On 1/25/2025 6:34 PM, Alan Grayson wrote:
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?) *
Yes. Just what Jesse wrote above. It means the two events were so
close together in time and distant in space that something would have to
travel faster than light to be at both of them.*
*
*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*
That's why you should talk about events being spacelike...the
relativistic analogue of simultaneous. Spacelike is an /*invariant*/
concept. It */does not/* depend the reference frame. If it's true in
one frame, it's true in all. But the time order of two spacelike events
is frame dependent. So the same two spacelike events F and R can be
both simultaneous and not simultaneous. Changing from one state of
motion to another can reverse their time order. They can be in the order
F before R and also R before F. There will be some intermediate state of
motion that makes the two spacelike events simultaneous in that
particular reference frame. The car/garage paradox doesn't depend on that.
Brent
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
<https://groups.google.com/d/msgid/everything-list/609ffc0d-f654-407d-a8f0-5020c646ac1dn%40googlegroups.com?utm_medium=email&utm_source=footer>.
--
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/7b1af710-bb9c-48e8-a6fd-00d65e07d8a4%40gmail.com.
