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

[The Boston Dangler]

i hope the planet the OP is standing on is perfectly motionless relative to the star 2.5 LY away

 

[drinkmorejava]

I want to cry right now.

You pushing the stick is no different than any sort of physical wave traveling though the air, water, or ground. The speed of sound through a medium is that fastest that mechanical energy can travel though it.

To again refute this silliness...pretend you're moving the stick ever so gently. Again, much like something involving my penis and someone's mother.

But, like, ridiculously slowly. Say it takes a year to move the stick five inches. Are you still going to argue that some kind of shockwave has to propagate through the damned thing?

Also, go back to my example of the tube full of ball bearings, and assume that, because we're traversing empty space, you do NOT have to fight the mass of them, anyway. Are you still waiting for this 'wave' to reach the last bearing?

I would just say 'pretend the stick has zero mass,' but then there would be 'oh noes that is unpossible!' complaints.

We are absolutely saying that after a year the end of the stick will not have experienced the push/pull.

And too bad mass still applies in empty space. You pulling a 10 ton rock towards you will still be much harder than a 1 lb brick. F=ma. With the same force applied by your arm, it will take much longer for the rock to accelerate towards you.

 

[SlitheryDee]

i hope the planet the OP is standing on is perfectly motionless relative to the star 2.5 LY away

Yes it is. Also the stick is perfectly rigid and weightless, there are no stellar objects on a collision course with any part of its entire length, and the op is infinitely strong and capable of observing things light years away while pushing on the stick. The universe is also unable to disintegrate into a slurry of disconnected particles due to having no laws of physics.

 

[flexy]

He can't "touch the star at the same speed as he moved the arm", since the information" or physical movement (if you will) first will have to traverse through the stick.

Even in a hypothetical scenario where the stick would be made of atoms lined up "without any space between".... and taking away ANY physical problems this would in reality cause..the "movement" of/through the stick cannot exceed light speed so we can expect that the information that the stick was pushed would AT LEAST take 2.5 years..if not far, far longer.

So..in a best case scenario...the information that the stick has been pushed takes 2.5 y til the push happens on the other side....and another 2.5y for the pusher to get any info or feedback that the stick in fact pushed the star. Any OTHER explanation would simply ignore the fact that information cannot travel faster than LS. You can't "beat" light speed with a simple stick

 

[phucheneh]

I want to cry right now.

You pushing the stick is no different than any sort of physical wave traveling though the air, water, or ground. The speed of sound through a medium is that fastest that mechanical energy can travel though it.

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.

 

[phucheneh]

I figured this was not the OP's thought experiment (or maybe it's just coincidence) and Google confirmed that this question has already been asked.

http://www.askamathematician.com/20...-faster-than-it-would-take-like-to-get-there/

This is a classic thought experiment! If you had an infinitely rigid stick, then you could definitely send poking information faster than light. In fact, this is one argument for why you’ll never find perfectly rigid materials.

Just like you'd never find a fifteen trillion mile long stick. But if you assume it's not perfectly rigid, the stick never moves, collapsing at a point that, given the vagueness of the problem, no one can find. If you feel a thought experiment ends with an answer of 'cannot be calculated,' you're fuckin' doing it wrong.

How anyone brought the speed of sound into this, I have no idea.

 

[Paratus]

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.

Dude you're wrong. While it may seem like solids are "solid" they aren't. Each atom of the solid acts like a little springs pushing on each other. Pushing in the stick will propagate through the stick slower than the speed of light.

And your aerospace engineers know that the sonic speed a wave propagates through air is orders of magnitude slower than through a liquid which is orders of magnitude slower than through a solid.

Isaac Newton doesn't cut it here.

 

[SlitheryDee]

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 understand what you're saying, but I think you're still wrong. If power that starts in his arm reaches the star in less than 2.5 years, it moved faster than the speed of light. No kind of energy can do that; Not kinetic energy, not electromagnetic energy, not anything. Even if the stick itself doesn't move faster than light, nothing you do on one end can possibly happen to the other end in less time than it would take light to travel that same distance. It just can't. All this talk about compression waves and such is basically the universe's way of making certain this is true.

Oh and the speed of sound is an entirely different matter. It is nothing like the hard, universal limit that the speed of light is. What we call the speed of sound probably only applies here on earth where the atmosphere is of a certain density and composed of a certain mixture of gases. Somewhere else it might be entirely different. The speed of sound traveling through the metal body of the jet is not the same speed as the sound traveling through the air, and it doesn't represent a limit to the speed at which the jet can be pushed through the air.

 

[yhelothar]

This sounds like a question that radiolab addressed with a falling slinky. It's a very interesting one indeed, and counter intuitive as evidenced by many of the responses in this thread.

You'd expect gravity to pull the entire slinky down immediately after dropping, but the bottom of the slinky doesn't actually know it's being dropped until the top collapses and thus "propagates" this information to it.

http://www.radiolab.org/blogs/radiolab-blog/2012/sep/10/what-slinky-knows/

 

[Paratus]

I understand what you're saying, but I think you're still wrong. If power that starts in his arm reaches the star in less than 2.5 years, it moved faster than the speed of light. No kind of energy can do that; Not kinetic energy, not electromagnetic energy, not anything. Even if the stick itself doesn't move faster than light, nothing you do on one end can possibly happen to the other end in less time than it would take light to travel that same distance. It just can't. All this talk about compression waves and such is basically the universe's way of making certain this is true.

Oh and the speed of sound is an entirely different matter. It is nothing like the hard, universal limit that the speed of light is. What we call the speed of sound probably only applies here on earth where the atmosphere is of a certain density and composed of a certain mixture of gases. Somewhere else it might be entirely different. The speed of sound traveling through the metal body of the jet is not the same speed as the sound traveling through the air, and it doesn't represent a limit to the speed at which the jet can be pushed through the air.

Just posted this in the other thread on the 3 new exo-planets found but hypothetically there maybe a way around the light speed limit.
White-Juday Warp Field Interferometer

This is actual basic research going on at my work.

 

[ShadowOfMyself]

This thread brought me great joy, in fact Im making this my new sig:

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.

LOL

 

[phucheneh]

I understand what you're saying, but I think you're still wrong. If power that starts in his arm reaches the star in less than 2.5 years, it moved faster than the speed of light. No kind of energy can do that; Not kinetic energy, not electromagnetic energy, not anything. Even if the stick itself doesn't move faster than light, nothing you do on one end can possibly happen to the other end in less time than it would take light to travel that same distance. It just can't. All this talk about compression waves and such is basically the universe's way of making certain this is true.

Oh and the speed of sound is an entirely different matter. It is nothing like the hard, universal limit that the speed of light is. What we call the speed of sound probably only applies here on earth where the atmosphere is of a certain density and composed of a certain mixture of gases. Somewhere else it might be entirely different. The speed of sound traveling through the metal body of the jet is not the same speed as the sound traveling through the air, and it doesn't represent a limit to the speed at which the jet can be pushed through the air.

We can agree to disagree. Upon reflection, my aggravations are more based in philosophy than math. At least you probably get where I'm going with my objections, insofar as the whole 'if we're going to disregard this law, me may as well disregard that law,' and so forth.

As posed by the OP, in my pure semantical brain, my answer seems like the right answer. He says he extends his arm, holding the magic stick, and touches a star. I think that justifies the infinitely rigid stick.

Not just because of semantics, but because, as I tried to express previously, any other answer to the problem ends with an uncertainty. In my mind, you've still made the same amount of assumptions, if not more, but not arrived at a result other than 'more mathematical figures needed.'

In comparison, someone like Paratus who is trying to explain the interaction of the atoms to me, is not pickin' up what I'm puttin' down.

 

[Paratus]

We can agree to disagree. Upon reflection, my aggravations are more based in philosophy than math. At least you probably get where I'm going with my objections, insofar as the whole 'if we're going to disregard this law, me may as well disregard that law,' and so forth.

As posed by the OP, in my pure semantical brain, my answer seems like the right answer. He says he extends his arm, holding the magic stick, and touches a star. I think that justifies the infinitely rigid stick.

Not just because of semantics, but because, as I tried to express previously, any other answer to the problem ends with an uncertainty. In my mind, you've still made the same amount of assumptions, if not more, but not arrived at a result other than 'more mathematical figures needed.'

In comparison, someone like Paratus who is trying to explain the interaction of the atoms to me, is not pickin' up what I'm puttin' down.

Well shit dude, if you just want to assume everything away then what's the point? The question he asked wasn't a semantic one, it was to try and shed light on a physical phenomenon.

But if you want to play how many angels can dance on the head of a pin feel free.

 

[Paul98]

It's not a physics answer is you just make up your own physics so you can send information faster than light.

No a 2.5 ly stick would not be able to send information faster than the speed of light it wouldn't matter what it was made of.

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html#4

http://www.physicsforums.com/showthread.php?t=386687

 

[WelshBloke]

I thought the whole "nothing goes faster than the speed of light" thing just applied to stuff with mass.

No part of this big, magic stick is moving faster than the speed of light. No part of it is moving more than 5 inches.

 

[Paratus]

I thought the whole "nothing goes faster than the speed of light" thing just applied to stuff with mass.

No part of this big, magic stick is moving faster than the speed of light. No part of it is moving more than 5 inches.

It actually applies to mass, energy, and strangely enough information. What can actually move faster than light is the expansion of space.

 

[Pulsar]

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.

Accelerating something takes energy. As something nears the speed of light, it's mass increases to infinity, taking an infinite amount of energy input to reach that speed.

Basic physics education is about understanding how your basic assumptions affect your experimental outcome.

For instance, I know I won't get perfect power transmission out of a gearset because of friction, but for computational purposes we ignore friction.

You are ignoring the biggest possible variables of your experiment: the mass and compressibility of the stick.

For instance, taking a page out of XKCD's 'what if', if you were to smack the surface of a planet with a stick approaching the speed of light (so having infinite mass) and you assume a completely elastic collision, you would smack the planet right out of orbit like a pool cue hitting a pool ball. The people on the planet would not fare well.

If, on the otherhand you assume an inelastic collision, the amount of energy transferred into the planet would cause it to summarily disengrate. The people on planet may not appreciate that either.

But playing interstellar pool just sounds SO cool.

 

[phucheneh]

I thought the whole "nothing goes faster than the speed of light" thing just applied to stuff with mass.

No part of this big, magic stick is moving faster than the speed of light. No part of it is moving more than 5 inches.

What is being said is that each atom bumps the next atom in line, which takes an infinitesimally small amount of time, but when you multiply that one collision by billions of trillions or what-have-you, assuming each collision is at the speed of light (it's not), it will take 2.5 years for the chain reaction to hit the last bit in line. So rather than, say, a push taking five seconds moving five inches, you've got an unfathomably large number of tiny atomic collisions, and if you divide that number into your five seconds, each atom would have to break the speed of light to move the stick ANY distance in that amount of time.

I'm liking that answer more, now that I put it in my words. ;P

But it's the answer to a different question.

 

[Paul98]

Just think, your body is made up of almost entirely empty space.

 

[DrPizza]

Just think, your body is made up of almost entirely empty space.

Once you realize how large a proton is, and how incredibly small the three quarks are that make up the proton, it leaves you in awe realizing how much empty space there is in "solid" matter. Or, to put it another way, just this past second, billions of neutrinos passed through your nose & never collided with any matter.

 

[dave_the_nerd]

Once you realize how large a proton is, and how incredibly small the three quarks are that make up the proton, it leaves you in awe realizing how much empty space there is in "solid" matter. Or, to put it another way, just this past second, billions of neutrinos passed through your nose & never collided with any matter.

So... we're all essentially empty-headed, heheh.

 

[Paratus]

Once you realize how large a proton is, and how incredibly small the three quarks are that make up the proton, it leaves you in awe realizing how much empty space there is in "solid" matter. Or, to put it another way, just this past second, billions of neutrinos passed through your nose & never collided with any matter.

Here's a weirder thought.

If that's all empty space are quantum fluctuations causing virtual particles to pop in and out existence inside your atoms?

 

[Zeze]

Accelerating something takes energy. As something nears the speed of light, it's mass increases to infinity, taking an infinite amount of energy input to reach that speed.

Basic physics education is about understanding how your basic assumptions affect your experimental outcome.

For instance, I know I won't get perfect power transmission out of a gearset because of friction, but for computational purposes we ignore friction.

You are ignoring the biggest possible variables of your experiment: the mass and compressibility of the stick.

For instance, taking a page out of XKCD's 'what if', if you were to smack the surface of a planet with a stick approaching the speed of light (so having infinite mass) and you assume a completely elastic collision, you would smack the planet right out of orbit like a pool cue hitting a pool ball. The people on the planet would not fare well.

If, on the otherhand you assume an inelastic collision, the amount of energy transferred into the planet would cause it to summarily disengrate. The people on planet may not appreciate that either.

But playing interstellar pool just sounds SO cool.

I was disagreeing with him, and you are agreeing with me.

 

[disappoint]

Once you realize how large a proton is, and how incredibly small the three quarks are that make up the proton, it leaves you in awe realizing how much empty space there is in "solid" matter. Or, to put it another way, just this past second, billions of neutrinos passed through your nose & never collided with any matter.

What about how small the protons and neutrons in the nucleus are as compared to the electron clouds that separate the atoms from each other?

 

[disappoint]

So... we're all essentially empty-headed, heheh.

We are mostly comprised of fields.