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

[Zeze]

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.

 

[lxskllr]

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

 

[Oyeve]

Is the stick flexible at all or are we assuming there is no inertia?

 

[ThinClient]

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 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.

No, the stick did not travel faster than the speed of light.

 

[dave_the_nerd]

Then assuming you have enough upper arm strength to move a 2.5LY stick. And the stick isn't buckling, bending, etc.

The stick still has intertia - 2.5 LY of mass. That's a lot of inertia.

You wouldn't be moving it, you'd be compressing it. The other end of the stick would move that 5", but only after a period of time determined by the material's wave propagation speed.

 

[DnetMHZ]

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

This

 

[DrPizza]

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.

 

[PlanetJosh]

For the sake of argument, the earth and the stars aren't movie and the distance between them is static.

We can't be in a movie? I was really hoping for that. But as for the topic, wouldn't it be very difficult to have the end of the stick ever get that close due to rotations within our solar system alone? In other words I'm not an expert in physics, just know some things about it.

Edit. Never mind, forgot about your mention of a static environment. Doh, sorry.

 

[Zeze]

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

Is it that simple? The force I exerted from earth will instantly reach the other end of the stick 2.5 light years away?

The other end of the stick would move that 5", but only after a period of time determined by the material's wave propagation speed.

Right, this is what I was thinking of. What is the speed of such 'force'? It is same as speed of light or slower?

 

[dave_the_nerd]

Is it that simple? The force I exerted from earth will instantly reach the other end of the stick 2.5 light years away?




Right, this is what I was thinking of. What is the speed of such 'force'? It is same as speed of light or slower?

Much, much slower. (A couple thousand mph for most everyday materials.)

 

[ThinClient]

I like that he asks a question requiring an answer by someone who is "good at physics" and then in his hypothetical question, fully suspends the natural order of things, creating a question in a world where physics does not apply. Lol.

 

[Oyeve]

Is it that simple? The force I exerted from earth will instantly reach the other end of the stick 2.5 light years away?




Right, this is what I was thinking of. What is the speed of such 'force'? It is same as speed of light or slower?

I really think there is no answer, yet. I don't even know if man is accurate in LY measurement.

 

[dave_the_nerd]

Is it that simple? The force I exerted from earth will instantly reach the other end of the stick 2.5 light years away?

Only if you had an infinitely rigid, infinitely incompressible material with zero mass.

 

[Ruptga]

I like that he asks a question requiring an answer by someone who is "good at physics" and then in his hypothetical question, fully suspends the natural order of things, creating a question in a world where physics does not apply. Lol.

Uh, that is actually standard procedure for physics questions.

proof

 

[Blackjack200]

Is it that simple? The force I exerted from earth will instantly reach the other end of the stick 2.5 light years away?




Right, this is what I was thinking of. What is the speed of such 'force'? It is same as speed of light or slower?

Slower. I imagine it depends on the material, temperature, etc.

 

[lxskllr]

Only if you had an infinitely rigid, infinitely incompressible material with zero mass.

I figured that was implied. It's already an impossible setup, so adding that small bit of realism just obfuscates the answer.

 

[KMc]

A "light year" is just another term for measuring distance. It's approximately 6 trillion miles.

Now, restate your question, but replace "2.5 light years" with "15 trillion miles". Doesn't seem so complicated now, does it?

 

[Zeze]

I figured that was implied. It's already an impossible setup, so adding that small bit of realism just obfuscates the answer.

I wouldn't say impossible...

Let's say we're advanced enough in few thousands years. And we simply build a stick that's 2.5 LY long. And then simply move it 5 inches forward. It is fully testable.

 

[lxskllr]

I wouldn't say impossible...

Let's say we're advanced enough in few thousands years. And we simply build a stick that's 2.5 LY long. And then simply move it 5 inches forward. It is fully testable.

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

 

[Blackjack200]

I wouldn't say impossible...

Let's say we're advanced enough in few thousands years. And we simply build a stick that's 2.5 LY long. And then simply move it 5 inches forward. It is fully testable.

 

[Blackjack200]

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

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.

 

[SlitheryDee]

No it wouldn't move at the speed of light. I have little physics, but isn't it impossible for the energy from your arm to travel to the tip of the stick at faster than the speed of light anyway? It would have to be made of a material that compressed and the force would travel as a wave up the stick at some rate slower than the speed of light.

 

[DrPizza]

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

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.

 

[Zeze]

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

What if I swing the stick in an arc? The other end must be insane, travelling at thousand times faster than speed of light... Is that possible?

 

[Insomniator]

lol fully testable...