
Physicists Create World’s First Time Crystal - hrgeek
https://www.technologyreview.com/s/602541/physicists-create-worlds-first-time-crystal/
======
davesque
I figured this article would fly over my head (which it mostly did), but it
was actually a very fun read. My main takeaway was the paradox that the
interesting arrangement of matter could be in its lowest energy state, yet
still moving. And that no energy could be extracted from this movement. I'm
probably butchering the concept with my misuse of terminology but whatevs.

~~~
lisper
You're not that far off. The particles aren't really _moving_ , i.e. they are
not going from one spatial location to another. What is happening is that they
are changing quantum spin states, and the spin states are changing in such a
way that it appears that a circular arrangement of atoms is rotating. This is
a reflection of the fact that an atom isn't really a _thing_ (there are no
"things", i.e. there are no particles) it's just a quantum state, so if you
have a quantum system A in state 1 and system B in state 2, and system A
transitions to state 2 and system B transitions to state 1 then this end
result is indistinguishable from the two systems having swapped locations. We
call this "moving" because classical motion is the only mechanism we're
familiar with in everyday life that allows two systems to swap locations. But
that kind of moving is not what is happening here.

~~~
ams6110
Sounds almost like how words appear to be moving across a scrolling led (or
previously, incandescent bulb) display, when nothing is moving it's just each
led/bulb switching from lit to unlit.

~~~
lisper
That is (almost) exactly right. The only difference is that with classical
states it is possible to distinguish between the object (the light bulb) and
the state (on or off). With quantum systems the object _is_ the state, so
there is no way to distinguish between "the same atom" and "different atoms
with the same state".

~~~
zer0gravity
So by saying this, you're actually saying that we're living in some sort of
state machine / cellular automata universe, and in order to understand it, we
just have to find the rules of interaction/propagation of the states ?

~~~
lisper
No, we are living in a quantum universe (or a quantum multiverse if you
prefer). We don't yet know whether space and time are discrete, because we
have not yet unified QM and relativity. If space and time turn out to be
discrete then yes, the multiverse would be essentially a cellular automaton.
But if they aren't then it (probably) isn't.

~~~
zer0gravity
But "quantum universe" doesn't actually mean that we're working with
quanta(s), which translates to infinitesimally small but discrete quantities ?

Aren't Planck constants all about that ?

~~~
speeder
He is referring to spacetime actually. quanta we are sure are the smallest
objects in space.

Spacetime is a sort of cartesian representation of space and time, with
probably 4 axes (x, y, z, time).

Many relativity concepts obey this, for example stuff moving in space at the
speed of light, move literally zero on the time axis. And you can calculate
the relationship between time and speed by rotating vectors.

So back to quanta: we don't know if time is discrete. We don't even know if
time actually exists, or its properties, because the math right now has
results that are quite weird (like implying moving backwards in time should be
normal and common as moving forward...), also there are arguments over the
shape of "spacetime" with most people assuming it is a 4d cube, but maybe it
ins't.

~~~
Senji
What's been on my mind about these things is, we don't need to have "space" to
be a "thing" that "exists". You can simulate a universe where "space" is
encoded in each "particle"'s state as a scalar distance to some other
particle.

Thus you don't have a "full dimensional vector {x,y,z}" but you have a bunch
of particles each keeping a list of variables with distances to other
particles around them.

Maybe I'm not explaining it right, but no one has proposed anything like this
as far as I know.

~~~
Jarwain
I get what you're trying to say, and it's an interesting viewpoint on the
matter. However, i still think of "space" as a useful abstraction in this case

~~~
Senji
Would it even be possible to devise an experiment to test for this? It doesn't
seem likely to me.

------
dysfunctor
I don't know anything about anything, but I want to enumerate some things I
learned reading this article, and if someone actually knows what they're
talking about and sees fit to take pity on me, please correct me so that I can
understand what this actually means.

So a time crystal appears to be made up of real matter. The article mentions
ions that are arranged in a certain particular way, cooled in order to reduce
their energy, and this still makes sense so far.

So, the idea is to create a closed loop of sorts from a temporal perspective.
I'm imagining an object as a set of states that the object can be observed in,
and if there was a loop, it'd be possible to observe a certain sequence of
states over and over.

The arrangement of the ions is important, and one of the properties is the
spin, which is possible to change with a laser beam, because obviously.

Anyways, I guess the frequency of the oscillation of the ions changing spin,
since they interact with each other in a domino fashion, can be controlled
with the frequency of the laser.

They did this, and observed the ions changing in such a way where there was no
driving influence and it's implied that the reason that this behavior was
observed is because time symmetry was broken, which is just a fancy way of
alleging that the universe is non-deterministic, I think.

Maybe this will eventually be useful?

~~~
contravariant
>They did this, and observed the ions changing in such a way where there was
no driving influence and it's implied that the reason that this behavior was
observed is because time symmetry was broken, which is just a fancy way of
alleging that the universe is non-deterministic, I think.

Time translational symmetry and determinism have nothing to do with one
another. Even a classical pendulum breaks time translational symmetry yet it's
fully deterministic. In this cases they do break the symmetry in a more
fundamental way, but it still doesn't say anything about determinism.

~~~
dysfunctor
So what are the implications of an object that breaks that symmetry? Would it
be possible to observe an object in different times in the same state, or the
same time in different states?

~~~
semiel
> So what are the implications of an object that breaks that symmetry? Would
> it be possible to observe an object in different times in the same state, or
> the same time in different states?

The object would be in a repeating set of states. First state 1, then state 2,
then state 1, then back to state 2, etc.

This is not in itself surprising. Think of a pendulum, for instance. The
difference here is that the motion is the lowest energy state. Over time, a
pendulum swing decays. This does not: it will continue forever, if not
disturbed.

The obvious next question is: isn't that perpetual motion? According to the
normal dictionary definition of those words yes it is, which is why this is a
fascinating discovery. However, it doesn't violate the normal arguments
against perpetual motion, because there's no way to extract energy from the
system. Anything you did to influence the motion would require adding energy.

~~~
ivoras
But... don't the process by which this is observed (I mean literally, the
machinery used to measure it) introduce energy into (or draw it out) this
system?

------
hprotagonist
And somewhere, high in the ramtops, Lu-Tze has just developed a crick in his
neck and he almost knows why.

------
panglott
What are time crystals? Try this: _Physicists Predict The Existence of Time
Crystals_ [https://www.technologyreview.com/s/426917/physicists-
predict...](https://www.technologyreview.com/s/426917/physicists-predict-the-
existence-of-time-crystals/)

~~~
brathouz
This is also helpful: _How to Build A Space-Time Crystal_
[https://www.technologyreview.com/s/428334/how-to-build-a-
spa...](https://www.technologyreview.com/s/428334/how-to-build-a-space-time-
crystal/)

~~~
_puk
Thanks for both those links.

That article is from 2012 and quotes:

"If that’s the case, we ought to be reading the details about the first space-
time crystal sometime in the days and weeks to come. "

Was there something non obvious they had to overcome that took the extra few
years to produce these space-time crystals?

(I use the term non obvious as if this was not all way beyond my ken!)

~~~
brathouz
The 2012 article said they were using beryllium ions, Wikipedia says in 2013
they were planning on using calcium ions, and now the 2016 article says they
used ytterbium ions. Without more content to go on, we can only guess about
these changes.

In any event, they sure seem to have made a lot of progress in just a few
years. I look forward to reading more about this, as well as listening to Neil
deGrasse Tyson describe it in his infectiously enthusiastic way.

------
jdc0589
I'm definitely too dumb for this.

~~~
nwrk
Joining you. Saw some potential concept here [1]

[1] Back to the future (1985)
[http://www.imdb.com/title/tt0088763/](http://www.imdb.com/title/tt0088763/)

------
code51
Can someone explain what computations using __zero energy__ from related
article [1] actually means ?

[1] [https://www.technologyreview.com/s/426917/physicists-
predict...](https://www.technologyreview.com/s/426917/physicists-predict-the-
existence-of-time-crystals/)

""" Another is the possibility that it may be possible to exploit time
crystals to perform computations using zero energy. As Wilczek puts it, “it is
interesting to speculate that a…quantum mechanical system whose states could
be interpreted as a collection of qubits, could be engineered to traverse a
programmed landscape of structured states in Hilbert space over time.” """

~~~
Strilanc
They literally mean "not spending any energy doing the computation".

We spend energy on computation for two fundamental reasons: 1) zeroing data
and 2) error correction. You avoid zeroing data by doing reversible
computation. You avoid error correction by finding really really well behaved
/ stable systems.

Time crystals are reversible basically by definition, and Wilczek is saying
that maybe there might be some time crystals that are also well behaved and do
something interesting enough to encode computations.

~~~
dangirsh
IIRC reversible computations only take zero energy if you perform them
infinitely slowly.

~~~
lgas
Just curious, is there a difference between infinitely slowly and not at all?

~~~
cyphar
"Infinitely slowly" is a theme in physics. What is actually meant by the term
is "slow enough that you can approximate it as being infinitely slow". Now,
obviously the idea of approximating an infinite value with a finite one seems
dodgy, but the idea is that if some process converges to the "purely
theoretical and infinitely slow" solution quickly then you can make that kind
of approximation (physics is generally not obsessed with precision).

As a concrete example, most of thermodynamics becomes insanely complicated for
very rapid changes in pressure and temperature. And in many cases, you cannot
actually compute the state of the system (without making a bunch of
approximations). But, if you make some assumptions and approximations,
thermodynamics becomes much more simple even though you've added some error
factors due to your approximations (but it's definitely "good enough").

In general, the first thing you learn as part of a physics degree is that
approximations and assumptions are just part of how you do science. Without
them, we'd all be stuck dealing with insanely complicated equations that
probably are not solvable. And at the end of the day, the unsolvable part of
whatever equation you're dealing with wouldn't actually have a significant
effect on the result (so you can generally ignore it).

------
devnill
This is a fascinating concept. What kinds of applications could time crystals
be used for?

Time locked crypto that doesn't rely on proof of work jumps to mind, but I'm
by no means an expert on either cryptography or quantum mechanics.

------
skykooler
Could this be used for very stable time measurements, as an alternative to
atomic clocks?

~~~
_puk
From @brathouz link above..

"One reason why space-time crystals are interesting is that their periodicity
in time makes them natural clocks. So there should be plenty of people with
more than a passing interesting in making one."

So I took from that, yes, this could be an alternative to atomic clocks.

------
formula1
Correct me if If Im wrong. A time crystal is a cycle at atomic level.

\- matter / energy is neither added nor removed to retain shape/movement

\- the energy/matter within the "crystal" change state/position in a repeating
and/or predictable matter

\- pattern retains even when the energy is at extreme lows

This would be analogous to a water cycle. The water changes state in a
predictable manner, water heats up (due to the sun) and evaporates. As the
molecules get closer to space, the cool and attract each other to form clouds.
The clouds hit a maximum and rain occurs flowing back into bodies of water
again.

The difference is that the water cycle needs the presence of heat/cooling from
external sources while the time crystal can exist at "zero degree"
temperatures.

------
blippityBlop
So, states change without physical objects changing position. Meanwhile we
pitiful humans, have a hard time distinguishing the objects that exchange
states.

...and can someone tell me where the _actual_ time comes into play?

Sure, one can say it is "something not unlike" the manipulation of time, and
yet... somehow... it seems like we're just deciding to call it something it is
not, since it certainly seems similar enough.

If I carve a piece of wood, such that it resembles a gun, it can play the part
of a gun, but only until a person with an actual gun challenges me to a duel.

------
klunger
>But the laws of physics are not only symmetrical in space but also in time.

Can someone explain what this means? It makes sense that physical laws are
symmetrical in space. But in time? I thought that would _not_ be the case
because of entropy/irreversible processes etc. What am I missing? The whole
article rests on this premise.

~~~
cyphar
"The arrow of time" which you're referring to (entropy increasing in closed
systems) is something that is IMO still puzzling in the field of physics. To
be clear, entropy isn't a "force" its just a statistical effect (a very large
number of particles in a system are always going to be more likely to be in a
macrostate that has the most microstates -- meaning that the system will tend
towards more "disordered" states).

However, it should be noted that the arrow of time only applies to the
_macroscopic_ universe. All of the laws of physics (in this article's case
it's quantum mechanics) are time symmetric (if you play the experiment in
reverse you couldn't tell it was being done in reverse -- which is what you
can see in Feynman diagrams). So at the heart of it, the universe is very
symmetric in time.

To quote Primer: "What's the one variable in all of the equations of heat and
matter? What's the one variable that you can turn negative and still get
rational answers? Its not energy, it's not mass..." [It's time].

------
pera
wow that was fast!
[https://news.ycombinator.com/item?id=12474029](https://news.ycombinator.com/item?id=12474029)
("Time crystals might exist after all")

------
M_Grey
This is very interesting, but I'm frankly not convinced that they've actually
created a spacetime crystal. Either way though, it's a fascinating bit of
work.

------
gravypod
Could this be used like a piezoelectric in a clock except powered by time
rather then a charge applied to a quartz crystal?

------
edem
Can you explain in layman's terms what a time crystal is? I'm not sure I
understood it right. Is this like a RAM which has persistent state?

------
obi1kenobi
Dupe:
[https://news.ycombinator.com/item?id=12646342](https://news.ycombinator.com/item?id=12646342)

------
yarou
Could this _really_ be used for self-correcting quantum memory, as the article
suggests?

------
dschiptsov
Oh. From which substance?

~~~
dschiptsov
Not that much has been changed since the times of Egyptian pyramids -
producing himeras and pure abstractions out of words and socially conditioned
mental constructs is still one of the most rewarding occupation.

------
ge96
Super jail

Time police

------
happyslobro
Ugh, that title though... WTH is a time crystal, and who decided to call it
that? I'm not clicking the bait to find out.

~~~
lscharen
The core idea is not too strange, actually.

A "normal" crystal has a repeating structure in space; a time crystal is a
construct with a repeating temporal structure.

~~~
radarsat1
Does that mean it is continuously changing in a repetitive fashion?

~~~
krapp
apparently yes, but because it's in a low energy state, it's impossible to
extract any energy from it and do work (otherwise it would be a perpetual
motion machine.)

~~~
rbanffy
It's interesting it is a perpetual motion machine, but it works only as long
as you don't use it.

~~~
jacquesm
Any atomic nucleus with orbiting electrons fulfills that requirement, you
could loosely call those time crystals too.

Their half life for most stable atoms is so long that perpetual applies for
most practical uses of the word.

Which makes me wonder if these time crystals have a half-life too.

~~~
cohomologo
Electrons do not orbit atomic nuclei in the quantum description of atoms.
Instead, in the lowest energy state the electron wave function is spread out
in a sphere around the nucleus, and this wave function stays constant in time.
Almost all quantum systems do something like this in the ground state, which
shows why the time crystal is something new and interesting.

------
m3kw9
What are they used for? A required part for a time machine??

------
slackstation
I hope you like time paradoxes because this is how you get trapped in a time
paradox.

------
nchallak
Ever since I saw my parents' initial skepticism to the use of handheld devices
(smartphones, tablets etc.) I have always wondered what such a mental block
for my generation might be like. It could very well be an invention such as
this that is considered speculative today which might become viable overnight.
My kid may someday wonder why his dad doesn't understand basic quantum
phenomena.

