I’ve only just learnt that the speed of light is really the speed of causality and I’m trying to understand it. I’m sorry if this is a stupid question but imagine I had a seesaw a lightyear long. I sit at one end and the other end lifts instantaneously. If someone was sat at the other end I would be lifting them faster than light could reach them. Their being lifted would be faster than the speed of causality. Is this wrong? Does one end of a seesaw dropping and the other end lifting not happen instantaneously with one another?
EDIT: Thank you to the people who have all responded so far. I can see that my thought that the two ends of the sawsee moving simultaneously with one another was the error in my thinking, and that the reason I thought this was due to scale and in reality a seesaw seems instantaneous but it’s not. Thanks again to those who took the time to reply and I’m grateful for your kindness.
In: Physics
The causality thing means more deeply that any sort of mechanism you dream up to try and send any form of information faster than light will inevitably fail due to other laws of physics. In any form of information transmission that involves the movement of objects, the factor that blocks information from moving faster is indeed that movement of physical objects propagates at (roughly) the speed of sound in that material, not instantly.
Like many such things, this is fast enough to be effectively instant in most systems humans will ever deal with, and so is usually approximated as being instant in engineering calculations to simplify things. But when things get up to the speed, size, and energy levels where the speed of light is relevant, all sorts of weird effects that we usually ignore at human-scale things become relevant.
Just like General Relativity is technically better than Newtonian Gravity at explaining how objects move in gravitational fields. Yet all of the space agencies and companies in the world use Newtonian in all of their calculation because it’s much simpler and accurate enough at the scales and energy levels of not only human-made spacecraft, but also planets, asteroids, and even most stars.
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