When ice cracks, it can make the surface of a lake sing. It sounds like the music of the cosmos or like a quiet, high-frequency thunderstorm.
Water has unique phase transitions compared to other molecules because it has a larger volume after it freezes, leading to the sorts of cracks that can be heard on the surface of a lake. In liquid form, the molecules pack more tightly together and form loops and strings, but in the frozen state, they form a crystalline lattice that comes in several different forms when it is frozen under high pressure I, II, III, IV, V, … and if you’ve read Kurt Vonnegut’s Cat’s Cradle, there is the deadly and imaginary ice IX which freezes at room temperature and atmospheric pressure following a seeded, nucleation process. Thank goodness it doesn’t exist.
I will instead focus on regular old, run of the mill ice that freezes at zero degrees Celsius and explain why it is slippery and why it makes cosmic sounds.
Picture charge as something defined by a swirling motion. Things that swirl in the same direction repel and things that swirl in opposite directions attract. The atoms in a piece of ice have a swirling motion which is in the same direction as the swirling motion in another solid and that is why the two objects repel when they touch one another. It is why they are solid.
When ice is touched, it has a swirling motion on one length scale which is responsible for its solidity and it has a swirling motion in the opposite direction on another length scale which is responsible for its slipperiness.
Picture the surface of the ice trying to mix itself together with the surface of your shoe as you walk, thereby creating a turbulent, swirling flow which is in the opposite direction of the swirling motion responsible for the solidity.
In other words, the electrons on the surface of ice are less strongly bound than the electrons within ice. This allows them to move more freely, so that they move relative to the electrons in your shoe. Electrons which move in the same direction repel, of course, but if they are moving in opposite directions, they attract. The motion of the surface electrons on ice relative to the electrons in your shoe is responsible for ice’s slipperiness. Electrons in metal are also quite mobile and that is why an ice-skate slips more than your shoe does.
It isn’t particularly useful to describe ice’s slipperiness in terms of wetness, dryness, or melting as is done in the video below, because the friction coefficient of ice doesn’t get worse when you drop the ambient temperature.
If one insists, one might be able to describe the motion of the surface electrons or molecules as a sort of friction melting, but I decide whether or not I like a language based on how useful it is. I think that one could make a better quantitative model by imagining electric current rather than imagining an abstract form of melting. Then again, physics tastemakers usually have odd preferences in these aesthetic matters. Mystery is how you get people to give you money.
Back to the cosmic sounds from the surface of an icy lake. Why do they sound like softly rolling thunder or like the eerie noise picked up by space probes travelling through the solar system?
Perhaps the reason that ice and the cosmos sound similar is that the vacuum of space is actually quite energy dense and, in a sense, that makes it potentially extremely hard – like ice. Precisely how hard is the vacuum of space, though?
A hundred years ago, physicists would’ve had a lot to say on this topic, but today, not so much. Looking back at the (still valid) language of yesteryear, the hardness of space depends on how much it has been stretched or compressed by a gravitational or electric field.
Heaviside thought that lightning and sparks were what happened when space stretched too far in one direction and became thin and weak in the other direction, allowing space to press in from two sides and cause a crack. In more technical language, he would talk about sparks and lightning in terms of the elasticity of a nonconducting material.
I picture two clouds holding the ends of a network of rubber bands. The greater the distance between the clouds is, the longer the rubber bands are and the more they can potentially stretch. As the electric potentials between the two clouds grows, the clouds pull harder on the ends of the rubber band until it snaps like a bolt of lightening.
This book from 1920 is a great example of this very intuitive style of thinking: Dielectric Phenomena In High Voltage Engineering : F. W. Peek Jr. : Free Download & Streaming : Internet Archive
Below I’ll summarize some of the key concepts:
Space can be described with the permeability and the elastivity of space.
Permeability describes the ability to support the formation of a magnetic field.
Permittivity describes the ability to support the formation of an electric field.
Elastivity is the inverse of the permittivity and in free space, the permeability:permittivity ratio is 1.
Elastance is the inverse of capacitance and it results from the elastivity of a material. It is one of a suite of terms coined by Heaviside. -ance words corresponded to measurable things in electric circuits and -ivity words related to field descriptions.
Dielectric constant (relative permittivity) measures the ability of a material to store electrical energy in an electric field. It is equal to the permittivity of a substance divided by the permittivity of free space.
Hardness accounts for the strength of chemical bonds — of which there are none in completely free space, so that makes this question a bit difficult to interpret unless we redefine hardness as the ability to sustain an electric and magnetic field in perfect balance. When they are out of balance, things tend to fall apart or get bent.
The dielectric constant of a material tends to increase linearly with the hardness of a material.
Since the dielectric constant of free space is 1 and negative dielectric materials do not occur without careful engineering, it is safe to say that space is the softest material around when it is not getting stretched in the vicinity of electric or gravitational fields, but when it is, for example, stretched by the presence of a heavy sun and bending starlight, its dielectric constant is certainly not acting like it is equal to one. This space is acting rather viscous. Under even more extreme conditions, when lightning strikes, space cracks and acts extremely hard and brittle.
In more relativistic, less absolute terms, if you see a flying javelin (or comet) which is long enough to be bent by the gravitational field of a planet, then you are observing the effect of the changing hardness of space. We could split hairs over what it means to *see* the javelin and whether the hardness of space changed or the hardness of the javelin changed as a result of changes in spacetime, but that hurts my brain today. I think that a description which is true enough to our everyday physics is that the javelin got bent due to the varying hardness of the space around the planet. If you shot a small, flexible arrow into the rind of a giant watermelon, I believe it would lodge itself in the watermelon rind with a bent shape, however I have certainly never seen such an experiment performed.
Instead, I see flashes of lightning and hear rolls of thunder when space cracks in the sky, releasing echoing, rolling sounds that confuse gravitational wave detectors.
I also see young women going out alone to record the quiet thunder coming from the surface of an icy lake and young men teaming up to record the quiet thunder from space probes as they visit distant planets.
While I am sympathetic to these focused efforts, I’d rather write a poem.
Clouds, ghostly muses born of Zeus’ lightning
are thoughts condensing in our minds?
Precipitated by Apollo’s light, these immortals
cast shadows that determine their future forms.
In Plato’s cave, we fear such shadows of ourselves
Knowing their power to bewilder and ensnare.
By Prometheus’ firelight, we tell ghost stories
To remind ourselves of things that can’t be said.
Physics is full of things that cannot be said beacause they officially do not exist if you do not speak the correct language. A good example of a physics language that is so far out of fashion that it is practically taboo is that of the magnetic monopole. It has become a fnord for any well-trained physicist.
Why do I care about any of this? Why do people see beauty in these ideas? Why does anyone care?
I think we invest in physics to distract ourselves from our most basic fears of our mortality as individuals and as a species. This is good when it is distributed widely in the form of wonder and curiousity, but when it assumes a concentrated form as in the big science laboratories that emerged as spin-offs of the terror-driven Manhattan Project, we allow our distraction to consume us and consume the energy of our naive children who are taught that the transformation of a muon into an electron is an abstraction that is nothing like a layer of ice breaking free from a frozen vortex flying through space.
Set the children free from this abstraction! When people get too hard and pressurized, they crack.
This was composed while listening to this pleasant, cosmic sound:
I first posted some of this material on quora.com