On Monday, January 27, 2025 at 12:54:57 PM UTC-7 Jesse Mazer wrote:
On Mon, Jan 27, 2025 at 8:32 AM Alan Grayson <agrays...@gmail.com> wrote:
On Sunday, January 26, 2025 at 9:02:01 PM UTC-7 Jesse Mazer wrote:
On Sun, Jan 26, 2025 at 10:23 PM Alan Grayson <agrays...@gmail.com> wrote:
On Sunday, January 26, 2025 at 9:13:54 AM UTC-7 Jesse Mazer wrote:
On Sun, Jan 26, 2025 at 1:54 AM Alan Grayson <agrays...@gmail.com> wrote:
On Saturday, January 25, 2025 at 11:25:53 PM UTC-7 Brent Meeker wrote:
On 1/25/2025 10:13 PM, Alan Grayson wrote:
On Saturday, January 25, 2025 at 9:06:18 PM UTC-7 Brent Meeker wrote:
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 <agrays...@gmail.com>
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?) *
Brent writes > 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*
Brent writes > That's why you should talk about events being
spacelike...the relativistic analogue of simultaneous.
*I'd like to do that. BUT if the Parking Paradox is allegedly solved by
star**ting in the garage frame where the car fits, the pair of events which
define fitting are not spacelike since they occur at different times! *
You didn't read the definition of "spacelike" that I wrote above. You want
everything fed to you in tiny bites of knowledge which you forget eight
lines later, so the questions start all over again.
Brent
*I read it, but didn't like it. Big difference. Maybe you should stop
trying to read my intentions. You may be smart, but reading my intentions
is way above your pay grade. How could two events with the same time
coordinate be referred as "so close together". Moreover, in all discussions
of solutions to the paradox, events that are simultaneous in one frame, are
shown not simultaneous in another frame. This being the case, the two
events of the car fitting in garage frame are simply NOT simultaneous!
Also, Jesse seems to be referring to different events than the ones you
refer to. So there's a muddle IMO. As a teacher, your preferred method is
to intimidate students. Grade now D+. AG *
Why do you think I am referring to different events? I referred to the same
events F and R that Brent did (F is the event of the front of the car
coinciding with the garage exit, R is the event of the rear of the car
coinciding with the garage entrance).
If you don't like Brent's verbal explanation, I also gave you a
mathematical definition of "spacelike separation" in two recent posts on
the "Brent on Parking Paradox" thread at
https://groups.google.com/g/everything-list/c/QgVdhXi3Hdc/m/KC2lIKyrDQAJ
and https://groups.google.com/g/everything-list/c/QgVdhXi3Hdc/m/FF7TpbG-DQAJ
-- "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)".
Since I explicitly referred to a time interval t between the two events, if
you had paid attention to that you would have known not to say "the pair of
events which define fitting are not spacelike since they occur at different
times".
Jesse
*Yes, you defined spacelike separation, but without specific numbers for
events, one cannot automatically claim two events are spacelike separated.
Same goes for fitting in garage frame. I wasn't sure that all pairs of
events in garage where car fits are spacelike separated. And sometimes I
haven't caught up with your posts so I seem like I can't remember. And
occasionally I do forget what someone posted. AG*
I was responding to your statement "the pair of events which define fitting
are not spacelike since they occur at different times", one doesn't need
any specific coordinates to see that this statement is wrong because it
suggests spacelike separated events can't occur at different times. If you
hadn't read my definition or didn't remember it, fine.
*I meant above that I needed all the coordinate values to determine if two
events are spacelike separated; the time coordinates are not enough. AG *
I gave you both x and t coordinates for F and R in my last message, see
below. Or when you say "I meant above that I needed all the coordinate
values", is "above" referring to your original comment "the pair of events
which define fitting are not spacelike since they occur at different
times", i.e. are you saying that when you wrote that, what you really meant
was just that Brent hadn't provided the coordinates or R and F? Or would
you acknowledge that when you wrote that you were misunderstanding the
notion of spacelike separation?
I was referring to my original comment. I didn't misunderstand what
spacelike separation means. I don't recall what Brent posted. AG
If you want to know the coordinates of F and R in Brent's example, in the
garage frame the entrance to the garage is fixed at x=0 and the exit is
fixed at x=10, while in this frame the back of the car has position as a
function of time given by x = 0.8c*t and the front has x = 7.2 + 0.8c*t. F
occurs when the front of the car meets the exit of the garage i.e. 7.2 +
0.8c*t = 10, which you can solve for t to get t = 2.8/0.8c = 3.5 (assuming
units where c=1), and the x-coordinate is 10. And R is at the intersection
of x=0 and x=0.8c*t which is just x=0, t=0.
Jesse
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