What If Gravity is NOT Quantum?
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The holy grail of theoretical physics is to come up with a quantum theory of gravity. But after a century of trying we really have no idea how close we are, or it it's even possible. But we shouldn't feel bad because it turns out that the universe is doing everything it its power to make this as difficult as possible. Or it's telling us that it isn't. Should we take the hint?
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That bit with the equations ending up with the Schwarzschild radius is like the universe is doing stand-up comedy and going “thank you, I’m here all week”
It's always funny to me when stuff pops up where you wouldn't expect it to. Like, "oh wait, don't we already have that formula?" Or, "wait, the fine structure constant again?!?!?"
Seriously, first time I saw this. As soon as that equation popped up, didn't think twice. I was like wait a minute... isn't that the... (matt says the rest for me)
The fact that it's just past the edge of possibility (rather than way past it or even say 7.3 times past it) seems extremely suggestive.
To me, that coincidence strongly suggests the two are related somehow. The limit to measure something with the calculated properties of a graviton and the limit to which the curvature of spacetime matches the limit of causality feel conceptually very close to begin with. Though I'm sure people a lot smarter than me have already banged their heads against that obvious relationship for decades.
And adding "and you can do nothing about it".
My favorite channel where I don't understand 90% of what's going on but still continue to watch lol
At least you are honest. Most everyone else in the comments think they're Neil Degrasse
The only way to really get a deep intuition is to dive into the maths. I reccomens the channel Physics Explained and ViaScience
You understand 10% of this!? You're a genius!!! I'm still trying to figure out what a kHz is.
99%
Understand only 10% cos of the terrible sound audio compression
Considering how much crazy stuff gravity is responsible for I wouldn't be surprised if it was even more fundamental than everything else we know
I like it.
@@johnny12022 Personally I think modern politics would be a whole lot less insufferable if we could disentangle our collective concept of gender from ancient societal mores and mystical arcana.
@@boahnation9932good.
Gravity is a holistic phenomena, that's why.
@@johnny12022that's a long way for the Rabbi to say he's horny for gravity
I will never be not amazed by people who REALLY understand math. You people are gifted beyond believe.
You are only one good math teacher away from the same. My math inspiration came from a video game that actually made what I was trying to calculate perfectly visual (Kerbal Space Program) Bad unthinking teachers that teach for the money will make math seem impossible because they are either incapable or unwilling to make it relatable.
We humans are not, they are tho 😂
You have to learn it. Hard work. Nobody naturally understands it. It’s hard work and dedication
Study and work as hard as people who do and you will too
It's not really a gift, it's abstract thinking. Math doesn't exist in reality, these people just can imagine things better.
The fact that the graviton detector model maths spat out the Schwarzchild radius and so would prevent any confirmation of the existence of the graviton made me laugh more than it should have. The irony is amazing. "We did it! We made a graviton detector!" "Awesome! Where is it?" "In that Planck-sized black hole in the cor..."
Yeah that was dramatic irony worthy of a crime thriller.
But you need to read through the irony and observe the hint. When you have gravity manifesting on the plank length it is in the form of event horizons. So, what we really need to measure is the interaction of event horizons with gravitons. I guess we need to build a particle accelerator strong enough to produce nanoscale black holes.
Maybe the detector only turns into a black hole when it detects a graviton. That's still a detector.
As Susskind once said:"Quantum mechanics is always like that. You make an experiment to check whether something is happening and the experiment itself makes it happen".
@@cezarcatalin1406 if it's "Nanoscale black holes" then light can't fit in it?
I love how in all this insanely complex science the one thing Matt chooses to clarify is "1khz - that's a thousand hertz". Thanks Matt, it all makes sense now!
Yes!
:D
I felt smart that he had to clarify this when I already knew it
It's his version of the "Everything is just according to keikaku" meme :)
😂 lol. At that moment I was like, okay. I’m with you now. Lol
Us: what's gravity really? Universe: Shhh don't worry about it
Its a challenge to understand , for some of us . This Universe . Not you it seems , but many , many , many do .
It’s crazy how literally the most recorded/observed universal force still remains a mystery.
Of course "it's crazy" ! Because the [Universal Force] you are talking about is simply [Allah Force] God Almighty, and as mentioned in Surat Al-Hajj in the Holy Qur'an: "Do you not see that Allah has subjected to you whatever is on the earth and the ships which run through the sea by His command? And He restrains the sky from falling upon the earth, unless by His permission. Indeed Allah, to the people, is Kind and Merciful." God has bestowed upon us the gift of contemplation so that we may contemplate His creation and how He controls this great universe in a way that exceeds the ability of any creature and in a way that is unimaginable. "The Great" is one of the most beautiful names of God.
Lol. Thats only true if you assume gravity is a force and not a geometric property of space-time.
@@omarmassad3041😂
um....@@omarmassad3041
@@omarmassad3041there’s a bit of an issue with lack of peer review there.
This is what S tier quality content looks like KZhead. Promote more of THIS and less REACTIONS/PUNDITS/CLIP CHANNELS to the world. Signed the Internet.
Won't happen. It's about what makes them money.
11:51 - Thank you for clearing up what a kilohertz was. Everything else in this video is easily understood, but without knowing what this strange kilohertz thing was, none of it would have made any sense whatsoever. So, thank you again.
🤣
The fact that from quantum definitions, such as the uncertainty principle and Planck's distance, one can derive a relativistic concept such as the Schwarzchild radius, seems to indicate to me that there might be something there that connect both.
Matt I did the survey, just for you! To show my gratitude towards you. So kind of you for posting videos that helps me to increase my knowledge and intelligence time to time! I eagerly look forward to more videos from SpaceTime! ❤
This always confused me. Doesn’t Einstein’s theory mean that gravity is NOT a force but the curvature of Spacetime? If so, why would it act the same as the other “forces” and have any need to be quantized?
Because some physicists are stubborn and they want to be the new Einstein when in fact we already have a magnificent theory of gravity called General Relativity
Because you are right, not confused at all. Graviton is just a fantasy like the bigfoot
The issue is that relativity is not a theory of everything, its math doesn't work with quantum theories, so it explains gravity but ONLY gravity. Its success there doesn't man that it must be the final answer. I am locked out of my house. Einstein has the key to HIS house, it works 100% of the time, brilliant. I'd still like to know how to get into his house *without* the key, since it might help me get into all houses, including mine, especially since my key is on the kitchen table. His key is very nice, but a non-key solution would be best here.
The electromagnetic force is also the curvature of the electromagnetic field so it’s not unusual.
The primary problem is this. You know how "the electron goes through both slits"? Where's its gravity while it's doing that? You need to quantize gravity so you can have quantum particles (and all the weird that goes with them) that have gravity.
The way the slowly zooming stars do a parallax scroll when Matt is moved around the frame is just perfect.
AND his hair is gorgeous! lol
Right so true. I’d love to see the star effect giving some illusion of movement over the still background too
This is the natural consequence of Matt being several thousand light-years tall.
The more i become convinced Emergent Gravity proponents are onto something... gravity doesn't act at all like the other forces, most likely becouse it's not a fundamental force but rather an emergent one, like pressure
I think as we begin to grasp the fundamentals of our universe, we'll realize so much more "fundamental phenomena" are really emergent from other, simpler things
I agree. I’ve been saying this for decades. Einstein himself didn’t really believe gravity was a force. Even now, it’s sometimes described as a force under certain conditions, and as not under others.
Gravity is definitely not a fundamental force. My guess/theory is that its an emergent property - an artifact of the expansion of the universe. This would explain both why it appears to be irrelevant at the quantum level, and why its indistinguishable from velocity. If it has any association with quantum physics at all, it will be because the expansion of the universe is found to be a quantum phenomena.
@@Vorpal_Wit it’s interesting, but gravity depends on two factors, space and mass. Take either away and there’s no gravity. I compare it to a moire, where you need two (or more) sheets of lines of clear plastic, one over the other at some angle, to create it. If we think of one as mass and then other as space, then take one away, the moire disappears, showing it’s not fundamental as the lined sheets are. To me, this means that the search as to how to quantize gravity is useless, since it’s not a force to quantitze.
@ss agreed everyones way of thinking is wrong. for example when you jump out of a building. you are stationary and not moving its like being in a space ship and jumping off once the acceralation from the ship is gone your stationary in space.. you are not falling to the ground.. the earth is a spacehip moving through spacetimethe Earth is racing towards you and collects you like a bug on a windshield. there is NO gravity involved cause your not falling. I don"t Understand how you can detect something that doesn't Exist
You know one thing that Matt said in an earlier video that I'm going to keep with me for the rest of my life. There really aren't any singularities. A singularity points to a gap in our understanding. Solving the singularity leads to new knowledge.
I always wondered: why would it be quantum if gravity is just curvature of space?
Because if it is not, we are just left with an infinite curvature at the center of black holes. Yet at very small scales the interaction of forces (which are quantizied) and gravity has to happen and prevent this infinite curvature. If this is so then it means the gravity also has to be quantizied at least at the Planck's scale which is the common assumption in string theory and quantum loop gravity. Physicists really don't like infinites and making these infinites disappear is also one of the strong theoretical engines that led to the progressive unification of forces within more and more general theories.
"Why would EM be quantum if light is just a wave?" Gravity is just the curvature of space, and space itself could(and probably is) quantized.
According to GR, even a single electron must curve spacetime a tiny bit. And since an electron is a quantum object, its curvature of spacetime would have a quantum nature. That’s my understanding.
I also don't understand. I don't understand why gravity is regarded as a fundamental force at all. If it's the shape of spacetime that causes matter to move, it seems to me it's a property of spacetime rather than a separate field/force like electromagnetism etc., and gravity is a wave in the medium of spacetime rather than a wave in some field; and even if spacetime is quantized, then gravity would be quantized by association, not because it is carried by a boson of some kind. I'm sure I'm missing something. Also, how were weak and strong forces shown to be quantum without the positive/negative trick?
@ObjectsInMotion Prove it lmao
15:05 I literally got chills when that equation appeared. is that as weird/spooky as it feels?
Same, something about following the reasoning of the only method we've now got for measuring gravity waves ending up with a resounding "nope, that's actually *precisely* impossible" is pretty spooky.
It's incredibly ironic. Trying to quantize General Relativity leads us directly to a General Relativity law 😂
knowing math it's probably not a coincidence
Why must everything be "literally" these days? Can't you just say "I got the chills"? The English language is being raped....
@@matthews1256This is, quite literally, ridiculous.
"Your videos always leave me in awe and eager to learn more about the mysteries of the universe. Thank you for fueling my curiosity. "
I love the fact I just begin theorising and mindstroming as soon as we started the questioning!
I hope someday all of humanity understands how important these videos are. Incredible work by Matt and the rest of the team; truly a gift to humanity
THIS VIDEO AND ALL THE PHYSICS CHANNELS DO THEIR BEST AND THE KNOWLEDGE THEY OFFER IS VALUABLE BUT IT WILL TAKE A LOT OF TIME FOR THE YOUNG GENERATIONS TO UNDERSTAND THE REAL IMPORTANCE OF THESE VIDEOS BECAUSE THEY SPEND MOST OF THEIR TIME EVERY DAY WITH EVERY SILLY THING THEY SEE IN THEIR SMARTPHONES.
@@amaliaantonopoulou2644 Why are you screaming? Did you forget to take your medication again?
I guess this is what sets people apart. Interest reveals depth.
@@amaliaantonopoulou2644 Light the caps lock key?
It's VERY interesting, but a video saying we don't know, isn't overly important. We already knew that we don't know.
I want to thank Matt and the rest of the staff. This is my favorite channel of all time.
And space!🎉
Of all... Spacetime!
This is my favorite channel on the Citadel 👍
@@LandonKuhnhahaha you beat me to it!
*Kanye:* OF ALL TIME!
I'm a big fan of Freeman Dyson's book "Origins of Life" as someone belonging to a field of science. I had no idea he also had such a big contribution in the field of physics. The man's a legend.
I read his autobiography. It's not very long. It's inspiring. He was always his own man.
Amazing vacuums.
This is so unbelievably fascinating. Thank you for making this. I really wanna see quantum gravity figured out before I die
That might require extreme life extension to be developed before you die. I'd be happy with seeing fusion power become part of our energy mix.
This gives me a good enough reason to live the next few trillion years. Who can be done with life when we still don’t know if gravity is quantized?
You don't get it yet. There is no gravity. There is no distance. All illusions. There was never a Big Bang Tom. We're still in the singularity!!
it might be possible
The largest structure mimick the smallest so the quantum field is a ansitropic and chaotic strands and nodes system. In short, its literally impossible for two things to be the same and you could never cut something exactly in half. Everything is asymmetrical. But humans are so stupid idk if they figure this out before I die lol.
@@danmurray1143but... Cake!
This is basically my answer to "You wouldn't want to live forever because you'd get bored!" Nope. There's a lot of Universe, and it has mysteries.
1:36 I think you've got the strong and weak nuclear forces switched up there.
I was thinking the same thing and I was surprised. No one else had noticed it until I saw your comment. The strong force is the force that holds together atomic nuclei and the weak force is responsible for radioactive decay and the pictures that they showed were exact opposite of that and i was like why didn't they notice it? More than that, why haven't they responded to it?
Mistakes are nessissary. They allow for the testing of the quantum nature of knowledge and its force carrier education.
looks like nothing mediated your education on how to spell "necessary" @@blshouse
@@kjv35 Missed takes are necessary. They allow for the testing of the quantum nature of knowledge and its force carrier education.
Came to the comments section to see if anyone else was talking about this lol
Matt discusses the near insurmountable problems of detecting the graviton (if gravity is quantum). But the question was what if gravity was NOT quantum. What if it's entropic gravity as contemplated by Sakharov and Padmanabhan? That's the question I expected to be addressed. How could we test those theories.
I always try to come up with one takeaway from these very complex, wonderful videos. For this one: "Nature prohibits us from figuring out if gravity is a function of discrete bits of information called gravitons by forcing the production of a black hole if we try to measure something at the miniscule size needed to do so. Therefore, the best way to observe gravitons would be indirectly, but we aren't there yet." My 7-year-old brain's takeaway is "We'd better get cracking on this because being able to turn gravity on and off would be dope. Also, let's make some tiny black holes!"
We are probably making millions of neutron sized black holes that evaporate before detection in the large hadron collider every hour of runs. Not to worry though. They are as useless as a toothache because we can't get anything from them. They decay very quickly, like the higgs.
You know, some years ago when I first started watching these Space Time episodes I had assumed myself pretty knowledgeable on the topic for somebody without a formal education, only to find myself rewatching episodes again and again to grasp ideas... Nowadays, I acknowledge the fact I have absolutely no knowledge on the topic and yet somewhat bizarrely only require one playthrough to understand what is being taught. That is to say, Matt has a fantastic way with words that has managed to educate a Dunning-Kruger effected simpleton like myself.
Same here mate!
Add me to this club
Now I just need two playthroughs
Me too! I think it has to do with memory and retention… i fully understand as it is being explained, but a week from now it’s gone.
im a dumb smart person too hello
The best part is when, in the middle of this very complex subject, Matt says, "...one kHz, that's 1000 hertz." Thanks Matt 😂
1 kb is 1024 bytes
@@HoD999x no, 1KB is 1000 bytes, what you're talking about is a 1KiB (en.wikipedia.org/wiki/Binary_prefix#kibi)
@@feandil666 Quoted from the wikipedia article: Note: in information technology, especially for measurements of memory capacity in bits or bytes, it is still common to use the decimal prefixes "kilo" (with symbol "k" or "K"), "mega" ("M"), "giga" ("G"), etc, to mean the closest binary prefixes "kibi" so congrats on being pedantically correct. the worst kind of correct.
@@UODZU-Phe's very pedantic, granted, but riddle you this: who is even more pedantic with no sense of fun or self-awareness? 😂
Hey man, they're called minor attracted people now
Consider the curious link between the Schwarzschild limit, which defines the event horizons of black holes, and the Compton wavelength, crucial for understanding quantum mechanics. What if these seemingly disparate scales, a geometric limit and a dynamic one, are connected by a process known as dissipative entropy, as explored in Prigogine's work, along with non-local long-range correlations? Taking Rényi entropy, which was discussed in a previous PBS video, as a form of dissipative entropy, we might find intriguing possibilities. One hypothesis around Rényi entropy involves the processing of imaginary spacetime topologies within black holes and their connections to black hole simulacra. This concept could serve as a bridge between gravity and quantum mechanics, suggesting that the expansive scale of black holes and the minute scale of quantum particles are both products of the same cosmic processes that shape the diagrams of matter-spacetime. The synthesis of these concepts could lead to a novel understanding of quantum gravity, where the universe's behavior is governed by principles that seamlessly integrate quantum entanglement, gravitational fields, and entropic dynamics. This unified behavior would reflect a cosmos where quantum and gravitational phenomena are different expressions of a deeper, entropic-driven reality. This perspective could offer a bridge between gravity and quantum mechanics, suggesting that both the geometric scale (Schwarzschild limit) and the quantum scale (Compton wavelength) are products of a cosmic process that shapes matter-spacetime topologies. I wonder if someone, inspired by Weirstrass' understanding of limits, as not static by dynamic, i.e. generated, produced, so if someone could derive the Schwarzschild radius and the Compton ray from dissipative entropy. Dissipative entropy goes beyond mere chaos; it's about the self-organization of the universe, influencing quantum states and spacetime's curvature alike. Imagine long-range correlations, akin to those observed in non-equilibrium systems like black holes, functioning like quantum entanglement but on a cosmic scale. Such correlations could elucidate the profound connections across different scales, pushing us closer to a unified theory of quantum gravity where the behavior of particles at the microscale and the structure of spacetime at the macroscale are derived from the same entropic underpinnings. The 'extremes' represented by the Schwarzschild limit and the Compton wavelength might be more closely related than we think, potentially linked through cosmic processes similar to wormholes (that may be the epitome of long-range correlations). This perspective implies that gravitational phenomena, from the macroscopic to the quantum level, are emergent properties arising from the same entropic interactions within the fabric of spacetime, challenging the traditional view of gravity as a purely classical force. Central to this discussion is the concept of nonlocality, which lies at the heart of quantum entanglement. By extending nonlocality to include gravitational interactions, we propose a mechanism by which quantum characteristics can impact and be impacted by the broader cosmic structure. This suggests that the universe is governed by entropic dynamics that effortlessly integrate the quantum and gravitational domains, pointing to the intrinsic quantum nature of all forces, including gravity.
I think Wolfram's physics model that is computationally irreducible is going to give us the answer for how to quantise gravity.
This is definitely going in my "Most Mind Bogg-Ling stuff I watched in 2023" list. Love it.
Not
I'd love to see you explore this question more - what would be the implications if gravity simply is not quantum?
Um... we would feel the effects of gravity of everything in the universe, pulling us "outwards". The effect would be immeasurably small, and completely counteracted by far greater forces pulling things together, but it would be there nonetheless.
@@annoloki I think that would be way more interesting if explained at more length by a sexy Australian man, thank you 😃
@@recurse Did you just _assume_ that the person who just answered you _isn't_ a sexy Australian man?! 🤨
@@Takyodor2 I assumed they were a 780 pound Japanese Macaque, but it makes like difference when you can't see or hear them 🙄
@@recurse I'm going with sexy Australian, but each to their own 😆
I loved pretending like I understood any of this 😂
I do believe the reason higher-dimensional mathematics is so complex is because we've rooted the definition of orthogonality in perpendicularity, with no regard to implicit reducibility of composite numbers.
Wow! That’s uncertainty principle calculation for gravity beings us right back to general relativity 😮
amazing right? like if the universe is trying to tell us something
Relativity probably already explains quantized gravity, or relativity is a predictable result of quantum mechanics. Like an emergent force.
Survey completed 💯 Also - been watching since high school. Now a fourth year physics and math major. Thank you for inspiring me. Matt is the greatest.
Fantastic video as always! I am sorry to point it out and I only say it because I am Danish and super proud of Niels Bohrs achivements. You spelled his name as “Neils” but the correct way is “Niels”. Just thought I’d let you know. Fantastic video and Matt is fantastic at making it somewhat understandable.
It's strange that gravity is at the same time the "least quantisable" force of nature, but yet it's so fundamentally connected with light, whitch itself has been quantised. Great video!
@@Fantredath Time isn't a force. It's a concept, not anything tangible. You don't need time to exist for actions to take place. People mistakenly think of time like it's what allows for actions to occur in the first place, like some guiding hand. But that's energy and velocity's job.
@@Fantredath That's because everything involving time is just a reference in relation between something else. This is why photons are said to be outside of time, because when they're traveling through space on their own with nothing to encounter, no action is occurring. It may be moving at a fixed velocity, but it is essentially frozen in time. It's only when it encounters something that anything occurs or changes. Which means it needs to interact with matter in order for any time passage to occur, because we inherently tie the passage time to actions/change. Of course that's not entirely true, it's only a concept, because even light travelling through space has a reference point of time, and that is how long it takes for it to get to where it's headed, but we still only derive that passage of time from relation to other sets of objects, like the planet revolving around the sun. Since "time" is still occurring for everything else, that's the reference point, but time is still only ever a concept, not anything tangible. Even if you were to use a blackhole for time travel, you could only ever travel forward, not backward, and that's only because the nature of the blackhole changes the relation between other reference points. At that point it's not really time travel at all though, it's more like putting yourself in a stasis capsule. The main takeaway though is you don't need time to be tangible for things to occur. Time is merely our observation of interactions that we measure.
@@Fantredath Einstein did more to elucidate the nature of time than anybody. We know time is NECESSARY but we don't know if it's "real." Frank Wilzchek's work on Time Crystals may shine some light (pun intenended) on this topic. You should Google it. Fascinating work.
@@peoplez129 It depends. Photons, from their perspective, don't experience time. But that's based on the MODELS we use. See, time is a relational phenomenon. In quantum mechanics, particles make no distinction between "forward" moving and "backward" moving through time. However, WITHOUT time, all things would happen instantaneously. So surely time must have some relational meaning that is fundamental to all other phenomenon. I suspect the same "uncertainty principle" that limits how much knowledge we can extract from a system equally applies to time. How do we measure that which all else is measured by? It's a paradox.
It is not connected with light - it's just the light, having no mass, travels at the highest speed space-time allows. And even then perfect vacuum is impossible so light travels a tad bit slower than c.
That Schwarzschild radius equation is the biggest middle finger in physics since the vacuum catastrophe
Haha right (please explain, I have no idea what you’re referencing and want to know) 😬
@@Jay-nj1rq This channel made some videos on it. Essentially, empty space has energy that contributes to dark energy. We tried doing the math (on the quantum physics side), but we predicted that a teacup of vacuum has enough energy to boil the oceans. Like 10^120 times off what it should be. Widely cited as the worst prediction in all of physics.
I completely understood 1×10 to the -37th of this video.
Thx, pretty good explanation of one of the most important questions in Physics..
Best channel on YT by far. Keep up the amazing work. You inspire humanity
Thank you PBS Spacetime and Matt for teaching us. ❤
I need to stick to easier topics like "What if the tooth fairy really exists"
Matt? Oh, you mean Floating Matt? jaja
🐜 I still want to know how we quantize gravity to describe the scale of effect on each other of dancing ants at opposite ends of the universe... 🐜
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.
Amazing video. The appearance of the schwarzschild radius blew my mind. The relationship between Heisenberg, planck length, and black-holes is crazy. Did we stumble on a kind of circular reasoning? Or are we facing a fundamental relationship?
If gravitons indeed existed and were emitted by mass, wouldn't that mean that mass would have to be diminishing over time, equivalent to the energy emitted through gravitons?
It's always seemed a little strange to me. To use an analogy: Gravity is a measurement of the bending of space (space flowing around mass) like light around an object could be measured by the shadow being cast. But you'll never find the particles that make up a shadow.
Yes, I do like this comment!
That’s just excellent!
That is untrue, you can find the particles that make up a shadow. Not in every day life, but the absence of particles in a medium act just like particles do. For example, holes in a semiconductor are like electron “shadows”, but they act just like positrons. Particles are not physical in the way people think, they’re excitations in a field. All this is to say, just because gravity is “just” the bending of spacetime, doesn’t mean it doesn’t make sense to think of it as also being made of particles.
Yes....only the Shadow knows. 😉
It’s just as weird as things not having mass until they interact with a Higgs boson
Gravity pulled us all here
Or did it?
We simply followed the warp of space-time
Came here to make this comment. Well played sir, well played.😂
Gravity doesn't pull. It just is.
Pretty sure that electric potentials are more important for my brain than gravity 😂
Hahahaha! I have to admit that that is the funniest discovery I've heard of in all of physics that rearranging the formula for measuring a single graviton ends up being the Schwarzschild radius formula 🤣 The universe has a sense of humour after all :p We should've expected something like it as well, with things like special relativity and the uncertainty principle predicting things that we previously thought to just be observational quirks that we could perhaps just calculate and measure our ways out of, it makes sense that we'd run into something similar with gravity sooner or later. Apparently it was sooner 🤣
Every once in a while a presenter hits a superlative level of communication. I believe this video is an example of that. After doing so many videos, to achieve such excellence is amazing. Keep up the good work.
What are the alternative theories of everything that doesn't rely on gravity being quantum (if it is indeed not)? I feel like that was missing from this video.
I second this. It seems to me that if gravity isn’t quantum, the only options for understanding physics is either we need a new way of thinking of the unification of physics, or physics includes fundamental paradoxes and inconsistencies, which would be absolutely wild for science.
The alternatives are basically knows as "gravitization of quantum fields." Instead of quantizing gravity, we gravitize quanta.
@@SashaRomeroMusic do we need a unified theory?
I'm not sure we have any particularly good contenders honestly. The problem with gravity being non-quantizable is that it immediately re-introduces the concept of infinities and div/0 and a bunch of other paradoxes that quantization generally prevents - which is why most physicists are convinced that it has to be quantizable at some level, because reality basically shouldn't work otherwise. :D That's not to say there's not another possible non-quantum theory, but it would likewise have to sidestep those same problems, which is a fairly high hurdle.
To put it short: there are none.
Question: What if we assume gravitons are real? Can you make a video(if you haven't already) about what would that mean for quantum mechanics? Can we use hypothetical scenarios with gravitons to explain the universe with precision? Also, I love your show. You're the best!
there is no globally accepted maths for quantum gravity, and every single one doesn't explain all observations, everyone is waiting for experimental physicists to give them some weird anomalies so that they can find a path..
I appreciate the more in depth analysis even tho I have no idea what you're talking about
Error at 3:45. His name is Niels Bohr and not Neils Bohr....
Niels is a Scandinavian name (Danish) pronounced "nils", with a short i like in "bit". By the way, the Danish language is nearly the same as Norwegian and Swedish, but with an incredibly soft and blurred pronunciation. Everything said in Danish has a certain uncertainty that the listerner must take into account when listening to it. That also holds for Danish listeners. The phonetic opaqueness of this Scandinavian dialect makes guessing based on insuficient bits of information a great part of Danish culture. I am not joking. It has been studied scientifically by linguists. I wonder if the Danish man Niels Bohr's thinking was influenced by this cultural impact, because what he claimed about QM is far from clear. The Copenhagen Interpretation is as messy as it can be.
The I and the E are quantum entangled.
@@knutholt3486 I am in my comment stating the obvious fact, that his name is spelled/type wrong. I am not going into the pronounciation at all. I know ALL TO MUCH about how english speaking people tend to get that name wrong: The fact is, that I am danish and my name is Niels Peter + more than half my family is english speaking (scottish and new zealandish) - and for 50+ years my aunts still pronounce my name as Neils (which makes my ears cringe)
@@Rynas Well, I guess the Danish pronouciatian imply the phenomenon called "stød" in Danish that to an English listener may make it sound like "neils". The phenomenon is a slight and rapid restriction of the vocal cords. Swedish and Norwegian do not have that phenomenon, but instead tune differences. By the way, also English is a phonetically rather blurred language and with a crazy spelling standard, so giving all this you cannot expect otherwise. I remember my first English class at school when the teacher told that the words are not spelled quite like they are pronounced and said that each word you must learn it two times, as it is spelled and as it is pronounced. I immediately decided that this garbish I will not make any effort to learn. But over the time I learnt English well enough just from the sideline without much work. So after som years I got good marks also in English. But still I do not take English orthography really seriously, and I use rolled tongue tip R rather than the horrible retroflex approximant used in America and parts of England. But otherwise I use American pronounciation. Thus I manage to doctor up English to a reasonable level of clearity.
Looks to me like the programmers who coded the gravity didn't really talk with the people who coded all the other forces.
“You did everything with floats? But we did it all with ints! Ugh great, now I can’t just increment or decrement everything!“ And… black holes are a glitch from bodging them together somehow? I know a decent amount about how computers work on the circuit level for each module (register, accumulator, adder, what have you) but the wider structures in programming elude me so the metaphor breaks down there… (much like quantum gravity itself!)
It'd be cool a video about negative masses and why they are not considered. Thanks Matt for the cool video!
I read online a negative mass sphere drawn to ordinary mass would accelerate to infinite speed
If negative masses existed, it would likely be possible for a combination of particles to spontaneously appear without breaching energy conservation (eg some mass as a mix of particles and antiparticles, and some negative mass as a combination of particles and antiparticles (the idea of the mix is to ensure all conservation laws are respected). It's doesn't have to add up exactly - some kinetic energy will make it balance. As this is not happening it seems negative mass does not exist.
There _is_ a PBS SpaceTime episode on negative mass. It isn't taken seriously because it doesn't make any sense on multiple levels. Others have mentioned the stupidity that happens when you try to give gravitational equations negative masses, but it gets stupid under just conservation of momentum. Angular momentum, as well. In quantum field theory, all particles' masses are generated by psi•psi* terms where psi is a field, so it can only generate particles with real positive masses, as well.
@@davidhand9721 To be complete, it generates zero mass particles without problems.
Its "Dr" Matt
That is actually crazy. What an underrated video.
That was a great episode! Always watch y’all
Not Quantum Gravity, but Quantum Spacetime!! One theory is that Mass slows time, which in turn bends Spacetime, which gives us the gravitational effect. So if Spacetime is warped by the slowing of time, rather than directly by mass itself, could it be time that is the quantum property, and as gravity is a consequence (not a cause), gravity is quanta due to its dependency on time.
Quantum gravity is synonymous with quantizing spacetime. Both space and time are quantized. Maybe on the planck length/time scale.
@@handhdhd6522 but if gravity is the consequence, perhaps we should look for a quantum unit of time.
@@jsytac there is a quanta of time, Planck time…
If gravity ends up not being quantum, then I fully believe quantization will end up just being a more concrete example of some abstract quality that gravity also follows, similarly to how particles are just a convenient understanding of the excitations in fields. That said, the argument that "a graviton detector will turn into a black hole" is extremely compelling to me for non-quantized gravity, but it depends on how well-done that thought experiment was and whether there are any subtle assumptions lying in there that we can pick apart. (Maybe it's just because you guys and Dr. Becky posted at the same time, but I can't help but think of the issue with finding dark matter as particles too. Though that line of thinking has been pretty ravaged by bad PopSci and regurgitations, I feel like, so it's hard to approach as a layman who wants to be rigorous.)
Space belt 13 is mine just as soon as i do quad physics in a basic divine way. CN-12=N4 is dash light, but Bio 12 is inhalated light by some time lift thats out there beyond the sights of Jupiter.
I am always impressed with the massive effort and competence displayed in these S-T videos. This one above many others.
Amazing episode! Thank you, I've learnt so much about cosmology from your show 😀
Hey there, love your videos! I usually watch with subtitles on and noticed a few transcription errors in this video, some of which might make some people grumpy. 1:40 Quant gravity -> quantum gravity 3:28 the mid 192 -> the mid 1920s 4:49 one AIS of -> one axis of 5:33 field so bour and rosenell -> field so Bohr and Rosenfeld 7:32 principle but war and Rosenfeld -> principle but Bohr and Rosenfeld 8:42 B and Rosenfeld -> Bohr and Rosenfeld 9:11 B and Rosenfeld -> Bohr and Rosenfeld 10:41 the two Lio facilities -> the two LIGO facilities 11:06 gravitational W of detector -> gravitational wave detector 11:30 a ping 5 m 630 NM red -> a piddling 5 mW 630 nm red 11:47 10^ of -1 Jew per cubic M -> 10^-11 joules per cubic meter 12:00 3x 10^-48 Jew per Cub M -> 3x 10^-48 joules per cubic meter 12:20 10 37 -> 10^37 12:29 10 ^ of 37 -> 10^37 15:16 for the SQA Shield radius -> for the Schwarzschild radius 15:27 black coal -> black hole 16:49 vein as the B Rosenfeld -> vein as the Bohr-Rosenfeld
Thanks for putting in the effort! Some of these are hilarious...Jew per cubic meter... lol
thank you please @PBS see this and bless you @nicodemusAllenTonar
As we express our gratitude, we must never forget that the highest appreciation is not to utter words, but to live by them.
Unless these words , they are wrong .
The equation for gravity, includes the mass of two objects and the distance between them. These objects are normally moving over a period of time. One could say, gravity is just a function of the movement of an object over time through space. Or space time. Maybe gravity isn't a force at all, but just a measure of how space time is affected by masses moving through it.
I'm still confused: what is the answer to the question "what if gravity is not quantum?" In other words, what are the implications for physics if gravity really is non-quantum? Would that be in any way paradoxical? (btw, loved the episode as always -- it's amazing how much awesomeness you fit into one of these little videos)
Good question.... The real paradox would be if two quantum particle (that occupy a different time slice) come in close proximity? Would one particle know the future event about to effect both??? I know that sounds kind of sloppy, but you know what I mean?
Gravity doesn't need to be quantum. But everything else is so it's the obvious first thing to try. We need SOME new explanation for gravity, though, because our current theory breaks down at quantum scales. I was assuming he was going to explain what non-quantum ideas existed, but I guess not. I don't actually know if they do exist myself.
@@Merennulli Also, if quantum mechanics is correct and complete but gravity isn't, then you'd end up with mass being attracted to places things… could have been? So if gravity isn't quantum yet that doesn't happen, then you need to augment quantum mechanics with an actual collapse mechanism that actually happens rather than just using it as a good approximation. And that would be MESSY.
@@drachefly Whether gravity is quantum or not, the attraction between masses is between the average of the probability distribution. You're just applying a Feynman diagram to gravitational attraction either way. If gravity is a quantum field, then it just makes the factors quantized, it doesn't change the result. That quantization adds granularity to it, but that granularity is so small the detector for it would become a black hole (the equation he gave in this episode).
@@Merennulli But when do you cut off the quantum treatment? If you position a large mass based on quantum-generated information, gravitational attraction is not going to be based on the CM position of the widely separated wavefunction parts - it's going to be based on the outcome we've observed. Gravity is inside a quantum world; it can't just be not quantum at all.
matt im a neuroscience researcher now, i started watching the channel when i was 13 or 14 when the other host was still there. I am super excited about your documentary and i think itll be the only documentary ill pay for directly... when is it coming out? (the documentary analyzing how our brain constructs reality and the biases that arise in our conception of physics as a result) thanks for pbs space time for being an S tier channel for years now... you guided my intellectual development in ways i probably will never be able to truly appreciate
Sorry if these questions are very dumb, but I'm genuinely curious about this: 1) Is this the reason why scientists are looking for a "Theory of Everything" that can combine General Relativity and Quantum Mechanics? 2) Is there a chance that anti-matter particles could be connected/related to negative mass?
so, we have officially reached the unknowable, but possibly manipulatable. how abstractly challenging! now that is food for thought! love it!!!
Fantastic explanations and visuals, as always!
I want a followup on this episode about Jonathan Oppenheim's theory of stochastic gravity (idk if that's actually what he calls it, but that's what I remember about it). He shows how we could resolve the black hole information paradox by assuming that, beneath certain scales, gravity is fundamentally stochastic, but not quantum. I.e. it is probabilistic but for different reasons than quantum mechanics is, so quantum mechanical laws like "information cannot be destroyed" do not apply. This means that infalling information is destroyed in his theory
Extraordinary claims require extraordinary evidence
@jasonsmith8500 He usually ends his lectures by proposing a pretty legit experiment to test it. It interests me solely because it seems easy to affirm or rule out based on experimentation
Gravity can never be stochastic, that's just a magician confusing people enough that they'll believe anything. As far as The Universe is concerned information can certainly be destroyed and it is quite regularly. You have to realise that these weird propositions are little more than logical game where you follow assumptions and develop a theory which need not have any actual basis in reality .. but the funding pays the bills.
I have another idea which solves the quantum gravity problem: The Z0 Code challenges the traditional notion of gravity as an attractive force, proposing instead that it arises from the flow of quantized energy. This shift aligns gravity with quantum mechanics, where energy is discrete and exists in packets, or quanta. The Z0 Code links gravity to changes in the speed of energy linked to the energy density of the system through the impedance of space. This connection implies that gravity is not caused by mass, as Einstein's theory suggests, but rather by the flow of energy using E=mc². The Z0 Code introduces the concept of gravitational acceleration, Gv=-∂c/∂x, which specifies the relationship between gravity and the rate of change of the speed of light. This formulation explicitly connects gravity to the quantum nature of energy.
No offense intended, just using the technical term, but this nonsensical post, the silly name for your grand unifying theory of everything, and the fact that you came here to promote something you even created a website for and are likely trying to pitch everywhere you can makes you a classical crackpot. I don't mean to offend you but can you ... stop? Read a bit more physics and math maybe.
I love the 16sig disproval of MOND. This is why science is everything & everything better hold still so we can make some measurements! 😊
I haven't waved away MOND.. Oh, no-no-no.. I am just going to poke around & think about 8D MOND -ish -ness. I pray I get something severely wrong! That's almost as good as getting it severely right! Mark it off the list & continue. Let's eat this elephant! Who's with me? Now just the scientist! Now just the garage guys! Now just the AIs! Let's GO!
Thanks for the explanation of Freeman Dyson's analysis. I wasn't aware of it before. Loved the idea that a 10^37 improvement in sensitivity was "challenging, but ... not impossible"!
Physicists are extremely careful in choosing the words they use - that kind of sentence is very typical example of that.
FYI, Freeman is his first name and Dyson is his surname.
@@Duiker36 Lol, I better fix that!
So what happens when you consider the possibility of black hole analogues for the other force carrying particles at sizes beyond the planck length?
I love how intriguing reality can be.
Haven't watched the whole video yet, but my initial thoughts on Gravity is that it is more of an emergent behavior of other parts of physics, rather than its own entity to find. The quantum uncertainty of other interactions creates a constant variable shift in gravity.
Exactly my point, as stated in my comment earlier. Good to know I am not alone in that thought. :)
Is explored in ORCH-OR i.e. Penrose's theory
Why in the fragment with four forces you have strong force for decay and weak force for holding nucleus together? Shouldn't it be vice versa?
Someone made a boo boo
Thank you for covering this subject. I have thought gravity may not be quantified but was always told you’re wrong campbell
8:15 Forgive my confusion but which complex interactions are you referring to here? With electrodynamics I can see how the magnetic fields may complicate the results but I am unaware of any analogous gravitational phenomena. Can someone assist?
As previously posted recently on this site, the number of dimensionless quantum unit squares needed to reconcile the universal gravitational constant with the Coulomb constant is M/m, where M is the (mostly hidden) mass of the universe, an m is the rest mass of an electron.
If gravitons exist, then what do we need curved space for? Honest question. I see that other people have asked about the "gravity is not a force" that we thought we learned from Einstein, but I couldn't find any answers in the ensuing conversations. Near the end Matt seemed to be saying that the notion of gravitons is kind of an open question, subject to potential future experimental confirmation, but that's the first I've ever heard that. Everyone always just glibly says that scientists want to unify the four forces, as though it's already known that gravity is a force (sorry Einstein!). Please, someone explain it to me like I'm 5.
that's why graviton doesn't exist
In classical mechanics the EM force is described by field lines that charged particles fallow. But this didn't stop physicist from quantizing it. Maybe the same could be done with gravity
There are some explanations in the comments already. If I understood them correctly, it is assumed that gravitons create the field that shows up as curvature of space.
Graviton laser? I always wondered if that's what a 'tractor beam' was.
It would presumably be a device made up of some complex configuration of singularities. Once formed, I don't think you could move it except maybe by gravity tractoring it with an immense diffuse mass. Although electrically charged black holes theoretically exist, so maybe...?
If gravity turns out to be quantum in nature, then gravitons should be bosons - therefore useful to produce a "laser", at least on paper ;)
This is a great educational tool for everyone. Than you!
3:40 Bohr's first name is misspelled: It should be NIELS not Neils.
I was reading an article by Ethan Seigel today where he was answering a question about if gravitational waves had wave and particle duality. He responded that we just don't know but that if we could figure out a way to do the double slit experiment with gravitational waves we could find out if gravity is quantum or not.
He clearly is a bit of a dip stick. Gravitational Waves are an effect not a thing.
Very interesting! So, to do the experiment we'd need a way to "block" gravity to construct slits, or perhaps use something that already exists and distorts gravity like the gravitational lensing caused by galaxies that we can observe in space. I wonder how big would our 'sensor' need to be to measure see the interference pattern? Could we use the ones we have already for measuring the gravitational waves?
I have a question/idea. Preface - there is a lot of evidence that we exist in a false vacuum as well as a holographic universe and all observable stuff on the most basic level everything are just waves of electromagnetic energy. Irregardless if you agree or not, hear me out. Idea: Imagine that gravity is the surface of a body of water. The water has a surface tension strength which directly affects how things float before sinking as well as the density of the water underneath. What if our understanding of the universe and electromagnetic energies which we require to directly observe our universe is nothing more than an oil floating ontop of the water. The oil is its own medium that mostly doesn’t homogenize with the water it floats on, however you can directly observe the effects of the waves of water on the medium of the oil. This would mean that a thing with the Schwartzchild radius and the level of energy required to exist within our oil medium might just be too dense and would fall through the surface tension of the water which would then rapidly sink as the pressure from the surface tension is not longer acting upon it. (I.e. black hole) This would also explain things like the Higgs boson as well as possible dark energy/matter. Imagine a dense piece of styrofoam that would normally sink in the water our oil medium is floating on, but the styrofoam is very close to the less dense styrofoam that does float. As the dense styrofoam would encounter and move through the oil, it would accumulate the oil upon its surface and would increase mass/energy but its buoyancy compared to the surface tension would improve, perhaps allowing it start to float. As the dense styrofoam would start to float or at the very least slow down, it would start to saturate with the oil instead of just being a layer on its outside. Which in this case would become observable matter. However if it does not accumulate enough oil on its surface as it transitioned through the oil, it would continue past the surface tension and then sink but the oil would separate from the dense styrofoam and stay with the rest of the glob of oil. This would provide an observable effect on the oil medium, without an observable object. (I.e. dark matter/energy) This idea may also explain how the universe expands space in ways we can’t fully explain. Because the forces from the water affecting the oil can move and expand the blob much faster than the limits that exist within the oil blob. Just some random thoughts. I am curious what others might think?
I really appreciate this channel in all it's in depth videos, but I must admit not being a physisist, it's mostly very hard to understand. I would love some more items that bridge the gap a little more for us mere mortals
Thank you for the video. I love this content so much. Some maths today and also a strong question. If we can't detect a single graviton, do we really need to struggle to extract that theory from our beloved space-time? That's kind of fundamental. What about a non-serious video about muon-mediated cold fusion :) ? Or a video about spin echoes, Larmor procession and NMR ? I'm now working with it. Going for the patreon !!
At timecode 1:38, I think you misslabelled the strong and the weak force. Besides, great video as usual :D
Thanks Matt, To my simple mind, gravity is a function of mass. Mass is quantised (atoms, protons, neutrons, electrons,quarks etc) thus so is gravity, end of issue.
im not even here for pbs space time, i watch these videos because of matt. they help me go to sleep
Measuring one graviton would be a massive event 😂
It would just be a small thing.
I see what you did there
we would understand the gravity of the situation. And also the situation of gravity.
I love any GR + quantum episode from Spacetime!
“We shall not cease from exploration And the end of all our exploring Will be to arrive where we started And know the place for the first time.” ― T. S. Eliot, Four Quartets
My pet theory of gravity is that the fabric of our universe is a lot like a non-Newtonian fluid, and atoms (which move around a lot) cause the fabric to want to “wrap itself” around the atoms, dragging nearby atoms towards each other. The space-time fabric being like a non-Newtonian fluid would also fundamentally limit the speed at which things can move, and thus giving us the speed of light as the fundamental speed limit of the universe. TL;DR: I think gravity is kinda like the effects of a moving thing in a non-Newtonian fluid.
I also think that the gravitational field is a lot like a “4D swirl” that is only expressed in 3D as a simple attractive force instead of a spinning one. To elaborate on my theory: particles have a mass (purely physically expressed energy), which means that in the space-time fabric, they have a “speed even when the overall object they are in isn’t moving. This minuscule speed in the fabric (which I’ll remind you acts like a non-Newtonian fluid) causes the field to “bunch up” in the direction of motion. Assuming that all particles move with a spin-like trajectory (in 4D) this would lead to the fabric twisting around the object (again in 4D). With regular matter, this causes all particles to be gravitationally attracted to one another.with light, which is conventionally massless, there is a fundamental speed limit because it’s motion is so fast that the fabric “bunches up” in front of it, but is relatively unaffected at any significant distance from the photon. But hey, that’s just a theory! And it’s probably wrong, but it’s cool to think about.
Unified semi-classical theories have been available at least since David Apsel in 1978-81, or maybe even Kaluza-Klein in the 1920s. Maybe we should try quantizing those. Also, if you put the (Newtonian) gravitational potential into the Schrödinger equation, then the shifts in quantum phase frequency with energy look eerily similar to gravitational time dilation (in fact they're identical to first order); following that idea leads to some interesting perspectives.