It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
When you push something you push the atoms in the thing. This in turn pushes the adjacent atoms, when push the adjacent atoms all the way down the line. Very much like pushing water in the bathtub, it ripples down the line. The speed at which atoms propogate this ripple is the speed of sound. In air this is roughly 700mph, but as the substance gets harder* it gets faster. For example, aluminum and steel it is about 11,000mph. That’s why there’s a movie trope about putting your ear to the railroad line to hear the train.
If you are talking about something magically hard then I suppose the speed of sound in that material could approach the speed of light, but still not surpass it. Nothing with mass may travel the speed of light, not even an electron, let alone nuclei.
*generalizing
There’s no such thing as a perfectly rigid object.
There was, but now I’m getting older and more tired
Have you spoken to your healthcare provider about Viagratm? It may be able to help with your issue. (Please seek immediate medical help with an erection lasting more than 4 hours).
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.
The idea that the velocity of a person walking forward on a train is simply the velocity of the train plus the velocity of the person walking with respect to the train is called “Galilean relativity”.
Einstein realized that Galilean relativity has a big problem if you take for granted the idea that the speed of light is the same for all observers, regardless of reference frame, and people had a lot of reasons at the time to suspect this to be true.
In particular, he imagined something like watching a train passing by him, but on board the train is a special clock which works by shooting a pulse of light at a mirror directly overhead which reflects back down and hits a sensor. Every time the light pulse hits the sensor, the clock ticks up by one and another light pulse is sent out. People usually call this the “light clock thought experiment” if you want to learn more about it.
Anyway, Einstein realized if he was watching the light clock as the train passed by him while he’s standing on the station, the path the light beam traces out will take the form of a zigzag. Meanwhile, for a person standing on the train, it will just be going straight up and down. If you know anything about triangles, you will realize that the zigzag path is longer than the straight up and down path. So if everyone observes the speed of light to be the same exact thing, it must be the case that it will take the light a longer amount of time to traverse the zigzag path. And so the person standing on the platform will see that clock ticking slower than the person on the train will. This phenomenon is called “time dilation”.
From this point, you can apply some simple trigonometry to figure out just how much slower things would be appearing to move on the train. And it turns out that the velocity the person watching the train observes the person walking on the train to have is not the velocity of the train plus the velocity of the person walking on the train. But rather, it’s something like that velocity, but divided by 1 + (train velocity)•(walking velocity)/c^2, where c is the speed of light (and this is called “Lorentzian relativity” if you want to read more about it).
It’s important to notice that since trains and walking come nowhere close to the speed of light, the value you’re adding to one is very small in these kinds of situations, and so what you’re left with is almost exactly the same thing you would get with Galilean relativity, which is why it still is useful and works. But when you want to consider the physics of objects that are moving much much faster, all of this is extremely important to take into account.
And lastly if you wanna read more about this stuff in general, this is all part of “the theory of special relativity” and there’s probably helpful YouTube videos covering every single thing that I’ve put in quotation marks.
Dang there goes my patent
Things get really unintuitive when you go near the speed of light. Einstein’s “Special Relativity” is describing that. Watch a couple of videos on the topic. It’s mindbending but seriously cool.
In short: The speed light is always constant FOR EVERY OBSERVER. That means, if you would hold a flashlight in a very fast moving train, the light would travel as the same speed for you as for a stationary person that is watching your flashlight from outside the train.
But how could that be? Aren’t you “adding” the trains speed to your flashlight? So shouldn’t the light in your train travel faster in your train? Or maybe slower? No. Light speed is always constant - but what is NOT constant is space and time. It is relative to the observer. Time and space can stretch/dilate to make up for what seems to be a paradox. E.g. your trains would shrink in length the faster you go. But it would look different to you than it does to an outside observer.
As I said, it’s mindbending, but there are a couple of cool and simple videos on the internet to get a better grasp on the matter.
That’s where time dilation will kick in
Relativity would prevent this. If the train moves at the speed of light, then nothing inside it will move because time will stop. The amount of trains inside trains doesn’t really change much except the effect of time dilation (slowdown) on each train. You can’t actually accelerate to the speed of light.
as a software engineer that watches too much youtube, this is the first time it’s clicked for me:
If the train moves at the speed of light, then nothing inside it will move because time will stop.
the pieces of information:
- time moves slower the faster you travel, and
- nothing can travel faster than the speed of light
have never been concretely connected in my head, but this makes a lot of sense now: time moves slower (for you) the faster you travel BECAUSE that’s the thing that stops you from moving faster than the speed of light… AND that holds true from all perspectives because it’s like… a trade-off?
Because of relativistic effects, from your point of view on the train you would just walk forward. But you would notice a strange effect while the trains were accelerating:
your atomically synchronized wristwatchthe clock you can see out the window has slowed down and stopped counting time. So it seems that your journey to the front of the train takes no time at all.From someone standing on the side of the tracks catching a glimpse of you and the train as you whizz by, the front of the train is moving at light speed. You’re at the back of the train completely frozen still, unable to move forward because the front of the train is moving away at light speed.
Weird things happen when you’re talking about the limits of physical reality.
your atomically synchronized wristwatch has slowed down and stopped counting time.
Wait, surely time would move at a normal speed within your own reference frame. The act of you walking to the front of the inner-most train you are in would be a normal occurence to you, but if you looked out of the window you would see a completely frozen scene.
Only once you measure time afterwards with an observer would you notice the gaping time difference.
You are correct, I should have said there was an atomic clock out the window that the walker looked out at.
Not a science nerd. But I would assume the inner trains would like to push forward, stealing some kinetic energy from the outer train because it pushes itself away from the outer train and making the outer train slower or even push back.
That’s a great guess when you try to answer the problem with traditional (Newtonian) physics. However, space and time do not behave in a way we would expect when we go nearly at light speed. So Newtonian laws do not apply in the same sense anymore.
Perfectly rigid sticks don’t exist.
Matter is made of atoms. Things are only truly rigid in the small scales we deal with usually.
I predict we’ll have FTL travel before we can invent a stick that’s “unfoldable”.
A wooden stick is pretty much unfordable in an unaltered state Or a glass stick
Glass easily bends
Next, I suppose you’ll want to know about the speed of dark 🤨
Damn it even on Lemmy I can’t get to the comments before someone else has the samr idea as me ahaha
The problem lies in what “unstretchable” and “unbendable” means. Its always molecules and your push takes time to reach the other end. You think its instantaneous because you never held such a long stick. The push signal is slower than the light
I would liken it to a long freight train starting to move. Once the front starts moving, it will still be a minute before the back starts moving. The space between the train couplings is like the spring effect between atoms, or something.
You think its instantaneous because you never held such a long stick.
Speak for yourself! 😏
Tbh I thought someone would make that joke when i wrote it lol
Is it instantaneous though?
Basically the speed of sound in that material
Probably wiggly wiggly
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.
Go find a 30’ stick and let us know if you can point it at the moon.
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.)
EDIT: It’s in Polish, but it’s still a good video.
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/
Actually, the thing that applies to the pole is the speed of sound (of the pole material), which is the speed the atoms in the pole move at. Not even close to the speed of light.
Yeah, everyone else had already answered that, which felt like we’re picking apart that specific thought experiment, even though there is actually a much more fundamental reason why it won’t work.
Correct answer is here.
I think relativity demonstrates that light does have mass?
They might not have “rest mass” but they do have mass!
The eclipse experiment proved it, solar sails whilst hypothetical demonstrate it.
Relativistic mass is not helpful to our everyday understanding of mass, it’s more helpful to discuss momentum, like the other commenter pointed out
Photons don’t have mass, but they do have momentum.
If you’re openminded enough to listen to those who disagree with the standard model,
take an elastic band and turn one end. Instead of the band turning, you’ll have a twist in your band
and it takes time to unravel the twist if you let go on the other end.
That’s what will happen to the stick and this travels at lightspeed,
because this is how light works. Light works like ‘the stick’ in your example.
And if you try turning it faster the ‘elastic band’/stick/‘atom on the other end’ starts breaking.If you need FTL communication, then use gravity…somehow.
Probably quantum entanglement, which we (and certainly I) don’t fully understand yet
I think the standard model says the same thing, tbh…
The problem is that when you push an object, the push happens at the speed of sound in that object. It’s very fast but not anywhere near the speed of light. If you tapped one end of the stick, you would hear it on the moon after the wave had traveled the distance.
For example, the speed of sound in wood is around 3,300 m/s so 384,400/3,300 ~= 32.36 hours to see the pole move on the moon after you tap it on earth.
Wow, TIL that the speed of sound has this equivalence
It’s also why rocket nozzles can’t be infinitely thin :)
I swear I’ve seen a video of someone timing the speed of pushing a very long pole to prove this very thing. If I can find it I’ll post it here.
*Found it! https://www.youtube.com/watch?v=DqhXsEgLMJ0 I can’t speak to the rigorousness of the experiment, but I remember finding it enlightening.
AlphaPhoenix is definitely one of the best scientists on YouTube, that video is good.
Cool vid, thanks for sharing
Your math is off. The Moon is about 384,400 KILOmeters from the Earth, not meters. So 116,485 seconds, or a bit over 32 hours.
Oh right. I’ll edit my comment
Damn, so that means no FTL communication for now… 😅
Hear me out… What about a metal stick?
🤘
Metal is a lot heavier than wood. You’d never be able to lift it to the moon.
You should make it out of feathers. Steel is heavier than feathers.
But can you lift it from the moon? Gravity is a lot lower there.
Large if factual
NASA: “Hold my beaker.”
What if you had a crane?
Or a duck.
Or hope
For now
deleted by creator
deleted by creator
Exactly
