Hi, Huw!

I am mainly writing to ask how it is going, and how your thoughts are evolving about collaboration,
co-authorship and such.

I have mentioned your book to a number of people, which may help stir up interest in some
new quarters.

For a possible joint paper on the astrophysics side -- I tried (briefly) without much success
to get an authoritative update on where Gold and Hawking really stand -- on how much
documentation we might cite regarding the importance of investigating backwards-time effects.
I can try again, through new routes... but my personal time is unbelievably constrained.


I have thought a bit more about the temperature issue, as well. I did some thinking about it
'way back in quant ph 0008036... but if you look at the relevant section, you can see that I fumbled
a lot around that issue. Do we expect photon absorption to be enhanced or reduced
when the absorber is hot or cold? Do we expect backwards-time free energy to be available
ONLY in cosmological sources which only have half a chance of existing anyway?
Does a local arrow of time have some other effects besides what we measure with gross temperature?

Thinking more about it...

I think about a kind of "thermodynamics" picture... idealized, of course, as in all mathematically tractable
models... made up of Objects floating free in space, never colliding, interacting only
by absorbing and emitting "photons." (There is a discussion of cosmology by Wheeler which paints a similar picture,
though he adds neutrinos as well...).

IN EQUILIBRIUM (i.e. far away from a perfect time-forwards or time-backwards extreme!)... an Object acts
a lot like a big quantized "atom," with lots of energy levels and modes of excitation. At higher energy
levels, there are more "modes" of emission available... which is what causes more emission of
photons in forwards time. But there are also more "holes" available, which lead to more absorption.
The "negative time brightness" of an object is not directly due to semi-magical concepts like
the arrow of time (magical in THIS context), but simply to the abundance of "holes".
Equilibration tends to lead to a balance of holes and excited modes.


But then what happens in FORWARDS time, particularly in OUR nonequilibrium realm?

For ordinary Bell's Theorem types of experiments, we use OPTICAL frequency photons,
which are ultimately sent to MUCH COLDER detectors (room temperature or less).
The hypothesis would be that the density of OPTICAL FREQUENCY holes is pretty
much the same, for temperatures much less than the "temperature" of the photon.
(I am defining the temperature of the photon as basically that temperature
of solid matter at which photons of that frequency are the peak of the "black body emission spectrum.")

HOWEVER: this does NOT rule out backwards-time (or just backwards-causal) absorption effects
even with laboratory experiments with no cosmological content.

As a thought experiment, I asked myself the following question: "If an optical system... emits photons...
with a certain probability distribution as a function of solid angle... COULD a backwards effect
ever CHANGE the intensity of light emitted in different directions? Is this nuts? Does it violate all
known experiments?"

And then I realized: "No way. Consider VCSELS -- vertical cavity surface emitting lasers."
(Scherer at CalTech is perhaps the world's leader in VCSEL technology, which is well along
as an option for better optical displays. Real hopes of killing the usual LED technology used
in the flat monitor I am using right now...) The zero point energy people have had a field day
talking about VCSELs as if they proved the ideas of zero point modes; they argue that
VCSELS involve cavities which suppress the usual vacuum modes which explain simulated emission
in semiclassical models...

But this is a case where TRUE PDE models actually are closer to rigorous QED than they are
to semiclassical models!

The most accurate analysis of VCSELs, used by folks like Scherer, is based on QED. The story
they give is as follows: "The probability of a transition... from an excited state of the local material..
to a state with a photon... is based on the matrix element BETWEEN the excited state and the
AVAILABLE photon states. In VCSELs, we eliminate the usually available photon states. By shaping the cavity
properly, we ensure that the only available states... are those pointing in the right direction(s)...
the main axis of the cavity... particularly, the excited levels of the coherent modes..."

**IF"" photon emission were really just a matter of photons leaving an atom, and then finding a home later,
this explanation would not work! (Yet many people using quantum theory ASSUME exactly that picture.
It SEEMS to be a basic part of quantum field theory!) But if we THROW OUT free photon states
as possible outcomes of a MACROSCOPIC experiment... if we insist instead on connecting
the PHOTON EMITTER to an "available eigenstate" which INCORPORATES information about available absorbers...
we do in fact ALREADY assume backwards-causal mechanisms into the calculation!!!!

In summary -- our EXISTING successful calculations of how VCSELs work ALREADY show
how the direction of emission of light can be STRONGLY influenced by the availability of
appropriate absorbers!!!!

In fact, even Planck's and Einstein's black body calculations could be revisited as an example
of this kind of effect.

I wouldn't want to push this TOO hard quite yet. Solid state calculations/estimates of
emitter spectra AND OF hole spectra will ultimately be needed. But a quick guess
would be... that we COULD expect to start seeing absorber effects when
the temperature of the photons and of the absorber start to be closer.

So here are some REALLY crazy ideas for how this might work out....

I mentioned two possible ways of trying to image reverse-time brightness, in cosmology --
one based on semiconductors (reverse-time photmultipliers, roughly) and another based on
SPDC effects, which Yanhua Shih understands empirically better than anyone else in the world.
The reverse time photomultipliers would be more efficient, but involve heavy initial costs.
Thus for initial feasibility demonstrations, SPDC may be more practical....

You may even want to look up the paper by Kim and Shih which I cite on the "Popper" experiments.
It is much easier to read than my versions... and it does cite the philosophy literature, after all.

Crudely... it might be possible somehow to put a very hot "black" ceramic piece of material ..
or other hot black material... on an image plane entangled (positionally) with another
image plane on which there are detectors, to see whether the enhanced absorption
propensity DRAWS photons to the hot object, in a way which creates an image on
the other channel. (This is not so simple as some of the other ideas
I have discussed with Yanhua, and so should perhaps not have top priority.
I suspect that sharp color filters would be important, to make sure that the positive-time photons emitted
from the ceramic do not overload the right-channel detection, given that we would have to rely on
single-photon counting on the right channel. Fortunately, the photon pairs would
be at a VERY narrow frequency band... and it would be good enough to get a measurable increase in
single-photon counting in the right areas, keeping the ceramic hot but turning the laser pump on and off.)

In fact... it may also be possible to do CALCULATIONS analogous to those used with VCSELs for
this and other macroscopic arrangements, so as to PREDICT macroscopic absorber-state effects!!!

An alternative approach to true BTT?

I wonder. Somewhere in the condensed matter literature... there must be calculations on absorption or
"hole" spectra, relevant to black body calculations, just as exact as calculations of the emission or
excitation spectra which give rise to black body emission...

** IF AND WHEN** such laboratory experiments work,
the  motivation would be there to drive much larger levels of accuracy and funding
for this kind of work. I am reminded of what venture capital people say -- about how
the first million is typically much, much harder to raise than the next ten.
Once there is something WORKING PHYSICALLY....


I have also done some more thinking about polarizers, in regards to the solid state
physics. The story is easy to explain QUALITATIVELY... but the cos**2 functional form
is a bit hard. I even find myself halfway wondering... when there are two or more polarizers
along the SAME channel... we know that the cos**2 rule applies for attenuation of light
in each polarizer when there is a macroscopic beam... but are we REALLY
sure experimentally that it works through multiple polarizers on the same channel when
there are individual non-coherent photons coming through one at a time?
Has that really been proven empirically? (I am not sure how to handle probabilities
associated with the momentum transfer which occurs when light comes
in at one polarization and goes out at another polarization.)


Best of luck,

    Paul W.