Fun with spacetime diagrams

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Re: Fun with spacetime diagrams

Postby ralfcis on August 28th, 2017, 8:53 am 

Bangstrom,
I'm interested in what you're saying but don't quite grasp the context of c being a dimensional constant. I get that length is a dimension and time is a dimension but you're somehow saying c is something more than just length over time? Wouldn't that make it a dimensionless constant if it's not dependent on dimension?

I know something's not quite right where in the M-std light is always 1 light distance over 1 light time but in the E-std the speed of light varies with the relative velocity between 2 spacetimes plus it's infinite in its own spacetime. It has no units in either but in the M-std I've seen it necessary to consider 1 ly/yr as units for c. Of course musings like this just provoke Jorrie to close down threads without providing any relativistic explanations, if they even exist, for these questions. The forum administrators are content to remain silent.

P.S. If I ever feel like getting back into understanding relativity, I'm going to start a thread in the PHYSICS forum about relative velocity. If Alice leaves earth at .8c, she goes 4 ly in 5 yrs earth time but if Bob and Alice both leave earth in opposite directions at .5c, their relative velocity is still .8c but they separate 4ly in 4 yrs earth time. The relative velocity's the same but the dimensional velocity is not? Is this what you're talking about?
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Re: Fun with spacetime diagrams

Postby ralfcis on August 29th, 2017, 10:01 am 

Oh no, I've moved back into Dave Oblad's absolute relative velocity universe. I've been thinking about pure relative velocity and there's no need for it. There's no need for a universally synchronized Earth time clock network so there's no need to express velocity relative to it. Proper time is universal within each frame and the accuracy of atomic clocks being a physical invariant allows us to trust atomic clock readings without needing to compare them to a master clock. Proper distance can be established when frames are stationary relative to each other. That's not even a requirement as stationary distance info can be messaged to a moving frame, it does not have to physically experience it.

So if a ship from earth takes only 3 yrs of its own proper time to travel to a planet 4 ly away, it can be calculated, using relativity, that its Minkowski-std relative velocity to Earth is .8c and its Epstein-std relative velocity is 1.25c since velocity in an E-std is not limited to c. But this brings back the huge problem of the age difference between a flyby of the distant planet and a stop there. There can be no aging difference between 2 inertial frames in a flyby even though the ship has flown by the 4ly miarker in 3 of its years.

I can't get past this paradox using relativity: the ship's clock clearly reads it has aged 2 yrs less than it should have at the 4 ly marker but it doesn't count unless the ship stops there? I can only understand it using ralfativity: age difference can only occur, between the participants, when there is a relative velocity mismatch that is unknown to one of them because of the speed of light delay. This means the propagation delay of any change causes age difference, not just a stop. The rate of age difference also occurs smoothly during the info delay interval. If relativity can show me the same behavior, I'd be more inclined to accept it.
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Re: Fun with spacetime diagrams

Postby ralfcis on August 29th, 2017, 5:30 pm 

Hmmm I got some glimmer of insight from a new physics post about c. In the E-std, the faster your gamma velocity Yv, the longer it takes for your light message signal to reach the other participant. So as your velocity approaches infinity using your proper time and the other's proper stationary space, the time for information transfer back to the other participant also approaches infinity. So the E-std is offering an alternative explanation of the trade off between c and relative velocity as an information transfer trade off rather than a spacetime contraction to maintain constant c for any relative velocity as is shown in the M-std. Just spitballin', this has not been explored yet.
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Re: Fun with spacetime diagrams

Postby BurtJordaan on August 29th, 2017, 5:36 pm 

ralfcis » 29 Aug 2017, 16:01 wrote:There can be no aging difference between 2 inertial frames in a flyby even though the ship has flown by the 4ly miarker in 3 of its years.

And the other party of the "2 inertial frames in a flyby" has flown by the ship's 4 lyr marker in 3 of its years. Completely reciprocal, as it should be for any two fully inertial frames.

Your problem still seems to be not defining the scenario properly and then tackling it with assumptions that do not hold for the scenario. Or it is so ill defined that answers are impossible. I said before: define the scenario and the question properly, then think through relativistically, then calculate (or draw a STD) and finally make a conclusion...
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Re: Fun with spacetime diagrams

Postby ralfcis on August 29th, 2017, 8:36 pm 

And the other party of the "2 inertial frames in a flyby" has flown by the ship's 4 lyr marker in 3 of its years. Completely reciprocal, as it should be for any two fully inertial frames.


You say this every time like it's my first time seeing it. The reciprocal time is not using the same clocks. There are 2 different clock networks and 2 different pocket watches. If Alice is not being followed through space by her proprietary clock network, then there is no reciprocal time measurement data. Even if there were, it does not cancel out the fact that Alice will see her pocket watch at 3 yrs and the external earth network clock she passes at the 4 ly mark at 5 yrs. Yes I get the fact that the invariance of the light-like spacetime interval will yield the result that Alice has actually aged 5 yrs unless she comes to a stop. I'm just paraphasing what you told me in the thread you didn't shut down. Maybe you could just show me the math proof which should be easy and would make me more sure of what I am saying. s2= (ct)2-x2.

I already went through an extensive STD analysis in another thread. Whatever Bob or Alice do does not affect the result that at the flyby, a clock comparison yields Alice = 3 and Bob =5. Bob can make a move that will allow him to overcome this disadvantage and eventually end up younger at the end of the spacetime interval but it still does not effect the result at the 4 ly mark. You don't even need to do the analysis with 4 clocks. you could arrive at the same result using light signal messaging or seeing how the tv image is reciprocally slowed at each ship.
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Re: Fun with spacetime diagrams

Postby phyti on October 18th, 2017, 4:02 pm 

ralfcis;
spacetime graphics are fun and instructive. They depict multple relations better than text.
Keeping them simple and uncluttered is key.

Showing clock synchronization via Minkowski.

Calibration curves (as labeled by Max born in his book on Relativity) are used to show clock synchronization. A and B agree to synch clocks at separation, and send signals (blue) at (.68) local time. The return signals include the remote clock reading (1.00) and return at local time of (1.47). We can conclude the A and B clocks will remain synched while maintaining their constant speeds.
Per the SR synch convention) (red) A and B assign the remote reading of (1.00) to a local time of half the round trip time. For both observers, the assigned local time is later than (1.00). Each concludes the other clock is running slower than their own clock, i.e. perceived doppler effects
Attachments
sync signals.gif
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