Thursday, February 3, 2022

Does the Brain Cause Consciousness? Part 2

Is there an afterlife?  Can a computer be conscious?  In Part 1, I pointed out that the popular science answers to these questions depend on an often unstated assumption:

Assumption: The brain causes consciousness.

I am going to show in this and subsequent posts why there is very good reason to doubt this assumption, and why it’s almost certainly false.  To do that, I’m going to try to convince you of two statements [1] which, taken together, imply that the brain does not cause consciousness:

1)     A brain can be copied.  (Even if it cannot be done today due to technological limitations, there is no physical law preventing the physical state of a brain from being copied.)

2)     A person’s conscious state cannot be copied.

In today’s post, I’ll address Statement 1.  First of all, I think most people, particularly scientists, would already agree with it.  And since my goal is to convince you, the reader, then if you already agree with it, there’s no need to read further.  Instead, just move on to the next post in this series, where I’ll address Statement 2.

Of course, no one thinks that a brain can be copied today.  But what physical law prevents copying a brain in the future?  The only known physical principle of which I’m aware is the quantum no-cloning theorem, which says that a quantum state cannot be copied.  And a brain, like all things in the universe, is presumably in a quantum state, so in that sense it can never be perfectly copied.  But that doesn’t matter as long as quantum effects are not relevant to the brain and its functions.  In other words, the only thing that would prevent a brain from being copied adequately to replicate consciousness is if consciousness depends on quantum effects. 

For example, if a conscious state depended on quantum entanglements with objects outside the brain, then there is inadequate information in the brain to specify a conscious state.  Quantum entanglement is “nonlocal,” which means that Object A can affect entangled Object B instantaneously, even if they are separated by a large distance, and the effect is not limited by the speed of light.  So if my current conscious state depends at least in part on an event in another galaxy (which we cannot detect until we receive light from the event), then consciousness is nonlocal.  This recent paper argues that consciousness is nonlocal, but I doubt many in the scientific community have taken notice.

Another way that consciousness may depend on quantum effects is if, to copy the brain, you’d have to measure the state of objects in the brain (like neurons) so precisely that the Heisenberg Uncertainty Principle kicks in, and the measurement itself starts changing the brain’s physical state.  For example, Scott Aaronson suggests in this paper that if a brain is “unclonable for fundamental physical reasons,” then that unclonability could be a consequence of quantum no-cloning if the granularity a brain would need to be simulated at in order to duplicate someone’s subjective identity was down to the quantum level. 

In general, though, few scientists believe that consciousness or brain function depend on quantum effects, and most who discuss the possibility are quickly dismissed as mystics or pseudoscientists.[2]  As long as consciousness does not depend on quantum effects, then we don’t need to worry about quantum no-cloning, and there is nothing that would prevent a future engineer from scanning a person’s brain and then reproducing a functional duplicate with the same conscious state.

Are you convinced of Statement 1 yet?… that a brain can be copied in principle?  Maybe you’re still concerned about possible quantum effects.  OK, here’s another argument.

The amount of information that can be contained in a volume of space is limited.  This is called the Bekenstein bound.  It’s a ridiculously large number but it’s still finite.  For example, the Bekenstein bound Wikipedia page calculates that the maximum information necessary to recreate a human brain, including its entire quantum state, is on the order of 10^42 bits (where a single “bit” of information is either a 0 or 1).  That’s a huge number… it looks like 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000, but it’s still much, much smaller than the number of particles in the universe.  Also, the Bekenstein bound for the brain is an upper physical limit that’s based on a brain so dense with information that it’s right on the verge of collapsing into a black hole!  I think it’s reasonable to surmise that we aren’t walking around with potential black holes in our skulls, so the actual information necessary to specify the quantum state of a brain is probably much, much, much, much smaller than 10^42 bits.  But it doesn’t actually matter.  Here’s why.

Even if we can’t in practice copy a human brain, the universe should be able to.  I’m referring to a Boltzmann Brain.  Physicists currently believe that essentially any physical state can be created by randomness (i.e., accident).  So even though it’s extremely unlikely, a physicist will say that there is some chance that atoms and particles will accidentally come together somewhere in the universe to create your brain.  And even if we include quantum effects, and even if that accidental collection of atoms has to specify the 10^42 bits that could potentially be specified in the physical state of your brain, there is some nonzero probability that it will occur. 

In other words, there is no known physical law that will prevent the exact recreation of your brain elsewhere.  The universe can copy your brain, even if your brain’s function depends on quantum effects.  Therefore, a brain can be copied.  Statement 1 is true.

In my next post, I’ll address Statement 2.  As for now, do you have any questions or concerns about Statement 1?

[1] As I mentioned previously, I would ordinarily try to be more precise with my words, arguments, and proofs.  But the purpose of this and subsequent posts is to write more colloquially without alienating lay readers.  Better precision can be found, e.g., in my papers.

[2] Don’t forget that consensus does not equal truth.  There is, and perhaps always has been, a bully culture in science, which is why scientific paradigms tend to be changed only by independent mavericks.

Wednesday, February 2, 2022

Does the Brain Cause Consciousness? Part 1

I have spent so much time and effort trying (and ultimately failing) to successfully communicate with people in the physics and philosophy academies, using their complicated and abstruse language and math equations, that I’ve made many of my insights, discoveries, and contributions completely inaccessible to the rest of the world, including my own friends and family.

My close friend Adam recently asked me some important questions, like whether computers could be conscious.  Of course, I’ve answered this question many times, and in great detail, on this blog and in my papers (particularly this and this).  But I realized that I really only addressed people who already knew the language of quantum mechanics, computer science, philosophical logic, and so forth.  So in this and subsequent posts, I’m going to try to address some important questions in direct, ordinary language without all the bullshit jargon.

Today, I want to mention two such questions:

·       Is there an afterlife?

·       Can a computer be conscious?

Ask these questions of a physicist, biologist, or computer scientist, and probably the vast majority will answer firmly and with conviction: No, there is no afterlife; Yes, a computer can be conscious.  And if you probe them further as to why they are so certain of these answers, you’ll find that there is an (often unstated) assumption that pervades the scientific community about consciousness:

Assumption: The brain causes consciousness.[1]

Is that assumption true?  If it is, then it’s not unreasonable to believe that consciousness ends when the brain dies.  Or that someday we’ll be able to copy the brain and recreate a person’s consciousness.  Or that a person’s brain could be simulated in a computer, thus producing consciousness in a computer.

But again, all these popular ideas stem from that one assumption, and there aren’t many scientists who question it (or even acknowledge it as an assumption).  So that’s where I’ll start.  Consider, again, the assumption:

Assumption: The brain causes consciousness.

Several questions for you about that assumption:

·       Do you believe it?

·       If so, why?  What evidence do you have that it is true?

·       What evidence has the scientific community offered to support it?

·       Which beliefs depend on it?  For example, anyone who believes that consciousness ends with brain death necessarily makes the above assumption.  Anyone who believes that a computer will someday be conscious by simulating a brain also makes the above assumption.  Many, many other popular science beliefs depend on this assumption.

·       What if the assumption is incorrect?  Is it possible to prove that it is false?  How might it be disproven?  If the assumption could actually be disproven, how might that impact your beliefs?  How might it impact the popular scientific beliefs about consciousness?

Next in this series: Part 2
Last in this series: Part 3

[1] Note on this post: Ordinarily, I would try to be more precise with my words.  For example, the assumption is actually that a conscious state entirely depends on the physical state of a living brain, but this is where the eyes of ordinary readers start to glaze over.  So I won’t be so precise in this and related future blog posts.

Sunday, November 7, 2021

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.

Wednesday, November 3, 2021

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? 


“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.

Sunday, May 30, 2021

Physics, Immortality, and the Afterlife

What does physics tell us about the possibility of immortality or an afterlife?

First, let’s address the elephant in the room.  To the physics community, “afterlife” often implies “religion” often implies “stupidity.”  Bullies like Richard Dawkins have made it very clear that anyone who even suggests the existence of God or an afterlife is intellectually inferior.  Oddly, this assertion directly conflicts with several arguments based on currently-understood physics (and often made, ironically, by atheists) that immortality is possible.  I’ll discuss below some of these arguments.  Importantly, any physicist who tells you with certainty that there is no afterlife is not only mistaken, but is ignorant of the direct logical implications of his/her own beliefs about physics.

Note: “Afterlife” and “immortality” are not technically the same.  Immortality might be interpreted as “never dying,” while an afterlife might be interpreted as “consciousness after one has died.”  However, from a physics standpoint, this is often a distinction without a difference.  For example, if mind uploading is possible, then it can be done before or after a person’s brain is dead.

Postponing Death

My close friend (and former MIT debate champion) once made the following (valid) argument:

·       Technology (e.g., medicine) is allowing humans to live longer and longer.

·       There is some tiny but nonzero probability 0<p<<1 that we will develop the technology to indefinitely postpone death.  For example, imagine that in the next 50 years we figure out how to make humans live to age 150, and in the following 50 years we figure out how to make humans live to age 200, and so on.  Then someone born today could indefinitely postpone death.

·       The universe will continue expanding forever.  (Most physicists believe that the universe has positive curvature.)

·       p * ∞ = ∞.

·       Therefore, the life expectancy of a person born today is infinite!

The argument applies equally to an afterlife as to immortality if we simply replace the second statement with “There is some tiny but nonzero probability 0<p<<1 that we will develop the technology to reanimate a dead person’s brain.”  (After all, that’s why the quacks at the Brain Preservation Foundation recommend cryogenic freezing of one’s brain, which I’m certain is not cheap.)  If we can agree that it is at least physically possible to indefinitely delay death (or to reanimate a dead brain), then physical immortality/afterlife cannot be ruled out.

Mind uploading

If you can upload your conscious awareness onto a computer, then you can live forever because a computer can be indefinitely operated and repaired.  Okay, okay, you still need energy to flow, which will stop when the universe experiences its predicted heat death in at least a googol years.  Even still, Michio Kaku in his fascinating book, Parallel Worlds, points out that conscious awareness would slow down commensurate with decreased energy transfer so that one’s subjective conscious experience wouldn’t notice.

Again, there’s no difference here between “immortality” and “afterlife” since the fundamental assumption of mind uploading (and algorithmic consciousness) is that a conscious state is just software running on a computer, and that can be done long after one’s death.  (It can also be done before one’s death, which leads to all kinds of ridiculous paradoxes that I discuss in this paper.) 

The problem is that I showed in this paper (and this) that consciousness is not algorithmic, which means it cannot be uploaded to or executed by a computer (whether digital or quantum).  Mind uploading is not physically possible.

Quantum Suicide

Max Tegmark, proponent of the wacky and unscientific Many Worlds Interpretation (“MWI”) of quantum mechanics, proposed the notion of quantum suicide (although really it’s just “quantum death” because it applies independently of intention) as an empirical test of MWI.  The idea is this:

·       Stand in front of a “quantum gun” that is designed so that when the trigger is pulled, whether a bullet actually fires from the gun (and kills you) depends on the outcome of a quantum mechanics (“QM”) event.

·       Universal linearity of QM – i.e., the assumption of U which I dispute here – implies that the quantum event entangles with the bullet, which entangles with you, to produce a Schrodinger’s-Cat-like state involving you in a superposition of states |dead> and |alive>. 

·       If MWI is correct, then both states actually occur/exist (albeit in different “worlds” that are exceedingly unlikely to quantum mechanically interfere).

·       Since you cannot consciously survive death – a huge assumption! – then the only state you can consciously observe is the one involving |alive>, which means that you are guaranteed to “survive” the pull of the quantum gun trigger.

·       You can repeat this as many times as you want, and every time you will be guaranteed to observe the outcome in which you are alive.

The argument is wrong for several reasons that I point out in the Appendix of this paper.  One problem is that every chance event is fundamentally (amplification of) a quantum event, which means that essentially every death-causing event is akin to quantum suicide/death.  But that means that, if Tegmark’s argument is correct, then nobody can actually die

But the main problem is that the argument depends on the unjustified and irrational assumption of U.  If Schrodinger’s Cat and Wigner’s Friend can’t exist, then the quantum suicide experiment can never get off the ground. 

Boltzmann Brain

The Boltzmann Brain concept is the notion that, given enough time, every physical state will repeat itself.  Or: due to random quantum fluctuations, given enough time, every possible physical configuration that can fluctuate into existence will fluctuate into existence.  So, eventually, even trillions of years after humanity has gone extinct, the conscious state you are experiencing at this moment will be recreated (and presumably re-experienced) again.  And again and again. 

Whether such experiences count as immortality or afterlife makes no difference, because the Boltzmann Brain concept is impossible.  I showed in this paper that physical instantiations of the same conscious state cannot exist at different points in spacetime. 

Tipler’s Physics of Immortality

Frank Tipler is a Christian who was largely ostracized from the academic world for showing how what is currently understood about physics could support the notions of a Christian God and afterlife.  His book, The Physics of Immortality, is interesting but dense.  At the risk of oversimplifying his analysis, I think his fundamental argument is really the Boltzmann Brain in disguise.  He relies heavily on the Bekenstein Bound (which I discussed here) and the notion of Eternal Recurrence to show that consciousness cannot end.

His analysis is wrong for several reasons.  First, the Bekenstein Bound assumes the constancy of the informational content in a given volume (i.e., that Planck’s constant is constant, which may be false).  Second, and more importantly, it assumes that a conscious state is just a list of numbers (even if it’s a huge list) that must be contained within the volume of a brain, and therefore that consciousness is algorithmic, which I’ve shown is false.  If consciousness cannot be reduced to a set of bits (and/or their algorithmic manipulation), then the number of bits that can fit in a given volume is irrelevant.


If physical systems are truly reversible, then – at least according to some – it should be possible in principle to physically reverse a person’s death (or even some or all of a person’s life).  It’s certainly not obvious that constantly “undoing” someone’s death results in a meaningful kind of immortality.  Still, maybe the goal of reversing someone’s death is to copy their consciousness into another physical system or upload it to a computer.  But I’ve already pointed out several times that this is impossible.  Either way, the entire argument is moot because physical reversibility of large systems is a logical contradiction.

What do I actually believe?

First, let me point out the crazy irony of this blog post so far.  I, the crackpot who believes in God, am trying to explain why several physicists’ arguments for immortality or afterlife are wrong!  In fact, the only one of the above arguments that I can’t completely rule out is Postponing Death, even though I regard it as extremely implausible to postpone death indefinitely.

Having said that, we do not understand consciousness.  No physicist, neurobiologist, physician, psychologist, computer scientist, philosopher, etc., understands consciousness, and anyone who claims to understand it is likely introducing unstated assumptions.  For example, most scientists who academically discuss consciousness assume that consciousness is created entirely by the brain, which is why the hackneyed “brain-in-a-vat” thought experiment – the namesake of this blog – is so pervasive in the literature. 

After all, if consciousness is entirely a product of the brain (or, more generally, on a local region of spacetime that may enclose the brain), then the above arguments are a lot more tenable.  That is, if a conscious state supervenes on a physical state that is entirely (locally) contained in some volume, then Tipler’s argument based on the Bekenstein Bound seems to apply; the total information specifying that conscious state is finite and, as nothing more than a string of numbers, can be copied and uploaded to a computer; and so forth.

In fact, given so many physical arguments for immortality, one might even wonder what physical arguments there are against immortality.  There is only one: assume that consciousness is entirely a product of the (living) brain; then death of the brain ends consciousness.  And if that assumption is wrong, then there is literally no existing scientific evidence against immortality or an afterlife.

But that assumption is wrong.  Conscious states are not local and they cannot be copied to different places in spacetime.  (Stoica makes a related and fascinating argument here that mental states are nonlocal.)  If they’re nonlocal, then they must physically depend on nonlocal (quantum) entanglements among objects and particles throughout the universe.  That is, what physically specifies my conscious state logically must extend beyond my brain.  There is certainly no doubt that my brain affects my consciousness, but it cannot be entirely locally responsible for it.  The fact that events and physical relationships that extend far beyond my brain are at least partially responsible for my consciousness leads me to surmise that these conscious-identity-producing physical relationships will persist long after the atoms in my brain are no longer arranged in their current configuration.  This is the beginning of an as-of-yet undeveloped physical argument for immortality/afterlife.

So, what do I really believe about an afterlife?  I won’t mince words.  I am certain that my consciousness is eternal; I am certain that my consciousness awareness will not permanently end if/when my brain dies.  In future posts, I will give logical and physical arguments to support these assertions, but I wanted first to devote a blog post to what currently-understood physics implies. 

Thursday, May 20, 2021

Quantum Computing is 99% Bullshit


In this post, just before beginning a class on quantum computing at NYU, I predicted that scalable quantum computing ("SQC") is in fact impossible in the physical world.

I was right.

And I can finally articulate why.  The full explanation (“Scalable Quantum Computing is Impossible”) is posted here and in the following YouTube video.

Here is the general idea.  Let me make a few assumptions:

·       A system is not “scalable” in T (where T might represent, for example, total time, number of computation steps, number of qubits, number of gates, etc.) if the probability of success decays exponentially with T.  In fact, the whole point of the Threshold Theorem (and fault-tolerant quantum error correction (“FTQEC”) in general) is to show that the probability of success of a quantum circuit could be made arbitrarily close to 100% with “only” a polynomial increase in resources.

·       Quantum computing is useless without at least a million or a billion controllably entangled physical qubits, which is among the more optimistic estimates for useful fault-tolerant quantum circuits.  (Even "useful" QC isn’t all that useful, limited to a tiny set of very specific problems.  Shor’s Algorithm, perhaps the most famous of all algorithms that are provably faster on a quantum computer than a classical computer, won’t even be useful if and when it can be implemented because information encryption technology will simply stop making use of prime factorization!)

o   There are lots of counterarguments, but they’re all desperate attempts to save QC.  “Quantum annealing” is certainly useful, but it’s not QC.  Noisy Intermediate-Scale Quantum (“NISQ”) is merely the hope that we can do something useful with the 50-100 shitty, noisy qubits that we already have.  For example, Google’s “quantum supremacy” demonstration did absolutely nothing useful, whether or not it would take a classical computer exponential time to do a similarly useless computation.  (See the “Teapot Problem.”)

Given these assumptions, what do I actually think about the possibility of SQC?

First of all, what reasons do we have to believe that SQC is possible at all?  Certainly the thousands of peer-reviewed publications, spanning the fields of theoretical physics, experimental physics, computer science, and mathematics, that endorse SQC, right?  Wrong.  As I pointed out in my last post, there is an unholy marriage between SQC and the Cult of U, and the heavily one-sided financial interest propping them up is an inherent intellectual conflict of interest.  Neither SQC nor FTQEC has ever been experimentally confirmed, and even some of their most vocal advocates are scaling back their enthusiasm.  The academic literature is literally full of falsehoods, my favorite one being that Shor’s Algorithm has been implemented on a quantum computer to factor the numbers 15 and 21.  (See, e.g., p. 175 of Bernhardt’s book.)  It hasn’t. 

Second, SQC depends heavily on whether U (the assumption that quantum wave states always evolve linearly or unitarily… i.e., that wave states do not “collapse”) is true.  It is not true, a point that I have made many, many times (here here here here here here etc.).  Technically, useful QC might still be possible even if U is false, as long as we can controllably and reversibly entangle, say, a billion qubits before irreversible collapse happens.  But here’s the problem.  The largest double-slit interference experiment (“DSIE”) ever done was on an 810-atom molecule.  I’ll discuss this more in a moment, but this provides very good reason to think that collapse would happen long before we reached a billion controllably entangled qubits.

Third, the Threshold Theorem and theories of QEC, FTQEC, etc., all depend on a set of assumptions, many of which have been heavily criticized (e.g., Dyakonov).  But not only are some of these assumptions problematic, they may actually be logically inconsistent… i.e., they can’t all be true.  Alicki shows that noise models assumed by the Threshold Theorem assume infinitely fast quantum gates, which of course are physically impossible.  And Hagar shows that three of the assumptions inherent in TT/FTQEC result in a logical contradiction.  Given that FTQEC has never been empirically demonstrated, and that its success depends on theoretical assumptions whose logical consistency is assumed by people who are generally bad at logic (which I’ve discussed in various papers (e.g., here and here) and in various blog entries (e.g., here and here)), I’d say their conclusions are likely false.

But here’s the main problem – and why I think that SQC is in fact impossible in the real world:

Noise sometimes measures, but QC theory assumes it doesn't.

In QC/QEC theory, noise is modeled as reversible, which means that it is assumed to not make permanent measurements.  (Fundamentally, a QC needs to be a reversible system.  The whole point of QEC is to “move” the entropy of the noise to a heat bath so that the evolution of the original superposition can be reversed.  I pointed out here and here that scientifically demonstrating the reversibility of large systems is impossible as a logical contradiction.)  This assumption is problematic for two huge reasons.

First, measurements are intentionally treated with a double standard in QC/QEC theory.  The theory assumes (and needs) measurement at the end of computation but ignores it during the computation.  The theory's noise models literally assume that interactions with the environment that occur during the computation are reversible (i.e., not measurements), while interactions with the environment that occur at the end of the computation are irreversible measurements, with no logical, mathematical, or scientific justification for the distinction.  This is not an oversight: QEC cannot correct irreversible measurements, so proponents of QEC are forced to assume that unintended interactions are reversible but intended interactions are irreversible.  Can Mother Nature really distinguish our intentions?  

Second, and more importantly, the history and theory of DSIEs indicates that noise sometimes measures!  All DSIEs have in fact depended on dispersion of an object’s wave packet both to produce a superposition (e.g., “cat” state) and to demonstrate interference effects.  However, the larger the object, the more time it takes to produce that superposition and the larger the cross section for a decohering interaction with particles and fields permeating the universe.  As a result, the probability of success of a DSIE decays exponentially as the square of the object’s mass (p ~ e^(-m2)), which helps to explain why despite exponential technological progress, we can't yet do a DSIE on an object having 1000 atoms, let alone a million or a billion.  What this means is that DSIEs are not scalable, and the fundamental reason for this unscalability – a reason which seems equally applicable to SQC – is that noise at least sometimes causes irreversible projective measurements.

This is fatal to the prospect of scalable quantum computing.  If a single irreversible measurement (even if such an event is rare) irreparably kills a quantum calculation, then the probability of success decays exponentially with T, which by itself implies that quantum computing is not scalable.  But DSIEs demonstrate that not only does noise sometimes cause irreversible measurement, those irreversible measurements happen frequently enough that, despite the very best technology developed over the past century, it is practically impossible to create controllably highly entangled reversible systems larger than a few thousand particles.  

Quantum computing is neither useful nor scalable.