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Notes & Queries 22 September 2008

Hugh Everett’s ‘many worlds’ interpretation of quantum mechanics spawned not just the idea of a multiverse, but apparently quite a few interpretations on what a multiverse implies. If you’re intrigued by the notion that our cosmos is one of what may be an infinite number of universes, you’ll want to read Dan Falk’s report in Sky & Telescope on the recent multiverse conference held at the Perimeter Institute for Theoretical Physics (Waterloo, ONT). Particularly interesting is the growth of multiverse thinking as string theory has come to the fore, with all the controversy that implies.

And then there’s the notion of ‘eternal inflation,’ which conceives of endless big bangs, each creating a separate cosmos. Laura Mersini-Houghton (University of North Carolina) is concerned about how multiverses spawned by quantum theory, string theory and inflation can be reconciled, as Falk notes:

…it’s not at all clear how these different kinds of multiverses – grounded in quite different physical theories – may be related to one another. Still, the fact that three different lines of reasoning, all rooted in modern physics, seem to be pointing the same way makes some feel there must be a connection. “My gut feeling is that these multiverses have to be related,” said Mersini-Houghton.

Nor should we forget the interesting philosophical questions such thinking suggests. What happens if every possible outcome happens with 100 percent probability? A many-worlds quantum theory leads to that result, but how does quantum theory live with the disappearance of probability itself? Hilary Greaves (Oxford) went at that one in this small session (about twenty participants) that examined not only the concept of a multiverse but the possibility that it doesn’t exist. Thus the Perimeter Institute’s own John Moffat, a specialist in general relativity, who says the multiverse “…is not the kind of science we’ve been doing since Galileo.” A good multiverse has plenty of room for skeptics.


If things closer to home carry more appeal, last month’s conference The Great Planet Debate: Science as Process got into familiar and controversial terrain in its discussion of how to define a planet. We now have eight planets as per the International Astronomical Union, but feeling at the conference seems to have been widespread in favor of revising that definition. The trick, of course, is in just how to do that. Possible definitions are all over the map, and I send you to this Planetary Science Institute news release to get the overview. Personally, I prefer the wider perspective that Larry Lebofsky (PSI) has to offer:

“We all have a conceptual image of a planet. Therefore, we need a term that encompasses all objects that orbit the Sun or other stars. The debate is a great teaching moment. Whether dwarf planets are grouped together with the classical planets is not as important as the process by which scientists arrived at their conclusions. Scientists look at the same information in different ways; there may be more than one ‘answer.’ Facts change. What we know now may not be what we know in two or three years. Learning to think critically and understanding how scientists organize facts to develop theories are lessons that will serve students for a lifetime.”

I’m assuming that what Lebofsky means is not so much that facts themselves change, but that our data continue to bring us new information about those facts. In any case, a call to think critically about the data influx is a worthwhile reminder that the way we do science carries implications for thinking and learning in any discipline.


This brief squib from the BBC relates European plans for a potential mission known as Marco Polo, now in feasibility studies. It’s an asteroid lander with the possibility of sample return, involving a small near-Earth asteroid of less than a kilometer in size. Mission launch would be approximately 2017. As I’ve often opined in these pages, an asteroid mission is a needed first step as we begin to develop the understanding — and the tools — we may one day need for possible asteroid deflection. The more we learn about the objects that could someday collide with Earth, the better prepared we’ll be should the need ever arise.

Comments on this entry are closed.

  • andy September 23, 2008, 5:09

    It is interesting that those who claim that the dynamics of how an object fits into a solar system should not be the criterion for planethood, but the physical properties should are not willing to go the whole way and relax all requirements of where the object is located. At times I’ve seen the argument that it is a problem if a planet undergoes a perturbation in its orbit and moves into a region where it is no longer a planet, yet the fact that this has apparently happened to Triton (which has gone from being an independent dwarf planet to a moon of Neptune) seems to be ignored. If the physical properties are the over-riding criterion for planethood, then worlds such as Triton and the other major moons in our solar system should be regarded as planets that happen to be in orbit around other planets…

  • Benjamin September 23, 2008, 7:34

    I attended an excellent lecture by Lawrence Krauss tonight, and he displayed this cartoon regarding string theory:

    Two stick figures are having a conversation. One says, “I just had an awesome idea. Suppose matter and energy are made of tiny, vibrating strings.”
    “What does that imply?”
    “I dunno.”

  • andy September 23, 2008, 8:25

    Benjamin: It’s from xkcd.

  • James M. Essig September 23, 2008, 13:19

    Hi Folks;

    Hilary Greaves’ position that the Multi-verse might not exist, even if such a position turns out to be correct, should not put a damper on humanities quest to venture out into the cosmos and explore.

    For those familiar with the concept of Cardinality, Aleph 0 is the infinity associated with the number of integers. Aleph 1 is the infinity associated with the number of real numbers. Likewise, there is said to exist Aleph 2, Aleph 3, and so on in a never ending series of ever greater cardinalities.

    Since the universe might be of infinite spatial extent, perhaps the Cardinality associated with the number of light-years in its spatial extent is greater than Aleph 0, for all we know, it may be of Aleph (10 EXP 12) or even a greater number of light years. We may literally have all eternity to explore the universe even if there is no multi-verse.

    If there is no multi-verse, we perhaps have a whole future eternal existence of the present universe to look forward to including all of the wonderful and perhaps non-predictable structures, phases changes, periods of inflation, new and exotic ETI life-forms and other entities to explore and that are yet to develop..
    However, I hope and very much want to believe that at least one multi-verse exist, perhaps even an unknown cardinality of multi-verses in a set of such of ever increasing number of elements.

    We as a civilization that has developed language with terms such as spirit, immaterial, eternal, and other such seemingly non-physical entities can do well to be open minded to the possibility of vast realms defined as such or having characteristics as such. If we could somehow explore or discover any such realms, that would entail a whole now frontier for exploration and discovery.

    Either way, regardless of whether there exists one or more multi-verses or not, our own universe can probably give us room to explore and travel ever further outward in an eternal process of exploration and progress. Heck, even just our observable universe has a scale which is hard to visualize and I think many phenomenon await our discovery within. One can imagine the potential huge number of ETI species and beings that we might discover and share with as well as learn from.

    So hopefully, there are innumerable multi-verses. But in case there is no multi-verse, I still say to all of us space heads take heart and prepare for an eternity of fun exploration. May the process of discovery never end.



  • Ronald September 23, 2008, 16:03

    James: thanks for yor vision.

    With ref. to you views on the universe and possible multiverse(s), have you ever had a look at my post of 28 August and Adam’s response, under post 2769 ‘Advanced Propulsion: The Next Steps’. I ask some questions with regard to the possible size of the total universe as opposed to the observable universe.

    Would you also care to have a (theoretical) go at it?

  • James M. Essig September 23, 2008, 23:50

    Hi Ronald;

    Thanks for the kind words.

    I just read your post of 28 August as well as Adam’s response.

    An interesting take on some possible limits or proposed values of the size of the Universe, or perhaps our portion of the multi-verse which we refer to as the Big Bang range, according to some aspects of Chaotic Inflationary Theory, from some huge number of light-years, in mathematical jargon, an ensemble number of light-years such as 10 EXP (10 EXP 12) light-years to an infinite extent.

    In some versions of the theory, the Big Bang as the entirely of the universe that resulted from our Big Bang has accordingly an ensemble, perhaps an infinite number, of so-called domains wherein each domain has its unique physical laws, fundamental constants, number of particle species etc. Each domain accordingly may be separated by some sort of boundary or topological barrier that accordingly keeps the laws of physics and fundamental constants in a given domain from destroying the integrity of the laws of physics, structures, and fundamental constants, etc., of the other domains, especially adjacent domains.

    These domains would have arisen in a manner that is analogous to the random orientation of the crystalline structures as subsets within a ice-cube, or the magnetic domains that exist within a permanent magnet, or the crystalline structure within a sample of an alloy. Each domain in space-time would have resulted from phase transitions that would have occurred within the overall big bang but wherein the freeze out of the laws of physics, fundamental constants, numbers and types of particles, etc, that are domain specific arose in a manner that is similar to the non-simultaneous and gradual freeze out of the sub-structures within a naturally forming ice cube with all of the variety of substructure crystalline orientations, undulations, and geometric boundary shapes that define the volume of the given crystalline sub-structures within an ice cube.

    Our Big Bang would accordingly have domains that would have a size ranging from perhaps as great as 10 EXP (10 EXP 12) light-years to domains that are of infinite extent in themselves. The really cool possibility is that there could be, accordingly, just within our Big Bang, which may be just one of an infinite number of Big Bangs, and infinite number of domains wherein each domain is of infinite extent.


    Your Friend Jim

  • Ronald September 25, 2008, 5:07

    James: thanks! In fact we are being served right away: see today’s (24 Sept.) post ‘A Dark Flow in the Cosmos’, which seems to pertain to the same issue!

  • ljk October 24, 2008, 7:47

    October 21, 2008

    The Many Worlds of Hugh Everett

    After his now celebrated theory of multiple universes met scorn, Hugh Everett abandoned the world of academic physics. He turned to top secret military research and led a tragic private life

    By Peter Byrne

    Editor’s Note: This story was originally printed in the December 2007 issue of Scientific American and is being reposted from our archive in light of a new documentary on PBS, Parallel Worlds, Parallel Lives.

    Hugh Everett III was a brilliant mathematician, an iconoclastic quantum theorist and, later, a successful defense contractor with access to the nation’s most sensitive military secrets. He introduced a new conception of reality to physics and influenced the course of world history at a time when nuclear Armageddon loomed large. To science-fiction aficionados, he remains a folk hero: the man who invented a quantum theory of multiple universes. To his children, he was someone else again: an emotionally unavailable father; “a lump of furniture sitting at the dining room table,” cigarette in hand. He was also a chain-smoking alcoholic who died prematurely.

    At least that is how his history played out in our fork of the universe. If the many-worlds theory that Everett developed when he was a student at Princeton University in the mid-1950s is correct, his life took many other turns in an unfathomable number of branching universes.

    Full article here:


  • ljk November 16, 2008, 23:18

    De Broglie-Bohm Pilot-Wave Theory: Many Worlds in Denial?

    Authors: Antony Valentini

    (Submitted on 5 Nov 2008 (v1), last revised 5 Nov 2008 (this version, v2))

    Abstract: We reply to claims (by Deutsch, Zeh, Brown and Wallace) that the pilot-wave theory of de Broglie and Bohm is really a many-worlds theory with a superfluous configuration appended to one of the worlds. Assuming that pilot-wave theory does contain an ontological pilot wave (a complex-valued field in configuration space), we show that such claims arise from not interpreting pilot-wave theory on its own terms. Specifically, the theory has its own (‘subquantum’) theory of measurement, and in general describes a ‘nonequilibrium’ state that violates the Born rule.

    Furthermore, in realistic models of the classical limit, one does not obtain localised pieces of an ontological pilot wave following alternative macroscopic trajectories: from a de Broglie-Bohm viewpoint, alternative trajectories are merely mathematical and not ontological. Thus, from the perspective of pilot-wave theory itself, many worlds are an illusion.

    It is further argued that, even leaving pilot-wave theory aside, the theory of many worlds is rooted in the intrinsically unlikely assumption that quantum measurements should be modelled on classical measurements, and is therefore unlikely to be true.

    Comments: 31 pages, 2 figures. To appear in: ‘Everett and his Critics’, eds. S. W. Saunders et al. (Oxford University Press, 2009)

    Subjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Theory (hep-th)

    Cite as: arXiv:0811.0810v2 [quant-ph]

    Submission history

    From: Antony Valentini [view email]

    [v1] Wed, 5 Nov 2008 20:34:46 GMT (88kb)

    [v2] Wed, 5 Nov 2008 21:55:12 GMT (88kb,D)


  • ljk November 17, 2008, 0:17

    November 13, 2008

    Parallel Universes: Are They More than a Figment of Our Imagination?

    “The multiverse is no longer a model, it is a consequence of our models.”

    – Aurelien Barrau, particle physicist at CERN

    The Hollywood blockbuster, The Golden Compass, adapted from the first volume of Pullman’s classic sci-fi trilogy, “His Dark Materials” portrays various universes as only one reality among many, but how realistic is this kind of classic sci-fi plot? While it hasn’t been proven yet, many highly respected and credible scientists are now saying there’s reason to believe that parallel dimensions could very well be more than figments of our imaginations.

    “The idea of multiple universes is more than a fantastic invention—it appears naturally within several scientific theories, and deserves to be taken seriously,” stated Aurelien Barrau, a French particle physicist at the European Organization for Nuclear Research (CERN).

    There are a variety of competing theories based on the idea of parallel universes, but the most basic idea is that if the universe is infinite, then everything that could possibly occur has happened, is happening, or will happen.

    Full article here:


  • ljk October 15, 2009, 9:10


    Thursday, October 15, 2009

    Physicists Calculate Number of Universes in the Multiverse

    If we live in a multiverse, it’s reasonable to ask how many other distinguishable universes we may share it with. Now physicists have an answer

    One of the curious developments in cosmology in recent years has been the emergence of the multiverse as a mainstream idea. Instead of the Big Bang producing a single uniform universe, the latest thinking is that it produced many different universes that appear locally uniform.

    One question that then arises is how many universes are there. That may sound like the sort of quantity that is inherently unknowable but Andrei Linde and Vitaly Vanchurin at Stanford University in California have worked out an answer, of sorts.

    Their answer goes like this. The Big Bang was essentially a quantum process which generated quantum fluctuations in the state of the early universe. The universe then underwent a period of rapid growth called inflation during which these perturbations were “frozen”, creating different initial classical conditions in different parts of the cosmos. Since each of these regions would have a different set of laws of low energy physics, they can be thought of as different universes.

    What Linde and Vanchurin have done is estimate how many different universes could have appeared as a result of this effect. Their answer is that this number must be proportional to the effect that caused the perturbations in the first place, a process called slow roll inflation, and in particular to the number “e-foldings” of slow roll inflation.

    Of course, the actual number depends critically on how you define the difference between universes.

    Linde and Vanchurin have applied some reasonable rules to calculate that the number of universes in the multiverse and have totted it up to at least 10^10^10^7. A “humungous” number is how they describe it, with no little understatement.

    How many of these could we actually see? What’s interesting here is that the properties of the observer become an important factor because of a limit to the amount of information that can be contained within any given volume of space, a number known as the Bekenstein limit, and by the limits of the human brain.

    Linde and Vanchurin say that total amount of information that can be absorbed by one individual during a lifetime is about 10^16 bits. So a typical human brain can have 10^10^16 configurations and so could never disintguish more than that number of different universes.

    10^10^16 is a big number but it is dwarfed by the “humungous” 10^10^10^7.

    “We have found that the strongest limit on the number of different locally distinguishable geometries is determined mostly by our abilities to distinguish between different universes and to remember our results,” say Linde and Vanchurin

    So the limit does not depend on the properties of the multiverse but on the properties of the observer.

    How profound is that!

    Ref: arxiv.org/abs/0910.1589: How Many Universes Are In The Multiverse?

  • ljk February 15, 2010, 22:23


    Wednesday, February 10, 2010

    The Drake Equation for the Multiverse

    The famous Drake equation estimates the number of intelligent civilizations in the Milky Way. A new approach asks how many might exist in the entire multiverse.

    In 1960, the astronomer Frank Drake devised an equation for estimating the number of intelligent civilizations in our galaxy. He did it by breaking down the problem into a hierarchy of various factors.

    He suggested that the total number of intelligent civilizations in the Milky Way depends first on the rate of star formation. He culled this number by estimating the fraction of these stars with rocky planets, the fraction of those planets that can and do support life and the fraction of these that go on to support intelligent life capable of communicating with us. The result is this equation:

    which is explained in more detail in this Wikipedia entry.

    Today, Marcelo Gleiser at Dartmouth College in New Hampshire points out that cosmology has moved on since the 1960s. One of the most provocative new ideas is that the universe we see is one of many, possibly one of an infinite number. One line of thinking is that the laws of physics may be very different in these universes and that carbon-based life could only have arisen in those where conditions were fine-tuned in a particular way. This is the anthropic principle.

    Consequently, says Gleiser, the Drake Equation needs updating to take the multiverse and the extra factors it introduces into account.

    He begins by considering the total set of universes in the multiverse and defines the subset in which the parameters and fundamental constants are compatible with the anthropic principle. This is the subset {c-cosmo}.

    He then considers the subset of these universes in which astrophysical conditions are ripe for star and galaxy formation {c-astro}. Next he looks at the subset of these in which planets form that are capable of harbouring life {c-life}. And finally he defines the subset of these in which complex life actually arises {c-complex life}.

    Then the conditions for complex life to emerge in a particular universe in the multiverse must satisfy the statement at the top of this post (where the composition symbol denotes ‘together with’).

    But there’s a problem: this is not an equation. To form a true Drake-like argument, Gleiser would need to assign probabilities to each of these sets allowing him to write an equation in which the assigned probabilities multiplied together, on one side of the equation, equal the fraction of universes where complex life emerges on the other side.

    Here he comes up against one of the great problems of modern cosmology–that without evidence to back up their veracity, many ideas in modern cosmology are little more than philosophy. So assigning a probability to the fraction of universes in the multiverse in which the fundamental constants and laws satisfy the anthropic principle is not just hard, but almost impossible to formulate at all.

    Take {c-cosmo} for example. Gleiser points out a few of the obvious parameters that would need to taken into account in deriving a probability. These are the vacuum energy density, matter-antimatter asymmetry, dark matter density, the couplings of the four fundamental forces and the masses of quarks and leptons so that hadrons and then nuclei can form after electroweak symmetry breaking. Try assigning a probability to that lot.

    Neither is it much easier for {c-astro}. This needs to take into account the fact that heavy elements seem to be important for the emergence of life which only seem to occur in galaxies above a certain mass and in stars of a certain type and age. Estimating the probability of these conditions occurring is still beyond astronomers.

    At first glance, the third set {c-life} ought to be easier to handle. This must take into account the planetary and chemical constraints on the formation of life. The presence of liquid water and various elements such as carbon, oxygen and nitrogen seem to be important as do more complex molecules. How common these conditions are, we don’t yet know.

    Finally there is {c-complex life}, which includes all the planetary factors that must coincide for complex life to emerge. These may include long term orbital stability, the presence of a magnetic field to protect delicate biomolecules, plate tectonics, a large moon and so on. That’s not so easy to estimate either.

    Many people have tried to put the numbers into Drake’s equation. The estimates for the number of intelligent civilisations in the Milky Way ranges from one (ours) to countless tens of thousands. Drake himself put the number at 10.

    Gleiser’s take on the Drake equation for the Multiverse is an interesting approach. What it tells us, however, is that our limited understanding of the universe today does not allow us to make any reasonable estimate of the number of intelligent lifeforms in the multiverse (more than one). And given the limits on what we can ever know about other universes, it’s likely that we’ll never be able to do much better than that.

    Ref: http://arxiv.org/abs/1002.1651: Drake Equation For the Multiverse: From String Landscape to Complex Life

  • ljk February 24, 2010, 8:51

    Questioning the anthropic principle


    Feb. 23, 2010

    MIT physicists have showed that universes quite different from ours still have elements similar to carbon, hydrogen, and oxygen, and could therefore evolve life forms quite similar to us, even when the masses of elementary particles called quarks are dramatically altered. Some physicists have theorized that only universes in which the laws of…