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

[Zeze]

It would be instant± assuming the stick isn't flexible or compressible.

Also that can't be right. If I poke the star with a morse code. I just communicated to someone 2.5 light years away in an instant.

 

[Blackjack200]

No it wouldn't. First, it it would, I believe it would violate relativity in that we could use such a device to send a signal faster than the speed of light. Bringing relativity into it, all sorts of fun things happen. I'm thinking/wondering if length contraction doesn't happen as a result.

We're already violating every physical law we can find, why should relativity be any different?

So yeah, you can dial a phone on Alpha Centurai. Just need your super stick.

 

[OILFIELDTRASH]

Not sure if serious. I hope for your sake this is a joke.

 

[z1ggy]

It would touch it at the speed you moved your arm, but you wouldn't see it for 2.5 years.

This assuming the stick is 100% rigid, etc etc as others have said. If you are holding on to the stick, it's essentially an extension of your arm...So it moves as fast as you move your arm, but if you had a telescope watching the very tip of the stick, you would see it happen 2.5yrs after you did it.

 

[Zeze]

We're already violating every physical law we can find, why should relativity be any different?

So yeah, you can dial a phone on Alpha Centurai. Just need your super stick.

Or we can simplify the question into more 'realistic' settings.

I'm really just asking what the speed is of that inertia.

What if the stick was only 1 light minute / 11 million~ miles long? (about 1/8th distance between our sun and earth, only 1/200th distance to Mars).

Would there be an 1-minute lag until the other end of the stick moves 5 inches forward?

 

[dank69]

Everything is simple when you preface it with "simply."

 

[phucheneh]

No.

Period. dot

It is no different than poking something three inches away with your penis.

 

[dank69]

Yes, but there's no such thing as a perfectly incompressible or inflexible material. So this has nothing to do with physics, it's just an arbitrary thought exercise.

So yes, if you had a 2.5 LY stick that was massless, incompressible, and inflexible, and it was pointed at a star and the end was 5 inches from that star, and you pushed the end of the stick the plane takes off.

Let's not forget able to withstand the surface temperature of a star.

 

[Zeze]

Let's not forget able to withstand the surface temperature of a star.

http://forums.anandtech.com/showpost.php?p=35184436&postcount=30

 

[Blackjack200]

It seems like you're asking how quickly the movement will propogate through the stick. You don't need a 2.5 light year or even 8 light minute stick to test that.

Keep in mind that the stick will be made of molecules composed of atoms that are mostly empty space. So when you push the stick you are simply pushing atoms close to other atoms and then those atoms are repelled by physical forces, that's how the movement propogates.

 

[lxskllr]

No it wouldn't. First, it it would, I believe it would violate relativity in that we could use such a device to send a signal faster than the speed of light. Bringing relativity into it, all sorts of fun things happen. I'm thinking/wondering if length contraction doesn't happen as a result.

I'm not smart enough to argue, but where did the stick go? If you pushed it 5" and it didn't bend or compress, where is it?

 

[darkewaffle]

The star would burn the stick!

 

[Zeze]

It seems like you're asking how quickly the movement will propogate through the stick. You don't need a 2.5 light year or even 8 light minute stick to test that.

Keep in mind that the stick will be made of molecules composed of atoms that are mostly empty space. So when you push the stick you are simply pushing atoms close to other atoms and then those atoms are repelled by physical forces, that's how the movement propogates.

I'm not smart enough to argue, but where did the stick go? If you pushed it 5" and it didn't bend or compress, where is it?

Right, so it's not instant.


The stick would 'lag' until the movement reaches the other end. So is the stick actually contracting? (kind of like when you whip a garden hose) What if it's made of diamond?

 

[Blackjack200]

I'm not smart enough to argue, but where did the stick go? If you pushed it 5" and it didn't bend or compress, where is it?

It didn't "go" anywhere. I think that DRP was referring to time-space, maybe suggesting that the stick would experience some time dilation.

But as has been pointed out in this thread, it's really hard to throw out some physical laws and then speculate what would happen as a result of other physical laws being followed.

 

[phucheneh]

And inertia wouldn't figure any differently, either. Yes, if we assume a multi-trillion-mile long stick to be pretty heavy, it would require lots of force to push and generate a lot of force on the other end. The heavier (no pun intended) question would be exactly how would the mass of the stick be affected by reaching into space between the two planets. To which the answer is 'who the fuck could know,' as you'd have to assign some values to your hypothetical stick, a mass and a diameter to the 'receiving' planet, and figure the gravitational effects of said planet, plus the Earth, plus everything inbetween with gravitational influence.

Here's a better way to look at the original problem, IMO: you run a fixed tube between the two planets. The tube is about the diameter of a BB, as you would use in your typical Red Ryder carbine-action, two hundred shot Range Model air rifle. You fill the tube with BB's except for the last five inches.

When you push the BB's forward that last five inches, nothing magical is happening. Every BB simply moves five inches forward, while acting upon all the BB's in front of it to simultaneously also push them five inches forward.

 

[Blackjack200]

Right, so it's not instant.



The stick would 'lag' until the movement reaches the other end. So is the stick actually contracting? (kind of like when you whip a garden hose) What if it's made of diamond?

I think contract is the wrong word, I think it would compress.

Why is diamond (carbon) special? It follows the same physical laws everything else does.

 

[OILFIELDTRASH]

How would the weight of said stick effect earth? Obviously I have no calculation to figure out what a 1" -wide stick 2.5ly long would weigh. Infinity? Would the stick collapse upon itself? Throw us out of the suns orbit?

 

[SlitheryDee]

I'm not smart enough to argue, but where did the stick go? If you pushed it 5" and it didn't bend or compress, where is it?

I suppose the simple answer is that no material in the universe can be pushed from one end without compressing somewhat. If you can move it 5" at all, then it must necessarily bend or compress to keep the force from traveling to the other side of it faster than the speed of light. It has to obey the rules of the universe it is a product of.

 

[Zeze]

I think contract is the wrong word, I think it would compress.

Why is diamond (carbon) special? It follows the same physical laws everything else does.

My dumb way to think of a material that doesn't compress or expand.

So in any given time, the stick is shorter than its actual length when you apply a force.

 

[clamum]

"It is fully testable"

LEL

 

[phucheneh]

My dumb way to think of a material that doesn't compress or expand.

So in any given time, the stick is shorter than its actual length when you apply a force.

It's also dumb to think that reactionary forces induced by the movement of someone's arm will cause something to move faster than the speed of light. Outright fucking retarded, in fact.

edit: not replying to your statement so much as using it to reply to the guy above you, btw.

 

[Zeze]

"It is fully testable"

LEL

In few thousand years? Why not. Are you predicting what we're capable and not capable of in few thousand years? You must be the genius of mankind's history.

 

[clamum]

In few thousand years? Why not. Are you predicting what we're capable and not capable of in few thousand years? You must be the genius of mankind's history.

I am. U MAD BRO?

 

[Rakehellion]

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?

Assuming it's a solid stick made of incompressible mass and you have a robo-arm capable of moving such a heavy object.

Nothing moved anywhere near the speed of light. The entire stick moved at the speed of your arm. Same as if you moved a stick that's ten feet long, it isn't necessarily moving at ten feet per second or any function of its length.

 

[Blackjack200]

Hey OP, I have a better question for you. I actually struggled with this one for a while and I think I even created a thread here about it. You can answer it with some internet research.

Every day, the tides come in, and they go out. As they go in and out, they produce friction between water and the surfaces the water is flowing against. In some cases, the tides are captured to produce electricity.

BUT

We know that energy can neither be created nor destroyed, only conserved or transformed from mass or to mass. So... where does all this tidal energy come from?

The answer might surprise you. It surprised me!