
Transfer of atomic mass with a photon solves the momentum paradox of light - metafunctor
http://physics.aalto.fi/en/current/news/2017-06-30/
======
GolDDranks
"Presently the Hubble’s law is explained by Doppler shift being larger from
distant stars. This effectively supports the hypothesis of expanding universe.
In the mass polariton theory of light this hypothesis is not needed since
redshift becomes automatically proportional to the distance from the star to
the observer”, explains Professor Jukka Tulkki."

If this proves to be true, is there a chance that our whole picture of the
expanding cosmos needs a full revisiting?

~~~
ninkendo
Such an explanation for observed redshift apparently comes up again and again,
but thus far hasn't held up to experiment... it even had a name: "tired
light".
[https://en.wikipedia.org/wiki/Tired_light](https://en.wikipedia.org/wiki/Tired_light)

It'll be interesting to see if this sparks new debate on the subject.

~~~
nothis
If it's proven true, though, would that mean the "expanding universe" theory
would be disproved as well?

~~~
GolDDranks
Not necessarily. It might be that this effect is real (this was a
computational simulation so an experimental verification is needed.) and needs
to be accounted when doing cosmology. But it might very well account just a
part of the redshift, and the remainder then needs to be accounted by
something else, the default explanation being the expanding universe.

Edit: A clarification: I'm not an expert.

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thisrod
I'm unconvinced by the paragraph beginning, "However, the above result leads
to a striking contradiction with the covariance principle, which is a
fundamental prerequisite of the special theory of relativity."

It is pretty well accepted that light can have mass, in the sense that the
authors are using the term. For example, light trapped as a standing wave
between two mirrors in an etalon must have zero momentum. (By symmetry: if it
has momentum, which way does the vector point?) But that light has energy, so
it has mass in the sense that m must be non-zero to satisfy E² = p²c² + m²c⁴.
More precisely, the momentum-energy vector of the light is timelike instead of
lightlike.

This makes me suspect the whole paper, because it seems really plausible that
a light wave in a medium is partly like a standing wave. In particular, there
is a limit of a dense medium whose momentum is negligible. (Maybe the
refractive index approaches 1 in a very dense medium, but I can't imagine why
that would be so.) I'd have to spend a morning reading and thinking about it
to be sure.

Also, the paper is suspiciously detailed; these questions should be resolvable
at a much higher level of abstraction, and certainly without computer
simulations.

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jessaustin
Seems important:

 _Presently the Hubble’s law is explained by Doppler shift being larger from
distant stars. This effectively supports the hypothesis of expanding universe.
In the mass polariton theory of light this hypothesis is not needed since
redshift becomes automatically proportional to the distance from the star to
the observer”, explains Professor Jukka Tulkki._

------
adamnemecek
Does anyone know how they made the pictures? In particular this one
[http://physics.aalto.fi/en/midcom-
serveattachmentguid-1e75d6...](http://physics.aalto.fi/en/midcom-
serveattachmentguid-1e75d6478acc1145d6411e7957e5f655f3745a645a6/aalto_university_mass_density_wave_image_jyrki_hokkanen_csc_700_400_en_en.jpg)

~~~
BrandonSmithJ
Fairly certain it's done using mayavi -
[http://docs.enthought.com/mayavi/mayavi/index.html](http://docs.enthought.com/mayavi/mayavi/index.html)

~~~
adamnemecek
This looks something I've been looking for. Are there some products
(commercial sw, or libraries) in this space?

~~~
BrandonSmithJ
I'm unsure about the commercial licensing aspect of it if that's what you're
asking, but mayavi has both a GUI interface as well as a scripting interface
depending on how you want to use it. In my experience it's essentially the
library to use for 3D plotting when matplotlib isn't cutting it.

(I just checked wikipedia and it seems it's released under BSD license. Unsure
if other products available which are built on top of it)

------
babyrainbow
>alto University researchers show that in a transparent medium each photon is
accompanied by an atomic mass density wave. The optical force of the photon
sets the medium atoms in motion and makes them carry 92% of the total momentum
of light, in the case of silicon.

Wait a min. Can this be used to build optical logic gates?

~~~
wyager
Could you explain your reasoning further? Are you just saying that because you
see "photon" and "silicon" in the same place?

The answer, unless I misunderstand you, is "probably not"; I don't see how
this discovery would help us to implement optical transistors.

~~~
babyrainbow
No.

Isn't the problem with optical computers is that we don't have a way to switch
light using light only. I though maybe this will enable to do something like
that..because it says that light through a medium affecting a physical
property, and that too at the speed of light...

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webnrrd2k
if you would like some background on this question, as I do, there is a SE
discussion that makes it a bit easier...

[https://physics.stackexchange.com/questions/3189/is-the-
abra...](https://physics.stackexchange.com/questions/3189/is-the-abraham-
minkowski-controversy-resolved)

There is a summary statement that I found to be especially helpful in framing
the question:

"To summarize... it's probably OK to "redo" the budget in such a way that a
part of the momentum of the photon is attributed to the dielectric material
when the photon enters it, and then it is returned back to the photon. In this
way, one may justify the Abraham's form - and probably many other forms - but
why should one really do it?"

------
k2xl
EL5? What is the paradox of light?

~~~
metafunctor
That is explained in the second paragraph of the article:

 _In the literature, there has existed two different values for the momentum
of light in the transparent medium. Typically, these values differ by a factor
of ten and this discrepancy is known as the momentum paradox of light._

~~~
lisper
[https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy](https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy)
if you want the gory details.

However, IMO none of these explanations are particularly satisfying because
none of them (AFAICT) explain where these two different formulations come
from. They all leave you with the impression that two physicists just pulled
two different equations out of their ass and now they're arguing over which
one is right as if it were some sort of theological discussion. (This is a
common problem in physics pedagogy.) I would really love to hear from a
physicist who understands and can explain the basis for the two different
formulations.

