Time crystals what?

[Starstruck69]

Link: https://www.sciencealert.com/it-s-official-time-crystals-are-a-new-crazy-state-of-matter-and-now-we-can-create-them

Ok don't hate me for posting this it is a difficult one to comprehend. As usual quantum physics throws a spanner in the works.

I hope somebody out there can shed light on my confusion.

Lots of physicists getting excited about this and upon reading it my initial thoughts were 'this is very weird'. But after reading the paper i am now more confused than ever. 

It states and i quote 'a bizarre state of matter with an atomic structure that repeats not just in space, but in time, allowing them to maintain constant oscillation without energy.'

but later states that 'The key to turning that set-up into a time crystal was to keep the ions out of equilibrium, and to do that the researchers alternately hit them with two lasers. One laser created a magnetic field and the second laser partially flipped the spins of the atoms.'

Is the change not due to the imput of energy into the system via the use of lasers (heat) or am i missing something? If so why is this groundbreaking?

 

Research paper: https://www.nature.com/articles/nature21426.epdf?referrer_access_token=9crfkP48nZizQPG-CR8FCtRgN0jAjWel9jnR3ZoTv0P5YskvuciglCkbvCoxSf55bH4nW2RFSTh6o6hRlsTTH3AVZUVzzI_DzfdV2IuC5jIYczBOTbUQfO5kvuTi2pSyJ0SxhdA5kGHGch9cX66V6_oRy2rxb1neAP_tkMFk8fafJgx45QGfE799TszB6FmAPe6ltzan0UUWcnA5kkEpPv0SdEzgGHUumsTouxUrws-XJdj3mo5-8dIcAmY0DiZUzQHX5dzoduq05QBmvBlHsdRaz_koTIZaBssvMlp8InFI0PPLT7p9xk9uhVe_lzcYs5h8MoK3fKlZ2m1SOtaGqsmxFCRPUA1wyyWy6Eh1YEDWhaO1N-7BhRjMzzAY625V&tracking_referrer=gizmodo.com

 

[Rakaydos]

16 minutes ago, Starstruck69 said:

 

Is the change not due to the imput of energy into the system via the use of lasers (heat) or am i missing something? If so why is this groundbreaking?

Boise einstine condensates (super cold matter) are also often cooled by using lasers to destructively interfere with their thermal vibration.

Once a time crystal is... well, crystalized, it is an actual perpetural motion machine that breaks the moment you try to make it do anything useful.

[Starstruck69]

Perpetual motion defies the laws of physics, specifically thermodynamics? The quantum world it seems defies many things. This is where my confusion lies because it states ' But certain objects can break this symmetry in their ground state without violating the laws of physics.' If it is perpetual then it clearly does violate them. Doesn't it?

I'm going to bury my head in the sand

[RealKerbal3x]

3 minutes ago, Starstruck69 said:

I'm going to bury my head in the sand

I've never made any attempt to understand quantum mechanics. The only thing I know is that adding 'quantum' to the start of a name makes it sound more dramatic and sciencey

[Rakaydos]

9 minutes ago, Starstruck69 said:

Perpetual motion defies the laws of physics, specifically thermodynamics? The quantum world it seems defies many things. This is where my confusion lies because it states ' But certain objects can break this symmetry in their ground state without violating the laws of physics.' If it is perpetual then it clearly does violate them. Doesn't it?

I'm going to bury my head in the sand

Perpetural motion only violates thermodynamics if you can get work out of it, because thermodynamics  refers to energetic states, not actual motion. Time crystals are actually less energetic in their specific time-crystal motion, than they are stationary

[Starstruck69]

19 minutes ago, Rakaydos said:

Perpetural motion only violates thermodynamics if you can get work out of it,

Ahh ok that makes sense

20 minutes ago, Rakaydos said:

Time crystals are actually less energetic in their specific time-crystal motion, than they are stationary

I am struggling with this one though. Motion costs energy does it not?

[cubinator]

8 minutes ago, Starstruck69 said:

I am struggling with this one though. Motion costs energy does it not?

Nope. For example, a pendulum will keep swinging until friction or air resistance brings it to a stop, and the planets drift very fast through the universe without losing energy for it. Seems these crystals are sort of like a pendulum - it takes energy to get it oscillating, but once it's there you can just let it go, as long as it doesn't get disturbed.

[sevenperforce]

15 minutes ago, Starstruck69 said:

Motion costs energy does it not?

Actually, motion is the case for all quantized systems. The lowest possible energy state is not rest, but an oscillating "ground state". The simplest possible quantum system (and the first one you learn to evaluate in QM or MP) is the infinite square well, in which a particle is trapped within an infinitely deep potential well with no energy gradients. If such a particle loses all the energy it can, it will still retain a "zero point" or "ground state" energy which is nonzero; in essence it is "bouncing" back and forth between the walls of its energy well, forever.

The "time crystal" is much more complex than a particle in an infinite square well, but it too has a collective ground state. The individual particles would have their own individual ground states if they were not in a crystal form, but the ion disequilibrium in the time crystal means that the overall system has more energy in its minimum ground state than the sum of the energies of the ground states of its particles. As a result, the "extra" energy of the system's ground state ends up being transferred back and forth between the particles, forever, and there is no way to extract any of that energy, so it will continue ad infinitum.

Of course it is not an overunity system. There is no energy being produced. It's just a system in which there is lossless oscillation between states.

[Starstruck69]

12 minutes ago, cubinator said:

Nope. For example, a pendulum will keep swinging until friction or air resistance brings it to a stop, and the planets drift very fast through the universe without losing energy for it. Seems these crystals are sort of like a pendulum - it takes energy to get it oscillating, but once it's there you can just let it go, as long as it doesn't get disturbed.

Got it

 

50 minutes ago, Rakaydos said:

Perpetural motion only violates thermodynamics if you can get work out of it, because thermodynamics  refers to energetic states, not actual motion. Time crystals are actually less energetic in their specific time-crystal motion, than they are stationary

 thankyou both Rakaydos and cubinator for taking the time to explain. I can remove my head from the sand now

[Bill Phil]

Perpetual motion may have been a poor choice of words. Perhaps perpetual engine would have been better?

Newton’s First Law implies “perpetual motion” unless outside forces act on an object. 

The problem is that perpetual has a few meanings.

[sevenperforce]

A little more detail on QM and ground states...

Consider a ball bouncing back and forth between the walls of a well. Left to right, right to left, left to right, ad infinitum. Although there is energy (the "zero-point energy" of the system) in the system, the system does not change states with respect to time.

Now, let's imagine that instead of a single particle, we have two identical particles that are coupled together:

Now, because these two subsystems are coupled; energy can be transferred between the two particles if they happen to bounce against the central "bar". In certain configurations, there could be additional energy in this system, so that even though one of the particles is above its individual ground state, the overall system is in a ground state. The energy would be transferred back and forth in a reliable, predictable way. Even though the entire system is in its ground state, we now have a system that is changing with respect to time.

The reason this is interesting is that time is defined rigorously in reference to entropy. The only way to say that a system is moving forward in time is to show that a system is moving from a state of low entropy to higher entropy. This is a system which seems to be changing with respect to time -- energy is moving around -- and yet there is no increase in entropy. Thus, the system can be seen as moving forward or backward in time.

[Starstruck69]

Great explanation Sevenperforce. Thanks for that. 

Just quickly squeezing the math through my tiny brain and its making sense thanks to you guys. The maths generally makes more sense to me but a good explanation is equally valuable. If n=1 (ground state) the rest falls into place.

I pulled the formulae from a quick unsourced google search if it is wrong please let me know..

 

 = energy of particle

[sevenperforce]

2 minutes ago, Starstruck69 said:

Just quickly squeezing the math through my tiny brain and its making sense thanks to you guys. The maths generally makes more sense to me but a good explanation is equally valuable. If n=1 (ground state) the rest falls into place.

I pulled the formulae from a quick unsourced google search if it is wrong please let me know..

 = energy of particle

Yep, that's the equation for the energy of a particle in an infinite square well. The energy can only change as the square of multiples of the lowest energy state. 

[Starstruck69]

3 hours ago, Bill Phil said:

Perpetual motion may have been a poor choice of words. Perhaps perpetual engine would have been better?

Newton’s First Law implies “perpetual motion” unless outside forces act on an object. 

The problem is that perpetual has a few meanings.

Yes it can get confusing, i think the problem here is my understanding of QM, or lack off. I am back on track now though thanks all for the input folks very helpful

 

Edited April 9, 2019 by Starstruck69