Can someone smart or good with physics answer this dumb Q I came up with?

[PlasmaBomb]

Something I've been thinking about.

I'm on Earth, and there is this star 2.5 light years away. I have this stick that's exactly 5 inches short of 2.5 light years long (or appx 18 trillion miles long) and it's pointing at the star.

It's only 5 inches away from touching the star's surface. If I extend my arm with the stick and touch the star, how long would that take?

Same time as it took my arm to extend forward (few seconds)?

If so, did that stick just travel much faster than speed of light?

For the sake of argument, both the earth and the star aren't moving and the distance between them is static.

[edit] words.

The stick only moves 5", so unless you can move it 5" in under 0.423626401 nanoseconds you won't be breaking the speed of light, and to be honest you are much more likely to achieve that with a smaller stick... lol

 

[PlasmaBomb]

It would take more than 2.5 light years for the stick to touch the star.


Your stick is not an absolutely incompressible solid. It's made of protons, neutrons, and electrons.

A light year is a measure of distance not time...

 

[zinfamous]

'the fuck? What is with the answers of 'well, if we assume the stick is perfect, it would distort.' Uh...no. You're negating the point of qualifying that the stick, being an impossible fictional item, has its own properties that are in line with the behavior of any 'normal' stick. I.e. you're not worried about the mass of the stick causing it to compress when you push it. Especially because that thought would be to invite gravity to the party, and the gravitational forces at play are essentially incalculable.

This makes me want to punch babies.

The stick moves, people, just like my penis did into your moms.

you're funnier when you post under the Alkemyst handle.

 

[WelshBloke]

you're funnier when you post under the Alkemyst handle.

 

[TwiceOver]

If you were standing on top of a train that was moving at the speed of light and you stepped forward, for that moment, would you be moving faster than the speed of light?

 

[edro]

If you were standing on top of a train that was moving at the speed of light and you stepped forward, for that moment, would you be moving faster than the speed of light?

Yes, you would; but you can't.

 

[Gibsons]

you're funnier when you post under the Alkemyst handle.

Yeah, but he had sex with your mother. Mine too, I think. :\

 

[flexy]

If you were standing on top of a train that was moving at the speed of light and you stepped forward, for that moment, would you be moving faster than the speed of light?

No you would not. If you presume you could it shows you didn't grasp what Einstein actually said, the fundamental law that nothing can go faster than light. LS can not "add up", you cannot shine a light from a spaceship and then have the light 2x the speed of LS.

 

[phucheneh]

If you were standing on top of a train that was moving at the speed of light and you stepped forward, for that moment, would you be moving faster than the speed of light?

Assuming it was possible for a train to move at the speed of light and there was no air or other forces to resist your movement (i.e. another 'what happens if we ignore reality' question)...

The basic answer is that special relativity and quantum mechanics trump Galilean/Newtonian relativity. You just can't make the ball go faster than the speed of light, Newton be damned. Picture Rick James shouting 'fuck your reference frame' right here.

At least, I think that first sentence would be how to describe it. I've always been confused by the use of 'general' and 'special' relativity to refer to related principles. It seems like it should be that 'general' relativity is the standard principles we use on a daily basis (where reference frames matter), and 'special' relativity is the exceptions. But it's not, so you have to use 'Newtonian' or some such to describe the more basic stuff.

 

[Mark R]

Right, so it's not instant.

Your push would travel at the speed of sound through the stick.

During the time when your arm has gone forward and the end of the stick has not, the stick will be compressed by the force of your movement

This sounds very weird, but not all things in physics scale up in size as your "gut" would tell you. A super long stick would not act rigid, it would be very flexible and soft.

That's why a domestic cat has slender, delicate legs, but a lion has chunky legs in comparison to its body. They both have the same body plan, but by scaling up the cat to a lion, the stress on the legs (body weight) increases faster than the strength of the legs increases with scaling - the result is that the legs must bulk up more than the body, otherwise they would be too weak and would collapse.

 

[drinkmorejava]

There are some aircraft engineers that would like a word with you.

Or would you stick by a claim that a jet engine cannot possibly push an aircraft past the speed of sound without it collapsing? 'Cause that's what you're saying. To propel a plane at mach 2, you would physically be shoving the back of the plane through the front of it and destroying it. Because science.

Better yet, explain how C4 detonates at ~mach 23 without imploding the universe. If you have a brick of it that is set off by a blasting cap, do only the molecules touching said cap detonate? You know, because they would blow the rest of the brick apart while waiting for the wave to propagate at the speed of sound?

edit: I give up. How the fuck can people not grasp this? Nothing. has. to. travel. faster. than. light. Everything moves five fucking inches.

I am an aerospace engineer. I suppose I should have been clearer. The air coming out of the back of the engine is the same as a ball going through the air or a space ship going through space. It's a physical object moving though the universe and it is limited to less than the speed of light. You seem to understand this. This is not to be confused with the wave propagation speed of the medium.

What you don't get is that by pushing the stick you're either limited by quantum physics saying the object can't move faster than the speed of light (and you contend you're not actually moving the stick this fast, so ignore this point) or you're limited by the wave propagation speed of the material, which is much slower than a physical object can travel though space.

So you have two options. Throw your end of the stick as fast as the speed of light and its molecules will collide with the molecules in front of it, and continue to keep hitting the molecules in front of them at the speed of light (assuming you have infinite energy and this collision never slows down, and btw you're destroying your stick in the process), or you can hit it with a hammer and let a wave propagate on it's own.

Either way you're SOL.

 

[disappoint]

Something I've been thinking about.

I'm on Earth, and there is this star 2.5 light years away. I have this stick that's exactly 5 inches short of 2.5 light years long (or appx 18 trillion miles long) and it's pointing at the star.

It's only 5 inches away from touching the star's surface. If I extend my arm with the stick and touch the star, how long would that take?

No one said the stick would fall into the star under it's gravitational pull? You wouldn't have to push it. It's only 5" away. The star will poke itself long before your puny push propagates anywhere.

 

[darkxshade]

What if instead of a star it was another planet pointing at me. What if at that moment I simultaneously grabbed the stick and pushed forward as well... does the universe blow up?

 

[Ruptga]

No one said the stick would fall into the star under it's gravitational pull? You wouldn't have to push it. It's only 5" away. The star will poke itself long before your puny push propagates anywhere.

I said that

 

[disappoint]

I said that

Sorry I missed it. Just read it now.

 

[Ruptga]

Sorry I missed it. Just read it now.

Whatever, we're all just having a good time neffing in here.