Asklemmy

Perhaps also worth pointing out that the speed of light is that exact speed, because light itself hits a speed limit.

As far as we know, light has no mass, so if it is accelerated in any way, it should immediately have infinite acceleration and therefore infinite speed (this is simplifying too much by using a classical physics formula, but basically it's like this: a = f/m = f/0 = ∞). And well, light doesn't go at infinite speed, presumably because it hits that speed limit, which is somehow inherent to the universe.

That speed limit is referred to as the "speed of causality" and we assume it to apply to everything. That's also why other massless things happen to travel at the speed of causality/light, too, like for example gravitational waves. Well, and it would definitely also apply to that pole.

Here's a video of someone going into much more depth on this: https://www.pbs.org/video/pbs-space-time-speed-light-not-about-light/

What about the speed of the earth's rotation though, could that fuck up the stick holding?

always had this question as a kid

And then went, draw it out, and asked.
I applaud that (and the art), good for you.

(And the good people already provided answers.)

I predict we'll have FTL travel before we can invent a stick that's "unfoldable".

That would not work. Pushing an object is transmitting kinetic energy to it. The object will push back, and energy would not be distributed to the whole object at the same time.
If the object cannot be altered in any way, then the energy would not be transferred to it, and if it has enough plasticity to absorb the kinetic energy, it would be spread in a wave to the tip. A wave that would always be slower than light.

Now stop fooling around and give Ruyi Jingu Bang back to Sun Wukong.

So folks have already explained the stick, but you're actually somewhat close to one of the ways you can sort of bend the rules of FTL, at least when it comes to a group of photons.

Instead of a stick, imagine a laser on earth pointed at one edge of the moon. Now suddenly shift the laser to the other side of the moon. What happens to the laser point on the moon's surface?

Well, it still takes light speed (1.3 seconds to the moon) for the movement to take effect, but once it starts, the "point" will "travel" to the other side faster than light. It's not the same photons; and if you could trace the path of the laser, you'd find that the photons space out so much that there are gaps like a dotted line; but if you had a set of sensors on each side of the moon set up to detect the laser, they would find that the time between the first and second sensor detecting the beam would be faster than what light speed would typically allow.

It's not exactly practical, and it's such an edge case that I doubt we can find a good way to use it, but yeah; FTL through arc lengths can kind of be a thing. At least if you tilt your head and squint funny at it.

Matter is made of atoms. Things are only truly rigid in the small scales we deal with usually.

I'm not a scientist, but when I asked the same question before they said, "compression."

Like, the stick would absorb the power of your push, and it would shrink (across its length) before the other end moved. When the other end does finally move, it's actually the compression reaching it.

Next, I suppose you'll want to know about the speed of dark 🤨

Move a sheet up and down rapidly

You can see the wave travel across it

Because you put the apostrophe in the wrong place?

Short version: forces applied to solid objects move at the speed of sound in that object.

Lets say your stick is made of steel. The speed of sound in steel is about 19,000 feet/second. Assuming you could push hard enough for the force to be felt on the other end, it'd take over 18 hours for your partner on Earth to feel your push from the moon.