Can the universe evolve while in superposition?

[Varon]

Anyone familiar with both quantum mechanics and cosmology here. Say. How much dynamics can occur in the deterministic Schroedinger Equation in its evolution while it is in unitary state (before collapse)? For example. Is it possible for the Big Bang and evolution of stars to solar system and planets to occur while everything is inside a superposition (that doesn't involve Many Worlds but just as superposition of possibilities)? I'm trying to analyze the physicist Wigner who proposed that consciousness caused collapse of the wave function. Before life begins on earth. He seems to be saying that the universe is in a state of superposition. After life reaches a certain theshold. It finally collapsed the wave function of the Earth and the surrounding. Is this possible? Does the Schroedinger Equations allows for instance the evolution of a solar system while it is still unitary and before the wave function collapse? Or is it not possible?

If not possible. At least let me know why did this physicist Wigner propose it? Those in the QM forum are not familiar with cosmology so I have to post the question about Big bang in superposition here.

 

[edgepflow]

Wave functions of the universe such as the Hartle Hawking and Tunnerling wave functions have a function for both the "underbarrier" and "classical" regions.

In Hartle Hawking context, all universes in the normalized probability distribution coexist and there is an infinite number of parallel universes. I think the idea that the wave function collapsed after a measurement was done on it is rooted in Copenhagen interpretation.

This information is speculative, however, and there are many interpretations.

 

[Varon]

Wave functions of the universe such as the Hartle Hawking and Tunnerling wave functions have a function for both the "underbarrier" and "classical" regions.

In Hartle Hawking context, all universes in the normalized probability distribution coexist and there is an infinite number of parallel universes. I think the idea that the wave function collapsed after a measurement was done on it is rooted in Copenhagen interpretation.

This information is speculative, however, and there are many interpretations.

So you think an entire galaxy can evolve even if it is inside a superposition?

 

[Chalnoth]

So you think an entire galaxy can evolve even if it is inside a superposition?

A large, complex object like a rock can't really be in a coherent superposition, let alone a galaxy.

Basically, the way we know about objects in coherent superpositions is through oscillation: we can observe the results of an object oscillating through, for instance, interference effects. But complex wavefunctions have oscillation times that tend to be very long, often much longer than the age of the universe.

And when your oscillation time is that long, there just isn't any way for the different components of the same wavefunction to obtain any information about one another. In fact, the different components of the wavefunction, when they are complex enough, interact so weakly with one another that they might as well be in different universes.

So anything as large as a galaxy in a superposition of states will behave exactly as if there was no superposition at all.

 

[Varon]

A large, complex object like a rock can't really be in a coherent superposition, let alone a galaxy.

Basically, the way we know about objects in coherent superpositions is through oscillation: we can observe the results of an object oscillating through, for instance, interference effects. But complex wavefunctions have oscillation times that tend to be very long, often much longer than the age of the universe.

And when your oscillation time is that long, there just isn't any way for the different components of the same wavefunction to obtain any information about one another. In fact, the different components of the wavefunction, when they are complex enough, interact so weakly with one another that they might as well be in different universes.

So anything as large as a galaxy in a superposition of states will behave exactly as if there was no superposition at all.

But if you can isolate the rock completely. It can be in pure state and be in superposition. Isn't it. Bottomline is. The universe is a close system. After the Big Bang, the universe is in pure state. And pure state means in quantum coherence. So the universe evolves completely inside the pure state. The famous physicist Wigner proposed consciousness cause collapse. So I figured that after human evolved, all the wave function of the universe collapsed because our consciousness become the observer. I don't know why he proposed this or maybe I misunderstood it. If anyone is familiar with Wigner, please share what's in his mind when he proposed it.

 

[Chalnoth]

But if you can isolate the rock completely.

Nah, the rock itself has too complex a wavefunction to have a very quick oscillation time.

 

[Varon]

Nah, the rock itself has too complex a wavefunction to have a very quick oscillation time.

How how come in Many World interpretation, it doesn't have this problem? In the MWI, even the entire universe can be in superposition. Everett called it the Universal Wave Function.

 

[Chalnoth]

How how come in Many World interpretation, it doesn't have this problem? In the MWI, even the entire universe can be in superposition. Everett called it the Universal Wave Function.

This is why it doesn't have a problem. Complex objects simply don't interfere with one another to any significant degree (except in extremely contrived scenarios). They are in a superposition, yes. But because the oscillation time is so extremely long, the different components of the wave function cannot interact to any significant degree.

 

[Varon]

This is why it doesn't have a problem. Complex objects simply don't interfere with one another to any significant degree (except in extremely contrived scenarios). They are in a superposition, yes. But because the oscillation time is so extremely long, the different components of the wave function cannot interact to any significant degree.

Ok. But how does the Many worlds interpretation differ to this? Cosmologists love this version because it makes sense general relativity and ties it with the universal wavefunction.

 

[Chalnoth]

Ok. But how does the Many worlds interpretation differ to this? Cosmologists love this version because it makes sense general relativity and ties it with the universal wavefunction.

What I've been describing is the essence of the Many Worlds Interpretation, the motivation for why it is most likely to be the correct interpretation: even without wavefunction collapse, quantum mechanics automatically retains the appearance of collapse.

 

[Varon]

A large, complex object like a rock can't really be in a coherent superposition, let alone a galaxy.

Basically, the way we know about objects in coherent superpositions is through oscillation: we can observe the results of an object oscillating through, for instance, interference effects. But complex wavefunctions have oscillation times that tend to be very long, often much longer than the age of the universe.

And when your oscillation time is that long, there just isn't any way for the different components of the same wavefunction to obtain any information about one another. In fact, the different components of the wavefunction, when they are complex enough, interact so weakly with one another that they might as well be in different universes.

So anything as large as a galaxy in a superposition of states will behave exactly as if there was no superposition at all.

The physicist Wigner should know complex objects can't be in superposition. So why did he propose that consciousness is what collapse the wave function? Consequence of this is that in far regions of the universe not sighted by any astronomer using a telescope, the region is in superposition.

 

[Dmitry67]

I think all structures we see are the result of the gravitational condensation of matter based on the pattern, created by the Dark matter. Dark matter is unique because it has jeans mass=0, hence, it magnifies any fluctuations. Very likely, these fluctuations had evolved from quantum fluctuations in the very early universe.

So either the structure we see now was encoded in the initial conditions (Bohmican Mechanics), or had evolved naturally but differently in different branches (MWI). I can’t interpret it, however, in Stochastic mechanics, because it just defines the probability of macroscopic events, but I don’t know how “macroscopic events” can be defined in early Universe.

 

[Chalnoth]

The physicist Wigner should know complex objects can't be in superposition. So why did he propose that consciousness is what collapse the wave function? Consequence of this is that in far regions of the universe not sighted by any astronomer using a telescope, the region is in superposition.

Yes, he should have known better. That idea is quite nonsensical.

 

[Varon]

This is why it doesn't have a problem. Complex objects simply don't interfere with one another to any significant degree (except in extremely contrived scenarios). They are in a superposition, yes. But because the oscillation time is so extremely long, the different components of the wave function cannot interact to any significant degree.

Chanoth. If complex objects can be sufficiently isolated. You said it can still be in superposition but the different components of the wave function cannot interact to any significant degree. And the relevance of this is that an object can be in superposition yet doesn't behave like in superposition? How can this be? A superposition that is not a superposition?

 

[bcrowell]

Keep in mind that general relativity is a nonlinear theory, so superposition fails.

 

[Chalnoth]

Chanoth. If complex objects can be sufficiently isolated. You said it can still be in superposition but the different components of the wave function cannot interact to any significant degree. And the relevance of this is that an object can be in superposition yet doesn't behave like in superposition? How can this be? A superposition that is not a superposition?

It's still formally a superposition of states. It's just that the two (or more) components of the wavefunction don't interact in any meaningful sense, and thus each behaves as if the other components aren't even there.

Keep in mind that general relativity is a nonlinear theory, so superposition fails.

Well, I think we generally expect that this fact of General Relativity has to be reconciled with quantum mechanics somehow, and that since superpositions of states have been observed on small scales, quantum gravity must allow such superpositions as well.

 

[Varon]

It's still formally a superposition of states. It's just that the two (or more) components of the wavefunction don't interact in any meaningful sense, and thus each behaves as if the other components aren't even there.

What is the difference between each case of superpositions where one has the components interacting strong (oscillation very quick) and one where the components interacting poorly (oscillation very long)? Can you give an actual example for each of them?

 

[bcrowell]

Keep in mind that general relativity is a nonlinear theory, so superposition fails.

Well, I think we generally expect that this fact of General Relativity has to be reconciled with quantum mechanics somehow[...]

Hmm... "we" wouldn't include me. Clearly GR and quantum mechanics are incompatible. The question is which one has to change its fundamental principles to be reconciled with the other. (Or maybe both have to change.) I would consider that an open question.

Keep in mind that general relativity is a nonlinear theory, so superposition fails.

[...] since superpositions of states have been observed on small scales, quantum gravity must allow such superpositions as well.

IMO it would be more relevant if superpositions of states had been observed not just on small scales, but on the Planck scale.

 

[Chalnoth]

Hmm... "we" wouldn't include me. Clearly GR and quantum mechanics are incompatible. The question is which one has to change its fundamental principles to be reconciled with the other. (Or maybe both have to change.) I would consider that an open question.

Well, this is just nitpicking, but I didn't actually specify which needed to change.

Still, most do expect it's GR that has to change, largely because it has proven to be much more difficult to think of ways to modify quantum mechanics.

IMO it would be more relevant if superpositions of states had been observed not just on small scales, but on the Planck scale.

I don't understand. Why aren't observations of Bell's Theorem enough?

 

[bcrowell]

Well, this is just nitpicking, but I didn't actually specify which needed to change.

Still, most do expect it's GR that has to change, largely because it has proven to be much more difficult to think of ways to modify quantum mechanics.

I haven't seen any evidence that "most" physicists expect this.

I don't understand. Why aren't observations of Bell's Theorem enough?

We have lots of observations that confirm quantum mechanics, including tests of Bell's theorem. We have lots of observations that confirm GR. We don't have any experiments that simultaneously test QM and GR. We know that QM and GR seem to contradict one another in a variety of different ways. QM is linear. GM is nonlinear. Therefore I would say that no experiments have ever probed whether quantum gravity would be linear or nonlinear.

 

[Chalnoth]

What is the difference between each case of superpositions where one has the components interacting strong (oscillation very quick) and one where the components interacting poorly (oscillation very long)? Can you give an actual example for each of them?

Well, take the particle in a box as an example. The energy of a particle in a box is proportional to $n^2$. So if we imagine a particle in a box that is in a superposition between states 1 and 2, then its recurrence time will be the energy difference between these two states, or a number proportional to $4 - 1 = 3$.

Now, imagine we throw a second particle in the box, in a superposition between states 3 and 4. If this particle were alone, it would have a recurrence time of $16 - 9 = 7$. However, since the total wavefunction of the two particles now requires that both wavefunctions recur to get back to its original state, it now takes a time equal to $3*7 = 21$ to recur.

Add more particles, and the recurrence time will increase still further. Granted, you can contrive special scenarios, such as equal energy difference between levels, where the recurrence time is still short even for large numbers of particles. However, these special scenarios don't apply to normal matter, which tends to be rather more complex.

 

[Chalnoth]

I haven't seen any evidence that "most" physicists expect this.

Well, the number of people working under the idea that GR doesn't need to be modified but QM does seems to be vanishingly small. And I should mention that GR itself has singularities which are quite unphysical, strongly indicating that GR, independent of concerns about compatibility with quantum mechanics, needs to be modified at small scales. Quantum mechanics has similar concerns, granted, so it's rather more a question of which theory needs to be modified more, not which theory needs to be modified.

We have lots of observations that confirm quantum mechanics, including tests of Bell's theorem. We have lots of observations that confirm GR. We don't have any experiments that simultaneously test QM and GR. We know that QM and GR seem to contradict one another in a variety of different ways. QM is linear. GM is nonlinear. Therefore I would say that no experiments have ever probed whether quantum gravity would be linear or nonlinear.

That's fair enough, I suppose.

 

[Varon]

Well, take the particle in a box as an example. The energy of a particle in a box is proportional to $n^2$. So if we imagine a particle in a box that is in a superposition between states 1 and 2, then its recurrence time will be the energy difference between these two states, or a number proportional to $4 - 1 = 3$.

Now, imagine we throw a second particle in the box, in a superposition between states 3 and 4. If this particle were alone, it would have a recurrence time of $16 - 9 = 7$. However, since the total wavefunction of the two particles now requires that both wavefunctions recur to get back to its original state, it now takes a time equal to $3*7 = 21$ to recur.

Add more particles, and the recurrence time will increase still further. Granted, you can contrive special scenarios, such as equal energy difference between levels, where the recurrence time is still short even for large numbers of particles. However, these special scenarios don't apply to normal matter, which tends to be rather more complex.

Up to what extend of the components interfering with each other can you treat object as still in superpositiona and what is the boundary when it's already classical (like what threshold of the components interfering before superposition disappears)?

 

[Chalnoth]

Up to what extend of the components interfering with each other can you treat object as still in superpositiona and what is the boundary when it's already classical (like what threshold of the components interfering before superposition disappears)?

As with so many things, the boundary is always going to be arbitrary. Imagine taking a person with a full head of hair, and removing those hairs one at a time. At which specific hair does the person transition from "not bald" to "bald"? Your question is rather the same thing: it's easy to say whether a person is bald or not if they are near the extremes, but there is a massive middle ground where it's not so obvious.

 

[Dmitry67]

Keep in mind that general relativity is a nonlinear theory, so superposition fails.

Check http://www.hedweb.com/everett/everett.htm#faq
Q38

A theory of classical gravity also breaks down at the scale of objects that are not bound together gravitationally. Henry Cavendish, in 1798, measured the torque produced by the gravitational force on two separated lead spheres suspended from a torsion fibre in his laboratory to determine the value of Newton's gravitational constant. Cavendish varied the positions of other, more massive lead spheres and noted how the torsion in the suspending fibre varied. Had the suspended lead spheres been gravitationally influenced by their neighbours, placed in different positions by parallel Henry Cavendishs in the parallel Everett-worlds, then the torsion would have been the averaged sum of all these contributions, which was not observed. In retrospect Cavendish established that the Everett-worlds are not detectable gravitationally. More recent experiments where the location of attracting masses were varied by a quantum random (radioactive) source have confirmed these findings.

 

[Chalnoth]

Check http://www.hedweb.com/everett/everett.htm#faq
Q38

I really don't get what these experimenters were expecting. Were they testing the idea that maybe gravity acts on the expectation value of states or something of that sort?

 

[Dmitry67]

They were testing if geometry can be in superposition (in MWI sense) or not. The result is quite expected and does not give anything new. It was just a response to bcrowells comment - somehow gravity does not work on a cross-branch level. If quantum gravity theory would prove somehow that gravity is universal and it must affect wavefunction everywhere (so geometry can't be in superposition) then it would be an end of MWI

 

[Chalnoth]

They were testing if geometry can be in superposition (in MWI sense) or not. The result is quite expected and does not give anything new. It was just a response to bcrowells comment - somehow gravity does not work on a cross-branch level. If quantum gravity theory would prove somehow that gravity is universal and it must affect wavefunction everywhere (so geometry can't be in superposition) then it would be an end of MWI

I'm pretty sure that these experiments were completely and utterly unnecessary for that. It is blatantly obvious that an idea of gravity working completely differently from all other forces and acting across all branches of the wavefunction cannot describe our universe, because if so then gravity would be perfectly uniform everywhere (that is, there wouldn't be any gravity except for the overall expansion).