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
Yeah the others are right the key is the seesaw isn’t actually instantaneous. Everything has *some* flex, and the flex moves at the speed of sound in that material. Even if you just pushed straight on the end of a steel rod, the far end doesn’t move ahead instantly, it compresses and the compression moves along the rod at the speed of sound in steel and the far end extends when the compression wave gets that far.
Gravity and light don’t have a physical material so the “flex” moves through them at speech c.
You know how light from the sun takes 8 mins to get here right? Well that means if the sun instantly disappeared from existence, not only would it still be bright in Earth for 8 minutes, but we’d also continue orbiting the spot where the sun used to be for those 8 minutes as well! Then it would simultaneously go dark and Earth would fly off in a straight line as the lack of light and gravity both reached us.
Latest Answers