Obviously theoretical but if I took a light year long stick and say pushed a button at the other end would that button be pushed at the same time for me as say someone standing at the button? How does the frame of reference work when physically moving something? And could that “work” as a method of instant communication?
In: Planetary Science
Your “stick” would act more like a tube full of balls in such scenario on molecular level. And you can probably imagine that a lot of pushing energy will get lost by each colliding ball. So, some way in, some or all the force is gone. So you’re not pushing entire stick, just part of it, because materials can compress and expand, even ones that look very stiff to us – like steel or tungsten.
To be able to push such a long stick, it has to infinitely stiff. Which is already science fiction – a tube filled with water would one of better options maybe, since water is quite hard to compress – but even water might act in unknown ways over such distance. And the force you have to apply would be insanely bigger than “move a stick to push a button”. And your stick has to not disintegrate from such force applied to one end. We know what insane forces do – breaks molecules apart, generates a lot of heat, etc. This would all likely happen.
And then, it would about speed of sound, (if not less), for push to propagate through your stick, as other have responded.
Technically, we do sort of “stick pushing” at closer to speed of light on a daily basis—it’s called electric cables. However, instead of pushing the entire material, we’re pushing electrons, and they’re “pushed” by electric fields (created by voltage), not by kinetic force. Just like your insanely long stick has to be very stiff and initial force high, electricity needs to be converted to higher voltage if we’re to carry it over bigger distances. That’s why we have high voltage towers and transformers. Roughly same idea applies: some electricity gets dissipated along the way (it heats cables due resistance in wires), so it’s wiser to pump “more” in to account for that.
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