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Luke_A_Somers comments on timeless quantum immortality - Less Wrong
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Thanks for the criticism.
summary: If, hypothetically, I tried to catch a terminal-velocity bowling ball with my face, your theory says I would experience the bowling ball doing nonfatal damage and then stopping just before killing me, and my theory says I would experience changing my mind and getting out of the way of the bowling ball. It looks like our key disagreement is whether Quantum Immortality only operates over short timescales. You say it only acts in an instant, and I say it acts over long time intervals as well.
longer argument: I'm not convinced by your argument yet. Specifically:
1) I agree that two worlds may be very similar or very different or many places in between. However, my consciousness observes exactly one world at once. Do we have a disagreement about reality, or only about word definitions?
2) I agree that splitting events produce massive numbers of worlds (I have no idea how many, but I'm guessing no more than the volume of the Universe divided by the cube of the Planck length). Does this invalidate my argument (that I'll live forever without appearing to get lucky)?
3) I agree that the likelihoods are a sum over various paths whose magnitude ranges from approximately 1 to approximately 0. I also agree with your intuition that if I ended up in a situation with a high-velocity bowling ball partially inside my head then my survival paths are much much less likely than my death paths. However, my argument is that Quantum Immortality works backward in time, if that makes sense. For example, consider all the ways I can walk through a bowling alley -- a 10-minute-long time interval. Quantum Immortality means I will not experience death during that 10 minutes. Looking at all of the different worlds in which I don't die in the bowling alley, it's most probable I'll find myself in one where I walk safely and nothing weird happens, and really really improbable that I'll throw a bowling ball straight up in the air and then try to catch it with my face and then have the bowling ball spontaneously lose its momentum right before impact. This looks like where we disagree. This is clearer in your next point...
4) I'm kept off of those doomed states by Quantum Immortality. I disagree with you here, and I'll make two arguments why...
4a) My conscious experience already averages over large lengths of time relative to quantum processes. The brain runs at about 10Hz. In the time it takes for one neuron to fire, many many quantum processes have time to happen. Since my consciousness only collapses the universal wavefunction once every 1/10th second, I see no problem with looking at the problem as if my consciousness only collapses the universal wavefunction once every 10 minutes, or once every lifetime.
4b) When I look at the real world, it looks like I'm kept away from doomed states. Why was I so ridiculously lucky as to be born in the current era, where human immortality is a possibility for the first time in history? Timeless Quantum Immortality provides an answer: because it's more probable that I'll live forever from the World I experience now, than it would be for me to live forever from most other worlds. Being born an ancient Sumerian or a dolphin would require many more improbable events to get me to immortality. Being born in a post-Singularity culture where immortality already exists would require a more complicated Universe. My existence looks like it's one of the most likely ones of the set of all possible Universes in which I don't die.
4c) I go to sleep (lose consciousness) and wake up again. QI seems to predict that I would never fall asleep, because I stop observing when I'm asleep and so I couldn't observe that instant. Timeless QI has no problem with me falling asleep and then observing I'm alive and awake hours later.
5) QI is all about the timeless perspective because it requires looking at worlds splitting into other worlds from a perspective outside of time. I'm just doing what regular QI is already doing, just on a longer timescale.
(Rather than start with the main point I'll follow your responses and conclude)
1 - word definitions. This was one of those that was not wrong, but unclear.
2 - another point that was kind of sketchy-looking. It wasn't directly wrong, but it looked overly simplified. You'll see why in a few points.
A better limit would be not more than 2 to the power of that. Hilbert space is very, very large.
3 - this seems to be going out of order.
Regular old Quantum Immortality takes as an axiom that you cannot experience death. If you could, then the whole thing falls to pieces.
As for the universe putting you in a safe place, well then, you are fortunate. How does this argument apply to people who die? Did they not have subjective experiences? What makes them different from you?
4 - the heart of the matter
This is seriously, majorly wrong, and the reason I complained about point 2. Your brain decoheres a zillion times per second. Your consciousness is far, far, far into the classical regime.
Observing does not cause collapse. Events which cause the wavefunction to split into dynamically separate parts do, and those happen at the same rate in a system regardless of how you cut it.
Depends on how you formulate it, doesn't it? Anyway, arguing against regular QI does not argue for your variant.
That doesn't look like immortality to me. It looks like you dying eventually. You look at the history of your lifeline and it peters out, little by little, sometimes more at once than other times. Those decreases? Those are dying. The only way QI works is if you ignore the parts that died, and the only justification I've seen for doing that is by locking your viewpoint to your subjective experience. That's what allows you to discard any cases where you don't survive. If you're looking from a distance, you see a whole lot of dead you-s out there.
I believe the argument goes that they, too, are immortal... from their own perspective. Your consciousness traces its worldline, taking branches where you stay alive, and theirs does the same, but picking worlds where they stay alive. In other words, you can see them die, and they can see you die, but the consciousness, the qualia of the person who's supposedly dying is not there; it's gone down a different worldline.
I think that the theory is cute and quite seductive, but quite clearly wrong. The problem is, for example, brain damage: does quantum immortality allow you to experience Phineas Gage-type brain damage, or doesn't it?
Also, I've been blackout drunk in college, and if quantum immortality is a thing, it's not clear why my consciousness didn't trace a path through the universes where I wasn't blackout drunk. It was, after all, a loss of self, even if it was only temporary. The arguments QI uses for keeping you alive could be used equally easily to prove that you cannot become blackout drunk.
That was my point. The above QI argument broke that by going timeless and universal.
Thank you again for the thoughtful reply.
Eh? Observing is the only thing that causes collapse.
I agree that there are constant tiny thermodynamic events that, if observed, could cause decoherences a zillion times a second. But, usually these events are not observed.
Decoherence is me finding out which world I end up in, and this only happens as quickly as I think, once every ~1/10 seconds when I'm awake.
I'm guessing you would say that decoherence is my brain ending up in some world, and this happens every time any entropy-increasing chemical event happens.
How can I experimentally tell the difference between these? It's not obvious because even a high-speed detector requires me to read the readout with my (slow) brain. From my perspective, the detector doesn't collapse any wavefunctions until I look at it. I agree with you that if I looked at another brain I would see that brain decohering / doing thermodynamic stuff all the time. I also agree with you that if I looked at my own brain I would see my own brain doing a bunch of stuff really rapidly. You would say that my brain decoheres as quickly as a detector measures it. I would say that my brain decoheres only as quickly as I notice detector readouts. Until I look at the detector, my brain and the detector are in a superposition of states with different possible detector readouts.
I don't know how to test this.
That isn't the relationship between decoherence and observation.
Decoherence events are when a quantum system splits into multiple parts that are no longer dynamically accessible to each other. At this point, they are in different worlds.
Observation events have to be decoherence events. Observation has no other role in quantum mechanics other than that in order to observe, you must decohere.
So, whether or not you observe things, you are in some world of dynamically mutually accessible states, and this will evolve into many dynamically inaccessible components with or without your observing it. By the time you've observed anything, it's way too late to get from one to another.
In that case, it seems like Quantum Immortality doesn't work.
And here I thought I was safe. Dammit.
Well, the nice form you described here doesn't work. The kind of lousy usual form does, with the usual caveats.
I agree provided the many-worlds interpretation is correct, which seems likely.
If the consciousness-causes-collapse interpretation is correct (which seems less likely), then the special form I described might still work. But I can't count on it.