
Sound waves transport a small amount of mass, according to theory - JPLeRouzic
https://physics.aps.org/articles/v12/23
======
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.

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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.

~~~
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.

~~~
whatshisface
The article said that it involved interaction with gravity and wasn't from GR,
so that doesn't sound like a complete explanation. Nonlinear phonon
interaction has already been demonstrated experimentally, but that doesn't
seem to include the additional complexity of the interaction with gravity.

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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?

~~~
petters
The water moves in circles/ellipses.

~~~
Majromax
Not in closed circles/ellipses. With finite wave amplitudes, a fluid parcel in
wave motion experiences Stokes Drift
([https://en.wikipedia.org/wiki/Stokes_drift](https://en.wikipedia.org/wiki/Stokes_drift)).

In water, this effect arises because the fluid is deeper at the crest of the
wave than at the trough, and wave velocities are faster in deeper water. The
fluid parcel moves up -> forwards quickly -> down -> backwards more slowly.

I'm curious about whether the researchers here have demonstrated a similar
effect for sound waves. Pressure waves have similar dynamics (with faster
particle movement at lower pressures), and the researchers mention that this
is a finite-amplitude effect.

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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.

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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.

~~~
whatshisface
I think you might have got transverse swapped with longitudinal, transverse is
perpendicular to the axis of propagation (string waves and EM waves),
longitudinal is parallel (sound waves in fluid), and mechanical solids can
support both (you can have a transverse sound wave in an iron bar but not in
the air).

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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](https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations)

~~~
vectorEQ
does light make sound?

~~~
espeed
Gravitational waves resonate at audio frequencies [1], but I am not aware of
any findings on that wrt light.

However, you can convert light into sound through the photoacoustic effect
[2], and curiously enough, you can recover sound from images through light
[3].

[1] Listen to the sound of the kilonova -- the Gravitational Waves
Announcement Chirp [https://www.ligo.org/science/GW-
Inspiral.php](https://www.ligo.org/science/GW-Inspiral.php)

[https://theconversation.com/explainer-why-you-can-hear-
gravi...](https://theconversation.com/explainer-why-you-can-hear-
gravitational-waves-when-things-collide-in-the-universe-92356)

[2] Converting sunlight into audible sound by means of the photoacoustic
effect: The Heliophone [pdf]
[https://core.ac.uk/download/pdf/80794107.pdf](https://core.ac.uk/download/pdf/80794107.pdf)

[https://en.wikipedia.org/wiki/Photoacoustic_spectroscopy](https://en.wikipedia.org/wiki/Photoacoustic_spectroscopy)

[3] Veritasium: Can You Recover Sound From Images? [video]
[https://www.youtube.com/watch?v=eUzB0L0mSCI](https://www.youtube.com/watch?v=eUzB0L0mSCI)

See the research Abe Davis is doing on visual vibration analysis:
[http://abedavis.com](http://abedavis.com)

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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

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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?

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plutonorm
Possible explanation for the emdrive?

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vectorEQ
does low frequencies have more mass? ;D

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Causality1
Really, "phonon"?

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

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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.

