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wayn3 · 01-28-2012, 04:25 AM

Quote:

Originally Posted by lukep

Stick: Instantly or sooner if gravity can pull & stretch it.

Your first answer is incorrect.

On top of that, you are allowed to ignore gravitational effects.

Quote:

Originally Posted by tspesh

There is always Catholicism

Catholicism opens up more to science than youd think.

Quote:

Originally Posted by bobsoap

So in essence, the photon that arrives at the mirror is the 2nd one in the chain of reacting electrons?

- 1st photon gets emitted by the light source (eg a light bulb); it arrives on your skin
- an electron of an atom of a molecule of your skin picks up the photon, gets excited, eats the 1st photon, copies it and radiates a 2nd one
- this 2nd photon is the one that arrives at the mirror.

How long does this chain get? If the photon coming from the mirror (the 3rd one in this chain) hits your skin again, it causes a 4th reaction, or does it not? So the 4th photon gets sent back to the mirror again, and so on, in perpetuity.

Could one then conclude that what we see (both in a mirror and through our eyes) is not how it REALLY exists (not saying "how it looks"!), given that it's a copy of a copy of a copy? This is assuming that no copy can be 100% the same as the original, given various diffusing and distorting variables that are being introduced in the process.

That chain goes on til your photon hits something black. But even black bodies radiate. Thats the heat radiation. Thats the mechanism that makes infrared cameras work. Body temperature corresponds to the wave-length of infrared light. If you heated the human body to the temperature of the sun, it will glow white, just like the sun.

You can obviously make that kind of interpretation. But photons dont lie. In the process of "reflection", energy is not lost. The adjustments your brain and eyes make are far bigger than the copying you describe.

Quote:

Originally Posted by Kerkat

I thought the speed of light was the maximum speed anything was capable of so the missile wouldn't fire beyond the first spaceship.

Interesting question - Are you Sheldon?

In the case of a missile being fired, youd need to take a look at the amount of fuel the rocket contains. Its certain that it wouldnt get much faster than the spaceship it originated from and would take a very long time to reach its target. But that was not the point of the question, we were specifically exploring the behaviour of light.

Im not sheldon, but I understand whats written on the boards.

Quote:

Originally Posted by zimok

A stick that reaches the sun from the Earth?

Ignoring all physical limitations, it would arrive instantly? Or, the time it takes you to push enough for the stick to touch the Sun depending on how far it was initially.

It "touches" the sun already. But since youve already learned that nothing can travel faster than light, this holds for sticks as well. So the correct "special relativity only" answer would be about 8 minutes. Just like the light takes 8 minutes to arrive at the earth. Thats a piece of info I assumed to be common knowledge.

But in reality, it gets weirder. Your stick is made of molecules. When you push it, each of those molecules has to be pushed by a molecule that is closer to you. This sends shockwaves through the stick and creates friction and your push would never arrive at the sun.

papajohn56 · 01-28-2012, 04:58 AM

Quote:

Originally Posted by wayn3

We can talk theoretical physics if you want, but youd lack the very basics.

lol.

papajohn56 · 01-28-2012, 05:03 AM

Quote:

Originally Posted by wayn3

But in reality, it gets weirder. Your stick is made of molecules. When you push it, each of those molecules has to be pushed by a molecule that is closer to you. This sends shockwaves through the stick and creates friction and your push would never arrive at the sun.

er, no. you might do well to look up what a "phonon" is.

Phonon - Wikipedia, the free encyclopedia

there's a reason I was working on a PhD and researching in solid state/condensed matter with work at the national high magnetic field lab.

wayn3 · 01-28-2012, 06:52 AM

Then I should apologize for assuming that you are not educated to an appropriate level. I dont want to make this some hostile discussion.

That I dont know much about solid state physics is a fact. Its not something that Im really interested in. The answer to that question is not something I have made up. It was being taught by a tutor and should, in restrospect, maybe not have been shared.

Would you like to share what you have worked on exactly?

lukep · 01-28-2012, 09:05 AM

^Oh man wayn3, you really messed up. PJ here is actually Stephen Hawking. He told me so at ASW last year.

BTW, I refuse to believe that since one stick is longer than another it no longer behaves like a terrestrial stick when you move it. I still say an inch of movement at one end of the stick is an instantaneous inch of movement 8 light minutes away at the other end. (It might take a shitload more force to move the stick 1 inch tho...)

For anything else to happen, the molecules between any two given side-by-side atoms inside that stick would have to behave differently, despite the fact that those atoms can't know if they're in a 1 foot stick or an 8 light-minute stick.

wayn3 · 01-28-2012, 09:14 AM

Quote:

Originally Posted by lukep

^Oh man wayn3, you really messed up. PJ here is actually Stephen Hawking. He told me so at ASW last year.

BTW, I refuse to believe that since one stick is longer than another it no longer behaves like a terrestrial stick when you move it. I still say an inch of movement at one end of the stick is an instantaneous inch of movement 8 light minutes away at the other end. (It might take a shitload more force to move the stick 1 inch tho...)

For anything else to happen, the molecules between any two given side-by-side atoms inside that stick would have to behave differently, despite the fact that those atoms can't know if they're in a 1 foot stick or an 8 light-minute stick.

Stephen Hawking didnt do a PhD on condensed matter

.

You approach the problem the wrong way. Your terrestrial stick subject to relativity just as much as the long stick is. Its just such a small object that you dont observe the impact. If your stick went from east to west coast, the movement would surely not be "instantaneous". Definitely not faster than the time it takes for light to travel that same distance.

lukep · 01-28-2012, 09:27 AM

Ok, so let's zoom down to the molecular level. When you move one molecule 1 inch forward, the one in front of it moves the same amount of distance forward, being pushed by the molecule you moved.

Why would the front molecule in the long stick move LESS than 1 inch forward than a front molecule in the short stick does? It doesn't know which stick it's in... And gravity isn't forward.

wezcountry · 01-28-2012, 09:27 AM

Quote:

Originally Posted by wayn3

I happen to be an astrophysicist. Feel free to ask interesting questions.

I have a question. Please don't send mockery in my direction if this is a stupid question. I barely did high-school physics.

Is the speed of light really the fastest anything can travel at?

lukep · 01-28-2012, 09:30 AM

^Only things with mass.

wayn3 · 01-28-2012, 10:16 AM

Quote:

Originally Posted by wezcountry

I have a question. Please don't send mockery in my direction if this is a stupid question. I barely did high-school physics.

Is the speed of light really the fastest anything can travel at?

As far as physicists are concerned, yes. This is not set in stone or some absolute truth or something like that, but its relatively likely that it is. There have been recent results by a group that might or might not have measured neutrinos at a speed faster than light. They are at the moment trying to figure out whether it was caused by faulty measurements or some actual new physics, of which the latter is way less likely.

Quote:

Originally Posted by lukep

Ok, so let's zoom down to the molecular level. When you move one molecule 1 inch forward, the one in front of it moves the same amount of distance forward, being pushed by the molecule you moved.

Why would the front molecule in the long stick move LESS than 1 inch forward than a front molecule in the short stick does? It doesn't know which stick it's in... And gravity isn't forward.

You probably imagine matter like this: Solid balls sitting tightly packed next to each other. If one of them moves the next one has to move as well because they cant occupy the same space.

Heres how it really is:

Lets take an atom. Atoms are made of protons and neutrons, which are made of even smaller particles. Thats the core of the atom. Its about 10^-15meter wide. Then there is the space around the core which is occupied by the electrons in some way. Thats the shell. The shell extends orders of magnitude beyond the core.

Maybe if you want to visualize that, imagine one of those big balls some people use instead of a chair because its good for the back or something. If that was the size of a real atom, the core would the sharp end of a needle sitting in the middle.

When two atoms bump into each other, they do that in a way similar to how two such balls would bump into each other. By approaching the other atom, they would invade their shell, feel a repulsive force and get pushed due to that force. That process is not instantaneous but takes very small amounts of time.

A very big part of an atom is just empty space, governed by strong fields that exert forces when you enter them.

Back to your question:

If you push a long stick an inch, every molecule travels 1 inch, just like in a short stick. What changes is the fact that it takes a while for the "push" to arrive at the molecules at the end.

Bofu2U · 01-28-2012, 10:27 AM

You all got it wrong. You're completely looking at this on the wrong level entirely, including you John.

The answer is: I wouldn't try to figure it out, I would hire someone to figure it out for me. It's more time and cost efficient.

Now go back to it. PS:

Quote:

Originally Posted by wayn3

Just like the light takes 8 minutes to arrive at the earth. Thats a piece of info I assumed to be common knowledge.

Didn't know that. But then again what most of us consider common knowledge most others wouldn't.

Keep it going guys, I'm actually learning a lot. More-so on the "thinking about shit differently" rather than actual "this is the right answer". Keep it rollin', it sounds like me debating with Mattseh over how certain things could be optimized :P

Chianti · 01-28-2012, 10:53 AM

I don't know shit about this subject, but the stick thing seems wrong.

You already spent a fuck of a lot longer than 8 minutes getting the end of the stick to be a foot away from the sun. Whether it travelled there near the speed of light and you did it in 8.5 minutes, or whether it was a construction job that took years, getting the end of the stick in place did not break any laws of physics.

So when you nudge it a foot, the molecules are only moving a foot from their start position, not 57 million kilometres. It seems reasonable that this theoretical stick can poke the sun instantaneously without breaking any laws.

wayn3 · 01-28-2012, 11:14 AM

Quote:

Originally Posted by Chianti

I don't know shit about this subject, but the stick thing seems wrong.

You already spent a fuck of a lot longer than 8 minutes getting the end of the stick to be a foot away from the sun. Whether it travelled there near the speed of light and you did it in 8.5 minutes, or whether it was a construction job that took years, getting the end of the stick in place did not break any laws of physics.

So when you nudge it a foot, the molecules are only moving a foot from their start position, not 57 million kilometres. It seems reasonable that this theoretical stick can poke the sun instantaneously without breaking any laws.

Ok then. When does the molecule that is 37 million kilometres away from you get informed of the push?

lukep · 01-28-2012, 11:23 AM

Inter-Atom compression? Like a bunch of beach balls in a line being pushed?

So essentially you're saying that the 800 billion-long string of atoms making up the short stick doesn't "give" enough for us to notice every time we push it one inch... But when dealing with a string of atoms 12 googolplex long the "give" is noticeable. I guess I could buy that... But only if the material making up that stick is an all-important factor...

(i.e. A Balsa-wood stick 8-light-minutes long "gives" so much there is no movement at the other end, ever, and meanwhile a Diamond stick 8-light-minutes long gives so little that it really is almost instantaneous on the other end.)

wayn3 · 01-28-2012, 11:28 AM

Quote:

Originally Posted by lukep

Inter-Atom compression? Like a bunch of beach balls in a line being pushed?

So essentially you're saying that the 800 billion-long string of atoms making up the short stick doesn't "give" enough for us to notice every time we push it one inch... But when dealing with a string of atoms 12 googolplex long the "give" is noticeable. I guess I could buy that... But only if the material making up that stick is an all-important factor...

(i.e. A Balsa-wood stick 8-light-minutes long "gives" so much there is no movement at the other end, ever, and meanwhile a Diamond stick 8-light-minutes long gives so little that it really is almost instantaneous on the other end.)

Im not saying that the material stays compressed after you push it. Thats not going to happen. Ive just tried to describe how the push propagates through the stick, which takes time. Since we have already established that nothing can travel faster than light, by explaining that the molecules have to bump into each other in order to move the "stick" forward, it should become clear that the earliest a molecule at light minute 4 feels the push is after about 4 minutes. Material doesnt matter at all.

zimok · 01-28-2012, 11:29 AM

Quote:

Originally Posted by papajohn56

wat? force does not depend on mass, and light's direction can be changed. you're trying to use Newton's laws...on a relativistic question. Stop it. I think I just answered my own question in the above post.

Strong gravity bends light *all the time*.

It's my understanding that gravity is the result of mass bending space time - and the warped space time gives the illusion of bending light. Is this not correct?

Similarly, light falls into a black hole because space time is collapsing so light follows that path, but the path of light never actually bends... it just follows a straight path through what space time it is passing through.

I'm a laymen at this, but I've been reading science for a long ass time and would love to know why what I just said is wrong from you Papajohn.

wayn3 · 01-28-2012, 11:36 AM

Quote:

Originally Posted by zimok

It's my understanding that gravity is the result of mass bending space time - and the warped space time gives the illusion of bending light. Is this not correct?

Similarly, light falls into a black hole because space time is collapsing so light follows that path, but the path of light never actually bends... it just follows a straight path through what space time it is passing through.

I'm a laymen at this, but I've been reading science for a long ass time and would love to know why what I just said is wrong from you Papajohn.

You didnt make any big mistakes

zimok · 01-28-2012, 11:37 AM

Quote:

Originally Posted by wayn3

You didnt make any big mistakes

Would you explain? I'm here to learn.

The word illusion might of been the wrong choice, but my meaning was that light always travels in a straight path on the medium its traveling in.

So if the medium(space time) is bent, then light traveling on that medium gets bent in the process.

wayn3 · 01-28-2012, 11:46 AM

Quote:

Originally Posted by zimok

Would you explain? I'm here to learn.

I dont know whats left to explain. General relativity is a very math heavy topic. I cant make some funny examples with space ships and lasers up.

Especially the black hole or the big bang thing. What happens there is singularities which is nothing more than a flaw in the mathematical theory describing the physical process. A "singularity" is more like a physicist saying "we dont really know whats up because the model blows" than a physical event.

If you have any specific questions, feel free to ask them, but if you want me to explain general relativity, ill have to pass. Its a 4th year theoretical physics only lecture for a reason. Even the images people use to illustrate that cant even scratch the surface.

greenleaves · 01-28-2012, 12:00 PM

Quote:

Originally Posted by greenleaves

100 light years.

The laser fired by 'behind craft' is 1 light year away. But the other craft is traveling at 99% the speed of light. So in 1 light year when the laser reaches the place where the 'ahead spacecraft' was, the ahead spacecraft will have already traveled another .99 light years. 1 light year latter; it will be .98, another light year latter .97 and so forth.

Of course, this is assuming you could 'point' a beam of light under the mentioned conditions.

Warning: I'm ignorant on the topic and this is just my best guess.

Wait, so am I right or wrong and why?

wayn3 · 01-28-2012, 12:02 PM

Quote:

Originally Posted by greenleaves

Wait, so am I right or wrong and why?

Youre wrong. Its exactly 1 year. Space-time is lights bitch.

SUP3RNOVA · 01-28-2012, 12:24 PM

intergalacticpissingcontest.jpg

Chianti · 01-28-2012, 01:27 PM

> Material doesnt matter at all

Well, it does a bit. In my mind, the theoretical stick was perfectly rigid (not being affected by gravity, etc), whereas yours needs to be made of some real-world material to properly illustrate your point (which I get now, thank you).

papajohn56 · 01-28-2012, 09:14 PM

Quote:

Originally Posted by wayn3

Stephen Hawking didnt do a PhD on condensed matter

.

You approach the problem the wrong way. Your terrestrial stick subject to relativity just as much as the long stick is. Its just such a small object that you dont observe the impact. If your stick went from east to west coast, the movement would surely not be "instantaneous". Definitely not faster than the time it takes for light to travel that same distance.

If you were to have a stick that goes from the earth to 1 inch off the surface of the sun, ignoring gravity, if you pushed the stick exactly with a 100% parallel force towards the sun for that 1", the push would make it reach the sun. It wouldn't lose anything due to friction at all, but the time it takes for it to reach the sun would not be faster than light of course - the speed of phonon propagation is actually the speed of sound within the lattice, so whatever the stick's material is, the speed of sound determines how fast it reaches.

Bofu2U · 01-29-2012, 04:57 PM

Quote:

Originally Posted by papajohn56

If you were to have a stick that goes from the earth to 1 inch off the surface of the sun, ignoring gravity, if you pushed the stick exactly with a 100% parallel force towards the sun for that 1", the push would make it reach the sun. It wouldn't lose anything due to friction at all, but the time it takes for it to reach the sun would not be faster than light of course - the speed of phonon propagation is actually the speed of sound within the lattice, so whatever the stick's material is, the speed of sound determines how fast it reaches.

I was going to say the same thing, but you beat me to it.

Moxie · 01-29-2012, 06:34 PM

Quote:

Originally Posted by Bofu2U

I was going to say the same thing, but you beat me to it.

kingofsp · 01-29-2012, 08:02 PM

Great, now I'm going to be watching science shit all night. Thanks guys.

Clarkey · 01-30-2012, 11:51 AM

Seen this before, amazing video none the less. I just still cant comprehend how small the earth actually is. Mind = blown.

01-28-2012, 06:52 AM	#54 (permalink)
wayn3 Senior Member Join Date: Feb 2009 Posts: 438 iTrader: 12 / 100%	Then I should apologize for assuming that you are not educated to an appropriate level. I dont want to make this some hostile discussion. That I dont know much about solid state physics is a fact. Its not something that Im really interested in. The answer to that question is not something I have made up. It was being taught by a tutor and should, in restrospect, maybe not have been shared. Would you like to share what you have worked on exactly? Share Share this post on Digg Del.icio.us Technorati Twitter __________________ ALNBlast.com ALN Blasts, Other Private Blog Network Blasts, High PR Posts, High PR Blogrolls High DA/PA coming soon Get 10% off - Use Coupon: WF10OFF

01-28-2012, 10:53 AM	#62 (permalink)
Chianti Senior Member Join Date: Apr 2010 Posts: 581 iTrader: 0 / 0%	I don't know shit about this subject, but the stick thing seems wrong. You already spent a fuck of a lot longer than 8 minutes getting the end of the stick to be a foot away from the sun. Whether it travelled there near the speed of light and you did it in 8.5 minutes, or whether it was a construction job that took years, getting the end of the stick in place did not break any laws of physics. So when you nudge it a foot, the molecules are only moving a foot from their start position, not 57 million kilometres. It seems reasonable that this theoretical stick can poke the sun instantaneously without breaking any laws. Share Share this post on Digg Del.icio.us Technorati Twitter

01-28-2012, 12:24 PM	#72 (permalink)
SUP3RNOVA Goober Gay Join Date: Mar 2007 Posts: 2,067 iTrader: 1 / 100%	intergalacticpissingcontest.jpg Share Share this post on Digg Del.icio.us Technorati Twitter __________________ am I allowed to link to my forum here?

01-28-2012, 01:27 PM	#73 (permalink)
Chianti Senior Member Join Date: Apr 2010 Posts: 581 iTrader: 0 / 0%	> Material doesnt matter at all Well, it does a bit. In my mind, the theoretical stick was perfectly rigid (not being affected by gravity, etc), whereas yours needs to be made of some real-world material to properly illustrate your point (which I get now, thank you). Share Share this post on Digg Del.icio.us Technorati Twitter

01-29-2012, 08:02 PM	#77 (permalink)
kingofsp WF Premium Member Join Date: Mar 2008 Location: Los Angeles Posts: 4,269 iTrader: 37 / 100%	Great, now I'm going to be watching science shit all night. Thanks guys. Share Share this post on Digg Del.icio.us Technorati Twitter __________________ W4 - Like Hуdra, but like way better.

01-30-2012, 11:51 AM	#78 (permalink)
Clarkey Apprentice Join Date: Mar 2011 Location: UK Posts: 36 iTrader: 5 / 100%	Seen this before, amazing video none the less. I just still cant comprehend how small the earth actually is. Mind = blown. Share Share this post on Digg Del.icio.us Technorati Twitter

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