Scientists Discover New State of Matter Called “Time Crystals”
A new state of matter called a time crystal has been created in the lab using two different methods by two different teams of scientists.
In regular crystalsâ€”an ice cube or a diamond, for instanceâ€”atoms are arranged in a repeating spatial pattern. In time crystals, patterns repeat in time instead of in space.
Two different teams of scientists reported the discovery in the journal Nature on Wednesday. They are the first to directly create and observe time crystals, the long-theorized quantum systems that spin at their own pace independent of their environment, seemingly breaking the rules of normal timekeeping.
This discovery could pave the way for quantum computers and quantum sensors.
To build a useful quantum computer, scientists have to increase the number of qubits, or quantum bits, a machine has. But as qubits increase, the probability qubits will lose coherence goes up. Coherence is a prerequisite for functioning quantum computers. For time crystals, that coherence â€ślasts for a very long time and the density of quantum bits is very big,â€ť said Mikhail Lukin, a Harvard University quantum physicist who led one of the studies. The time crystals in both experiments lasted on the order of milliseconds before â€śmelting,â€ť much longer than expected for quantum systems with imperfections, he said.
A time crystal can never be in equilibrium with its environment. While normal crystals only crystallize in 3 dimensions, time crystals crystallize in 4 dimensions, meaning they are always in perpetual motion. Let’s learn a little more about that.
Perpetual motion is motion of bodies that continues indefinitely. This is impossible because of friction and other energy-dissipating processes. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics.
One classification of perpetual motion machines refers to the particular law of thermodynamics the machines purport to violate:
A perpetual motion machine of the first kind produces work without the input of energy. It thus violates the first law of thermodynamics: the law of conservation of energy.
A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. When the thermal energy is equivalent to the work done, this does not violate the law of conservation of energy. However, it does violate the more subtle second law of thermodynamics (see also entropy). The signature of a perpetual motion machine of the second kind is that there is only one heat reservoir involved, which is being spontaneously cooled without involving a transfer of heat to a cooler reservoir. This conversion of heat into useful work, without any side effect, is impossible, according to the second law of thermodynamics.
A perpetual motion machine of the third kind is usually (but not always) defined as one that completely eliminates friction and other dissipative forces, to maintain motion forever (due to its mass inertia). (Third in this case refers solely to the position in the above classification scheme, not the third law of thermodynamics.) It is impossible to make such a machine, as dissipation can never be completely eliminated in a mechanical system, no matter how close a system gets to this ideal (see examples in the Low Friction section).
So I wonder which kind of perpetual motion machine time crystals are?
Once set in motion, a time crystal could remain in motion forever, with no outside force needed to keep it going. This type of perpetual motion machine would not violate any known physical law because no energy could be extracted from the system without first adding energy. Such systems might even be arranged to convey information that would persist after everything else around them has died.
Instead of using energy to fuel its movement, a time crystal uses a break in the symmetry of time to fuel its movement. While a time crystal is always moving, its energy is zero.
Here is more detail on exactly what a time crystal is.
Wilczek says he started wondering whether the concept of an ordinary three-dimensional crystal could be extended to four dimensions, with the extra dimension that of time. A time crystal would spontaneously break what Wilczek calls “the mother of all symmetries”â€”the symmetry of time translation, which holds physical laws remains the same regardless of what time it is. A time crystal would change with time but keep coming back to the same form it began with, like a clock whose moving hands periodically return to their original positions.
The difference from an ordinary clock or other periodic process is that a time crystal, as with a spatial crystal, would be a state of minimum possible energy. At first glance, that poses a contradiction. A time crystal by definition must change with time in order to break time translation symmetry. But a system with minimum energy ordinarily can’t move. If it could, then additional energy could still be extracted, until the system achieved a true minimum energy, a motionless state.
So what is all this talk about breaking symmetry?
When matter crystallizes, its atoms spontaneously organize themselves into the rows, columns and stacks of a three-dimensional lattice. An atom occupies each â€ślattice point,â€ť but the balance of forces between the atoms prevents them from inhabiting the space between. Because the atoms suddenly have a discrete, rather than continuous, set of choices for where to exist, crystals are said to break the spatial symmetry of nature â€” the usual rule that all places in space are equivalent. But what about the temporal symmetry of nature â€” the rule that stable objects stay the same throughout time?
They might give insights into the theory of time, but how?
In Albert Einsteinâ€™s theory of general relativity (the body of laws governing gravity and the large-scale structure of the universe), the dimensions of time and space are woven together into the same fabric, known as space-time. But in quantum mechanics (the laws governing interactions on the subatomic scale), the time dimension is represented in a different way than the three dimensions of space â€” â€śa disturbing, aesthetically unpleasant asymmetry,â€ť Zakrzewski said.
If time crystals are able to break time symmetry in the same way that conventional crystals break space symmetry, â€śit tells you that in nature those two quantities seem to have similar properties, and that ultimately should reflect itself in a theory,â€ť HĂ¤ffner said. This would suggest that quantum mechanics is inadequate, and that a better quantum theory might treat time and space as two threads of the same fabric.
It is definitely a bit hard for me to grasp, but seems worth looking into more.