At 11:57 PM 9/17/02, Doug wrote:
>The Fool wrote:
>
>>>From: Alberto Monteiro <[EMAIL PROTECTED]>
>>
>>>The Fool wrote:
>>>
>>>>
>>>>>No, they can't. Why those guys can't read what they wrote? There ain't
>>>>>no "signal" travelling FTL.
>>>>No individual particle is traveling above c. But the pulse is.
>>>>Pulse-Modulation.
>>>Sure. Then send some information at 4c using this
>>>Pulse-Modulation :-P
>>
>>Can they detect this pulse at the destination? Does it arrive at a
>>predictable / repeatable rate? The pulse does not have to carry any
>>frequency or amplitude information. The information is the existence or
>>nonexistence of the pulse.
>Well, there's this: "the phase velocity and group velocity of a wave may
>exceed the speed of light, but in such cases, no energy or information
>actually travels faster than c."
>http://scienceworld.wolfram.com/physics/Superluminal.html
>
>but I don't pretend to understand what they mean. If no energy or
>information traveled faster than light, what did, and how could they
>tell? Alberto's analogy was just a trick of the eye, is that what this is?
The classic example of the latter is to consider a rotating beacon such as
a lighthouse or an airport beacon which sends out a bright beam of light
that falls on a distant wall or perhaps the side of a cliff. The spot of
light cast by the beam moves across the wall with a linear velocity v equal
to r<omega>, where <omega> is the rate at which the beacon turns in
radians/second. For sufficiently large r, v can be greater than c, that
is, the time it takes the light to swing from point A on the wall to point
B, divided into the linear distance between A and B yields a result which
is >c. However, no _information_ can be transmitted from an observer at
point A to another observer at point B at a speed greater than c. Frex, if
A has a switch which can turn the light on or off, and as soon as he sees
the beam he hits the switch to turn the light off, it will take longer for
the electrical signal from the switch to reach the light than it will for
the light to swing to B, so the light will still be on when it reaches B.
Unfortunately, on another list, there has been one poster who has been
insisting for several months that he has come up with a way to transmit
information faster than light using a slight modification of such a setup,
regardless of what everyone else has pointed out to him . . .
--Ronn! :)
I always knew that I would see the first man on the Moon.
I never dreamed that I would see the last.
--Dr. Jerry Pournelle
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
