Physicists Attempting To Test 'Time Crystals' 231
ceview writes "This story at Wired seems to have lots of people a bit confused: 'In February 2012, the Nobel Prize-winning physicist Frank Wilczek decided to go public with a strange and, he worried, somewhat embarrassing idea. Impossible as it seemed, Wilczek had developed an apparent proof of "time crystals" — physical structures that move in a repeating pattern, like minute hands rounding clocks, without expending energy or ever winding down. ... [A] Berkeley-led team will attempt to build a time crystal by injecting 100 calcium ions into a small chamber surrounded by electrodes. The electric field generated by the electrodes will corral the ions in a "trap" 100 microns wide, or roughly the width of a human hair. The scientists must precisely calibrate the electrodes to smooth out the field. Because like charges repel, the ions will space themselves evenly around the outer edge of the trap, forming a crystalline ring.' The experimental set up is incredibly delicate (Bose Einstein Condensate), so it implies this perpetual motion effect can't really be used to extract energy. What is your take on it? It's unlike to upend anything, as the article suggests, because at a quantum level things behave weirdly at the best of times. The heavy details are available at the arXiv."
Re:Newton? (Score:5, Informative)
That makes sense if you don't take into account that these puppies will be going around in a circle - without the initial velocity. First law of motion works for orbits - the objects are effectively moving in a straight line but the curviture of space around the planet/body/star is making their straight line circular. From what I can understand of this article (I haven't read the arxiv version, nor will it likely make sense to me anyhow) the interesting thing is that the scientists aren't starting them in a spin - they expect that they will start spinning on their own.
Re:What does this have to do with time? (Score:5, Informative)
IINAScientist but here's how I understand it. Three-dimensional crystals form a regular, repeating lattice in the three spacial dimensions. These lattices are stable and need no energy input to retain their structure. Hypothetically, time crystals extend that lattice into a fourth dimension (time), treating time more-or-less as a spacial dimension. Given that the structure is crystalline, no energy is needed to maintain it even though its 3-dimensional structure, dimensions, etc. may appear to vary over time. Such structures are so far only hypothetical; the goal of this experiment is to attempt to create one.
Re:Newton? (Score:5, Informative)
If i understand the article correctly it's not just going round in a circle like a planet but "jumping" around specific point around the circle like a clock hand. it appears from one point to the other without being in between. But rest of your point still applies.
Thiotimoline (Score:4, Informative)
Thiotimoline, or a Shipstone, perhaps? (Score:5, Informative)
Wasn't all of this in "The Endochronic Properties of Resublimated Thiotimoline" by Asimov?
heh...glad I'm not the only one who made that connection. That was a specific carbon compound, IIRC, that dissolved 1.12 seconds before water hit it, and Asimov's clever scientists and engineers figured out how to power a stardrive with it. Wonder what would happen if engineers figured out how to move energy into this time cube and then extract it later on. Might be a shipstone in the making... :) (I like Asimov a lot, but Heinlein is a better story teller.)
Re:How is this different to harmonic oscilator? (Score:5, Informative)
Ok, I'll have a stab at it. First of all, ignore the 'crystals of time' hoopla. This is not helpful.
Imagine a hydrogen atom with one electron and a fixed nucleus. The electron will be in a certain orbital. If you are thinking of the atom according to the Bohr model, the the electron is going around the nucleus like a planet around the sun. However, the position of the electron, or rather the probably of finding the electron in any particular position, is determined by a wave-function. This wave-function is a complex number that varies with space, and possibly with time too. You cannot measure this complex function directly, but if you can detect the particle somehow, you might learn something about the value the wave function had before the measurement started.
Actually, the stable hydrogen atom wave-function is simple and calculable, and just like the simple harmonic oscillator, it does not change with time. The electron is in a stable orbit, and will need to lose energy or gain energy to go to a different orbit. The same is true for many much more complex wave-functions. If you have a current running in a superconducting loop, then all the electrons in the superconducting band can be described by a single giant wave-function. You still have all the individual electrons, but they are all moving in a coherent manner, so they are not losing energy. Indeed, they probably got into that state by taking energy from the giant wave-state, until it reached some local stable minimum. And even though you may have billions of electrons in the wave-state, the wave-function does not change with time unless something disturbs it.
Okay, the idea of sucking out energy until a particle or a system reaches a stable state is pretty common, but it is not necessarily universal. You could have two hydrogen atoms, one with the electron in the ground state, and one with the electron in an excited state; and the second atom loses its energy to the first one, and after a while, the first atom gives it back to the second one again, and so it goes on. In real life, the atom would probably emit a photon that would not get caught by the other one, and that would be the end of it. But if you could somehow constrain the photon to just bounce between the two atoms, then you have two electron wave functions that are perpetually flipping between two states in such a way that energy is preserved. This cyclic flipping would mean that the whole system gets back to where it was a short while ago: it is something that happens at regular intervals in time, hence the 'crystals in time' bit. Ugh. Can we describe the whole system, including whatever it is that constrains it by a bigger wave-function that does not change with time, like our superconductors? It's a bit unlikely, because the jumping between states and emitting or absorbing a photon is a sudden transition, where the super-electron interactions were smooth and continuous. But there might be a way.
Re:Isn't this just a frictionless surface? (Score:5, Informative)
As usual, the summary and the article somewhat mis-state the interesting part. They talk about 'perpetual motion' but there are lots of examples of things that move seemingly without end: e.g. a planet orbiting a star. However if you think about it a bit more, you'll realize that those kinds of motion can't be used to get "free energy" and actually are not even perpetual. If you try to extract energy from some kind of bound system that exhibits motion, you decrease the energy of the system and alter the motion. So you can extract energy from a planetary orbit (in principle), but then the planet will have less energy, and orbit more slowly (its orbit will decay). As other posters mention, all kinds of natural processes inherently perform this kind of "energy extraction": e.g. random collisision with space-dust, or tidal interactions between planetary bodies, will slowly alter these 'perpetual' orbits. Even if you imagine a highly idealized system (perfectly rigid objects orbiting one another in perfect vacuum), we have reason to believe that such a system will radiate away energy (slowly) by emitting gravitational waves.
What this all amounts to is saying that the system has some 'extra energy' that could be extracted. In physics we would say that the system is not in its ground state [wikipedia.org], or "minimum energy state". This is the key phrase that the quoted physicists use which the article doesn't properly explain.
The idea is that a system in its ground state will have lost all the energy it can possibly lose. There is no extra energy left. And, conventionally one would assume that a system in the ground state would no longer exhibit any kind of motion: because any motion is extra energy that could be extracted, obviously. So an idealized orbital system has motion, but is not in the minimum energy state. What Wilczek is proposing is that he's discovered kinds of systems which exhibit motion in their ground state. In other words, the system oscillates as a function of time, and yet one cannot extract energy from this oscillation. Cool!
The analogy to crystals is this: as you cool atoms, they vibrate less and less, and eventually they settle into their minimum energy state. This state is usually a crystal, where all the atoms are frozen into perfect rows. This is the minimum energy state. Interestingly, at high-temperature the system was spatially homogeneous (a gas has atoms all over the place), whereas the ground state has spontaneously broken space-translational symmetry: the atoms exist in well-defined positions and don't occupy intervening points. Thus the ground state spontaneously breaks a symmetry (space-translation). Wilczek's proposed states, if they really exist, would upon cooling to their ground state (no excess energy left) settle into an arrangement where they are in motion. Thus along the time axis the system is not constant/homogeneous. The system has spontaneously broken time-translational symmetry. Hence this is like a crystal along the time axis: a 'time crystal'.
I'm not qualified to say whether this is right or wrong. It would be exciting if true. But it doesn't seem to violate any known laws (e.g. you can't use it to violate conservation of energy, so no 'perpetual motion' in the 'free energy' sense), so it seems possible that these states could exist.
Re:Newton? (Score:5, Informative)
From the article: "How can something move, and keep moving forever, without expending energy? It seemed an absurd idea — a major break from the accepted laws of physics. "
This is a real groaner to a physicist. Is there any solid matter near you right now? Matter does seem to be real, doesn't it? In the classical regime, accelerating electrons radiate energy. According to Newton, matter should collapse into itself. The electrons should spiral in until they hit the nucleus.
Electrons in atomic orbits move without losing energy. The orbits are stable. Negatively charged electrons are attracted to the positive nucleus, yet they don't combine. Matter does not collapse on itself. It's not Newton, it's quantum mechanics, in particular, Heisenberg's uncertainty principle. Heisenberg uncertainty explains the solidity of matter.
What is different here is the size and mass scale has been upped by orders of magnitude from electron orbits in atoms and molecules in this supercooled atom trap. It remains to be seen if the experiment will produce results. The scientific jury is out.
Re:Implies? "Can't really"? (Score:5, Informative)
Yeah, that sentence is bogus. The pure physics all by itself says that you can't extract energy from it.
What the delicacy of the setup "implies" is that it's not immune to the second law of thermodynamics, or the first law of motion. The "time crystal" is only perpetual as long as nothing else impinges on it. Which is precisely the same as the frictionless pendulum you saw in first-year physics.
The remarkable part of this experiment has zilch to do with perpetual motion, either in the "free energy" sense or the "first law of motion" sense. It's about a remarkable quantum effect involving transitions even at the lowest possible energy, which wouldn't be allowed by classical physics but is allowed by quantum mechanics. The rest is just mainstream science writers who don't know what they're talking about and are trying to make it sound like magic to attract eyeballs.