(Not an expert) I read the first few paragraphs on that link. So, by analogy, we might call (normal) crystals with flaws "space crystals". Or maybe they should be "space-flawed crystals" and "time-flawed crystals" - a "flaw", in the usual sense, being a break in the regular crystalline structure. The adjective describes the (nature of the) breakdown in regular structure, not the regular structure. No? I wouldn't defend "space crystal" as a "technically very accurate name".
> Time crystals should be stable and coherent over long time periods, because they - theoretically - oscillate at their lowest possible energy state. The team's research shows that driven magnonic time crystals can be easily manipulated, opening a new way to reconfigure time crystals. This could open up the state of matter for a range of practical applications.
> "Classical crystals have a very broad field of applications," said physicist Joachim Gräfe of the Max Planck Institute for Intelligent Systems.
> "Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
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?
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.
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.
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.
In the experiment, the crystals were driven by RF excitation. Do time crystals generally require a constant energy source to oscillate? I would assume not, since they're called crystals...
Also, is the oscillation frequency temperature dependent?
I can't tell if you're joking, but in case anyone else is wondering: Most people can perceive between 30-60 frames per second. Some (mostly gamers) reportedly perceive up to 120 frames per second. Though whether this counts as recording is a matter for philosophers.
Its wierd because I could differentiate between 120Hz and 240Hz but I think its because the computer generates still images without motion blur. So 120Hz with perfect motion blur would be indistinguishable from 240Hz I think
If only it were that simple! There's no-such-thing as 'perfect motion blur', it's all a matter of taste.
You can do things like open the virtual shutter to full-open (so that not a single virtual-photon reflected off the virtual-motion will be missed by the virtual-sensor), which makes the motion recorded during one frame continue directly (with no time 'gap') into the next frame. This can help make things seem 'smoother' for sure but it's still relying hugely on persistence-of-vision.
I'm super surprised (and a bit incredulous tbh!) to hear of a perceivable difference between 120 and 240fps! need to go double-blind on that stuff to be sure I reckon!
On a computer game you can spot the 240fps because of the intermediate frames when you have visual elements moving very quickly across the screen. It's not because of 'faster eyes' I don't think. Like when you move your mouse very quickly you'll see twice as many mouse cursors en route.
You can detect very small numbers of photons (sometimes a single photon), your eyes don't care about the frame rate. The question is, can you tell the difference between 120FPS and 240FPS
Still an excellent question! There's this (no proper references) that seems to suggest ppl lose the ability to make meaningful judgements about frame rate (or ~differentiate differences) after around 150fps:
This (150>120) seems to suggest that many people would be able to see (maybe it'd be better to call it "feel" the difference at this point) the difference between 120 and 240fps. but they most likely couldn't tell 150 from 240fps.
Our vision is not frame-based at all. Each receptor cell can trigger inependently. Chopping up the signal into image frames is simply a technical trick that makes us perceive continuous motion due to the finite recovery time of the cells (persistence of vision).
When quantum mechanics are involved, I feel like someone from 400 years ago might feel today using a smartphone. And probably as a society we are now like starting to experiment with electricity. I wonder what will be the smartphones in that future.
>"Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
Could anyone expand on this in an accessible way? What kinds of changes could we see in imaging or communication technology?
just a random guess and hypothesis with absolutely no basis besides this article. I think they may be able to 'sync' up transmitters which are then used to encode and decode based on time and space. Like time-sensitive antennas which adds another means of encoding....???
Since the article doesn't do a good job of explaining what a time crystal is, here's my attempt at summarizing the Wikipedia article [0].
Normally, a system 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.
The analogy with normal 'spatial' crystals is through this symmetry breaking: Empty space is symmetric under all translations, but a crystal spontaneously breaks the symmetry group down to the smaller set of 'translations by a multiple of the lattice constant'.
The continuous symmetry of time translations cannot be spontaneously broken, due to thermodynamic arguments. Instead, we explicitly break down the time translation symmetry to 'delays by a multiple of the period duration'. A time crystal then spontaneously breaks the symmetry down even further, by multiplying the period duration / dividing the frequency.
How does this compare to the behavior of nonlinear optical crystals like lithium triborate? They are also pumped at a lower frequency (e.g. 1064nm photons) but lase at twice that (532nm).
In some way, it's the inverse: a nonlinear optical system can multiply frequencies, while a time crystal divides a frequency. That's not as easy as multiplying, due to the symmetry concerns I mentioned.
It's basically a frequency divider, but as a system of cold atoms instead of an electronic circuit, and in a different frequency regime.
I don't know... atomic clocks are approaching precision that can measure the effects of time dilation due to gravity on the order of inches. They have to take into account daily tectonic tides.
> The precision of current optical clocks is astounding. You may have heard that time goes more slowly when gravity is strong due to general relativity. Optical clocks are so sensitive they can measure the different flows of time 2cm apart in height. If I lay a book on the table, the bottom of the book is slightly closer to the center of the Earth than the top, so experiences slightly stronger gravity. This difference is measurable with an optical clock. Optical clocks are so sensitive we can no longer average the time of multiple clocks together—the ground you or a clock are sitting on typically rises and falls by ~5cm a day due to land tides. The seismic motion of the ground currently limits our ability to measure time.
https://arstechnica.com/science/2021/01/a-curious-observers-...
Certainly for atomic clocks (nearly the very definition of precision), but the vast majority of lab work isn't anywhere near that level of precision. So yes, you may need to factor in GR if your goal is to measure the smallest possible thing, but for general work with macroscopic items, it's such a small difference it is completely unnecessary.
Not a physicist by a long shot. But that's makes no sense. Gravity waves maybe can behave like an object with mass. But them having mass makes no sense.
Energy and momentum, sure. But not mass. Same as light.
You're right, and your parent is not, for two reasons.
Firstly, gravitational radiation is observed to obey the classical massless wave function, just as in the large-number-of-photons-limit light obeys the classical massless wave function.
The second quantization [1] of each such massless wave function leads to a massless gauge boson of spin-2 and spin-1/2 respectively: the graviton and the photon. There is excellent experimental and observational support for this approach as an effective field theory -- as one takes the energies of the particles in either field (in isolation) higher, one runs into theoretical questions that have not been resolved.
However, this second-quantization approach conflicts with the approach taken in the Standard Model, which defines a massless gauge boson (also called a photon) and is silent about the quantum content of gravitation [2]. The photon is massless because it moves at "c", and vice-versa. For a Standard Model graviton to be defined, it must also be massless, or light must not always move at "c", leading to photons of different energies moving at different speeds (in vacuum) relative to an observer of those energies. This conflicts with experiment.
The "bigravity" [3] family of gravitational theories probes this variable-speed-of-light problem, and are amenable to study under the Parameterized Post-Newtonian Formalism with results that conflict with evidence [4]. In General Relativity, distant emitters of electromagnetic radiation and distant emitters of gravitational radiation must line up in the sky barring intervening matter that interacts with light. This is in fact what we observe in the Ligo/Virgo era, and since the Mercury MESSENGER experiments. In this case it's because our universe is Lorentzian, having 3 dimensions of space and 1 of time. In Lorentzian universes in General Relativity there is one type of geodesic ("lightlike" [5]) along which massless objects may move, and that geodesic is forbidden to massive objects.
The idea of "massive" gravitational radiation is a theoretical curiosity that is undermined by new evidence gathered practically daily (e.g. in the results of sky searches for supernova and binary eclipses (and other multibody eclipses) by e.g. ASAS-SN : http://www.astronomy.ohio-state.edu/asassn/index.shtml ).
Secondly, gravitational radiation can be included in exact vacuum solutions to the Einstein Field Equation of General Relativity, and this is grad student textbook and lecture note material. The notable feature of vacuum solutions is that the stress-energy tensor T_{\mu\nu} is defined to be zero everywhere in the spacetime. That one introduces "test probes" into the spacetime to see how they move under the influence of gravitation does not change this crucial feature.
For the most part, one should take "energy" and "momentum" as referring to coordinate-system-dependent components of the stress-energy tensor. If we write down the stress-energy tensor as a 4x4 matrix, labelling 0..3 on the rows and columns, with a different matrix at every point, then we can think about the matrix at one point pretty straightforwardly as showing the flux of momentum into the point from each dimension of space or time, and the flux of momentum out of the point along each dimension of space or time. One conventionally takes energy or mass-energy as the time-time component: momentum that comes to this spacetime point from the past and leaves this spacetime point for the future, the spatial coordinates being constant. (We'd write this as T_{00} != 0. Compare the totally inelastic absorbtion of a photon from "the left" (spacetime direction 1) that we'd write as T_{10} != 0 because the momentum s...
When I hear "time crystal", I think "the wielder of this object can travel through time, or at least do something far out, like see past events", not "a crystal that when vibrated breaks symmetry".
And whenever I hear time crystal, I think of bad sci-fantasy 80s movies.
“Mondor, you must grab the time crystal before the second moon equinox, or the Flarborg will be released from their electronic pen and ravage us like they’ve never ravaged before!”
I believe the most recent iteration of star trek is particularly guilty of stealing "time crystals" from the science news headlines and applying it to this sci-fi trope.
Every time the discussion of time crystal comes up, a simple analogy can explain what it is.
Regular crystal has repeatable structure in space, i.e. its lattice is the same shape over and over again across in space.
Time crystal is the kind of material that has repeatable structure across time, at the lowest energy state. It just means it changes its shape periodically over time.
An example of that is quartz crystal vibration where its structure bends and unbends over time. Quartz bending and unbending (vibration) is due to the piezoelectric effect when an external electric force is applied. The external force requirement disqualifies it as a time crystal.
The "at the lowest energy state" requirement means time crystal can "vibrate" by itself without external force applied. "Vibrate" is used loosely here. It could be the nuclear-spin flipped periodically, or some other structural changes that need no outside influence.
If you could coax work out of it in a ground state, that would be a perpetual motion machine, so no, it had better not emit energy. But you could detect the spin flips to make a clock
Spin waves are similar to vibrations (phonons) in a lot of respects, you still need energy to change a spin.
That said, some aspects of thermodynamics are counter-intuitive (well, actually most of it is). Vibrations are present even at 0 K because of the uncertainty principle, and that’s true for spin waves as well as actual vibrations. It does not mean that any energy is created. The difference with time crystals is that usually these vibrations don’t involve any symmetry breaking.
Time crystals are consistent with standard thermodynamics.
Yes it’s true. Kinetic energy is never exactly zero, that’s called zero-point energy. Perfect stillness does not exist at the atomic scale. It would involve knowing perfectly both positions and velocities (in case of atoms, the equivalent is true for spins).
What you have described is an ideal time crystal.
Unfortunately the time crystals we can create in the lab do need an external force, but this force can have a higher frequency than the oscillation of the crystal.
For anyone struggling to make sense of this: I have a physics PhD, I have spent most of my career in fundamental research, I have read the Wikipedia article and other references multiple times, and attended several talks, and I still don't understand what qualifies as a time crystal. All I know that it seems to have something to do with subharmonic response.
That was a good little read and mirrors my sentiments about media consumption exactly. People who have a specialized knowledge about a subject will often find themselves reading false information about serious topics from media about their subject of knowledge. Lowering the credibility of that media in their eyes and preparing themselves to be more skeptical of information output from that media. Then flip to another subject they are totally uninformed on and believe word for word everything that is said to them no matter how utterly ridiculous.
I don't really know what those people in physics do, but as a mathematician my definition of a time-crystal would be a 4-dimensional discrete structure. You have some 4-dimensional symmetries.
Just rotating in 3D is a bit boring. Interesting symmetries would be where you get the time-axis involved.
4D is most likely a bit boring - having more dimensions and more time-dimensions helps greatly to get more symmetries to work with...
I wonder how this links in to optical crystals? KTP, used in solid state lasers, will halve the frequency of a IR laser (1064nm) to produce green light (532nm).
I suppose this is equivalent to adding electrical energy to a crystal to make it oscillate.
532 nm corresponds to double the frequency of 1064 nm, not half. Any nonlinear response generates harmonics of a signal but not subharmonics. This is why in electronics a single diode can be used as a frequency doubler, but a digital flip-flop is required for frequency division.
This is a wonderful development! Learning about far-out advances in physics is amazing, but they sometimes feel like they are too removed from everyday reality beyond helping us understand some semantic piece of how the Universe works. Does anybody know if time crystals have any practical uses?
from the article at the end. suggest u read it hashman.
"Classical crystals have a very broad field of applications," said physicist Joachim Gräfe of the Max Planck Institute for Intelligent Systems.
"Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
why aren't electrons spinning round an atom called "time particles"? Technically by the time they run out of energy, the universe will have died so they are "super time particles".
I think they are not actually spinning, they are around the nucleus in a probability cloud. I dont think we could use that as a timing mechanism but Im not a physicist
> So, where the structure of regular crystals repeats in space, in time crystals it repeats in space and time.
Does that mean anything that behaves like a wave is a form of time crystal? For example ocean currents moving in unison causes all atoms in that wave to follow a very specific pattern similar to what is described in the article.
I wish someone would show that charge parity time (CPT) symmetry can be broken so we'd have to rewrite the entire laws of physics from scratch but this time would do it more efficiently.
It sounds like these room-temperature time crystals must be driven by continually applying external energy via the driving frequency, or did I misread that?
Is it feasible to create my own time crystals? Or acquire one?
I would love to add a time crystal to my existing space crystal collection, even if it requires some sort of support to maintain the driving frequency.
I haven't read the paper yet, but it sounds like I could apply a particular frequency to a strip of nickel-iron alloy and practically achieve such an effect?
Do any physicists here know whether that would be feasible?
Yes, with microwave RF and a magnetic strip in a static field you can make one, but just keep in mind you'll need an X-ray synchrotron and a 40 billion fps camera to see it.
In 2001 I worked on spectral analysis of a jet-type flow and realized a PIV software with matlab. Of course images that I used issued from a high speed camera, have nothing to do with the 40 billion frames per second we are talking about here ! It was just fascinating to see the particles moving in milliseconds.
We are talking here about 40 Cycles Per Nanosecond !! It's not just fascinating, it's Hilariously crazy !
110 comments
[ 4.2 ms ] story [ 120 ms ] threadI've never seen such a weird aspect ratio on YouTube either.
> "Classical crystals have a very broad field of applications," said physicist Joachim Gräfe of the Max Planck Institute for Intelligent Systems.
> "Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
Time crystals move at the ground state - you cannot stop them by removing the energy.
A time crystal, however, will oscillate with a fraction (or rational multiple) of the driving frequency. This breaks the original time translation symmetry.
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.
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.
Also, is the oscillation frequency temperature dependent?
that's quite a feat on anyone's watch
This is many orders of magnitude more than that.
You can do things like open the virtual shutter to full-open (so that not a single virtual-photon reflected off the virtual-motion will be missed by the virtual-sensor), which makes the motion recorded during one frame continue directly (with no time 'gap') into the next frame. This can help make things seem 'smoother' for sure but it's still relying hugely on persistence-of-vision.
I'm super surprised (and a bit incredulous tbh!) to hear of a perceivable difference between 120 and 240fps! need to go double-blind on that stuff to be sure I reckon!
https://www.quora.com/What-is-the-highest-frame-rate-fps-tha....
Could anyone expand on this in an accessible way? What kinds of changes could we see in imaging or communication technology?
Normally, a system 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.
The analogy with normal 'spatial' crystals is through this symmetry breaking: Empty space is symmetric under all translations, but a crystal spontaneously breaks the symmetry group down to the smaller set of 'translations by a multiple of the lattice constant'.
The continuous symmetry of time translations cannot be spontaneously broken, due to thermodynamic arguments. Instead, we explicitly break down the time translation symmetry to 'delays by a multiple of the period duration'. A time crystal then spontaneously breaks the symmetry down even further, by multiplying the period duration / dividing the frequency.
[0]: https://en.wikipedia.org/wiki/Time_crystal
It's basically a frequency divider, but as a system of cold atoms instead of an electronic circuit, and in a different frequency regime.
> The precision of current optical clocks is astounding. You may have heard that time goes more slowly when gravity is strong due to general relativity. Optical clocks are so sensitive they can measure the different flows of time 2cm apart in height. If I lay a book on the table, the bottom of the book is slightly closer to the center of the Earth than the top, so experiences slightly stronger gravity. This difference is measurable with an optical clock. Optical clocks are so sensitive we can no longer average the time of multiple clocks together—the ground you or a clock are sitting on typically rises and falls by ~5cm a day due to land tides. The seismic motion of the ground currently limits our ability to measure time. https://arstechnica.com/science/2021/01/a-curious-observers-...
Energy and momentum, sure. But not mass. Same as light.
Firstly, gravitational radiation is observed to obey the classical massless wave function, just as in the large-number-of-photons-limit light obeys the classical massless wave function.
The second quantization [1] of each such massless wave function leads to a massless gauge boson of spin-2 and spin-1/2 respectively: the graviton and the photon. There is excellent experimental and observational support for this approach as an effective field theory -- as one takes the energies of the particles in either field (in isolation) higher, one runs into theoretical questions that have not been resolved.
However, this second-quantization approach conflicts with the approach taken in the Standard Model, which defines a massless gauge boson (also called a photon) and is silent about the quantum content of gravitation [2]. The photon is massless because it moves at "c", and vice-versa. For a Standard Model graviton to be defined, it must also be massless, or light must not always move at "c", leading to photons of different energies moving at different speeds (in vacuum) relative to an observer of those energies. This conflicts with experiment.
The "bigravity" [3] family of gravitational theories probes this variable-speed-of-light problem, and are amenable to study under the Parameterized Post-Newtonian Formalism with results that conflict with evidence [4]. In General Relativity, distant emitters of electromagnetic radiation and distant emitters of gravitational radiation must line up in the sky barring intervening matter that interacts with light. This is in fact what we observe in the Ligo/Virgo era, and since the Mercury MESSENGER experiments. In this case it's because our universe is Lorentzian, having 3 dimensions of space and 1 of time. In Lorentzian universes in General Relativity there is one type of geodesic ("lightlike" [5]) along which massless objects may move, and that geodesic is forbidden to massive objects.
The idea of "massive" gravitational radiation is a theoretical curiosity that is undermined by new evidence gathered practically daily (e.g. in the results of sky searches for supernova and binary eclipses (and other multibody eclipses) by e.g. ASAS-SN : http://www.astronomy.ohio-state.edu/asassn/index.shtml ).
Secondly, gravitational radiation can be included in exact vacuum solutions to the Einstein Field Equation of General Relativity, and this is grad student textbook and lecture note material. The notable feature of vacuum solutions is that the stress-energy tensor T_{\mu\nu} is defined to be zero everywhere in the spacetime. That one introduces "test probes" into the spacetime to see how they move under the influence of gravitation does not change this crucial feature.
For the most part, one should take "energy" and "momentum" as referring to coordinate-system-dependent components of the stress-energy tensor. If we write down the stress-energy tensor as a 4x4 matrix, labelling 0..3 on the rows and columns, with a different matrix at every point, then we can think about the matrix at one point pretty straightforwardly as showing the flux of momentum into the point from each dimension of space or time, and the flux of momentum out of the point along each dimension of space or time. One conventionally takes energy or mass-energy as the time-time component: momentum that comes to this spacetime point from the past and leaves this spacetime point for the future, the spatial coordinates being constant. (We'd write this as T_{00} != 0. Compare the totally inelastic absorbtion of a photon from "the left" (spacetime direction 1) that we'd write as T_{10} != 0 because the momentum s...
Do the allow some kind of special optical devices?
“Mondor, you must grab the time crystal before the second moon equinox, or the Flarborg will be released from their electronic pen and ravage us like they’ve never ravaged before!”
“Oh. Well, we wouldn’t want that would we?”
Vision is far out: https://www.youtube.com/watch?v=FjHJ7FmV0M4
Regular crystal has repeatable structure in space, i.e. its lattice is the same shape over and over again across in space.
Time crystal is the kind of material that has repeatable structure across time, at the lowest energy state. It just means it changes its shape periodically over time.
An example of that is quartz crystal vibration where its structure bends and unbends over time. Quartz bending and unbending (vibration) is due to the piezoelectric effect when an external electric force is applied. The external force requirement disqualifies it as a time crystal.
The "at the lowest energy state" requirement means time crystal can "vibrate" by itself without external force applied. "Vibrate" is used loosely here. It could be the nuclear-spin flipped periodically, or some other structural changes that need no outside influence.
That said, some aspects of thermodynamics are counter-intuitive (well, actually most of it is). Vibrations are present even at 0 K because of the uncertainty principle, and that’s true for spin waves as well as actual vibrations. It does not mean that any energy is created. The difference with time crystals is that usually these vibrations don’t involve any symmetry breaking.
Time crystals are consistent with standard thermodynamics.
Are you sure that's true? I can't remember the exact details but recall that being a common misinterpretation of the uncertainty principle
https://en.m.wikipedia.org/wiki/Zero-point_energy
Just rotating in 3D is a bit boring. Interesting symmetries would be where you get the time-axis involved.
4D is most likely a bit boring - having more dimensions and more time-dimensions helps greatly to get more symmetries to work with...
I suppose this is equivalent to adding electrical energy to a crystal to make it oscillate.
* Physicists Predict The Existence of Time Crystals https://www.technologyreview.com/s/426917/physicists-predict...
* How to Build A Space-Time Crystal https://www.technologyreview.com/2012/06/26/255685/how-to-bu...
(Reposted from an earlier submission in 2016: https://news.ycombinator.com/item?id=12655530)
"Classical crystals have a very broad field of applications," said physicist Joachim Gräfe of the Max Planck Institute for Intelligent Systems.
"Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
Does that mean anything that behaves like a wave is a form of time crystal? For example ocean currents moving in unison causes all atoms in that wave to follow a very specific pattern similar to what is described in the article.
This is what's wrong with model based "science".
Is it feasible to create my own time crystals? Or acquire one?
I would love to add a time crystal to my existing space crystal collection, even if it requires some sort of support to maintain the driving frequency.
I haven't read the paper yet, but it sounds like I could apply a particular frequency to a strip of nickel-iron alloy and practically achieve such an effect?
Do any physicists here know whether that would be feasible?
We are talking here about 40 Cycles Per Nanosecond !! It's not just fascinating, it's Hilariously crazy !