Timeline for Can changing the past ever be a coherent concept?
Current License: CC BY-SA 4.0
10 events
| when toggle format | what | by | license | comment | |
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| Dec 16, 2022 at 11:32 | comment | added | Professor Sushing | @gs I said nothing about simultaneity. In any case, simultaneity is a complete red-herring. A plane of simultaneity in an inertial frame is just a set of points to which you assign a common t coordinate in that frame- it has nothing to do with the present. | |
| Dec 16, 2022 at 8:43 | comment | added | g s | @MarcoOcram I'm not sure that this criticism is coherent. Do physics interactions only happen at the origin - in which case are all those things that I keep measuring as having happened elsewhere not consequences of physics interactions? If physics interactions happen in a time-translating present plane of simultaneity, who gets to pick it, and how could we possibly tell if we were on it? | |
| Dec 15, 2022 at 22:12 | comment | added | Professor Sushing | Ergo all the so called paradoxes of time travel disappear. All physics interactions happen where matter is, ie in the present, so it is impossible to change what happened in the past. | |
| Dec 15, 2022 at 22:10 | comment | added | Professor Sushing | @DavidGudeman Understood. The key point, however, is that according to modern physics, matter moves through spacetime in a direction of increasing time. So if matter passes through a region of spacetime with a t coordinate t1 and later reaches a region with t coordinate t2, it is no longer at t1. If you send some matter back to the t1 region, then there will be no other matter there for it to interact with... | |
| Dec 15, 2022 at 18:26 | comment | added | David Gudeman | OK, I did say that. I thought it was clear from my previous wording, "fiddle the knobs to send it back to t1" that I was talking about the intentions of the experimenter and not what was actually happening, especially since my point was that the intentions of the experimenter don't make sense. | |
| Dec 15, 2022 at 13:00 | comment | added | Professor Sushing | But your equation actually contains the words 'Then at T2 you send C back to T1'. | |
| Dec 15, 2022 at 8:38 | comment | added | David Gudeman | No, my question does not explicitly state that I'm sending a cue ball back. I simply describe various scenarios of what might be observed. I didn't say that the cue ball goes back in time because the point of the question is that I don't know what it means to say that. | |
| Dec 15, 2022 at 8:32 | comment | added | Professor Sushing | Your question explicitly states that you are sending a cue ball back from t2 to t1, and when it gets to t1 there is a pool table there. In other words, you are assuming that the objects that were present at t1 will 'still' be there if the cue-ball goes back to t1. | |
| Dec 15, 2022 at 8:18 | comment | added | David Gudeman | "Your question assumes that if you send the cue ball back in time to t1, the pool table and nine ball are still there waiting to meet it" I very carefully described the thought experiment to make no such assumption. Can you explain where you see this assumption appearing? | |
| Dec 14, 2022 at 16:30 | history | answered | Professor Sushing | CC BY-SA 4.0 |