Light bends matter, surprising scientists

[jayfish]

http://www.msnbc.msn.com/id/36021551/ns/technology_and_science-science/

Light can twist matter, according to a new study that observed ribbons of nanoparticles twisting in response to light.

Scientists knew matter can cause light to bend — prisms and glasses prove this easily enough. But the reverse phenomenon was not shown to occur until recently.

The researchers assembled strings of nanoparticles, which are tiny clumps of matter on the scale of nanometers (one nanometer is one billionth of a meter). In a darkened lab, the scientists linked nanoparticles together into ribbons. At first the nano ribbons were flat, but when a light was shone on them, they curled up into spirals. The discovery was so novel, the researchers were skeptical of their own results at first.

I don't know what to think about this. Light doesn't have mass so how is it effecting an object that does in this manner?

FSH

[timtom]

1. It reminds me of Firesign Theatre's "Everything You Know is Wrong"

"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy." (This, from William Shakespeare, not FT.)

[Warpy]

2. Photons have long been called "wavicles," with

properties of both energy waves and particles. At least they were called that back in the physics dark ages in the 60s when granny went to school.

This doesn't surprise me.

[sudopod]

3. Light does have energy, though.

the energy of a photon is:



where omega is the angular frequency in radians/sec, nu is the frequency in Hz, h is Planck's constant, h-bar is plancks's constant divided by 2pi (the reduced planck's constant), and lambda is the wavelength.

Photons also have momentum given by:



where rho is momentum and k is the wave vector, which points in the direction of the particle's travel and is equal to 2pi/lambda.

For photons, energy and momentum are related by the equation E = cp, where c is the speed of light.

Isn't that odd?


The reasons for all of this touch on quantum mechanics and the essential weirdness of the laws of nature on small scales. Wikipeida does a pretty good job of giving an introductory explanation. :) http://en.wikipedia.org/wiki/Photon

It looks like the motion (according to the article) is due to electric potentials being created by the incoming light striking the nanoribbons, which isn't surprising, but what is surprising is the novel pattern of curling, if I understand correctly.

[HiFructosePronSyrup]

4. What a particular bad article.

It cites a March 17th issue of Science, but there is no March 17th issue but March 19th. It's not in the March 19th, but the March 12th.

As for the science- the scientists created some new linear nanoparticles. When exposed to light, photochemical reactions create charges on the surface of these particles. As the charges accumulate, the charges repel each other.

This is an article concerning chemistry and nanomaterials.

There is no new physics.

[laconicsax]

6. Is it really that bad when viewed in context of most science reporting?

I mean, there isn't exactly much to expect when the best science reporting only gets half of the premise and half of the conclusions right.

[caraher]

5. Nothing surprising here

As noted, light does carry momentum; but there are plenty of other ways light can make something twist.

Light also carries angular momentum. Miles Padgett, whose web page I linked, says he got interested in this field when someone said to him, "Did you know that you can turn a doorknob with light?" (In principle, that is; you really can't.) This paper from 1996 shows rotation of an optically trapped particle using light's angular momentum.

[BadgerKid]

8. You could turn a doorknob using a radiometer

in theory, I suppose.

[Dover]

7. I'd probably be more surprised if we hadn't already begun using the concentrated light of lasers

to effect matter. Or perhaps it's apples and oranges relative to the type of light
being discussed here due to the laser's stimulated, monochromatic state and manipulation using mirrors, etc.



The surface of the nanoparticles in this experiment were made of cadmium sulfide. To begin with, they had a slightly negative electromagnetic charge. But when photons, or particles of light, hit the nanoparticles, their energy excited electrons on the nanoparticles, causing chemical reactions that made them even more negatively charged. Since two negative charges repel each other, the nanoparticles began to repel more strongly.

"What's happening is a layer of nanoparticles starts repulsing from the others, so it creates mechanical stress, and in order to release this stress the ribbon twists itself".