Here’s a strange claim that will change old views in physics … if valid and verifiable: Sound waves float upward very slightly because the particle-like units of vibration which make sound waves appear to have negative mass. Does sound really anti-gravitate?
Sound has negative mass, and all around you it’s drifting up, up and away — albeit very slowly.
That’s the conclusion of a paper submitted on July 23 to the preprint journal arXiv, and it shatters the conventional understanding that researchers have long had of sound waves: as massless ripples that zip through matter, giving molecules a shove but ultimately balancing any forward or upward motion with an equal and opposite downward motion. That’s a straightforward model that will explain the behavior of sound in most circumstances, but it’s not quite true, the new paper argues. [The Mysterious Physics of 7 Everyday Things]
A phonon — a particle-like unit of vibration that can describe sound at very small scales — has a very slight negative mass, and that means sound waves travel upward ever so slightly, said Rafael Krichevsky, a graduate student in physics at Columbia University.
Phonons aren’t particles of the sort most people typically imagine, like atoms or molecules, said Krichevsky, who published the paper along with Angelo Esposito, a graduate student in physics at Columbia University, and Alberto Nicolis, an associate physics professor at Columbia.
When sound moves through air it vibrates the molecules around it, but that vibration can’t be easily described by the movement of the molecules themselves, Krichevsky told Live Science in an email.
Instead, just as light waves can be described as photons, or a particles of light, phonons are a way to describe sound waves that emerge from the complicated interactions of the fluid molecules, Krichevsky said. No physical particle emerges, but researchers can use the mathematics of particles to describe it.
And it turns out, the researchers showed, these emergent phonons have a tiny mass — meaning that when gravity tugs on them, they move in the opposite direction.
“In a gravitational field phonons slowly accelerate in the opposite direction that you would expect, say, a brick to fall,” Krichevsky said.
To understand how this might work, imagine a normal fluid in which gravity acts downward. Fluid particles will compress the particles below it, so that it’s slightly denser lower down. Physicists already know that sound typically moves faster through denser media than through less-dense media — so the speed of sound above a phonon will be slower than the speed of sound through the slightly denser particles below it. That causes the phonon to “deflect” upward, Krichevsky said.
This process happens with large-scale sound waves, too, Krichevsky said. That includes every bit of sound that comes out of your mouth — albeit only very slightly. Over a long-enough distance, the sound of you saying “hello” would bend upward into the sky.
The effect is too tiny to measure with existing technology, the researchers wrote in the new paper, which has not been peer-reviewed.
But it’s not impossible that, down the road, a very precise measurement could be made using super-precise clocks that would detect the slight curvature of a phonon’s path. (The New Scientist suggested heavy-metal music would be a fun candidate for such an experiment in their original report on the subject.)
And there are real consequences to this discovery, the researcher wrote. In the dense cores of neutron stars, where sound waves move at nearly the speed of light, an anti-gravitational sound wave should have real effects on the whole star’s behavior.
For now, though, this is entirely theoretical — something to ponder as sound falls upward all around us.
This is all very small scale, but wouldn’t it be an interesting universe if we could levitate huge rocks with certain kinds of sounds? Could a person or group sing tons of stones into the air?
Except as a signal, there isn’t much power in the human voice.
Assuming a source-receiver distance of 3 feet, the average human voice is 60 dB.
The average voice is about 60 decibels (60db) at 3 feet, which is 10^-6 Watts, or 0.000001 Watts, or one micro watt, that is, 1 millionth of a Watt, a very small amount of force. This is a rough estimate, but another source is in the same ballpark:
It would take the power of two million people in conversation to power a 50 watt electric lightbulb.
So, if you plan to move huge rocks by singing at them, you will need a very powerful amplifier and perhaps a way to make a flat laser-like sheet of sound on which to float your megaliths.
If sound does fall upward, however, and if that effect can be magnified with some low energy catalyst, you might be able to build your pyramid with sound… or move those 60 ton blocks in the Queen’s Chamber of the Great Pyramid over the 500 miles from where they came. Probably not, but it’s a fun theory.
I’m frequently moved by sound and many sounds can be uplifting, but I’ll be surprised if sound itself falls upward. Then again, before this I did not think phonons existed outside of linguistics. Wait, do you mean phonemes?
The 44 Phonemes in English. Despite there being just 26 letters in the English language there are approximately 44 unique sounds, also known as phonemes. The 44 sounds help distinguish one word or meaning from another.
Ah. No, phonon is not to be confused with a phoneme.
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. Often designated a quasiparticle, it represents an excited state in the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.
Phonons play a major role in many of the physical properties of condensed matter, like thermal conductivity and electrical conductivity. The study of phonons is an important part of condensed matter physics.
Phonon: a quantum of energy in a crystal lattice or other system of bodies that has momentum and position and can in some respects be regarded as a particle.
In physics, quasiparticles and collective excitations (which are closely related) are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in free space.
Are phonons real? Yes and no. It depends on how you look at them. They are patterns of movement. Here is a phonon propagating through a square lattice, with the atomic distances exaggerated.
Do phonons anti-gravitate because they have negative mass? See the above question… I don’t see how a pattern of movement of positive masses could collectively be considered a negative mass moving through them, but perhaps that is the case.
A trio of physicists with Columbia University is making waves with a new theory about phonons—they suggest they might have negative mass, and because of that, have negative gravity. Angelo Esposito, Rafael Krichevsky and Alberto Nicolis have written a paper to support their theory, including the math, and have uploaded it to the xrXiv preprint server.
Is negative mass possible? Again, fittingly, the answer seems to be yes and no. A tachyon is a hypothetical negative mass particle that always moves faster than light.
Negative mass? Who ever heard of an apple with a mass of minus 100 grams? Even antimatter has positive mass. In a recent series of experiments, most notably at the Stanford Linear Accelerator in California, researchers looked to see if positrons, the antimatter partners of electrons, fell upwards in the Earth’s gravitational field. But like balls, people, and all the other matter that we know about, they fall towards the centre of the Earth. Yet surprisingly enough, there is nothing in physics that rules out things having a negative mass. In fact, several leading physicists have dabbled with the idea over the years.
– NewSci 2004
Physicist Peter Engels and a team of colleagues at Washington State University claimed to have observed negative mass behavior in rubidium atoms. On 10 April 2017 Engels team created negative “effective” mass by reducing the temperature of rubidium atoms to near absolute zero, generating a Bose-Einstein condensate. By using a laser-trap, the team were able to reverse the spin of some of the rubidium atoms in this state, and observed that once released from the trap, the atoms expanded and displayed properties of negative mass, in particular accelerating towards a pushing force instead of away from it. This kind of negative effective mass is analogous to the well-known apparent negative effective mass of electrons in the upper part of the dispersion bands in solids. However, neither case is negative mass for the purposes of the stress–energy tensor.
Before we can even vaguely understand the last sentence, we must know: What is a tensor, in general and what is the stress–energy tensor in particular?
Tensor (Physics): a mathematical object analogous to but more general than a vector, represented by an array of components that are functions of the coordinates of a space.
Clear as mud? This video explains what a tensor is:
Here’s a tutorial on the stress tensor:
This third video which covers the basics of Einstein’s field equations including the Stress Energy Momentum Tensor (aka stress–energy tensor): About 1:38:46 in the video.
I like watching things I don’t understand at times, don’t you? How long would it take to research every term I don’t understand in this video until I do really “get” everything he is saying?
Lost? In conclusion, my position is that “sound does not have negative mass for the purposes of the stress–energy tensor.”
Just memorize that and you’ll be good at a geek cocktail party when the topic of sound having antigravity properties comes up.