Home > My Fiction, Science > Quantum teleportation: maybe not?

Quantum teleportation: maybe not?

After my earlier post on quantum teleportation, I’ve been wondering about whether I wanted to include it in my science fiction in some way, but first I wanted to get some handle on whether it was feasible in practice to teleport a macroscopic object rather than just individual particles or a Bose-Einstein condensate in a single coherent quantum state.  Finding detailed discussions online is a bit tricky just using Google, but I found a discussion thread that goes into a fair amount of depth:

“Quantum teleportation of macroscopic objects” at Physics Forums

Granted, BBS threads, even on science forums, aren’t the best way to get information about the subject, but I’m in no mood to try to wade through a bunch of technical papers, and I’m only looking at it from the perspective of a fiction writer, so for now I’m content to let other people do the interpreting for me, though I still have to try to filter out the informed posts from the less informed ones.

It sounds like there may be some fundamental limitations that would prohibit teleporting humans or the like.  Apparently what gets teleported are discrete properties like spin or charge.  Teleporting a continuous variable, like the relative positions of multiple atoms or their momentum, would require infinite amounts of data, so one of the posters says.  Another poster countered that some measurement of continuous states was possible, citing a paper on Arxiv.org, but the first replied that it was a limited, classical-resolution measurement and not precise enough to allow replicating a macroscopic object accurately.  (Kind of like how Star Trek replicators have only “molecular resolution” and not “quantum resolution” so they can recreate nonliving matter but not living beings, because the error rate would be fatally high.)

Then there’s this thread at the Bad Astronomy and Universe Today Forum (which seems to have been started by the same poster under a different username), in which it’s pointed out that a macroscopic object can never be truly isolated from its environment, which again would suggest that the amount of information you’d need to define its state exactly would be effectively unbounded.

And this thread from the same forum (which is definitely by the same poster since it has the same original post as the Physics Forums thread above) clarifies that thermal effects in the body would interfere with getting a precise scan; ideally you’d need to freeze the subject to extremely near absolute zero, which isn’t exactly conducive to survivable teleportation.

Another factor raised in this article from Null Hypothesis: The Journal of Unlikely Science is a simple matter of bandwidth: even if you didn’t need infinite information to transmit continuous states, you’d still need to transmit so much data to replicate a human body that it would take a great deal of time and energy to send — billions of years at our highest current transmission rate.  And if you could get a much higher transmission rate, according to the link in the previous paragraph, you’d need to send such intense energy that it would become unfeasible — you’d basically be firing a very powerful beam of gamma radiation at the receiving station, and that’s more a death ray than a transporter beam.  At the very least, in most instances it would take less time and energy just to travel physically than to send a teleport signal.

So the question this raises for me is: how “exact” do you actually need to get?  It could be feasible using advanced nanofabrication technology to “print out” a human body that’s a good molecular-level match for the original person.  As long as you recreated the DNA and RNA in the cells accurately, you could probably settle for just knowing how many of which type of cell the body had, and where they were located, so you could reduce the amount of data that needed to be sent by using these “generic” substitutions.  You could even improve on the body, say, write out excess fat or burgeoning tumors, or rewrite defunct hair follicles as functioning ones, or add extra muscle, or even make more radical changes.  (See Wil McCarthy’s The Queendom of Sol tetralogy for an illustration of this.)

Aside from matching (or refining) the genetic and epigenetic data, then, the key information you’d need to transmit a person with their identity intact would be an accurate brain scan.  Otherwise you’ve just created an identical twin rather than duplicated the original person.  So the question is, just how accurate would it have to be?  As far as science is able to determine, thought and memory are classical-scale processes.  According to this page which I used as a reference for quantum theory in DTI: Watching the Clock:

 In quantum terms each neuron is an essentially classical object. Consequently quantum noise in the brain is at such a low level that it probably doesn’t often alter, except very rarely, the critical mechanistic behaviour of sufficient neurons to cause a decision to be different than we might otherwise expect. The consensus view amongst experts is that free-will is the consequence of the mechanistic operation of our brains, the firing of neurons, discharging across synapses etc. and fully compatible with the determinism of classical physics.

Sure, there are some theorists who argue that consciousness is based on quantum processes, and you hear a lot of talk about “microtubules” in the neurons operating on a quantum level, but there’s no experimental support yet, and the general consensus is that quantum effects in the brain would decohere well before they reached the scale at which the neurons’ activity occurs.  So it might be possible to faithfully duplicate the entire mental state of a human brain using classical-level accuracy, so that mechanism in the research paper mentioned above might be applicable.

So the key issue that remains is the one that was the focus of my previous post: Is there continuity of consciousness between the original and the duplicate?  What I reasoned there is that what creates our perception of ourselves as continuous beings is the ongoing interaction, and thus the quantum entanglement/correlation, among the particles of our brains.  The specific particles may be expended and replaced, but the correlations within the entire overall structure give us our sense of continuity.  So if the original subject and the teleported replica are quantum-entangled, that would make them the same continuous entity on a fundamental level even if separated in space and time.  The question is, would that same principle apply even if the entanglement were between the original and a body that was not an exact quantum duplicate?  I.e. if you used classical-level fabrication to synthesize a duplicate of a person and only quantum-teleported partial information about the state of the brain?  You’d synthesize a brain and body that were almost exact replicas, and then transmit enough quantum data about the brain to essentially cancel out the discrepancies and make it effectively the same brain, with the entanglement providing the continuity.  Thus you have a replica of the body but preserve a single continuous consciousness.

So the original body would not need to be scanned to destruction but the brain would.  Remember, teleporting quantum state information requires changing the original state.  You’d essentially be teleporting just the brain/mind into a new, possibly modified body, and leaving the old body behind as a corpse with a destroyed brain.  Ickier than the ideal situation.  But it still precludes the possibility of creating a viable “transporter duplicate.”

But the question is, how much “cheating” can you get away with?  How small a percentage of the information defining you needs to be quantum-teleported rather than classically copied in order to ensure that your consciousness survives intact?  How could science measure the difference between a synthesized replica that thinks it’s you and one that actually contains your original consciousness?  How much entanglement, how much equivalence, is enough for continuity?  Even if we assume the teleportation of the brain states alone is enough to make it the same brain, we run into the mind/body problem: the two are more linked than we have traditionally tended to think, and it may be premature to define consciousness as something that resides solely in the brain.  The entire nervous and hormonal systems may play a role in it too.  Still, if you were to have your legs amputated and replaced with prosthetics, that wouldn’t destroy your consciousness.  So maybe teleporting just the brain states is enough.

But then there’s a simple mathematical question: does that really reduce the amount of data by a significant amount? The mass of the brain is about 2 percent of the total mass of the body, so that’s only reducing the amount of data by roughly two orders of magnitude.  So it would take 2 billion years to transmit instead of 100 billion, say.  To make it feasible, you’d have to “compress” the data still further — and we’d need a much deeper understanding of how the brain works before we could estimate how little of its structure we could get away with teleporting at a quantum level versus substituting with “generic” cellular/structural equivalents.  (Of course it’s a total myth that “We use only 10% of our brains; fMRI scans show conclusively that we make use of just about all the brain’s volume over the course of a day.  But on a cellular level, a lot of that may be underlying substructure that could be “generically” replicated.  Or maybe not.  I don’t know enough about neurology to be sure.)  Even so, I doubt the threshold percentage would be low enough to reduce the amount of data by even one order of magnitude, let alone many.

And there’s still the thermal problem.  There’s a lot of molecular motion in the brain, not just from its temperature but from the constant chemical exchange among neurons.  You might not be able to get a detailed quantum scan of a living, active brain as opposed to a deep-frozen corpse, and I don’t have enough confidence in cryonics to believe a person could be frozen to near absolute zero and then revived.

Still… depending on what fictional universe I’m in and how much I’m willing to bend the rules, I might be willing to fudge things enough to include quantum teleportation if I have a good enough story reason for it, using the ideas discussed above to make it relatively more plausible.  Maybe there are ways to transmit data at far higher rates than we can now conceive, and with less energy expenditure.  And come to think of it, having a requirement that a subject has to be frozen solid before teleportation adds an interesting twist.  Though it would rule it out as a routine commute as it is in Star Trek or Niven’s Known Space.

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  1. December 19, 2011 at 2:06 pm

    What makes you unconfident about the potential of cryonics/suspended animation? I have some doubts whether today’s cryonics procedures work, but that is because of the degree of damage that is done by current cryoprotectants. There is little doubt in my mind that it will eventually be possible to chill a human body to less than 1 Kelvin without accruing significant damage.

    Note that the current state of the art is vitrification, which does not involve freezing (ice crystal formation) but converts the water into a glass-like state. Since this requires that it be replaced with something like 70% antifreeze, most of the damage that occurs is from the toxicity of the compounds used at concentrations needed for vitrification. If the compounds could be administered and removed quickly and the body cooled quickly, there would be virtually no damage. A good device for hard sci-fi set in the near future would be a laser microtome that very quickly sections the entire brain into slices and immediately immerses them into a cooling and perfusing bath.

    From the standpoint of transporting the minimum amount of data, if you want to make teleportation more realistic you might go with the connectome hypothesis. Rather than modeling every single molecule of the brain, the idea is that you can simply map out the connections between the brain cells. In theory, a brain reprinted from neural stem cells with the same connections (or a virtual brain made with virtual neurons with the same connections) would have the same personality and memories.

    If that’s the case, you could probably get away with immersing the brain in formaldehyde or something similar and scanning it. The main reason for bringing the tissue to near absolute zero would be in case you want to make direct repairs to it. Many kinds of nanomachines would likely require a near-zero degree vacuum to operate.

    If you could ignore the difficulties of transporting the data of warm matter, it makes an interesting story idea to have a “portal” that disassembles a layer of matter and reprints an atomically identical layer from stock chemicals on the other side. Thus you could easily put your hand through, grab say an apple from the other side of the room, and pull it back through. (Various physics would need to be simulated, such as the rushing of blood to the hand, electrical nerve impulses, etc.) The philosophical conundrum comes when you put say half of your head through the portal and pull it back out, or your whole head. Presumably you wouldn’t feel a thing even when half or all of your brain is completely destroyed/replaced.

    Transporting a cryopreserved person would obviously be more feasible by this method though. If you want it to be useful for commute purposes, you could postulate implanted nanotech that accelerates the perfusion of cryoprotectants and the cooling process (say there’s an implanted alternate circulatory system composed of carbon nanotubes), so the cooling happens too fast for toxicity to be a problem. Thus the person would turn vitreous within a matter of seconds, following which the layer-by-layer scan and reprint operation (to whatever feasible/desired level of detail) commences.

    Note that even if the scan must be destructive, there is always the possibility of printing two copies of the person, each as real as the other.

    • December 19, 2011 at 2:45 pm

      “What makes you unconfident about the potential of cryonics/suspended animation? I have some doubts whether today’s cryonics procedures work, but that is because of the degree of damage that is done by current cryoprotectants. There is little doubt in my mind that it will eventually be possible to chill a human body to less than 1 Kelvin without accruing significant damage.”

      But it isn’t yet known whether a sentient mind could survive such a process, could be completely shut down and be “rebooted” afterward. I mean, that’s not just a deep sleep, that’s literally killing someone and then resurrecting them, and that’s a tall order. I don’t remember the issue, but I once read an essay on the subject in an issue of Analog, and it raised doubts about whether it was feasible. A thinking brain isn’t just an inert piece of hardware, but an ongoing process. Moreover, consciousness is an emergent property, something that isn’t just the sum of its parts but that arises from the complexities of their interaction. Such emergent properties can be unpredictable, and dependent on initial conditions. Stop the process and start it again with different initial conditions, and the outcome, the personality that forms, may not be quite the same. Even if it were the same, you’d still have the same question of continuity raised by QT itself — is the mind that comes out of the process the same original consciousness that went in, or just a copy? To me, the only way to be sure that you haven’t just killed the original and created a duplicate is if you can be sure of the continuity of thought.

      “From the standpoint of transporting the minimum amount of data, if you want to make teleportation more realistic you might go with the connectome hypothesis. Rather than modeling every single molecule of the brain, the idea is that you can simply map out the connections between the brain cells. In theory, a brain reprinted from neural stem cells with the same connections (or a virtual brain made with virtual neurons with the same connections) would have the same personality and memories.”

      But then there’s blatantly no continuity, and it is just a copy, not the same original individual. Nobody else might be able to tell the difference, but the original person’s awareness would not magically leap into the copied body. After all, with a classical copying process, it wouldn’t necessarily require destroying the original, so you could have the original and the copy coexisting. Obviously, the original person’s awareness would remain in her own body while the copy led an independent existence. So if you did destroy the original in order to make a copy through non-quantum means, the copy would still be a separate (if identical) consciousness and the original person would simply have been killed, her consciousness terminated rather than transferred. The only way that it actually is the same person by any physically definable definition is if it’s quantum-teleported.

      Maybe what you describe could serve as the first stage as I proposed above, but there’d still need to be some degree of entanglement and teleportation of states between the original brain and the duplicate in order to achieve continuity. Quantum teleportation isn’t about transmitting descriptions of states — that’s faxing, not teleporting — but rather transposing the original quantum states onto the particles at the receiving end. That’s what makes them literally the same particles by quantum definition. And it’s that direct entanglement between the original and duplicate that, according to my hypothesis, allows continuity of awareness and identity.

      “Note that even if the scan must be destructive, there is always the possibility of printing two copies of the person, each as real as the other.”

      But it’s still not quantum teleportation, just classical replication. You can’t turn one set of quantum states into two without violating conservation laws. So you can’t use quantum teleportation to create an evil twin for Captain Kirk. It’s one-to-one. If you can print multiple copies, they’re just copies, separate from the original person’s consciousness, and the original person is dead.

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