Question about "A Brief History of Time", S.Hawkin

[Guest]

Very nice book !

I've got one question. The author shows that something B that is too far from an event A could not be influenced in anyway by this event A before light could go through the distance from A to B.

In other words, he says that as long as the speed of light is the highest speed possible, we can ignore the effect of an event on anything that exist in a time and distance that is out of range from light.

For example, the fact that i'm writing now can not influence anything right now, but after 1 minute, it could influence anything that is max. 1 minute light away.

Now let's imagine that my friend Zo and me are holding a very very very long wire across the universe. One end of the wire is in my hand on earth. The other end is in my friend's hand on a planet in anoter galaxy.

If I draw three times the wire, Zo will feel the three movements in the wire almost immediately, though he is very very far away, and though my light couldn't reach him before years.

This way we can communicate (Morse) and influence the behavior of each other faster than light could !

Where am I wrong ?

Thanks and sorry for the poor english

[AkroBat]

you say : "If I draw three times the wire, Zo will feel the three movements in the wire almost immediately, though he is very very far away, and though my light couldn't reach him before years. "

Nothing can travel speeder than the light !!!!!
Nothing travel immediately.
Morse technology use wave and wave travel at the speed of light.

And finally, when you reach your planet, your friend will be dead since thousand of years.

[Guest]

So the force takes time to propagate itself in the wire (maybe I should say "rope" instead of "wire", it's less confusing).. ? At what speed does this force travel ? light speed ? If we hold a rope and suddenly i draw hard on it, you don't have much time to anticipate and to prevent from falling down, do you ?

[maxim]

That's an old thought experiment - usually done with a stick - and you already answered the question yourself.
The force is propagated along the atoms of the wire/rope/solid body. This force propagation won't be faster than light. I fact it will be reasonable slower, as there is mass to move. Your example doesn't work in human dimensions - the distances are far to short. If I light a flash it will surely blind you because you don't have time to anticipate - this will surely work for any distance, as there is no information about the action in the forehand.

maxim

[Guest]

That's an old thought experiment - usually done with a stick - and you already answered the question yourself.

Actually I thought about this answer a few hours after posting my question ! But it's good to have a confirmation BTW I didnt know it was a "old thought experiment"

If I light a flash it will surely blind you because you don't have time to anticipate - this will surely work for any distance, as there is no information about the action in the forehand.

What can I say ? You're right !

[Guest]

"If I draw three times the wire" -- apology accepted for the poor english. that did confuse ME for a while! ("if I pull on the wire three times" would have been much better)

anyway,

this 'force propogation' notion is new to me. do i infer from this that no object in existence is inelastic?

this is probably a bit too silly --

but what if this wire or rope, was a "string" of photons somehow contained so they touched eachother back to back and reached from one galaxy to the other?

if i fill a tube with ball-bearings, the time it takes to expell a ball from the other end is about the same time it takes to add one at my end. the "information" travels much faster than the speed of one ball along the tube, whether propogation time is considered or not. is this not the same with photons?

as you can tell, i dont know much about photons or wave-particle duality.

[Guest]

When You pull the wire - You do not act by any force on the other end, You just launch the wave of displacement along this wire. The wave travel at the speed of the sound, which is greater in the solid body (including the wire in tension) several times, that in the air, but still be much-much-much lover, that the speed of light.

[Juan Marino]

S. Hawking said:

Finite universe = does not exist God:
True or false?:

That they think?????

[jestr]

Static Universe=God ?
Dynamic Universe=No God

[Cham]

The exitence of God CANNOT be proven or disproven using science. No cosmological model, be it quantum or not, relativistic or not, can say if God exist or not. It is just unrelated.

Whatever if the Universe is closed or open, dynamic or not, God may or may not exist.

IMHO, the God concept is a nonsense. Any question about God is meaningless and is just a matter of personnal opinion.

[t00fri]

The exitence of God CANNOT be proven or disproven using science. No cosmological model, be it quantum or not, relativistic or not, can say if God exist or not. It is just unrelated.

Whatever if the Universe is closed or open, dynamic or not, God may or may not exist.

IMHO, the God concept is a nonsense. Any question about God is meaningless and is just a matter of personnal opinion.

Well, while still in high school, I attended a philosophy class where this subject was treated. Apparently there are so-called "existence proofs" of God that are roughly based on the following argumentation in various variations:

The extremely high amount of 'order' in Nature combined with probabilistic arguments that all this had a random origin.

The arguments are intellectually interesting but far from convincing or even rigorous in a scientific sense.

Bye Fridger

[Cham]

A true believer (I'm not) could say even the probabilistic nature have been created by God, and space-time topology too.

[Juan Marino]

Generalized Laws of Thermodynamics (Newton, Ginsberg, etc.) AND Universe Self-Containing (S. Hawking):

Every major philosophy that attempts to make life seem meaningful is based on the negation of one part of Generalized Laws of Thermodynamics. To wit:

Capitalism is based on the assumption that you can win.
Socialism is based on the assumption that you can break even.
Religions is based on the assumption that you can quit the game.

The official line of science is the desperation. To wit:

You can't win.
You can't break even.
You can't even quit the game.

That they think?????

[Guest]

Existence of God is NOT in the field of science, it's the field of faith. Philosophical arguments and so-called "proofs" of god do exist, but they don't make really sense.

Belief can be irrational - science cannot kill God in the name of rational arguments.

To make it clear, you could even say ?« Credo quia absurdum. ?»
= I believe it, because it is absurd. (actually a misquote of Tertullian, but i like the idea)

Peter

[AskHL]

When one end of the rope is pulled, the "pull" is transmitted by the forces acting between the atoms or molecules in the wire. These forces are electromagnetic, and the electromagnetic forces are transmitted by photons. Photons travel no faster than the vacuum speed of light (slower depending on the medium) and thus it is impossible to affect the other end faster than that.

More specifically, the speed at which the atoms/molecues of the wire transmit the impulse is much slower because they take time to accelerate. Since sound is exactly the propagation of (longitudinal) waves through vibration of the atoms/molecules, the speed about which we are talking is actually the speed of sound in the material.

Right?

[Guest Andy]

Anyone else got the multimedia CD Rom edition, ISBN 0-7167-2648-3

Comes in handy when the words get too big, you can watch the videos and pictures instead, even a little ditty by Marilyn Munroe.