Asklemmy

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.

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

Objects like an unbreakable stick are still composed of atoms suspended in space and held together by the fundamental forces of nature. When you push on one end, the other end doesn't immediately move with it but rather the object experiences a wave of compression traveling through it. This wave of compression travels faster than we can perceive but still cannot travel faster than light.

Look up why arrows bend after they've been released by a bow, it's essentially the same mechanic.

There's a bunch of these thought experiments that try to posit scenarios where C is violated.

Here's one I remember from uni involving scissors. Similar to what OP was thinking, but really really big scissors.

At this scale, the stick isn't as solid as your intuition would lead you to believe. Instead, you have to start thinking about the force at the atomic scale. The atoms in your hand have an outer shell of electrons which you use to impart a force to the electrons in the outer atoms of the stick on your end. That force needs to be transferred atom to atom inside the stick, much like a Newton's Cradle. Importantly, this transfer is not instantaneous, each "bump" takes time to propagate down the stick and will do so slower than the speed of light in a vacuum. It's basically a shockwave traveling down the length of the stick. The end result is that the light will get to the person on the other end before the sequence of sub-atomic bumps has the chance to get there.

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

This is actually a great example for why that stick must not exist.

You can also do this with a unbreakable stick and an unbreakable shorter tube. Throw the stick at a high velocity through the tube and it contracts for the point of view of the tube. Then close it shut. Now you have a stick that's longer than the tube fully contained in it.

Well no. As others have said the force in the pole will travel at the speed of sound.

Though if you were to wiggle the flashlight back and forth really fast the spotlight on the moon would travel "faster" than the speed of light.

Think of it like this. If our universe is a simulation, then the speed of light is the maximum speed at which information can propagate through reality. We know that for anything to move through space, it must move from one adjoining position to another, then another, then another, incrementally. Each one of those increments takes, at minimum, one 'tick' of the universe. That's one tick to increment each bit of information, that is, the position of something moving at light speed from position x,y,z to x+1,y,z. Light moves as fast as the universe allows; if there was a faster speed, light would be doing it, but it turns out that our universe's clock speed only supports speeds of up to 299,792,458 meters per second.

What you have here is sound. Motion propagates through material, at its fastest, at the speed of sound in that material. That's part of the reason why moving large scale objects quickly gets weird.

Edit: to be clear, I am not making the case that we're in a simulation. I'm only trying to use computers to make it relatable.

This doesn't account for blinking.

If your friend blinks, they won't see the light, and thus would be unable to verify whether the method works or not.

But how does he know when to open his eyes? He can't keep them open forever. Say you flash the light once, and that's his signal to keep his eyes open. Okay, but how long do you wait before starting the experiment? If you do it immediately, he may not have enough time to react. If you wait too long, his eyes will dry out and he'll blink.

This is just not going to work. There are too many dependent variables.

How heavy would a stick of this size weigh?

Ok so since there's a bunch of science nerds on here and I'm sleep deprived I'm gonna ask my dumb ftl question.

If you're on a train and you walk towards the front of the train, your speed measured from outside of the train is the speed of the train (T) plus the speed of you walking (W).

So if there was a train inside of that train, and you walked inside of that, you'd go the speed of the outside train, plus the speed of the inside train, plus your own walking speed.

So what if we had a Russian nesting doll of trains, so that the inner most train was, from the outside, going as fast as light and you walked towards the front? Wouldn't you be going faster than light if you measured your speed from the outside?

Didn't come at me with how hard it would be to build a Russian nesting doll of super trains it's a hypothetical and I'm tired.

Go find a 30' stick and let us know if you can point it at the moon.

Putting it on the moon is just a distraction. It doesn't matter if the rod is 1m long or 100,000km.