Re: Universal non-point of light

Hal Finney (
Tue, 4 Feb 1997 16:51:17 -0800

From: Michael Lorrey <>
> I just read about it in scientific american. What it does is polarize a
> laser beam, split the beam, and put one of the splits through a
> polarizer at 45 deg from the first, plus some other steps I can't
> remember, but basically it allows one to observe without influencing.

I read that article too, and although it was truly a remarkable result it
would not lead to faster than light communication.

What the article describes is a method to determine whether a photon
path is blocked or not, while reducing the photon flux in that path to
an arbitrarily small amount. It uses quantum interference to determine
whether a photon might have gone down that path, even though no photons
ever actually do go that way.

Theoretically you could scan the photon path across an object and
take a picture of it, without actually hitting it with any photons.
If X-rays could be manipulated optically as easily as visible-light
photons, you could take an X-ray photo of a specimen without exposing
it to damaging X-ray radiation.

I'm not sure what would be needed for faster than light communication, but
this isn't it.