Multiverse Cosmology: Exploring Physicists' Views

[Chalnoth]

How, in the name of science, does one jump from a range of possible (not actual) outcomes at the quantum level to actualized, yet unobserved multiple worlds? i want to call this hogwash, but instead will suggest that it is a very VERY liberal interpretation.

If you simply consider the wave function of the system and evolve it forward in time, you get two things:

1. Multiple outcomes occur.
2. Each observer within the system sees only one outcome.

Adding anything to this to get rid of the multiple outcomes is just tacking on extra baggage that the theory doesn't need.

 

[Chalnoth]

well, it's my personal take that this is lawyer-speak. Chalnoth believes we live in a multiverse, something that has absolutely no measurable nor experiential effect on any of us and has no promise to have such. it is not testable nor falsifiable.

I see you have utterly disregarded my entire argument. And now we see that your ignorance is not just due to a lack of exposure, it is willful.

 

[sahmgeek]

If you simply consider the wave function of the system and evolve it forward in time, you get two things:

1. Multiple outcomes occur.
2. Each observer within the system sees only one outcome.

Adding anything to this to get rid of the multiple outcomes is just tacking on extra baggage that the theory doesn't need.

Thanks for your reply. Please correct me if I'm wrong but isn't #2 the more likely conclusion given experimental data? How does #1 come into play for scientists?

 

[Chalnoth]

Thanks for your reply. Please correct me if I'm wrong but isn't #2 the more likely conclusion given experimental data? How does #1 come into play for scientists?

These are not opposing statements. These are what you get when you consider only Schroedinger's equation (for classical quantum mechanics), and do not add any particular mechanism for wavefunction collapse. Both statements immediately follow only from Schroedinger's equation, once you apply it to a system within which a measurement could conceivably be taken.

And if simply considering Schroedinger's equation automatically gets you the experimental prediction that observers will see what looks like wavefunction collapse, then there is no reason whatsoever to add an additional collapse mechanism to the theory.

 

[rbj]

well, it's my personal take that this is lawyer-speak. Chalnoth believes we live in a multiverse, something that has absolutely no measurable nor experiential effect on any of us and has no promise to have such. it is not testable nor falsifiable.

I see you have utterly disregarded my entire argument. And now we see that your ignorance is not just due to a lack of exposure, it is willful.

we'll let my words speak for themselves and let your words speak for themselves.

 

[rbj]

Thanks for your reply. Please correct me if I'm wrong but isn't #2 the more likely conclusion given experimental data? How does #1 come into play for scientists?

These are not opposing statements. These are what you get when you consider only Schroedinger's equation (for classical quantum mechanics), and do not add any particular mechanism for wavefunction collapse. Both statements immediately follow only from Schroedinger's equation, once you apply it to a system within which a measurement could conceivably be taken.

And if simply considering Schroedinger's equation automatically gets you the experimental prediction that observers will see what looks like wavefunction collapse, then there is no reason whatsoever to add an additional collapse mechanism to the theory.

sahm, take this with at least a small grain of salt. it sounds like, essentially, a "Many Worlds" interpretation of QM, and is speculative.

strictly speaking, the Schrödinger equation will give you probabilities (if you normalize $\Psi$) of the existence of a particle at some place in space and (if they didn't pull time dependence out of it) some point in time. in its ordinary and everyday use, QM and Schrödinger's eq. are applicable to the domain of the very, very small, the microscopic. it works very well when applied to electrons and other elementary particles. one of the problems with QM, that they are trying to solve with a Theory of Everything, is getting the principles to apply to the macroscopic. we simply do not apply the Schrödinger equation to bricks or balls that we see in everyday life, much less so to entire universes. they haven't yet been able to unify QM, which works to describe what's going on with 3 of the 4 fundamental interactions (EM, weak, and strong nuclear), with GR (which describes pretty well what is going on with the 4th fundamental interaction).

now there are (at least theoretically) some nasty objects like black holes with spin and charge that have (theoretical) descriptions that include both QM and GR. you will see all of $\hbar$, $c$, and $G$ in these equations. but, normally, when we look out at the universe and at the bodies and things in it, normally gravitation (described by GR) is the only interaction going on. and, unless it's one of these hypothesized Theories of Everything (of which M-theory is a candidate) you don't see quantum mechanics or the Schrödinger equation applied at all. (well, for the nuclear reactions in stars and the like, there is QM.) not for solving problems like the behavior of galaxies or the expansion of the universe.

in established physics where speculative results are deprecated, the Schrödinger equation is applied to the microscopic not to the macroscopic. and usually, to get results that are measurable and useful, it is ensemble averages of what happens that are used to compare experimental results to theory. not always. and then there are the curiosities like Schrödinger's cat.

 

[sahmgeek]

I think I'm hung up on the distinction between CAN occur (range of probabilities) and WILL occur (speculating that all probabilities actualize themselves, albeit in alternate worlds). The first I get, the second seems like a leap. Or am i missing something? I'm only thinking conceptually. this may be the problem.

 

[rbj]

I think I'm hung up on the distinction between CAN occur (range of probabilities) and WILL occur (speculating that all probabilities actualize themselves, albeit in alternate worlds). The first I get, the second seems like a leap. Or am i missing something? I'm only thinking conceptually. this may be the problem.

it's a difficult thing to think about conceptually. is Schrödinger's cat alive or dead? or both? check it out at Wikipedia, if you want:

http://en.wikipedia.org/wiki/Schrödinger's_cat

also

http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics

despite what he said, Chalnoth is using various principles of quantum mechanics to speak to our understanding of the universe (or an understanding of the universe). it's not a settled issue among physicists. physicists are not all in agreement in how to interpret the "greater implications" of QM.

when it comes to how the holes and electrons move around in the solid state of silicon in a transistor, what percentage of these particles are able to overcome a potential barrier, then all of the physicists agree on the meaning and results of QM. some physicists (the wiki article cites Leslie E. Ballentine from Simon Frasier U) are pretty much strict ensemble guys. they say that about the only thing that QM tells us are probabilities and then to get a handle on quantitative behavior, you need a lot of particles and you get ensemble averages.

Chalnoth appears to subscribe to some (or one) specific interpretation that is a sort of reach, when you apply the concept of wave function collapse to get the Many Worlds concept and from that then "... it is extraordinarily likely, given what we know today about cosmology, quantum mechanics, and high-energy physics, that we live in a multiverse". it's a reach, but Chalnoth appears to want us all to believe that it is settled physics. it's not, and as you can see, he reacts kinda caustically when someone else points it out.

 

[sahmgeek]

thanks. I'm somewhat familiar with most of these things. Schrödinger's cat thought experiment is nonsensical as it relates to quantum superposition. the cat has already BECOME a cat, the poison has already BECOME a poison. Wave functions have already collapsed, superposition is NOT occurring. Who cares if the cat is alive or dead. It's irrelevant. I need a better explanation for the leap from quantum superposition to MWI.