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How the Many-Worlds Theory of Hugh Everett Split the Universe

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Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#81

Post by jfengel »

lordnacho wrote: post #2

I'm not sure if the Aeon article explains what Everett really meant, at least I still have questions. Suppose we're eternally branching, as in the example about the up/down spin. If there's no way to visit other branches, how will we ever confirm this? Second, what is the benefit of the branching interpretation? It seems to simply be a way to think about probabilities?

1. No, there is no way to visit other branches.

2. The benefit is that it's a very direct translation of the math into concepts. If you actually build the mathematical model, the "other worlds" are right there in the model, as the other half of a superposition.

It doesn't go away. You just can't get to it. Nor can you ignore it, because it's sitting there as a term in the equation, persisting as you evolve it over time. It just becomes smaller and smaller without ever becoming zero. That's why you observe a classical universe even though it's really quantum: the odds of the other parts of a superposition having an effect are on the order of Avogadro's-number-to-1 against.

Copenhagen works by just arbitrarily defining that number as zero, which is easy to work with but conceptually incomplete. MWI keeps it there in another "world", which is more in keeping with the math but unedifying because it sounds so unfalsifiable.

Hope that helps. (Which is always code for "... but it probably doesn't", I'm afraid.)

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#82

Post by monktastic1 »

fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

This is also known as the Wigner's Friend paradox.

Your explanation is not the standard understanding of Many Worlds today, however. The party line is that world splitting happens when decoherence has become "sufficiently irreversible" (for some arbitrary definition of "sufficiently", since there's no evidence of genuine irreversibility anywhere in physics), which in almost all real-world setups happens almost immediately.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#83

Post by platz »

zwkrt wrote: post #80
platz wrote: post #70

Earlier quoted context omitted.

> The fact that we observe interference patterns shows that the wavefunctions are real. well, not quite - remember that what we actually observe for a given particular event is something that looks like particle that is localized in space. If you're referring to the double slit experiment, the interference pattern emerges as a property of the whole collection of individual photon strikes. Yes, you need to use the wav…

Non-physicist perspective, if I’m out of line, please say so. It seems silly to expect that the wavefunctuon is “real” just like it is silly to assume that the gravitational field is “real” or inches are “real”. They are mathematical constructions we use to make predictions about what we see. Just because the predictions are good doesn’t make the mathematical formalism real. As a contrived example, imagine an advance…

I think this is the view that scientists if they are interested more in the task of prediction than anything else https://www.youtube.com/watch?v=ka9KGqr5Wtw

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#84

Post by gizmo686 »

platz wrote: post #79
gizmo686 wrote: post #78

Earlier quoted context omitted.

If we put the sensor in the slits themselves, what we would observe is individual photons passing through one slit or the other. What the double slit experiment shows is that there is still something of a wavefunction (whatever that actually is) at the moment the photons pass the slit, because that is how we get the interference pattern. As before when we observe the photons, we see them as single discreet particles.…

Right, but in that case we never observe the wavefunction, the quantum state of the particle, or the particle interacting with itself. In that sense, the wavefunction predicts the outcome but it does not have to "real". It is real in Pilot Wave theory, but it could simply be a mathematical or calculational tool . In either case, you are right that one has to use it get the right result. Let me ask you a similar quest…

I think virtual particles are a different question, as it is at least clear what is being asked (I think they are real, but have seen no convincing arguement one way or the other).

With wavefunctions, I am not actually clear on what the object "wavefunction" is. If you are asking if I believe the wave exists independent of the particle, then no. But I also do not think it is merely a calculation tool.

My view is that it is analogous to "velocity" in classical mechanics. In that it is a property of the object in question. I do not know if that qualifies as "real" or not.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#85

Post by bvinc »

yters wrote: post #27
fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The problem with many worlds is why do I think I'm in a particular timeline? If many worlds is correct, there is no "I", there are many rapidly branching "I"s, which intuitively doesn't make sense. Of course, each "I" will have the perception of being the sole "I", but the overall view that there is no singular "I" is very counter to my self conception. I prefer to preserve intuitions over conjectures, so I count tha…

> but the overall view that there is no singular "I" is very counter to my self conception

And the idea that the Earth being round and rotating around the sun is also very counter to my intuition.

Think of it this way. Instead of asking "Does this feel correct to me?", ask, "If this was correct, would I feel any different?"

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#86

Post by krzat »

yters wrote: post #27
fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The problem with many worlds is why do I think I'm in a particular timeline? If many worlds is correct, there is no "I", there are many rapidly branching "I"s, which intuitively doesn't make sense. Of course, each "I" will have the perception of being the sole "I", but the overall view that there is no singular "I" is very counter to my self conception. I prefer to preserve intuitions over conjectures, so I count tha…

It's definitely a mindfuck but I'm not sure if you can dismiss MWI based on that.

Everything that was intuitive was already discovered. That's why each new theory is harder to visualise than the previous one: newtonian physics, electromagnetism, relativity, quantum physics, etc.

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#87

Post by triMichael »

fallingfrog wrote: post #8

You can do a really simple thought experiment that provides a persuasive argument in favor of the many worlds theory. Or at least, it shows that wave function collapse is relative to an observer, not universal everywhere. Start with Schroedingers cat: the cat is in a box, it’s in a state of quantum superposition. It’s 50/50 alive or dead. Now a researcher opens the box: the cat is found to be either alive, or dead, a…

The answer to this which makes the most sense to me is that the wave function collapses when the information exists that determines the quantum state. In Schrodinger's cat, this would be when the Geiger counter detects the quantum state, but by the time the cat dies/does not die and the researcher opens the box, everything is already in the classical world.

Schrodinger's cat was made to be a thought experiment to show how absurd some of the ideas about the quantum world are. We are unable to prove whether the cat does go into a superposition or does not. Personally, the ideas that superposition is tied to whether consciousness observes it doesn't make sense to me. After reading about some of the stranger experiments such as the quantum eraser experiment, I've gravitated towards information theory being the missing link. If that is true, then the astounding conclusion would be that the fabric of our universe is information!

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#88

Post by kgwgk »

"Let me address another issue with many-worlds. It is a deterministic theory, even a hyper-deterministic theory, i.e. determinism applies to everything in the entire universe. Indeed, since there can’t be any influences coming from outside and since the Schroedinger equation - the only dynamical equation of the theory - is deterministic, everything that happens today, e.g. what I am writing, the way each reader reacts, the details of all solar eruptions, etc, was all encoded in some “quantum fluctuations” of the initial state of the universe. Given the complexity of the (many-) worlds, it had to be encoded in some infinitesimal digits of some quantum state, possibly in the billionths of billionths decimal place. I am always astonished that some people seriously believe in that."

- Nicolas Gisin "Collapse. What else?" https://arxiv.org/abs/1701.08300

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#89

Post by vilhelm_s »

kgwgk wrote: post #88

"Let me address another issue with many-worlds. It is a deterministic theory, even a hyper-deterministic theory, i.e. determinism applies to everything in the entire universe. Indeed, since there can’t be any influences coming from outside and since the Schroedinger equation - the only dynamical equation of the theory - is deterministic, everything that happens today, e.g. what I am writing, the way each reader react…

This seems wrong to me? A lot of "things that happen" seem to be created by randomness generated along the way, from only observing subsystems.

I.e., suppose I create a random bit generator by shining photons on a half-silvered mirror and then measuring which way they go. I might then decide what to write depending what the bit is---if it's 0 I will write a HN comment, if it's 1 I will reply to an email.

In this case, the things that happen are determined deterministically, but it's not the case that there is some quantum fluctuation in the initial state of the universe which determines what I write. Rather, when I do the measurement of the bit, I create two branches, one with a HN comment and one with an email. Observers entangled with the first branch can only see the HN comment, but this complexity was created at the time of the measurement, not at the time of the big bang...

Re: How the Many-Worlds Theory of Hugh Everett Split the Universe

#90

Post by kgwgk »

vilhelm_s wrote: post #89
kgwgk wrote: post #88

"Let me address another issue with many-worlds. It is a deterministic theory, even a hyper-deterministic theory, i.e. determinism applies to everything in the entire universe. Indeed, since there can’t be any influences coming from outside and since the Schroedinger equation - the only dynamical equation of the theory - is deterministic, everything that happens today, e.g. what I am writing, the way each reader react…

This seems wrong to me? A lot of "things that happen" seem to be created by randomness generated along the way, from only observing subsystems. I.e., suppose I create a random bit generator by shining photons on a half-silvered mirror and then measuring which way they go. I might then decide what to write depending what the bit is---if it's 0 I will write a HN comment, if it's 1 I will reply to an email. In this case…

There is no "randomness generated along the way" in the MWI. Schroedinger's equation is deterministic and according to many-worlders is the only thing that "makes things happen". Everything that happens in every "world" was bound to happen since the beginning of the evolution of the "multiverse".
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