Talk:Universal wavefunction

Criticism

I don't know what Ray Streater's exact rationale is for his criticism, but to me the universal wavefunction is meaningless because it purports to say something about the totality of existence, which is a concept that abuses the logic of universal quantification. I do think Everett's relative state idea is brilliant though. It handles the Wigner's friend gedankenexperiment in a very elegant way. But extending the wavefunction to include everything is asking for trouble. To paraphrase Streater: What is the universal wavefunction a function of? --Shastra 11:14, 22 August 2006 (UTC)

Denying the existing of a universal wavefunction makes as much sense (to me) as denying the existence of a classical universe. The universal wavefunction is a function of the same things as other wavefunctions are. --Michael C. Price ^talk 11:57, 22 August 2006 (UTC)

Even classical universes can run into problems if we aren't careful about unobservable entities and infinities... Examples of ordinary wavefunctions are functions on Fock spaces that describe the quantum fields that have been observed in our universe. In the many-worlds picture that last phrase should be translated into: the quantum fields that have been observed in our current branch of the many-worlds. Is the universal wavefunction also limited to these Fock spaces? If that is the case, then (to paraphrase Everett) why draw the line there? --Shastra 15:44, 22 August 2006 (UTC)

Obviously we can only describe the operation of that part of the wavefunction we know about -- again, the same situation that existed with classical physics. Broader speculations are outside the scope of many-worlds and the universal wavefunction, with its extended Fock spaces or whatever emerges from a TOE, but may be discussed within the arena of the Multiverse (science). --Michael C. Price ^talk 17:47, 22 August 2006 (UTC)

Specifically, the wavefunction is a function of the positions of all fundamental particles - a space with a dimensionality of 3n where n is the number of particles. The mathematics are quite clear on this; there isn't any mysticism here. Warren Dew (talk) 03:37, 17 January 2010 (UTC)

Whilst all physical theories are essentially subsystem theories (the motivation behind Ray Streater's first point) that arise as a natural consequence of conservation laws (via Noether's Theorem), the en-vogue phenomena of quantum entanglement, uniquely, allows us to probe this contentious topic. In this context quantum entangled systems are essentially mini-universes by the "Universal wavefunction" definition - they can only be described as entangled until some physical process sufficiently couples with the wavefunction to cause the perturbation generally described as "collapse of the wavefunction". This coupling that disturbs the original system is a quantum event but we lack the microscopic details of the perturbing wavefunction. This lack of knowledge constitutes the boundary around our quantum (subsystem) description of the original entangled system. What I'm proposing here is that we conduct a thought experiment where multipartite entangled systems are set up such that components are arbitrarily allowed to interact with each other and see what happens. What we have set up are mini-universes but more realistic ones in that they contains interactions of the "parts". In addition to the wavefunction for the overall system you can also describe the wavefunction for a subsystem. When a component of the subsystem interacts with a component in the rest of the system this is like performing a measurement, the difference being that you can compare the behaviour described by the subsystem wavefunction to that from the full system wavefunction. Such an approach is consistent with the fundamentals of quantum mechanics (QM) but does not rely heavily on the "interpretative" aspects of QM that have come to dominate understanding of this non-intuitive physics. Unfortunately I lack the requisite skills to set up the physics and math... but I put it out there for someone to try. Peter Canfield (talk) 08:00, 25 March 2011 (UTC)

Isn´t this pantheistic math on infinity and totally useless? While science often reject illogicalness, they accept pantheism, such as in hinduism with all its idols? Which probably stems from Tengri, the worlds maddest idol, a provokation and innovation against the real deity, that claims amanita legal and "the deity is all". Also known as the Tor of Vikings. — Preceding unsigned comment added by Devote9000 (talk • contribs) 14:51, 13 July 2023 (UTC)

Some Mathematical Linguistics Carrying on from Above Discussion - Potentially Nonsensical Observations

Be weary of the below comments, for I am certainly not a physicist. The key thrust of all of the below is the apparent lack of mathematical details governing the Universal Wavefunction together with the Axiomatic basis underlying the Universal Wavefunction on this Wikipedia page.

It would be good to understand what likely Mathematical Formalism (or axiomatic assumptions) are associated with the idea of the "Universal Wavefunction". Such ideas would only be tentative dependent upon our knowledge. The following are some points, typed out without any particular ordering principle:

1) In simple systems, the Wavefunction has to be defined in relation to some co-ordinate system (ie: Psi=Psi(x,t)). This assumes that we can use the co-ordinate system in a manner which specifies spatial and temporal locations in spacetime (not ignoring the detail that some would argue that we can only construct such a co-ordinate system if we are predetermined to do so in a deterministic system - however, it may be good to ignore this viewpoint in practice). Some would argue that having an "in-principle" co-ordinate system is not sufficient for specifying the wavefunction. We must actually construct (physically) such a co-ordinate system - however, this is just a "Philosophical" viewpoint.

2) The Type of Partial Differential Operator that Constrains the Temporal Evolution of the Wavefunction or determines how the Universal Wavefunction will evolve with time. Clearly, we should be aware of the Schrödinger equation and the fact that this is a Partial differential equation which relates the rate of change of the Wavefunction (a notion which most people conceive of in terms of real variables, but which could potentially find its "correct" description in terms of the Heim theory difference equation description - though how such a difference equation that governs the Universal Wavefunction emerges from the physical substrate of reality is something I would not say I have the answer to) to the Hamiltonian operator or a 'Laplacian plus Potential-Translation'. The point would be that (dependent upon whether the deterministic state of affairs allows the experimenter to do so), we should be able to use such 'knowledge' to predict the behaviour of quantum systems *to an extent* (at the very least, we ought to be able to determine how quantum systems are NOT going to behave by ruling out what the Equation governing the Universal Wavefunction is NOT).

3) The issues in (2) relate to the precise form of the equation governing Universal Wavefunction. There are two forms to the Schrodinger Wavefunction According to the Wikipedia Page Schrodinger Equation - A Time Dependent equation and a Time Independent Equation. From our perspective, the Time Dependent Equation seems to be in operation - Whether there is a perspective (co-ordinate system, whatever words you choose to use) from which the Time Independent Equation holds for the Universal Wavefunction is worth considering.

4) Non-local hidden variables and their importance to the Universal Wavefunction. There are deterministic interpretations of Quantum Mechanics (which may or may not be true, dependent upon your viewpoint), including the De Broglie-Bohm Pilotwave viewpoint. How such a theory impacts upon the above points I would not wish to conjecture at this time. I observe that, according to some sources which I can't currently find on the internet, the number of nonlocal hidden variables that could be associated with a given Quantum state (assumed to be the Quantum state of a system at a particular moment in time) could be more than one. This might mean that there is more information within a Quantum system than we could ever find out from physical interaction with the system. There are potentially other oddities concerning the Nature of Non-local hidden variables - but I would need time to consider these. The fact that we have to deal with a configuration space of dimension 3n, where n is the number of "particles" (which could be very large) would likely make computational modelling based upon this theory highly expensive, or impractical. So the natural question arises as to whether this theory has any practical utility beyond philosophical mumbo-jumbo. This is a question I cannot answer.

5) i) The equation governing the Universal Wavefunction has already been stated as possibly not being a Differential Equation but rather a Difference equation (possibly as per Heim theory - but who knows?). This is just conjectural, and the precise details of this would likely be difficult to do Mathematically. ii) It may turn out that an alternative formulation of the De Broglie Bohm theory ought to use difference equations as well.

6) The use of Difference equations would SEEM to presuppose that reality is quantised in some sense. However, that seems to me to be experimentally feasible (as per the Heisenberg Uncertainty Principle) but not absolutely clear - for instance, there is the Weyl Tiling conjecture (and the isotropy of space) which would appear to be difficult to reconcile with quantised views of reality (there's a paper out there entitled "Turning Weyl’s tile argument into a no-go theorem" which is worth a look - it states that "The continuum limit of a periodic graph, as experienced by a classical point particle, cannot be isotropic"). These views together would strongly seem to indicate the need for some "new" Mathematics UNLESS I have missed something more obvious.

7) Not sure how String Theory or M-Theory fits into all this.

I hope I have not broken Wikipedia rules by making the above points - though the overall assertion that the likely Mathematics of the Equation governing the Universal wavefunction should at least be eluded to or mentioned within the Article still stands.

ASavantDude (talk) 13:59, 10 May 2018 (UTC)

Consistent spelling

Why not be consistent in the spelling and change the title to "Universal wave function" (not "Universal wavefunction")?

--Mortense (talk) 14:39, 20 June 2021 (UTC)

You have the wrong title to Everett's PhD dissertation, don't you?

It's correctly called a dissertation, isn't it, not a "thesis." The dissertation was titled "On the foundations of quantum mechanics." The other title you refer to was a separate document Everett wrote that appeared in a publication published by Bryce DeWitt. That's the information I have. I could be wrong. I don't think so. 2600:8801:BE31:D300:35FC:30A7:384F:12D5 (talk) 03:43, 26 July 2022 (UTC)

Everett's response to Streater

This section is a complete fabrication. There is no information that Everett ever read Streater's web page, given that Everett died long before web pages were invented. Johnjbarton (talk) 23:51, 11 September 2023 (UTC)

I removed the self-published web site quote in favor of two, from Wigner and from Wheeler.

Resolved

Johnjbarton (talk) 00:06, 12 September 2023 (UTC)

Connection between Everett and Hartle&Hawking

Is there really a connection between Everett's universal wavefunction and Hartle's and Hawking's wave function of the universe? Hartle and Hawking cite Wheeler and DeWitt, but not Everett. We would need a reliable secondary source which makes the connection.

I have removed the mention of Hartle and Hawking for now. (diff) Reading the intro of their paper, it seems no 'Universal wave function' is invoked, and also Wallace does not mention their paper in his book. Jähmefyysikko (talk) 05:56, 12 September 2023 (UTC)

If anyone should be removed it's Everett, not Hartle and Hawking. Everett wanted to make a universal wavefunction conceivable, but didn't propose any. Hawking and Hartle did the technical work.

As for the connection between them, I'll see if I find a source. Tercer (talk) 06:14, 12 September 2023 (UTC)

The redirect Wavefunction of the universe might also be better pointed at Hartle–Hawking state. That article makes a claim that they are synonyms. Jähmefyysikko (talk) 06:49, 12 September 2023 (UTC)

Please don't try to make a distinction between "universal wavefunction" and "wavefunction of the universe". They are synonyms, the only thing you'll succeed is making the articles difficult to find.

As for the connection between them, I think it's rather straightforward. Hartle and Hawking were solving the Wheeler-DeWitt equation. The original paper by DeWitt is explicit that the universal wavefunction he is talking about is Everett's.

In any case, a quick search got me this paper by Hawking mentioning en passant that the relevant interpretation is the "Everett-Wheeler" one, in the context of solutions to the Wheeler-DeWitt equation, including the Hartle-Hawking state. I also found this paper by Tipler which is entirely dedicated to interpreting the "wavefunction of the universe" using Everett. He is explicit that such a thing should be a solution of the Wheeler-DeWitt equation. Tercer (talk) 14:08, 12 September 2023 (UTC)

Ok, I agree that it then makes sense have them a single concept since the only distinction remaining is the emphasis. For Everett (Universal wave function), the main focus was on the role of the observer. In quantum cosmology (Wave function of the Universe) the focus is on the evolution of the Universe.

Currently there is not much content here. When we transform those verbose quotations into our own words (MOS:QUOTE), we end up with a very short article discussing the MWI approach to measurement problem. The quantum cosmology point-of-view should be included also, and that is currently discussed at Hartle-Hawking state. Are there other notable wave functions for the Universe than the one proposed by Hartle and Hawking? Jähmefyysikko (talk) 16:11, 12 September 2023 (UTC)

It would be great to expand this article from the quantum cosmology point of view. I must confess that's outside my area of expertise. Any solution of the Wheeler-DeWitt equation would do, but I don't know of any notable one besides Hartle-Hawking's. Tercer (talk) 16:52, 12 September 2023 (UTC)

Let me use this space as a stash for some potentially useful references. These are Master's theses, so the claims will need validation, but they may serve as a useful starting point, as they are on a reasonable level of technicality:

• George Flinn (2020) Wave function of the universe
• Deon Mark Solomons (1993) Wave function of the universe supervised by George F. R. Ellis

We learn that Wheeler-deWitt equation needs to be supplemented by boundary conditions to uniquely determine the solution. There seems to be two main proposals, obtained by different boundary conditions: the Hartle-Hawking no-boundary wave function and the tunneling wave function by Alexander Vilenkin. In addition, there is something from Hawking about wormholes. Jähmefyysikko (talk) 21:18, 13 September 2023 (UTC)