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Ok, so let's cut through the woo: A crystal is a repeating pattern of elements in space. For example, a diamond is carbon atoms - the same thing in ordinary co
by kmeisthax 4y ago
Ok, so let's cut through the woo:
A crystal is a repeating pattern of elements in space. For example, a diamond is carbon atoms - the same thing in ordinary coal - arranged in a particular shape of grid.
You can have patterns that are made in time rather than space, such as by hitting a drum with a stick in time with music. Of course, this isn't really very crystal-like, because the drum doesn't try to resist you hitting it off-time. However, there are certain atomic-scale materials that do resist your horrible off-beat drumming, and you "hit" them with a laser rather than a drumstick. These systems are time crystals[0].
You can also have crystal patterns that don't repeat, which are called quasicrystals. For every quasicrystal, there's a higher-dimension crystal that it is a shadow of. You could imagine, say, a 3D grid or lattice that you can shine a light through onto a piece of paper to get an irregular 2D pattern, which would be your quasicrystal. The two structures are related to one another, but that doesn't necessarily mean that the flatlanders living in it have proof of the existence of a third dimension.
The new development is time quasicrystals: i.e. a drum that you can bang with some non-repeating pattern and it will also keep in time with the pattern even if you are off. The stuff about "acting like it has two time dimensions" is more woo; there is a 2D time relation to the 1D time quasicrystal, but there is no actual 2D time shenanigans going on. The non-repeating pattern apparently also makes the time crystal better at "keeping time" which may help build more stable qubits for quantum computers.
[0] Note that you can't have spacetime crystals in the same material. You can either have atoms that link to one another with chemical bonds to form a pattern, or atoms that trade their bonds in rhythmic patterns, but not both.
- function_seven 4y ago> You could imagine, say, a 3D grid or lattice that you can shine a light through onto a piece of paper to get an irregular 2D pattern, which would be your quasicrystal. This is where I lose it. I actually can't imagine such a thing. Every regular 3D crystal I imagine has a repeating pattern in its shadow. For every ray of light passing through one part of the 3D lattice, I can locate parallel rays that produce the same result in other parts of the lattice. What am I missing here? Just not imagining the right lattice types? Or are we assuming a point-source of light so that no 2 rays are parallel?
- mensetmanusman 4y agoIf you angle the 3D lattice at an irrational angle relative to the 2D plane the points will not be perfectly periodic in the plane.
- boppo1 4y agoWhat is an irrational angle? Is this something I can actually do physically, or is it more of a theoretical math thing? For example, if I'm holding a toy that is a lattice showing the 3d structure of carbon between my dining room table and ceiling lamp, how do I rotate it such that it is irrational relative to my table?
- McBeige 4y agoI'm guessing it's irrational as in rational vs irrational numbers. Rational means a fraction of whole numbers, so irrational numbers are those which cannot be represented as such a fraction. A 1/4 turn is rational, a 1/pi turn is irrational. I feel like the light has to be parallel for it to work, so sunlight is a better example than a table lamp. Although I can't imagine any rotation of a simple 3D lattice having a nonrepeating shadow. Perhaps a more complex 3D crystal is necessary?
- mcswell 4y agoRational/ irrational here depends on the unit of measurement. A full circle (360 degrees) is rational if you measure it in degrees, but irrational if you measure it in radians (it's 2 pi radians).
- anamexis 4y agoBy that logic, couldn't any number be deemed rational by just declaring it as a unit?
- function_seven 4y ago
- wnolens 4y ago> there are certain atomic-scale materials that do resist your horrible off-beat drumming whoa.
- evilos 4y agoThanks this was an excellent explanation and even though I don't really understand, I feel like I do.