How to control the future

[0player]

Oh, we brought quantum mechanics onto table! Then here's a brain teaser: how can you observe only one state of the system, when you are the part of the quantum system yourselves?

[Foxy Boxes]

Oh, we brought quantum mechanics onto table! Then here's a brain teaser: how can you observe only one state of the system, when you are the part of the quantum system yourselves?

My initial, completely unjustified, response would be: Do you? For instance, we receive two sets of images from our eyes that our brains turn into a single image, who's to say it doesn't be the same with the varying states of the system?

[Sinornithosaurus]

Wow, from comics made in MS Paint to quantum mechanics

[0player]

My initial, completely unjustified, response would be: Do you? For instance, we receive two sets of images from our eyes that our brains turn into a single image, who's to say it doesn't be the same with the varying states of the system?

We seem to have no means of percepting mutiple posiibilities. Anyway, if we were to conduct true quantum experiment of probability 1/2, we would still observe only one outcome, though our brain should have no preference on which outcome to observe.
Also, our brain is powered by physics, therefore it is a quantum object too and cannot do meta-quatum magic.

[icynewyear]

Ha! As a schizophrenic my brain processes multi realities all the time! I have a leg up on your normies.

[BinoAl]

Granted, I haven't study much quantum mechanics, and just know the basics... But it's always seemed, to me, to stem from our inability to perceive things past a certain point. We can make estimations, but probability seems to play a large part in it. That, to me, wouldn't disprove that all possible future outcomes are set in stone, simply that we can't predict future outcomes with 100% accuracy because we can't observe them at a fine enough resolution, or without changing them.

But what do I know, this is uninformed drivel anyway.

[ExpHP]

Oh, we brought quantum mechanics onto table! Then here's a brain teaser: how can you observe only one state of the system, when you are the part of the quantum system yourselves?

And with that, I once again return us to the many-worlds interpretation! Because it explains wavefunction collapse with this neat little concept known as quantum decoherence.

Basically: You just answered your own question. We are part of the quantum system! When you set up an experiment where two superposed states can result in different outcomes (e.g. a particle passing through a plate versus reflecting off) those states of the particle will decohere. The two states can no longer interfere with each other, making the particle less wavelike and more... particle-like.

Now let's say those two different states result in macroscopically different outcomes. E.g., the particle enters detector A and makes the computer go *beep*, or it enters detector B and causes it to go *boop*. The state of these detectors is now entangled with the state of the particle! And if you're sitting in the lab when that sound happens, so are you! You, who heard *beep* (who will go off to win the Nobel prize), is no longer in phase with you, who heard *boop* (and who will marry a donkey). Thus, in any given state of the universe, you only remember one of the two events occurring.

Welcome to physics. 8)

[0player]

And with that, I once again return us to the many-worlds interpretation! Because it explains wavefunction collapse with this neat little concept known as quantum decoherence.

Basically: You just answered your own question. We are part of the quantum system! When you set up an experiment where two superposed states can result in different outcomes (e.g. a particle passing through a plate versus reflecting off) those states of the particle will decohere. The two states can no longer interfere with each other, making the particle less wavelike and more... particle-like.

Now let's say those two different states result in macroscopically different outcomes. E.g., the particle enters detector A and makes the computer go *beep*, or it enters detector B and causes it to go *boop*. The state of these detectors is now entangled with the state of the particle! And if you're sitting in the lab when that sound happens, so are you! You, who heard *beep* (who will go off to win the Nobel prize), is no longer in phase with you, who heard *boop* (and who will marry a donkey). Thus, in any given state of the universe, you only remember one of the two events occurring.

Welcome to physics. 8)

That doesn't count, you knew the correct answer! Might have let the others guess.

[ExpHP]

That doesn't count, you knew the correct answer! Might have let the others guess.

I rescind my post.

The universe is a mystery. Discuss!

[jkievlan]

Oh, we brought quantum mechanics onto table! Then here's a brain teaser: how can you observe only one state of the system, when you are the part of the quantum system yourselves?

And with that, I once again return us to the many-worlds interpretation! Because it explains wavefunction collapse with this neat little concept known as quantum decoherence.

Basically: You just answered your own question. We are part of the quantum system! When you set up an experiment where two superposed states can result in different outcomes (e.g. a particle passing through a plate versus reflecting off) those states of the particle will decohere. The two states can no longer interfere with each other, making the particle less wavelike and more... particle-like.

Now let's say those two different states result in macroscopically different outcomes. E.g., the particle enters detector A and makes the computer go *beep*, or it enters detector B and causes it to go *boop*. The state of these detectors is now entangled with the state of the particle! And if you're sitting in the lab when that sound happens, so are you! You, who heard *beep* (who will go off to win the Nobel prize), is no longer in phase with you, who heard *boop* (and who will marry a donkey). Thus, in any given state of the universe, you only remember one of the two events occurring.

Welcome to physics. 8)

Yep, it's a very elegant explanation, and I admit that many-worlds is one of the few attempts at explaining wavefunction collapse that strikes me as logically sound. BUT -- you should add the caveat that while this is a neat and logical explanation, we don't actually have any evidence that it's the *correct* explanation :)

[ExpHP]

Yep, it's a very elegant explanation, and I admit that many-worlds is one of the few attempts at explaining wavefunction collapse that strikes me as logically sound. BUT -- you should add the caveat that while this is a neat and logical explanation, we don't actually have any evidence that it's the *correct* explanation :)

Well... there is that one experiment...

Spoiler

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Put a scientist in a chamber with an explosive device, and make a measurement on a quantum system (say, spin of a proton) that has a 50/50 chance of detonating the bomb. Do this twice, and he has a 1/4 chance of living. Do this a hundred or so times, and his chance of survival is effectively zero.

In the many worlds interpretation, from the subjective experience of the scientist, he will live, because the universe where he lives is the only one where his subjective experience continues.

Of course, this won't do a whole lotta good for everyone else, as everyone else will continue living in the 99.99999% of universes where the lab crew gets carried off straight to prison. ("Did you really find it necessary to continue the experiment after he survived the first 15 times?")

...

Now, if you put the entire planet in one of those chambers...

[jkievlan]

Spoiler

Show

Put a scientist in a chamber with an explosive device, and make a measurement on a quantum system (say, spin of a proton) that has a 50/50 chance of detonating the bomb. Do this twice, and he has a 1/4 chance of living. Do this a hundred or so times, and his chance of survival is effectively zero.

In the many worlds interpretation, from the subjective experience of the scientist, he will live, because the universe where he lives is the only one where his subjective experience continues.

Of course, this won't do a whole lotta good for everyone else, as everyone else will continue living in the 99.99999% of universes where the lab crew gets carried off straight to prison. ("Did you really find it necessary to continue the experiment after he survived the first 15 times?")

...

Now, if you put the entire planet in one of those chambers...

Well...that experiment doesn't exactly prove the theory. You'd have to be able to check whether there is a universe in which his subjective experience continues.

[ExpHP]

Read the last sentence in that spoiler. :)

...C'mon, everybody, it'll be fun! Promise!

[jkievlan]

Read the last sentence in that spoiler. :)

...C'mon, everybody, it'll be fun! Promise!

It still wouldn't make a difference. You see, the possibility of landing in a timeline in which the bomb doesn't go off is *identical* to the possibility that, statistically, the bomb doesn't go off in a single universe. In other words:

I run the experiment once. Assuming many-worlds is correct: there is a 50/50 chance that, after the test, I am looking at a universe in which the bomb doesn't go off. Assuming many-worlds is false: there is a 50/50 chance that the bomb doesn't go off as a matter of statistics. We can continue the experiment as many times as we like. Say we do it 100 times and the bomb still doesn't go off. This is statistically very unlikely: there is about 1 in 13x10^27 chance that this will occur. So, doesn't that mean it's just that likely that we're in a many-worlds multiverse, and we're just ridiculously lucky enough to be the people in one of the universes where it doesn't go off? No -- because there is *exactly* the same chance that we were simply that lucky in our single universe. So, however much evidence you might try to accumulate with this experiment in favor of many-worlds (and remember, only the universe where the planet *doesn't* blow up would have any evidence at all), it could just as easily be evidence that there's one world and we're just ridiculously lucky (and very, very stupid).

[TheGatesofLogic]

Yep, it's a very elegant explanation, and I admit that many-worlds is one of the few attempts at explaining wavefunction collapse that strikes me as logically sound. BUT -- you should add the caveat that while this is a neat and logical explanation, we don't actually have any evidence that it's the *correct* explanation :)

OBVIOUSLY! Everbody knows that wave function collapse is a direct result of the power of psychokinesis and conscious interaction between the brain and matter, also intelligent design is kool :P [Sarcasm]

[0player]

The quantum immortality thought experiment relies on non-necessarily-true assumtion that it is somehow necessary for our perception to continue indefinitely. In other words, we actually live in both universes -- but in one of them, not for very long -- so it's impossible to predict which one we would land into.

[jkievlan]

Yep, it's a very elegant explanation, and I admit that many-worlds is one of the few attempts at explaining wavefunction collapse that strikes me as logically sound. BUT -- you should add the caveat that while this is a neat and logical explanation, we don't actually have any evidence that it's the *correct* explanation :)

OBVIOUSLY! Everbody knows that wave function collapse is a direct result of the power of psychokinesis and conscious interaction between the brain and matter, also intelligent design is kool :P [Sarcasm]

It strikes me you're saying there's no other reasonable explanation other than many-worlds theory :) Am I understanding you right?

[0player]

Also, Everett interpretation isn't necessary to explain observation phenomenon. In standard interpretation, there is a concept of quantum entanglement, that means the same. (If two systems are entangled, then every state of one system experiences the other system as if it suddenly collapsed to one state).

[TheGatesofLogic]

Yep, it's a very elegant explanation, and I admit that many-worlds is one of the few attempts at explaining wavefunction collapse that strikes me as logically sound. BUT -- you should add the caveat that while this is a neat and logical explanation, we don't actually have any evidence that it's the *correct* explanation :)

OBVIOUSLY! Everbody knows that wave function collapse is a direct result of the power of psychokinesis and conscious interaction between the brain and matter, also intelligent design is kool :P [Sarcasm]

It strikes me you're saying there's no other reasonable explanation other than many-worlds theory :) Am I understanding you right?

hehe, no. If that were the case i would not be a PhD in Quantum Mechanics :) I was just joking about the von Neumann interpretation of wave function collapse and the apparent ridiculousness of it

[ExpHP]

The quantum immortality thought experiment relies on non-necessarily-true assumtion that it is somehow necessary for our perception to continue indefinitely. In other words, we actually live in both universes -- but in one of them, not for very long -- so it's impossible to predict which one we would land into.

There seems to be a bit of a misconception that you only 'land in' one of the universes in MWI. You land in all of them. You perceive all of them. I mean, what makes one specific version of you any special? Are the others not real? Do they not percieve? Are they Zombies?

From a materialist standpoint, perception, consciousness, and sentience must be included as a part of the physical package. Once we posit the existence of a separate "soul" and whatnot, we're getting into metaphysical territory, and no physics major is ever going to win an argument there. :P

So, doesn't that mean it's just that likely that we're in a many-worlds multiverse, and we're just ridiculously lucky enough to be the people in one of the universes where it doesn't go off? No -- because there is *exactly* the same chance that we were simply that lucky in our single universe.

This is true for an outside observer, but not for the people in the death chamber.

Spoiler

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For the victim, there is a differential probability of observing the outcome of the experiment, based on what the outcome would be. The probability of observing the outcome given that you are dead is 0, meaning that you can only observe an outcome under the exceedingly rare chance that all measurements turned out to be safe.

Let O represent the event that we survive to see the outcome of the experiment.
Let M represent the event that MWI (or some other model where P(O)=1) is accurate.
Let C represent the event that the Copenhagen interpretation is accurate.
Let P(A|B) mean the probability of A, given B.

For a person in the chamber, P(O|M) = 1, and P(O|C) = 0.5^n.
For an outside observer, P(O|M) = P(O|C) = 1.

This is what results in the discrepancy. Using Bayes Theorem, it can be shown that, for those in the death chamber, P(M|O) > P(M) (meaning that, rationally speaking, they should believe MWI is more likely to be true after observing this outcome). For outside observers, P(M|O) = P(M) (meaning that neither theory is supported, even if the victim miraculously survives).


(the guy I just linked is the HPMoR guy, to anyone who remembers that. ;))

[jkievlan]

Spoiler

Show

For the victim, there is a differential probability of observing the outcome of the experiment, based on what the outcome would be. The probability of observing the outcome given that you are dead is 0, meaning that you can only observe an outcome under the exceedingly rare chance that all measurements turned out to be safe.

Let O represent the event that we survive to see the outcome of the experiment.
Let M represent the event that MWI (or some other model where P(O)=1) is accurate.
Let C represent the event that the Copenhagen interpretation is accurate.
Let P(A|B) mean the probability of A, given B.

For a person in the chamber, P(O|M) = 1, and P(O|C) = 0.5^n.
For an outside observer, P(O|M) = P(O|C) = 1.

This is what results in the discrepancy. Using Bayes Theorem, it can be shown that, for those in the death chamber, P(M|O) > P(M) (meaning that, rationally speaking, they should believe MWI is more likely to be true after observing this outcome). For outside observers, P(M|O) = P(M) (meaning that neither theory is supported, even if the victim miraculously survives).


(the guy I just linked is the HPMoR guy, to anyone who remembers that. ;))

Yes, see, the problem is that P(O|M), for an observer inside the chamber, is not equal to 1. Assuming that every instance of an observer existing in a possible world is an outcome of the experiment, there are many instances of the observer which do *not* survive to see the outcome of the experiment, namely those that are in timelines in which the bomb explodes. Thus, "your" probability of surviving the experiment, given many worlds, is a function of not only the instances of "you" who exist in universes in which the bomb does *not* explode, but also all instances who exist in universes in which it *does* explode. Yes, when the bomb explodes, the observer dies...however, the observer *did* observe the event of the bomb's explosion, although he/she does not exist afterwards to describe the event.

[0player]

There's no point in discussing Copenhagen versus Everett; as of last year, they were showed to be equivalent interpretations (as in, they make exactly the same predictions). Back then, Everett's theory was much better, because Copenhagen contained that handwave about observers and non-observers (most people have heard about that version, which is why I came here with my trick question), but decoherence is now the part of both interpretations.
(Sorry, I cannot find the exact article I'm thinking about; the magazine doesn't publish its old articles on the Internet for free, and my paper copies are in another town).
In MWI, it could be said that we simultaneously "survive and do not survive" to see the outcome of an experiment, and only those of us who will survive, will see it. But, look at the C interpretation: the chances of (us surviving | us observing) is obviously 1, too. As all probabilities exist only from a viewpoint of observer (for us outside of cat box, the probability of it being dead is 0.5; for dead cat inside, it's 1.0, and for alive cat inside, it's 0.0), P(O|C) is 1, too, as it is nonsensical to speak about the probability of us "not-surviving" if the bomb indeed vaporizes us.
LessWrong is no less wrong in this case.
Let's conduct a thought experiment. I have a coin. The first hypothesis is "coin always lands heads". The second is "coin is fair". I flip the coin, but I can either show it to you or not. It just happens so that, the all flips I showed to you are heads. Bayes says that the first hypothesis is more probable. But what's actually going going on is that I hide all tails from you, creating a referential bias in your brain.
Universe iseven more of a cheating bitch as I am. She flips the coin and says: hypothesis A: Coin always lands "life". Hypothesis B: coin is fair. She flips the coin and kills you off if the coin lands "death". Should you be lucky enough to survive for several times, you would have "reasons" to believe that coin always lands "life". In reality, the coin is fair; you perception is faulty (it goes dysfunctional when you die).

The ultimate answer is, of course, "you die in every case", because what you call "you" is one state of a system (or an instance of a system in one of the worlds, if you prefer MWI), and any change will contain states and worlds that are different from now. To quantum mechanics, there is no alive-you or dead-you. You don't get to survive; the guy quite similar to you, who did survived, does. (You also will not see the next second; some other guy will).

[0player]

Yes, see, the problem is that P(O|M), for an observer inside the chamber, is not equal to 1. Assuming that every instance of an observer existing in a possible world is an outcome of the experiment, there are many instances of the observer which do *not* survive to see the outcome of the experiment, namely those that are in timelines in which the bomb explodes. Thus, "your" probability of surviving the experiment, given many worlds, is a function of not only the instances of "you" who exist in universes in which the bomb does *not* explode, but also all instances who exist in universes in which it *does* explode. Yes, when the bomb explodes, the observer dies...however, the observer *did* observe the event of the bomb's explosion, although he/she does not exist afterwards to describe the event.

Yep, it ultimately boils down to this dichotomy.
1) we accept that it is possible to observe the bomb's explosion. Then quantum immortality doesn't work.
2) we say that it is somehow forbidden to observe the bomb's explosion. Then quantum immortality is another name for referential bias, that stems from our inability to observe certain things.
Sorry, Einstein, but God didn't listen when you told him not to gamble.
Edit: yeah, and the final sentence of that LessWrong page is just bullshit, since humanity doesn't have uniform perception (and it isn't proven that we have some non-zero chance to continue forever). It is basically like saying "lol, so if we die, we don't get to see it, so for all intents and purposes, humanity is immortal!"
She (or is she "he") is alright, but seems to be too zealous and amazed by certain topics. It shows up in several places of HPMoR, too.

[TheGatesofLogic]

is the experience of dying not an event an obsever can observe of itself? ;) i'll let you guys play with that for a bit

[ExpHP]

She (or is she "he") is alright, but seems to be too zealous and amazed by certain topics. It shows up in several places of HPMoR, too.

Yes, quite. About a year ago, I was going through some of the "sequences" on his site, and I got a little annoyed by some of his articles, because whenever I'd find that valuable piece of insight I'd like to share, it was always sitting 3 lines above a steaming piece of bullshit. :)

Oh, hey, how about this: Let O = "the event where you go on to publish a report about the outcome of your experiment."

EDIT: Neglecting the probability that everybody just assumes a cord was unplugged somewhere.