speed of thought question

[gib65]

A friend of mine was trying to convince me the other day that thought can travel faster than light. His example was this: you take a stiff rod of some solid enough material and long enough length (long enough for light to take a humanly noticeable amount of time to travel). Take two people and put one at each end. Have one person send a message to the other by pushing on the rod length-wise (that is, on its end). Have the sender do this according to some binary code (like moris code). The recipient will receive the message instantly (faster than light) therefore proving that thought (or information) can travel faster than light.

 

My qualm with this scenario was that I had a funny feeling that not all parts of the rod would move in unison. Although it may seem like all parts of some everyday object all move together when it gets pushed or pulled or whathaveyou, I suspect there is a slight time delay between those parts that are in direct contact with the pushing/pulling force and all other parts of the object. Isn't it true that the solidity of an object is maintained by the electromagnetic bonds between its constituent atoms/molecules, and that for any one atom/molecule to move with another it is bonded to, it must wait for the photon (or whatever the messenger particle it is that keeps them bonded) to travel to it from the first atom/molecule? If this is the case, then when the message sender pushes on the rod, the only instantanious effect he has is on the local atoms/molecules in the rod. For other atoms/molecules to move, they must wait for the photons/messenger-particles to get to them. Essentially, the message gets sent down the rod as a wave. And since photons/messenger-particles travel no faster than the speed of light, thought travels - at best - at the speed of light, or - worse than best - slower.

 

Is this right?

[YT2095]

considering that the firing patterns of the nerves used in the brian travel at about 200mph (certainly less than light speed) he can`t possibly be correct?

 

even if you consider the electrical part of the signal to be AT light speed (and it`ll be a little less), it`s still not possible

 

ALL must work within the frame of light-speed.

I may look at 1 star and then turn my head and look at another 500 light years away in less than a second, I`ve not moved 500 lightyears.

in My frame, all I`ve done is chossen to receive the light from a star as it was and looked 500 years ago

[5614]

indeed. i cant say i knew that figure was correct, however the brain works via electrical impulses and chemical reactions which will certainly not travel (or happen) faster than the speed of light.

 

sorry man... but the fact is that NOTHING that we know of can travel faster than light and unless you deny some basic laws of physics, it wont happen!

[Severian]

Yes - you are right, not your friend. The impulse which your friend gives the rod will travel down the length of the rod at a speed <c for pretty much the reasons you say. This shows by the way that there is no such thing as a 'rigid body'.

[Ophiolite]

This shows by the way that there is no such thing as a 'rigid body'.

Though Gib65's friend seems to have demonstrated the capacity for 'rigid thinking'.

[swansont]

sorry man... but the fact is that NOTHING that we know of can travel faster than light and unless you deny some basic laws of physics, it wont happen!

 

Actually "nothing moves faster than c" is not a valid interpretation of relativity, and it often causes confusion. There are things that happen at a rate faster than c, but they are either not causally connected, or no information is transmitted by them. Invariably, anything that is purported to be faster-than-light (and isn't fiction) is one of those two.

[5614]

but they are either not causally connected, or no information is transmitted by them.

can you give me an example... not because i dont trust you, but because i dont know

[[Tycho?]]

You are correct, and your friend is not.

 

Plus signals used by the brain move at less than c anyway, so it doesn't even matter.

[Severian]

can you give me an example... not because i dont trust you, but because i dont know

 

The classic example is a spotlight moving over low clouds. Lowering the spotlight beam, as the angle of the beam to the plane of the clouds becomes small, the beam moving over them becomes arbitrarily fast. Faster than c! Bit since the end of the spotlight is not an object as such, there is no information flow and no causility problem.

[Woxor]

The classic example is a spotlight moving over low clouds. Lowering the spotlight beam, as the angle of the beam to the plane of the clouds becomes small, the beam moving over them becomes arbitrarily fast. Faster than c! Bit since the end of the spotlight is not an object as such, there is no information flow and no causility problem.

Correct me if I'm wrong, but the end of the spotlight would also not actually travel faster than c, for the same reason that a jet of water (unaffected by gravity) directed similarly would not result in an intersection with the clouds traveling faster than the jet itself.

[swansont]

can you give me an example... not because i dont trust you, but because i dont know

 

Another example is the anomalous dispersion of light, where the pulse peak exits a material before it "should" and faster than c. The light is coherent, so all the information is located in the leading edge - reshaping the pulse to have the peak toward the front does not violate relativity.

[Sayonara]

even if you consider the electrical part of the signal to be AT light speed (and it`ll be a little less), it`s still not possible

Yes, the peak speed of nervous transmission is about 100ms^-1, which is a tiny fraction of light's whopping 299,792,458ms^-1.

 

Sounds like this guy is just decorating the push-a-pole argument to make it sound more "oooooooh".

[zaphod]

this question was posed in a book that i read about a while back... my conclusion was that when one of the two people pushes on the rod, it creates a compression wave on the rod, like pushing on one end of a slinky.

 

this compression wave on the rod will obviously be faster than the conpression wave in a slinky, but by relativistic principle, this wave cannot be faster than light. so if a flash of light goes off at the same time as the rod is pushed, then the person at the other end will still see the flash of light before feeling the rod.

[Glider]

Just for the sake of pedantry: Nerve transmission rates depend on the fibre. For example, small non-myelinated fibres (e.g. C fibres) have a transmission rate of around 0.2 - 0.5 metres per second. Large myelinated afferent and efferent fibres have transmission rates of around 300 - 400 metres per second.

[mtong]

The way I see it,

 

If the rod was to be tapped and a compression wave traveled down the rod it would travel the same speed that sound travels in that medium, a lot slower than c.

 

If the rod was pushed by hand then it would accelerate according to the force applied by hand,say at a rate of .5m/s^2.

 

So if the person at the other end required the rod to be pushed into his hand .001 m (so that he could feel it) and the rod accelerated at .5 m/s^2 then the time taken for the 'information' to be sent, t=sqrt((2*.001)/.5)=>.063s.

 

The only way the 'information' could be sent faster that c would be if the rod was accelerated faster than c => the hand must have and infinite energy source to do so.

 

The only way the 'information' could be sent instantaneously would be if the rod had to travel only 0m for the pulses to be noticed, which is impossible.

 

PS. Sorry if i am alittle confusing, kind of hard to explain what i am thiking

[zaphod]

 

yeah.. thats almost what i said.

[Kygron]

Actually "nothing moves faster than c" is not a valid interpretation of relativity, and it often causes confusion. There are things that happen at a rate faster than c, but they are either not causally connected, or no information is transmitted by them. Invariably, anything that is purported to be faster-than-light (and isn't fiction) is one of those two.

Another example is the anomalous dispersion of light, where the pulse peak exits a material before it "should" and faster than c. The light is coherent, so all the information is located in the leading edge - reshaping the pulse to have the peak toward the front does not violate relativity.

 

Would you (or anyone) mind elaborating on this example or perhaps giving others? Let us know why people might think it violates GR, and why it actually doesn't.

 

Thanks

[swansont]

Would you (or anyone) mind elaborating on this example or perhaps giving others? Let us know why people might think it violates GR' date=' and why it actually doesn't.

 

Thanks[/quote']

 

I gave links in the original thread. Why not post there, instead of starting a new one?

[5614]

http://www.astro.ucla.edu/~wright/anomalous-dispersion.html

 

and

 

http://physicsweb.org/articles/world/13/9/3/1

 

should explain it pretty well... if not check out that thread for the other posts or do a google search. if you ask here and someone has already explianed it - tell them which part you dont understand so that they can explain that part rather than aimlessly repeating the same explanation!

[TWJian]

The neurons in the brain works by firing off electrical and chemical messages.Therefore,it WILL NOT exceed the speed of light.

[swansont]

I gave links in the original thread. Why not post there, instead of starting a new one?

 

OK, now we're in the "speed of thought" thread, but that's...OK. I actually was thinking of this thread when I said I gave some examples.

[Kygron]

I gave links in the original thread. Why not post there, instead of starting a new one?

 

I'm quite upset that my post got attached to this thread. Maybe I misunderstand the forum rules, but I had intended to start a topic about RELATIVITY and not be grouped into a topic about chemicals and the brain. The fact that I quoted from this thread was that swansont's statement about relativity (originally just an example) was interesting in it's own right and I was hoping to discuss it outside of its relavence to this thread.

 

I'm an amature to all this. I see this forum as a way to discuss ideas in less technical terms than in purely techincal papers (which I often don't have the vocabulary to understand). If I had wanted a question answered I would have asked directly or looked it up myself. Instead I wanted to DISCUSS the reasons why realativity holds true even in the face of special phenomina. I was hoping someone might have some better examples because I have no clue how to look up this sort of thing.

 

swansont: I'll try to be nice, but we're in the original thread now... take a look, there's no links!

 

5614: thank you for the links, the first was an excellent explaination of the effect. I'm sure now that we're back in this brain topic I'll never get to discuss.

 

edit: swansont, sorry I must have been typing when you wrote the previous. I see the link now... 5614 did EXACTLY what I tryed to do. I looked in relativity for my topic, I din't think it'd be in modern when it was all based of GR. I'll read and post in that thread now, thanks. (could the mod have just added mine to his somehow?)