Everett Versus Schrodinger

busyliving

Did Huge Everett's work on the "many worlds interpretation" disprove or back up Erwin Schrodinger's work...

I'm mainly refereeing to Schrodingers cat experiment...

Cheers in advance:D

krd

busyliving wrote: »

Did Huge Everett's work on the "many worlds interpretation" disprove or back up Erwin Schrodinger's work...

I'm mainly refereeing to Schrodingers cat experiment...

Cheers in advance:D

Someone correct me if I'm wrong.

I think the 'many worlds interpretation' is a misunderstanding of quantum indeterminacy.

Just because you have no way of precisely determining where something is, does not mean it is everywhere at once.

In "many worlds", the position of an electron has an infinite number of possibilities. But, for every absolute position, it would need a world it could be in that position for - an infinite number of worlds would be required.

I think the whole idea is wrong, because it just sounds stupid.

The only way we have of measuring particles that exist at the quantum level is by getting them to interact with measuring devices on a much higher level. There is no way of telling if the maths or experimentation that describes these particles isn't just some illusion - a more convoluted version of Chicken Licken and his acorn. No one has ever seen an electron, with the naked eye.

I think the multi-world theory is wrong for another reason: It sounds like an awful Sci-fi plot device. Really terrible sci-fi.

Now, sorry I have to run along now.... I have to assignate Napoleon VI, in an alternative world.....Nanu,Nanu...My friend.

Nanu Nanu!!!

busyliving

krd wrote: »

Someone correct me if I'm wrong.

I think the 'many worlds interpretation' is a misunderstanding of quantum indeterminacy.

Just because you have no way of precisely determining where something is, does not mean it is everywhere at once.

In "many worlds", the position of an electron has an infinite number of possibilities. But, for every absolute position, it would need a world it could be in that position for - an infinite number of worlds would be required.

I think the whole idea is wrong, because it just sounds stupid.

The only way we have of measuring particles that exist at the quantum level is by getting them to interact with measuring devices on a much higher level. There is no way of telling if the maths or experimentation that describes these particles isn't just some illusion - a more convoluted version of Chicken Licken and his acorn. No one has ever seen an electron, with the naked eye.

I think the multi-world theory is wrong for another reason: It sounds like an awful Sci-fi plot device. Really terrible sci-fi.

Now, sorry I have to run along now.... I have to assignate Napoleon VI, in an alternative world.....Nanu,Nanu...My friend.

Nanu Nanu!!!

I'm pretty much a physics layman...

But i have seen a documentary about Everett and there was a laser experiment that apparently proved Everett's theory about the Many Worlds Interpretation was correct...

But as i said i'm just a layman, who has an interest in physics, mainly from watching way too much sci-fi

Professor_Fink

busyliving wrote: »

Did Huge Everett's work on the "many worlds interpretation" disprove or back up Erwin Schrodinger's work...

I'm mainly refereeing to Schrodingers cat experiment...

No. Everett's work removed the necessity for one of the original postulates of quantum mechanics which was included to allow for measurements. Everett showed that in fact this postulate was not necessary and you get mathematically identical behaviour. This doesn't contradict earlier work, it just shows that wave function collapse is not a requirement to get the behaviour we observe from measurements. Whether or not wavefunction collapse does occur has become more a matter of philosophical debate than physics, as the various interpretations predict the same outcomes to all experiments.

Schroedinger's work wasn't the "cat experiment", that was just an illustration. He's known for the wave equation that bares his name.

krd

busyliving wrote: »

I'm pretty much a physics layman...

But i have seen a documentary about Everett and there was a laser experiment that apparently proved Everett's theory about the Many Worlds Interpretation was correct...

But as i said i'm just a layman, who has an interest in physics, mainly from watching way too much sci-fi

I have studied physics - but at a much lower level than the guys who hang out here. I think the Doctors are off in their Tardis at the minute - battling with Daleks and the like. Or just watching it on the BBC.


I'm not sure about Everett's proof. As far as I am aware, even if the Many Worlds Interpretation were true, there isn't any way of seeing from one world into another. The only way you could really tell is if you could pass from one world to another. Then it really gets into the territory of sci-fi. Do the worlds leak into each other? Do we have evil doppelgänger worlds?

If the worlds are infinite, then in some of those worlds there would be people capable of travelling or flitting from one world to the next. You'd have to ask a mathematician who has a speciality in infinities. There are possibly limits to infinity too - some parts of infinity possibly expand faster than others - you'd need to ask a mathematician. A doctor of infinity.

Professor_Fink

busyliving wrote: »

But i have seen a documentary about Everett and there was a laser experiment that apparently proved Everett's theory about the Many Worlds Interpretation was correct...

I don't doubt you saw someone claiming that some experiment separated the Everett interpretation from the Copenhagen interpretation. People occasionally get it into their heads that this can be done, but it can't. The freedom to set where the collapse occurs means that the problem is only semi-decidable in favor of collapse, meaning you can never prove that collapse doesn't occur.

Professor_Fink

krd wrote: »

Someone correct me if I'm wrong.

I think the 'many worlds interpretation' is a misunderstanding of quantum indeterminacy.

It's not, in fact it is based on quite a deep insight into quantum mechanics (basically that creating entanglement with an ancilla system looks indistinguishable from measurement).

krd wrote: »

Just because you have no way of precisely determining where something is, does not mean it is everywhere at once.

That's a misunderstanding of the interpretation, and of quantum mechanics. Quantum mechanics is a linear theory, which means that quantum states can be represented as vectors in a linear vector space. The indeterminacy of position for certain states (i.e. position eigenstates) is because they are really in a superposition of many positions at once. Think of this as the vector representing the state as being the sum of many orthogonal "position" states. Because it is a linear theory, each of these components evolves independently, as it would if it were the state.

Where the Copenhagen interpretation (the one usually adhered to by people who don't believe in the Everett interpretation) and the Everett interpretation differ is that the Copenhagen interpretation says something magic happens when we measure a system: All but the measured component magically disappear. The Everett interpretation says that this bit of magic is not necessary, as Everett showed that we observe the same physics in either case.

krd wrote: »

In "many worlds", the position of an electron has an infinite number of possibilities. But, for every absolute position, it would need a world it could be in that position for - an infinite number of worlds would be required.

I think the whole idea is wrong, because it just sounds stupid.

100 years of physics disagrees with you. Superpositions exist, and are an integral part of quantum mechanics. The observed violations of Bell's inequalities prove this (modulo loopholes). It is nothing specific to the many worlds interpretation, and the only difference is how long lived these superpositions are. (Many worlds=forever, Copenhagen=until measurement, Spontaneous collapse=spontaneous, etc.)

krd wrote: »

The only way we have of measuring particles that exist at the quantum level is by getting them to interact with measuring devices on a much higher level. There is no way of telling if the maths or experimentation that describes these particles isn't just some illusion - a more convoluted version of Chicken Licken and his acorn. No one has ever seen an electron, with the naked eye.

I think the multi-world theory is wrong for another reason: It sounds like an awful Sci-fi plot device. Really terrible sci-fi.

As I've mentioned, the first part of this is based of the false premise that superpositions arent an integral part of quantum mechanics and are some weirdness of the Everett interpretation.

The Everett interpretation has one massive point in its favour: logical succinctness. It has one less postulate than other formulations of quantum mechanics, which is a -big deal-.

Lastly, one of the reasons it may sound like a scifi plot is because it has proved the inspiration behind much scifi.

krd

Professor_Fink wrote: »

the Copenhagen interpretation says something magic happens when we measure a system: All but the measured component magically disappear.

And that is what happens. When you step in to measure a system - you have to stop the system at some point to take a measurement.

The next bit I'm going to say, I would like you to explicitly correct me if I am wrong.

The wave-particle duality of light.

There is no duality. Light is always a wave. Only when you stop the wave and have measured its' energy at that point can you quantify it as a particle -just because you've quantified the energy at the point you've stopped it. Light as a "particle" only happens when you measure it as such - for the rest of the time it appears as a wave.

Professor_Fink

krd wrote: »

And that is what happens. When you step in to measure a system - you have to stop the system at some point to take a measurement.

No it isn't. Quantum mechanics doesn't simply stop because you want to interact with the system. Either there is no collapse, or there is some unknown physical mechanism for collapse. There is no concept of the system stopping so you can measure it.

krd wrote: »

The next bit I'm going to say, I would like you to explicitly correct me if I am wrong.

The wave-particle duality of light.

There is no duality. Light is always a wave. Only when you stop the wave and have measured its' energy at that point can you quantify it as a particle -just because you've quantified the energy at the point you've stopped it. Light as a "particle" only happens when you measure it as such - for the rest of the time it appears as a wave.

This is wrong, and is entirely inconsistent with quantum field theory, although I can see how it would sound reasonable if you have only encountered popularizations of quantum mechanics. Light is the thing we understand best in all of physics. Basically to fully understand it you need quantum field theory. Basically photons are excitations in a field. Because the field is quantized the excitations are discretized, and hence behave like particles. However, because quantum mechanics is the way it is, the amplitudes for each orthogonal component (which behave independently) make it disperse like a wave. Hence it has behaviour similar to both a particle and a wave, but it's not really either in the classical sense of the words.

krd

Professor_Fink wrote: »

This is wrong, and is entirely inconsistent with quantum field theory, although I can see how it would sound reasonable if you have only encountered popularizations of quantum mechanics.

It's really a case of when and where I studied physics - and what it was I was studying. I did an applied physics course in an RTC back in the days before the internet and when I was very young. For lots of reasons, it wasn't a good experience. We did dabble in quantum theory, but there was a huge amount we didn't touch. There's a huge amount I've completely forgotten. Anyway, more on the practical applications of physical phenomena than the theory.

I'm not completely clueless. I wouldn't have the skills to explore quantum theory by myself - my maths is incredibly scratchy - I don't really believe you can fully understand any of these theories without having hacked through the maths. I'm kind of waiting for someone to come up with a more digestible version.

I don't like the Many Worlds theory. As it does seem too close to sci-fiction. If there is a mathematical proof of its' existence - that proof may be a proof of something that doesn't exist. Once you allow yourself to play with infinity anything becomes possible. I could say there are an infinite number of worlds, all existing in the same place at the same time, but we can't see them because they don't interact with this world.

I think it was Turing said, give me two variables and I will tell you everything you want to know about an elephant. Give me three and I'll tell you when it's going to fly.

Professor_Fink

krd wrote: »

It's really a case of when and where I studied physics - and what it was I was studying. I did an applied physics course in an RTC back in the days before the internet and when I was very young. For lots of reasons, it wasn't a good experience. We did dabble in quantum theory, but there was a huge amount we didn't touch. There's a huge amount I've completely forgotten. Anyway, more on the practical applications of physical phenomena than the theory.

Don't worry, it's essentially impossible to get a good feeling for quantum mechanics unless you have studied it for quite a while. It's very counter intuitive, but it is by far the best description we have of the world.

krd wrote: »

I don't really believe you can fully understand any of these theories without having hacked through the maths. I'm kind of waiting for someone to come up with a more digestible version.

I agree 100%. Actually, I doubt you'll ever see a simpler version. What we have at the moment is actually based on very simple ideas. The barrier is that much of physics makes use of the idea of smoothly varying quantities, which inevitably leads to calculus. Discrete-time discrete-space formulations are much simpler to understand, but that doesn't accurately reflect quantities like position.

krd wrote: »

I don't like the Many Worlds theory. As it does seem too close to sci-fiction. If there is a mathematical proof of its' existence - that proof may be a proof of something that doesn't exist. Once you allow yourself to play with infinity anything becomes possible. I could say there are an infinite number of worlds, all existing in the same place at the same time, but we can't see them because they don't interact with this world.

I think perhaps you misunderstand the many worlds interpretation (and really it's an interpretation rather than a theory). It doesn't fundamentally rely on infinities. To give you a concrete example, consider an electron which is sitting in a magnet field (this is basically a more concrete and less ambiguous version of Schroedinger's cat). The electron has a spin, which can have only one of two states, rotating either clockwise or anticlockwise about a magnetic field line. Now, we can prepare an equal superposition of these, so that the spin is rotating one way in one branch of the wave function, and the opposite way in the other. Now there are measurements we can make to confirm that this superposition is real, and not just a probabilistic distribution over the two possibilities, so we know such states really do exist. They have nothing to do with the specific interpretation of quantum mechanics you subscribe to, but rather are an integral part of the theory.

Now, if we measure the spin, we get one of two outcomes (we usually call these spin-up and spin-down). In the Copenhagen interpretation, a measurement is essentially a magic operation that randomly brings you to one of the two outcomes while making the other vanish from existence. The most significant criticism of the Copenhagen interpretation is that it is not at all clear what constitutes a measurement, as at some point in the device the wavefunction must collapse, and we have never been able to isolate any such physical mechanism. In spontaneous collapse theories, this happens randomly rather than there being some special operation to trigger it, and so is much harder to pin down or to rule out. In the many worlds interpretation, this collapse simply doesn't happen. When we make a measurement, we simply interact with the system we are measuring and become correlated with it in whatever way is predicted if we threat every part of the apparatus and ourselves quantum mechanically. In this case there are only two branches to the wave function. Initially we are in a state where we don't know the spin of the electron, and the electron is in a superposition. We then measure the electron. In the many worlds interpretation this results in a superposition of two states: us knowing the electron is up and the electron being spin-up, and us knowing the electron is spin-down and the electron is spin-down. Mathematically both interpretations give us exactly the same probability of obtaining a given result, so can be separated by a simple experiment. The difference is that in many worlds the second branch of the wavefunction doesn't go away, even though we can't perceive it.

As it is indeed fundamentally impossibly to interact with any such branch which is significantly dissimilar to our own, which makes it impossible to verify their existence, but also kills off some of the scifi stuff.

Kohl

Professor_Fink wrote: »

100 years of physics disagrees with you. Superpositions exist, and are an integral part of quantum mechanics. The observed violations of Bell's inequalities prove this (modulo loopholes). It is nothing specific to the many worlds interpretation, and the only difference is how long lived these superpositions are. (Many worlds=forever, Copenhagen=until measurement, Spontaneous collapse=spontaneous, etc.)

I think it's something to keep in mind that real world phenomena like quantum key distribution relies on entanglement (i.e. the Ekert protocol). This is a real world application of quantum mechanics.

The detection and locality loopholes have been closed in separate experiments. I'm not sure if a Bell test without any loopholes is going to do much to confound the critics of quantum mechanics. Though for me, the closing of both these loopholes, is definite evidence that local hidden variable theories are false.

Professor_Fink

Kohl wrote: »

The detection and locality loopholes have been closed in separate experiments. I'm not sure if a Bell test without any loopholes is going to do much to confound the critics of quantum mechanics. Though for me, the closing of both these loopholes, is definite evidence that local hidden variable theories are false.

As it happens, the randomness loophole can never be closed, because in a universe with hidden variables then you can't generate the required random basis choices, though they may look random.

krd

Professor_Fink wrote: »

I agree 100%. Actually, I doubt you'll ever see a simpler version. What we have at the moment is actually based on very simple ideas. The barrier is that much of physics makes use of the idea of smoothly varying quantities, which inevitably leads to calculus. Discrete-time discrete-space formulations are much simpler to understand, but that doesn't accurately reflect quantities like position.

I'm not sure. I have a feeling eventually a much more simpler version could appear. And what I mean by that. I have a copy of Roger Penrose's The Road to Reality - because I own a copy, doesn't mean I've actually read it. I haven't. I have skimmed through it, and I know what's in it.. It's over a thousand pages long. A more simplified version, if it could exist, might be 100 pages, or 200 pages. That's with the maths, and the other bits.

Maths is something you need to practice. If you don't, you lose the ability and the understanding. When I was a student, there was lots of maths I could do without having to think. Now, some very plain differentiation would have me scratching my head.

Now, Penrose's book - which I haven't read but own - supposedly, has the necessary maths in it. And he says, if you work through all the maths (I think he says give yourself four or seven years), everything should make sense. And I suppose, if I sat down with it and when methodically through it - I could crack it eventually.


There might be other simplifications that are just unknown for the minute. An example, although it's a poor example. Galileo, is supposedly to have taken the very complicated mathematical calculations of the astronomers of his day - who placed the earth at the centre of the universe in their equations - and by placing the earth orbiting the sun, the equations lost their contortions and became simpler. I don't know if this is true. I saw it on a television documentary. And I wonder about the astronomers. They were mathematicians - you'd wonder, that with a bit of experimentation, they might have realised the mistakes in their own calculations. Or were they in some way blinded to the errors.

Intuition and counter intuition are tricky. Intuition is guided by evidence. And it depends on what evidence is apparent. Ancient people, who lived inland, would have more reason to be convinced the earth was flat than round. Whereas, the ancient Greeks, living on the coast, with a strong maritime tradition, would have more reason to be convinced that the earth had to be round. But then you have a terrible problem for the first person who realises the earth is round - suddenly, they have the awful question "Well....if it's round, why don't we fall off it?"


Newton's view of gravity appears to be correct - up to a point. Einstein's view makes Newton's ideas look like trompe l'oeil. Einstein's maths is a lot trickier. Newton's only requires basic addition, multiplication and division, and belief that mass exert a force on each other - by some unknown mechanism. Something is transmitted through the either. Then to understand quantum gravity - which I don't - requires knowledge of the cannon of quantum theory. Which requires a lot tricky maths.

Looking at the map of theories on Wikipedia. It looks like a serious headache. It is a headache.

Professor_Fink

krd wrote: »

I'm not sure. I have a feeling eventually a much more simpler version could appear. And what I mean by that. I have a copy of Roger Penrose's The Road to Reality - because I own a copy, doesn't mean I've actually read it. I haven't. I have skimmed through it, and I know what's in it.. It's over a thousand pages long. A more simplified version, if it could exist, might be 100 pages, or 200 pages. That's with the maths, and the other bits.

Penrose's book is not exactly concise. You can go through a basic derivation of non-relativistic QM in a few pages. It's only tricky because it uses calculus, but then so does all of physics. The only reason you may have seen classical physics done without any calculus is because in school the example questions are picked specifically to avoid it. To put this in context, imagine I were to ask you the following question:

"I have an an elastic string of length L and elasticity k, of mass m per meter of length. It is suspended between two points a distance d apart. What is the height of the string some horizontal distance D from one of the end points?"

Such a question uses similar mathematics to quantum mechanics, but is purely classical.