robphy's latest activity
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.Probably off-topic, how would one even type an em-dash in the forum software? -
robphy replied to the thread High School Is there anything in the Universe that is not fundamentally made up of matter?.In General Relativity, the Einstein field equations read ##G_{ab}=\kappa T_{ab}##, where ##T_{ab}## is the stress-tensor, where all...
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.I would prefer your thoughts.
-
robphy reacted to Dale's post in the thread Graduate Can a causal or time-like structure emerge without assuming a metric? with
Like.
@OmniThoughts Please don't post chatbot output here. If any of us wanted to have a conversation with a chatbot then we would just ask... -
You can't travel faster than ##c##. So your question is "how should I interpret some maths I've applied in a regime where the same maths...
-
robphy replied to the thread High School Light & Time."Proper time" does not exist for the photon. However, there must be a sense of causality, The Emission-event occurs before the...
-
robphy replied to the thread Undergrad Photons & Time: t=0 What?.I should probably write the relevant formula involving hyperbolic-trigonometry. ##\beta=(v/c)=\tanh\theta ## so...
-
robphy replied to the thread Undergrad Photons & Time: t=0 What?.For a ship (with nonzero rest mass), it cannot achieve "the speed of light" physically. Although your Newtonian intuition suggests that...
-
No. Light does not experience time. There is no valid frame of reference for a photon. This is a direct result of the postulates of...
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.Did you look at the Szekeres "Signal Space" reference? His S relation is reflexive, but not symmetric.
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.This might be of interest: E. H. Kronheimer & R. Penrose (1967) "On the structure of causal spaces" Mathematical Proceedings of the...
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.Along these lines (assuming (3+1)-spacetime): "The causal order C determines the conformal structure of space-time, or nine of the ten...
-
robphy reacted to renormalize's post in the thread Graduate Can a causal or time-like structure emerge without assuming a metric? with Like.
Take a look at https://en.wikipedia.org/wiki/Causal_sets: "The causal sets program is an approach to quantum gravity. Its founding...
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.You might be interested in David Malament’s dissertation: “Does the Causal Structure of Space-Time Determine its Geometry”...
-
robphy replied to the thread Graduate Can a causal or time-like structure emerge without assuming a metric?.I think that’s a fair statement.