Sound waves transport a small amount of mass, according to theory

[ricardobeat]

If this negative mass measurement turns out correct, does it mean that a powerful enough sound wave at a frequency outside hearing range could be the answer to the anti-gravity belt?

Disclaimer: I have no idea what I’m talking about.

[hwillis]

> The new calculation indicates that for ordinary sound waves in most materials, the mass carried is equal to the sound wave energy multiplied by a factor that depends on the speed of sound and the medium’s mass density.

Since the effect is proportional to the density of the medium, you can't get actual antigravity. The mass is always positive. It can just be lighter than the other matter around it.

Practically speaking, you definitely can't use this for levitation or anything. This is E=mc^2 stuff; you need far more energy than conventional levitation would take. The energy in normal sound waves is very low, so high energy sound waves are very destructive.

For reference, the reference level sound intensity is 1 picowatt per square meter. That's zero decibels, the human audible threshold or the quietest sound we can hear under ideal conditions. A conversation is ~60 decibels, or 1 microwatt/m^2. Hearing damage comes at >90 dB or 1 milliwatt/m^2. >140 dB is quite painful, but it's only 100 watts/m^2. A household extension cord can carry about a kilowatt in less than a square centimeter- millions of times more power.

[empath75]

The soundwaves float, not the thing producing them.

[725686]

Your disclaimer just put a smile in my face.

[bshell]

If Xmen taught me anything it is that this is old news

[mjfl]

If you have a nonlinear interaction of a wave with a media, you might have a quadratic term A^2 cos^2(wt). If you remember your trig identities, you'll remember that two sinusoidal functions multiplied together decomposes into the sum of signals at the sum and difference frequencies: cos(w_1 t)cos(w_2 t) = 1/2*(cos((w_1 + w_2)t) + cos((w_1 - w_2)t)).

In this case the sum wave is at twice the frequency of the original wave, and the difference wave has 0 frequency - it is just mass transport. I have a feeling that is what is going on here.

[whatshisface]

>you might have a quadratic term A^2 cos^2(wt). If you remember your trig identities, you'll remember that two sinusoidal functions multiplied together decomposes into the sum of signals at the sum and difference frequencies: cos(w_1 t)cos(w_2 t) = 1/2(cos((w_1 + w_2)t) + cos((w_1 - w_2)t)).*

The DC component isn't the same as mass transport, because the system still returns to its original state every period of cos(wt). The amplitude of the DC (A^2/2) is also much higher than the one part in a thousand the article was describing.

[Tomminn]

Agree. It's standard quadratic medium rectification, and they've dressed it up so much they can't see it. The rectification will be associated with a uniform translation of the sample the sound wave travels through.

[dschuetz]

In fact, sound waves literally means moving matter! Transporting mass along the wave propagation is a whole different thing. It depends on the matter that is moving/vibrating. While the propagation of kinetic energy through a medium cannot have mass, the mean mass transport through a closed surface should equal zero. However, if they've discovered that it, in fact, isn't - then it's a big deal.

[dmurray]

Sound waves are often compared to water waves in this way. The water just moves up and down, and the horizontal movement is (mostly) an illusion.

But everyone knows intuitively that the water is moving horizontally at least a little bit. Some ocean water gets left on the beach or the boardwalk, or perhaps your toy or ball gets swept out to sea on the waves.

Is this the right analogy, or are they talking about something different?

[tranchms]

I was on a plane today thinking about recent research that uses vibrational/waves to interact with objects. Researchers can suspend and manipulate objects with these waves.

I was thinking, why isn’t it possible to use this technology to create levitating objects or vehicles???

Like UFO type flight.

Just attach powerful emitters around the craft.

This article makes me think this might be possible.

F= m*a

If waves possess mass, then it could be used as a means of force.

[jerf]

"I was thinking, why isn’t it possible to use this technology to create levitating objects or vehicles???"

It can, at least if we squint a bit. There is a clear mathematical relationship with all the various bits involved. Compute the amount of energy required to create the amount of sound to levitate, say, something with the mass of a car.

You'll compute an amount of energy sufficient to destroy any conceivable emitter and any object it is targeted at. My intuitive guess is that you'll actually require an amplitude of sound that isn't sound anymore; there's actually a maximum volume that sound can have, because the bottom of the wave can only go to zero pressure. It can't go past vacuum.

Also, I'd have to think about it a bit more, but I believe it would require the emitter to be separate from the thing being levitated... I think trying to self-levitate with a sound emitter would be the mathematical equivalent of trying to fly by pulling up on your hair.

So don't think full-sized UFOs dapperly zipping about with discreet little "blip blip blip" sounds in the distance... think a train car running underneath a levitating car, with a speaker giving off energy comparable to continuously-exploding bunker-buster bombs, if not nuclear bombs.

Definitely better off with a helicopter.

There is a reason all the things you've seen lifted are little bits of styrofoam and ping pong balls.

[espeed]

Sound waves can move matter [1], and to a lesser degree light can too [2].

[1] Acoustophoretic contactless transport and handling of matter in air https://www.pnas.org/content/110/31/12549

https://en.wikipedia.org/wiki/Sound

https://en.wikipedia.org/wiki/Longitudinal_wave

http://www.people.fas.harvard.edu/~djmorin/waves/longitudina... [pdf]

[2] https://en.wikipedia.org/wiki/Photoelectric_effect

[schoen]

I guess the aviation application is very focused on the magnitude of the force generated per watt of power expended, and pushing really hard on air (like airplane engines do) is pretty effective for that, even if there's also some way to make sound waves generate thrust. Are the sound wave lifters and manipulators (which are super cool) very power-efficient compared to a fan or a jet engine?

[nenadg]

Which again proves Tesla's quotes about frequency and vibrations.

[novacole]

Do sound waves have mass or transport/displace matter? The article does seem clear on this to me. Not a physicist so I could be totally wrong here, but having mass is not necessarily the same as being matter, correct? Since matter is made of atoms, and sound is just waves. Maybe someone can help explain this to me.

[epicwhaleburger]

Electrical engineer here. Sounds waves are called transverse waves because their displacement moves in the positive/negative y directions, which appears to give the impression that the wave is a single traveling particle. Instead the sum of the displacement creates the "traveling wave", which is similar to a wave an audience might do at a sporting event. I don't think this article did a great job describing what they meant by mass. I believe they blow the word "Phonon" a bit out of proportion. High energy physics is an incredibly hard topics where very few people are smart enough to read such a paper with confidence so these are just my humble thoughts.

[goldenshale]

Random idea this brings up... Some of the faster than light drive concepts worked by compressing space in front of the ship and expanding it behind. If sound waves carry mass maybe they could be harnessed and focused in a way to warp space time and impact travel speed? I wonder how the medium impacts the mass?

[espeed]

Here's one for ya ~> Which came first: Sound or light?

https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations

[WebDanube]

Interesting. Assuming this theory gets verified in duplication studies, I feel there's a good market opportunity for vocalization (voice) therapy in the weight- and inch-loss industry

[ggm]

Does the mass have to be transported at the same speed as the sound or like electron drift in a conductor is the mechanistic speed of movement/translation far far slower?

[plutonorm]

Possible explanation for the emdrive?

[vectorEQ]

does low frequencies have more mass? ;D

[Causality1]

Really, "phonon"?

[drjesusphd]

Yes, vibrations in a lattice are quantized: they can only occur at a discrete set of frequencies and energies.

[_Microft]

Check this out, there's more of these quasi-particles:

https://en.wikipedia.org/wiki/List_of_quasiparticles

[lightedman]

Yes, really. It's a very important part of condensed matter physics.

[Tomminn]

I can't read the paper but the physical mechanism for how anything like this manifests is so obvious they'll be embarrassed to miss it: the entire solid must translate a small distance.