Thread by @FQXi

Now, panel “Is Time Real?” #FQXi2019

Bernard Carr: Conscious experience exists over a very narrow timescale ('specious present'). But we know perception of time can change.

Jayne Thompson: If there is a thermodynamic arrow of time. We have a finite memory and ability to track all information, leads to perception of entropy increasing. Time is real.

Carlo Rovelli: Time is real. By time we mean many different things. Some refer to our experience -- depends on our mind and emotions -- some refer to fundamental physics -- measured in the lab. Not the same. Mistake to force experiential time and elementary physics together.

James Weatherall: quantum measurement problem is deep, so we can have partial stories about how we get to classical phenomena without fully understanding. Seems to be something missing. With time, even though not part of fundamental physics, how can it come about from physics?

Bernard Carr: Specious present is something psychologists and philosophers talk about, but physicists don't. Speed of time isn't always one second per second. Mental time does not equal physical time. But kind find it through relativity of quantum physics.

Jayne Thompson: Physics may not need these concepts. Doesn't need a "theory of cats". But information theory should encompass all of these things.

Carlo Rovelli: I agree there are plenty of missing steps. But we don't understand thunderstorms, more work needs to be done. With fundamental physics, I agree something is missing, but don't think fundamental physics has to be changed. It's just that more work needs to be done.

Carlo Rovelli: I am a naturalist. The "I" (who can't keep track of information, thus I perceive entropy grows, as Jayne T suggested) is itself a subsystem of the universe.

Moderator Andreas Albrecht: We all agree something is missing. Question is can it emerge from known physics, or do we need something fundamentally new?

Bernard Carr: "My crazy idea": I'm interested in string theory, where you have extra dimensions, which are compactified. I'm interested in models in which the specious present is associated with the compactification scale. String theory could explain consciousness.

Background on Carr's thoughts on consciousness: closertotruth.com/interviews/1926

Question from Fred Adams: What about cosmological time? You can measure time by how big the universe is. Is that related to the arrow of time in small scale lab experiments?

Rovelli: Yes, related, because time in the lab is related to the low entropy of the early universe.

Carr: Controversy over whether you have a block universe (no preferred now) or an evolving block universe (fqxi.org/community/arti…). So when talking about the passage of time, you do need cosmological time.

Questions from Laura Mersini-Houghton: is nature of time emergent or fundamental? If emergent, why are the laws of nature time symmetric? Are laws emergent? How has information theory helped us advance our understanding of past, present, future?

Jayne Thompson: Info theory describes any series of interactions, so bigger scope than entropy. Time is a label given to a sequence of events in physical conception. Or a conscious experience reconstructed by the observer. Simulation in someone's mind. Follows laws of info.

Question from Max @tegmark: Why does time flow? Hard question in quantum gravity and in quantum theory. Albrecht wrote about how you split universe into a 'clock' and the rest. Have there been any new insights into this?

Albrecht: I have backed off from my 'clock ambiguity' paper.

Rovelli: Wheeler-DeWitt equation doesn't have a time variable, what does that mean? Disappearance of time in quantum gravity. See this in classical general relativity, which can be formulated without time.