TIME CRYSTALS
They change shape by themselves, have their own rhythm and should not exist at all. But now, scientists have created the bizarre time crystals, which may make future computers work at extreme speeds without using energy.
(Nothing To Do With Astrology)
Imagine a ball lying on the ground. Like all other objects, the ball has a number of physical properties, which describe its three- dimensional shape: It is completely round and has a certain diameter, which is decisive for its circumference – just like any other round object. Nevertheless, this ball is completely different, as its shape also depends on the fourth dimension: Time. Every ten seconds, the ball changes shape by itself and becomes eggshaped , and then, ten seconds later, it turns back into a ball. It is a 4D ball.
Until recently, any physicist would have denied the existence of such a ball, as this would break with some of the most fundamental scientific laws. But now, independently of each other, two teams of scientists have made particles in microscopic crystals turn and change patterns by themselves as time passes. The crystals are a completely new state of matter, which is neither fixed, nor liquid, gaseous or plasma, but dependent on time. Time crystals, as the scientists have named them, can be the key that computer engineers have been missing in order to make future quantum computers stable and, not least, extremely energy-saving.
SCIENTISTS INVENT PERPETUAL "MOTION" MACHINE
Originally, time crystals only existed as an idea in the head of Nobel Prize-winning physicist Frank Wilczek. His idea was based on ordinary 3D crystals like salt or ice.
At the level of the atom, crystals are interesting to physicists, because they break with spatial symmetry. Spatial symmetry can be found in a cup of liquid water, for example: Water molecules fill up the cup in a homogeneous pattern, which means that two samples taken from different places in the cup have the exact same molecular pattern. When the water in the cup freezes and turns into ice crystals, the molecules arrange themselves in a repeated pattern of fixed units, which are spatially asymmetrical. Thus, two random samples taken from the ice crystal will not have the same pattern.
The difference is similar to cutting swatches out of two carpets – one plain-- coloured and one patterned. No matter where the scissors cut in the plain-coloured one, the swatches will be similar in appearance, while two pieces from the patterned one will almost never be 100 % identical.
Frank Wilczek was studying these crystal structures in 2012, when he had an idea: What if there are substances, which are not only spatially asymmetrical like crystals, but also asymmetrical in time? This would mean that an object, where energy is neither added nor taken, might change its characteristic, just because time passes. In the example, the pattern in a piece of time-related asymmetrical carpet would not only depend on where the piece was cut, but also when it was cut.
The idea was received with fascination, but also indignation. Particles, which change by themselves over time, break with one of the basic principles of physics: All energy in the universe is constant. This means that energy will neither appear nor disappear, but only change from one state to another, e.g. from light to heat. If Wilczek’s time crystals changed shape without energy being added, they would have to create energy out of nothing. So the time crystals would be perpetual motion machines, which, according to the laws of physics, cannot exist.
TIME CRYSTALS MET WITH RESISTANCE
The idea was not left untested. In 2015, two scientists from University of California and The University of Tokyo appeared to definitively bring the impossible perpetual motion machines to their graves when, theoretically, they proved that, according to the laws of physics, time crystals cannot exist in a so-called thermal equilibrium.
When an object is in thermal equilibrium, it cannot give off or receive heat from its surroundings. In the world of physics, heat is a measure of the kinetic energy of particles. The scientists discovered that time crystals could only move if they were “pushed” by their surroundings. Thus, it was physically impossible for the time crystals to change shape without any help from the outside, which was the very basis for Wilczek’s idea.
But other physicists refused to give in. If the time crystals could not exist in thermal equilibrium, it may be possible to create them in a state of disequilibrium. In recent years, quantum physicists have studied a phenomenon called many-body localisation, which occurs when a group of atoms is not in thermal equilibrium. Atoms in this state are invisibly connected and can affect each other.
In a container filled with air, the atoms would normally fill up the bulk of the container evenly and move randomly among each other. However, by means of many-body localisation, the atoms can affect each other and cause them to gather on the one side of the container or move around in a special pattern.
FROM IMPOSSIBLE THEORY TO REALITY
The major breakthrough came in 2015 when researchers at Princeton University proved how, in theory, the “impossible” crystals could exist if they moved at fixed time intervals using many-body localisation. The crucial point in the scientists’ new idea was that the atoms would not move all by themselves, as this goes against the fundamental laws of physics. Neither would they move because they were affected from the outside. Instead, they would make each other move.
This loophole in the world of physics inspired scientists to go to their labs and test the theory in practice, and in early 2017, two teams from University of Maryland and Harvard University, used different approaches, but still managed to get the same end result.
In Maryland, scientists shot laser pulses at a chain of ions of the substance ytterbium. The laser pulses pushed at the ions and made them change the direction of their magnet fields upside down and back again in sync. Quite remarkably, the frequency in the change of the ions’ magnet fields remained unchanged, even though the frequency of the laser pulses changed. The chain of ytterbium ions had its own rhythm, which could be considered one of its fundamental characteristics, like its mass or electric charge. At Harvard, scientists used microwave pulses to push at small particles inside a diamond. The particles turned around at precise intervals – just like in the Maryland test.
QUANTUM COMPUTERS GET SUPERPOWERS
The new phenomenon, which has now been proved in the laboratory, has aroused excitement in the world of physics. The time crystals are the first evidence that matter is capable of organising itself in a time dimension. The crystals may be seen as the clockwork of the universe, which only needs a push to get going and which will then move in a set rhythm of its own – forever.
One area, which may benefit from these clockworks, is quantum computers, which computer engineers are still struggling to make fit for use. In quantum computers, quantum bits will replace the transistors in ordinary computers. The transistors are small, physical switches, which are either on or off and used by the computer software to represent 1s and 0s. The regular changes of the time crystal magnet fields can assume that function, but without using energy like transistors. Also, they will be far smaller, so more computing power can be gathered in less space. At the same time, the ability of time crystals to maintain the rhythm in spite of outside influences from e.g. laser pulses is also good for their use as quantum bits. So far, it has been a problem to find particles that can be used as quantum bits, which were not too fragile to use in practice.
The experiments with time crystals may mark the beginning of a completely new field within physics, says one of the scientists behind the Maryland experiment. Although the crystals in the experiments only existed briefly and in very small sizes, the basic concept has been proved. And just like salt crystals are naturally found in relatively large pieces, like the ones we use in cooking, Monroe thinks that time crystals may be naturally occurring. In other words, the Universe may be full of four-dimensional crystals that no one thought could exist.