Radio Waves Now Can Travel Faster Than Light. | Hacker News Reader

Radio Waves Now Can Travel Faster Than Light.

current.com

12 pointskeltecp1117 comments

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?

I opened this article with reluctance, because I must have seen 5 "breaking the light barrier" stories now, all of which are based on a fallacy.

So, is it the scientist who is professing the fantasy or the reporter ?! I am just interested to know this that's all

I'm assuming the reporter, exaggerating what the scientist describes.

I'd say that's a wise default assumption. Researchers are very often frustrated at what reports write about their work.

John Singleton seems to be respected in the field. Perhaps this is a case of a poor analogy on his part. Regardless, nothing here violates relativity.

Perhaps the focus should be on the possibility that he has found a way to create a highly focused pulse that can propagate to far greater distances than normally are possible - albeit still under the speed of light.

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.

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

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.

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

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

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.)

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).

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

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?

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?

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

But radio waves are light.

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