Recent content by JVNY

I agree entirely. The cartoon accepts that the pitcher can throw the ball at 0.9c without using infinite energy. But even so, 0.9c plus 0.99c does not result in the ball traveling at c or greater relative to the batting machine as the ball passes it -- even without worrying about what would...

Here is another try at asking expell's question. Consider a batting machine and a pitching machine in a vacuum. There are no atmospheric particles to strike anything as described in the comic. Someone expends nearly but not quite infinite energy to accelerate the batting machine to 0.99c...

Thanks.

OK, thanks. A.T., how is the cylindrical scenario modeled? Does it yield the same physical observables?

Agreed. However, if lightning later strikes again simultaneously in S at the left side of the rectangle and the right side of the rectangle, the result will again be the same; the rectangle will be 32 long on each side in S, for a total perimeter of 64, and the entire train will have 64 length...

Here is a Minkowski diagram of the train in the rectangle, with the worldline of each point on the train stopping when it hits the track rectangle's right side (TR). For simplicity, the diagram does not show the worldline of the rectangle's left side. The diagram reflects inertial frame S in...

That is fine. Let's stick with that for the moment and then go on with the analysis of the train in the rectangle.

Start with Einstein's train and platform example. A train passes a platform. Simultaneously in the platform frame, lightning bolts strike the left side of the platform (L) and the right side of the platform (R). Platform observers know that the strikes were simultaneous in the platform frame...

Right. I disagreed with the statement "There is no way for the train riding observer to measure the length of the train 'all at once.' Just as Einstein measures the train passing the platform all at once (platform time), an observer on the segment RM can measure the length of the segment NF...

By "this" I mean your statement that "some questions we are used to asking, like 'what is the length of the train?' . . . do not have unique answers." I agree that there is not a unique answer to the question "what is the length of the train?" There are many correct answers. One correct...

On this we disagree. The segment RM is simply the platform in Einstein's example, and segment NF is the train. If two bolts of lightning strike simultaneously in the inertial RM frame at RM time 113.33 between sides A and B at points R and M, then the one on the left will scorch R and F, and...

PeterDonis, I think that we actually agree except perhaps on language. You write: I wrote: So we agree that the train's proper length is 100. You wrote: I wrote: So we both agree that the two segments are 32 each, thus the sum of the segments is 64. As to this sum, I wrote: Of...

Agreed. So my goal is more limited, which is to be able to understand and demonstrate what might be true about the two different theories of why the rotating disk is non-Euclidean (circumference larger v. shorter than 2 pi r). The circular barn/pole discussion supports Einstein's conclusion...

Yes, it is a derived result. It is an extension of the prior thread of the circular barn/pole linked in Ibix's response 3 above. The group agreed that if a one spatial dimensional train is shunted into a circular track then its proper length is unchanged as it becomes a circle and travels...

Here is a link to a classic article by Rossi and Hall. It has summary data from their experiments. http://www.physics.princeton.edu/~mcdonald/examples/EP/rossi_pr_59_223_41.pdf Here is a link to an online simulator from the King's Center for Visualization in Science that let's you re-run the...