Another Sunday is upon us again and it’s time to take a look at the top physics news of the week. As always, if you enjoy these articles, register for our email newsletter here. Also, more news can be found here.
Einstein’s equivalence principle states that an object in gravitational free fall is physically equivalent to an object that is accelerating with the same amount of force in the absence of gravity. This principle, which is at the hearth of general relativity, has been tested countless times by increasingly accurate experiments. Now a new paper demonstrates a unique way of testing the equivalence principle.
“Testing the equivalence principle, or the equivalence of inertial mass and gravitational mass, means testing the validity of one of the fundamental principles of general relativity,” co-author Guglielmo Tino, Professor at the University of Florence, INFN, told Phys.org. “In our experiment, we use a quantum sensor to investigate gravitational interaction; this allowed us to search for new effects.” In the new study, the researchers have for the first time tested the equivalence principle by comparing the gravitational interaction for a bosonic particle to that of a fermionic particle. This new method shed light on the role of spin in gravitational interactions. For detailed results of the study see the link in the title.
2. Is the Universe a Bubble? (July 17)
The exotic idea of the multiverse is often considered hardly scientific, since it is so difficult to test. The work by Matthew Johnson and his colleagues at the Perimeter Institute, however, might eventually bring the idea to the realm of scientifically testable hypotheses.
“That’s what this research program is all about,” he says. “We’re trying to find out what the testable predictions of this picture would be, and then going out and looking for them.”
Specifically, Johnson has been considering the rare cases in which our bubble universe might collide with another bubble universe. He lays out the steps: “We simulate the whole universe. We start with a multiverse that has two bubbles in it, we collide the bubbles on a computer to figure out what happens, and then we stick a virtual observer in various places and ask what that observer would see from there.”
3. New Material Puts a Twist in Light (July 18)
Scientists at the Australian National University have uncovered the secret to twisting light at will. It is the latest step in the development of photonics, the faster, more compact and less carbon-hungry successor to electronics. A random find in the washing basket led the team to create the latest in a new breed of materials known as metamaterials. These artificial materials show extraordinary properties quite unlike natural materials.
“Our material can put a twist into light — that is, rotate its polarisation — orders of magnitude more strongly than natural materials,” said lead author Mingkai Liu, a PhD student at the ANU Research School of Physics and Engineering (RSPE).
“It’s another completely new tool in the toolbox for processing light,” also said the co-author Dr David Powell. “Thin slices of these materials can replace bulky collections of lenses and mirrors. This miniaturisation could lead to the creation of more compact opto-electronic devices, such as a light-based version of the electronic transistor.”