Henry Margenau was born on 30 April 1901, and left his old jacket on 8 February 1997.
He was a great man. I will always remember his moral support, from 1985 to 1990, at the time I needed it most. I wrote him a letter in June 1990, in which I stated that his Latency Interpretation of Quantum Mechanics  is the correct one, and explained my interpretation of his crucial phrase:
Twenty years later, I can elaborate a bit more.
The act of measurement will always 'force the eigenvalues out of latency', yet there exists a fundamental 'potential quantum state' resembling Platonic ideas, which can never be explicated at the length scale of tables and chairs, because it does not have any eigenvalues whatsoever. It does not live in the Hilbert space either. It is the Kochen-Specker (KS) state.
Thus, Henry's “not always there” can be fragmented into two "parts": speakable (possessing latent eigenvalues) and UNspeakable. The former is subject to 'choice'  made by 'everything else in the Machian universe', while the latter is a pre-quantum state resembling Platonic ideas, which keeps all "non-commutative" quantum states en bloc , and the Genidentität (Kurt Lewin) of an elementary particle through measurements. It is the KS state, again.
One obvious merit of such interpretation of Henry's “not always there”  is that one can think of a single quasi-local trajectory of a single quasi-local quantum particle, because each and every explicated 'quantum state' along such quasi-local trajectory is an emergent state, and is being actualized with unit probability -- one-quantum-state-at-a-time.
Thanks to the pre-quantum state (never in plural) resembling Platonic ideas, all-but-one from its latent "eigenvalues" are cancelled from the outset; for example, we never encounter a superposition of |alive cat> and |dead cat>, hence can solve the macro-objectification problem  and reconcile QM with Special Relativity.
What we observe at macroscopic scale is a perfect continuum of events explicated with unit probability -- one-at-a-time along the Arrow of Space. We perceive this emergent continuum as 3-D space, but are unaware of its pre-quantum dynamics, which allows perfectly smooth transitions between the quantum and macroscopic worlds, while keeping the complex phase of quantum waves intact, and without any "quantum jumps". The latter are nothing but artifacts from the measuring devices that cannot screen the quasi-local nature of quantum phenomena.
"Wenn es doch bei dieser verdammten Quantenspringerei bleiben soll, dann bedauere ich, mich mit der Quantentheorie überhaupt beschäftigt zu
haben," Erwin Schrödinger.
"Our thesis is that quantum mechanics leaves our body, our brain, at any moment in a state with numerous (because of its complexity we might say innumerable) possible futures, each with a predetermined probability. Freedom involves two components: chance (existence of a genuine set of alternatives) and choice. Quantum mechanics provides the chance, and we shall argue that only the mind can make the choice by selecting (not energetically enforcing) among the possible future courses."
To explain the quasi-local exchange of energy in General Relativity, and the failure to produce anything that can be physically interpreted as a local "energy-momentum tensor" , look carefully at  (emphasis, links, and comments added - D.C.):
In order to determine the energy of each part of the detector, one must first specify a timelike vector field -- the “time direction” conjugate to the energy -- with which to form an energy current-density (ibid.).
First things first.
It's not a "timelike vector field" though. One cannot define 'time direction' by splitting the spacetime into two entities, and then "define" one of them (called "time") with respect to the other one, which has nowhere to move. If one "part" from spacetime is deprived from any dynamics, the other "part" will also be dead frozen, and we cannot pinpoint the global "time" at which the total energy is conserved (see ExplanatoryNote.pdf, pp. 35-36). To address the issue of (quasi-local) energy conservation in GR, one needs to specify an arbitrarily large isolated system with "cut off" placed at Finite Infinity, to capture the global characteristics of 'space' pertinent to a global time. The former is missing from current GR, hence it is not surprising that the latter is missing as well. Consequently, the so-called 'problem of time' in canonical quantum gravity is an inevitable result from the fact that what we call 'spacetime' is actually one entity, and if one "part" from it (called 'space') is frozen, there will be no dynamics from the outset. The problem stems from the lack of global time in present-day GR: it does not originate from 'coordinate change in space', but from 'global change of space' bzw. Arrow of Space. The latter makes any observable of the gravitational field "necessarily quasi-local" (Laszlo Szabados).
We need an Arrow of Space and non-unitary dynamics of 'space', because "the appearance of additional energy which was not already present" (ibid.) is just too much (some people call this additional energy "dark", and offer tantalizing insights about how "spacetime can give energy to matter, or absorb it from matter" ).
Let me try to explain my viewpoint, in the framework of 'the universe modeled as a brain'. I take for granted that matter can interact with matter only. Corollary: any direct action of geometry on matter is banned. It is like direct action of the human mind on its brain or other physical objects. To avoid such "psychokinesis", we should investigate how matter interacts with matter in a Machian universe, in which the non-linear negotiation and feedback from 'everything else from the school/universe' is encoded in the emergence of what has been called gravitational "field" -- a holistic effect common to biological, quantum, and gravitational systems. The end result is an emergent geodesic of quasi-local objects bootstrapped by their gravitational "field". The additional input from 'everything else in the universe', exerted on every quasi-local object, will be inevitably camouflaged as "self-force" and "more gravity". The source of this additional input will be always "dark", because there is no way in GR to be traced back - it is simply an omnipresent, ether-like 'reference fluid'.
The first off task is to identify the infinitesimal cracks through which the physicalized (=converted into positive) vacuum energy gets smuggled into the local mode in the Arrow of Space. What is needed is a new energy conservation equation (cf. ExplanatoryNote.pdf, pp. 35-36) in which the additional "dark" energy is compensated by an equal amount of positive energy density spread evenly, without any irregularities, over the whole space en bloc. There isn't any "privileged observer" (M. Montesinos) associated with such ether-like 'reference fluid in GR', because the "ether" is omnipresent "inside" each and every point from the spacetime manifold, hence there is no "point" at which it is 'not there', to be used as a reference object with respect to which we could identify such "ether". Notice that the dynamical object in question is the spacetime manifold which is being re-created along the Arrow of Space. And again, we have here one-compensation-at-a-time along the Arrow of Space.
The prerequisites for this task have been laid out by Henry Margenau . He also stressed the most acute unresolved task in Quantum Theory -- the absence of a 'chooser' (the alleged "decoherence" is a myth, and of course doesn't work for quantum cosmology). Henry suggested that "only the mind can make the choice by selecting (not energetically enforcing) among the possible future courses" , but in the framework of 'the universe as a brain' one can safely replace the notion of 'Universal Mind' with 'the whole universe as ONE', and recover the ultimate 'chooser': it is the universe itself which makes the choice. It is ONE pre-quantum entity resembling Platonic ideas (global mode of spacetime), hence the choice of 'one possibility among infinitely many' does not imply any "observer" nor pre-existing macroscopic world equipped with measuring devices. Thus, the universe is self-correlated and bootstrapped, and by exercising its 'free will choice' it re-creates, as a genuine Phoenix Universe (Georges Lemaître, 1933), a perfect continuum of such 'choices' -- one-choice-at-a-time along the Arrow of Space.
All this is encapsulated in the motto of this web site: Dead matter makes quantum jumps; the living-and-quantum matter is smarter.
Many experts in quantum gravity do not appreciate
this proposal (most notably Chris Isham), but
haven't so far offered any viable alternative to the 'chooser' in
May I propose 'a shift of attention', by comparing the two main approaches toward quantum gravity, string theory and loop quantum gravity (LQG), with the third one outlined at this web site, which will be called 'Machian quantum gravity' (MQG).
Carlo Rovelli, who has studied the fundamental research in quantum gravity by Karel Kuchar and has been coached by Chris Isham, has published extensively in support of LQG. He explained his criticism of the string approach, as a theory "over a background Minkowski spacetime (perhaps in high dimensions)", and stated:
"But success, I think, can only be granted by scrupulous intellectual honesty."
Beautiful words. But it seems to me that the proponents of LQG are also short of this quality.
Here's the common feature of string approach & LQG: they consider only those particular bits and pieces from Quantum Theory and General Relativity, which work fine in their respective domains of application (ignoring the unsolved issues), and try to blend them into some new theory of quantum gravity.
Metaphorically speaking, consider a car that runs quite well on straight dry roads, but fails miserably on twisted icy roads, and a helicopter that flies well in quiet weather, but is totally useless in windy conditions. Then try to blend the car and the helicopter, hoping that the problems of the car may be fixed with the problems of the helicopter and vice versa, and keep dreaming of some brand new vehicle which will run better than the car and fly better than the helicopter, and will also dive deep into the ocean, like a perfect submarine.
The proposed 'shift of attention' is to start with fixing the old problems of Quantum Theory and General Relativity: (i) resolve the macro-objectification problem  and reconcile QM with Special Relativity, and (ii) find 'the right answer to the right question' regarding the gravitational energy-momentum , clarify the exact meaning of the Equivalence Principle and Finite Infinity, and the (quasi-instantaneous?) propagation of gravitation in the context of Mach 11 . Which obviously requires a modern formulation of 'the reference fluid in GR' .
Then all pieces from the jigsaw puzzle will snap to their places -- effortlessly. All we need is a scrupulous intellectual honesty.
I intend to deliver a talk on November 25, 2015 , commemorating the 100th anniversary of the joint work by Levi-Civita, Einstein, and Hilbert. Attendance is free, but seats are limited to 35. The whole bundle of issues is quite dense (similar to my previous talk), and is by no means purely academic, as it offers a glimpse at a new possibility for unleashing "dark energy" from the quantum vacuum : depending on the macroscopic boundary conditions, which must be kept under tight control, the energy release may vary from an almost vanishing flux up to 1054 ergs/pulse, which is much larger than the mundane nuclear energy release of ~1022 ergs/pulse.
If you're interested, please email me by September 25, 2015.
To avoid misunderstandings regarding the use of Platonic ideas and the general concept of 'potential reality', please read the NB note (30.11.2010) at the end of my posting here.
"The canonical response to the gravitational
energy-momentum problem is to dismiss it as “looking for the right answer to the
wrong question” ; but while the well-known argument
presented by Misner, Thorne and Wheeler is certainly compelling, it is far from
"And in my experience, saying “there’s energy
in the gravitational field, but it’s negative, so it exactly cancels the energy
you think is being gained in the matter fields” does not actually increase
anyone’s understanding — it just quiets them down.
"The particles of the reference fluid identify
the points of space, and clocks carried by these particles identify the instants
of time. In this way, the fluid fixes the reference frame (the space) and the
time foliation (the time). In that frame and on that foliation (there
isn't such "foliation", however - D.C.), the entire intrinsic metric, not
just two selected components of the intrinsic geometry, becomes dynamical.