On 1/24/2025 5:06 PM, Alan Grayson 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*
*You mean you just want to keep trolling Jesse.
Brent
*
It's pairs of points in spacetime, or equivalently pairs of local
physical events occuring at each point (like the event of the back
of the car passing the entrance of the garage vs. the event of the
front of the car reaching the back of the garage), that can be
spacelike separated. If you know the distance x and time interval
t between the two points/events in the coordinates of any inertial
frame, to say they are spacelike separated just means that x > ct
(and an equivalent definition is that neither point is in the past
or future light cone of the other one). For any two such
points/events A and B with a spacelike separation, you can always
find some frames where A occurs before B and other frames where B
occurs before A, that's something that can be derived from the
Lorentz transformation equations.
Jesse
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