4 ms·
Thanks, I’ve never heard this and it’s quite profound. It’s always bothered me that there even is a top speed, and further that mass becomes infinite as it’s ap
by jerb 2y ago
Thanks, I’ve never heard this and it’s quite profound. It’s always bothered me that there even is a top speed, and further that mass becomes infinite as it’s approached. But “speed of causality” makes these less strange.
- dyauspitr 2y agoWhy does speed of causality make it any better? It’s still an arbitrary limit that’s even more abstract and intangible than speed.
- adastra22 2y agoIf the universe’s causal mechanisms were infinitely fast, the entire history of the universe would play out instantly in zero time, and we’d skip straight to the heat death of the universe. The fact that time even exists is implied by / a result of causal actions having some finite propagation time.
- jiggawatts 2y agoThat doesn’t work that way. Imagine a universe simulated in a computer with “ticks” where the entire state is updated. It would be different to ours, but it would work just fine.
- BoiledCabbage 2y agoWhile what you say is true, it seems to me like what you're describing isn't quite the same definition of causality being infinitely fast. The fact that causal effects happen in the next tick means some minimal time has passed. So in your definition causality can cover the entirety of a finite universe in an incredibly short amount of time (one tick). But it seems like that's not the same as covering the entirety of a finite universe in zero time. In that case, every result would happen within the same tick as its cause.
- jiggawatts 2y agoThere's more than one way to "implement a universe", but one hypothetical way to run a simulation is to alternate the simulation of forces and effects/causes. A simulation could use particles with attributes like position, velocity, and also a "sum of forces". Then each update has the following steps: 1. Reset the sum of forces for all particles to zero. 2. For all particles, add the contribution to the forces on it from all other particles. 3. For all particles, update the next particle position based on the collected forces. In the above, there's no intermediate state between updates, everything moves to the next position synchronously from the perspective of in-universe observers. (The external simulation can update particles one-at-a-time, but this is not an "observable" inside the simulation.)
- adastra22 2y agoThe cellular automata view of reality is entirely compatible with what I said.
- Terr_ 2y ago> causal actions having some finite propagation time. I think I know what you're getting at, but somehow the phrasing bothers me, as if there is meta-time or as if cause and effect have time between them... for the photon at light speed, time isn't passing, it's emitted and then zero "time" later it hits something very far away. It's more like we somehow need to think of cause and effect chains that have orderings without time. I wonder if future generations will ever look back and casually quip something about "well they believed X existed, that was their problem, it all makes intuitive sense if you just..."
- linuxdude314 2y agoThis is not true. You can easily measure TOF of a photon using an APD in Geiger mode or other detectors easily purchasable in 2024. So what exactly are you talking about?
- lijok 2y ago> for the photon he’s talking about the photons frame of reference
- linuxdude314 2y agoIt’s still not true.
- deleted 2y ago[deleted]
- mikhailfranco 2y agoYes, the basic idea is that photons do not 'experience' time. They 'experience' creation, all points along their path, and absorption 'simultaneously'. However, you have to be careful with terminology. There is no inertial frame co-moving with the photon. All we can say is: as a massive particle gets faster relative to an observer's frame, the time it experiences relative to the observer's frame becomes shorter, and in the limit, as it approaches the speed of light (but never reaches c), the experienced relative time approaches zero (but never reaches 0). This is well explained by Don Lincoln on the Fermilab YT channel: Do photons experience time? https://www.youtube.com/watch?v=6Zspu7ziA8Y https://www.youtube.com/watch?v=6Zspu7ziA8Y
- BoiledCabbage 2y agoThat's really profound - thanks for sharing that insight. I've never looked at it that way before.
- kingkongjaffa 2y agoWell because its decoupled from light itself or its properties. If there’s some universal limit for causality itself, then light just happens to be the fastest thing among all the other things subject to causality.
- thiagotomei 2y agoBut it is not a coincidence. Light — the EM field waves — propagates at causality speed because the EM field respects a particular property of the universe, the so-called gauge symmetry. That is intimately connected to the fact that the photobs has no mass. Other similar particles, like the W and Z bosons, are manifestations of the weak field. Since that field breaks the symmetry, those particles have mass and move slower. BTW, that symmetry breaking is the very same one that physicists talk about when we discuss the Higgs boson.
- linuxdude314 2y agoFirst person in this thread to make any sense… The level of physics knowledge has declined on this site.