On the (Im)possibility of Scalable Quantum Computing

I just finished a paper entitled, “On the (Im)possibility of Scalable Quantum Computing,” which is the expanded article version of the YouTube presentation in this post.  I will submit it to the arXiv but fully expect it to be rejected, like some of my other papers, on the basis that it questions a fashionable religion within the physics community.  While this paper does not specifically reject the Cult of U, it does argue that the multi-billion-dollar quantum computing industry is founded on a physical impossibility.

The paper can be accessed as a preprint here, and here is the abstract:

The potential for scalable quantum computing depends on the viability of fault tolerance and quantum error correction, by which the entropy of environmental noise is removed during a quantum computation to maintain the physical reversibility of the computer’s logical qubits. However, the theory underlying quantum error correction applies a linguistic double standard to the words “noise” and “measurement” by treating environmental interactions during a quantum computation as inherently reversible, and environmental interactions at the end of a quantum computation as irreversible measurements. Specifically, quantum error correction theory models noise as interactions that are uncorrelated or that result in correlations that decay in space and/or time, thus embedding no permanent information to the environment. I challenge this assumption both on logical grounds and by discussing a hypothetical quantum computer based on “position qubits.” The technological difficulties of producing a useful scalable position-qubit quantum computer parallel the overwhelming difficulties in performing a double-slit interference experiment on an object comprising a million to a billion fermions.

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.