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

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.