Physicists create world’s first multiverse of universes in the lab

[littlebabyjesus]

I find these things tough to fully understand, but each time I see grand claims for quantum computational supremacy, the test used seems to have been specifically set up to be suited to a quantum computer - ie you ask it a question about quantum states, in this case a quantum circuit. So it can model this in a way a classical computer clearly cannot as we're talking vast Hilbert spaces of possible classical states. But I'm not entirely sure what this proves. It feels like a cheat.

 

[PTK]

Ok, so we've got "proof" that at least one another universe exists. That universe has chips slightly better than ours...

Google says its new quantum chip indicates that multiple universes exist | TechCrunch

Google announced its latest quantum chip, Willow. But what really caught the industry's attention was a wild claim tucked into the blog post.

techcrunch.com

“It lends credence to the notion that quantum computation occurs in many parallel universes, in line with the idea that we live in a multiverse, a prediction first made by David Deutsch”, Hartmut Neven is quoted as writing.

The “many worlds” interpretation of quantum mechanics was actually devised by Hugh Everett a few decades before David Deutsch, and it is not a “prediction”, but a hypothesis. A hypothesis that is wrong.​

 

[littlebabyjesus]

“It lends credence to the notion that quantum computation occurs in many parallel universes, in line with the idea that we live in a multiverse, a prediction first made by David Deutsch”, Hartmut Neven is quoted as writing.

The “many worlds” interpretation of quantum mechanics was actually devised by Hugh Everett a few decades before David Deutsch, and it is not a “prediction”, but a hypothesis. A hypothesis that is wrong.​

If we're being picky, it's a hypothesis that is consistent with the evidence. It can be declared ontologically extravagant, perhaps, but there are serious physicists who take it seriously.

 

[PTK]

If we're being picky, it's a hypothesis that is consistent with the evidence. It can be declared ontologically extravagant, perhaps, but there are serious physicists who take it seriously.

There are serious physicists who believe in the existence of Heaven and Hell, too. "Other worlds" is simply a belief.

 

[littlebabyjesus]

There are serious physicists who believe in the existence of Heaven and Hell, too. "Other worlds" is simply a belief.

No it's not. It is the hypothesis that the wave function does not collapse but rather that every possibility plays out in separate universes. This is consistent with the evidence.

Where do the probability amplitudes come from? That's one question to ask of it that does not have an entirely satisfactory answer, but every interpretation of QM has an aspect that is not entirely satisfactory.

 

[WouldBe]

Is that proper chips or crisps?

What if they're fries.

 

[PTK]

No it's not. It is the hypothesis that the wave function does not collapse but rather that every possibility plays out in separate universes. This is consistent with the evidence.

Where do the probability amplitudes come from? That's one question to ask of it that does not have an entirely satisfactory answer, but every interpretation of QM has an aspect that is not entirely satisfactory.

When a particular uranium nucleus decays, there is no evidence that another universe is created in which that nucleus has not decayed.

These other universes are not observable. There is no possible way of establishing that they exist. The generation of another universe in this way would violate the law of the conservation of mass/energy.

The wave function is a mathematical representation of our state of knowledge of a system, but it is not a material reality. The cat is either alive or dead; it cannot be both at the same time, and a uranium nucleus is either decayed or not decayed.​

 

[littlebabyjesus]

The various laws of conservation would appear perfectly maintained to any observer within each branch.

Thing about Schrodinger's cat is that he created the thought experiment to illustrate an uncomfortable consequence of his own equation. He wasn't totally happy with it. Nobody is.

Is it even valid to talk about a material reality? We can talk about the results of observation, but we have to admit that our prodding of the system itself produces those results. Where is the electron before it is measured, before it interacts with something else in a particular way? The answer there has to be that it exists as a cloud of mathematical probabilities. It is everywhere and nowhere. Our intuitions about space and time break down. Can anything be said to exist except as part of a relation with something else?

QM produces only probabilities when we do measurements, but the wave function itself evolves in an exact way. Which of those is the more satisfyingly 'real'?

 

[littlebabyjesus]

Personally I find the idea that we're missing dimensions appealing. The electron must 'spin' twice to return to its original state. The 4-dimensional equivalent of a sphere would do that seen in just three dimensions.

But whatever ideas you may like, one thing is inescapable - what we call material reality is not the whole picture. We are missing something. We are inhabitants of Flatland.

 

[PTK]

The various laws of conservation would appear perfectly maintained to any observer within each branch.

Thing about Schrodinger's cat is that he created the thought experiment to illustrate an uncomfortable consequence of his own equation. He wasn't totally happy with it. Nobody is.

Is it even valid to talk about a material reality? We can talk about the results of observation, but we have to admit that our prodding of the system itself produces those results. Where is the electron before it is measured, before it interacts with something else in a particular way? The answer there has to be that it exists as a cloud of mathematical probabilities. It is everywhere and nowhere. Our intuitions about space and time break down. Can anything be said to exist except as part of a relation with something else?

QM produces only probabilities when we do measurements, but the wave function itself evolves in an exact way. Which of those is the more satisfyingly 'real'?

The probabilities are there before the measurements. Once we measure, then there are certainties, rather than probabilities.



A single slit experiment is an illustration of this. We send a stream of particles through a slit in a barrier. We do not know where an individual particle will hit a screen on the other side of the barrier.



We know that it is more likely to hit in the central region of the screen, and less likely to hit off to one side. We represent our state of knowledge using probabilities. Once the particle has hit the screen, and thereby been detected, we are certain where it hit the screen. There is no longer any need to quote the probability that it will hit that spot.



Yes, it does make sense to talk of material reality. If you were to inhale a cloud of uranium atoms, it would make a material difference to the cells in your lungs if the atoms decayed and emitted alpha particles.
​

 

[littlebabyjesus]

The probabilities are there before the measurements. Once we measure, then there are certainties, rather than probabilities.



A single slit experiment is an illustration of this. We send a stream of particles through a slit in a barrier. We do not know where an individual particle will hit a screen on the other side of the barrier.



We know that it is more likely to hit in the central region of the screen, and less likely to hit off to one side. We represent our state of knowledge using probabilities. Once the particle has hit the screen, and thereby been detected, we are certain where it hit the screen. There is no longer any need to quote the probability that it will hit that spot.



Yes, it does make sense to talk of material reality. If you were to inhale a cloud of uranium atoms, it would make a material difference to the cells in your lungs if the atoms decayed and emitted alpha particles.
​

The first bit is not right I'm afraid. When and where you measure affects the distribution of the 'particles' you detect. Classically, probabilities are statements to with incomplete knowledge, but in QM it's not that simple.

The second bit is fair, so maybe I should rephrase - there is such a thing as a material reality but its nature is not necessarily that of things in space and time. Space and time are not fundamental descriptions.

EtA:

How Bell’s Theorem Proved ‘Spooky Action at a Distance’ Is Real | Quanta Magazine

The root of today’s quantum revolution was John Stewart Bell’s 1964 theorem showing that quantum mechanics really permits instantaneous connections between far-apart locations.

www.quantamagazine.org

This is a nice article about Bell's inequality. Note that measuring spin in one direction means that spin along other axes is now undefined. You can prod reality in various ways but that prodding produces results that didn't preexist the prodding.

 

[littlebabyjesus]

Dp

 

[PTK]

The first bit is not right I'm afraid. When and where you measure affects the distribution of the 'particles' you detect. Classically, probabilities are statements to with incomplete knowledge, but in QM it's not that simple.

The second bit is fair, so maybe I should rephrase - there is such a thing as a material reality but its nature is not necessarily that of things in space and time. Space and time are not fundamental descriptions.

EtA:

How Bell’s Theorem Proved ‘Spooky Action at a Distance’ Is Real | Quanta Magazine

The root of today’s quantum revolution was John Stewart Bell’s 1964 theorem showing that quantum mechanics really permits instantaneous connections between far-apart locations.

www.quantamagazine.org

This is a nice article about Bell's inequality. Note that measuring spin in one direction means that spin along other axes is now undefined. You can prod reality in various ways but that prodding produces results that didn't preexist the prodding.

You seem to be arguing that wave functions do not collapse. We cannot say where a particle is before we measure it, and represent it using a wave function. Once we detect it, we know where it is at the moment it is detected. The wave function has "collapsed". Then the wave function arises again, and we can once again no longer say for sure where it is.
Thanks for the link to the Bell article. I will read it with interest.

 

[littlebabyjesus]

The implications of the fact that Bell's inequality is indeed violated are startling.

Because of it, Bohmian QM requires pilot waves that travel backwards in time, or alternatively travel in no time at all, probably through other dimensions.

Meanwhile the old 'wave collapses on observation' Copenhagen interpretation has no real explanation as to why it collapses. Various, often rather crazy, ideas have been proposed for the privileged role of the observer. See eg Wigner.

I'm not sure the Many Worlds Everettian picture is even that far out in comparison. There is no non-far-out interpretation of QM.

 

[existentialist]

No it's not. It is the hypothesis that the wave function does not collapse but rather that every possibility plays out in separate universes. This is consistent with the evidence.

Where do the probability amplitudes come from? That's one question to ask of it that does not have an entirely satisfactory answer, but every interpretation of QM has an aspect that is not entirely satisfactory.

And it gets even better when you venture into string theory.

But the unthinkable has a way of becoming thinkable, over time. Newton wasn't on his own, and Einstein had peers who would conceivably got there if he hadn't (some French bloke, IIRC).

ETA: oh, you got into string theory

 

[existentialist]

The probabilities are there before the measurements. Once we measure, then there are certainties, rather than probabilities.



A single slit experiment is an illustration of this. We send a stream of particles through a slit in a barrier. We do not know where an individual particle will hit a screen on the other side of the barrier.



We know that it is more likely to hit in the central region of the screen, and less likely to hit off to one side. We represent our state of knowledge using probabilities. Once the particle has hit the screen, and thereby been detected, we are certain where it hit the screen. There is no longer any need to quote the probability that it will hit that spot.



Yes, it does make sense to talk of material reality. If you were to inhale a cloud of uranium atoms, it would make a material difference to the cells in your lungs if the atoms decayed and emitted alpha particles.
​

But that is because you inhaled ten-to-the-power-of-gazillion uranium atoms, nicely flattening out the quantum fluctuations. There is a theoretical possibility, via the laws of quantum mechanics, that all of the oxygen molecules in a room could migrate to one corner. But, given the number of molecules involved, that probability is so tiny as to be unlikely to occur in the life of the Universe.

 

[PTK]

But that is because you inhaled ten-to-the-power-of-gazillion uranium atoms, nicely flattening out the quantum fluctuations. There is a theoretical possibility, via the laws of quantum mechanics, that all of the oxygen molecules in a room could migrate to one corner. But, given the number of molecules involved, that probability is so tiny as to be unlikely to occur in the life of the Universe.

The oxygen atoms moving to the corner of the room is thermodynamics, not quantum mechanics. It is a different sort of probability.

 

[existentialist]

The oxygen atoms moving to the corner of the room is thermodynamics, not quantum mechanics. It is a different sort of probability.

It's only thermodynamics because of the quantity of molecules.

 

[PTK]

It's only thermodynamics because of the quantity of molecules.

In principle, we could calculate where all the oxygen molecules would be, but we can't do so because there are so many. In quantum mechanics, we can't say for sure where even one when particle is located. We can say where it is more likely to be, but there is a small probability that it could be somewhere else altogether. An alpha particle is most likely to be in a uranium atom, but there is a small probability that it can be outside the nucleus.

 

[littlebabyjesus]

It's only thermodynamics because of the quantity of molecules.

Different kind of probability, though. The classical kind. You're entitled to think of the atoms as being in a certain place moving a certain way before you measure them. You just have limited knowledge.

Not the case in QM. How you measure one particle affects the result of measurements of other particles. In a real, practical sense, you cannot speak of those particles existing in definite states before you measure them.

This is not just a question of lack of knowledge. We cannot think of the states as being real while we don't know what they are. That's one of the attractions of Many Worlds. It doesn't require us to consider what or where some particle was before we measured it. The question has no meaning.

 

[littlebabyjesus]

You seem to be arguing that wave functions do not collapse. We cannot say where a particle is before we measure it, and represent it using a wave function. Once we detect it, we know where it is at the moment it is detected. The wave function has "collapsed". Then the wave function arises again, and we can once again no longer say for sure where it is.
Thanks for the link to the Bell article. I will read it with interest.

To come back to this, there is a reason why I've been putting 'particle' in scare quotes. Generally, physicists nowadays talk of fields, with 'particles' as localised waves within those fields and nothing more than that.

This neatly explains, for example, why all electrons, say, are identical to one another. They are all local disturbances in one single electron field that extends across the whole universe. If we bump that field in the right way, we will produce a localised wave disturbance and that disturbance is the electron.

Each field associated with matter is coupled with at least one field associated with a fundamental force. That's how we can do the 'bumping' to see 'where the particle is'. 'dark matter' appears to be a matter field that is not coupled with EM. Hence we cannot see it.

So really we need to forget about 'where the particle is when we're not looking at it'. It isn't anywhere. We made the particle in our interaction with the field.

Many Worlds is ugly in the sense that it feels like a cop-out to say that everything that can happen happens and propose an almost infinite number of parallel universes to allow it to happen. But in other senses, it is elegant. It elegantly captures the idea of fields extending across the whole of spacetime.

If we reverse our intuitions here, is it more fanciful to talk of a single wavefunction that never collapses and a near-infinite set of universes that manifest from that than to talk of a single universe with a near-infinite set of separate parameters needed to describe it in full?