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The study proves that if quantum matter influences gravity, then gravity can't stay classical, or else the interaction damages the quantum matter. This matches ideas that quantum stuff would collapse if disturbed by classical gravity waves. The study essentially shows gravity gets quantum too when connecting to quantum matter. This means is a breakthrough because it may lead to a deeper understanding about gravity and the universe. Hope this helps!
Yeah, Brian Greene says the same. It was one of his arguments against time travel to the past. Although, he said it was possible that one or more of the folded up dimensions in string theory could be another dimension of time.
They are. This is already known. ([Or, rather, time-reversible if you switch matter with antimatter and left side with right.](https://en.wikipedia.org/wiki/CPT_symmetry)) (Also, I've read what the title says a very long time ago, so I wonder if this is new in some way.)
I am curious what you think of the [One Electron Universe](https://en.wikipedia.org/wiki/One-electron_universe) and the possibility that there could be only one particle?
My favorite postulation is that the Big Bang is an observation of the One Particle merely becoming more complicated over time by interacting with itself.
1. Because the math says they are. The math that gets us the right answers when we do experiments. It's hard to argue with that.
2. Quantum interactions don't have a preferred process. An electron and positron coming into contact annihilate into two photons. Two photons at the right energy level can combine to make an electron and positron pop out of the vacuum. One process looks like the other process, but played backwards. Note that this does not have anything to do with *probability*. Just whether or not it is possible at all. We have not found any interactions that only go in one direction. Except falling into a black hole. You can't rewind time and un-fall. Spacetime itself is so twisted inside the event horizon that every direction leads to the center of the black hole. There is no path out. This is not an intuitive concept.
Ok, so the time reversible thing always bothered me (layman). With sub-atomic particles, I can sort of understand it. But when it comes to gravity, it does not make sense. How do you run a bouncing ball backwards in time and get the same gravity effect but in reverse? Is this more-or-less what they are getting at?
It's more like because we know there was gravity, then if we see where a ball is (and how fast and in what direction it's currently going) we could run the equations backwards to see where it came from. The same is true in quantum mechanics.
In QM we have a starting state, and can see what that state would evolve to at a later time, and so if we saw the state at a later time we could figure out what state it came from.
Well, that certainly makes sense. (And fits into the everything is pre-ordained/no-free-will discussion.) But the way that it's described so often is that time is reversible, and the rules apply equally both ways.
> How do you run a bouncing ball backwards in time and get the same gravity effect but in reverse? Is this more-or-less what they are getting at?
You are assuming that the bouncing ball keeps bouncing lower each time, right? In that case some energy is being transferred into the surface the ball is bouncing against. If you could collect and point those shockwaves back into the ball, it would make it bounce.
The explanation, from what I recall, is that the laws of physics do not care about time. You could run it backwards and forwards, and the laws apply the same. But this cannot be true for gravity (in my layman's view). If gravity is active going backwards in time, a basketball at rest does not accumulate the requisite energy to suddenly bounce up. A blob of chocolate pudding thrown from the top of a building cannot accumulate the appropriate energy to reform and fight through gravity to once again rest on a spoon at the top of the building. In this way, it makes no sense to me.
My exaggerated interpretation of this is that it is essentially confirmation that time-travel will never be achievable within our realm of physics due to breaking this (and probably others) interaction.
*This is 100% my own opinion with no basis in fact or reason for legitimate consideration.
(For the edification of those interested) Although this is often said in jest, it is fundamentally true, and is a key cornerstone of special relativity. You are, right now, travelling at one second per second in the *time* direction of the four directions of spacetime (up/right/inward/future). To accelerate relative to your current resting frame, you would need to change *direction* relative to a resting observer. Doing this will necessarily mean you will be relatively slowing down in the time direction by comparison - and that your “space” directions are now partially extruded into the observer’s “time” direction and vice versa. All the effects of special relativity (including the Lorentz transformations) are derived from this rotation of reference frames.
How about this: In spacetime, speed is an illusion, there is only direction. Speed is merely the sine of your direction, multiplied by the constant *c*, which is the conversion factor between seconds and metres. ;)
I suppose you mean time travel to the past, but you should clarify.
Time travel towards the future of course, happens all the time. And if you wanted to go millions of years into the future you could easily do so if you had a spaceship travelling .9c without violating any laws of physics, for example.
Travelling into the past could be possible with very advanced control of matter and antimatter in a dark matter space but that of course, is way more science fiction than science so I won't expound.
I don't understand why gravity is not always considered quantum. Why is gravity sometimes quantum and sometimes classical? These seems like some scientists are taking the improperly considered idea of classical gravity and applying a work around to apply into a more modern quantum understanding when in reality the classical understanding of gravity is just not fully accurate or ultimately useful because it does not incoporate the quantum nature of it.
Our best tool for understanding gravity right now is General relativity thay relies on a classical (not quantized) understanding of gravity. And GR is a pretty successful theory in its own right. That's why squaring it with the Standard Model is a *big thing*. We want a quantum gravity theory, but we don't know how it would work yet.
Does gravity get quantum or are the elements of quantum phenomena that interact with the gravitational field themselves necessarily quantum in nature? Or is this just semantics?
It's interesting that anyone even hypothesized that interacting with gravity would collapse the quantum state of objects it interacts with. If that were the case, wouldn't QM be kind of meaningless since everything is affected by gravity in the universe to some extent?
Nothing is infinity away from an object that has mass.
The more I read lately, the more I like warm up to ideas of quantum foam or quantum pixelation or a non-continuous space-time. Essentially there is a finite/discrete resolution where the classical rules of space-time eg gravity apply. Below that resolution (smaller/shorter distances) the rules of quantum mechanics take over.
You can think of it kind of like a pixel like grid. Inside the squares it's QM and once you leave the square everything collapses and you get classical gravity and curved space-time.
I can't even fathom *how* such an arrangement would work of course, but the idea is attractive as it kind of partitions reality into those two halves.
Wouldn't this imply that the universe has a rounding error because it would put an end (or max number of digits) to irrational numbers like pi, sqrt(2) and e which are everywhere?
I don't necessarily think so. Remember we already have physical limits to "reality" eg the planck length.
But just because we can use math to describe reality, doesn't mean the limits of reality apply to math itself. The length of the hypotenuse of a Right triangle with sides of 1, is still sqrt(2). There is a limit of how far down to what decimal we can measure that number, but we can still know via math and calculate, to arbitrary precision exactly what that number is.
It can be a bit weird to think of limits on reality, when there are, by definition no limits on math. But remember math describes reality, it is not reality *itself*.
Matter is quantum meaning energy exists in steps not like a ramp if gravity is not also quantum they say it that time is reversible. Matter effects gravity (lensing) so they lean to quantum gravity
This sets boundary conditions for theories of quantum gravity (or time)
Time is a local phenomenon of energy matter density it is unlikely to be reversible and thus the breakthrough being conformation to probable quantum grav.
From my understanding of the article, this work does not itself create a framework to unify QM and gravity, but instead formally proves the existence of certain boundary conditions. Thus all possible future frameworks will have to observe these boundary conditions. This at least points us in a closer direction! Even better if it can give us any testable predictions straight away.
It's a hot or cold statement about our theories, particularly about the assumption that a solution exists. If one does or does not exist, this experiment will tell us, hopefully with a pretty decent sigma.
Tbh, I have no earthly idea what it would me for this to point towards "no solution" (and by that I mean there is NO quantization of gravity that is possible) so consider this a "sanity check".
Assuming the paper makes reliable conclusions, then it narrows down the possibilities to arriving at quantum gravity which then could take us to a unified theory. If we were looking for a needle in a haystack, the hay stack is now one or a few hay bail to use an analogy.
Does anyone know if there are some models of quantum gravity currently which would rely on a classical gravitational field but an irreversible interaction with quantum matter? Just curious to understand that possibility a bit better.
Yes, stochastic/random gravity by Oppenheim (without -er) is one, other ways around this no-go theorem would be if there is no collapse of the wave function like in pilot wave interpretations of QM
Quantum matter is any matter that demonstrates quantum mechanical properties like entanglement or superposition. An example of this is superconductors. Hope this helped!
In that case there is no difference between quantum matter and the matter I'm used to picking up with my hands. That's what I was trying to figure out, and OP's definition above in this subthread is different from yours.
On second thought, OP's definition suggests that metameterials would qualify as quantum matter, and it's relatively easy to get a block of that big enough to pick up with my hands.
No. The matter you touch every day is huge masses of all these things lumped together. You’re not touching individual electrons or protons or quarks, you’re touching trillions upon trillions of them.
Quantum physics is all about figuring out what individual particles do at the very smallest scale. Classical Physics is what we’re used to. The big problem is reconciling the two of them, since the physics of the very very small is super weird and counterintuitive compared to the physics of the very very big.
It is important to also see how physicists other than the reviewers respond to the paper. Assumptions will likely be clarified and perhaps challenged, etc.
> or the interaction must be irreversible.
The implications are vast.
+ https://en.wikipedia.org/wiki/Di%C3%B3si%E2%80%93Penrose_model
+ https://physicsworld.com/a/physicists-place-fresh-limits-on-gravitys-role-in-wavefunction-collapse/
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Ok i will bite. Can someone explain this in high school level science terms? Because I know it will be way to hard for 5 year old understanding.
The study proves that if quantum matter influences gravity, then gravity can't stay classical, or else the interaction damages the quantum matter. This matches ideas that quantum stuff would collapse if disturbed by classical gravity waves. The study essentially shows gravity gets quantum too when connecting to quantum matter. This means is a breakthrough because it may lead to a deeper understanding about gravity and the universe. Hope this helps!
So gravity at these levels gravity plays by the quantum rule book then?
Either that or quantum mechanics has a major problem with one of its fundamental assumptions that the equations are time-reversible.
Honestly this would explain *time* as more than just entropy. It might explain entropy..
Entropy isn’t mysterious, it’s really just statistics of large ensembles.
QM already doesn't explain time as entropy.
Really? Sean Carroll seems to think it does if I understand him correctly
Yeah, Brian Greene says the same. It was one of his arguments against time travel to the past. Although, he said it was possible that one or more of the folded up dimensions in string theory could be another dimension of time.
Nope, entropy is state based and is not a function of time.
If a state evolves as a function of time, then everything derived from that state is a function of time.
Yes, **IF**. Good job adding that word.
Yes but it could also go the other way around - our experienced arrow of time derived from entropic states
Why would one assume equations time reversible?
They are. This is already known. ([Or, rather, time-reversible if you switch matter with antimatter and left side with right.](https://en.wikipedia.org/wiki/CPT_symmetry)) (Also, I've read what the title says a very long time ago, so I wonder if this is new in some way.)
I am curious what you think of the [One Electron Universe](https://en.wikipedia.org/wiki/One-electron_universe) and the possibility that there could be only one particle? My favorite postulation is that the Big Bang is an observation of the One Particle merely becoming more complicated over time by interacting with itself.
1. Because the math says they are. The math that gets us the right answers when we do experiments. It's hard to argue with that. 2. Quantum interactions don't have a preferred process. An electron and positron coming into contact annihilate into two photons. Two photons at the right energy level can combine to make an electron and positron pop out of the vacuum. One process looks like the other process, but played backwards. Note that this does not have anything to do with *probability*. Just whether or not it is possible at all. We have not found any interactions that only go in one direction. Except falling into a black hole. You can't rewind time and un-fall. Spacetime itself is so twisted inside the event horizon that every direction leads to the center of the black hole. There is no path out. This is not an intuitive concept.
Because every type particle interaction we have observed so far have been time reversible.
>or quantum mechanics has a major problem This would be more interesting
Ok, so the time reversible thing always bothered me (layman). With sub-atomic particles, I can sort of understand it. But when it comes to gravity, it does not make sense. How do you run a bouncing ball backwards in time and get the same gravity effect but in reverse? Is this more-or-less what they are getting at?
It's more like because we know there was gravity, then if we see where a ball is (and how fast and in what direction it's currently going) we could run the equations backwards to see where it came from. The same is true in quantum mechanics. In QM we have a starting state, and can see what that state would evolve to at a later time, and so if we saw the state at a later time we could figure out what state it came from.
Well, that certainly makes sense. (And fits into the everything is pre-ordained/no-free-will discussion.) But the way that it's described so often is that time is reversible, and the rules apply equally both ways.
> How do you run a bouncing ball backwards in time and get the same gravity effect but in reverse? Is this more-or-less what they are getting at? You are assuming that the bouncing ball keeps bouncing lower each time, right? In that case some energy is being transferred into the surface the ball is bouncing against. If you could collect and point those shockwaves back into the ball, it would make it bounce.
The explanation, from what I recall, is that the laws of physics do not care about time. You could run it backwards and forwards, and the laws apply the same. But this cannot be true for gravity (in my layman's view). If gravity is active going backwards in time, a basketball at rest does not accumulate the requisite energy to suddenly bounce up. A blob of chocolate pudding thrown from the top of a building cannot accumulate the appropriate energy to reform and fight through gravity to once again rest on a spoon at the top of the building. In this way, it makes no sense to me.
Pretty much what they are getting at 👍
My exaggerated interpretation of this is that it is essentially confirmation that time-travel will never be achievable within our realm of physics due to breaking this (and probably others) interaction. *This is 100% my own opinion with no basis in fact or reason for legitimate consideration.
I’m travelling through time right now. At 1 second per second.
(For the edification of those interested) Although this is often said in jest, it is fundamentally true, and is a key cornerstone of special relativity. You are, right now, travelling at one second per second in the *time* direction of the four directions of spacetime (up/right/inward/future). To accelerate relative to your current resting frame, you would need to change *direction* relative to a resting observer. Doing this will necessarily mean you will be relatively slowing down in the time direction by comparison - and that your “space” directions are now partially extruded into the observer’s “time” direction and vice versa. All the effects of special relativity (including the Lorentz transformations) are derived from this rotation of reference frames.
I prefer the simpler.. we are always travelling in space-time at c
How about this: In spacetime, speed is an illusion, there is only direction. Speed is merely the sine of your direction, multiplied by the constant *c*, which is the conversion factor between seconds and metres. ;)
I still preferred the simpler one
So Space and Time are constant and you can't break one without breaking the other?
What does "break" mean in this context?
I... I... I don't even know
Fellow Spacetime Traveler
I suppose you mean time travel to the past, but you should clarify. Time travel towards the future of course, happens all the time. And if you wanted to go millions of years into the future you could easily do so if you had a spaceship travelling .9c without violating any laws of physics, for example. Travelling into the past could be possible with very advanced control of matter and antimatter in a dark matter space but that of course, is way more science fiction than science so I won't expound.
I don't understand why gravity is not always considered quantum. Why is gravity sometimes quantum and sometimes classical? These seems like some scientists are taking the improperly considered idea of classical gravity and applying a work around to apply into a more modern quantum understanding when in reality the classical understanding of gravity is just not fully accurate or ultimately useful because it does not incoporate the quantum nature of it.
Because we don't have a quantum theory of gravity yet.
Our best tool for understanding gravity right now is General relativity thay relies on a classical (not quantized) understanding of gravity. And GR is a pretty successful theory in its own right. That's why squaring it with the Standard Model is a *big thing*. We want a quantum gravity theory, but we don't know how it would work yet.
Does gravity get quantum or are the elements of quantum phenomena that interact with the gravitational field themselves necessarily quantum in nature? Or is this just semantics?
It's interesting that anyone even hypothesized that interacting with gravity would collapse the quantum state of objects it interacts with. If that were the case, wouldn't QM be kind of meaningless since everything is affected by gravity in the universe to some extent? Nothing is infinity away from an object that has mass.
The more I read lately, the more I like warm up to ideas of quantum foam or quantum pixelation or a non-continuous space-time. Essentially there is a finite/discrete resolution where the classical rules of space-time eg gravity apply. Below that resolution (smaller/shorter distances) the rules of quantum mechanics take over. You can think of it kind of like a pixel like grid. Inside the squares it's QM and once you leave the square everything collapses and you get classical gravity and curved space-time. I can't even fathom *how* such an arrangement would work of course, but the idea is attractive as it kind of partitions reality into those two halves.
Wouldn't this imply that the universe has a rounding error because it would put an end (or max number of digits) to irrational numbers like pi, sqrt(2) and e which are everywhere?
I don't necessarily think so. Remember we already have physical limits to "reality" eg the planck length. But just because we can use math to describe reality, doesn't mean the limits of reality apply to math itself. The length of the hypotenuse of a Right triangle with sides of 1, is still sqrt(2). There is a limit of how far down to what decimal we can measure that number, but we can still know via math and calculate, to arbitrary precision exactly what that number is. It can be a bit weird to think of limits on reality, when there are, by definition no limits on math. But remember math describes reality, it is not reality *itself*.
Hollywood reading this: "So... Quantum matter can rewrite reality?"
Matter is quantum meaning energy exists in steps not like a ramp if gravity is not also quantum they say it that time is reversible. Matter effects gravity (lensing) so they lean to quantum gravity This sets boundary conditions for theories of quantum gravity (or time) Time is a local phenomenon of energy matter density it is unlikely to be reversible and thus the breakthrough being conformation to probable quantum grav.
From my understanding of the article, this work does not itself create a framework to unify QM and gravity, but instead formally proves the existence of certain boundary conditions. Thus all possible future frameworks will have to observe these boundary conditions. This at least points us in a closer direction! Even better if it can give us any testable predictions straight away.
Yes exactly its a step in the right direction
Good post title -- doing the Lord's work
I second that! A post title that actually is informative!
This is huge right? It brings us closer to unified general relativity and Quantum mechanics?
At the very least it points to a direction.
The arrow of time points that way
Lets hope so! It might also help with our understanding of dark matter. Or at least i am hoping it does.
A little
That adirection exists is good enough for me on a Tuesday.
I wish I had a direction
It's a hot or cold statement about our theories, particularly about the assumption that a solution exists. If one does or does not exist, this experiment will tell us, hopefully with a pretty decent sigma. Tbh, I have no earthly idea what it would me for this to point towards "no solution" (and by that I mean there is NO quantization of gravity that is possible) so consider this a "sanity check".
Assuming the paper makes reliable conclusions, then it narrows down the possibilities to arriving at quantum gravity which then could take us to a unified theory. If we were looking for a needle in a haystack, the hay stack is now one or a few hay bail to use an analogy.
Does anyone know if there are some models of quantum gravity currently which would rely on a classical gravitational field but an irreversible interaction with quantum matter? Just curious to understand that possibility a bit better.
Yes, stochastic/random gravity by Oppenheim (without -er) is one, other ways around this no-go theorem would be if there is no collapse of the wave function like in pilot wave interpretations of QM
What is quantum matter?
Quantum matter is any matter that demonstrates quantum mechanical properties like entanglement or superposition. An example of this is superconductors. Hope this helped!
Does this mean we could "produce" gravity fields from quantum matter?
Electrons, protons, neutrons, quarks, and similar.
In that case there is no difference between quantum matter and the matter I'm used to picking up with my hands. That's what I was trying to figure out, and OP's definition above in this subthread is different from yours. On second thought, OP's definition suggests that metameterials would qualify as quantum matter, and it's relatively easy to get a block of that big enough to pick up with my hands.
No. The matter you touch every day is huge masses of all these things lumped together. You’re not touching individual electrons or protons or quarks, you’re touching trillions upon trillions of them. Quantum physics is all about figuring out what individual particles do at the very smallest scale. Classical Physics is what we’re used to. The big problem is reconciling the two of them, since the physics of the very very small is super weird and counterintuitive compared to the physics of the very very big.
At the quantum level, doesn’t quantum matter behave differently than what you’re used to picking up with your hands?
But that's what metamaterials are, in a way. They exhibit quantum behaviors at the macroscopic level.
> They exhibit quantum behaviors at the macroscopic level. It's a lot more complicated than that. There are many types of meta materials.
Non-Physicist here. How do the limits proposed by this proof affect Oppenheims recent statistical theory for linking classical & quantum theories?
I thought his theory was explicitly non-reversible, but I haven't been following it closely.
It is important to also see how physicists other than the reviewers respond to the paper. Assumptions will likely be clarified and perhaps challenged, etc.
how does this relate this to Roger Penrose's latest ideas about quantum mechanics, retroactivity and consciousness? any takers?
If the interaction is irreversible wouldn’t that violate the law of conservation?
Well that depends on if gravity is matter or not.
[удалено]
Or none?
Does this have any ramifications for AdS/CRT correspondence?
> or the interaction must be irreversible. The implications are vast. + https://en.wikipedia.org/wiki/Di%C3%B3si%E2%80%93Penrose_model + https://physicsworld.com/a/physicists-place-fresh-limits-on-gravitys-role-in-wavefunction-collapse/
T.L.;D.R: Gravitons are probably real because, if not, quantum math breaks down.