A New Test for Quantum Gravity
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- čas přidán 15. 05. 2024
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I suspect that one of Einstein’s nightmares was that his theory of gravity would be turned into a quantum theory. I also suspect that we’re inching closer to that nightmare situation every day -- but not how Einstein might have expected. After countless attempts to develop a theory of quantum gravity, physicists are now trying their hand at measuring it through various experiments. This week we have a new proposal for an experiment, and it's a quite clever idea. Let’s have a look.
Paper here: journals.aps.org/prx/abstract...
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The problem with notifications is that I don't want notifications
They are hella annoying.
Turn them off.
If I'm subscribed, I'll watch the video if I want to. I don't need a notification to encourage me further.
Silence is golden.
I wish there was a section for showing everything I'm subscribed to. Not personalized, literally everything in chronological order. But that gives these companies conniption fits for some reason, since they give up the ability to promote things they'd make more money on I'm guessing
Worth mentioning that the eccentric Henry Cavendish used a torsion pendulum to be the first to measure normal gravity. He was an incredibly rigorous experimentalist.
And the true one who discovered and explained electrostatics well before Coulomb. Unfortunately he just didn’t publish his papers including the related discoveries …
@@dankurth4232 Also discovered hydrogen.
@@petercumpson6867 He was a genius and actually tried to relate gravity to electrostatics … yet he was a very eccentric genius.
I like that Jonathan Oppenheim actually takes recourse to a refined version of Cavendish experiment to try to prove his Post Quantum Gravity. At certain times (the history of) science becomes atemporally present
I figure experimentation and measurement is the best way to work. Theories can and will be proven wrong time and time again until we find the ultimate truth of reality, if we ever do. An experiement is forever. The conclusions drawn from the experiment may be wrong. The circumstances of the experiment may not be what we thought they were at the time, but the experiment ultimately happened.
My favourite kind of research is "fucking around and finding out". What happens when we do this? What happens when I change that? Do I have preconceptions going into the experiment? Of course I do. But my working theory is a working theory. Who cares if its wrong.
The basic problem with the Cavendish experiment is that it assumes gravity is an attractive force between two masses and the core reason why it is the most variable and lowest accuracy of all the so called physics constants. By carrying out the Cavendish at the surface and then at ever increasing depths down a mine shaft it has been shown experimentally that the deeper down the lower the value of G. Because this contradicts current theory the experiment by the University of Queensland at Mt Isa was deemed faulty and scrapped. What it did show was that “ gravity “ is indeed a repulsive force that is blocked by mass.
This experiment is easily replicated but as the result does not align with current theory it is studiously avoided.
I am very much NOT a PhD physicist, but I seem to recall that the wave function collapses every time a quantum particle is measured or observed. So, I am not understanding how these measurements of quantum gravity effects would not collapse the function and deliver no result. Also, since gravity is so ridiculously weak (in comparison to the other forces), it seems like we are trying to count the number of electrons in an elephant before and after it inhales. Sure, there is a discreet, correct answer, but I can see no reasonable way to measure that to any degree of accuracy.
The only answer seems to be to send someone into a black hole with a long string and a paper cup. I nominate my brother-in-law for the job. If you knew him you would agree.
The wave function collapses when you measure things yes, but you can see the quantum effects depending on when/where you measure. For instance, in the double slit experiment you "observe" the wave function if you let the particles hit the screen, but you don't observe it if you measure which slit the particles pass through.
@erikrehn2584 you have just explained the measurement confusion everyone needs to hear lol
I always wondered how the experiment changes when you measure it vs observe it
the wave function does not collapse, like some kind of event or something. it's just an end to the inquiry. it's like, take any bit of mathematics that describes some behaviour, like how a coin moves as it spins on a table. there comes a point when the coin suddenly falls over. the math is like "ummm... helllo? anyone home?'. the math is totally abandoned at this point, it feels lost and misplaced and just ridiculous for existing. it has no purpose. there is nothing interesting about this situation of this math becoming nothing. It's just not applicable. game over. Now imagine someone was there, and they said "OMG, the math collapsed!!". What are you supposed to say to this person? How about this: "This is physics, not poetry class". The math just became inapplicable. How could probability math be applicable when there is Fact rather than possibility? Ever bring a car to a donut shop to get an oil change? He might even say things different. He might look at the coin flat on its belly and say (as he keeps looking at this coin) "Well, the angular congregate function collapsed folks". Same deal. Guy needs to settle down because he's out of line. Question is HOW does Nature go from no fact of position TO fact of position? And that's a fair, important question (because it IS true that there is NO fact of position prior to measurement; Bell, etc). But saying there is _Actually_ a wave function out there that runs its course then collapses as some process or fast snap (Not just saying there is a certain mathematics we Call the wave func which we use to MIMIC whatever is going on (tbd by an Einstein), and then stop using when we stop needing it) -- is pure saturated poetry, and dangerous.
Gravity is not a force
Short answer: Yup!
Any effect would be overwhelm by EM fields that are always present. QD is very likely limited to ElectroMagnetism (EM). Gravity is perfectly uniform it does cause patterns seen in Magnetic or photons (no field lines or interference), nor does it have charge effects (repulsive fields). It should be pretty obvious to anyone that thinks about it, there are no quantum effects for gravity.
I am pretty sure Gravity is just the Strong interaction, either directly or a derivative (ie decays quickly into gravitation). There are only two real forces: EM & strong interaction: Gravity = Strong interaction beyond the nucleus of protons & neutrons EM = weak interaction (EM effects inside the nucleus of an atom causing radioactivity).
Since gravity is the curvature of space time might quantising space time make more sense? We know there is an interaction between space and a spinning mass. Frame drag. Might it be easier to test how matter has friction of this type with the fabric of space time?
You burned my brain
Gravity fed ocean water into Death Valley will incentivize name change to Life Valley now that any type of non potable water can be purified as free byproduct of zero pollution energy.
The Eirex Technology in Canada has breakthrough cavitation technology cracking any type of water more valuable than oil, nuclear or hydro electricity.
I think thats the Higgs field you just described.
Maybe. I'd have to find my text books on the subject matter. And they are stored about 800 km away from me at the moment, this is where knowlege itself gets fuzzy, no less mine! 😅
The gravity of cavitation bubbles collapsing yields over unit energy by Eirex Tech smashing water bubbles together like a million hammers smashing on single nail.
Thanks for saying "pendula". Few people bother forming proper plurals of Latin words. It pleased me to hear it!
I took Latin in the UK 50 years ago. We called the Latin Master, "Chalkie" because of his dusty robes.
To be fair I don't turn on notifications for any channel. I just stick to my subscription page and scroll through the new uploads daily.
her channel rises in the YT ranking tough, so more people get aware of it. Just a small favor...
The only CZcamsr who can verify the entanglement of Einstein and Shakespeare.
To be or not to be. Yes.
Shakespeare is both at the theater and not at the theater!
To be AND not to be.
Quantum Shakespear can 'Be" and "Not Be" at the same time...
@@user-hh1xo4rn2k He's only "to be" if there is an audience to measure the performance.
IIRC, Penrose posited that wavefunction collapse was mediated by gravity and the impossibility of the state in superposition.
My notifications are on and off at the same time. They are entangled...
In post grad physics I was taught "Gravity is not a force"... but a change of space-time. How can it be a quantum "force" ? Space-time would need to be quantized. Not a continuum. According to Einstein Gravity is not a force but a manifestation of the curvature of spacetime.
Massive objects cause spacetime to curve, and other objects move along the curved paths in this spacetime, which we interpret as gravitational attraction.
Exactly my point.
This is actually not a contradiction.
In Newtonian physics forces simply exist as vector quantities and are described by the global distribution of particles. There are no “force carriers” according to Newton, because forces are global phenomenon in his theory. This is analogous to saying forces act instantaneously across infinite distances.
In Einsteins theory, gravity is not a force. It is a LOCAL effect due to LOCAL variations in spacetime that curve the geodesic of an object. There is no force carrier in this theory because there is no direct interaction between any two particles. Particle A bends space around it, Particle B reacts to how space is bending near it. But particle A and B have absolutely no way of ever knowing about the others existence (only gravitationally I mean, when you add in E&M then they can detect each other).
In QM, all operators are local operators like in Einsteins theory. But all forces must be carried by a Boson. E&M has photon, weak has W and Z bosons, and strong has the gluon. In order for gravity to be quantized, there must be some local symmetry group it obeys, SU(5) is a possible example, and any local symmetry group requires a gauge boson to mediate the force.
It isn’t a contradiction. Newton says gravity is a force. Einstein says it isn’t. QM says it is. It’s just different models.
If you can make both interpretations act such that the math corresponds, does it matter?
Doesn't really matter what einstein thinks. The standard model of particle physics describes fundamental interactions and particles through the framework of quantum fields, with particles being excitations of these fields. Given this framework, it is hypothesized that gravity, like other fundamental forces, could also be mediated by a particle, known as the graviton. In theory...
@@gavinriley5232why would gravity have a finite symmetry group? It doesn't make any sense. It is difeomorphism invariant.
I am glad someone actually thinks about measuring those effects. Otherwise, we could be discussing this for the next hundred years
Well alot of bright minded people really wants to measure them .. they just don't have the funny thing called "funds"
@@xeqqail3546 And hardworking intellectual clowns like Elon Musk have way too much 'funds', so let's all start a revolution and end this market capitalism idiocy, or we will be complaining about 'funds' for another 100 years.
True I am infinite and Eternal, but even I was shaped by forces outside myself…you know what they are.
Human species shares all bodies composed of itself across all time, regardless of the ego that thought of that idea.
Entanglement witness is an observer of someone watching another pass away
General relativity and quantum mechanics will never be combined until we realize that they take place at different
moments in time. Because causality has a speed limit(c)
every point in space where you observe it from will be the closest to the present moment. When we look out into
the universe, we see the past which is made of particles
(GR). When we try to look at smaller and smaller sizes and
distances, we are actually looking closer and closer to the present moment (QM). The wave property of particles appears
when we start looking into the future of that particle. It is a probability wave because the future is probabilistic.
Wave function collapse happens when we bring a particle into the
present/past. GR is making measurements in the predictable
past. QM is trying to make measurements of the probabilistic future
Time is even stranger than gravity, and may be an emergent property of entropy as one theory posits. The puzzle of time and gravity have a lot of parallels it seems. I think they're intertwined in ways we don't understand yet. I'm fascinated by time and gravity, more so time, I suspect if they crack the time or gravity puzzle, both fall into place and their interrelationship is explained. I regret I can only get so far with the topic.
@@willbrink Be careful. I am regular being attacked in these channels for speaking about anything to do with time.
This is an interesting way of thinking about QM. Thank you.
I find that I can extract what you have said just from the geometry in the Minkowski light cones.
@@willbrink is entropy a mathematical (like if bell curve exists in Plato's type of exists, then entropy exists) thing or physical?
This is interesting - a video on Sabine's actual area of expertise! And it's funny that the number of canonical experiments for quantum gravity phenomenology has now risen to three. It reminds me of the three "classical tests" of general relativity.
What I love about you, Sabine, is that you are the epitome of what I respect in one who professes science and knowledge. In that just because you don't agree with the "norms" of a subject, doesn't mean you are disrespectful when laying out your counterarguments.
One of the reasons your videos on the fallacies of String Theory are important for the dialogue, is that they are arguments alone. On top of the fact that you produce your arguments with legit evidence, and again, without having to bring the conversation down into almost dare I say an intellectual schoolyard scrap-fight, should be commended.
The actual Art of Debate would pay heed to learn from people such as yourself.
Thanks so much for creating and sharing this informative video. Great job. Keep it up.
4:00 this is a beautiful haunting sequence and looks as if it makes a lot of sense.
6:29 “Please turn on notifications” I did this a while ago and now every night at 7 PM California time, I receive a general notification that you have uploaded content but nothing specific. I don’t find that helpful so I just switched it to PERSONAL instead of ALL notifications to see what will happen.
3:19 Groningen? Hey! That's where I live and where I studied 😀
You should not mention this to anyone.
Sabine, is there any experiment that demonstrates that the process where a wave function goes from a superposition state to a non-superposition state is a non-local process? Is this testable? Does this question make any sense?
What I thought was that, in the bomb experiment (without the bomb), you could place a detector (d0, t0) in the bottom path after the photon has passed through the first beam splitter (this would take the state from a superposition to a non-superposition). After positioning d0 a second detector (d1, t1) would be positioned on the top path, so that t1-t0 would be a shorter time than the time it would take for a signal to travel from d0 to d1. So, every time d0 does not activate d1 would have to activate (the presence of d0 forces the state to leave the superposition and as d0 was not activated the state now corresponds to the top path). This would demonstrate that the wave function went from superposition to non-superposition in a non-local manner. If this does not occur (d0 does not activate and d1 also does not activate), the process could be local.
You do a great job clarifying these quantum things, thank you.
I'm using a pair of dice to examine quantum gravity. E/n=L^2*m. The wavelength of the variance x,y,z changes w/ the density of the cube. It's discrete in nature.
Loved the Shakespeare graphic!
Yes!
Your recent video on quantum entanglement as the origin of gravity was truly enlightening. I am particularly fascinated by your ability to simplify the complex concept of gravity-particle interaction. The Big Bang theory, as you explained, suggests that our universe was once a dense, tiny ball of material. Your insight that entanglement might occur in such an incredibly compact state was truly remarkable. This prompted two questions.
First, As I delve deeper into the theoretical implications of Big Bang, I find myself wondering: Could entangled particles, once liberated during expansion, retain their state of entanglement as the source of gravity? {Alain Aspect, John Clauser, and Anton Zeilinger}, I'm eager to hear your thoughts on this intriguing possibility.
There's a recent study [1] that suggests quantum entanglement experiences entropy. If the hypothesis holds true would the particles no longer entangled be "squeezed" from the remaining entangled particles. Could then the entangled particles might strive to rejoin, leading to the emergence of gravity. What are your thoughts on this?
1. Lin, ZK., Zhou, Y., Jiang, B. et al. Measuring entanglement entropy and its topological signature for phononic systems. Nat Commun 15, 1601 (2024). doi.org/10.1038/s41467-024-45887-8
Such helpful info all the time from this channel. This will now be the only notification I've turned on, as a thank you!
Nice🙂
Reminds me of Orson Welles in the Lady From Shanghai in the hall of mirrors. "Where am I?" To say a particle can be in 2 or multiple places at once means it takes every path...until observed. As Yogi Berra said, "When you come to a fork in the road, take it!"
I'm thankful for your channel.
Hey look: if electrons can be "not affected by" QCD, then why do we need QED and/or QCD to be affected by gravity? To put it another way, why would a force that is very strong only at SMALL distances (I mean gravity, in case I'm not asking the question well...) interact with a force that is only strong as distances get larger?
In other words: The activity (big numbers) of QCD seems to get infinite at the boundary of the proton. BUT The activity (big numbers) of gravity gets infinite ONLY(?) at the bottom of a black hole...
By the way: I don't like QCD but I don't know what to say about that huge mass of evidence in favor of QCD. But I'm telling you there's another interpretation. Gravity and QCD have to work the same way. 🤔
Okay, why don't they just cancel out? Done. Now take a picture, erase the chalkboard, and let's go get a drink!
Newton's Cannon. The same reason our satellites and thd Solar System's other planets don't, have you ever seen something spinning while being attracted to a center? It's called orbiting@@geosynchronous4386
I think something about the fact that the bosons of QCD and the fermions of QED having mass makes them a better candidate for observation gravitational effects.
@@geosynchronous4386it is orbiting in free fall
@@geosynchronous4386 That's because the moon is really BOOKING man!
"2g or not 2g" wrecked me
quite simply the best breakdown of subjects like this. outstanding.
Fascinating! Thanks.
Getting back to attempting to test the hypothesis over relying only on the maths is encouraging. I hope it leads to a breakthrough on the mystery that is gravity. I know one theory is it's an emergent phenomena (from entropy?) and is not itself fundamental.
I really think that this theory has a lot more going for it than thinking that gravity is quantised. Only time, space and energy are quantum - gravity is a shape within that tuple array.
@@CosmicGorilla "Quantized time"? Please continue.
We know what gravity is. Your gps works because we know what gravity is. Look up Einstein. We didn't know what it was at time of Newton
@@LisaBlooper Agreed, but neither GR or QM are complete theories.
@@drbuckley1 Agreed. But QM is a joke in completeness compared to GR.
Sabine: If I understand correctly, these tests of quantum gravity are potentially also tests of the Everettian interpretation of QM. If the Everettian view is correct, gravity HAS to be quantum; otherwise we would feel gravitational effects even from branches of the wave-function that have diverged far from our own. If gravity is non-quantum, the Everettian view is dead, as far as I can tell. Is my reasoning here correct?
No, not necessarily. If the Everette view is correct, then gravity is almost certainly quantum mechanical, but the inverse statement is not true.
As a simple counterexample, the Penrose interpretation. Gravitation could be a quantum force, but state vector collapse could be an objective process. Penrose's suggestion was that gravity mediates this process.
In his model, at some mass scale (the Planck mass, roughly the scale of a gain of salt), the collapse time becomes too quick for a superposition state to survive for long enough to measure. This would be the energy scale at which a graviton can be created; collapse would be nearly automatic at this scale.
The Everettian interpretation of QM is pure mathematical speculation and has no way of being proven.
@@jmcsquared18 Yes, of course.
your conclusion may hold in De Witt‘s many world interpretation of Everett’s relative state interpretation. If the branching is of worlds or universes gravitational effects should arise.
If the branching is of accessibility of information there need to be no gravity involved at all.
The many world interpretation is a proper model of the relative state interpretation and probably an intuitively intelligible (or so to say: somehow more easily comprehensible) one, but it is not the only consistent model of Everett’s original relative state interpretation which can be consistently described as of attainable information vs not- attainable information and then with much less of the ‚metaphysical baggage‘ John Wheeler didn’t like so much
@@dankurth4232 fair enough but all of that just makes me return to my original feeling about Everette generally, which is that we don't even know how to interpret that interpretation lol
Honestly, I doubt Everette is salvagable without gravity, because it is not clear how branching even occurs or what basis it occurs with respect to. I know e.g., Carroll has tried to resolve this by getting the Born rule from Everette in other ways, but the unambiguous nature of the state's decoherence still isn't clear to me.
Sabine, that might be my favorite thumbnail yet! Made me LoL! Thanks for all the great videos over the yesrs. You actually make hard to understand topics seem simple. That's an envious skill to have.
Hope some of this pans out, it would be EPIC!
Hey Sabine, what can't I watch your channel member videos with screen off, as all other videos? 🤔
This seems to be issue with the CZcams premium subscription that several people have told me about. I have actually reported this to CZcams, but there is nothing I can do about it, sorry.
@@SabineHossenfelder Yes, it happens also for me, a Premium user. But why would anyone want to watch your videos and miss all the visual jokes?
@@arctic_hazebecause some people like going for walks and listening to science news
At the scales we're talking about gravity is basically negligible. It's less relevant than friction in your average mechanics introduction in school. I am not kidding.
Yes. But we pretend that QM (probabilistic approximation) only applied to the micro scales.
Yes, that's why measurement precision is so important, as Sabine said. If it were easy, the experiments would have been done decades ago.
And the gravitons are very, ……very small.
Gravity is not a force, if so. Dust particles are still heavy enough to fall, situation. So gravity is more or less left out of the equation in the invisible world, you would think. Thus the findings. ... Pushed around instead. .....if gravity were a force, like the graviton idea, it seems gravity would have a more serious effect on the particles.
@@consciouspi Nothing is a force. (but that's for another day).
Love your work
So I read that the 1st LIGO detection (which was a ridiculously tiny measurement), involved a GW with a graviton occupation number on the order of 1e30. So we're not seeing gravitons anytime soon.
Graviphon.
First.... my break and your uploads are entangled dr sabine.
Why not combine them?.....😂
Thanks!
There is no rush. I can watch your videos year after they were published
Will probably end up like light. An experiment that assumes gravity has quantum properties will prove gravity has quantum properties and an experiment that assumes gravity is consistent with Relativity will prove gravity is consistent with Relativity.
But light literally has properties of both waves and particles. I don't think it's possible for that confusion to happen in case of gravity being quantum or not
Wouldn't this just prove, that gravity IS quantized? When it can quantize, it is quantized.
@@richardglander6340 Not being a scientist hasn't the quantization of light failed to settle the quandary over the double slit experiment?
These measurement idea's wont work from my point of view.
All these experiments are heavily based on the Copenhagen interpretation. They assume that quantum means the LOCATION of the particle is uncertain, therefore the gravitational field also have probability imprinted on it. The problem in that: they want to catch the imprint of quantum gravity on top of another quantum effect assuming they follow the same basic rules.
If QM works any differently as they assume, for example it is more like the pilot wave version, where there is no ghost particle being all around until measured, than it is not possible to deduce quantum gravity properties from the overall quantum effects. Even if they measure an anomaly, there is no sensible way to deconvolute that from thee overall QM mess going around.
In my humble opinion the only way to decide if gravity is quantized, if an experiment is created where all other quantum effects are completely neutralized, so any remaining quantum anomaly must come from gravity.
I'm convinced that solving the quantum gravity problem will happen iff we solve the quantum measurement problem. The potential solutions to the two problems seem to be too deeply interconnected to not be able to affect each other.
¡Gracias!
Thank you for the awesome vids!
The more I hear about gravity the more I think gravity isn't actually an elementary phenomenon, but rather an emergent one. I am no physicist, I cannot possibly even begin to understand if or why I'm wrong, but I have been having this thought lately that gravity is the wrong thing to look at, and a real understanding of spacetime will not happen until physicists figure out what gravity emerges from.
(edit: and before anyone says, yes I know about gravity being a side-effect of curvature around mass. the way I see it, it's the same thing to talk about gravity or about curvature of spacetime -- what causes spacetime to curve where there's mass?)
It's unknown how mass causes spacetime curvature. But a couple of possibilities might be:
1. The exchange of virtual particles between mass and spacetime. The further away a region of spacetime is from the mass, the weaker is the curvature-inducing "force."
2. Mass tugs on the small neighboring region of spacetime, which tugs on its neighboring regions of spacetime, etc. Analogous to how pulling on the end of a strand of a spiderweb creates tension distributed on the entire web, or how pulling on the end of a spring stretches the entire spring.
Gravity (as a force) is emergent. That's the essence of spacetime tells matter how to move and matter tells spacetime how to curve, because then you don't have two objects separated by whatever huge distances that somehow know where the other is and move to there. I can understand that feeling of us needing a better understanding of what spacetime is. People tried it with loop quantum gravity; though that seems more interesting than it seems physical. I have my doubts about particles being in two places at the same time, because to me, what the wave function seems to encode most of all is just our human knowledge about a system and of course it collapses when we attempt to measure stuff. We measure an interaction and post-haste label the participants particles. But hey, nature has no obligation to prove me right. It doesn't even have an obligation to prove me wrong. I just don't think we'll have any insights into quantum gravity without better answers to what is spacetime? And what is mass? I have heard people phrasing mass as a resistance to change; think F=ma and the more mass the more force you need.
@@FrancisFjordCupola If gravity is emergent, why try to quantize it? The thing that should be quantized should be whatever interaction is happening that "looks like" gravity. Is it not possible that the elementary interaction that induces gravity is quantum, but its indirect effect on objects happens such that there's no quantization based on the distance?
Honestly I don't believe that the whole "a particle can be in two places at the same time" can be a real phenomenon, so I feel like it's a waste of time, but people much smarter than me (or at least people who have dedicated a lot more of their brainpower to that area of knowledge and hold many orders of magnitude more expertise in the matter) seem convinced enough to make it their life's work, so I'm prepared to be wrong.
@@brothermine2292 The first one involves virtual particles but the whole idea of virtual particles rings wrong to me. I do understand that they are needed to explain stuff so as I said in the other message, I'm okay to be wrong in this. The second seems like just an explanation for why gravity might extend infinitely, but it doesn't actually explain why mass might "pull" spacetime. I assume the real hypothesis goes deeper than that?
>gigaherz_ : Both 1 & 2 are attempts to explain how mass curves spacetime that's far from the mass.
There's no consensus among quantum physicists that superposition implies a particle is in two (or more) places at the same time. There are other interpretations of quantum mechanics. For instance, in the Many Worlds interpretation a superposition of a particle implies there are particles in different universes, each particle is in only one position in its universe, and a measurement merely reveals to the experimenter which subset of the universes s/he is in. I don't understand why Sabine often asserts that the orthodox (Copenhagen) interpretation is correct when she knows it hasn't been proved correct.
Would love to see your take on the Russell periodic table.
For the second experiment is there a difference between the mass for different interpretations of quantum mechanics. That makes sense for the Copenhagen interpretation, but for the Everett interpretation I would have thought it would be one mass in either of the locations and we happen to find ourselves in one.
I just wanted to say. I loved the surprised face in the thumbnail. Made my morning~
With two quantum particles in two places at the same time (1:05), perhaps the question of quantum gravity depends less on place and more on time. As with a quantum particle's duality of place, perhaps there is likewise --- or instead --- a time dichotomy.
I am glad someone actually thinks about Einstein nightmares.
Sabine, what if the wiggle is quantum gravity in effect? Would that track mathematically?
loved it :)
Please, tell us about Bekenstein's quantum gravity experiment!!!
What was that?
[reposted]
Thanks Sabine. I always enjoy your presentations.
I really how they settle this whole gravity thing one day. Gravity sux.
>
Don't take too much notice of my drible below.
"The particle is in one place and in another place at the same time". I have been blasted off of YT comments by other users for saying that :(
>
But putting that grievance aside I personally see no issue in the idea of a particle being in two separate places at the same time.
Probably what I say that is controversial (And this is a thought, not an assertion) is that a particle can be in 2 separate places in space but at the same place in time. I also include entangled particles being at separate spacial coordinates but at the same time coordinate; aka there is no separation between the particles in time, only in space.
>
Yes yes, I know it's unhinged hocus pokus., but it also allows me to get rid of gravity, like completely and just call it clumpiness due to mass and time instead lol
quantize the causal field energy. Mass concentrates causal field energy, creating a causal depletion zone adjacent to the mass boundary. Gravity correlates with Entropy. High causal energy states "move" towards low causal energy states.
About the first kind of experiment:
some people have argued that it is possible to create entanglement even if gravity is fully classical via a hybrid quantum-classical model. So, it's not clear that such experiments would reveal the quantum nature of gravity.
These measurement idea's wont work from my point of view.
All these experiments are heavily based on the Copenhagen interpretation. They assume that quantum means the LOCATION of the particle is uncertain, therefore the gravitational field also have probability imprinted on it. The problem in that: they want to catch the imprint of quantum gravity on top of another quantum effect assuming they follow the same basic rules.
If QM works any differently as they assume, for example it is more like the pilot wave version, where there is no ghost particle being all around until measured, than it is not possible to deduce quantum gravity properties from the overall quantum effects. Even if they measure an anomaly, there is no sensible way to deconvolute that from thee overall QM mess going around.
In my humble opinion the only way to decide if gravity is quantized, if an experiment is created where all other quantum effects are completely neutralized, so any remaining quantum anomaly must come from gravity.
Yes, about that quantum particle being in two different places at the same time… here we're not really talking about its contribution to space-time curvature. The curvature is on the left side of the equation. The particle contributes to the right side where we find the stress-energy tensor. The tensor is a macroscopic, not a quantum object. So the particle's contribution to it manifests only in the thermodynamic limit in which it classicalizes and smears with Avogadro number of similar quantum particles. This thoroughly classical object then tells space-time how to curve. Yes, gravitation is an emergent phenomenon, as are pressures, temperatures, and stresses of the stress-energy tensor.
That is such a great idea
This is so very encouraging to hear. All the news relating to 'quantum gravity' or generally unification has for decades been theoretical, or best observational (astronomical). I personally am a theoretician, but we simply cannot let theory keep drifting and getting more and more decoupled from the empirical world. Then it devolves into mere mathematical games. (*Cough* string theory)
As Feynman, that eternal source of good physics quotes, once said: "It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."
A Type IX civilization could be able to explore the paradimension, the megadimension and the omnidimension of the hyperverse. A civilization of this scale could create and destroy multidimensions.
Size scale matters so much more than we currently admit: 1) in planetary scale attraction/gravitational force prevails 2) in macro scale attraction and repulsion (+ and - charges) make almost everything work 3) in subatomic scale colour charge (3 of them) works. These realms are somewhat(!) overlapping but colour charge does not really affect “huge” objects and gravitational force does not really affect extremely “small” subatomic particles. Size scales are much more than being small or big - these realms are inherently separated in every regards including the validity of the rules that apply to them. Very obvious that an increasingly different set of rules of physics apply to the small and the huge to the point where the very large (the far end or outer boundary of the discoverable universe) becomes undiscoverable, as well as the very tiny objects and “forces”, the inner end of our scope of discovery, becomes, too, undiscoverable (hence we are forced to call them “fundamental” which they are not). In order to something to be discoverable, their realms (rules of physics) must at least partly overlap that of our own size scale, the classical physics. What we perceive as “small” or “huge” in size is actually getting less and less EXISTING or discoverable for humans. I really wonder why is this obvious fact is so difficult to see and admit… Time will tell.
@3:35 Nope. The superposition quantum will cause an interference pattern to the moving quantum. This setup is similar to the two-slit experiment but not the exact same. It will form an interference pattern but not the same one.
Are you describing the resistance in the firmament? Or the ether, or the 'fabric' of the background universe?
No, there are certain, equally valid, interpretations of quantum mechanics which definitively state the particle has a fully defined position (singular) at all times.
I hope one day we can measure the effects of quantum time. String theory never bothered to quantize time. Quantum loop gravity is mainly about quantizing space but not so much a focus on quantizing time.
If a particle is on two locations at once, does it gravitational pull on its own counterpart?
Bet they cancel each other out.
I too am heartened at experiments on quantum foundations like this. Also loving the conceptual link to Cavendish! Yet, I remain puzzled/amused at the motivations involved in apprehending a show-stopping conflict between GR & QM.
The erstwhile quantizers strike me as folks especially proud of their shiny hammer (renormalization) yelling at the top of their lungs “Everything must be a nail!”.
Too much handwringing over prospects of a BH singularity, not enough awareness/investigation that classic GR does not attempt to address the fermion interior. Or that alternatives (that guy Albert again) that do are claimed to avoid singularities.
I’ll stick with Albert.
Here's some interesting questions: Considering that G propagates at c and quantum particles relocate instantaneously, would a quantum particle's gravity affect itself if it's 2 locations were close enough and repeating? And if so, would that particle find a "centre" and eventually end up instantaneously appearing and disappearing in 1 place? Would this cause it's gravity to no longer affect itself? Would each instance of the particle have it's own G field? Would those fields cause constructive interference and double the field strength causing the "extra gravity" that we see evidence of? Or, negative interference that cancels the fields causing gravity to "not exist on the quantum level" that we also have evidence of?
An insight in the nature of things can only be gained if an official alternative approach in physics would run parallel to the current model. Unfortunately, the gravitational pull of the current approach sucks up all the resources and prohibits escape from its framework.
Entanglement seems so strange? When do you know when you have entanglement? Will measurement change the state of the entanglement? Gravity seems to operate faster than the speed of light. Using Uncertainty principles measurement does not seem digital since virtual events can happen any where in the uncertain region and the event has it own uncertain extent? So is space continuous?
Yes, very good question. Proving entanglement is actually quite difficult, as you need to prove that you have a correlation which actually required true quantum effects. This is what Bell-type tests are done for. That this experiment doesn't need to prove the presence of entanglement is a big advantage imo!
I'm left wondering that a failure to deliver conclusive evidence of gravity's quantum nature, won't someone just keep devising more experiments? In the case of physics, it seems, failure to find confirmation just leads to more and bigger experiments.
Is it possible to devise an experiment that proves that gravity isn't quantum in nature?
on No 3: pendulums are damped. Things with damping fluctuate (Fokker-Planck), how is the QG signal going to be visible with that in the way?
You can’t test quantum particles because they’re using their twins to cheat on the exam. 😆✨
I feel this may be a bad question, but is there a delay to when gravity takes effect? For instance when a particle forms, it doesnt have a gravitational pull before it is a particle, but does after, so is there a delay in between when the particle forms and when nearby particles feel the pull?
I could write a book on just the three proposals let alone the various comments here. But I am directing this comment at the people here.
Here is what we think we know about a graviton (which really should be called quantum space because time appears to be an emergent property of space)
Spin = 2 (it’s a boson, not a fermion)
Manifests in very tiny, tiny scale interactions
It presents as an equilibrium dynamic called the field.
The mass is less than 6E-32EV/c^2 it’s believed to be massless and it evolves at its wave propagation rate, which C is dependent.
Moreover relativity tells us that there is no inertial reference frame, the closest we get is a comoving spacetime in which light generating particles provide information about average velocities relative to us. The is no 3D reference frame and 3 dimensions is probably an emergent property of space. It is entirely possible that if I somehow miraculously put 2 gravitons in a place that had none it recapitulate space and a local spacetime. However such a magic does not exist, if I had the power to take two gravitons and put them someplace in effect I am creating a wormhole since interactions between gravitons determine the curvature of space. To create that new space I would need to create them ex-nihilo.
So when people talk about quantum field theory what is not spoken about is the foundations. One assumed foundation is spacetime. The fields superposition on each other and various possible states super position on each other in their fields. For every tiny bit of space we can build up fields.
An electron for instance can exist in a set of spatially probabilistic orbitals around an atom. But there is nothing to prevent the electron from being inside the atom. It could, if it had enough energy merge with a proton to form a neutron. The electron is attracted to the charge of the proton, not its mass, so it can go right through the mass. But as it exists in the orbit the probabilistic interpretation of the electron is a wave. So if you placed very cold hydrogen atom in a vacuum chamber with no incoming or outgoing hv the electron and proton are in a coherent state. The electron is in many places including the nucleus, (tiny, tiny probability).
Why is this important, gravitons don’t cause decoherence under the majority circumstance of the universe. In the space within a proton (0.833 E-15 meters) there are 10E60 gravitons, each evolving with an atom 10E15 times more. The key is here is evolve, massless, and the fact there is no spatial reference frame or coordinate system. If we go think of a gravitons as a perturbation (of itself.) within a proton, it would remain in the proton for E-23 second. So if we think of graviton as discrete, then in a second 10E-100 gravitons have passed through a hydrogen atom.
So the question of whether gravitons can cause decoherence is moot. The fact that we can produce coherent states that last seconds or minutes means that graviton cause decoherence at exceedingly low frequencies as to argue that in normal spacetime they cannot cause decoherence.
So the interactions Einstein is talking about are indirect consequences of matter, energy and spacetime. Energy in space time alters the way in which gravitons interact with each other causing a distortion in the emergence of time resulting in a curvature of spacetime. This distortion is greatest at the event horizon of a black hole.
So in these experiments they are trying to measure outcomes the are the coupling of two indirect interactions in the process of the experiment gravitons in the >10E100 range. Any effect one’s thinks on is seeing is in fact noise, probably caused by perturbations in or their fields. It needs to be stated that earths gravitational field is a curvature in space time which is always changing in minute amounts (the Earths core is moving around inside the earth) and there are tides, there are interplanetary gravitational interactions. And experiment, just to get to a point where it claims it has some kind of sensitivity needs to be able to factor out, on the fly all types of noise.
I turned on notifications, didn't realize I hadn't.
Logically, this is correct: all mass are waves. So, mass vibrates. The vibration vibrates space and causes radiation. For a roughly spherical object, like the Earth, the waves are concentric spheroids. I decided gravitons are unnecessary to account for the inverse square law. The curvature of the spheres being less per area the further away from mass is sufficient. Besides, there are no gravitational optics that will show detail the way photons do with light.
Would you like chocolate chip or macadamia nut cookie?
The first difficulty in quantum gravity is understanding what the question is.
Suppose you have a massive object "in two places," and a small test mass nearby. It has an amplitude to be attracted to A, and it also has an amplitude to be attracted to B. This is exactly the same as with the electric force, and nobody says there's a puzzle there, right? So the difference is that space is curved. So we must say that the space has an amplitude to be curved in shape A and has an amplitude to be curved in shape B. So, what could that mean?
And how is Freeman Dyson's idea connected to this--he seems to postulate an additional uncertainty principle whereby we can measure quantum effects, or we can measure gravitational effects, but not both.
I don't understand a word, but sounds great 😂
I'm subscribed. That means Sabine's new videos are recommended to me within minutes of being posted. What I don't want are notifications - from any channel.
While I get the theoretical frustration angle, I'm old-schooled in my thinking that the experimental route isn't looking that promising. Back to the former, the issue is that nearly everyone framed the problem as: 'how do we quantize GR?' - rather than more broadly, 'how do we quantize gravity?'. The difference is important; e.g., yours truly developed a non-GR, classical theory of gravity and submitted some results to a respected journal (currently on the _second_ round of revision) with one of the guiding principles being that it be more 'quantum-friendly' than GR (good old potentials, rather than metric tensors - as well as the return of gravity-as-force). This means that the quantization route for this theory will be different than the traditional approach, and I think that's very exciting - but it's frustrating to have to wait so much between revisions (I submitted on last Chritsmas); in fact, it takes so long that not only I had time to work out a better model of the Sun than Newton's and show it passes the three 'classical' tests, but also managed to calculate the de Sitter precession from it, as well - literally as I wait for the final verdict. Oh, what to do? 🤞
Spooky action at a distance.
This is how we can make gravity compatible with quantum physics: "Novel quantitative push gravity/field theory poised for verification". That is provided you are prepared to start with a clean slate. Give it a try.
Good video.
Thanks. At last, there is hope!
01:15
How does Quantum Electrodynamics solve this for the electrostatic pull of a charged particle?
I left some things on Reddit on the grand unified theory just questions related to this
I'm amazed, as always for the thought provoking subjects.
Quantum Gravity was codified as One (1) Earth mass, good enough for quite a while :)
Now, if the math is right (Lorentz), then the standard becomes 1 (one) Hydrogen atom, the conceptual Plus (+) and Minus ( - ) of that Hydrogen state as Plasma (the ancient charge separation in space, as it were).
Aren't 'Atoms' fun!?! ;)
A Type V civilization would be advanced enough to to escape their universe of origin and explore the multiverse. Such a civilization would have mastered technology to a point where they could simulate or build a custom universe. They will have mastered the new laws of physics and have almost complete control over the fabric of reality. Now, humanity is basically impossible to destroy by its own inhabitants, which has reached the decillions.
If two electron wave functions are entangled, then how do we calculate the resulting gravitational field if we have not made a quantum measurement yet?
I hope they can do the pendulum experiment..use mercury generate torsion field that be interesting...
I like the idea of "entropic gravity," i.e. that what we call gravity is the result of systems evolving toward equilibrium. We know the amount of gravitational influence is a function of mass. I have an idea that might be crazy or just flat out wrong, but I'm going to just say it anyway. I think what we call mass might be, at bottom, basically just one of several types of intrinsic momentum (e.g. quantum spin, electromagnetism, weak force, strong force). We know that a vast majority of the effective mass of any bit of condensed matter does not come from its rest mass, but rather its "binding" energy, which I'm just going to call intrinsic momentum, because I really think that's what it actually is, so I think that this is a big reason to not just see the idea of mass being a type of intrinsic momentum as completely crazy. It's easy to say that matter is behaving in the way that it does because it's just taking the most energetically favorable path, but what could have started all the matter itself moving? What is the origin of momentum? Perhaps space itself is not fundamental, and therefore there is nothing to quantize.
With regard to the problem of particules being in several places at the same time (which GR doesn't like), why don't we simply "ventilate" the mass of a particle according to its wave function and call it a day ?
I have a question at the end of this.
I was looking at my fan today (AC is out) and noticed how clear the image of the wall was behind it as it spun in low settings. It has 5 blades with space of blade size between them and a ring for stability about halfway through the radius. The ring was visible but the blades were not. Moving closer, I could even see the details of the paint rollers as clearly as looking at the paint directly. At night, the clarity is not as great, as I can see the effects of the spinning blades when not backlit.
I am totally aware of the perception effects of seeing the wall because the blades are too fast to see. My question is, what do the blades see? Nothing, as they have no eyes. But you get the drift. Does the motion of the blades have any quantum uncertainty effect, since they cannot be observed (by me) as they spin faster than I can perceived them - although a high speed camera would see them and the photons they emit when the speed of the image is slowed down? I would love to see the Maths. Your students may not.
@@LisaBlooper I know all that. I want to see the Maths.
I think that gravity of all sorts is some sort of white noise. Not so far fetched when one considers that some sounds cab either attract or repel and correspond to color tones. Maybe quantum particles behave the same such ways.
I was literally trying to figure out how “mouses” fit into the experiments. The volume wasn’t super high, surrounding noise was a lot and I wondered if this crossover to biology.
When you explain these complicated concepts you are far easier to understand than that PBS guy
Might be a stupid set of question(s), but just wondering... This is probably just nonsense... but... morning logic.
If instead of the problem with the gravity of a particle in superposition , what if it's such that space is curved in such a way that multiple places curve into the same space (ie. local wormholes?) ...
Since it's one source of gravity, is the gravitational effect distributed and preserved over some contiguous warping of the multi-local curvature?
Would the measurable gravity that particles have just be a 'virtual' effect of their sort of multi-faceted local curvature? (ie. even though it appears to be "in superposition" it still has a singular real center of gravity that "fixes" local the curvature across, or through, any and all facets?)
Would it even be measurably different than superposition?
"the particle is entirely in one place and entirely in another". So, how does conservation of mass work when entanglement is involved? Do entangled particles each have half mass? Or is there some sort of "mass sharing" system? Or is entanglement rare enough to have it not affect simple (macro) mass measurements?
I see a lot of people share the same hate for the “tugging of the attention sleeve” that you call notifications.
The point is, I like you Sabine, but not enough to feel the need to “run” as soon as yours or anyone else whistle blows. Please keep your whistle silent, and let me enjoy my peace, when I feel it I’ll come and watch your videos, that I like very much!👏🏼👏🏼👏🏼
What I've always wondered is if the other fundamental interactions behave in a quantum manner too?
I keep hearing of this primary conflict between gravity and QM that says, because of entanglement, you would have two particles in different localities in space, which would violate gravity because, which particle is gravity working on? But what is really spatially separated is the wave function, which may not couple with gravity. Gravity would only begin to act upon wave function collapse into a real particle. What am I missing?
you are missing the ability to be ridiculous.