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Re: [Phys-l] how to prove relativity



I assume you agree that when a ruler has been rotated,
"the" length of the ruler (i.e. the proper length) is
not changed. If this is a false assumption, please
explain.

By the same token, when a ruler has been boosted, "the"
length of the ruler (i.e. the proper length) is not changed.
Right?

And when a clock has been boosted, "the" time between
ticks (i.e. the proper time) is not changed. Right?

It may be that the /projection/ of the length onto this-
or-that reference frame is changed. It may be that the
/projection/ of the time onto this-or-that reference
frame is changed. But the shadow of a thing does not
behave the same as the thing itself.

Thanks for a great discussion, JD! But when I think about communicating relativity to a layperson, I need help still on one sticking point (down below, after this summary):

distance != path
easy to visualize with the ruler/odometer pairing
clock is not to ruler; clock is to odometer; clock ticks are to ruler

It is easy to convince someone in the example of spacelike distance. We start with rulers that we can agree are the same. When we go on a trip and arrive at the same distant location, our odometers may differ because of path. When we again compare rulers at that distant location, they are still the same, and nothing seems suspicious.

With the convincing arguments in hand, we actually have a good chance here to convince our correspondent that (although we made sure our clocks read the same time, and ticked the same, before we started) there is also nothing suspicious about the fact that at our distance location, the clocks do not read the same time. That is, that time also "follows a path," in layspeak. This is a pretty nice triumph by itself, but there is the one issue remaining: one of us is in fact older (demonstrably, unquestionably so if we take the appropriate trip).

Although when we ended the trip and compared rulers, they were still identical, and when we compared clock ticks at the end of the trip, they were still identical too, even while the odometers and times were different, there remains, in the layperson's eyes, this one amazing asymmetry: one person is actually older (without, for example, also being shorter).

The OP was about a layperson who would not accept relativity. I'd bet that the arguments laid out here (even without data) would be extremely persuasive, except for this one last part (the aging). And what do we then have left:

1. Talk about esoteric evidence (eg muon lifetimes or accelerator operation) that they will resist?

2. Try to convince them that our aging must also be dictated by some biological clock that simply cannot work differently (proof by blatant assertion)?

3. Merely quote Minkowski, that we must abandon space and time and combine them instead into spacetime?

OK fine, fair enough, perhaps that *is* all we got. More than enough for us, but in every discussion I can imagine with a layperson, I'll lose them at the very end of what is otherwise a brilliant presentation.

Any suggestions on how to resolve, other than the 3 points above? It occurs to me in pure speculation that maybe we have to abandon the deeply human paradigm of aging itself. To replace it with what though - anything?


Stefan Jeglinski