subluminal

Sean sent me a link to a java applet which demonstrates a nifty information transmittal trick that seems to send messages faster than the speed of light: Subluminal.

Subluminal shows how a wave composed of a multitude of frequencies moving at different velocities %u2014 all less than or equal to c, the speed of light in a vacuum %u2014 can appear to have features moving faster than c.

The grid that crosses the screen is moving with a velocity of c, and no individual frequency outpaces it. However, the total wave (the bottom trace, in white) has its strongest peaks where all the individual frequencies are in phase, and the places where that happens shift with time, at a %u201Cspeed%u201D that is greater than c. Nothing is actually travelling with these peaks, though; they're just an artifact of the way the different frequencies are slipping in and out of phase.

It seems interesting. However I'm a little unclear how information could actually be sent this way, as from the applet it appears that the aggregate waves that are travelling at or below c (and the resulting "envelope" wave which is travelling faster than c) are uniform and therefore containing little value as information. Also the line on the applet page that begins with "This illusion of superluminal motion..." seems to indicate the actual value of the method is suspect.

But then, I'm not a mathematician and it's too early in the morning to try and make sense of the provided mathematical details...

Comments

[Sean]

Apparently information -can't- be sent that way. The caption on the applet says this is impossible, and it says you can activate something called a "shutter" in the visualization to demonstrate why it's impossible.

Trouble is, I don't see what the shutter indicates, or how it demonstrates that signals can't be sent. It seems to suggest that if you cut off the same portions of all the waves somewhere between starting point and endpoint, the wave patterns on either side (including the aggregate pattern) seem to pass right through it... But what if you turned on and off just -some- of the waves (say the yellow ones); wouldn't that translate into changes in the faster-than-light aggregate pattern?

Anyway I'm completely lost as to the math too so I take their word that we don't have an ansible yet. (Ansible = communication device from Enders Game books that allowed instantaneous communication between any two points in the universe.)

But we still have other freakish theories that might provide an ansible, like quantum tunneling and like the idea that paired subatomic particles will instantly react to changes in one another's spins no matter how far from each other they're separated.

The most credible hypothesis along those lines suggests that items or persons placed into a large-enough afro will emerge instantly from another afro somewhere in the universe; the real difficulty is predicting or influencing which afro will become the destination-fro in any given fro-jaunt.

[Anonymous]

> Trouble is, I don't see what the shutter
> indicates, or how it demonstrates that
> signals can't be sent

I think the idea is that, if someone were to give me a uniform stream of faster-than-light blobs, then I might try to transmit information by using a shutter to alternately block/un-block some of these blobs. I'd try to turn my uniform stream of fast-moving-blobs into a stream with an on-off pattern in it.

But these faster-than-light pulses move right through the shutter, so the applet is demonstrating, you can't transmit info that way.

> But what if you turned on and off just
> -some- of the waves (say the yellow ones);
> wouldn't that translate into changes in
> the faster-than-light aggregate pattern?

No, because the aggregate pattern, at any horizontal position, is just the sum of the individual waves at that position. If you induced changes into the yellow waves, those changes would move forward only at the speed of the yellow waves -- less than c.

If the applet allowed you to induce some flaw into the yellow waves, of course you'd see that flaw reflected in the aggregate wave. But the faster-than-light pulses would -move-right-through- this flaw, just like they move right through the shutter.

The flaw would just move forward at less than c, right under the yellow waves responsible for it.