Many Worlds Interpretation and act of measuring

[RUTA]

hahaha, where are this "weird place" ?
and from what I've read on many forums and wikipedia, the theory says that there are many Universes, and all other possibilities happen in OTHER universes, not in our universe.

That's the point I was making ...

 

[bhobba]

"MWI's main conclusion is that the universe (or multiverse in this context) is composed of a quantum superposition of very many, possibly even non-denumerably infinitely[2] many, increasingly divergent, non-communicating parallel universes or quantum worlds."
Many-worlds interpretation - Wikipedia, the free encyclopedia

Wikipedia is usually reliable - but on that its wrong. The worlds are NOT in superposition. That's exactly what a mixed state after decoherence isn't.

Thanks
Bill

 

[stevendaryl]

You're right, we do talk as if there is a "weird" place in the universe where someone is always seeing heads when they flip a coin. Likewise, if all possibilities are realized with equal weight and the universe is infinite, then there are many places that don't agree with the 50-50 outcome of flipping a coin. And, we can't say by virtue of our experience, that indeed the probability is 50-50 just because that's what we observe. Yet, we're talking as if our 50-50 observation represents the "real" probability and those other "anomalous" regions are occurring according to our probability. It's exactly Kent's complaint with MWI, which is a legitimate complaint,

But I don't see how it's more of a complaint against MWI than any other interpretation. In any probabilistic theory, to make sense of the data in light of the theory, we have to assume that the results we have are "typical".

so what we must *really* believe, despite claims otherwise, is that *every* region in the universe finds empirically the 50-50 outcome -- there are no "anomalous" regions. Otherwise, we can't do empirical probabilistic science.

I don't see how the fact that some people experience anomalous results doesn't prevent US from doing science. We don't need to assume that everyone observes 50/50 outcomes from coin flips in order for us to reason about probability. As a matter of fact, probability theory implies almost certainly that there WILL be anomalous regions. If you flip coins long enough, eventually you'll have a run of 1,000,000 heads in a row. If the world lasts long enough, and people continue to flip coins, eventually there will be a generation in which nobody alive remembers ever seeing a coin land on tails. That's just probability. It isn't special to MWI.

 

[stevendaryl]

Wikipedia is usually reliable - but on that its wrong. The worlds are NOT in superposition. That's exactly what a mixed state after decoherence isn't.

I'm sure you already know this, but your remark sounds as if it's saying something different: If the universe starts out in a pure state, then it will ALWAYS be in a pure state. That's what unitary evolution implies. The appearance of mixed states comes from "tracing out" environmental degrees of freedom. But that's not something that the universe does, that's something that WE do.

 

[bhobba]

that's something that WE do.

No - that's something the theory implies from a theorist doing it - as with any deduction from a mathematical model.

There is a deep problem here about how a random environment comes about in such an explanation. That requires explanation in a deterministic theory. My hunch is QFT vacuum fluctuations have something to do with it, and may even provide a natural way to factor systems. Just a thought - as I have said many times I think this stuff requires a lot more research before firm conclusions can be reached.

Thanks
Bill

 

[RUTA]

But I don't see how it's more of a complaint against MWI than any other interpretation. In any probabilistic theory, to make sense of the data in light of the theory, we have to assume that the results we have are "typical".
I don't see how the fact that some people experience anomalous results doesn't prevent US from doing science. We don't need to assume that everyone observes 50/50 outcomes from coin flips in order for us to reason about probability. As a matter of fact, probability theory implies almost certainly that there WILL be anomalous regions. If you flip coins long enough, eventually you'll have a run of 1,000,000 heads in a row. If the world lasts long enough, and people continue to flip coins, eventually there will be a generation in which nobody alive remembers ever seeing a coin land on tails. That's just probability. It isn't special to MWI.

But, if you *really* believe that, then why do you believe the probability we find here is the correct one? No, we're clearly (although tacitly) assuming everyone and anyone in the universe will discover the same probability, which means there is no place that always sees heads.

 

[stevendaryl]

But, if you *really* believe that, then why do you believe the probability we find here is the correct one? No, we're clearly (although tacitly) assuming everyone and anyone in the universe will discover the same probability, which means there is no place that always sees heads.

Well, that belief is actually inconsistent.

 

[stevendaryl]

Well, that belief is actually inconsistent.

Let me expand on that reply. Suppose you believe that, for a sufficiently large number of trials, the relative frequency of an event will approach the probability. Then what's the probability of getting all heads when you flip a coin 1 million times? It's $P = 2^{-10^{6}}$. To say that it never happens is inconsistent with saying that it happens approximately once in $2^{10^6}$ times.

 

[bhobba]

Let me expand on that reply. Suppose you believe that, for a sufficiently large number of trials, the relative frequency of an event will approach the probability. Then what's the probability of getting all heads when you flip a coin 1 million times? It's $P = 2^{-10^{6}}$. To say that it never happens is inconsistent with saying that it happens approximately once in $2^{10^6}$ times.

Its this applied math thing. In many problems, and this is just one, you pick a very small number and assume FAPP its zero. It isn't really - but you assume it is. For example velocity is dx/dt. But you approximate it by delta x/delta t because that's all you can do.

Thanks
Bill

 

[stevendaryl]

Its this applied math thing. In many problems, and this is just one, you pick a very small number and assume FAPP its zero. It isn't really - but you assume it is. For example velocity is dx/dt. But you approximate it by delta x/delta t because that's all you can do.

Right. And making the assumption that sufficiently small probability events don't happen is a perfectly good heuristic, provided that we're only running an experiment a small number of times. But the assumption becomes inconsistent if the number of trials is very large. An example is the lottery. There's a 1 in a million chance of winning the New York State lottery. So if you have a small sample size, say the set of all your closest friends and relatives, you can get away with saying that nobody in that set is going to win the lottery--it's effectively a probability zero event. But if your sample size is the entire state of New York, it's obviously inconsistent to believe that nobody will win.

 

[bhobba]

Right. And making the assumption that sufficiently small probability events don't happen is a perfectly good heuristic, provided that we're only running an experiment a small number of times.

Remember conceptually you can make the very small number as small as you like so you simply choose one that is good for whatever number of times you are doing it.

Thanks
Bill

 

[RUTA]

If you believe you can find the "real" probability empirically, then you believe one of two things:

1. Anyone in the universe can do so
2. Only those in the "right" places can do so

I pick 1.

 

[atyy]

But I don't see how it's more of a complaint against MWI than any other interpretation. In any probabilistic theory, to make sense of the data in light of the theory, we have to assume that the results we have are "typical".

It depends on how much one buys the assignment of a probability to an amplitude within Many-Worlds, since one typically uses probability, not amplitude, to assign typicality. In Copenhagen and Bohmian Mechanics, the amplitudes do pick up probability interpretations, so in those interpretations, one can argue that quantum mechanics describes what we see because the subsystems we observe are typical.

Also, there is still the preferred basis problem, since decoherence is not perfect. So one could choose a basis with cats that are dead and alive, and one still has to explain why there are no conscious observers in those worlds.

 

[stevendaryl]

If you believe you can find the "real" probability empirically then you believe one of two things:

1. Anyone in the universe can do so
2. Only those in the "right" places can do so

I pick 1.

But 1. is provably wrong. It's logically inconsistent to believe that.

 

[stevendaryl]

But 1. is provably wrong. It's logically inconsistent to believe that.

Suppose you have a million people, and they each flip a coin 20 times to figure out the probability of heads and tails. Then typically,

1. 1 person will see all heads. This person will assume that the probability is 1 of getting heads.
   
2. 20 people will see 19 heads and 1 tail. These people will assume that the probability is 95% of getting heads.
3. 190 people will see 18 heads and 2 tails. These people will assume that the probability is 90% of getting heads.
4. etc.

Around 185,000 people will correctly come up with 50% probability. A much larger number will come up with a probability between 0.4 and 0.6.

But it definitely will not be the case that everyone comes up with the observed probability of 50% heads.

 

[stevendaryl]

It depends on how much one buys the assignment of a probability to an amplitude within Many-Worlds, since one typically uses probability, not amplitude, to assign typicality. In Copenhagen and Bohmian Mechanics, the amplitudes do pick up probability interpretations, so in those interpretations, one can argue that quantum mechanics describes what we see because the subsystems we observe are typical.

Also, there is still the preferred basis problem, since decoherence is not perfect. So one could choose a basis with cats that are dead and alive, and one still has to explain why there are no conscious observers in those worlds.

I think you're mixing up two different questions:

1. Are Born probabilities derivable from MWI?
2. Are MWI inconsistent with the Born probabilities?

I thought that some people were saying that MWI is inconsistent with the Born probabilities, because some branches/worlds will have relative frequencies that don't agree with the Born predictions.

 

[TrickyDicky]

But 1. is provably wrong. It's logically inconsistent to believe that.

Suppose you have a million people, and they each flip a coin 20 times to figure out the probability of heads and tails. Then typically,

1. 1 person will see all heads. This person will assume that the probability is 1 of getting heads.
   
2. 20 people will see 19 heads and 1 tail. These people will assume that the probability is 95% of getting heads.
3. 190 people will see 18 heads and 2 tails. These people will assume that the probability is 90% of getting heads.
4. etc.

Around 185,000 people will correctly come up with 50% probability. A much larger number will come up with a probability between 0.4 and 0.6.

But it definitely will not be the case that everyone comes up with the observed probability of 50% heads.

I don't think the second quote proves 1 wrong or logically inconsistent. IMO it introduces misleading assumptions that make the coin example inconsistent itself. You are conflating frequencies after a finite number of events are the same as probabilities. The probabilities are always an ideal limit at infinity. The person getting 20 heads will not assume probability 1 of getting heads if he knows anything about probabilities. We don't have to assume that the results we have are "typical". The actual results are specific outcomes, not probabilities, if finding 20 or 200 heads implied we had to assume the probability is one of getting heads probability would be a very different discipline, but nobody does conclude that, the concept of 50% chace for coins is an ideal limit, it is independent of the outcomes found as a concept, it is of course approximately(never exactly) validated by outcomes, it is a tendency, the only way to prove it wrong would be performing infinite trials which is impossible.

 

[stevendaryl]

I don't think the second quote proves 1 wrong or logically inconsistent. IMO it introduces misleading assumptions that make the coin example inconsistent itself. You are conflating frequencies after a finite number of events are the same as probabilities.

That's what I was arguing AGAINST. My point is that you CAN'T assume that relative frequencies will correctly tell you the probability.

The probabilities are always an ideal limit at infinity. The person getting 20 heads will not assume probability 1 of getting heads if he knows anything about probabilities.

Maybe not, but if you're trying to figure out whether you have a fair coin, or not, you would very likely decide that it was not.

 

[TrickyDicky]

That's what I was arguing AGAINST. My point is that you CAN'T assume that relative frequencies will correctly tell you the probability.

But then your example goes against what you are arguing for. And option 1 from RUTA is the only one consistent, certainly not 2.

Maybe not, but if you're trying to figure out whether you have a fair coin, or not, you would very likely decide that it was not.

Exactly, because the concept of probabiliy is independent of the specific outcome you get. Getting those outcomes make you think there's something wrong with your physical coin, not assume the probability is different from 0.5.

 

[atyy]

I think you're mixing up two different questions:

1. Are Born probabilities derivable from MWI?
2. Are MWI inconsistent with the Born probabilities?

I thought that some people were saying that MWI is inconsistent with the Born probabilities, because some branches/worlds will have relative frequencies that don't agree with the Born predictions.

I think we were both talking about (2). Is one able to say that branches are unlikely in which observers cannot verify the Born rule?

 

[RUTA]

Suppose you have a million people, and they each flip a coin 20 times to figure out the probability of heads and tails. Then typically,

1. 1 person will see all heads. This person will assume that the probability is 1 of getting heads.
   
2. 20 people will see 19 heads and 1 tail. These people will assume that the probability is 95% of getting heads.
3. 190 people will see 18 heads and 2 tails. These people will assume that the probability is 90% of getting heads.
4. etc.

Around 185,000 people will correctly come up with 50% probability. A much larger number will come up with a probability between 0.4 and 0.6.

But it definitely will not be the case that everyone comes up with the observed probability of 50% heads.

Would you make your inductive inference from 20 flips? No reasonable scientist would. This is a straw man.

My point stands, as does my choice.

 

[stevendaryl]

Would you make your inductive inference from 20 flips? No reasonable scientist would. This is a straw man.

No, it is not. Replacing 20 by 20,000 or 20,000,000 does not change the conclusion.

My point stands as does my choice.

Do you see that replacing 20 flips by 20,000 or 20,000,000 won't change the conclusion? Your choice seems to me to be mathematically inconsistent. A contradiction.

 

[stevendaryl]

But then your example goes against what you are arguing for. And option 1 from RUTA is the only one consistent, certainly not 2.

I don't know what you're saying. My point is that

1. "Empirically determining the probability" means a FINITE number of observations. Nothing that requires an infinite number of observations could be called "empirical".
2. If you only have finitely many observations, then there is the possibility that the statistical results are a fluke.

In other words, what RUTA was demanding, that everyone everywhere at all times must come to the same conclusions about the probabilities, is just not possible to guarantee. It's mathematically inconsistent.

 

[Quantumental]

After being AFK for a while, I am just going to leave this new paper here: http://arxiv.org/abs/1504.01063 it explains what is so wrong with the current approach to probabilities in MWI

 

[Rodrigo Cesar]

so problem solved, MWI is bull****, time to move on.

 

[TrickyDicky]

I don't know what you're saying. My point is that

1. "Empirically determining the probability" means a FINITE number of observations. Nothing that requires an infinite number of observations could be called "empirical".
2. If you only have finitely many observations, then there is the possibility that the statistical results are a fluke.

In other words, what RUTA was demanding, that everyone everywhere at all times must come to the same conclusions about the probabilities, is just not possible to guarantee. It's mathematically inconsistent.

The reason you don't understand what I'm saying seems to lie on your ignoring the difference between the abstract mathematical probability theory and statistics in this discussion. But without making that basic distinction is impossible to say anything meaningful about the problem with MWI.

 

[RUTA]

I don't know what you're saying. My point is that

1. "Empirically determining the probability" means a FINITE number of observations. Nothing that requires an infinite number of observations could be called "empirical".
2. If you only have finitely many observations, then there is the possibility that the statistical results are a fluke.

In other words, what RUTA was demanding, that everyone everywhere at all times must come to the same conclusions about the probabilities, is just not possible to guarantee. It's mathematically inconsistent.

You're making an assumption (#2) about the nature of reality that I deny. It's that simple.

 

[stevendaryl]

The reason you don't understand what I'm saying seems to lie on your ignoring the difference between the abstract mathematical probability theory and statistics in this discussion

I understand what you're saying, but it isn't relevant to the claim being discussed.

 

[stevendaryl]

You're making an assumption (#2) about the nature of reality that I deny. It's that simple.

Yes, I understand that you are denying it. But it is logically inconsistent of you.

 

[stevendaryl]

After being AFK for a while, I am just going to leave this new paper here: http://arxiv.org/abs/1504.01063 it explains what is so wrong with the current approach to probabilities in MWI

That's the paper that we've been discussing for the last week or so.