# Experiment to test the basic assumption of SR

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Now, this is one of many examples where considering time dilation alone is not enough. You also have the relativity of simultaneity. There is actually a nice paradox here (better than the twin paradox in my view). If you can resolve it, you go a fair way to understanding SR.

However, sadly, I can see from this and others posts that you have chosen the path where "relativity must be wrong" and "I'm going to disprove it".
No I'm questioning it. I'd be more than willing to see a counter-argument to my own. I understand how simultaneity comes into this.It builds up a huge bank of time that is created when the twins separate. This bank of time can only be cashed in once the twins reunite. This still doesn't explain why during the outbound journey, I believe experimental evidence will show that the relatively moving party will be aging slower without having to go back to the starting point.

But this is a critically different scenario from your rocket one. In this case, the planes set off from one location and returned to it. They are able to unambiguously compare their clock readings at both start and end of the journey and agree that they started at the same time, and that they arrived at the same time. They will also agree that they were under acceleration at all times.

A simpler version of the above is a space station with two ships that set out at high speed in opposite directions and then return. In this case they will both agree that their clocks will end up showing the same time, although their reasoning for why this should be will be different for themself and for their opposite number. You should try it with maths.

However, in your spaceship scenario the ships start out separated so do not have an unambiguous way to determine whether or not they started at the same time. This is the mirror image of your one-way trip to Pluto, of course.

I am not wrong. I strongly suggest that you deploy some maths instead of hand waving.
Ok I've tainted the evidence. a bit because relativity CAN handle reunification scenarios. My point is when there's no reunification, relativity says there can be no determination. My experiment, with the one way spaceship to the station or the one way trtip to pluto or the outbound hafele-keating plane says the clocks WILL have a reading. If relativity is right, the reading will show from the ship's perspective, that the relatively stationary point's clock will be slower than the ship's clock. I say, if the experiment is done, the opposite will be true. I guess we'll never know for sure.

Dale
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I'll give you an example of why it's not wrong. Consider 2 planes in a hafele-keating experiment doing orbits from pole to pole to avoid the spin of the earth making things more complicated. Now if the planes fly together, their relative velocity is zero and both will have dilated equally relative to the earth clock once they return to the pole. They will not have dilated with respect to each other. Now asssume both take off in opposite directions from the pole. Their relative velocity has doubled with respect to each other however their timedilation with respect to the pole clock must be the same as in the first scenario. Now their clocks can't differ in respect to each other so even though their relative velocity went from 0 to double their individual speed, their relative time dilation has not changed at all, it is still zero.
The GPS system does this experiment continuously with 24 satellites all moving in one of 6 different orbital planes. Of course, this is a GR experiment, not a SR experiment.

Orodruin
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This is a thought experiment. Any extraneous physical results can be nullified and accounted for. The importance of the Pluto experiment is that the twin paradox shows that the away twin will age slower only if it turns around and returns to his twin. Before the turnaround, relativity forbids one from making a judgement on who is actually aging slower because they must both see each other as time dilating. The trip to Pluto is a one way trip. There is not turnaround or reunification. Hence, the twin paradox cannot be used to determine the away twin is aging slower because he will never return. But I'm saying during the journey, the clocks can be compared. Relativity states the Pluto bound twin will not see our clocks as going faster than his, he must see our clocks as going slower. But once he reaches pluto we can ask him how old he is and we can tell him how old we are and he will not have aged as much. Now how can relativity reconcile that? Proof of age.
You are focusing way too much on the word "see". What we talk about when we talk about time dilation is a set of globally synchronised clocks in a given inertial frame and how moving clocks behave in relation.

Once the Pluto traveller has reached Pluto and is again at relative rest there is a common inertial frame for him and the Earth, namely the Earth rest frame. It is different when the Pluto traveller is moving wrt to the Earth because they are referring to a different set of synchronised watches. What people actually see is more related to the doppler effect than to time dilation.
Ok I've tainted the evidence. a bit because relativity CAN handle reunification scenarios. My point is when there's no reunification, relativity says there can be no determination. My experiment, with the one way spaceship to the station or the one way trtip to pluto or the outbound hafele-keating plane says the clocks WILL have a reading. If relativity is right, the reading will show from the ship's perspective, that the relatively stationary point's clock will be slower than the ship's clock. I say, if the experiment is done, the opposite will be true. I guess we'll never know for sure.
Yes, the clocks will have a reading, but the bottom line is that what the simultaneous reading on the other clock is will depend on the inertial frame. You do not have a well defined simultaneity definition for separated events.

Dale
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they must both see each other as time dilating
This is already confirmed by experimental tests of the relativistic Doppler effect. The Pluto bit and the spacecraft bit are cosmetic differences only.

I understand how simultaneity comes into this.It builds up a huge bank of time that is created when the twins separate. This bank of time can only be cashed in once the twins reunite.
Uh, no. The relativity of simultaneity is not a bank that builds up and it is not cashed in nor limited to when the twins reunite. In fact it is almost the opposite. The relativity of simultaneity is critical to understand when comparing spatially separated clocks which are not reunited.

My point is when there's no reunification, relativity says there can be no determination.
No, it says that the determination is frame dependent.

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Why are we engaging ralfcis? We already had a thread locked because, well, let me just quote Jedishrfu

The goal here is to strip away the various wrong preconceptions and misinterpretations that people latch onto in trying to understand Relativity theory and begin to see the real physics behind it all. This can only be done with an open mind and a desire to learn what others have discovered in their pursuit of this rich theory of physics.

We're right back in the same mess. Repeating the same arguments to someone who won't accept them is wasting everyone's time.

PeroK
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Ok I've tainted the evidence. a bit because relativity CAN handle reunification scenarios. My point is when there's no reunification, relativity says there can be no determination. My experiment, with the one way spaceship to the station or the one way trtip to pluto or the outbound hafele-keating plane says the clocks WILL have a reading. If relativity is right, the reading will show from the ship's perspective, that the relatively stationary point's clock will be slower than the ship's clock. I say, if the experiment is done, the opposite will be true. I guess we'll never know for sure.
To make the maths easy, let's have a ship set out from the Earth to a space station one light hour away, travelling at 0.6c. At the time (according to the Earth) that the ship reaches the station, Mission Control hosts a celebratory party. This gives us three events. Working in the frame of the Earth, these are:
• Departure, D, which occurs at ##(x,t)=(0,0)##
• Arrival, A, which occurs at ##(x,t)=(1,5/3)## (we're measuring time in hours and distance in light hours)
• Party, P, which occurs at ##(x,t)=(0,5/3)##
What does the ship determine will have happened? You need to Lorentz transform each event into the coordinates of a frame moving with velocity v=0.6c in the +x direction. This gives us:
• D', which occurs at ##(x',t')=(0,0)##
• A', which occurs at ##(x',t')=(0,5/3)##
• P', which occurs at ##(x',t')=(-5/4,25/12)##
So now we can describe how each party describes the trip.
• According to the Earth, the ship took 1 hour and 40 minutes to cross the distance. Due to time dilation, its clocks only read 1 hour and 20minutes.
• According to the ship, the crossing took 1 hour and 20 minutes (in fact, the ship stayed still and the station came to it). For some reason, Mission Control decided to throw a party two hours and five minutes after launch.
Actually your scenario is a little more complex because you are expecting to stop at the station - but you are talking about what happens in flight, so I'm supposing that the ship just does a flyby of the station and continues on. The point is that both descriptions are self consistent and consistent with one another. Neither is quite what the observers will see because we have not factored light speed delay in to work out when they see what they see, but you can do this if you wish. The point is that A' and P' are not simultaneous, so the ship has no problem reconciling the Earth's slow clocks with the "arrival" party - Mission Control held the party late.

DrClaude
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