WEIRD PHYSICS
High strangness from the quantum realm: invisibility, but not as we know it, nanoscale warp drive craft and entangled tardigrades
INVISIBILITY (SORT OF) While it won’t be possible to use this discovery to make yourself vanish any time soon, researchers at the Massachusetts Institute of Technology (MIT) have managed to demonstrate a quantum effect that can make matter invisible – but only a very specific kind under very specific conditions. Long known to be theoretically possible, the process, known as Pauli blocking, has never been experimentally created in the lab before. It relies on a fundamental feature of the quantum world, the Pauli exclusion principle – that within an atom two subatomic particles cannot coexist in the same energy level. Once one particle occupies a level, it excludes any others, meaning that every atom has a finite number of energy states that its subatomic particles can have. It is this that gives us the different properties of the chemical elements, and indeed it is what makes matter solid and able to interact with other matter.
Normally, when a photon, a particle of light, hits an atom, it bounces off one of the subatomic particles in that atom, pushing the particle up to a higher energy state. This deflects the photon, which, if it then reaches our eyes, enables us to see the object of which the atom is part. What researchers have done is to take lithium gas and use lasers to both squeeze it and cool it, making it very dense and taking it to within a tiny fraction of a degree of absolute zero (-273.15 °C/-459.67 °F). At this temperature, the subatomic particles lose energy and take on a highly specialised form known as a Fermi sea where they are packed together at the lowest energy, unable to move up or down in energy states because other particles already occupy them; this is Pauli blocking. In this state, the subatomic particles are so packed they cannot interact with light, so photons pass through the gas as if it was not there, making it invisible. While this isn’t going to lead to invisibility cloaks, it may be useful in quantum computers, which are sensitive to disruption from light interacting with their quantum components. livescience. com, 19 Nov 2021.
QUANTUM TARDIGRADE
One of the weirder aspects of the quantum world is “entanglement”, a phenomenon in which two subatomic particles, such as photons, become bound to each other so that a change to the properties of one particle instantaneously causes the same change in the other, no matter how far apart they are, even if they are separated by the width of the Universe. This “spooky action at a distance” disturbed Einstein, as relativity makes it impossible for anything at larger scales to travel faster than light, but whatever leads to this entanglement clearly has the effect of doing so at subatomic levels, and while multiple experiments have confirmed the reality of entanglement over the last century, how it works remains mysterious. Despite this, researchers seeking to define the boundary where quantum effects no longer work and classical physics takes over have been attempting to entangle larger and larger objects, managing to do so with things up to the size of living bacteria. Now they claim to have entangled a multicellular organism: a tardigrade. Notoriously indestructible, these tiny creatures – between 0.008 and 0.018in (0.2 to 0.45mm) long – can survive both extremely high and very low temperatures, having walked away unscathed after being shot from guns, boiled, exposed to intense ultraviolet radiation, and even crashed onto the Moon (see FT385:9, 395:19, 410:21). They do this by turning into tough, dehydrated barrel-shaped structures known as “tuns”, suspending all their biological functions. Now, an international consortium of physicists say they have successfully put a tardigrade tun into temporary quantum entanglement. They did this by freezing the creature to within a fraction of a degree of absolute zero, then putting it into a circuit where it formed what is called a “qubit”, a unit of information used in quantum computing. They then entangled that with two other qubits and were able to get all three to change frequency together, indicating that quantum entanglement of the tardigrade had indeed occurred. After the experiment, they warmed up the three tardigrades and found that while two had died, one reanimated successfully, saying, “the tardigrade survived the most extreme and prolonged conditions it has ever been exposed to,” making it the first quantum entangled animal in history. livescience.com, 21 Dec 2021.
ACCIDENTAL WARP DRIVE
For a long time, warp drives that would allow spacecraft to travel at speeds faster than light by warping the fabric of the Universe seemed to belong firmly in the realm of science fiction, but in 1994 mathematician Miguel Alcubierre came up with a mathematically valid solution to creating such a drive without violating the laws of physics.
While this worked in theory, it was dismissed as impractical due to its need for exotic materials and vast amounts of energy that would make the whole thing impossible to engineer. Early this century, though, NASA warp drive specialist Harold G White reworked the maths and found a solution, coming up with a theoretical design known as the “Alcubierre/White Warp Drive”. This would create a bubble of warped space around an object that could then move across the Universe at incredible speeds as the light speed limit only applies to things moving within the Universe, not the structure of the Universe itself. Now, White reports that his Limitless Space Institute has accidentally created one of these bubbles, saying: “To be clear, our finding is not a warp bubble analogue, it is a real, albeit humble and tiny, warp bubble.”
When the team made their discovery they were carrying out research on Casimir cavities, micro-scale structure subject to quantum effects that have all kinds of promising applications, but which, until now, were thought to have nothing to do with warp bubbles. It was pure coincidence that when the phenomenon manifested, White was on hand to recognise it for what it was. He says that the finding confirmed the theoretically described shape of a warp bubble and its negative energy features, and suggests paths that might, one day, result in a warp drive craft. While his team is not funded to do warp drive research and this was simply a serendipitous discovery, they have come up with a proposed design for a testable nanoscale “warp drive craft” that other researchers could investigate. They also outlined an experiment that would involve stringing several Casimir-created warp bubbles together in a chain-like configuration that would allow researchers to better understand the physics of the warp bubble structure. thedebrief. org, 6 Dec 2021.