Afterlife, Reversibility, and the House of Pleasure

Eleven years ago, I posted a philosophical problem, which I called “The House of Pleasure,” on various online forums, such as this.  (The complete problem is copied at the end of this post.)  I posted this long before my foray into the philosophy of physics and consciousness, beginning in 2018, and I just realized how incredibly insightful it was, particularly regarding my recent innovations and realizations about the impossibility of physical reversibility (also here and here).

Physically reversible systems can only be made so large – and that threshold is significantly smaller than a cat, Wigner’s Friend, or any reasonably useful quantum computer.  (That de facto threshold is what renders impossible the scalability of quantum computing.)

Essentially, the House of Pleasure (“HOP”) problem asks what you would consciously experience if, after a four-hour intensely pleasurable event, your brain and body are returned to their exact physical state just prior to the event.  I realized, correctly, that you would not consciously experience the event at all; you would consciously experience “skipping over” the event as if it hadn’t happened.  Therefore, if you did consciously experience the event, you could be certain that your brain/body would not later be returned to their physical state prior to the event.

As it turns out, this insight parallels the actual reasoning for why macroscopic physical systems are irreversible.  For instance:

·       In a system (that has evolved from state Ψ(t₁) to Ψ(t₂)) that is time reversed back to state Ψ(t₁), there remains no physical evidence of the existence of the system in state Ψ(t₂); thus from a scientific standpoint, the system never evolved to state Ψ(t₂) in the first place.

·       Time does not pass/progress in a system that ostensibly evolves Ψ(t₁)à Ψ(t₂)à Ψ(t₁).  Any and every internal clock of the system (including, but not limited to, radioactive decay, entropy increases, quantum collapse events, the ticking of an actual clock, etc.), when the system is in state Ψ(t₁), states the time as t₁, even if external observers would disagree.

·       A conscious measurement by Wigner’s Friend is impossible as a logical contradiction.  (I’ve argued that in lots of papers and posts, but this Physical Review Letters paper makes an incredibly similar point.)

In other words, by the time an event has been consciously experienced, it is already too late to turn back time and return your physical state to an earlier state.  I’ve argued that irreversibility happens long before conscious awareness – and therefore that consciousness does not cause collapse of the wave function – but one’s conscious awareness of an event is sufficient evidence that the possibility of reversibility has been foreclosed. 

Having said that, I’ll analyze the original HOP problem and point out an error.  First, the intent of the thought experiment was to give a logical argument for the existence of an afterlife (specifically, eternal consciousness). 

When you leave after four hours, your brain will be scanned again.  It will be returned to the exact physical state it started in when you first entered.  In other words, your memory of the experience will be completely erased. 

It’s true that returning your brain/body to their exact physical states prior to entering HOP implies a complete and permanent erase of memories; however, the converse (that a complete and permanent erase of memories implies returning your brain/body to their exact physical states prior to entering HOP) is not necessarily true. 

I correctly concluded that my conscious experience of HOP precludes the possibility of my brain/body being returned to their exact physical states prior to HOP.  (My “problematic” intuition that my “perception of the experience depends on what happens afterward” is not actually problematic; it simply indicates the impossibility of physical reversibility after my conscious observation of HOP.)  However, the argument (as presented) did not properly conclude that my conscious experience of HOP precludes the possibility of complete and permanent memory erasure.  If it did, then the following argument and conclusion would have been correct:

If my memory of a time period will be permanently erased immediately after that time period, then my stream of consciousness skips over that time period…

…implies that if I am consciously aware right now (I am), then my stream of consciousness is not skipping over this time period, and my memory of this time period will not be immediately permanently erased…

…seems to imply eternal consciousness.

There is a correspondence between the history dependence inherent in physical state evolutions (that prevents physical reversibility) and the history dependence of conscious state evolutions.  In this post and this post (among others), I discuss the history dependence of conscious states, which implies that a person cannot re-experience an earlier conscious state.  (I came to a related conclusion – that special relativity requires that conscious states cannot be physically copied or created de novo – in this paper.)  Therefore, not only does my experience of HOP preclude the possibility of returning my body/brain to an earlier physical state, it also precludes the possibility of my returning to an earlier conscious state.  

A couple of questions then arise:

·       Is there a way to permanently and completely erase one’s memories of an event without returning the person’s body/brain to their exact physical state prior to the event (which is impossible)?  Without returning the person to their exact conscious state prior to the event (which is likewise impossible)?

·       Why the fixation on memories?  I used the HOP example because it’s so hard to imagine having an otherwise very memorable and intense 4-hour orgasm and then to immediately and permanently forget it.  But maybe the memory created by a conscious experience need not be the kind of explicit visualization we often associate with a memory (like envisioning the faces of the people who yelled “Surprise!” on your birthday), but rather something that affects future conscious experiences.  This notion is much more consistent with my insight that conscious states are history dependent (and embed their own history).

·       Imagine that my first conscious state was C₁.  Whatever existed before that… let’s call it C₀, which is certainly a state of no consciousness.  If it’s impossible to return to an earlier conscious state, then it’s impossible for me to return to state C₁.  But what about C₀?  And wouldn’t any state of no consciousness be identical to C₀?  In some ways, I think this is just another way of saying that it’s impossible for me to (consciously) experience a state of unconsciousness, which seems both obvious and circular.  On the other hand, this may underscore the deeper insight that a conscious perception cannot subjectively end because there is no time at which that end is subjectively experienced.

·       That begs a deeper conundrum about the nature of “now”: what is now, why is it now, and by whose observation? 

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“The House of Pleasure”

It’s a Saturday night and a guy is walking to a party.  On the way, he notices something he hasn’t seen before: a neon sign obnoxiously blinking “The House of Pleasure.”  Intrigued, he approaches the doorman. 

“That’ll be $100, sir.”

“What?  That’s crazy!  What is this place?”

“Oh,” the doorman says with a glimmer in his eye, “you’ve never been to The House of Pleasure?  Let me explain.  After you pay me and walk in, your brain will be scanned to identify everything that you subjectively enjoy: physically, sexually, emotionally, and intellectually.  You’ll then spend the next four hours experiencing pure, untainted pleasure based on your personal desires.  Whatever you enjoy most about life, you will experience intensely and without interruption for four hours.  Think of it as a four-hour spiritual orgasm.”

“Incredible!  This sounds great…”

“However,” the doorman warned, “there’s a catch.  When you leave after four hours, your brain will be scanned again.  It will be returned to the exact physical state it started in when you first entered.  In other words, your memory of the experience will be completely erased.  Also, your body will be returned to its original state, so any feelings of physical euphoria will likewise be eliminated.”

Should the man enter The House of Pleasure?  Assuming he could have spent the evening at a party where he would have formed lasting memories, there is both a time and a memory cost to the HOP.  Further, does the entrance fee affect whether or not the man should enter? 

My take on it is this.  If he enters HOP, his stream of consciousness experiences walking through the entrance and then immediately walking out the exit, four hours later.  In essence, his consciousness perceives nothing; it’s as if no time has passed.  He walks in and then out feeling exactly the same way, as if it never happened, except that he is out $100 and four hours’ time.

But my intuition, if correct, is problematic, because his perception of the experience depends on what happens afterward.  That his stream of consciousness seems to skip over the time at HOP depends on an event (the erasure of his memories) that occurs after leaving HOP.

My intuition further seems to imply the following oddity: If my memory of a time period will be permanently erased immediately after that time period, then my stream of consciousness skips over that time period.  Equivalently (contrapositive), if my stream of consciousness does not skip over a time period, then my memory of that time period will not be permanently erased immediately after that time period.

The above statement is strange in part because it implies that if I am consciously aware right now (I am), then my stream of consciousness is not skipping over this time period, and my memory of this time period will not be immediately permanently erased.  But, if true, I can never reach the moment just before my conscious death, because that conscious moment just before my conscious death requires that that final glimpse of consciousness not be immediately permanently erased.  In other words, my intuition regarding the House of Pleasure seems to imply eternal consciousness.

Another Comment on “Physical Reversibility is a Contradiction”

Scott Aaronson, whose argument on reversibility of quantum systems I mentioned in this post, responded to it (and vehemently disagreed with it).  Here is his reply:

Your argument is set out with sufficient clarity that I can unequivocally say that I disagree.

Reversibility is just a formal property of unitary evolution.  As such, it has the same status as countless other symmetries of the equations of physics that seem to be broken by phenomena (charge, parity, even just Galilean invariance).  I.e., once you know that the equations have some symmetry, you then reframe your whole problem as how it comes about that observed phenomena break the symmetry anyway.

And in the case of reversibility, I find the usual answer -- that it all comes down to the Second Law, or equivalently, the "specialness" of the universe's past state -- to be really compelling.  I don't see anything wrong with that answer.  I don't think there's something obvious here that the physics community has overlooked.

And yes, you can confirm by experiments that dynamics are reversible. To do so, you (for example) apply a unitary transformation U to an initial state |Ψ>.  You then CHOOSE whether to
(1) apply U^-1, the inverse transformation, and check that the state returned to |Ψ>, or
(2) measure immediately (in various bases that you can choose on the fly), in order to check if the system is in the state U|Ψ>.

Provided we agree that Nature had no way to know in advance whether you were going to apply (1) or (2), the only way to explain all the results -- assuming they're the usual ones predicted by QM -- is that |Ψ> really did get mapped to U|Ψ>, and that that map was indeed reversible.  In your post, you briefly entertain this obvious answer (when you talk about lots of identically prepared systems), but reject it on the grounds that making identical systems is physically impossible.

And yet, things equivalent to what I said above -- by my lights, a "direct demonstration of reversibility" -- are now ROUTINELY done, with quantum states of thousands of atoms or even billions of electrons (as with superconducting qubits).  Of course, maybe something changes between the scale of a superconducting qubit and the scale of a cat (besides the massive increase in technological difficulty), but I'd say the burden is firmly on the person proposing that to explain where the change happens, how, and why.

I sincerely appreciated his response... and of course disagree with it!  I’m going to break this down to several points:

You then CHOOSE whether to
(1) apply U^-1, the inverse transformation, and check that the state returned to |Ψ>,

First, I think he is treating U^-1 as a sort of deus ex machina.  If you don’t know whether a system is reversible, or how it can be reversed, just reduce it all down to a mathematical symbol corresponding to an operator (such as H, for Hamiltonian) and its inverse, despite the fact that this single operator might correspond to complicated and correlated interactions between trillions of trillions of degrees of freedom.  Relying on oversimplified symbol manipulation makes it harder to pinpoint potentially erroneous assumptions about the physical world.

Second, and more importantly, if you apply U^-1, you cannot check that the state returned to |Ψ>.  Maybe (MAYBE!) you can check to see that the state is |Ψ>, but you cannot check to see that it “returned” to that state.  And while you may think I’m splitting hairs here, this point is fundamental to my argument, and his choice of this language indicates that he really doesn’t understand the argument, despite his compliment that I had set it out “with sufficient clarity.”

The reason you cannot check to see if the state “returned” to |Ψ> is because that requires knowing that the state was in U|Ψ> at some point.  But you can’t know that, nor can any evidence exist anywhere in the universe that such an evolution occurred, because then the state would no longer be reversible.  (You also can’t say that the state was in U|Ψ> by asserting that, “If I had measured it, prior to applying U^-1, then I would have found it in state U|Ψ>,” because measurements that are not performed have no results.  This is the “counterfactuals” problem in QM that confuses a lot of physicists as I pointed out in this paper on the Afshar experiment.)  So if you actually apply U and then U^-1 to an isolated system, this is scientifically indistinguishable from having done nothing at all to the system. 

or
(2) measure immediately (in various bases that you can choose on the fly), in order to check if the system is in the state U|Ψ>.  …In your post, you briefly entertain this obvious answer (when you talk about lots of identically prepared systems), but reject it on the grounds that making identical systems is physically impossible.  And yet, things equivalent to what I said above -- by my lights, a "direct demonstration of reversibility" -- are now ROUTINELY done, with quantum states of thousands of atoms or even billions of electrons (as with superconducting qubits). 

In this blog post, I pointed out that identity is about distinguishability.  I didn’t say that it’s impossible to make physically identical systems.  It’s easy to make two electrons indistinguishable.  By cooling them to near absolute zero, you can even make lots of electrons indistinguishable.  But the only way to create Schrodinger’s Cat is to create two cats that even the universe can’t distinguish – i.e., not a single bit of information in the entire universe can distinguish them.  In other words, for Aaronson's argument (about superpositions of billions of electrons in superconducting qubits) to have any relevance to the question of SC, we would have to be able to create a cat out of fermions that even the universe can’t distinguish. 

Tell me how!  Don't just tell me that this is a technological problem that the engineers need to figure out.  And do it without resorting to mathematical symbol manipulation.  I'll make it "easy."  Let's just start with a single hair on the cat's tail.  Simply explain to me how the wave function of that single hair could spread sufficiently (say, 1mm) to distinguish a dead cat from a live cat.  Or, equivalently, explain to me how the wave functions of two otherwise identical hairs, separated by 1mm, could overlap.  Tell me how to do this in the actual universe in which even the most remote part of space is still constantly bombarded with CMB, neutrinos, etc.  So far, no one has ever explained how to do anything like this.

Of course, maybe something changes between the scale of a superconducting qubit and the scale of a cat (besides the massive increase in technological difficulty), but I'd say the burden is firmly on the person proposing that to explain where the change happens, how, and why.

I strongly disagree!  As I point out in “The Invalid Inference of Universality in Quantum Mechanics,” the assumption that QM always evolves in a unitary/reversible manner is an unjustified and irrational belief.  Anyway, my fundamental argument about reversibility, which apparently wasn’t clear, is perhaps better summarized as follows:

1)     You cannot confirm the reversibility of a QM system by actually reversing it, as it will yield no scientifically relevant information.

2)     The only way to learn whether a system has evolved to U|Ψ> is to infer that conclusion by doing a statistically significant number of measurements on physically identical systems.  That’s fine for doing interference experiments on photons and Buckyballs, but not cats. 

Comment on "Physical Reversibility is a Contradiction"

Someone famous in the field of philosophy of mind (although I’m not at liberty to say) asked me the following question regarding my most recent blog post on the logical contradiction of quantum mechanical reversibility:

If one can't prove that Schrodinger’s Cat was in a superposition, I presume the same goes for “Schrodinger’s Particle.”  But we seem to get that evidence all the time in interference experiments.  Are particles different in principle from cats, or what else is going on?

 Here’s my reply:

That's kind of a technical question about how superpositions are "seen."  Of course, we never see a superposition... that's the heart of the measurement problem.  

What we do in a typical double-slit interference experiment is start with a bunch of "identically prepared" particles and then measure them on the other side of the slits.  The distribution we get is consistent with the particles having been in a linear superposition at the slits, where the amplitudes are complex numbers.  The fact that they are complex numbers allows for "negative" probabilities, which is at the heart of (the mathematics of) QM.

The key is that no particular particle is (or can be) observed in superposition... rather, it's from the measurement of lots of identically prepared particles that we infer an earlier superposition state.

The problem is that it's technologically (and I would argue, in-principle) impossible to create multiple "identically prepared" cats.  If you could, you would just do lots of trials of an interference experiment until you could statistically infer a SC state.  But since you can't, you have to rely on doing a single experiment on a cat, by controlling all its degrees of freedom, so as to reverse any correlations between the cat and the quantum event.  But by doing so (assuming it was even possible), there remains no evidence that the cat was ever in a SC superposition at all.  So, since science depends on evidence, it's not logically possible to scientifically show that a SC ever existed... and no one seems to have addressed this in the literature.

Amazingly, this paper just came out in Physical Review Letters, so it's something that people in the physics community are just now starting to wrap their heads around.  The paper doesn’t go far enough, but it at least points out that if WF makes a “measurement” but then is manipulated to show that WF was in a superposition, then even that “measurement” has no results.

Physical Reversibility is a Contradiction

I’m working on a project/presentation on whether scalable quantum computers are possible.  A quantum circuit can be simplified as application of a unitary matrix to an initial state of qubits.  Unitary matrices represent reversible basis shifts, which means that the computation must be shielded from irreversible decoherence events (or subject to quantum error correction to the extent possible) until the purposeful measurement of qubits at the end of the computation.

The word “reversibility” has come up a lot in my reading.  Essentially, the idea is that physical laws seem, for the most part, to be the same whether time is run forward or backward.  For example, if you were shown a video of a planet orbiting some distant star, you would not be able to tell whether the video was being played forward or in reverse.  Yet we experience time to move in a particular direction (namely, the future).  This has led to a centuries-long debate about the “arrow of time”: whether physical laws are reversible or whether there is actually some direction built into the fabric of the physical world.

It’s time to nip it in the bud: the physical world is not time-reversible.

As an example of a typical argument for classical reversibility, imagine dropping a porcelain teapot on a wooden floor.  Of course, it will irreparably break into probably hundreds of pieces.  “In principle,” they say, “if you know the positions and trajectories of all those pieces, you can then apply forces that will completely reverse the process, causing the pieces to recombine to the original teapot.” 

But that’s crap.  We already know, thanks to the Heisenberg Uncertainty Principle (“HUP”), that the pieces don’t have positions and momenta to infinite precision.  That alone is enough to guarantee that any attempt to apply time-reversed forces to the pieces will, thanks to chaos, fail to result in a perfect recombination of the pieces.  (One of my favorite papers discusses how even “gargantuan” black holes become chaotic over time, thanks to HUP.)  This problem is only compounded by the fact that any measurement of the positions and/or momenta of the pieces will inevitably change their trajectories very slightly also. 

So quantum mechanics guarantees that the classical world is not and cannot be time-reversible.  But I’ve recently realized that the notion of time-reversibility in quantum mechanics is not only false… it’s actually a contradiction.  In Section F of this post, I had already realized and pointed out that there is something logically contradictory about the notion of Schrodinger’s Cat (“SC”) or Wigner’s Friend (“WF”).  (I copied the most relevant section of that post below.)

The idea is simple.  To actually create SC, which is a macroscopic superposition state, the cat (and its health) has to correlate to a vial of poison (and whether it is broken), which has to correlate to some quantum event.  These correlations are colloquially called “measurements.”  But to prove (or experimentally show) that the cat is in a macroscopic superposition state, you have to do an interference experiment that undoes the correlations.  In other words, to show that the measurements are reversible (as assumed by the universality of QM), you have to reverse the measurements to the extent that there is no evidence anywhere in the universe (including the cat’s own clock) that the measurements happened. 

Remember, scientific inquiry depends on evidence.  We start by assuming that SC is created in some experiment.  But then the only way to show that SC is created is… to show that it was not created.  The very evidence we scientifically rely upon to assert that SC exists must not exist.  Proving SC exists requires proving that it does not exist.  This is gibberish.  (David Deutsch tried to explain away this problem in this paper but failed.  Igor Salom correctly pointed out in this paper that any attempt to correlate the happening of a measurement inside the otherwise “isolated” SC container will inevitably correlate to the result of that measurement, in which case the measurement event will be irreversible.)

Whether discussing WF, SC, quantum computers, etc., if the evolution of a quantum mechanical system from time t₁ to t₂ is actually reversible at t₂, then that must mean there is no evidence at t₂ of its evolution.  And if you actually reverse the system to how it was at t₁, then there can be no evidence of (and thus no scientific fact or meaning about) its having evolved or done anything from t₁ to t₂.  There can be no evidence anywhere, including as “experienced” by the system itself, because even by its own internal clock, there was no evolution to t₂.  For a reversible system that is actually reversed, there just is no scientific fact about its having had any evolution.  And for a reversible system that is actually measured, so that information exists in the universe about its state (correlations, etc.), then that system is no longer reversible.

Finally, I want to mention that even for a quantum mechanically reversible system, in order to reverse it, you must have already set up the system to be reversible.  For example, if you want an exploding bomb to be reversible, you can’t let the explosion happen and then go hunting for all the fragments to measure their trajectories, etc.  Setting aside the classical problems I mentioned earlier (e.g., by measuring the particles you change their positions/momenta), the problem quantum mechanically is that once the happening of the event correlates to some particle that you don’t already have full control over, it’s too late… evidence now exists.  If a quantum superposition did exist at an earlier time, it no longer does because it has now, thanks to the decoherence event, irreversibly reduced to a definite state.

This is an error that Scott Aaronson seems to make.  Aaronson, one of the most brilliant people ever to discuss the relationship between physics and consciousness (such as in this paper), makes a compelling argument here (also here) that consciousness might be related to irreversible decoherence.  However, he seems to think of quantum mechanical reversibility as something that depends on a future event, like whether we take the time to search for all the records of an event and then reverse them.  For example, he posits that the irreversible decoherence related to one’s consciousness means that “the records of what you did are now heading toward our de Sitter horizon at the speed of light, and for that reason alone – even if for no others – you can’t put Humpty Dumpty back together again.”

But that’s wrong.  The reason you can’t put Humpty Dumpty back together again is not because evidence-carrying photons are streaming away… it’s because the fall of Humpty Dumpty was not set up before his fall to be reversible.  So a system described by wave function Ψ(t) can only be reversible at t₂ if it is set up at earlier time t₁ to be reversible (which means, at least in part, isolating it from decoherence sources).  But if you actually do succeed in reversing it at time t₂ to its earlier state Ψ(t₁), then there can never be scientific evidence that it was ever in state Ψ(t₂).  Therefore, as a scientific matter, reversibility is a contradiction because the only way to show that a system is reversible is to show that it did not do something that it did.

Of course, assuming you could prepare lots of systems in identical states Ψ(t₁), you could presumably let them evolve to state Ψ(t₂), and then measure all of them except one, which you would then reverse to state Ψ(t₁).  If the measured systems yield statistics that are consistent with the Born rule applied to state Ψ(t₂), then you might logically infer that the system you reversed actually “was” in state Ψ(t₂) at some point.  However, there’s a real problem, especially with macroscopic objects, with producing “identical” states, as I discuss here.  It is simply not physically possible, “in principle” or not, to make an identical copy of a cat.  Therefore, any attempt to scientifically show that SC exists requires showing that it does not exist. 

Physical reversibility is a contradiction.

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From Section F of this post:

Consider this statement:

Statement Cat: “The measurement at time t₁ of a radioactive sample correlates to the integrity of a glass vial of poison gas, and the vial’s integrity correlates at time t₂ to the survival of the cat.” 

Let’s assume this statement is true; it is a fact; it has meaning.  A collapse theory of QM has no problem with it – at time t₁, the radioactive sample either does or does not decay, ultimately causing the cat to either live or die.  According to U [the "universality" assumption that quantum states always evolve linearly and reversibly], however, this evolution leads to a superposition in which cat state |dead> is correlated to one term and |alive> is correlated to another.  Such an interpretation is philosophically baffling, leading countless students and scholars wondering how it might feel to be the cat or, more appropriately, Wigner’s Friend.  Yet no matter how baffling it seems, proponents of U simply assert that a SC superposition state is possible because, while technologically difficult, it can be demonstrated with an appropriate interference experiment.  However, as I pointed out above, such an experiment will, via the choice of an appropriate measurement basis that can demonstrate interference effects, necessarily reverse the evolution of correlations in the system so that there is no fact at t₁ (to the cat, the external observer, or anyone else) about the first correlation event nor a fact at t₂ about the second correlation event.  In other words, to show that U is true (or, rather, that the QM wave state evolves linearly in systems at least as large as a cat), all that needs to be done is to make the original statement false:

1)         Statement Cat is true;

2)         U is true;

3)         To show U true, Statement Cat must be shown false.

4)         Therefore, U cannot be shown true.