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Comment by armada651 | Hacker News Reader

How do Time Crystals differ from the quartz crystals used for time keeping in electronics? Is the only difference that Time Crystals oscillate without needing an electric field?

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From my very limited knowledge of physics, time crystals can theoretically oscillate forever without any excitation at their ground state, though laws of theromodynamics are not broken and energy cannot be extracted from their oscillations. In a normal crystal oscillater, power is needed to keep the crystal oscillating.

I have no knowledge of them but the article says it oscillates at lower energy levels, almost nil, compared to a quartz crystals. Since it is still unexplored territory there are lots of possible applications.

While this may be that they can oscillate forever, measuring it is an act of removing energy from it.

So could it be said then that it's more efficient? Say, you'd need less energy to measure time with a time crystal than a quartz crystal?

Not necessarily. You can measure things in ways that add energy: e.g. radar waves contribute a tiny bit of energy to the things they bounce off. Yet they measure where objects are.

You can also measure some things in ways that add exactly 0 energy. If some quantum system absorbs exactly nothing of a certain wavelength, that tells you something about the system.

You don’t need to remove energy from an object to measure it.

If you shine a flashlight into a dark room, you are measuring the positions of objects inside, and those objects don’t lose their energy.

you are changing the momentum of the things you are mentioning. the considerations here are on a more quantum scale than furniture in a room.

I also wonder how a time crystal is different from a harmonic oscillator.

Harmonic oscillator can have a ground state where it doesn’t move (i.e. you can stop it if you remove the enegy).

Time crystals move at the ground state - you cannot stop them by removing the energy.

You actually can't remove all the energy from a quantum harmonic oscillator, 1/2 hbar omega will be in it even in the ground state.

Normally, a system (like a quartz) which is driven by an external frequency, oscillates at the same or a multiple of the driving frequency. This is because the external conditions are symmetric under a time translation (i.e. a delay) by the period duration. This symmetry is normally preserved by the system.

A time crystal, however, will oscillate with a fraction (or rational multiple) of the driving frequency. This breaks the original time translation symmetry.

I think you said that already :-)

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