of the above can be overcome by gravity. When it does you still can't have electrons disobeying the rules, but the potential energy barrier to merge electrons and protons into neutrons is overcome. THEN you have neutron degeneracy pressure, and in theory after that you have a black hole (spacetime singularity surrounded by an event horizon.
However... that may not be the case. It is true that observation has confirmed the existence of objects that are so dense and massive they must have an event horizon, but beyond that we have no way of direct observation, right now (even in principle). A lot of people believe this indicates that a singularity doesn't really exist; it's the usual lesson when a singularity appears in your math: your math is wrong. In the end maybe there's another sort of degeneracy pressure from quarks or something even more fundamental like strings that ultimately prevents final collapse to a true singularity.
ed: typos
I assumed they can occupy the same space due to superposition principle, as waves could stack and modulate each other, sort of like wave A and wave B occupying the same space could produce a wave A+B
So a singular point would be the sum of all waves occupying the space.
But maybe gravity or spacetime itself is a recursive function and black holes are functions without a base case and there is no singular point, only non-terminating recursion.
Some ideas to funnel into AI so I can entertain myself hah
In a black hole though … who knows
Now, say we have an experiment where two different sources each fire one electron in some direction; and say the electrons have the same spin and other properties except for their initial position and momentum. We can meaningfully say that for a certain location between the two sources there is some > 0 probability for either electron to be there, so the amplitude of each electron's wavefunction at that position is > 0. However, that doesn't mean we can ever find both electrons at that same postion at the same time: the individual wavefunctions are just parts of the two-electron system's wavefunction, and, per the Pauli exclusion principle, that one will be 0 for any state of the form "electron A at position x and electron B at position x". So, for any position, you can find either electron there, but never both.
An additional wrinkle is that this only applies for two identical electrons. If the electrons have different spins, then they can actually be found at the same location at the same time. You can have a spin-up and a spin-down electron in the same place at the same time, but not two spin-up electrons. This is the fundamental property of fermions. However, you can have any number of identical photons at the same location - that's the fundamental property of bosons.
https://www.youtube.com/watch?v=CfjnTJos_no
Can you tell me why it is non-sense?
We, through our senses perceive a world. This world we try to understand using physics. But these perceptions itself stands on top of consciousness. So consciousness is at least, as real as the world that physics conventionally tries to reason about. It could be even more fundamental, because you can have only consciousness in this universe, but still could sense a whole universe with "things" inside it. But without consciousness, and just a universe with "things", there is no "sensing"...
Point is, physics should include study of consciousness...
There’s plenty of evidence for unconscious perception.
We need physicists to come up with and develop novel ideas to consider no matter how many of them might be entirely wrong.
Grossly simplifying: he is a dualist, he wants to reconcile his belief in the soul and his physicist's materialist view of biology, so he resorts to putting the source of consciousness in quantum phenomenas, and seeks to prove that they occur in the brain. I disagree that there's an immaterial soul, I disagree that it puppets the material universe through quantum phenomenas, and I disagree that there are important quantum phenomenas in the brain. Most physicists are with me on these.
I think he should look for consciousness as the source of quantum phenomena. Not the other way around. But as he is a physicist, all nails looks like a physics problem.
It is the same situation where people might have struggled to explain the heavenly observation using an earth centric model. Once you invert the wrong premise that you consider as fundamental, the answer, previously so elusive, becomes trivial...
Because I hardly think so.
This is not like alternative medicine where there is harm for people who don't follow the mainstream. And I stress again that Penrose (in the interviews I saw) doesn't actually claim that he absolutely has to be right.
No of course not, people should be free to discuss and believe in dualism. What I find regrettable, is how often Penrose's name is invoked in an appeal to authority, as if his past (and very valuable) contributions to physics were enough to make him right on everything, including this subject.
Ultimately, I believe dualism is wrong, and I believe I have good reasons to think so. My previous comment was simply my attempt at deconstructing Penrose's argument, participating in the ever-ongoing popular debate.
That may be so, but just the mention of Penrose's name in the context of something else caused you to start a whole subthread that had nothing to do with the subject.
> "Any explanation by Roger Penrose is bound to be good"
Is something wrong with my original comment?
That does not follow at all.
I don't know Penrose's view deeply enough to defend it further (view which I for the record do not share).
Many phenomenon emerge from randomness with very high probability just because the law of large number.
Damn Deepak Chopra and his ilk of idiots for making any conversation of quantum mechanics and biology tinged with pseudoscience. Hopefully we’ll keep getting experimental evidence as we go that it’s not at all absurd to consider quantum effects in biology.
That said, those effects are going to look nothing like sustained coherence for long periods of time.
> The phase of free fall is predicted in a purely quantum manner to have a dependence m/6 g^2T^3/ℏ + gmzT on the free-fall time T, where m is the mass of the object, g is the gravitational acceleration relative to the surface of Earth, and z in the spatial coordinate in the direction of gravity. This prediction follows the calculated phase accumulated by an object accelerating in a linear potential, and has been made starting from almost one hundred years ago by Darwin, Kennard and others.
Apparently the phase shift is derivable from just adding a linear potential term mgz to the Hamiltonian.
[0]: https://arxiv.org/pdf/2502.14535
* https://www.youtube.com/@pbsspacetime/search?query=graviton
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.
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.
Thus, if you extend QED/QCD/SM in a similar way (thinking of QED/QCD/SM extensions in terms of acceleration and curved space with the equivalence principle in mind) that may lead to a quantized theory of gravity. -- Sir Roger Penrose has a similar idea/thinking [3].
One of the key challenges with quantizing gravity is in how the terms in the expressions resulting from analyzing the Feynman diagram interactions behave [4] which prevent them being renormalized. For electromagnetism you can formulate the terms using the fine structure constant (via the coulomb potential, ħ, and c) which results in successive terms decreasing in value and thus stabilizing to a single value.
For gravity using Newton's relationship between two masses in a similar way to deriving the fine structure constant you get Gm^2/ħc. Applying E=mc^2 gives GE^2/ħc^5. Using the Planck energy constant gives (E/E_p)^2 for the energy coupling strength. This means that unlike electromagnetism, the successive terms in the Feynman diagram analysis grows exponentially instead of decreasing to 0. Thus, this approach to quantization doesn't work for gravity.
Note: you can still use this to analyze quantum gravitational effects at small energies by evaluating to a given number of terms.
[1] https://www.britannica.com/story/how-albert-einstein-develop...
[2] https://www.ebsco.com/research-starters/physics/equivalence-...
[3] https://www.youtube.com/watch?v=VQM0OtxvZ-Y "We need to 'gravitise' quantum mechanics, not quantise gravity | Roger Penrose | Full interview"
[4] https://www.youtube.com/watch?v=yTEPm5d6mrI "Why Quantum Gravity Doesn't Work"
Not being renormalizable actually isn't a problem in itself if you view the theory as an effective theory, valid only up to some energy scale, not beyond that. You can still use the theory to make some predictions, as long as you're careful. But that does mean that the QFT of a massless spin-2 field can't be a fundamental theory of gravity; it can only be an effective theory, that approximates something deeper.
As I said, this is not correct. Early on, in the first years after Einstein published his papers, there were physicists who believed this (and IIRC Einstein was initially one of them), but that was well over a century ago. We've made a lot of progress since then, and part of that progress is understanding that SR can handle acceleration just fine, as long as spacetime is flat.
> when Einstein considered acceleration as well as gravity via the equivalence principle which lead to GR
The equivalence principle as Einstein first came up with it was actually about free fall. What he called "the happiest thought of my life" was "if a person falls freely, they will not feel their own weight". In modern terminology, we would say that, if you are dealing with a small enough piece of spacetime, you can treat it as flat, even if the spacetime globally is curved. And that means you can use all of the physics of SR in that small piece of spacetime. And that turns out to be a key piece of getting to GR, how to handle spacetimes that are globally curved.
> The key insight of the equivalence principle was that the force from gravity (e.g. standing on the Earth) is no different to the observer in their frame of reference to them being in a room in a rocket accelerating at the same rate as gravity
This was a further development of the equivalence principle from the free-fall version I described above. But note what it implies: it implies that, in modern terminology, treating a small enough piece of spacetime as flat works even if we adopt an accelerating reference frame in that small piece. Physics ultimately looks the same whether we adopt the frame of the object freely falling in the elevator/towards the Earth's surface, or the accelerated frame of the elevator/observer standing on the surface of the Earth. SR handles both just fine.
Where SR breaks down is when we need to extend our analysis beyond a small piece of spacetime--when the effects of spacetime curvature start to show up. That's when we need GR.
Again, all these implications were not necessarily clear to physicists a century ago. But they are now, and have been for decades.
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
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
https://www.youtube.com/watch?v=Uey_mUy1vN0
Hopefully we'll see a result in the next decade
https://news.ycombinator.com/newsguidelines.html
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?
See: https://en.wikipedia.org/wiki/One-way_speed_of_light
Anyway, reading that should help you answer your own question, or at least give you a lot more questions to ask.
I hate this one because it's true Einstein said we cannot measure the speed of light in one direction that is independent of the clocks' synchronization technique being used to measure.
And yet, somehow we changed that to "we don't know the speed of light in one direction!!!" Which is bogus - can you imagine if speed of light was different if you were pointing east vs west? In space, what is even a direction vs another?
Did you even read the wiki you linked? We've done one-way speeds, it's down below.
You run into a similar problem with Michelson-Morley: because the apparatus and the light both get distorted by any motion, you can’t even in principle detect the aether wind with interferometry. You need a non-comoving dynamic source, eg, LIGO with black hole collisions.
Their one-way experiments seem to require similar, ie, we can observe dynamics but cannot measure a static bias.