FQXi/Springer
Our latest podcast has been posted and we're catching up with a couple of old friends of FQXi to talk about their recent work, and making a couple of new ones.
First up we have quantum physicist Martin Ringbauer, of the University of Queensland, discussing tests investigating whether the quantum wavefunction is real. You may remember that Martin took part in one of our most popular podcast pieces last year, when he chatted to us about simulating time travel in the lab with photons. Now, he and his colleague Alessandro Fedrizzi, also from Queensland, and others have carried out tests to try to uncover whether the mathematical term used to calculate the evolution of quantum systems, the wavefunction, simply represents our lack of knowledge of the true state of reality (an idea favoured by Einstein) or whether it directly corresponds to reality itself. In other words, is Schrödinger's cat really alive and dead at the same time, or is it actually in some set state, and we just don't have the tools to measure it?
The question was discussed in depth on the site a few years ago, when FQXi's Jonathon Barrett and his colleagues Matthew Pusey and Terry Rudolph came up with a no-go theorem that appeared to favour the interpretation that the wavefunction is real. Physicist Oscar Dahlsten wrote a nice summary of that whole debate and of PBR's claims, for us at the time. Now Ringbauer, Fedrizzi and their colleagues are tackling the same question from a different angle, performing experiments with polarised photons to try and close in on an answer. In some cases, different polarisations are indistinguishable by single measurements in the lab, and the team have calculated whether the measured level of ambiguity can be explained by the more intuitive classical-style models favoured by Einstein (Psi-Epistemic models) or not. Their results point to the "not" side, indicating that the wavefunction is real. On the podcast they talk about what exactly their tests have shown so far, which quantum interpretations they have ruled out, and which remain.
Next, we visit another long-running debate, this time based on black hole firewalls. Last year, at the FQXi conference in Vieques, we held a panel discussion, featuring Anthony Aguirre, Raphael Bousso, Andrew Hamilton, Seth Lloyd and David Lowe about what actually happens in and near a black hole:
[youtube: 3H6C_45LuXg, 560, 340]
That debate was inspired by the so-called AMPS paper (by Almeiri, Marolf, Polchinski and Sully) that predicted that if certain quantum laws hold, and information is not lost from the universe when black holes evaporate, then the black hole event horizon must be replaced by a ring of fire. If true, this would contradict one of the founding principles of general relativity, which requires that the event horizon displays "no drama".
Physicists have been analysing the theory to try to come up with a resolution and to answer to whether firewalls really exist or not. Now cosmologists Niayesh Afshordi and Yasaman Yazdi have found a new way to think about the issue. They have been looking for possible observational signatures of firewalls, and have come up with the idea that neutrinos may be generated as matter falls through a firewall. It may be even be possible that highly-energetic neutrinos that have been picked up by the Ice Cube Detector at the South Pole are due to firewalls. (Although, of course, they also might also be explained by other sources too, as Afshordi explains in the podcast. However, as of yet, the most conventional explanations don't fit that well with the data.)
FQXi/Springer
Afshordi is fond of off-the-wall ideas, as you may remember from another extremely popular interview we ran a couple of years ago, about whether our universe was created by the collapse of a 5D star (see "Bye Bye Big Bang?". On the podcast, Afshordi talks us through how the firewall paradox arose and his ideas for observing them. FQXi member Sabine Hossenfelder has also blogged in some detailed about the paper over on Backreaction.)
In our last item, reporter Carinne Piekema talks to quantum physicist Jacob Biamonte about the new discipline of quantum network theory, and how it could explain the emergence of classical reality and the origin of time's arrow. You can read about his work in an article by Carinne too.
Finally, a quick plug: Our second FQXi essay compilation volume (above, right), in collaboration with Springer, is now on sale too: "It from Bit, or Bit from It?" As with our first volume, "Questioning the Foundations of Physics: Which Of Our Fundamental Assumptions Is Wrong?", the collection brings together revised essays from our contest winners (right). These modified essays have been beefed up to include a but more technical detail and also to take into account feedback from those of you that commented on the essays on the site.
And, off course, our current contest, "Trick or Truth?," about the mysterious link between physics and maths, is still open for comments and votes.