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Dale
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The “Space Ship” lines are discontinuous at the turn around on all of your plots except the first.obtronix said:What discontinuity?
The “Space Ship” lines are discontinuous at the turn around on all of your plots except the first.obtronix said:What discontinuity?
I mean it's instantaneous so it has to be discontinuous.Dale said:The “Space Ship” lines are discontinuous at the turn around on all of your plots except the first.
As @Dale says, your "space ship" worldlines have gaps in them in your second and third diagrams. That's because, in those diagrams, you did not adjust the times of the "kinks" in the space ship worldlines for relativity of simultaneity. If the two "kinks" are simultaneous in the stay at home twin's rest frames, they will not be simultaneous in either the outbound or the inbound "traveling" frames. When you correct for this, your "space ship" worldlines should be continuous (no gaps at the kinks) in all frames.obtronix said:What discontinuity?
Not in the sense @Dale meant. See my post #38.obtronix said:I mean it's instantaneous so it has to be discontinuous.
oh, okPeterDonis said:As @Dale says, your "space ship" worldlines have gaps in them in your second and third diagrams. That's because, in those diagrams, you did not adjust the times of the "kinks" in the space ship worldlines for relativity of simultaneity. If the two "kinks" are simultaneous in the stay at home twin's rest frames, they will not be simultaneous in either the outbound or the inbound "traveling" frames. When you correct for this, your "space ship" worldlines should be continuous (no gaps at the kinks) in all frames.
No. Instantaneous acceleration makes a sharp bend in the line, not a jump. What you have drawn is not instantaneous acceleration but teleportation.obtronix said:I mean it's instantaneous so it has to be discontinuous.
Now that’s just patently false.obtronix said:Literally every twin paradox example assumes infinite acceleration
anorlunda said:This video from Fermilab shows an explanation of the twin paradox that has no acceleration at all. Instead, we have a fixed observer A, a traveler B moving to the right with constant velocity, and another traveler C moving to the left with constant velocity.
Dr. Lincoln thinks that it is. Or at least, it is the equivalent. Review what he says is the point at 7:21 in the video.obtronix said:But that's not the twin paradox
The worldlines in spacetime are the same, and the "paradox" is ultimately about comparing the lengths of worldlines. There is no need for a single observer to follow the entire "traveling twin" worldline in order to have the worldlines be what they are.obtronix said:that's not the twin paradox
The point is that the essence of the twin paradox is the nature of Minkowski geometry and acceleration is irrelevant.obtronix said:But that's not the twin paradox thought experiments
To put it yet another way, Lincoln's version has three straight lines forming a triangle where the usual version has one straight line and one > shaped line. Same triangle either way.obtronix said:But that's not the twin paradox thought experiments because they not are together to begin with and they never meet up at the end. They would have to jump for one spaceship to another which is acceleration.
Yes but where/when does the thought experiment start and end in his thought experiment? To compare World lines you need a start and ending event. The twin paradox gives you those two events.PeterDonis said:The worldlines in spacetime are the same, and the "paradox" is ultimately about comparing the lengths of worldlines. There is no need for a single observer to follow the entire "traveling twin" worldline in order to have the worldlines be what they are.
The same places as in yours. As several posters have already pointed out, the curves in spacetime are exactly the same.obtronix said:where/when does the thought experiment start and end in his thought experiment?
Same as in your version.obtronix said:To compare World lines you need a start and ending event.
You don't actually care how anyone's clocks are set, since you are measuring differences in clock readings, not absolute clock readings. All you need are the differences in clock readings between the start and end of the three line segments in spacetime: the "stay at home" line segment, the "traveling outbound" line segment, and the "traveling inbound" line segment. Then you just compare the sum of the second and third with the first; the latter will be larger.obtronix said:He says in the beginning of his thought experiment everyone sets their clock to zero
But, you do get the same numerical answer, which ought to make you stop and think.obtronix said:In any event to have different velocities they would have to accelerate he just kind of starts in the middle of the thought experiment after the acceleration and then claimed acceleration is not needed kind of disingenuous in my opinion.
All they need do is synchronize clocks as they pass each other.obtronix said:They would have to jump for one spaceship to another which is acceleration.
Well that's not true he's saying you start the clocks simultaneously and measure time from that start. (e.g. spaceship C to event 2).PeterDonis said:You don't actually care how anyone's clocks are set, since you are measuring differences in clock readings, not absolute clock readings.
He's probably expecting that you will exercise some intelligence and not take everything he is saying exactly literally.obtronix said:that's not true he's saying you start the clocks simultaneously and measure time from that start
No, he has A (stay at home) and B (outbound) zero their watches as they pass, and C (returner) zero her watch as she passes B, and make a note of B's clock reading. B and C's times get reported to A, and their sum is the same as a single out-and-back traveller's total time. (At the 5.15 mark in the "no maths" video.)obtronix said:Well that's not true he's saying you start the clocks simultaneously and measure time from that start. (e.g. spaceship C to event 2).
Okay he doesn't say that but maybe he misspoke.Ibix said:No, he has A (stay at home) and B (outbound) zero their watches as they pass, and C (returner) zero her watch as she passes B, and make a note of B's clock reading. B and C's times get reported to A, and their sum is the same as a single out-and-back traveller's total time. (At the 5.15 mark in the "no maths" video.)
No you can't - all those measures are invariant. Your own diagrams show you that!obtronix said:But I could assume C at rest, perform similar SpaceTime interval calculations, and have them record the longest time.
My diagrams have acceleration in them! He's creating a "ghost being" that is jumping from one ship to the other without accelerating. So he's kind of adding apples with oranges intervals.Ibix said:No you can't - all those measures are invariant. Your own diagrams show you that!
No, they have instantaneous acceleration, which in your words would be a "ghost acceleration" as it's physically not possible.obtronix said:My diagrams have acceleration in them!
You are quibbling. There is no need for anyone to jump from the outbound to the inbound ship at the turnaround event. All that needs to happen is that the inbound ship records the outbound ship's clock reading as they pass each other. And, as has already been pointed out, that's what the video specifies.obtronix said:He's creating a "ghost being" that is jumping from one ship to the other without accelerating.
Spacetime geometry. As has already been pointed out, there is a triangle in spacetime with three sides, A, B, and C. The fact that A > B + C is just the spacetime version of the triangle inequality; we have > instead of < because of the minus sign in the spacetime metric.obtronix said:what makes A so different than B and C?
Yes, but that doesn't imply the other (wrong) claims you are making.obtronix said:Relativity says motion is relative.
You could define a different triangle in spacetime, sure. That would be a different scenario from the one we are discussing in this thread. And it would have a different relationship between the lengths of its sides. But that relationship would still be invariant, independent of any choice of frame.obtronix said:I certainly can make a situation where events start and stop on the C World line.
If he did, then so did you when you posed the scenario in your OP.obtronix said:He just arbitrarily picked A.
No, he's just copying information from one to the other.obtronix said:My diagrams have acceleration in them! He's creating a "ghost being" that is jumping from one ship to the other without accelerating.
The experimental setup. For example, A is the only one who sees the others as moving with equal and opposite velocities.obtronix said:If you think that's untrue what makes A so different than B and C?
Of course. But that would be a different scenario.obtronix said:I certainly can make a situation where events start and stop on the C World line. He just arbitrarily picked A.
Not a different scenario a different point of view, everybody will be traveling exactly in the same way, same speed same distance, just the handoffs of times will be different.With the original twin paradox thought experiment you get the same answer from everyone's perspective.Ibix said:Of course. But that would be a different scenario.
But not the proper times, because they are invariant. And that's what we're measuring.obtronix said:Not a different scenario a different point of view, everybody will be traveling exactly in the same way, same speed same distance, just the handoffs of times will be different.
And this one too. The triangle in the Minkowski diagram is identical to yours!obtronix said:With the original twin paradox thought experiment you get the same answer from everyone's perspective.
In which case whatever it is that you are calling "the handoffs of times" have no physical meaning and are irrelevant to the scenario.obtronix said:everybody will be traveling exactly in the same way, same speed same distance, just the handoffs of times will be different
According to the OP, ##\gamma = \frac{5}{4}##. Than means, the turnaround event of the "left spaceship" mirror (##\tau = 2##) has in the "left spaceship's" outbound rest-frame a simultaneity-line to the ##T= 2 \cdot \frac{4}{5} = 2- \frac{2}{5}## event of the (time-dilated) "left earth" mirror and (for symmetry reasons) in the "left spaceship's" inbound rest-frame a simultaneity-line to the ##T= 3+\frac{2}{5}## event of the "left earth" mirror.Lluis Olle said:If we draw the lines of simultaneous events for the "left spaceship" mirror, at the turnaround event there's a velocity discontinuity, and so we can draw two lines of simultaneous events, one line connecting with T=2, and the other connecting with T=3 (so to speak, obviously).
I'm not sure what "traveling-twin centered calculation" you are referring to here. Do you have a reference?FactChecker said:Looking only at the first and second derivatives, the problem is completely symmetric wrt the twins. One might think that a traveling-twin-centered calculation should be just as valid as the Earth-centered calculation. Yet the two calculations give conflicting answers.
Again, can you give a reference?FactChecker said:I have seen a calculation that used the traveling-twin-centered reference frame from beginning to end, took an acceleration profile into account, and came up with the same answer as the Earth-centered IRF calculation. That was intellectually satisfying.
FactChecker said:IMO, a lot of the "solutions" to the paradox are dodging the real paradox by changing the scenario so that the paradox is removed.
I think you are misidentifying the "paradox". The "paradox" is that the two twins have aged differently when they meet up again. But that "paradox" is resolved by spacetime geometry: the two twins follow different worldlines between the same starting and ending events, and those different worldlines have different lengths.FactChecker said:The real "solution" to the original paradox is to point out that the Earth-centered calculation uses an intertial reference frame whereas the traveling-twin-centered calculation is in an accelerating frame. Acceleration is the key in distinguishing between an IRF and a non-IRF. To explain the original paradox, acceleration can not be ignored.