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Surprising Discovery Hints Sonic Waves Carry Mass (scientificamerican.com)
jbmartin6 shares a report from Scientific American: In a paper published in Physical Review Letters, a group of scientists has theorized that sound waves possess mass, meaning sounds would be directly affected by gravity. They suggest phonons, particle-like collective excitations responsible for transporting sound waves across a medium, might exhibit a tiny amount of mass in a gravitational field. "You would expect classical physics results like this one to have been known for a long time by now," says Angelo Esposito from Columbia University, the lead author on the paper. "It's something we stumbled upon almost by chance."
Esposito and his colleagues built on a previous paper published last year, in which Alberto Nicolis of Columbia and Riccardo Penco from Carnegie Mellon University first suggested phonons could have mass in a superfluid. The latest study, however, shows this effect should hold true for other materials, too, including regular liquids and solids, and even air itself. And although the amount of mass carried by the phonons is expected to be tiny -- comparable with a hydrogen atom, about 10^-24 grams -- it may actually be measurable. Except, if you were to measure it, you would find something deeply counterintuitive: The mass of the phonons would be negative, meaning they would fall "up." Over time their trajectory would gradually move away from a gravitational source such as Earth. "If their gravitational mass was positive, they would fall downward," Penco says. "Because their gravitational mass is negative, phonons fall upwards." And the amount they would "fall" is equally small, varying depending on the medium the phonon is traveling through. In water, where sound moves at 1.5 kilometers per second, the negative mass of the phonon would cause it to drift at about 1 degree per second. But this corresponds to a change of 1 degree over 15 kilometers, which would be exceedingly difficult to measure.
Esposito and his colleagues built on a previous paper published last year, in which Alberto Nicolis of Columbia and Riccardo Penco from Carnegie Mellon University first suggested phonons could have mass in a superfluid. The latest study, however, shows this effect should hold true for other materials, too, including regular liquids and solids, and even air itself. And although the amount of mass carried by the phonons is expected to be tiny -- comparable with a hydrogen atom, about 10^-24 grams -- it may actually be measurable. Except, if you were to measure it, you would find something deeply counterintuitive: The mass of the phonons would be negative, meaning they would fall "up." Over time their trajectory would gradually move away from a gravitational source such as Earth. "If their gravitational mass was positive, they would fall downward," Penco says. "Because their gravitational mass is negative, phonons fall upwards." And the amount they would "fall" is equally small, varying depending on the medium the phonon is traveling through. In water, where sound moves at 1.5 kilometers per second, the negative mass of the phonon would cause it to drift at about 1 degree per second. But this corresponds to a change of 1 degree over 15 kilometers, which would be exceedingly difficult to measure.
Sound travels through matter, so consists of, well, "phonons" that are really just the slightly altered movements of the matter the sound travels through. Sound exists for as long as that extra movement exists, and for it to exist, the matter needs to be excited, ie possess energy, over and above ambient. So that means sound waves traveling perpendicular to a gravity field have a tendency to be a little less affected by that field than ambient matter. So it looks like phonons have negative mass.
So this apparent mass is an artifact of the way you look at it.
Says I, who is so very much not a physicist. Nor a patent examiner.
Wouldn't this then imply that sound should be able to pass, at least in part, through a vacuum? If sound itself has mass, then sound itself isn't a vacuum...
Is dark matter just ... sounds?
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“He’s not deformed, he’s just drunk!”
If it turns out that sound has a negative amount of mass, does this fix many of the problems with dark matter and the weight of the universe? Is dark matter just ... sounds?
No, but we can use phonons to make a really cool anti-gravity hoverboard. Just be sure to wear hearing protection, because it will be loud.
Given the idiocies all the other commenters wrote at this point, including TFS, you're the only one here who hit the nail on the head.
It seems people don't get that infomation is not a physical object (matter/energy) itself, but only the *structure* of matter/energy. So it's a meta level. In a medium. With different meta laws.
Hence the whole "intellectual property" oxymoron confusion.
TL;DR: Sound does not have mass. The particles that form the medium of sound, do.
Sound is a meta level, so it can only have meta mass. Its "mass" isn't real, just as phonons aren't real. They are only a useful construct.
Come on now. Science is not limited to the domain of experimental science.
Science broadly construed is the search for hypotheses that unite various phenomena. Experimental science merely attempts to falsify these hypotheses.
If anything, experimental science is the ugly stepsister here ...
For something to exist, it has to be observed.
For something to exist, it has to have a position in time and space.
And this explains why nine-tenths of the mass of the universe is unaccounted for.
Nine-tenths of the universe is the knowledge of the position and direction of everything in the other tenth. Every atom has its biography, every star its file, every chemical exchange its equivalent of the inspector with a clipboard. It is unaccounted for because it is doing the accounting for the rest of it, and you cannot see the back of your own head.
Nine-tenths of the universe, in fact, is paperwork.
Terry Pratchett, Thief of Time.
Dude, Phys. Rev. Lett. is quite substantial. Physicist here.
Does compressed spring have more mass than uncompressed one? Apparently yes. From that soundwaves having mass doesn't surprise me at all. What I don't quite understand is where the negative value comes from.
Helium balloons don't have negative mass, they still have weight and are attracted by the earth. It's the heavier surrounding air that pushes the balloon up (pressure gradient provides more force than gravity).
So you're saying that phonon traveling through some medium (like air) is pushed up by the rest of the medium? That's not really "negative mass", just "less mass than the surrounding medium".
Not real mass.
Because phonons aren't real elementary particles. They are artifacts of the structure of real elementary particles that make up the medium.
It's a nice useful construct, but don't confuse information meta-space with real space.
And we have a winner. And if you calculate the mass of the medium out, then waves of lower density which temporarily thins the medium, will carry a negative mass if perceives as particles.
In water, where sound moves at 1.5 kilometers per second, the negative mass of the phonon would cause it to drift at about 1 degree per second. But this corresponds to a change of 1 degree over 15 kilometers, which would be exceedingly difficult to measure
Uh, if sound moves at 1.5 km/s, and drifts by 1 degree/s, then in 1 second it should have drifted by 1 degree and travelled 1.5 km, not 15km? After 10 seconds it will have travelled 15 km and drifted by 10 degrees, which surely would be measurable. (PS: I read the article, the summary quotes the article correctly.)
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I'm quite sure that the geniuses at Monster Cable have already patented some gravity cancelling cables with gold plated connectors, which will allow the sound to reach your ears at the proper angle.
Wouldn't this then imply that sound should be able to pass, at least in part, through a vacuum?
No. By definition sound cannot pass through a vacuum. Oversimplifying here but sound is defined as a pressure wave through a medium. No medium = no sound.
If sound itself has mass, then sound itself isn't a vacuum..
Probably an imprecise statement. It's not that sound has mass so much as that it carries energy which has an effect on mass of the medium through which it travels. I've never really thought about it explicitly but it makes some sense that sound and mass would have some relationship. (E=mc^2 and all that)
If you get into the weeds of it, mass doesn't actually mean what your intuition probably tells you. Particles don't actually have a mass that is a single value. What we think of as mass is really just the expected value but at any given time it can vary according to a probability distribution. Also there is the fact that if you add up the weight of the particles in a molecule it's common for the weight of the molecule to be different from the weight of it's constituent particles. Energy into our out of a system can often affect mass in some subtle and not so subtle ways.
But negative mass (according to TFA). And so negative energy.
Have gnu, will travel.
Sorry, but this is plausible. It would need careful calculation, but it's plausible. My reasoning is thus:
Sound (in air) originates as a wave of compression, which squeezes things away from it, followed by a wave of de-compression, which allows things to return. If the sound encounters a barrier (necessary to create a phonon), then the pressurization still squeezes molecules out, but the barrier prevents easy return, so the mass of the air within the phonon will be less than the mass of the air away from the sound wave, and therefore it will be pulled less strongly towards the closest gravitational source.
So. Plausible "negative mass" within the phonon when contrasted with external to the phonon. Not an absolute negative mass, but a relative negative mass caused by a lesser average density.
That said, I'm not sure how to translate this into waves moving through an incompressible medium, but it's been a long time since I took physics, and acoustics got only minor coverage when I took it.
I think we've pushed this "anyone can grow up to be president" thing too far.
No matter how many people lean to the west, they will not cause a west wind to blow. They'll just fall over and feel silly.
Don't confuse an immediate local interaction with causality.
I predict that an article like this is going to bring the cranks out of the woodwork. Two obvious flaws in this "journalistic impression" of the actual research: 1) The original article has nothing to do with antigravity, it discusses an effect more like buoyancy. 2) A change of one degree is not hard to measure, regardless of the distance it is measured over, because angles do not change with distance. These obviously nonsensical inventions are the result of some journalist's wild imagining about a topic they have no competence to discuss. The whoppers get bigger with the retelling.
A saner report. The original paper is paywalled.
When all you have is a hammer, every problem starts to look like a thumb.
How's life in the hypocrite lane?