William M. Briggs

Statistician to the Stars!

Philosophic Issues in Cosmology VII: Is there a Multiverse?–Guest Post by Bob Kurland

A meeting of the multiverse organizers.

A meeting of the multiverse organizers.

Bob Kurland is a retired, cranky, old physicist, and convert to Catholicism. He shows that there is no contradiction between what science tells us about the world and our Catholic faith.

Read Part VI. *Quotations, unless otherwise specified, are from Issues in the Philosophy of Cosmology, George F.R. Ellis.

It’s hard to build models of inflation that don’t lead to a multiverse. It’s not impossible, so I think there’s still certainly research that needs to be done. But most models of inflation do lead to a multiverse, and evidence for inflation will be pushing us in the direction of taking [the idea of a] multiverse seriously. —Alan Guth

“Well, there is the hypothesis…that all possible universes exist, and we find ourselves, not surprisingly, in one that contains life. But that is a cop-out, which dispenses with the attempt to explain anything. And without the hypothesis of multiple universes, the observation that if life hadn’t come into existence we wouldn’t be here has no significance. One doesn’t show that something doesn’t require explanation by pointing out that it is a condition of one’s existence. If I ask for an explanation of the fact that the air pressure in the transcontinental jet is close to that at sea level, it is no answer to point out that if it weren’t, I’d be dead. —Thomas Nagel, Mind and Cosmos.

The notion of an ensemble of many possible universes (small u), not causally connected, “a multiverse”, has been used to counter the unlikeliness of all the anthropic coincidences. To quote Ellis*:

If there is a large enough ensemble of numerous universes with varying properties, it may be claimed that it becomes virtually certain that some of them will just happen to get things right, so that life can exist; and this can help explain the fine-tuned nature of many parameters whose value values are otherwise unconstrained by physics…However there are a number of problems with this concept. Besides, this proposal is observationally and experimentally untestable, thus its scientific status is debatable.

One problem (other than the untestable aspect) is that the probabilistic character of the multiverse is never specified by authors who invoke it:

These three elements (the possibility space [the population description], the measure [the quantities that describe the particular universe], and the distribution function [for the measure]) ,must all be clearly defined in order to give a proper specification of a multiverse…This is almost never done.

What is also not usually specified are the possible types of universes contained in a multiverse. Which of the types below should be included?

  • “Weak Variation: only the values of the constants of physics are allowed to vary?…
  • Moderate Variation: different symmetry groups, or numbers of dimensions…
  • Strong Variation: different numbers and kinds of forces, universes without quantum theory or in which relativity is untrue (e.g. there is an aether), some in which string theory is a good theory for quantum gravity and others where it is not, some with quite different bases for the laws of physics (e.g. no variational principles).
  • Extreme Variation: universes where physics is not well described by mathematics, with different logic; universes ruled by local deities; allowing magic… Without even mathematics or logic?

Which is claimed to be the properties of the multiverse, and why? We can express our dilemma here through the paradoxical question: Are the laws of logic necessary in all possible universes?”

Although the existence of multiverses cannot be justified by measurements, do they offer good explanations for the anthropic coincidences? Ellis answers:

It has been suggested that they (multiverses) explain the parameters of physics and of cosmology and in particular the very problematic values of the cosmological constant (lambda, the constant for negative pressure). The argument goes as follows: assume a multiverse exists; observers can only exist in one of the highly improbable biophilic outliers where the value of the cosmological constant is very small…If the multiverse has many varied locations with differing properties that may indeed help us understand the Anthropic issue: some regions will allow life to exist, others will not. This does provide a useful modicum of explanatory power. However it is far from conclusive.

Firstly, it is unclear why the multiverse should have the restricted kinds of variations of the cosmological constant assumed in (these) analyses…If we assume ‘all that can happen, happens’ the variations will not be of that restricted kind; those analyses will not apply.

Secondly, ultimate issues remain. Why does the unique larger whole (the multiverse) have the properties it does? Why this multiverse rather than any other one? (emphasis added)

I will add to Ellis’s comment that even though one universe in a multiverse has an appropriate value for a particular constant (say, lambda), it will not necessarily be the case that other parameters will be appropriate. There still has to be a conjunction of values for all the laws and constants, which requires either a Theory of Everything to give that (something to wonder about in itself) , or more amazing coincidences.

Ellis further argues that probability-based arguments cannot demonstrate the existence of a multiverse:

Probability arguments cannot be used to prove the existence of a multiverse, for they are only applicable if a multiverse (that is to say, a population of multiverses) exists. Furthermore probability arguments can never prove anything for certain, as it is not possible to violate any probability predictions, and this is a fortiori so when there is only one case to consider, so that no statistical observations are possible. (emphasis in the original). All one can say on the basis of probability arguments is that some specific state is very improbable. But this does not prove it is impossible; indeed if is stated to have a low probability, that is precisely a statement that it is possible…probability arguments…(are) equivalent to the claim that the universe is generic rather than special, but whether this is so or not is precisely the issue under debate.

The issue of whether a multiverse can contain an infinite number of universes (thus justifying the claim that “whatever can happen will happen”) is addressed by Ellis as part of the question whether an infinite number can be considered as real (rather than as a mathematical construct) in his analysis of the philosophic/ metaphysical questions involved in cosmology, and will be discussed in the last post of this summary.

In conclusion, Ellis argues that Multiverses are a philosophical rather than scientific proposal.

The idea of a multiverse provides a possible route for the explanation of fine-tuning. But it is not uniquely defined, is not scientifically testable … and in the end simply postpones the ultimate metaphysical questions.

These philosophic issues will be discussed in the final post of this series.

See Dr Kurland’s original post, linked above, for a further discussion of Inflation.

54 Comments

  1. Of course there’s multiverses. One can catch glimpses of them trying to inch their way into ours. Having watched a lot of scifi, I know we can’t tell the other multiverses how to enter into ours because that never ends well. The multiverses can be anything–though without billions and billions of them, it’s unlikely that evolution on those planets could match ours, so I think it unlikely these mulitiverses are as similar to earth as some would like to believe. 🙂

    I’m looking forward to your next post concerning the reality of infinite numbers. Infinity is so fascinating to mull about in one’s head and the discussions of it’s reality versus mathematical construct are usually quite lively.

  2. It doesn’t matter how many universes there are. Gottfried Leibniz already showed us that this world must be the best possible of all worlds and that this universe must be indeed better than every other possible universe. This is my world and I am sticking to it!

  3. Why get grandiose and call it a “multiverse”?

    It’s Hilbert’s Hotel.

  4. http://space.mit.edu/home/tegmark/crazy.html

    “Level I: A generic prediction of cosmological inflation is an infinite ergodic universe, which contains Hubble volumes realizing all initial conditions – including an identical copy of you about 10^10^29 meters away.”

  5. Hans, I think the “crazy.html” says it very nicely.

  6. Nullius in Verba

    August 25, 2014 at 10:44 am

    Many of the ‘universes’ are causally connected – even if sometimes only via the past. That’s what quantum superposition is about.

    The mathematical details you mention (space, measure, and distribution functions) were defined or described in Everett’s thesis.

    The type of variation allowed depends on what’s possible. If there are as yet unknown reasons why particular laws must be as they are, there’s no variation. If there’s no restriction (and at the moment we know of none) then they must all exist.

    I’m not sure what is meant by “restricted kinds of variations”, or what is meant by “those analyses will not apply”. Why not?

    Why should the argument apply to only one constant? If every possibility exists, and different constants can vary independently, then every possible conjunction of constants must exist.

    The multiverse is just quantum superposition. Do superpositions exist? Can we study them? Can we make statistical statements about them?

    Feynman’s “sum-over-histories” approach integrates over every possible path, arguably covering an infinite number of possibilities. This may be a large-scale, low-energy approximation to a different theory, that if not infinite is at least a very big number. Is there any reason to think it’s not big enough? A mere 10^10^29 metres is pretty small, as big numbers go.

    I personally think using the anthropic principle to explain these things is a cop-out. It seems more likely that we just haven’t thought of it yet. There are lots of things that seem like amazing coincidences if you don’t know why they happen. But I don’t see that any of this is an argument against multiverses.

  7. Bob, ad hominems are an easy cop-out.

  8. Hans, with respect to Tegmark’s work, one ad hominem comment is worth 10,000 words.

  9. NIV, I’m not going to reply to your comments in detail, but I recommend you read “The Quantum Mechanics of Minds and Worlds” by Jeffrey Barrett, or his article in the Stanford Encyclopedia of Philosophy, “Many Worlds Interpretation of Quantum Mechanics”
    http://plato.stanford.edu/entries/qm-manyworlds/
    to find out some of the flaws and objections to the Everett Relative State Theory.
    and to variations on that theme.
    Then we can talk.

  10. Nullius in Verba

    August 25, 2014 at 12:40 pm

    Bob,

    I’m not going to reply to your reference in detail, but none of the objections in that article are valid.

    I’m happy to talk any time. 🙂

  11. This essay could have been summarized as:
    – Multi-verses might exist,
    – but we really don’t know for sure.
    – Either way, the science is ok with the Catholic Church.

    On to important matters: Sheri’s infinite numbers:

    http://www.youtube.com/watch?v=23I5GS4JiDg
    &
    http://www.youtube.com/watch?v=lA6hE7NFIK0

    Also, a humorous & rather accurate assessment of net neutrality — for those to advocate a free market & limited government intrusion…the lesson here seems to be that some government intrusion (“regulation”) is warranted, provided it’s the right sort of intrusion–and not intruding is the wrong answer:

    http://www.youtube.com/watch?v=NAxMyTwmu_M

  12. Ken—Is she inhaling those Sharpies?! Just kidding. Looks interesting—will watch in full a bit later today. Thanks.

  13. Ken, thank you for your comment–gracious and insightful as usual. Your first two bulleted points are correct, but pray, please tell me where in the post or in Ellis’s original article was anything said about the position of the Church with respect to a multiverse? Or, perhaps are you thinking of Molina’s Middle Knowledge proposition (about which I will be posting in the near future). And since, as pointed out in the post, the existence of a multiverse is not a scientific question, the Church would not concern itself with that aspect of multiverse existence.

  14. Nullius in Verba

    August 25, 2014 at 3:10 pm

    “Your first two bulleted points are correct, but pray, please tell me where in the post or in Ellis’s original article was anything said about the position of the Church with respect to a multiverse?”

    Right at the top:

    “Bob Kurland is a retired, cranky, old physicist, and convert to Catholicism. He shows that there is no contradiction between what science tells us about the world and our Catholic faith.”

  15. yo, Ken, is the video supposed to be Infinity for Dummies? I much preferred Rudy Drucker, “Infinity and the Mind”, for those willing to do more than a two minute video, or Augustine’s or Cantor’s thought’s … see http://www.erudit.org/revue/ltp/1995/v51/n1/400897ar.pdf
    or those which have been previously posted by Briggs.

  16. Ye Olde Statisician

    August 25, 2014 at 3:20 pm

    Any words on the distinction between a multiverse and multiple “universes”?

  17. YOS, I’m not sure whether multiple universes is equivalent to a multiverse. For example, multiple universes might refer to parallel universes, the quantum “many worlds/many minds” notion. Would, if one were to draw a Venn diagram, the circle containing “quantum many worlds” set lie inside the circle for the “multiverse” set”? I think so, but am not sure.

  18. NIV, that’s my bio. That’s not what’s in the post. Because I’m a cranky, retired old physicist, does that say what’s in the post is a tirade? Come, come, let’s not stretch for debating points.

  19. NIV, a postscript: I’ve posted on the Conway-Kochen Free Will Theorem. (see
    http://rationalcatholic.blogspot.com/2014/02/do-quantum-entities-have-free-will-and.html
    and also the corresponding post in this blog.
    Does this imply the Church has anything to say about that theorem? (It might, but it would be entirely unrelated to what I post.)

  20. NIV and YOS, here’s Ellis brief discussion of how quantum many worlds theory might enter into a discussion of the multiverse issue:
    “3: Quantum Mechanical. It could occur through the existence of the Everett-Wheeler “many worlds” of quantum cosmology, where all possibilities occur through quantum branching [32]. This is one of the few genuine alternatives proposed to the Copenhagen interpretation of quantum mechanics, which leads to the necessity of an observer, and so potentially to the Strong Anthropic interpretation considered above (see Sec.9.1). The manyworlds proposal is controversial: it occurs in a variety of competing formulations [119], none of which has attained universal acceptance. The proposal does not provide a causal explanation for the particular events that actually occur: if we hold to it, we then have to still explain the properties of the particular history we observe (for example, why does our macroscopic universe have high symmetries when almost all the branchings will not?). And above all it is apparently untestable: there is no way to experimentally prove the existence of all those other branching
    universes, precisely because the theory gives the same observable predictions as the standard theory.” Comments on this quote would be enlightening.

  21. Nullius in Verba

    August 25, 2014 at 4:52 pm

    “NIV, that’s my bio. That’s not what’s in the post.”

    Does it say so? If someone was to simply start reading the post, is it understandable that they might read it that way?

    “Come, come, let’s not stretch for debating points.”

    Sorry. It wasn’t meant as a ‘Gotcha!’ I was just pointing out where in the post someone could have found it said.

    “NIV, a postscript: I’ve posted on the Conway-Kochen Free Will Theorem”

    The Kochen-Specker theorem is specific to collapse theories, and describes some of the problems that arise as a result of trying to maintain collapse-at-the-time-of-measurement as part of the theory. It’s trying to show that you simply can’t maintain classical realism at the same time as collapse.

    Pseudorandomness would only work if the observer’s choice of experiment to perform was also pseudorandom, in a matching way. Assuming humans have free will, the particles must have something like it too.

    The MWI, on the other hand, is realist, local, and deterministic. It doesn’t have the problems that make Kochen-Specker necessary. A pair of particles is created with correlated states. A pair of observers observe the particles, and the observer states become correlated with the particle states, and hence with one another. Should the observers later compare notes, the observer superpositions will interact in such a way as to make the measurements they report follow all the quantum rules.

    The outcome of each measurement is predetermined – the answer is always “both”, in superposition. No collapse-on-measurement happens, so the conditions of the Conway-Kochen theorem don’t apply.

  22. Nullius in Verba

    August 25, 2014 at 5:01 pm

    “The proposal does not provide a causal explanation for the particular events that actually occur: if we hold to it, we then have to still explain the properties of the particular history we observe (for example, why does our macroscopic universe have high symmetries when almost all the branchings will not?).”

    So far as I understand what’s being said here, I think a causal explanation has been offered – but I’m unsure of what his objection is so I might have missed something. Why does he think that almost all the branchings will not show high symmetry?

    “And above all it is apparently untestable: there is no way to experimentally prove the existence of all those other branching universes, precisely because the theory gives the same observable predictions as the standard theory”

    Yes, that’s exactly right. It’s metaphysics, not physics. The only reasons for picking it are aesthetic – its simpler, more elegant, doesn’t depend on vitalist notions of ‘consciousness’ to trigger collapse, it’s linear, reversible, deterministic, local, and realist.

  23. Bob, Of course the church is indifferent about a multiverse, just like the church is indifferent about a static universe. The creation of the multiverse differs fundamentally not from the creation of the natural numbers, pi() , e or i: They were created outside of time.

    You are stil not seeing that the big bang is the same as the creation of a lightning bolt, the creation of life and the creation of your soul.

    You are still sticking with your god-of-the-gaps, you really should have some education from the Jesuits.

  24. Bob, NiV;

    I add to the hopper this blog post from Caltech physicist Sean Carroll:

    http://www.preposterousuniverse.com/blog/2011/05/26/are-many-worlds-and-the-multiverse-the-same-idea/

    When physicists are asked about “parallel worlds” or ideas along those lines, they have to be careful to distinguish among different interpretations of that idea. There is the “multiverse” of inflationary cosmology, the “many worlds” or “branches of the wave function” of quantum mechanics, and “parallel branes” of string theory. Increasingly, however, people are wondering whether the first two concepts might actually represent the same underlying idea. (I think the branes are still a truly distinct notion.)

    Heretofore, my understanding has been that MWI and multiverse are, and should be, treated as separate concepts. Having naively confused (conflated?) them in the past I’m actually somewhat pleased that there is literature suggesting a possible connection. “If this then why not that” is potentially fallacious, especially when layity such as myself are pondering concepts above our paygrades, but some illogical conclusions have been known to get lucky. Article continues:

    These two ideas sound utterly different. In the cosmological multiverse, the other universes are simply far away; in quantum mechanics, they’re right here, but in different possibility spaces (i.e. different parts of Hilbert space, if you want to get technical). But some physicists have been musing for a while that they might actually be the same, and now there are a couple of new papers by brave thinkers from the Bay Area that make this idea explicit.

    Physical Theories, Eternal Inflation, and Quantum Universe, Yasunori Nomura

    The Multiverse Interpretation of Quantum Mechanics, Raphael Bousso and Leonard Susskind

    Related ideas have been discussed recently under the rubric of “how to do quantum mechanics in an infinitely big universe”; see papers by Don Page and another by Anthony Aguirre, David Layzer, and Max Tegmark. But these two new ones go explicitly for the “multiverse = many-worlds” theme.

    There are four links to literature embedded in this block of text, all of which are NOT paywalled. I’ve skimmed all four and 99% of it went [wooosh!]. I don’t know whether any of them advance the discussion here or muddy the waters. So I end pretty much where I came in; a multiverse makes sense re: fine-tuning arguments, and is distinct from — as well as not necessarily dependent on — the MWI of QM.

  25. Brandon, that was a good comment on the distinction between MWI and multiverse.
    NIV, I wasn’t trying to make any points about how the Conway-Kochen theorem and the MWI of QM. The point I was trying to make is that I am the same person who posted that (and as I recall, it did appear on this blog also), and my bio is the same, but that has no implication that the Church “approves” of the Conway-Kochen theorem.
    Hans, I sometimes wish I had been educated by the Jesuits, but if I had had a religious education it would have been at a Yeshiva, and I imagine the Talmudists could give the Jesuits a good run for the money.

  26. Brandon, commenting again. All this about conflating the MWI, brane theory, and multiverses is very interesting, but it isn’t science. As pointed out in the post, it’s not testable (or if it is, even in principle, I would love to know how).

  27. Bob, Of course the church is indifferent about a multiverse, just like the church is indifferent about a static universe. The creation of the multiverse differs fundamentally not from the creation of the natural numbers, pi() , e or i: They were created outside of time.

    How can anything created be beyond time? We’re in married bachelor territory, methinks.

    You are stil not seeing that the big bang is the same as the creation of a lightning bolt,..

    This may be true but this would only mean that the ‘big bang’ was not creation ex nihilio, but the transformation of existing matter and energy. This leaves the Five ways untouched.

  28. RE: “yo, Ken, is the video supposed to be Infinity for Dummies? I much preferred Rudy Drucker, “Infinity and the Mind”, for those willing to do more than a two minute video, or Augustine’s or Cantor’s thought’s … see http://www.erudit.org/revue/ltp/1995/v51/n1/400897ar.pdf
    or those which have been previously posted by Briggs.”

    THE WHIMSICAL videos by “ViHart” on YouTube are, for the most part, surprisingly logically & technically solid; don’t let the style fool you.

    Part of her stated goal is to apply humor to entice youth that would otherwise be intimidated to give math a serious chance to become interested and give it more of a chance than they’d do otherwise. To some extent she’s succeeding; from that perspective it’s worth (my opinion) to pass her stuff along.

    AS FOR R. Drucker’s work, etc., I’m not too fond of it. I’ve yet to see/read anything along those lines to convince me that the underlying issue isn’t anything other than the author’s doubts gussied up in some noble/intellectual exercise — the espoused search for some truth is really just the search for proof to justify something that [per the Catholic Church] is ONLY available via faith; that the search is on indicates the “searchers” doubts–a lack of faith (or, see “reaction formation” in psychology/psychiatry literature). The Apostle Thomas got proof (and even that brief exchange is a subject of debate as to what actually transpired); the rest of us won’t. Efforts to contrive proof are invariably flawed & nowhere near as incontrovertible as the analyst pretends to think (i.e. there’s ample evidence, readily apparent to those indifferent to the “analysis” of the flaws inherent therein — which is to say much of the real purpose of such analyses is to allow the analyst to delude themselves*), and if one believes –especially in Roman Catholic Doctrine–one is perilously close to either presenting heresy and/or inducing others to perceive as truth what is really heresy. Good intentions aside, the results are what count.

    Somewhere, some documentary type show, was a somewhat lengthy interview with the Vatican’s astronomer, who made a very succinct explanation about science, how it didn’t exist when ancient foundational documents were written, etc….and….the futility of trying to contrive & reconcile science and Biblical references. It’s worth tracking down for anyone interested in such things.

    * A good movie that turns self-delusion around , illustrating how blind one can make oneself to the obvious flaws, into a sort of puzzle was “Angle Heart,” starring Mickey Rourke with Robert DeNiro. More recently, Sixth Sense (with Bruce Willis) did something similar (‘they see only what they want to see’ is also, partly, ‘they refuse to see what they don’t want to see’ — which are two complementary but different delusional tactics & mechanisms).

  29. Bob,

    I missed your earlier dismissal of Tegmark whose work was cited in my previous post. I’m glad you feel it added to the discussion.

    … commenting again. All this about conflating the MWI, brane theory, and multiverses is very interesting, but it isn’t science. As pointed out in the post, it’s not testable (or if it is, even in principle, I would love to know how).

    I’m less inclined to categorically declare it not-science. I’m of the mind that theology, philosophy, mathematics and empiricism all overlap in some way, and with fuzzy boundaries — not sharply delineated ones. Your comment leads me into some questions I’ve been asking myself of late: where does science begin? When does it depart into the realm of philosophy and/or theology? When does science become a belief based on articles of faith? I’ll give you an example from a recent discussion I had elsewhere with an atheist:

    Atheist: God is ruled out by the principle of parsimony, a common tool used by physicists and other scientists.

    Me: Here I disagree with you in the strongest polite terms I can muster: parsimony rules out NOTHING.

    I call his statement scientism.

    Me: IMO, many scientists could stand to have some more imagination. I see a difference between being fanciful and thinking outside the box.

    Atheist: Unfortunately, thinking up sci-fi scenarios is not a good means of getting oneself to think outside the box in science. The best route to eminence in the scientific world is work your [tail] off to obtain data, and then spend way more time thinking about your data than everyone else. Happy imaginative scenarios generally take you nowhere in that community.

    Now his statement looks more like science to me. However, he missed the overall point I was making about the limits of inductive inference. Occam’s razor is for hypothesis formulation and designing models. Period, full stop. A model needs observations to actually say anything further; to preach on about that to this choir would be redundant.

    More to your point on not-science: testable models must start with ideas. I think back to the origins of QM and the Standard Model … talk about the Wild West. As a layperson, it’s tough for me to sort the wheat from the chaff on the present bleeding edge of the field. But my kneejerk skeptical radar snaps to attention when GUT researchers claim the competition is not doing science. Einstein himself proffered similar laments, and yet today not too many physicists question whether God plays dice with the universe. Seems a lot of them “rule out” God though, albeit fewer of them than evolutionary biologists.

    Now I wish I had a poll … there may be some significance in that last bit.

  30. Whoops, looked like I hashed a closing bold tag; “faith” should be the only word bolded there.

  31. Brandon, if propositions / theories can’t be empirically tested they aren’t in the realm of science. Consider the following pieces of history that testify to the necessity of empirical, experimental, reproducible validation of theory:
    phlogiston was a neat theory of heat until disproved by Count Rumford’s cannon-boring experiments;
    the ether was a neat mechanism for the vibration of electromagnetism until disproved by the Michelson-Morley experiments;
    Planck’s hypothesis of a quantized black-body radiation was strange, but explained the Wien’s radiation law;
    Einstein’s General Relativity theory was up in the air, until verified by the occultation observed in the 1918 (?) eclipse and the advance of the perihelion of Mercury;
    And look in
    http://rationalcatholic.blogspot.com/2013/04/god-symmetry-and-beauty-i-standard.html
    for more instances where measurements verified that great achievement, The Standard Model (including the CERN measurements of the Higgs Boson).
    Without the possibility of empirical verification (or falsification) propositions/conjectures about multiverses, MWI or not science, but mathematical metaphysics. They may be interesting, attractive, profound, but they’re NOT SCIENCE.

  32. *or —> are… (too early in the morning).

  33. Sander van der Wal

    August 26, 2014 at 8:20 am

    @Bob Kurland

    There’s the difference between impossible to test on the one hand, and impractical to test on the other one.

    For a contrived example, if Catholic Faith states that the Mind of God is unknowable to man, then that is a theory that is impossible to test, according to the theory itself.

    But “what happens in the afterlife” is just impractical to test. Everybody will test it for themselves after they died and there is a kind of afterlife. But few people are willing to die to perform the test.

    A more down-to-earth example, if the test apparatus is very expensive then the theory is impractical to test too. The Large Hadron Collider is still within the realm of the affordable, but what about the machines needed for testing the next step?

  34. Brandon, as you point out there’s a difference between impossible to test and impractical to test. By definition, alternate / parallel/ other universes are not causally connected to ours; if they were, they would be part of our universe. So by definition, it is impossible to test (barring psychic phenomena of which we are presently ignorant) the presence of these other universes. In the same way it is impossible to test beyond the horizons mentioned in the first of these posts what things are like in our own universe. For all we know the laws of physics may be entirely different beyond the distance horizon.

  35. Dover_beach
    Even if the bing bang were are creation ex nihilo, you still can’t invoke magic to explain a physical event, that’s god-of-the-gaps thinking.

    Poof, magic. (How did he do that?)

  36. Even if the bing bang were are creation ex nihilo, you still can’t invoke magic to explain a physical event, that’s god-of-the-gaps thinking.

    Poof, magic. (How did he do that?)

    Hans, how is the creation of matter and energy identical to any subsequent transformation of that matter and energy? You are still not grasping the categorical difference between creation and transformation. The creation of the universe ex nihilio was not a physical event, it created the physical. To employ an analogy, the invention of chess was not a chess-event, the movement of chess pieces on a chess board, however, are. You are laboring under the illusion that the creation of matter and energy (or chess) is subject to the same constraints as its transformation (movements of chess pieces on a chessboard), when it ought to be obvious that they cannot be given that before creation, of matter and energy (or chess), there was no physical thing at all.

  37. Nullius in Verba

    August 26, 2014 at 2:16 pm

    “By definition, alternate / parallel/ other universes are not causally connected to ours; if they were, they would be part of our universe.”

    This isn’t quite right, although the distinction is subtle.

    If a quantum experiment has several possible outcomes, then all of these possible futures are ‘alternate universes’. The future is obviously causally connected to the past, and since they share the same past, they are indirectly causally connected to one another. One cannot causally affect the other because part of the path between them is past-directed, and the future can’t causally affect the past. But not being able to causally affect something is not quite the same thing as not being causally connected to it.

    It’s like correlation. X being correlated to Y may mean X causes Y, or that Y causes X, or that Z causes both X and Y. They’re causally ‘connected’, but the connections are one-way.

    “So by definition, it is impossible to test (barring psychic phenomena of which we are presently ignorant) the presence of these other universes.”

    Again, the situation is a bit more subtle. You can test for the existence of other universes for something else; another quantum system – particles or photons or whatever. What you can’t do is test whether they exist when applied to yourself. The ‘alternate universes’ is just quantum superposition, and we have lots of experimental evidence of that. When the electron is passing through the two slits, the part passing through one slit does not see a copy of itself simultaneously passing through the other. It thinks it is alone. But we see the interference pattern on the screen, that vanishes when one of the slits is blocked, so we know that both ‘universes’ exist: the electron passing through one slit in one and the electron passing through the other slit in the other.

    But once we observe the electron we enter a superposition of states, and just as the electron passing through one slit does not see itself passing through the other, so the observer seeing the electron passing through one slit does not see himself observing the electron passing through the other. There’s no interaction between them. However, there is still the potential for interference between them, an example of which is seen in the delayed-choice quantum eraser.

    In this experiment, photons pass through double slits and then are split into a superposed pair of photons that can be used to test for interference, and a pair of correlated photons that can be used to find out which slit the photon went through. But the choice of whether to do so can be delayed until after the first pair have been measured. So the decision whether to allow the interference pattern to appear or to find out which slit the photon passed through is not made until after the interference measurement has happened. If you suppose you cannot have both at once, and the choice is decided at the time of measurement, this experiment appears to allow a future decision to alter (collapse the wavefunction of) an event in the past.

    However, in the Everett-Wheeler interpretation it’s much more straightforward. The initial measurement puts the detectors in superposition. The later measurement decides which aspect (interference or which-path) of this superposition to observe. Because EWI does not require a final choice to have been made at the time of the first measurement, it doesn’t have a problem with the decision being made later. The detectors can interfere, even after having made the measurement.

    And because there’s no wavefunction collapse that has to travel faster than light or into the past, we can be certain that there is no way to use this sort of thing to violate causality or do time travel. (It’s been proved anyway, but this approach makes it obvious.)

    In the practical experiments done so far, the delay is only 8 nanoseconds, so there isn’t time for the experimenter to get directly involved. But in principle, it should still work even if he did.

    However, I am still forced to admit that since the both interpretations predict the same observable events, there is no experimental way to distinguish between the sensible, slower-than-light, everything-in-the-right-order EWI and the alternative superluminal backwards-in-time wavefunction collapse interpretation. You take your choice.

  38. Ye Olde Statisician

    August 26, 2014 at 3:36 pm

    And in the deBroglie-Bohm model, the effect has been duplicated at the macroscopic level using oil drops on the surface of water:
    http://www.wired.com/2014/06/the-new-quantum-reality/

    There will always be multiple theories that account for the same set of data because scientific theories are underdetermined. That’s why “falsification” works. It’s also why Nancy Cartwright emphasized that you cannot say a theory is correct simply because it accounts for the data. There really ought to be a causal explanation of what happens, not simply a mathematical model that predicts outcomes.

  39. Bob,

    … as you point out there’s a difference between impossible to test and impractical to test. By definition, alternate / parallel/ other universes are not causally connected to ours; if they were, they would be part of our universe.

    I completely agree. I would say that any speculations on such things are no better than hypotheses and that it would be unscientific to treat them as theory — i.e., to draw any conclusions from them. All I am saying is that it isn’t nececessarily unscientific to make such suppositions and extend them.

    I stress my argument is the perspective of a layperson. Our disagreement is almost certainly due to the fact that you’re far closer and more educated in the field than I. So I don’t wish to belabor the points I’ve alraeady made.

    Thanks again for the discussion and feedback. Overall I’ve been enjoying your series. Regards.

  40. YOS,

    There really ought to be a causal explanation of what happens, not simply a mathematical model that predicts outcomes.

    Which isn’t controversial … I see that as a foundational principle. I think what you’re saying to NiV is that the competing models proposed by the various interpretations of QM make predictions, but don’t offer causal explanations. Is that correct?

  41. @dover_beach, the problem i have with creatio ex nihilo is not the creation as such, but the fact that everything was created only 18 bilion years ago. (See i can write down the age of everything in a pronounceable number, that’s very odd)
    I would more prefer the big bang being the result of a big crunch, and the concept of an eternally oscillating universe. This also fits better in the buddist philosophy of eternal second chances.
    And from there it’s a logical small step to a multiverse of weakly interacting eternally oscillating black superholes.

  42. Multi-verse-ites is the ultimate expression of reification: the math says the electron ‘chooses’ a state – and the atheist [****] then says that this ‘really’ means both choices are made – in the process creating a new universe.

    So: a ‘choosing’ election has the power to COPY THE ENTIRE REST OF THE UNIVERSE each time it makes a ‘choice’.

    That is.. well. [****] stupid. Period.

    Edited Please watch your language.

  43. Sander van der Wal

    August 27, 2014 at 7:10 am

    @NiV

    But once we observe the electron we enter a superposition of states, and just as the electron passing through one slit does not see itself passing through the other, so the observer seeing the electron passing through one slit does not see himself observing the electron passing through the other. There’s no interaction between them. However, there is still the potential for interference between them, an example of which is seen in the delayed-choice quantum eraser.

    So, consider this experimental setup. Electron emitter, slit and measuring devices as usual. But instead of the experimentator looking at he interference pattern, and causing this state superposition, the measuring device takes pictures and stores them for retrieval. The experimentator also installs a switch enabling him to turn the experiment on from inside another room, where he cannot see the experiment at all, nor look at the pictures being taken.

    Now, when does this superposition of states start to happen? As soon as the first electron goes through the split? As soon as the first electron reaches the detector? As soon as the first image is stored? Do we need to wait until the experimentator looks at the pictures? What happens when his mother sees them first?

    Then, computers have been able to differentiate between pictures for a long time. What happens when we create a program that can turn the experiment on, and that can use image analysis techniques that are able to differentiate between the interference pattern and the image that a single slit will make. Does that computer program count as an observer?

  44. NIV, I apologize for being slow in answering your detailed post about the MWI. I want to chew on it. Actually, I’m not altogether opposed to that interpretation of quantum mechanics, in particular, the “many threads” or “many histories” version of it. There may be a connection to Molina’s Middle Knowledge proposition, and the general issue of God’s foreknowledge and man’s free will, about which I hope to post in the near future (a couple of weeks).

  45. Ye Olde Statisician

    August 27, 2014 at 10:09 am

    @Brandon:
    Feynmann once said that no physicist ever holds only one theory, because while there may be many theories that account for the same data, one of them may be a more fruitful source of ideas.
    Alas, in this day and age we find many folks more than ready to go with a theory because the math works out right without bothering with causal mechanisms. Sometimes the outputs of math models are even referred to as “data.” Worse, the models impose a Rube Goldberg version of causation, in which some things have to work backward or in obnoxious ways, just to save the equations.

    In addition to the Bohmian alternative, which has already reproduced the slit experiment on the macroscopic level, there is also Cramer’s transactional theory:
    http://www.npl.washington.edu/AV/altvw16.html
    http://www.analogsf.com/0412/altview.shtml

  46. Hans:

    @dover_beach, the problem i have with creatio ex nihilo is not the creation as such, but the fact that everything was created only 18 bilion years ago. (See i can write down the age of everything in a pronounceable number, that’s very odd)

    Why is that at all odd? BTW, you’re not writing down the age of ‘everything’, but only that which is susceptible to change.

    I would more prefer the big bang being the result of a big crunch, and the concept of an eternally oscillating universe.

    Either way, it doesn’t matter, given the philosophical argument Aristotle and Aquinas made.

    And from there it’s a logical small step to a multiverse of weakly interacting eternally oscillating black superholes.

    The Thomists were right to distinguish between the logical and the real.

  47. Nullius in Verba

    August 27, 2014 at 1:23 pm

    Sander,

    “So, consider this experimental setup.”

    OK.

    “Now, when does this superposition of states start to happen?”

    The electron enters a superposition of states when it goes through the slits. The measuring device enters a correlated superposition of states when the electron is detected. The picture enters a superposition of states when the detection is recorded. The computer enters a superposition of states when the picture is stored. The experimenter enters a superposition of states when he queries the computer.

    Whether the interference pattern appears depends on whether the superposition is correlated with the ‘which-slit’ aspect of the original electron. If you do a measurement that measures which slit it goes through, that’s saying that you split into a superposition of yourself seeing it go through one slit, and yourself seeing it go through the other, and each component of the superposition sees no interference pattern.

    But if you don’t measure which slit, then *both* parts of the wavefunction contribute in making up your state, these interfere, and you see the interference pattern. The interference occurs at every stage. It’s not just the electron’s wavefunction cancelling at the nulls of the pattern, it’s also the detector’s wavefunction cancelling those components detecting a particle at the null, and the observer’s wavefunction cancelling itself at those components observing the null outcomes.

    And as with the delayed choice quantum eraser, you can delay the decision whether to allow the components to cancel until after the initial detection stage. The detector detects the particles, but the superposition can still be resolved either way, so if the observer queries the detector one way he sees an interference pattern, but if he queries it another way he knows which slit the electron went through, but no interference.

    “Does that computer program count as an observer?”

    Yes. Any quantum system can count as an observer; it’s down to how the two systems interact.

    There’s a phenomenon in classical physics called ‘normal modes of vibration’. The classic example is where you tie a length of string loosely between two posts, and then hang two pendulums of almost the same length from it (a weight on another length of string will do). If you start one swinging, you’ll see an odd pattern of motion where it slows down while the other starts swinging, until they’ve swapped places. The second is now swinging while the first is stationary. Then they swap back.

    The weak interaction between them created by hanging them from the same string causes their motions to become correlated. The motion of one reflects the motion of the other. The state of one system becoming correlated with the state of another system is what we call ‘observation’.

    The equation for a pendulum is x” = -m x, where m is a positive constant, x is the position of the pendulum, and x” is the second derivative of x. If we have two pendulums x and y, swinging independently, we can represent their joint state with a vector X = (x, y), and their motion now obeys a matrix equation X” = M X where X” = (x”, y”) and M is a constant 2×2 matrix with m1 and m2 on the diagonal (the oscillators) and zero off the diagonal (meaning they are independent). Now we introduce a weak interaction between them. This can be done by making the off-diagonal elements in M non-zero. Now X” = MX can’t be split directly into independent components, the two parts have to be solved together. But there is a trick we can use, called diagonalisation. We can often write the matrix M as a product U^-1 D U where D is a diagonal matrix, U is another matrix, and U^-1 is it’s matrix inverse. The trick to doing this is to use things called eigenvectors and eigenvalues. The eigenvectors make up the columns of U, the corresponding eigenvalues appear along the diagonal of D. Thus, we have the equation X” = U^-1 D U X, which we can multiply on the left by U to get (UX)” = D(UX), which is a matrix equation of the original form only now being applied to the transformed state vector UX. Split this into independent equations, solve each independently to get the two elements of UX, then transform back to get X. And we find the joint solution of the interacting oscillators is the sum of two correlated oscillations. It’s the interference between these correlated states that causes the swing-swapping behaviour noted earlier.

    This phenomenon is quite general to interacting oscillators. The interaction causes them to enter a superposition (a sum) of correlated states, where one oscillator ‘knows’ the state of the other. And of course the wave of a wavefunction implies oscillations, so interacting quantum systems count as oscillators in this sense.

    The states entered into depend mathematically on the eigenvectors of a particular matrix associated with the ‘measurement’ interaction, which of course is what happens (simplifying things grossly) in quantum mechanics – a feature that may be otherwise somewhat mysterious. Eigenvectors have the property that they are always perpendicular to one another, which means that the separate solutions they represent don’t interact – which is reflected in the fact that the matrix D is a diagonal matrix, with all zeroes off the diagonal. Zero means the components associated with that row and column don’t affect one another. So the different solutions can’t ‘see’ each other. They pass through one another like the ripples on a pond.

    In quantum mechanics, there are a lot more dimensions – not just the two in the example above. Infinitely many, in fact. But the basic outline is roughly the same. Any interaction between quantum systems tends to correlate their states. If the eigenstates of the interaction are also eigenstates (solutions) of the non-interacting equation of motion, then these states persist indefinitely, even after the temporary interaction has ceased. Such a variable is called an ‘observable’ – it’s a conserved property of the isolated system that it makes sense to ask questions about.

    There’s nothing special about the process of observation in the EWI. It’s just ordinary interaction between quantum systems. So yes, a computer can be an observer.

  48. Sander van der Wal

    August 28, 2014 at 7:39 am

    @NiV

    Hmmm. People throwing coins have traditionally always been modelled using a single universe. A more interesting kind of coin is a program that generates the same kind of image as the electron-slit experiment. An experimentor won’t be able to tell the difference when the only thing he gets is that image. But because the image is generated by a quantum system, it must have generated a lot of superpositions. These should be different from the ones generated by a real experiment.

    Why then the need for the superposition machinery with the real experiment, while nobody feels that need for the fake one?

  49. Nullius in Verba

    August 28, 2014 at 1:59 pm

    Sander,

    I don’t understand your question.

    It would be pretty easy to write a computer program that outputs pseudorandom numbers in patterns that look like double-slit interference. It wouldn’t be easy to tell the difference. But what would be the point?

    If you’re asking “why would anyone propose a theory involving multiple universes when one universe will do?”, the answer is that it is mathematically and philosophically simpler and doesn’t require any ‘weird’ behaviour, like effects propagating backwards in time or faster than light.

    If you’re asking “why do we *need* multiple universes when one will do?”, the answer is that we don’t. You’re quite welcome to assume the superluminal-backwards-in-time single-universe version of events if you like. Just as you can accept the model of reality where everything disappears when you look away from it, and reappears when you turn back. Observationally, the two are the same. One of the theories implies there’s a lot of stuff hanging around out there where you can’t see it, which some people regard as inefficient or something. It implies there are a lot of trees falling in forests and making a sound when there’s nobody around to hear it – which seems like a pointless thing for them to do, and is in any case unprovable. How can you tell if things still happen when unobserved, without observing them?

    It’s openly acknowledged to be metaphysics – that’s why they call them ‘interpretations’. There’s no proof. Either model is as good as the other for all practical purposes of prediction. So it’s really a matter of which model you personally prefer.

  50. It implies there are a lot of trees falling in forests and making a sound when there’s nobody around to hear it – which seems like a pointless thing for them to do, and is in any case unprovable. How can you tell if things still happen when unobserved, without observing them?

    Wow. Just wow.

  51. Nullius in Verba

    August 29, 2014 at 3:27 am

    “Wow. Just wow.”

    Did you like my analogy? 🙂

    Yes, it’s the same philosophical issue. The unobserved is in principle unobservable, so how can you tell if it happens?

    Do you go for simplicity of theory – and assume the same simple rules apply universally, or do you postulate mysterious processes that collapse away the things you can’t see based on a special process of ‘observation’?

    The EWI simply asserts that the basic rules of quantum physics – sans collapse – apply all the way up, to everything. It implies that there are parts of the world that are not observable. The Copenhagen interpretation asserts that the simple rules apply up to a vaguely defined point, when the thing is ‘observed’, and then everything you can’t see vanishes and the universe collapses into a ‘classical’ single-valued physics consisting of just the things you observe. (While rushing around with subtle faster-than-light action-at-a-distance effects to keep everything consistent.) All the wibbly-wobbly quantum stuff only goes on when you’re not looking – as soon as you look, the quantum stuff disappears, somehow.

    I find the Copenhagen interpretation ‘philosophically inelegant’. But that’s not a scientific criterion.

  52. Yes, it’s the same philosophical issue. The unobserved is in principle unobservable, so how can you tell if it happens?

    How can we tell if a sound is made by trees falling in a forest when unobserved? Are you suggesting that mere observance causes the sound and not the tree falling? I’d check my premises if I were you; it sounds as if you’re confusing metaphysics with epistemology.

  53. Nullius in Verba

    August 29, 2014 at 11:41 am

    “Are you suggesting that mere observance causes the sound and not the tree falling?”

    Are you suggesting that mere observance causes a quantum wavefunction to collapse into a single outcome?

    “I’d check my premises if I were you; it sounds as if you’re confusing metaphysics with epistemology.”

    No, I’m not confusing it with epistemology. Epistemology is about what we know. Ontology is about what is. The question is, if something is not observed, does it exist? That’s a question of ontology.

    Epistemologically both options are identical – we do not and cannot ever know what things do when they’re not being observed, because by definition we cannot ever observe the unobserved doing it. But they are ontologically distinct, because in one the sound exists without it being observed, and in the other the act of observation causes the world as we know it to come into being.

    The tree-in-the-forest was intended as an analogy to illustrate why the collapse/many-worlds question is unanswerable scientifically. You can’t answer questions about what you can’t observe. It was also intended to illustrate why the Everett-Wheeler interpretation is nevertheless the better option – because it gives a simpler theory, without the need for peculiar long-range superluminal interactions needed to fill in the gaps and keep everything consistent.

    Perhaps a better analogy would be to ask: if a cat is in a box and there is nobody else inside to observe it, does it miaow?

  54. The biggest problem with saying umpteen kajillion universes solves anything is well, …..that more than there are.

    The price people seem willing to pay for this loophole is not even too high…….

    …..it’s simply ludicrous.

    Try this. Make up a story right now. Give your characters full names–dont even make the enlish names, how about Mr Dh hi yvpvuoyif and have him invrnt a jetpack, flying around fighting crime with a cape. Make up villians and get real detailed about whete they go and exactly what they say.

    Well that just happened precisely the moment you wrote it or hey…even before it happened.

    Poof, you’re a Prophet. That’s the price of infinite worlds. Forget it destroys probability and the very science used to even suggest it. Go to multiverse instead of just kickin the can down there so there’s a loophole –some excuse to explain the universe that conforms to atheism, because lets face it’s the only game in town.

    Everett was such a confused soul that he told his son to throw him out in the garbage when he died. Think about where these ideas are coming from. The people pushing them are atheist poster boys. When the data from fine tuning directly contradicts their worldview they do 3 things. They accept it…Flew, Crick etc. They pursue a way out thats not so obviously incoherent, Paul J. Steinhardt;. You invent myriad paths to multiverse and act like its just the logical consequences of their hypothesis, Guth Tegmark etc

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