Le mar. 10 déc. 2024, 11:41, Alan Grayson <[email protected]> a écrit :
> > > On Tuesday, December 10, 2024 at 3:20:20 AM UTC-7 Jesse Mazer wrote: > > On Mon, Dec 9, 2024 at 11:55 PM Alan Grayson <[email protected]> wrote: > > > > On Monday, December 9, 2024 at 9:08:33 PM UTC-7 Jesse Mazer wrote: > > On Mon, Dec 9, 2024 at 8:28 PM Alan Grayson <[email protected]> wrote: > > On Monday, December 9, 2024 at 4:54:34 PM UTC-7 Brent Meeker wrote: > > On 12/9/2024 3:24 PM, Alan Grayson 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 > > > Since the car's length can be assumed to be arbitrarily small from the > > pov of the garage, why worry about fitting the car in garage perfectly, > > and then appealing to difference in spontaneity to prove no direct > contradiction between the frames? It seems like a foolish effort to > > avoid a contradition, when one clearly exists. AG > > > What's the contradiction? > > > > *ISTM that the car can, or cannot fit in garage given the initial > condition that in the rest frame, the car is longer than the garage; in > other words there is an objective reality, but the frames differ on whether > the car fits or not.* > > > Can you define what "fits in the garage" would mean in objective terms, > i.e. a definition that does not depend on simultaneity or choice of frame? > If you can't even define that phrase in any objective terms, why do you > believe there is any objective reality here? Is it just some kind of strong > intuitive hunch that there "should" be some kind of objective reality > attached to such a notion? > > > *"Fits" means the car's length is equal to garage's length, or less.* > > > Do you define the "length" of each in the standard relativistic > frame-dependent way? > > > * If car exactly fits, this is ambiguous from the pov of garage frame due > to lack of simultaneity, and this is the consensus solution to an alleged > paradox. But what happens if the car's velocity is increased, so car fits > with room to spare? This is the case I have been posting about. AG * > > > * If one avoids the issue of simultaneity, by not requiring the car to > perfectly fit in the garage, we get opposite conclusions from the frames. > AG* > > > The paradox does not depend on the assumption that the car is the same > length as the garage in either the car frame or the garage frame (or that > they have the same rest length), > > > *I don't make this assumption. AG* > > > Then what did you mean by "not requiring the car to perfectly fit in the > garage"? What does perfect vs. imperfect fit mean here, if "perfect" does > not refer to them being exactly the same length? > > > > if that's what you mean by "perfectly fit in the garage". Even if the > car's rest length is much shorter than the garage's rest length, so it fits > easily in the garage frame, > > > *No, this isn't the initial assumed car length. Its length is assumed > larger than the garage, and the question is whether it can fit due to its > motion which causes length contraction. AG* > > > The paradox can refer to any scenario where the car fits in the garage > frame but not in the car frame, this can happen regardless of whether the > car's rest length is larger or smaller than the garage's rest length. > > > *If we assume as an initial condition that the car's length is smaller > than the garage's length, then for some velocity and greater, the car will > not fit in the garage from the car's frame, so we're in the same situation > as when we assumed as an initial condition that the car's length is greater > than the garage's length. The contradition persists and differences in > simultaneity does not come to the rescue, since it's measured the car's > frame and couldn't be used to show the car fits, exactly, or loosely, since > it doesn't fit. AG* > > > > you could always pick a sufficiently large relative velocity such that the > car would be longer than the garage in the car's rest frame, > > > *No, the car's length decreases in the garage frame only due to its > motion. In the car's frame, the car's length doesn't change. AG* > > > I didn't say the car's length changed in the car's frame, I just said that > if you pick a sufficiently high relative velocity, then in the car's rest > frame the car will be longer than the garage (in this case due to the > garage's length being shortened in that frame). > > > *I don't follow. If the garage's length is shorten, the length of the car > remains unchanged. AG * > > > > and thus it would not fit in that frame, so the paradox remains. Not sure > what "opposite conclusions from the frames" could mean if you don't have a > specific way to define "fits in the garage" in a way that doesn't depend on > picking some frame or another. > > > Jesse > > > *As I understand the problem, in the initial rest frame the car is assumed > to be larger than the garage. Then the question is whether it can fit when > the car is in motion due to length contraction. In the car's frame, the > garage length decreases, so there is no possibility of the car fitting. > OTOH, from the pov of the garage frame, the car's length shrinks, so there > is some velocity where it fits perfectly. If the velocity continues to > increase, the car fits with room to spare. So, I have shown that the frames > differ in concluding whether the car fits, or not, and the question is > whether this is a paradox. If you conclude it is not, then you deny there's > an objective reality such that the car fits, or doesn't fit. And "fits" > just means the car's contracted length is EQUAL TO or LESS than the > garage's length. AG* > > > Yes, I've said before that there's no objective frame-independent reality > about whether the car fits, that's part of the standard answer to this > paradox. Do you accept that this is a valid way of resolving it? You seemed > to be objecting in your earlier comment when you said "ISTM that the car > can, or cannot fit in garage given the initial condition that in the rest > frame, the car is longer than the garage; in other words there is an > objective reality, but the frames differ on whether the car fits or not", > but maybe I misunderstood? > > Jesse > > > *My conclusion is that there's a contradiction in evidence, since the > situation of the car fitting and not fitting makes no sense. AG * > And the answer only lies in disagreement of simultaneity of both doors being closed and the car fully inside the garage, and that is dependent on the frame of reference, there aren't any contradictions. > -- > 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/e61191fb-11b4-4c0e-82b1-36fc2ffcfa74n%40googlegroups.com > <https://groups.google.com/d/msgid/everything-list/e61191fb-11b4-4c0e-82b1-36fc2ffcfa74n%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]. 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