"Quantum General Covariance and the Problem of Time" presented by Philipp Höhn
Sponsored by the Physics Department and the Institute for Cross-Disciplinary Engagement at Dartmouth, which received generous funding from the John Templeton Foundation.
Philipp Höhn, a Professor in the department of Physics and Astronomy at University College London, presents a lecture on "Quantum General Covariance and the Problem of Time."
Abstract: Reference frames provide the vantage points from which to describe the remaining physics. General covariance essentially posits that “all the laws of physics are the same in every reference frame.” While this is an established pillar of general relativity and usually interpreted in terms of coordinate invariance, its fate in the quantum realm remains an open question. This is a challenge because treating frames fundamentally as quantum systems themselves is inevitable in quantum gravity, where coordinates are a priori unavailable, but also in quantum foundations once accepting that all frames are physical systems. Both fields thus face the question of how to describe physics from the perspective of quantum frames and how the descriptions relative to different such choices are related. Philipp Höhn summarizes a recent “perspective-neutral” approach to such quantum frame perspective changes, which works in analogy to coordinate changes on a manifold, except that these “quantum coordinate changes” proceed between different Hilbert spaces. He then focuses on temporal reference frames, i.e., quantum clocks, and uses this approach to argue for a new perspective on the infamous problem of time in quantum gravity and the “wave function of the universe.”
Filmed on Thursday, November 14, 2019
Room 202, Wilder Hall
Dartmouth College
Пікірлер: 3
Particle physics and the LHC have pretty much confirmed with the recent finding of the Higgs field/particle that our universe is made up of only fields. About a month ago I used to believe in space as a separate physical quantity independent of these fields and their respective particle/forces. This came about because of the precision of SR and GR. But if our universe is made up of only fields and of which all particles, quantums, and field waves emerge from and interact across why should we continue to believe space even exists? In my mind I see space as an aggregate of all the fields in the universe “sitting” in the background and interacting. SR and GR are extremely accurate but have imbedded principles that handcuff the advancement of physics in my opinion. SR adheres to the Galilean principle of relativity and “concludes” that there is no preferred reference frame which leads to several paradoxes with the twin paradox being the most notable. Yet there is empirical proof with the GPS satellites that the twin paradox does not exist which means there cannot be a no preferred reference approach - there must be a preferred reference frame - most likely the background fields that comprise our universe. Hence, the laws of physics are identical in all reference frames because all reference frames are chock full of the same background fields. This means we should be able to detect the movement of a reference frame relative to the stationary nature of the fields in its background. GR has a similar problem in that it connotes the existence of space. But again this contradicts the understanding that our universe is comprised of only fields. Hence, when a photon propagates through space it’s actually propagating through the electromagnetic field - remove this field and the photon has no medium by which to propagate through - so why do we need this thing called space? Your video was extremely detailed and I had a hard time understanding your one single argument. It seems to me you are leaning towards or trying to say that the Galilean principle of relativity is invalid and that there must be a preferred reference frame when two different reference frames move relative to one another - a thought experiment to visualize your theory would have been helpful. I believe there must be a preferred reference frame but cannot be absolute but it can be “local absolute”. Here is my vid explaining this - thx. kzread.info/dash/bejne/dIeuxcyyfZzPf8Y.html
@BrettHar123
3 жыл бұрын
The solution is just a change of variable, as in the Ashtekar formulation of GR used in Loop Quantum Gravity, simply rename "space" as "the gravitational field", there is no metric, only connections, which can be used to evaluate spacio-temporial quantities such as distance and time, along a given path. This procedure is analogous to calculating the magnetic flux passing through a given area by integrating around the the boundary.
@randykubick
3 жыл бұрын
Reckless Abandon - so do you believe space exists independent of the fields that make up our universe?