FQxI Physics

Exploring the foundations of physics & cosmology with Zeeya Merali & Gabe Fitzpatrick, of the Foundational Questions Institute, FQxI.

[FQxI Physics @FQXi]

In the first of a series of short documentaries from FQxI, Professor Natalia Ares shows us her research at Oxford University that uses carbon nanotube machines to investigate how we can use information as a fuel.⁠ @NAresgroup @geoffreylondon
⁠
https://t.co/EtHFBWR0Oj
⁠
#FQxI

[FQxI Physics @FQXi]

In quantum mechanics, a system can be in two states at once, until someone looks. But what happens if there’s another “someone” — an observer inside the system. The outer and inner observers will have contradictory views of the situation.

To quantify this situation, Howard Wiseman at @Griffith_Uni and Eric Cavalcanti with @NASAAmes’s Eleanor Rieffel set out a “thoughtful Local Friendliness” test in @quantumjournal in 2023.

They suggested that the inner observer could even be an AI. In their framing, an observer must have thoughts, so a real experiment would need human-level AI and fast, large quantum computers.

Veronika Baumann and Časlav Brukner at @iqoqivienna clarified the constraints: if the AI stores or shares a classical record, or becomes aware that its memory changed during the procedure, the effect vanishes.

On hardware, @wjzeng, @farrokhlabib and @captainhamptons encoded a simplified version of the scenario as quantum circuits and saw larger Local Friendliness violations as the branch factor increased, up to 16.

"Schrödinger’s A.I. Could Test the Foundations of Reality" — By @gmusser: https://t.co/6j2EGLr3cu

[FQxI Physics @FQXi]

[IMAGE THREAD]
Are we being too cheeky saying nothing is real until it is observed? Let us know.

[Michael Merrifield @AstroMikeMerri]

A damning critique of the University of Nottingham’s plans to make staff in physics redundant, from both a Nobel Laureate and a former university president… who happen to be the same person.

(https://t.co/hdCkkxUjn8)

[Sabine Hossenfelder @skdh]

A group of physicists have calculated that quantum mechanics allows sending messages into the past. I've had a look at the paper.

[FQxI Physics @FQXi]

Decades of @BBC science docs, and now a channel of his own. Go subscribe: https://t.co/sY6GBjvH6G
@jimalkhalili

[The Quantum Insider @QuantumDaily]

Most physics asks how things happen. Constructor Theory asks what's possible at all and why.

Anders Indset spoke with Oxford physicist Chiara Marletto about the framework she's building with David Deutsch, plus time, consciousness, AI, and why science funding is broken.

🎧 Watch here: https://t.co/9rUgyxb5k4

#Physics #ConstructorTheory #QuantumEconomy

[Sabine Hossenfelder @skdh]

Physicist Successfully Demonstrates the Origin of Time

Giovanni Barontini from the University of Birmingham, UK, has used a cloud of cold atoms to test the origin of time. This is an interesting contribution to the long-standing question of how to define time in a non-circular way (time is what a clock measures and a clock is what measures time). One of the proposed solutions is to define time in quantum physics from the interaction of two different subsystems. This interaction, so the idea, introduces an oscillation that serves as the ‘tick’ of the clock. If that was so, then time would be purely ‘relational’ — an emergent, derived quantity — rather than (as in Einstein’s theory), a fundamental property of the universe.

Barontini used about 24,000 ultracold rubidium atoms in a trap split by a thin light barrier into an observed “bright” part and an unobserved “dark” part. Atoms could move between the two, so the bright part expanded and collapsed in repeated cycles, rather like a toy version of a big bang and big crunch. Barontini then defined an internal “entropic time” from how the entropy of the bright part changed as atoms moved in and out. This internal time ordered the observed events almost as well as laboratory time.

This experiment lends support to the idea that time is not fundamental, but emerges from interactions between parts of a closed system, though one may ask how interactions can change a system if there is not already a time for them to change in, but then maybe that’s just Sabine being grumpy again.

Image: The device, called a ‘trap’, that holds the cloud of cold atoms in place using a combination of lasers and magnetic fields. Credits: Giovanni Barontini/University of Birmingham

[Sabine Hossenfelder @skdh]

Physicists from Austria and Germany have found a major clue to what makes “strange metals” so strange.

Strange metals are not materials themselves. The name refers to a quantum state which occurs in some metals at low temperature, where they violate the textbook rule that the resistance of a metal should rise with temperature squared. In a strange metal, the resistance often rises in direct proportion to temperature, which suggests that the electrons have stopped behaving like well-defined particles. Strange metals are interesting not just because it’s a curious phenomenon but also because the strange metal state often goes together with high temperature superconductivity.

The researchers have now found evidence that a strange metal is a deeply entangled quantum state. They cooled a material known to have a strange metal state to 60 millikelvin, fired a beam of cold neutrons at it, and measured how the scattered neutrons changed energy. From the results, they calculated how many parts of the material are acting together quantum-mechanically. As the strange metal formed, this number rose by almost a factor of 40! This is a big step on our way to understand the “strange” quantum states of matter.

Image: TU Wien / Harald Ritsch

[Tom Gauld @tomgauld]

My latest cartoon for @newscientist

[FQxI Physics @FQXi]

Two Max Planck papers retracted after probably tripping an algorithm. Springer Nature is nevertheless still selling the empty PDF for $39.95. “Why have papers by one of history’s most famous physicists been retracted?” https://t.co/ct6eQuELgy

[FQxI Physics @FQXi]

Full story: https://t.co/kUP9FFxPKX

[FQxI Physics @FQXi]

(thread) FQxI's Ekkehard Peik came up with the nuclear clock back in 2003, then waited nearly twenty years for anyone to build one. This June, his own team finally did.