

Radio Waves Now Can Travel Faster Than Light. - keltecp11
http://current.com/items/90301786_scientists-make-radio-waves-travel-faster-than-light.htm?xid=ch60

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teilo
What a crock. This paragraph says it all:

"'If you take a laser and shine it on the moon and swing it rather gently, for
example, the spot on the moon travels faster than the speed of light,'
Singleton said. 'If an effect can do that, it makes you wonder if you can do
things with light to get the equivalent of a sonic boom.'"

Um, no it doesn't. The "spot" is not a thing that is traveling at all. In
fact, the spot does not exist, because each of the photons from the laser, you
know, those little tiny wave-particle thingys which actually DO exist,
traveled at the speed of light to get to the moon. Other photons took a
different angle to get to another part of the moon, also at the speed of
light. So, just what, exactly went faster than the speed of light? Nothing.

And we are supposed to take this guy seriously?

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leecho0
Well, in normal waves, particles don't travel either. Water waves move up and
down while the wave moves forward. Compression waves like sound move air
particles back and forth, but in general they go back to where they started
from. Light is weird because it's both a wave and a particle.

But you're right, this is just a trick to make something look like a wave
that's travelling faster than light. It takes the same amount of time for it
to get to you, but when it does, it looks like it's travelling faster.

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teilo
I understand wave-particle duality, thank you. Irrelevant, really. We're
talking separate photons, not the same photon moving across the moon. If it
was actually moving across the moon, you would never see it, because it would
not be traveling back to your eyes

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leecho0
I think the example of the moon kinda sucks, I agree. but it doesn't mean that
this is totally irrelevant.

To measure the speed of a wave, you find the length between peaks, the
wavelength, and then the time it takes to go from peak to peak, the period.
Wavelength / period = speed, which has nothing to do with the motion of the
particle. But the interesting thing about waves is that it can stack without
disturbing each other, and if you can stack different waves just right, you
can make create something that looks periodic, but travels faster than any of
the combined waves.

Shining light on the moon or motion on a LCD screen uses a similar idea where
the peak intensity is moving much faster than the components (pixels don't
move at all in lcd screens). If this is periodic, you can call it a wave,
whether it makes sense or not to call it as such.

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asciilifeform
This applet demonstrates why the technique cannot be used for FTL
communication:

<http://gregegan.customer.netspace.net.au/APPLETS/20/20.html>

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russell
Even the article says that information cannot travel faster than the speed of
light. (Quantum entanglement seems to transmit information instantaneously,
but I make no claim to understand what is going on.)

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DenisM
This is similar to placing a set of lenses in front of a laser beam and
quickly changing the focus - the focal point can move towards you at
arbirtrary speed yet you can't pass information because focal point is an
imaginary object.

Similarly, you can spin the laser in front of a wall and then the spot on the
wall can move at arbitrary speed (provided the wall is far enough).

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stuff4ben
Regardless of what the domain name of the site is, this technology isn't all
that "current". Apparently it's been out since 2004,
<http://radio.weblogs.com/0105910/2004/08/18.html>

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bcl
So they have had 5 years to perfect their technology. Are there any more
recent reports on this, or did it go the way of Cold Fusion?

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tocomment
I never understand why people say communicating faster than light violates
causality. Can anyone give a simple example?

If I were to communicate with someone 2 light years away at 2x light speed,
they just get my message in one year instead of two. No one is sending
information into the past.

Any ideas?

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ns1
communicating faster than light violates causality when we assume the speed of
light is constant

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rjprins
But radio waves _are_ light.

