On Fri, Jan 24, 2025 at 8:06 PM Alan Grayson <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAPCWU3%2Bn5FGeVmxZgv_x%3DqqUZq%2BPopcUCqOopS8fxRdJDx4YSA%40mail.gmail.com.
