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> The idea was proposed by Frank Wilczek in 2012. His speculation was that a construct would have a group of particles that move and periodically return to their original state, perhaps moving in a circle, and form a time crystal. In order for this perpetual motion to work, the system must not radiate its rotational energy.

I thought perpetual motion violates the laws of thermodynamics. Does quantum physics cause the laws of thermodynamics to break down?

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The kind of perpetual motion that violates thermodynamics is the kind that can do useful work, i.e. that you can get energy out of, without putting any energy into it. So it violates conservation of energy.

A planet in orbit, or a spaceship like Voyager travelling through the galaxy, is in perpetual motion, but if you try to harness that kinetic energy, you'll slow it down.

Electrons and photons are in perpetual motion. Perpetual motion is only a thermodynamic problem when the system is shedding energy in some way (friction, radiation, photon smacking into a detector).

Or an example that's easier to visualize would be a spinning rock in space.

Thermodynamics are a statistical model to describe molecules behavior at a macroscopic scale. It is usually not very relevant in the quantum world.

Niels Bohr proposed that electrons don't have enough energy to radiate away, and thus are forced to continue to spin around the nucleus.[0] This was the seed that fruited the quantization of energy and eventually our modern understanding of Quantum Mechanics.

In a way, the quantization of reality at very small scales does appear to prevent the laws of thermodynamics from occurring. This is just one form of Zero-Point Energy[1]. Maybe these time crystals are another form - maybe some large objects radiate some kind of time-entropy, and these are too small (or configured in some other way), such that they are also mechanically prevented from doing so?

IANA theoretical physicist - I merely play one on the internet. Expert opinion and advice is welcome.

[0]https://physics.stackexchange.com/questions/18473/where-do-e...

[1]https://en.wikipedia.org/wiki/Zero-point_energy

Disclaimer: Theoretical physics postdoc, working in an unrelated subject area. Not necessarily an expert, but I do have some comments.

> Niels Bohr proposed that electrons don't have enough energy to radiate away, and thus are forced to continue to spin around the nucleus.[0] This was the seed that fruited the quantization of energy and eventually our modern understanding of Quantum Mechanics.

The first sentence is correct, though the history directly begins in 1900 with Planck's quantization hypothesis in the context of black body radiation. Bohr's paper, which I assume you're referring to, came in 1913.

> In a way, the quantization of reality at very small scales does appear to prevent the laws of thermodynamics from occurring. This is just one form of Zero-Point Energy[1]. Maybe these time crystals are another form - maybe some large objects radiate some kind of time-entropy, and these are too small (or configured in some other way), such that they are also mechanically prevented from doing so?

I do to take an issue with this paragraph, in that it doesn't really map to any well defined concepts in modern physics. The "quantization of reality at very small scales" (by which I assume you're referring to the speculative idea of fundamentally quantized spacetime) doesn't really have anything directly to do with thermodynamics - the laws of thermodynamics are necessarily statistical laws, produced by the behavior of ensembles defined by particular distributions. They have no particular validity in (most) very small scale systems and I don't see how the quantization is relevant here. Nor do any of these remarks help you violate the conservation of energy with respect to any larger systems.

I have no idea what "time-entropy" means, but generally speaking this notion of time crystals doesn't have anything intrinsically to do with violating energy conservation or producing useful work (in the physical sense) in any new fashion. Rather, it represents a fairly ingenious way of applying the established mathematical tools of analyzing symmetries to systems that exhibit complex periodic behavior rather than just spatial symmetries. In that regard, I think the example of satellite motion presented by Latham Boyle [1] was very illustrative without being misleading or overly suggestive.

I hope this response isn't overly snarky, I just wanted to clarify a few misconceptions I've seen a lot in the last few days.

[1] https://arxiv.org/abs/1407.5876

An electron at rest has 511 keV of energy, which is ~10^6 times the energy of visible light (~1 eV), so from energy considerations alone it has more than enough to "create" a photon. Accelerating electrons are a great source of light via Bremsstrahlung and synchrotron radiation.

This is the fundamental reason why electrons can't orbit the nucleus in a classical sense (and why we know the Bohr model is incorrect). The atom is a quantum object and as such it does not behave in a classical manner. You can describe it heuristically as an electron 'orbiting' the nucleus but that is not what's actually happening. The very concept of a path or trajectory does not have any meaning for quantum objects, which exist in probabilistic quantum states.

The first law of thermodynamics is basically conservation of energy. The internal energy in a closed system cannot change. In this case, if 'the system does not radiate its rotational energy', the particles will keep on moving indefinitely.

Since you ask, QM can sort-of 'break' this law though, very temporarily, via the uncertainty principle. Many particle decays are mediated by 'virtual particles', which are heavier than the input particles. For example, a neutron can decay into an electron+neutrino+proton (Beta decay), this is mediated by a W boson which is ~80 times heavier than the neutron. So in a way energy is 'borrowed' to create the W, which then promptly decays into the lighter electron+neutrino, so in the end energy is conserved.

Not really, It depends on the temperature of the particular system, but if the crystals are above something like 15 Kelvin then the particles should have a decent amount of energy each.

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