
Light Seems to Pull Electrons Backward - wwarner
https://physics.aps.org/articles/v12/88
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cwmoore
When an ocean wave hits a beach, the swashing action pushes grains of sand up
and pulls them down. The shape of the beach (as observable in any given
moment) is steady relative to a number of waves and governed by cumulative
averages of their features, but will change as the direction of waves, tide,
current, etc. shifts over time. A beach with finer sand but similar wave
action and angle will have a different incline from one with coarser sand or
pebbles.

I am optimistic, as is the article, that further research into variations in
metal, light, angle of incidence, and time will lead to a better understanding
of the parameters of this backwards electron motion effect, of the nature of
light and electromagnetic waves, and moreover, the substrate/matrix in which
both are active, perhaps even of dark matter and a moving-zero mass.

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otakucode
When light hits the metal, it imparts some momentum. Is it possible (and this
is a stupendously naive mental picture and not what would actually be
happening, I realize that) that the metal moves in one direction, kicking free
electrons back the other direction? Like if you had a sheet of drywall covered
in dust hanging from a rope and you threw a baseball at it. The drywall would
move in the direction of the balls flight, but the dust would get kicked off
back in the direction the ball came from. Is the amount of current created
consistent with this sort of picture, electrons being kicked off as the metal
absorbs the momentum and accelerates away?

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chris5745
[https://arxiv.org/pdf/1812.01673.pdf](https://arxiv.org/pdf/1812.01673.pdf)

> The photon-drag effect, the rectified current in a medium induced by
> conservation of momentum of absorbed or redirected light, is a unique probe
> of the detailed mechanisms underlying radiation pressure. We revisit this
> effect in gold, a canonical Drude metal. We discover that the signal for p-
> polarized illumination in ambient air is affected in both sign and magnitude
> by adsorbed molecules, opening previous measurements for reinterpretation.
> Further, we show that the intrinsic sign of the photon-drag effect is
> contrary to the prevailing intuitive model of direct momentum transfer to
> free electrons.

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mirimir
Doesn't light basically interact with atoms by changing electron energy
levels?

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colechristensen
Essentially the entire experience of existence on a human scale is exclusively
photons and electrons interacting.

Photons are basically packets of momentum that atoms exchange.

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amelius
> Photons are basically packets of momentum that atoms exchange.

Is the quantized nature of these packets caused by a limitation in the atoms
and their ability to form photons, or is it a fundamental limitation of the
photons themselves?

~~~
colechristensen
Fundamental behavior.

The energy of any photon is the Planck constant multiplied by the frequency.
The frequency and energy aren't quantized and can be any value as long as they
are proportional.

The energy of an electron in an atom isn't quite so simply expressed but is
limited to discrete levels.

This is where emission/absorbsion lines come from or to simplify, color.

Electrons can only accept/emit specific amounts of energy and photons of a
specific frequency have an exact energy therefore atoms can only absorb or
emit very specific frequencies and all others are ignored.

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aszantu
I always thought that electrons and photons could be of the same energy in a
way

