Hacker News new | ask | show | jobs
by jfengel 2429 days ago
Can you help me understand that? The concept of "temporal symmetry breaking" sounds exactly like oscillators.

Is it that it's a quantum-scale effect, creating a truly identical system at each cycle, as opposed to the approximate classical-scale system of a conventional oscillator?
2 comments
GistNoesis 2429 days ago
If I understand the article correctly, it is a less strong constraint on the signal than being periodic, like an oscillator would be. The signal is only periodic for specific value of time, in between those value of time the signal is not periodic.

To give a music analogy, the constraint is like always play the same chord on the first beat of each measure. In between you are free to play whatever chords you like.

How does a physical system can acquire such property? I have no idea that's the mystery a physicist will have to explain.

link
rfhjt 2429 days ago
Can it be just a sum of periodic signals? For example if one signal has a period of 7 and another of 11, the period of their sum is 7x11.
link
GistNoesis 2429 days ago
No, that's something different, there is a definite state that is visited at a regular interval.

I get your idea of using various periods : If instead of a sum of periodic signals, you do something completely nonphysical like a product cos(x)cos(x/3)cos(x/5)cos(x/7)any_f(x) you can observe indeed that the zero crossings come back periodically. (Edit: something kind of an amplitude modulation may not be so nonphysical after all)

link
munificent 2429 days ago
I think the difference is that an oscillator requires a continual driving force to stay periodic. Stop applying energy and it winds down. A time crystal, once it gets going maintains its periodicity.

Mapping it to spatial terms, I think: You could take a bag of beans and lay them out in a nice repeating grid pattern if you want, giving them spatial symmetry. But you have to keep making the grid yourself. The "bean crystal" does not naturally spread on its own. When a real crystal cools, the entire substance aligns into a regular repeating pattern on its own without any external force needed.

link