You are offered a deal in which you are asked to flip a coin ten times. If any one of the flips comes up tails, you are swiftly and painlessly killed. If it comes up heads ten times in a row, you are given a banana. Do you take the deal?
For the purposes of this thought experiment, we may assume it is a perfectly fair coin, and that you like bananas, although not any more so than would generally be considered healthy. We may also assume for simplicity that your life or death is of absolutely no consequence to anyone but yourself: you live in secret on a deserted island, isolated from contact with the outside world, where you have everything you need other than bananas. We may finally assume that we know for certainty that there is no afterlife; upon death, you simply cease to exist in any form. So, there is an approximately 99.9% chance that you will be dead, which by hypothesis implies that you will feel no regrets or feelings of disappointment. And if you survive, you get a banana. What do you think?
Now change the experiment a little. Instead of flipping a coin, you measure the x-component of the spin of an electron that has been prepared in an eigenstate of the y-component of the spin; according to the rules of quantum mechanics, there is an even chance that you will measure the x-component of the spin to be up or down. You do this ten times, with ten different electrons, and are offered the same wager as before, with spin-up playing the role of “heads” for the coin. The only difference is that, instead of a classical probability, we are dealing with branching/collapsing wavefunctions. I.e., if you believe in something like the many-worlds interpretation of quantum mechanics, there will always be a branch of the wavefunction of the universe in which you continue to exist and now have a banana. Do you take the deal?
Count Iblis writes:
Okay, but you wouldn’t find yourself in an unconscious state, you can’t because you’re unconscious!
I think this talk of probabilities is precisely what Tegmark is talking about in being careful to distinguish “inside” and “oustide” views. Assigning probabilities to states is an interpretation of QM we’re allowed to make by virtue of being sufficiently “outside” the system in question, which doesn’t apply to his suicide experiment.
Hi Indiana,
We certainly can’t find ourselves in an unconscios state. But that doesn’t mean that are allowed to throw away unconscious states when calculating probabilities of experiments. There is a very small probability that during an operation anaesthetics will fail to work. Does the MWI imply that for a person undergoing an operation the anaesthetics will fail to work with probability 1?
To briefly respond to Anthony in #65: I don’t think that counts as an experimental difference between MWI and collapse interpretations. In neither case is your vacuum-decay theory ruled out, but in both cases it has strong evidence against it. Even if the MWI is true, I’m not going to be very happy with a theory that is only consistent with the data if we live in an incredibly unlikely branch of the wavefunction. And even if Copenhagen is true, the only scientists around to be making judgments are those who haven’t been killed by vacuum decay, so we should really be looking at conditional probabilities as observed by that sample. Of course the “strong evidence against it” might be wrong, but that’s always the danger with arguments based on naturalness rather than strict disagreement with observation.
Sean: I disagree. In the Copenhagen interpretation, if I wait ten years, I should have destroyed by 10 bubbles, and my disbelief in my theory grows and grows with each passing year, even if I do away with the initial improbability of my existence by conditioning on the fact that I exist now.
I think we can clearly distinguish the two by making the universe finite. In that case, the probability of their being *any obervers at* all decreases exponentially with time. Since we exist, I think the theory would be ruled out at confidence 1-p, where p is the probability that even a single ‘observer’ (which we could conservatively take to be a Ly^3-yr) is still around after 13.7 Gyr.
In MWI, if we accept the reasoning behind the quantum suicide thought experiment (i.e. that when ‘I’ die I seamlessly continue in one of the branches where ‘I’ live), I would say I have no reason at all to doubt my theory, because although it implies that I am in a highly improbable branch, it also supplies a completely convincing reason for why I am there. (Yes, this is anthropic.)
The key point is that in Copenhagen, the ensemble is imagined, whereas in MWI, it ‘really exists’; in my mind, this is the whole distinction that the quantum suicide experiment is bringing out.
In an infinite universe, there appears to be, as I noted before, some interchangeability between the different branches of the wavefunction and the different copies that exist in the infinite universe. (In fact this is the basis for a new interpretation of quantum mechanics that I have been reading, and got me thinking about the whole matter.)
Although it is not apparent in what I have written, I actually think there must be something quite wrong with the quantum-suicide reasoning itself. But I have not decided what it is.
Also, I would quarrel with your distinction between ‘ruled out’ and ‘has strong evidence against’. All theories must be ruled out probabalistically, as all experiments have errors. It is nice if we can made the probability as small as we like by doing more, better experiments. In multiverse cosmology, this is not always possible; but in the present case it is (just wait longer), and I see no reason to shy away from saying the theory is ruled out (in Copenhagen).
Anthony A., I’m still unconvinced. Both cases are equally improbable. The odds that we are on the branck of the wavefunction that allows us to still exist are equally improbable as the odds that we haven’t already been swallowed up. Furthermore, the odds that , at a given instant, a bubble will blow up and swallow us up are also equivalent.
This debate between Copenhagen and MWI, and attempts to explicate it using quantum suicide experiments seems to me to be an attempt to predicate the existence of the universe on human perception. I don’t see how it is a sensible approach to do so.
Larry Niven’s story, “All the Myriad Ways”, is the paradigmatic fictional equiivalent of your problem.
I think Anthony is right. According to the quantum-suicide reasoning reasoning (which I believe is wrong), the ”improbable branch” is not improbable relative to the observer.
I think that our ”naive” way of evaluating probabilities breaks down in these sorts of experiments where the number of observers isn’t conserved. If you consider being copied and then one of your copies is copied again. So, you end up with three copies. The three copies are identical and asleep in different rooms. The moment they wake up they can see in which room they are. Suppose that the two copies that arose from copying one of the copies again end up in rooms 1 and 2 while the opther opy ends up in room 3. What is the probability of waking up in a particular room?
A Tegmark ”following the branches” type of reasoning goes as follows. After the first copy is made you have a chance of 1/2 of being the copy that will be copied again. So, the probabilities are 1/4, 1/4 and 1/2.
But of course, this result is completely nonsensical. You have a physical process that transforms you into three identitical copies. It doesn’t matter how exactly this process works, as long as you end up with three identical copies, the probabilities are simply 1/3.
So, one should not naively try to follow a branch and update probabilities along that branch. Instead one should look at the entire multiverse and calculate the probability of finding oneself in a certain state. That state will, in general, include memories of having been in different states previously.
In general one should ask questions like: ”What is the probability of finding spin up in the z-direction when I remember having polarized the spin in the x-direction a minute ago”. As long as the observer isn’t killed or copied depending on the outcome there isn’t any difference between this and the usual way of calculating these things.
In case of suicide experiments, the probability of finding yourslelf in a state in which you remeber have survived such experminets is much lower than states in which you don’t have recollections of participating in these experiments.
I had to commit Quantum suicide once, I had never heard of this at the time.
I was not offered a bet or given a choice. I had to work out what I had to do and I had to do it at the right moment. It’s the hardest thing there is to do, to try break your own neck when you don’t want to die. I stood there with a t-shirt over my head, which covered one eye, held my head in my hands and twisted my head round, of course this is not enough to break my neck, so I had to keep readjusting my hands and feet so I could force my head around further and further. My heart was absolutely pounding like it’s going to pop.
I was not trying to kill my self; I was breaking my neck in order to turn my brain over. When it reappeared after it had vanished, it was upside down, so I had to break my neck, turn my brain over, reattach my spinal column, without dieing of course .If I had died this system would not exist.
If I had a choice, I would never take that deal. It’s not worth it for a banana, if it’s to save everyone and everything, at the risk of losing my own life then it’s still not worth it.
If I have no choice, then I have no choice.
About Antony in #65 and #79 and Sean in #78, I remember reading Tegmark’s paper and considering a similar situation, which one may call ‘doomsday particle scenario’, related with speculation (in which I dont believe, bustjust for the sake of the argument) about a possible ‘end of the world’ triggered by high energy experiments in accelerators,for instance initiating a chain reaction turning the earth in ‘quarkonium’ (sure you read about that stuff in the news, say of newscientist). Now the strange situation would be if there is a threshold energy or intensity for such a thing to happen, but eventhough we have a perfectly good theory predicting that there should be particles coming out of the experiment with energies higher than that threshold, we never see those particles, so there is a cut-off that shouldn’t be there. The situation may be quite disturbing for astronauts in the space station, who would find themselves in a quantum branch looking out of the window to a sphere of quarkonium, or a black hole or whatever, intead of ye olde good earth. Just in this line of SF storyline that may be construed as an answer to the Fermi paraddox, maybe advanced civilizations go with open eyes into experimentation that will have somecatastrophic outcome branches, for the sake of Sean’s bananas (this may be some technosuperbananas), so we, like the astronauts would be most certainly in branches were the green fellas had checked out.
Now even behind the veil of anonymity I must say I don’t believe a word of all that, while in the spirit of Antony #79 it is clear that the fact that the earth has not undergone caastrophic events despite cosmic rays etc… of can’t be used to disprove the possibility, the moon and the other planets are doing just fine and there is no evidence of strange massive dark objects (a befallen planet) around. That doesn’t of course the cosmological scale kaboom scenario of Antony.
Still it seems interesting to think about this things.
Pablo
Living in secret on a deserted island? How about I give them a banana to kill me, and forget all this nonsense?
stop all this nonsense. everyone has already done this in all its parameters in mli because space/time is infinite. bananas give me indigestion in this universe.
It doesn’t matter what I do, because in any case, every possibility will take place in some alternate timeline. (If you buy that sort of thing.) But, c’mon, you’d have to be a moron to take the deal. Who cares if other “me”s get a banana if I get killed? Screw them, I’m not dying for their fruit.
What kind of a banana is it? Is it nice, firm, fresh and tasty or is it turning black, getting all soft and squishy?
I’d buy a banana with the coin.
depends on my situation- if i got nothing much to lose, Ill take the bet – hoping that if i can learn to surf through the universes then the banana is only the tip of the iceberg. If I can do that, then I can win the lottery, cure world-hunger, end poverty, set up a benevolent society, illuminate that which was hidden, and eventually learn to exploit quantum reality to the point that I can literally make reality do what I want by simply fast-forwarding as it were through the various universes until i get to the one i want.
i suppose.
i wouldn’t take the deal because i am afraid of taking risks i don’t understand.
R. Plaga has published an interesting paper in Phys. Lett. B recently, in which he applies a Tegmark ”quantum suicide” type of reasoning to show that some of the arguments for physics beyond the standard model may be invalid.
Count,
I don’t have to tell how confusing this stuff all is. 🙂 More on name.
Why the Higher energies?
John Ellis was good enough to transform our views, to the need required in cosmological conditions? It’s there these issues although quickly dissipated, raise more questions as to the conditions for that “new physics.”
Plato,
Yes, the proposals for new physics at high energies can yield new problems. But the fact is that there are problems with old physics and somehow it must break down at higher energies…
Of course more on name.
I think one needed to understand this movement, or how the false vacuum is understood, and how the true vacuum is created.
Without this, has the idea of the Coleman-De Luccia instanton been refuted?
So someone who may, or may not, be me may (or may not) get a universe encompassing banana? I’d rather have a pineapple if it’s all the same?
I’d be the one to take the coin, and go get my own danged banana with it.
What if one of your MWI incarnations is in a world where MWI is not true?