This video comes with a quiz: quizwithit.com/start_thequiz/1708902179498x963498281172992000

I would listen intently to the "long story" of why you left the field of quantum gravity, Dr Hossenfelder.

"Time exists so that everything doesn't happen at once. Space exists so that it doesn't all happen to you" - Susan Sontag

In your wonderful deadpan way you said, "In Physics we have experiments.", which reminded me of a Physics lecturer I once had, who introduced his topic by saying, "If it moves, its Biology, if it changes colour, it's Chemistry and if it don't work it's Physics!"

"Physics makes the simpliest things mind-bogglingly complicated." Reminds me of when I took quantum mechanics. The professor spent 30 minutes solving the Schrodinger eq for the potential V(x) = const*x, which involved Bessel functions and such. After that, as a joke I raised my hand and asked, "So with V(x) = const*x, that means we would use this result to understand dropping a ball." Professor just chuckled and said, "Something like that..."

It's raining today (Thursday), in Cambridge.

You're are first person to explain the quantum gravity issue in a way l could understand.

What a beautiful way to put it every time you go to your refrigerator and look at that magnet you realize that there's so much strength and force in that and it does change all around all the time❤❤❤❤❤

7:11 Sir Henry Cavendish - "Hmmm, this looks vaguely familiar to me for some reason..."

If all that happens in Cambridge is rain than it follows that Cambridge must be entangled with Seattle.

Thank you, so smart an experiment it is awesome how scientists progress. I find it great. The experiment of the Cavendish Balance is so awesome, "almost anyone" on Earth can him or herself determine the gravitational constant in the garage. And now we have these extremely refined experiments!

I’ve been waiting for you to discuss this study!!!

I'm excited to hear that there are experiments going on to try and test quantum gravity. I hadn't known that. I think I'll see if I can find out more. Thank you for covering this.

Sabine you are too smart for your own good and kinda cute. The only thing I know about gravity is I am touched by the ground. Mr. X

Cambridge is statistically one of the driest places in Britain. Try Wales or the Lake district.

I'm pretty sure it snowed in Cambridge once, too. It's nice to have a bit of variety

(Measurement of Quantum Gravity) 1.) Does Quantum gravity have density? 2.) Does Quantum gravity have a frequency? 3.) Can Quantum gravity be manipulated? 4.) Can Quantum gravity be artificially modified and amplified? 5.) Since Quantum Gravity can be measured, is it plausible for Quantum gravity to have a partical weight? I'm just curious.

Outstanding content and presentation. Thank you.

Excellent information 📚

This was a great episode. Lots of wonderful Sabineque dry humor to spice up the physics. Also, your particular interest in this topic really came across, the ideas were made understandable, and, the graphics very nicely fit the discussion. Compliments all around! Oh, and now a science question: at 6:20 you show their data as some amplitude of vibrations at different frequencies (or so i understand), but I fail to see how they distinguish the signal from the noise, at least if the signal is supposed to be at the position of vertical yellow dotted line. There are plenty of other spikes of similar amplitude at other positions in the plot. And an experiment idea: couldn't the search for quantum gravity be applied to those crystals representing the largest 'schrödinger cat' ever measured in a quantum superposition?

A very informative video. Thank you.

you're already the best science commentator/educator. Adding the quiz on the end just adds a great way to interact with your videos.

We may have units soon ❤😊. It may be the right and left hand rule with dimensions thrown in? Brilliant experiments. Congratulations. Thanks, Dr. Sabine.

Thank you for your content and your contribution to the dissemination of physics knowledge

Love your channel ❤️

Thank you Sabine

Thank you for the video.

Thanks as always Sabine, you are absolutely awesome.

love the editing

3:03 What I found interesting is the collection of magnets from at least the UK, France, Spain, Croatia, Canada, Australia, Cuba and maybe Portugal and perhaps even Egipt...

I have a question about something I don’t understand. Why do we keep hearing that superposition of an object means it is in two (in fact an infinite number of) places at once? It « is » actually nowhere, right? The superposition refers to the wave function of the object whose best interpretation is in terms of (square roots of) probability. It only acquires a position in space if and when it is measured (= interacted with, messed with) and at that moment it is in one place only. So where’s the problem? Am I missing something important? If so, could you please clarify it? Huge thanks again for your summaries.

Applause and compliments! Thank you.

Love it, hooray Sabine!

This topic is very interesting i will be following it

I'd like to express how amazed I am, but there are no words. Thank you for this 🙏🤓✨

Love the Cambridge joke 😂😂 it was a laugh out loud moment for me

Always interesting.

I absolutely love your content. Great videos, fantastic clear explanations of very complex ideas. As a video producer and editor myself, however, there's just one thing that I cannot help but notice. Your editor needs to work on your key. The fringing effect on your hair can be reduced with a combination of tricks. I can see they've used edge softening. Perhaps a bit more crop and some secondary colour correction could also help by isolating the spill colour and desaturating it. And interesting for you, perhaps, one technique for compositing it is actually based on the quantum behaviour of light. We know light spreads and bends around objects. Some compositing software allows you to spread and blur the light from your added-in background a little bit in front of the keyed subject. This makes things look even more natural. Well enough of the unsolicited compositing advice. Great content. Most people won't even notice what the hell I'm talking about.

WOW Sabine! This is the must succinct explanation of the problem with quantum gravity ever! Many thanks! What I'm confused about is why there isn't (or is there, I'm confused!) a minimum gravitional pull rather like a Planck length, below which there simply is no gravitional measurement possible? Any clarification would be appreciated, thanks.

Another fascinating video! Thank you, Sabine! At 4:43, the statement is that "...normally quantum properties go away the larger the object". Do the quantum properties really go away or do they just become so overly complex that they are immeasurable rather than disappearing? If space is discrete (quantized), wouldn't the probability of a particle's presence drop off in discrete increments from the point of highest probability such that it's probability of presence eventually falls off a quantum "cliff" and becomes zero? It seems like the probability of the macro object being in a certain point in space is an aggregate of all the particles' limited probable locations. So the "location" of the macro object can still be a bit fuzzy. but so immeasurably, quantum-wise, small that we cannot observe or measure it.

That's the paradox. Cambridgeshire is the driest County in the UK, but it always rains.

I love the way you consistently pronounce Einsteins name properly german-like (ein-schtein) 😭💯🔥

Sabine, your great scientific movies are attracting me to watch. What a great force!

Thank you

Fascinating stuff indeed, Sabine! 😃 But if I had to bet - and I'm not a betting person - I'd say that both theories would need some adjustment. But... We shall see. 😊 Anyway, stay safe there with your family! 🖖😊

Sabine, I would love to hear your thoughts on wolfram physics - it seems like it might solve intractable problems like this. Also I need it explained by someone smart enough to understand it 😅

Stupid question... does all mass have the same gravity regardless of atomic composition? e.g. For example for the same mass of say H2 or tritium , would the gravitational force the same?

4:25 yeah but that’s also why it’s so fast to integrate the quantum into the differences of earth and celestial bodies and such. It’s like the accumulation builds up connections and the differences are connected but aren’t aligned enough to see accurately

What an exciting topic.

Sabine; as time goes on your explanations are getting better and easier to understand. (Hat's off to you). As a layman, I don't understand the fixation on quantizing gravity. It seems like matter (and it's alternative form -- energy) are quantum. But Einstein described gravity as being a curvature of space. That is very different from mass and energy. Yes, mass can curve space, but that is different than saying that mass can be converted into gravity or vice versa. To put it differently, mass is a noun, and energy is a verb. But gravity is actually more of an adjective to use a linguistec analogy. It would seem to me that gravity needs it's own set of descriptors rather than trying to shoe-horn it into the system that apllies to matter/energy.

Fascinating!!!

Fourier series and Laplace transform!!! Like you, Sabine, I also have the sets of traits that humanity decided to name ‘autism spectrum’. My logical skill is above average, I’m not a savant; however, since before I could read I ‘knew’ about Fourier Series (impossible to explain in words). In my peculiar mind I can ‘see’ and predict how oscillating potentials in different proportions give ‘birth’ to physicality (I won’t mention metaphysicallity due to its inherent subjective and non empirical nature). After I truly studied this beautiful language in engineering college and got to know Laplace Transform, it made even more sense; I even wrote about how gravity itself is this infinite sum of tiny ‘forces’ (realized potentials) that are everywhere and everywhen; I also played a bit with this and the gorgeous Maxwell Equations, but my Calculus IV teacher did not enjoy my ‘disruptive’ ideas very much. Oh well. In terms of our zeitgeist, I am given the label of ‘non functional’ due to my incapacity to conform to unrealistic things such as ‘jobs’ and ‘schedules’. Thus, it is most heartwarming to hear about the existence of functional humans who can share and elaborate on the astounding beauty of ‘realized potential sums’ aka gravitation 😊😊😊

but if we measure anything won't that get rid of the "it's here AND there" property? are we hoping to find different results from many measurements even though we'd normally expect the same results given the same setup?

As a complete layman to the math, but a life long reader of anything digestible I find my understanding strangely correct. To me why wouldn't particles that have mass NOT have gravitational forces? Be they the same as larger scales? Probably not. Do they propagate waves? Or is it a constant. What is the gravitational field effect at such small scales. There are probably WAY more mysteries there then in colliding particles together. Just a laymans opinion. Sabine... you are my HERO man! 😂 P.S. the sophisticated humor is THE BEST IN THE INTERNET!!!!

For me, the most insightful part of the video happens between 4:30 and 4:45, where Sabine says, “If you take something heavy, like a planet, then you can measure the gravitational field, alright, but you can’t measure its quantum properties. That’s because normally quantum properties go away the larger the object. *Unless you treat them very very carefully.”* ∴ I draw the conclusion: _we must treat the planet very carefully._ 🌎 Scientific enough proof for me. 👍🙂

to cancel out vibration you can repeat, or you can do the same setup elesewhere *and repeat (the way ligo did it)

Great experiments brilliant.....

I'm sure Sabine realizes better than most how long it will take to validate these results, even if they are replicated. It could takes years to ensure the measurements are not influenced by other effects, much like the "impossible drive" recently tested in space.

The experiment is an interesting step forward, providing valuable hands-on experience in the quantum gravity area for labs.

I lived in Cambridge for a decade. It did indeed rain.

Hi @SabineHossenfelder ! About the course in Brilliant is it only introductory to Quantum Physics? One of the things I struggle with is finding courses that go more in-deep the mathematical formulation of its topic in this type of platforms. If it is not the case, what would you recommend to do without having to do a Physics bachelor's/master?

sorry to hear you were in cambridge, i hope youre feeling better now

If particle can exist in 2 places, ehat happens to its total energy? Does it double for a short time or it splits 50:50 or both versions share the same energy?

Sabine, are you familiar with the J. D. Bekenstein's variant of experiment of exposing the quantum gravity? What do you think of it? (I think it is quite similar to ones mentioned in your videos)

Sabine, you make me glad that I have eye atoms so I can watch you videos❤

Ms. Hossenfelder you are a great storyteller :)

Love your videos, Sabine. Just lay off the schnapps before pressing the record button (yes we can tell.) It's all good though.

I would like to hear your opinion about Wolfram's physics. I hope I haven't missed that.

I’ve heard physicists talk about classical relativistic gravity not working with quantum theory, but I’ve never heard anyone talk about what goes wrong when you put particles with superposition in relativistic spacetime. What happens when you assume that each location of a particle curves spacetime, and then add up the effects of sextillions of particles interacting in that spacetime? How much does this framework deviate from the well-established predictions of General Relativity on these well-observed scales? Could you please make a video on that?

Thanks Sabine, I read the news about this experiment a few days ago and the same question arose, they do something with quantum and they do something with gravity, but where is we measure quantum gravity part. My conclusion was that probably i missed something, now i know it was either not only me or the press releases just made something up and then one copies from the other ( i should have known better as i have seen this pattern so many times before).

Why did I miss this video. It's a realy good one!! All in line with my own visualizations and thoughts. I love it! I am almost certain they gonna find it. Because this would be very logical. It would explain alot of theories. And for sure means that you don't need all hocus pocus in space. It would mean that space is the actual container and that space itself gives way for all these forces to happen. Even when empty space itself cannot be measured. I am realy positive about this. Because in my opinion gravity is the force creating all the other forces. Creating the web that is needed to guide the forces. Like a true weaver ^^

Realy I like this video so so much its interestyng

Hey I have a question, just a tradie so forgive me if it sound silly. In the hadron collider, hypothetically, what would happen if I sent out three particles. One goes one way on the outside at max speed, one goes another way down the middle at a slower speed and another goes the opposite to the first one one the outside of the middle one’s track at max speed My question is what happens to the middle particle if the others pass it at the same time travelling at max speed? Would this work better if there’s two particles in the middle instead of one? I don’t want them to smash I want to know if time or gravity change on the middle particle. Since we can’t travel at light speed I wondered what happens if I have two particles at near light speed in opposite directions passing a stationary particle in the middle.

I was so hopeful in the beginning!!!!

if I could manipulate time backwards then to the present in a bubble around myself and maintain my physical location relative to the expanding universe until I want to move by returning time to the present could I travel through the universe? am I violating any rules?

I've both laughed and cried watching your shows. I don't know why. But I'm thankful for you and what you do. Very grateful!

@SabineHossenfelder Dr Hossenfelder, would you make someday a video about Wolfram physics and the concept of ruliad? I find this topic very fascinating from the perspective of computer scientist, but I would like to hear an honest opinion on that from a physicist. Especially, I would like to know whether this idea is thought to be useful in your field in terms of being an alternative to the standard model, and in terms of being a new way to describe and understand quantum mechanics.

No phone today ?? 😀😀 hi Sabine, I have a perhaps naive question. we all know that the universe is in accelerated expansion. we had to invent matter and dark energy to explain its properties. the question is, what would change if at this moment the universe was in accelerated contraction? how would matter and dark energy differ?

I actually have a question about quantum mechanics. I'm a graduate student but nowhere near dealing with QM. The QM I have dealt with was basically just Griffith's book (not even all of it) and I don't recall that we ever discussed the actual implications of the calculations we were doing. I understand how the different states arise and the probabilities linked to them, but do we actually KNOW that a particle "when not observed" to put it loosely is ACTUALLY in all of its states? What if the states are merely a representation of all the statistical possibilities, but in actuality the particle always was in a specific state, whether it was being observed or not? As I said, I haven't even looked at QM in like 2 years and we never really got into the implications of the theory, just basically used all of the equations and methods and whatnot, so my QM definitely is not on some high level. So, I might be missing something here

In a Field theory of Schrodinger equation (The ultimatum correct quantum mechanical object TO BE CONSIDERED !) , It is the field of probability density of the Wave function second quantized (which extends all over the space) which couples with the gravitational field , not its field excitations (the particles which you are referring for) . This is brilliantly confirmed in State Solid Theory ( everything is very much like the interaction of the second quantized Schrodinger theory with the Lattice of Phonons -crystal second quantized vibrations ) see the excellent advanced text book : H Haken Quantum Field Theory of Solids

I’ve heard you and others say the problem is that GR can’t accommodate a particle being in a superposition. Mathematically speaking, is this because the equations of GR are nonlinear? Clearly the (linear) equations of QM and QFT accommodate a particle being in more than one place simultaneously.

This one was of good quality. It's obviously closer to your expertise. I actually don't understand where the problem is when we put spacetime curvature into a state of superposion. But that's something else. Well, Einstein's field equations will look a little less elegant after that tiny adjustment. Should I try to elaborate the math? I'm hesitating. It might take more time than I can spend for that little exercise. And worse, we are far away from an experimental verification. It's maybe an exercise for people who are young enough to be eventually able to celebrate their success. Thinking about the gravity waves caused by the Bose-Einstein condensate in a physically accelerated atomic clock down to the effects of superposition is at least a challenge for future experimental physicists. Einstein would say that those effects are so tiny that we'll never be able to measure them. Hence the calculations aren't of much use for practical purposes. And "HE" won't do such things anyway, not Einstein, the other "HE".

1:05 "rain" hahahaha i love you

And Cambridgeshire or East Anglia is the warmest and dryest part of the UK because it juts out and is flat so can be a bit windy. It can be warm and sunny there in the summer but it still can rain in the summer.

If these different approaches yield the same results, bonus!

This is way better than your warped space videos. Taking a look at how quantum gravity might actually work. Or something that might reconcile the great divide between relativity and quantum physics. Intuitively, we know space isn't here nor there unless it has particles or something in it to define it. So the "what is space" joke describing it as something that prevents everything from happening at Cambridge is also timeless. See, I knew you knew about this stuff, and are willing to explore what we don't know. That's where innovation is. Thanks for tracking down this research. That's what makes this format of delivery exciting.

Is it the particles that are in two places at the same time, or is it just that the space is in two places at the same time and the particle moves with the space? Our conception of space as something that mostly stays put, stretches due to the expansion of the universe (dark energy), and is warped by mass due to gravity, is likely incomplete. Do particles move through space, or do they move with space, or sometimes through/across space dragging it as they go? Food for thought.

Please provide transcripts for all of your videos in the future so that the public can study further into your psyche using Gemini and AI that can ingest KZfaq videos.

pls correct me where necessary= according to GR a) matter curves space. b) the density of matter determines how much space is curved . c) infinite density (a.k.a. a singularity) means infinite curvature. d) according to published nuclear information, the density of a proton is of the order of 5 E 22 grams per cubic centimeter. e) using GR equations, not QM, what should be the space curvature around a proton?. if one wants quantum gravity, the best place to start is closer to home.

¡Gracias!

1:06 - THAT was very funny!

Good job explaining the incompatibility of General Relatively and Quantum Mechanics, but we need to remember quantum effects only happen at the smallest scales. It's inconsequential in the macro world. We don't need Quantum Mechanics to explain the macro world because it doesn't affect the macro world in terms of gravity. Sure, an item can be in two places at one time, in theory, but that's only because at the quantum scale, the MOVEMENT of a particle moves like a wave, but for it to interact with anything else, it must show itself even manifest itself as a full energy particle, such as the full energy level of a photon or electron, or small molecule for that matter (in a spacetime frame of reference). I say spacetime frame of reference because everything literally is in its own spacetime reference. A small molecule small enough to show the interference pattern does it because it's moving in its own spacetime frame of reference. If it were too large, it stops behaving like a wave because it's total mass in its own frame of reference prevents quantum mechanical effects. Energy and matter can't be created or destroyed, only transferred, so for a particle or energy photon to interact with the universe, its wave function must collapse and show itself in its full energy ripple glory. It'll only affect gravity at small scales we can't detect so it's still inconsequential. It's not like it's creating gravitational effects in multiple places. And quantum mechanics doesn't apply to the macro world because de Broglie's wavelength equation says a massive particle has an extremely small (probabilistic) "traveling" wavelength, which is why larger particles don't show wave-particle duality. The wave probability is so low it becomes an absolute. Saying there's quantum gravity is like saying the smallest quantum gravity is equivalent to the smallest possible energy ripple because energy, like matter, warps spacetime. That doesn't mean gravity itself is quantized. It only means gravity can be as small as the weakest energy in existence.

One clarification, it's not *just* that we can't measure the tinny gravitational forces, the problem is that we are trying to do it "ceteris paribus" (we need to repeat the experiment). The uncertainties on the other forces are orders of magnitudes greater than the gravitational effects for particles. One interesting bulk park calculation will be to use coulomb law to calculate the forces between two protons at say, 1 micrometer, and compare with the expected Newthonian gravitational force. We will find that an uncertainty of 1 part for billion in our effort to equilibrate the electromagnetic forces will render any gravitational effect moot in terms of the trajectory or behavior of the particles. That is why the "Antimatter falls up or down" was such a complex problem.

Hey, sometimes we don't have rain in Cambridge. Usually when we're having snow instead, but...

Simple question and I would love a simple response if available. What gives matter mass?

Honesty + humor = Albert + Sabine ❤️🖖

Question: Is the wave motion of the posited quantum fields in spacetime in any way related to the bending of spacetime by the presence of matter?

Why have I not been notified that you're visiting Cambridge? Yes, we've had quite a bit of rain here lately. :D In fact, it's been raining all day.

Isn't the curvature of space-time only applies to 2 dimensional geometries? If anything, space "curvature" in 3 diemensions is compression. I know it is a way to easilly conceptualize, but it seams wrong.

Another expect you should have mentioned is stability: how long will the information remain readable?