On Saturday, January 25, 2025 at 6:47:22 PM UTC-7 Jesse Mazer wrote:
On Sat, Jan 25, 2025 at 8:07 PM Alan Grayson <[email protected]> wrote: On Monday, December 9, 2024 at 2:01:28 PM UTC-7 Brent Meeker wrote: > > Nothing odd about dilation and contraction when you know its cause. > But what is odd is the fact that each frame sees the result > differently -- that the car fits in one frame, but not in the other -- > and you see nothing odd about that, that there's no objective reality > despite the symmetry. AG 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. Brent Jesse; it's the last two of Brent's sentences that I find ambiguous. What does he mean? What about them do you find ambiguous? He's just saying that if there's a spacelike separation between the events F and R (as there was in his numerical example), then you can find a frame where R happens after F (as is true in the car frame where the car doesn't fit), and another frame where F happens after R (as is true in the garage frame where the car does fit). *What does he mean by "But if F and R are spacelike, then there is no fact of the matter about their time order."? (What you wrote above?) More important I just realized that in the frame of car fitting, the events F and R aren't simultaneous, so how does one apply disagreement on simultaneity when one starts with two events which are NOT simultaneous? AG* I also wonder what happens when we transform in the reverse direction from the pov of simultaneity, from the car frame to the garage frame? TY, AG Brent didn't mention a direction in which the transformation is being taken, but regardless of whether you start with the coordinates of F and R in the garage frame and transform to the car frame, or start with the coordinates of F and R in the car frame and transform to the garage frame, you get the same answers about what the coordinates of these F and R are in each frame. For instance if you start with the coordinates x,t of F in the garage frame and apply the LT *But don't you have to start with two events which are simultaneous in one frame, to get a disagreement in simultaneity in a second frame, but F and R are not simultaneous in car fitting frame? AG* to get the coordinates x',t' of F in the car frame, then apply the LT to x',t' (this time using a velocity of -0.8c rather than +0.8c since the garage frame is moving in the -x direction as seen in the car frame) you will get back the original coordinates x,t for the garage frame. 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/609ffc0d-f654-407d-a8f0-5020c646ac1dn%40googlegroups.com.
