Draft Notes for My Obituary

From ChatGPT

We went to a funeral last Thursday. Iris Klim, aged 95, a parishioner. Her son gave a eulogy: pleasant, informative, affectionate, moving. A model of its type.

Nigel said he would prefer something different when his time comes …

Skate rapidly over my life, he said: youthful communist - a militant of the Fourth International; software developer turned researcher in Artificial Intelligence; successful freelance designer of telecoms networks.

Nigel's wife and children confirm his weird and bizarre opinions.

He claimed that the passage of time is a psychological illusion, that all times exist as if in amber. He claimed Albert Einstein as an authority on this. He said that, in any case, both space and time are not fundamental: the universe we live in is an emergent artefact of quantum entanglement - true reality is set in abstract Hilbert space.

Honestly!

Nigel had yellow belts in Judo and Karate, and years of T'ai Chi. He practised these arts to the end but never fought anyone for real (after an inconclusive  scrap when he was nine  - he was provoked!).

He died a Catholic, although for most of his life he was irreligious. He said that the apocryphal Martian anthropologist (a methodological nihilist) might say that human beings were simply biological machines. But ‘it is not like anything to be’ any of the machines we know about. The materialist faith that consciousness is reducible to neural net operations is no more than that; in any case explanations do not account for lived experience: that is the mystery and reality which theology encompasses better than anything else. Anyway, he was drawn more to Catholic deontology than any specific ontology: how we live is important.

Nigel puzzled over the continuity of personal identity. How do we know that we, now, are the same person who will wake up tomorrow morning? Actually, he said, we can’t know. Many people are quite like us, whoever we are. Personal memory is always mentioned, he said, but who’d die in a ditch for that when it comes to the foundational nature of our very selves?

So at this space-time moment, in this branch of the universal wave-function, you should say: Nigel has passed on. He wanted you to know that in the great enduring sea of consciousness and human experience, it’s not such a big deal. Except to those who shared our lives together, for whom it is everything.

What we think of when we think of death

The soldier: the first one can be hard; after that it's pretty easy.

The dualist: there may be some connection between the person I feel myself to be and the squidgy mass of cells-in-soup inside my skull - but the same thing?!

The neuroscientist: it's process - the mind is what the brain does; I concede we don't know how that could work.

The evolutionary biologist: natural selection has favoured the complex human nervous system. It supports sophisticated social behaviour in challenging, dynamic but mostly predictable environments. What's the problem?

The philosopher: to explain consciousness is categorically different to experiencing it. We both know you're in pain and why, but you're the one screaming.

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Me:

Sometimes when I think of dying I feel that a complex organ (my brain) will stop functioning and its constituents disperse into the biosphere. No big deal.

Sometimes I think that human subjective experiences are extraordinarily similar. Millions of people have sensations, feelings, thoughts and consciousness just like mine. My personal deletion in death is not dissimilar to me falling asleep and waking up next morning as a… slightly different person: someone very like me who is not me.

The human race (or successor conscious beings) may advance in times to come - or may become extinct. We all feel that to secure the former is worth any sacrifice (most of us!) but there is no evidence the universe is the kind of entity which could care either way.

The process of evolution ensures that we have to care - selection bias - so that's really no surprise. We each live within our individual consciousnesses, so structured that we have to care about ourselves and those others we take to constitute our mutually supportive community. If you like, those are the boundary conditions for being a socially adjusted human (not sociopathic, schizophrenic, psychotic, etc).

When we die, a universe may die with us and within us, but let's not be precious. The flow, the continuity of the collective consciousness of humanity gives me reassurance. Just like I'll not be too concerned about falling asleep tonight - as someone will likely awaken tomorrow morning with whom I identify.

Like most people trained in physics, I happen to accept the block universe concept in which the passage of time is a psychological construct, a product of local spacetime interaction between our bodies and the environment. In this sense the past and the future are equally existent and our lives exist in entirety - just as a DVD contains the whole movie, all at once.

(Maybe the universe is really some complex multiverse structure in Hilbert space - who knows?).

Anyway, because I'm a reasonably adjusted human being, I'm a fan of sensual, emotional, smart, prosocial consciousnesses having an indefinite, fulfilling future. I'm reassured by progress so far - at least in this branch of the universal wavefunction. These emotions are conditioned by my future-ignorance, of course.

And for reasons mentioned, I'm not too scared about the eventual unavoidable extinction of the personal consciousness of this author.

You, dear reader, will take up the torch.

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Greg Egan's short story "The Walk" in his collection "Axiomatic" uses this approach as setting. 

Roger Scruton in his book "On Human Nature" makes the distinction between being conscious and having a theory of consciousness.

And I wrote a short piece about this - 'Live Forever' - at sciencefiction.com.

See also Adam Carlton's short story, "Doppelgänger": memory discontinuity hangs heavy.

The quantum-theoretic block universe

Eternalism is not hard to justify.

Yesterday I contemplated my situation and concluded: "This is real, this is now."

Today, when I recollect that scene, I'm inclined to think it was indeed real, and shows the reality of the past (which has not flickered out of existence but is .. elsewhere).

Yesterday, I also thought, "Tomorrow, I will be writing a post."

Today, here I am doing it. For yesterday's me, that shows the reality of the future.

As Frank Sinatra observed, "You can't have one without the other."

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For greater conviction, we can appeal to special relativity. As I wrote in a piece for sciencefiction.com,

"Brian Greene in ‘The Fabric of the Cosmos’ (page 134) considers an alien in a galaxy ten billion light years away, at the edge of the visible universe. Simply by ambulating towards or away from us at 10 mph, the alien’s view of what is happening ‘right now’ on earth swings from 149 years in the past to 149 years in the future."

Still, the block universe is classical and therefore inaccurate. It's necessary to move to quantum theory where, as usual, one needs to take the red pill.

Theoretical physicist Jeremy Bernstein on 'A Quantum Past'.

"In FAPP (For All Practical Purposes) language we have a quantum mechanical system described by a wave function ψ(t), I am  only interested in the time variable.

The wave function obeys a Schrödinger equation with a Hamiltonian H. The formal solution to this equation is ψ(t) = exp(iHt)ψ(0). Throughout I am setting ћ = 1. Thus to recover Ψ(0) from ψ(t) all we have to do is to multiply by exp(-iHt).

Haven’t we then recovered the past? What is all the fuss about? The problem is that there is more to life than the wave function. There are the “observables” which represent what we really want to know about the system. These observables are described by Hermitian operators A. B. C and so on. We can expand ψ in a sum over the orthonormal eigenfunctions of any of these operators. The coefficients in the expansion are related to the probabilities that in a measurement the system will be found to have one of these eigenvalues. This is “Born’s rule” and in FAPP it must be assumed.

To find which of these eigenvalues the system actually has, we must perform a measurement. Stripped to its essence the apparatus that produces this measurement projects out from the sum of eigenfunctions one of them.

After the measurement the rest of the terms in the sum disappear. Using the term of art, the wave function “collapses”. It is at this point that we lose our capacity to reconstruct the past.

Projection operators are singular. They do not have inverses. All the king’s horses and all the king’s men cannot put the wave function back together again.

It was von Neumann in the early 1930’s who first noted that in FAPP mechanics there were two kinds of processes. There were processes that could be described by a Schrödinger equation and there were measurements which could not. He did not, as far as I know, comment on what this implied for retrodiction.

A case in point is an electron described by a spherically symmetric Schrödinger wave. If this electron strikes a detector is does so at a place - a spot. After this happens all trace of the spherically symmetric wave function vanishes.

I have certainly not made a careful search of the literature but among the founding fathers of FAPP I can come up with only two references that deal with the matter of the quantum past.

One is Heisenberg and the other is a paper by Einstein, Richard Tolman, and Boris Podolsky, “Knowledge of Past and Future in Quantum Mechanics” which they wrote in 1931 when Einstein was spending time at CalTech."

Bernstein talks about these two references, and then discusses where he thinks the problem resides, and what is to be done.

"It seems to me that any interpretation of the quantum theory that addresses this [the problem of wavefunction collapse] must have the feature that measurements are simply just another interaction like the rest.

Von Neumann’s notion that there were two classes of interactions one whose time evolution could be described by a Schrödinger equation and one of which couldn’t, has to be abandoned.

I will discuss two proposals for doing this each of which has its adherents and its detractors. On the one hand I am going to discuss what I will call “Bohmian mechanics” a term which David Bohm, who invented this approach , apparently did not like. As far as he was concerned, he was just doing quantum mechanics but in a different way. However nearly everyone else calls it Bohmian mechanics - so will I.

On the other hand, I am going to discuss the “decoherent history” interpretation which Murray Gell-Mann and Jim Hartle have done the most on. Sometimes this is called the “many worlds” interpretation, but not by them. I think that the term “many worlds” is misleading. As far as we know there is one world, the one we live in."

I'm not a fan of “Bohmian mechanics” and insofar as any quantum ontology works for me, it has to be "Many Worlds" (Sean Carroll explains why).

So I'll skip over Bernstein's description of Bohm's view of the quantum past and quote his take on “decoherent histories”.

"In the "Many Histories Interpretation" what indeed is history?

At first sight this might seem to be obvious. All we have to do is to run the chain backwards.

Yes this gives one history but there are others, possibly very many others. The reason is that if all we know is the present state vector there are many paths by which we could have arrived there depending on which initial state vector we started from. We have no way of knowing this from the data we have at hand.

Let us take an example discussed by Hartle - the Schrödinger cat (I can’t resist noting that when I spent an afternoon with Schrödinger in his apartment in Vienna there was no cat). In any event this unfortunate feline is put in a box that contains a capsule of poison gas and a sample of uranium. The capsule is triggered so that if the uranium has an alpha decay, the alpha sets off the trigger and the unfortunate feline expires.

After a time interval we open the box and happily the cat is alive. It could, according to the many history approach have arrived at this state in two ways. The initial state might have been a cat alive state or it might have been a coherent sum of a cat alive and a cat dead state. From the presence of the living cat we cannot decide.

The vision of the past given by the decoherent history interpretation and the Bohmian seems radically different. In Bohmian mechanics we could in principle follow all the cat molecules backwards in time and arrive at one and only one past.

I don’t know how you feel, but the ambiguity of the past makes me queasy. It might be entertaining to imagine that in an alternate past my grandmother who was born in a Polish stetl could have been Eleanor Roosevelt.

I readily accept that these pasts to not communicate but there seem to be too many of them from the point of view of economy. A trip to a barber wielding Occam’s razor seems warranted.

In any case when it comes to quantum pasts, as Duke Ellington taught us, “Things ain’t what they used to be.”

Perhaps Bernstein wrote this short paper just for that final joke at the end?

To summarise, if you take quantum theory seriously and you take eternalism (the block universe) seriously, then it seems that the past is as indeterminate as the future.

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How does this relate to the 'low entropy in the past' idea used to explain the 'arrow of time'?

Since quantum theory is consistent with the second law of thermodynamics, a picture emerges of backwards branching towards (superpositions of) Big Bang variants.

My ex-colleague Roy said as much in this comment, on an earlier post devoted to the MWI. See here for more.

Confessions of an eternalist

Confession: I am an eternalist.

Eternalist Sean Carroll has a post up commenting on recent books by Lee Smolin and philosopher Roberto Mangabeira Unger who argue to the contrary. Reading the comments there is depressing  - people either don't understand the issue at all, or don't appreciate how to think about the subjective nature of 'now'. Physicists!

One physicist, Sabine Hossenfelder, has written an excellent and definitive analysis: here's an extract.

"The decisive ability that allows us to experience the present moment as being unlike other moments is that we have a memory. We have a memory of events in the past, an imperfect one, and we do not have memory of events in the future. Memory is not in and by itself tied to consciousness, it is tied to the increase of entropy, or the arrow of time if you wish. Many materials show memory; every system with a path dependence like eg hysteresis does. If you get a perm the molecule chains in your hair remember the bonds, not your brain.

"Memory has nothing to do with consciousness in particular which is good because it makes it much easier to find the flaw in the argument leading to the problem of now.

"If we want to describe systems with memory we need at the very least two time parameters: t to parameterize the location of the particle and τ to parameterize the strength of memory of other times depending on its present location. This means there is a function f(t,τ) that encodes how strong is the memory of time τ at moment t. You need, in other words, at the very least a two-point function, a plain particle trajectory will not do.

"That we experience a “now” means that the strength of memory peaks when both time parameters are identical, ie t-τ = 0. That we do not have any memory of the future means that the function vanishes when τ > t. For the past it must decay somehow, but the details don’t matter. This construction is already sufficient to explain why we have the subjective experience of the present moment being special. And it wasn't that difficult, was it?"

I'm not so much into perms as my preferred physical model of subjective temporal experience. If you imagine a robot with an updating model of observed-reality obtained from its internal and external sensors, it's easy to see that examining its own memory store at any instant at all the robot can persuade itself that this instant "now" is special. But all introspective moments are like that. If we saved each database-state where:

"the robot notes that it is aware of itself and its environment now"

to disk, there would be nothing fundamentally distinct about any of them.

That robot is, functionally, me and you and sits easily in the block universe.