So, Negative Gravity Is a Thing


Thanks to Brilliant for supporting this episode
of SciShow. Go to Brilliant.org/SciShow to learn more. [♪ INTRO] In nature, most of our basic forces both attract
and repel. In fact, gravity is the only exception. As far as we can tell, anything gravity acts
on just goes one way: down. As long as there’s no other forces involved,
anyway. But there is actually an exception to the
exception. On a teeny-tiny scale, we’re exposed to
negative gravity every day. Because, according to theorists, sound waves,
of all things, have negative gravity. And what’s even more amazing is that you
don’t need fancy science like quantum mechanics or general relativity
to understand why. You can understand real-life negative gravity
using classical physics; the stuff you probably learned in high school. Now, I know the idea that gravity acts on
sound at all might seem a little sketchy, because sound waves aren’t some special
kind of matter. They’re just vibrations: the scrunching up and stretching out of molecules
like those in the air. Still, scientists argue that you can think
of them as particles. Kind of like you can think of light as particles,
or photons. In sound, though, they’re called phonons. Phonons aren’t like electrons or molecules
or any other particles you’re familiar with. They’re essentially packets of energy moving
at a similar speed. As a sound wave passes through the air, molecules speed up as they squish together
and slow down as they spread out. And a phonon is a tiny packet of those vibrations. So it’s not exactly a single physical particle. It’s more like a flock of birds. A flock is just a bunch of individual birds,
but you can still identify it as its own unit. And that’s the idea with phonons as well. It’s like a “flock” of vibrations that
emerge from a sound wave. The weird thing about these phonons is, according
to theory, they move upward in a gravitational field. It might seem like that just shouldn’t happen;
that’s not how gravity works. But the reason is actually pretty straightforward. Picture a sound wave moving through the air. Air pressure is slightly greater at the bottom
of that wave than at the top, because the lower air is denser. It’s just like how water pressure is greater
near the ocean floor than it is near the surface. Since sound vibrations travel faster through
denser fluids, the bottom of the sound wave, where the air
is under a lot more pressure, travels faster. And that makes the whole thing bend up. Just ever-so-slightly. That means the sound wave, and the phonons
that make it up, are going against gravity. In other words, phonons have negative mass. Because anything with a positive mass would
get pulled down. This is an actual, physical effect, not just
an illusion. It’s not like an airplane taking off, or
a bird flying, either. Gravity is still pulling down on those things,
even as they move up. But sound waves are actually falling up. And that comes with some pretty wild consequences. The first thing is, over large enough distances,
all sound waves should curve upward. This probably wouldn’t have any real-world
impacts, like, it’s not going to change how we communicate. The amount of predicted curving is so small that we don’t even have instruments sensitive
enough to detect it. But scientists think this effect could be
more relevant in objects like neutron stars, where sound waves travel through super-dense
fluids. There, phonons could significantly affect
the star’s behavior. But that’s not the end of the story, either. Because on top of defying gravity themselves, sound waves should also push away anything
with mass. See, anything with mass has gravity. And not just big things, like, you have your
own gravitational field. And so do phonons. Except, since phonons have negative mass,
they also have negative gravity. Meaning they should repel anything with mass. Again, we don’t have the technology to measure
this kind of effect yet, since gravity is pretty weak on a microscopic
level. But this is still fascinating. And this weird behavior is all based on pretty
simple, old-school physics; stuff that’s been sitting right in front
of us for literally hundreds of years. So, what do you know? It turns out, now and then, old physics can
do new tricks. If you’re the kind of person who likes using
what you know to figure out new things about the world, you might also
like courses offered by Brilliant. Brilliant offers courses in science, engineering,
and math, and they’re designed by professors at institutions
like MIT, Caltech, and Duke. The courses are hands-on, with interactive
quizzes and guided problems with explanations. Brilliant courses are also available offline
on their iOS and Android app, so you can keep learning when you’re on
the go. To find out more, head over to Brilliant.org/SciShow. If you’re one of the first 200 people to
sign up at that link, you’ll get 20 percent off an annual premium
subscription! And as always, thanks for watching SciShow. [♪ OUTRO]

100 comments

I'm not so convinced. Be it a single molecule, or a collective group, "packet", of molecules moving counter to gravity, if that movement is imparted by the previous molecules, then it isn't anti-gravity. Furthermore, the sound pressure front, moving counter to the force of gravity, seems more related to pressure differences, though that difference is caused by gravity. Maybe I missed something…..

???
This is like saying Helium has negative gravity though????
Heck, it's literally just the way energy moves through matter. There is no negative gravity here.

So, science – the school of thought that tells us not to accept anything as fact without experimental proof and to be skeptical of the unfalsifiable – is asking me to take as fact this thing that has not been proved by experiment and is effectively unfalsifiable? Ok. Seems legit.

3:23 I don't think so. Phonons, like photons, have no mass at all, therefore, no negative mass. The paper says they do, but it's far from conclusive.

Sound waves curve up because they bounce against the higher pressure region at lower altitude. Its a form of buoyancy, not negative gravity. Unless you are going to call hot air balloons negative gravity machines this video makes no sense.

Clickbait. This is fluid dynamics. This is just a perceived effect. This was a passing mention in a Tom Scott video on acoustics for airports. Shame.

"Sound can be used to push objects with mass."
Well of course I knew that already, Lucio taught me that.

Damn you LUCIOOOOOOooooooooo!

Most commenters here doesn't even bother to read the paper this video based on. In a nutshell this theory is treating sound waves as a particle like in quantum wave particle duality paradox.. No instrument sensitive enough to observe in nature but it sounded pretty solid since it has relevance with a different branch of physics eg. particle physics to observe. No it's not buoyancy.
Read here:
https://arxiv.org/abs/1807.08771

Gravitational force is an illusion that results from curved space-time. Real negative gravity would be space-time that is curved in the opposite direction. This is just a slightly more convoluted way to say that apparent attraction between massive objects is negligibly weaker as a result of sound waves.

this really has nothing to do with gravity but only with fluid density difference. that gravity is one of a number of things that can cause density differences is true but doesn't matter. also non existant sound particles are a nice math trick but have nothing to do with reality. some people just spend to much time in their books and then nonsense like this is the result of research projects.

Jesus these comments. Phonons are particles just as much as say photons. If this video was hard for you then you won't like quantum field theory.

I'm going to give this video a like, because I think many of the people are missing the point. A types of theory of gravity known as emergent gravity can have really interesting properties depending on what other theory gravity 'emerges' from, LQG or entropy being some of my favorite emergent theories of gravity.

What this SciShow video is saying is that from the perspective of the 'stationary' earth or the moving sound wave, using just the basic physical principles from newtonian mechanics, you'll see the two move relative to one another in a way that can be perfectly described as negative mass. They push this analogy so far as as to say that this negative mass is real and exerts a tangible negative gravity, and thus sounds waves actually repel mass. I'm not sold on this last interpretation, but I'd have to understand better why they think the math of sound waves deflecting upward is equivalent to negative mass. The math be correct, but the interpretation may be up for debate.

I don't discount the idea out of hand, tho, like most of these commenters seem to. A lot of weird things can happen in nature when you have a complex system that is constantly shuffling and is given very long time in which to reach a natural equilibrium. Think: life; humans, extremophiles. Why not emergent negative gravity?

"Phonons are cool and wacky, listen about em? uwu"
Way better title
+Zoomers would love it
+Wouldn't give people the wrong idea about a fundamental force
+Can talk about wave/particle duality without bLaCkHoLeS

I guess the trend is fake Physics now. I used to come here to learn something. I guess it's all about clicks now. Thumbs down SciShow. A few more like this and I'll be down the road.

So, the effect of buoyance is now called anti-gravity? Until the "pushing" effect of negative gravity from the phonons is proven, I call this BS.

This effect needs to be tested in a zeroG environment before making any conclusions

This is not exactly gravity but if all forces are carried by particles and all particles have ones with opposite charge it's only natural to assume that there would be an antigraviton.

?? Alright, y'all so unconvinced. She gave you a thought experiment you just didn't do it. Imagine a neutron star, consisting of ultra massive quaziparticles. The negative curvature of these huge phonons would directly counter a significant percentage of the stars gravity as a direct result of the stars gravity. Let me put it this way, the gravity shapes the fluid dynamics that allows for this effect. The effect is inherent to the gravity. You're look'n at gravity all wrong. Causality is to gravity what magnetic fields are to a circuit. Phonons are goofy gravitational circuits, at least when interacting with normal matter. To simply put it there angle is off.

Like, its cool that phonons have negative mass, but theyre… Not real, right? They dont exist, we cant trap or use them or anything like that.
This video was about nothing.

This channel's really got down hill the last year with clickbait titles, sponsored topics and large potions of the videos becoming ads… I've been subscribed for 7 years and a patreon for some of that but this last year I've started skipping over your videos in my subbox. I'm out.

The phonons are accelerating in the opposite direction to a gravitational field, due to the gravitational field. Negative gravity would imply all energy and mass accelerated away from the phonons. Right?

wait, does that mean buoyancy is a kind of anti-gravity since its always represented as a force directly opposing gravity?

while this is a property of fluid dynamics, its an interesting one to explore as it could have uses for suspending small objects midair. im also imagining a more accurate model of wave propagation could have all kinds of benefits from highway sound reduction in residential neighborhoods, to preventing shockwave damage near orbital launch sites. i remember videos about acoustic levitation, this research could be very helpful in that field.

My takeaway from this Is that as long as we make it loud enough, we can get to space on the power of rock ‘n’ roll.

cheesus, what a load of bull. run of the mill fluiddynamics does not make "negative gravity", what on earth are you people smoking?

Maybe I missed something, but the explanation had nothing to do with gravity. It's just another way things move up in air based on a density differential.

I've always taken these videos with a grain of salt but this is a new low.To call this negative gravity is like calling a ping pong ball with forward motion getting deflected up as negative gravity.

First time I've disliked a SciShow video. Pure clickbait. This has NOTHING to do with gravity. Sound waves travelling upwards is NOT anti gravity, in the same way water fountain shooting up water isn't.

Aww man, they had me all giddy for a second there… back to normal gravity with me, pulling me down to Earth with its damn negative force in -MmG/r^2 always bringing me down.

this is the kind of sensational clickbait crap that the scishow team often claims to be harmful.. … big dislike on this one. it's misleading and fallacious .

Gravity itself is a pressure gradient. Lower ether pressure inside the earth, higher ether pressure in space. This causes an acceleration of ether towards the earth at 9.8 m/s2 due to earth pulling the ether towards itself like a vacuum pump due to difference in ether pressure. Ether in turn pushes everything towards the earth with it similar to how water going down the drain pushes the objects in the water with it towards the drain, we experience it as gravity. Yes ether exist and every time mainstream scientists talk about dark energy, dark matter, quantum fluid, quantum foam, space-time curvature, etc. they are indirectly referring to the ether because there is no such thing as empty space. If space were empty, nothing can wave in it, and particles only wave when contained, water contained in a pond for example. If you figure out how to flip the gravitational pressure of ether around electrically, you have anti-gravity or negative gravity.

"Down" 😂

I really don't know if I wanna laugh or cry.

Every gravitational force in Newtonian mechanics has an equal and opposing force, and it usually acts on the other mass.

More specifically, every two pairs of masses feel a gravitational force that's proportional to the product of their masses and inversely proportional to the square of their relative distance, but more important is the fact that both masses feel the attraction to each other.

Thus, when you throw a ball of ~100g in the air, it experiences a gravitational force of 1N towards Earth, and in doing so it exerts a force of 1N towards itself on the Earth. The reason you don't observe the Earth moving is that because of it's great inertia (proportional to an objects mass) its acceleration is so small that it gets swamped in everything else, but it does happen.

Mechanical engineer over here. This is normal fluid mechanics, and not "negative gravity". In kind of the same way planes wings aren't negative gravity, but the air pressure is greater underneath the wings pushing it upward.

So warm air has negative gravity too? It rises in the opposite direction of gravity as well. What about warm water? You even unwittingly mention that water behaves the same way yourself. What about a balloon full of helium, does helium have negative gravity? I'm struggling to follow your reasoning here. Also, doesn't sound travel equally in all directions?

S̵c̵i̵-̵F̵i̵ ̵w̵r̵i̵t̵e̵r̵s̵:̵ ̵_H̵e̵a̵v̵y̵ ̵b̵r̵e̵a̵t̵h̵i̵n̵g̵_

Is this going to be yet another channel taken by the clickbait virus?

The first SciShow video I thumbed down 🙁 Because this was an obvious clickbait. It's just a video about aerodynamics or buoyancy.

Maybe this is a test on the intelligence of it's viewers. By looking at the likes, it seems to look not that good. Only a quarter of the voters unliked it.

Honestly Sci shows been kinda bs for a while. This is just a lot worse then usual. I’ll admit they’re entertaining especially when talking about simple geological things I didn’t know about. But the social science :/ and when they talk about things they certainly aren’t qualified to talk about. :/

Taken from the first link, "the same coupling must affect the field equation
for gravity: the (tiny) effective gravitational mass of the
phonon generates a (tiny) gravitational field." i.e this affect actually warps space, so the anti gravity is probably more legit than most of the commenters think.

Edit: the same coupling refering to to the coupling (basically interaction) of phonons and gravity

Hold on… So warm air traveling up in colder air is also negative gravity? Either I'm missing something important here or the whole concept just doesn't make sense.

So… When I jump (up) … I have NEGATIVE GRAVITY? Watch as my negative gravity displaces air, in a chain effect of negativity.

No

Gravity: Yo dude, I can't pull that phonon.
Air: Hold my beer pushes phonon upward
Gravity: I pushed that phonon real good.
Air: Stop taking credit for my work.

PBS Space Time
Anti-gravity and the True Nature of Dark Energy
https://www.youtube.com/watch?v=UwYSWAlAewc

I'll just leave that here for people interested in a scientific approach to the question.

This theory feels like its invented by a scientist who lost a bet and now wants to proof he actually won thanks to this idea. Then again, if this leads to anti gravity science I'd love it to be real.

"because of the way air moves over a plane wing, it forces the wing upwards, because of this we can say the plane has negative mass"

those episodes are getting shorter and shorter as well as shitter at the same time, maybe reconsider making longer in depth episodes with actual interesting and detailed information?

if the same kind of energy that causes sound is to be scaled up enough to have noticeable effects on neutron stars, I'm fairly certain the force of these vibrations would be too fast and violent to care which way is "up".

It's interesting how the comments are full of people griping that "this is buoyancy" and "phonons aren't particles" when those criticisms seem to be mutually exclusive. If sound traveling through water can't be treated as a distinct entity and it's just water, how could buoyancy apply to it?

I don't understand the argument for negative gravity. It get that the shape of the curve angles upwards but the sound should still propagate across the lower atmosphere too, just differently shaped. Unless the slower upper part pulls the lower faster part, but they didn't say that and I don't see why it would. Couldn't the lower part continue to go fast and pull away from the upper?

I have to agree with other commenters, but not for the same reason. I'm perfectly happy with the occasional clickbaity or twisty title.

What bothers me about this episode is that this was a submitted question. I don't think it's right to sidestep a submitted question to talk about something other than expected.

This was very interesting, but it wasn't what the question leads towards. That feels like a betrayal of the contract. It doesn't necessarily matter if the person involved gave the green light, it makes the rest of us feel that the spirit of submitted questions will not be respected.

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