Eternal Change for No Energy: A Time Crystal Finally Made Real | Hacker News Reader

Eternal Change for No Energy: A Time Crystal Finally Made Real

quantamagazine.org

98 pointstheafh35 comments

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What's the difference between this and this other work also from the Max Planck Institute published back in February?:

https://is.mpg.de/news/world-s-first-video-recording-of-a-sp...

So it needs a laser, but it doesn't absorb any energy from the laser? Hmm.

and with that, plain crystals are automatically upgraded to space crystals

Space is just time rotated 90 degrees

The laws of physics are only symmetric under euclidean rotations in the three dimensions of space. When mixing time and space, you have to use a hyperbolic rotation, and there is no hyperbolic rotation that turns time into space.

Minkowski concluded that time and space should be treated equally, and so arose his concept of events taking place in a unified four-dimensional spacetime continuum. Even though Minkowski space treats time differently than space unlike 4D Euclidean space that does not mean that a transformation can not exist that preserves the Minkowski space(time) interval between two events, which is the defining property of a Lorentz transformation. The action of a hyperbolic versor (https://en.wikipedia.org/wiki/Versor#Hyperbolic_versor) with the further development of special relativity came to be called a Lorentz boost (https://en.wikipedia.org/wiki/Lorentz_transformation#boost). Boosts are a rotation-free Lorentz transformation; should not be conflated with mere displacements in Minkowski space(time). They describe only the transformations in which the spacetime event at the origin is left fixed; can be considered as a hyperbolic rotation of Minkowski space(time).

Unfortunately, as Einstein was already aware, a quasi-Euclidean four-space that includes time is not valid, because it excludes the phenomenon of gravitation. In the presence of gravity, spacetime is described by a curved 4-dimensional manifold for which the tangent space to any point is a 4-dimensional Minkowski space. Further, the article takeaway describes a different bound on the applicability of Minkowski (physical) space: "the discovery that, in the case of time, only discrete time-translation symmetry may be broken by time crystals puts a new angle on the distinction between time and space."

I'm not sure what you're getting at - it's still impossible to have a rotation that transforms a spatial basis vector into a time basis vector.

damn those perpendicular-time crystals

You're right! But the rotation has to happen in opposite directions through the 7th and 9th dimensions.

can you explain what you mean?

Of course not! It's jibberish to the same extent that "space is time rotated through 90 degrees" is. Fun, but jibberish.

I don’t think exactly the same extent. In Minkowski space, if you pick an orthonormal basis, one of the basis elements will be timelike and the other 3 will be spacelike, and the timelike one will be orthogonal to any linear combination of the spacelike ones, which, I think almost justifies saying that they are “90 degrees from one-another”.

I agree that saying it is “space rotated 90 degrees” is, not really right. There’s no rotation that would rotate all the special directions to a time direction, that wouldn’t make sense. 1 ≠ 3 and all that.

But there’s a bit of something kind of right in it.

HNers take jokes far too seriously.

Isn't this just a perpetual motion machine? How can it change, while absorbing no energy from a laser, forever? If it's a perpetual motion machine, how can that be?

It's not more of a perpetual motion machine than the molecules of a gas moving around, or of a solid vibrating.

If the phase changes happen on any kind of non-random schedule, however, it would still be introducing information into the system. And therefore violating know laws. Right?

What known laws would it be violating?

If you're thinking of the second law of thermodynamics, bear in mind that popular descriptions that equate "entropy" with "information" or "non-randomness" are extremely oversimplifying things. A periodic change in a system does not necessarily imply a decrease in entropy.

The molecules of a solid also vibrate in a highly predictable schedule¹. One of the effects of quantum mechanics is that many of those things are much more predictable than one would expect naively.

1 - That's very useful for material identification, for example.

I think the difference is a perpetual motion machine ought to be able to do useful work. You can hook it up to a shaft and generate power ect. This merely moves. I guess this doesn't work for some reason (or maybe just doesn't count), but imagine a wheel rotating in a perfect vacuum. It can quite happily rotate forever without using any additional energy

It would still slow down. The blackbody radiation output by the wheel would cool it down, and in the same way, all the electrons the wheel is made out of will radiate energy as they are spun. (Spinning charges are constantly accelerated by centripetal force, and accelerated charges radiate.) So no, 2nd law of thermodynamics means you can't even keep pace, you are always losing energy. So how can these scientists claim to have invented perpetual motion?

The wheel has an overall neutral charge. Does this change whether it emits anything from these charges rotating?

If we are modeling thing with classical electromagnetism (I don’t understand enough to attempt to apply quantum mechanics to this), we can treat point charges as having a Dirac delta function for their charge density function. If you take linear combination of Dirac delta functions, with each having a positive or negative coefficient, and these being roughly evenly spaced out in a fixed region (e.g. the wheel shape), and take the limit as the magnitude of the coefficients goes to zero while the number of deltas goes to infinity (with the two being inversely proportional), shouldn’t the correspond signed measure converge to the zero measure, so, a charge density function of zero?

So, shouldn’t a macroscopic object (which has a very large number of atoms) be well approximated as having zero charge density? Of course, this is only an approximation, it doesn’t have exactly zero net effect on the electric field,

but if it is a good approximation, especially at a distance, I would think that would suggest that such an object accelerating should produce at least less EM radiation than a similar object with a large net charge?

But, I’m reasoning heuristically atm, and am not being especially careful, so I could very well be wrong here.

Hum, guess I'm definitely exposing my lack of physics knowledge, but my understanding was that entropy is only guaranteed to increase or stay the same in any isolated system. That the inequality is >= not >. If so while like this exact example might not work, there isn't anything clearly wrong with something that just has repetitive motion

This is how I am reading it as an wheel analogy;

1. Maintaining vacuum state costs energy.

2. Using energy you can change wheel rotation from clock wise to counter clockwise.

3. By using energy when changing wheel ration, wheel rotation energy is not effected.

I am almost sure it is false thought :)

It is really hard to follow context of article, guess is not written for us mortals. My primitive understanding that is most likely wrong;

> If it sounds implausible, it is: After much thrill and controversy, a 2014 proof showed that Wilczek’s prescription fails, like all other perpetual-motion machines conceived throughout history.

> Furthermore, the spins never absorbed or dissipated net energy from the microwave laser, leaving the disorder of the system unchanged.

Seems like maintaining stable quantum state A or B costs energy, but changing quantum state from A to B or from B to A does not somehow introduces additional order/disorder to a quantum system and changing state costs energy. (this still confuses me, obviously)

> As well as offering sexier terminology, they provided new facets of understanding, and they slightly generalized the notion of a Floquet time crystal beyond the pi spin-glass phase (noting that a certain symmetry it has isn’t needed).

What, were they going to fuck the particles? "sexier" is the wrong word for this progress; I hope that they meant "standard".

In this context, sexier is used interchangeably with cool. It’s a common phrasing.

And now I am imagining something that’s time-amorphous, like a time crystal, but that doesn’t cycle orderly over a predictable set of states at regular intervals, but that does so irregularly tracing itself into multiple paths between its possible states.

Doesn't a glass of water satisfy that definition?

That sounds very Stephen Wolfram to me.

I stopped listening to anything from quanta magazine after this video:

https://youtu.be/HL7DEkXV_60

Where they claim that that a "landmark proof" and one of the greatest accomplishments in computer science of 2020 solved THE HALTING PROBLEM using "a quantum AI supercomputer."

I looked up the proof and that's not even remotely what the authors paper seems to be talking about...

Not to mention you'd both win the Turing award and have it renamed after you if you solved the halting problem.

So I guess my question is: Is quanta magazine reputable or just more science clickbait? I'm curious what the hacker News audience thinks since I am definitely not a quantum physicist.

That video segment never mentions "AI", and it never says that the halting problem has been solved -- it explicitly says it's unsolvable. What it says is that solutions to the halting problem could be verified under a certain computational model.

That's obviously an extremely rough summary of what the paper shows, but I'm not sure how one could do better in a 3-minute summary for a non-expert audience. And based on Scott Aaronson's response to the paper, it seems like calling it a "landmark" result is very reasonable:

> Still, assuming this one stands (as I’m guessing it will), I regard it as easily one of the biggest complexity-theoretic (and indeed computability-theoretic!) surprises so far in this century. Huge congratulations to the authors on what looks to be a historic achievement.

https://www.scottaaronson.com/blog/?p=4512

Thanks, I appreciate you taking the time to correct me.

I looked at some articles from quanta on mathematics I am more familiar with and they were pretty good so I definitely misjudged them.

It's just getting so hard to figure out what's sensationalist and what is not these days.

I’ve read a few Quanta articles about topics in pure math, and they did about as good of a job as one could reasonably expect. E.g. they interviewed roughly the same people I would have chosen, and the author clearly spent a great deal of time trying to make the work accessible without saying anything untrue or misleading. Of course, there’s a certain amount of hype that tends to be a matter of opinion.

Here’s an example close to my heart: https://www.quantamagazine.org/mathematicians-find-polynomia...

> The time crystal is a new category of phases of matter, expanding the definition of what a phase is. All other known phases, like water or ice, are in thermal equilibrium: Their constituent atoms have settled into the state with the lowest energy permitted by the ambient temperature, and their properties don’t change with time. The time crystal is the first “out-of-equilibrium” phase: It has order and perfect stability despite being in an excited and evolving state.

So to recap, there are now 8 known states of matter: solid, liquid, gas, plasma, bose-einstein condensate, time crystal, and apparently water and ice.

So... Perpetual motion.

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