The Quantum Though Experiment

Quantum mystery In 1961 Eugene Wigner imagined a friend doing an experiment in a lab while he waits outside. The paradox is that Wigner and the friend predict different outcomes, yet both are right. (iStock/Floriana)








“Wigner’s friend” is a curious thought experiment that has stumped physicists and philosophers for more than 60 years. Robert P Crease, Jennifer Carter and Gino Elia advise on how to resolve this conundrum.

The quantum world provides fertile material for thought experiments that seem so strange-but-true as to defy logic. One of the most notorious is “Wigner’s friend”, which has challenged physicists and philosophers ever since it was first conceived by the Hungarian-American physicist Eugene Wigner. He published the thought experiment in a 1961 book edited by the mathematician Irving Good entitled The Scientist Speculates: an Anthology of Partly-baked Ideas.

Wigner’s thought experiment is a more humane version of Schrödinger’s less complex but more famous thought experiment a quarter century before, which involved a cat inside a box whose fate hangs on a quantum event. Inside the box Schrödinger’s cat is dead or alive, whereas for someone outside, the cat remains dead-and-alive; it’s in a “superposition”. The bizarre situation only vanishes when the box lid opens.     READ MORE...

High Energy Scattering Data

Messenger from the dark side: Dark matter may interact with normal matter via a hypothetical particle known as a dark photon. (Courtesy: Shutterstock/80's Child)



A new analysis conducted by an international team of physicists suggests that dark photons – hypothetical particles that carry forces associated with dark matter – could explain certain data from high-energy scattering experiments. The analysis, which was led by,  Nicholas Hunt-Smith and colleagues at the University of Adelaide, Australia, could lead to new insights into the nature of dark matter, which remains a mystery even though standard models of cosmology suggest it makes up around 85% of the universe’s mass.

Dark matter gets its name because it does not absorb, reflect or emit electromagnetic radiation. This makes it extremely difficult to detect in the laboratory, and so far all attempts at doing so have come up empty-handed. “No particle beyond the Standard Model, which describes all the matter with which we are familiar, has ever been seen,” says Anthony Thomas, a physicist at Adelaide and a co-author of the analysis, which is published in the Journal of High Energy Physics. “We have no idea what dark matter is, although it seems likely to be [a] beyond standard model particle (or particles).”
The dark photon hypothesis

Though dark matter is poorly understood, it is nevertheless the leading explanation for why galaxies rotate faster than they should, given the amount of visible matter they contain. But although we can observe dark matter interacting with the universe, the mechanism for these interactions is unclear. According to Carlos Wagner, a particle physicist in the High Energy Physics (HEP) division of Argonne National Laboratory and a professor at the University of Chicago and the Enrico Fermi Institute, dark photons are one possibility.   READ MORE...

Tardigrades and Quantum Entanglement

Quantum life: an electron microscope image of a tardigrade. (Courtesy: Elham Schokraie et al/PloS ONE 7(9): e45682/CC BY 2.5)

Tardigrades are tiny organisms that can survive extreme environments including being chilled to near absolute zero. At these temperatures quantum effects such as entanglement become dominant, so perhaps it is not surprising that a team of physicists has used a chilled tardigrade to create an entangled qubit.

According to a preprint on the arXiv server, the team cooled a tardigrade to below 10 mK and then used it as the dielectric in a capacitor that itself was part of a superconducting transmon qubit. The team says that it then entangled the qubit – tardigrade and all – with another superconducting qubit. The team then warmed up the tardigrade and brought it back to life.

To me, the big question is whether the tardigrade was alive when it was entangled. My curiosity harks back to the now outdated idea that living organisms are “too warm and wet” to partake in quantum processes. Today, scientists believe that some biological processes such as magnetic navigation and perhaps even photosynthesis rely on quantum effects such as entanglement. So perhaps it is possible that the creature was alive and entangled at the same time.

In the preprint, the researchers say that the entangled tardigrade was in a latent state of life called cryptobiosis. They say they have shown that it is “possible to do a quantum and hence a chemical study of a system, without destroying its ability to function biologically”.  READ MORE...