On Fri, Jan 24, 2025 at 8:06 PM Alan Grayson <agrayson2...@gmail.com> wrote:
> > > On Friday, January 24, 2025 at 2:21:43 PM UTC-7 Jesse Mazer wrote: > > On Fri, Jan 24, 2025 at 4:04 PM Alan Grayson <agrays...@gmail.com> wrote: > > On Friday, January 24, 2025 at 10:41:45 AM UTC-7 Jesse Mazer wrote: > > On Fri, Jan 24, 2025 at 8:53 AM Alan Grayson <agrays...@gmail.com> wrote: > > > > On Thursday, January 23, 2025 at 11:46:46 PM UTC-7 Brent Meeker wrote: > > That's exactly what my diagram shows. Didn't you look at it? > > Brent > > > Sure, I looked at it but I prefer text, and I forgot you're a deaf mute. > And NO, I didn't know that frame transformations can invert time > relations. Let's forget it. I forgot you prefer your riddles. Grade C- . AG > > > The point that the LT can change the order of events with a spacelike > separation is one I also talked about many times on the previous thread, > for example at > https://groups.google.com/g/everything-list/c/vcrAzg4HSSc/m/knVuCxHFAwAJ > where I wrote: "Because as you previously agreed, the question of whether > the car fits reduces to the question of whether the event A = back of car > passes front of garage happens before, after, or simultaneously with the > event B = front of car reaches back of garage. Since these events have a > spacelike separation in both Brent’s and my numerical examples, in > relativity different frames can disagree on their order, that’s the whole > reason we say frames disagree on whether the car fits." Likewise in > https://groups.google.com/g/everything-list/c/gbOE5B-7a6g/m/MwKDuJM-AQAJ > where I wrote: "Do you understand that when people talk about the > relativity of simultaneity in the context of the car/garage problem, they > are referring not just to events which are actually simultaneous in some > frame, but also the fact that different frames can disagree about the > time-ordering of events with a spacelike separation (i.e. neither event is > in the past or future light cone of the other event)? The events A and B I > was talking about earlier are not simultaneous in either the car frame or > the garage frame (at least not with the numerical values for rest lengths > and relative velocity given by Brent), but they happen in a different order > in the two frames, and the relativity of simultaneity is key to > understanding how that's possible, in Newtonian physics where all inertial > frames agree about simultaneity there could be no disagreement about the > order of any events." > > Brent has made this point in the past as well, for example at > https://groups.google.com/g/everything-list/c/gbOE5B-7a6g/m/WcxkopmjAAAJ > where he wrote: "The facts are events in spacetime. There's an event F at > which the front of the car is even with the exit of the garage and there's > an event R at which the rear of the car is even with the entrance to the > garage. If R is before F we say the car fitted in the garage. If R is > after F we say the car did not fit. But if F and R are spacelike, then > there is no fact of the matter about their time order. The time order will > depend on the state of motion." > > Did you really not remember any of these discussions, or did you just > misunderstand the meaning of "invert time relations" to be something > different than the idea that two events A and B with a spacelike separation > can have a different time-order in different frames? > > > Of course I recall, but I haven't had time to research the issue, such as > why the frames in the problem are, or might be, spacelike separated. AG > > > Frames have no specific location, they are coordinate systems covering all > of spacetime, so it doesn't make sense to say *frames* can be spacelike > separated. > > > *Right. I was skeptical about what I wrote, when I wrote it. OTOH, since > EVENTS can be spacelike separated, I don't see any such events in this > problem. For example, the ends of the car aren't spacelike separated; > neither are the ends of the garage. If Brent weren't a failing teacher of > SR, he would specify what he means. I am in no mood to guess his meaning. > AG* > The ends of the car are extended worldlines which include multiple events (just as a line contains multiple points in Euclidean geometry), you can pick a particular event A on the worldline of the back of the car and an event B on the worldline of the front of the car (or on the front and back of the garage) such that A and B have a spacelike separation. As I said, spacelike separation just means that if the spatial separation between the points is x and the temporal separation is t (as measured in some inertial frame), then x > ct; for example, this will be automatically true for any pair of events A and B at the front and back of the car that are simultaneous in that frame (because in the case of simultaneous events, the temporal separation t is 0, so the condition x > ct reduces to x > 0). Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAPCWU3%2Bn5FGeVmxZgv_x%3DqqUZq%2BPopcUCqOopS8fxRdJDx4YSA%40mail.gmail.com.
