Alex Vilenkin – Many Worlds in One

By Mark Trodden | September 9, 2006 9:03 pm

I have just finished reading Alex Vilenkin’s book, Many Worlds in One: the Search for Other Universes.

The anthropic principle is a topic that so easily prompts hysteria and overreaction and, since we’re going to be mentioning it a few times, I might as well make it clear what I think. It is a perfectly logically possibility that some features of our universe are anthropically determined. If such a possibility is predicted by a theory that is viable in all other ways, then one should take it seriously as long as it can be tested. If one cannot test this particular prediction, then one might find it a compelling argument, but one will never know if it is correct.

Vilenkin is one of the world’s leading theoretical cosmologists. He has made seminal contributions to the theory of cosmological inflation, the idea that the universe may contain topological remnants from particle physics phase transitions, to quantum cosmology, and to many other central topics. Perhaps most importantly for the ideas in his book, he has been an architect of the idea of eternal inflation, and one of the primary researchers embracing its implications for the anthropic principle.

Two things struck me right away when I picked up the copy that Alex’s publisher sent to me. First, it is a small book by the standards of popular cosmology writing; just over 200 pages. Second, when you read the author blurb inside the back dust cover, you find it to be just a bare bones description of Alex’s track to his Professorship at Tufts University. The lack of author promotion material is another unusual feature, and, to the extent that I know Alex, is an accurate reflection of his modest character. One finds this tone continued through the entire book; it is refreshing and adds to the appeal of the subject matter.

Almost exactly half of the book, with the exception of a brief discussion of the future of life in the expanding universe, is devoted to a description of the standard model of cosmology and its inflationary extension. I find it extremely difficult to know whether a given pedagogical approach is useful for the general public, although I think this material is at no more complicated level than other books on related topics. However, I do think that Alex’s description is an exceptionally clear and uncluttered account of the material for anyone with an undergraduate physics education. All the more impressive is that this cosmic tour contains enough personal information and anecdotes to give the reader a real feeling for the excitement and camaraderie that is an essential part of being a scientist. Vilenkin’s enthusiasm for the subject matter, and his affection for his collaborators and his students is infectious and carries the reader along into the second half of the book.

This is where Vilenkin gets into the more speculative material. First comes a description of eternal inflation. In many inflationary models, there is an argument that, due to fluctuations of the inflaton, there will always be regions of the space-time that are undergoing inflation, even as there are other regions in which inflation ceases and, in a subset of these, universes with properties somewhat similar to ours begin.

Given our understanding of quantum field theory, and some assumptions allowing one to try to understand the effect that such fluctuations would have on the background space-time, eternal inflation seems like a reasonable aspect of many inflationary models. But it is important to emphasize that this is not yet completely firmly established, and there are subtleties that one might worry about in trying to infer a nonperturbative effect on space-time from a quantum effect. It would be wonderful to see this settled definitively in a quantum theory of gravity, such as string theory.

If eternal inflation does indeed take place, then Vilenkin argues for infinitely many realizations of non-inflating patches of the universe, with all possible values of constants of nature. This is then used to argue for an anthropic understanding of, for example, the cosmological constant.

Whether or not all this holds true, as I mentioned briefly above, depends on the correctness of inflation, the ultimate nature of the inflaton, and details of the ultimate theory of quantum gravity. To this end Alex devotes a chapter to string theory and, in particular, to the idea of the landscape as an example of how many different vacua, with different values of the cosmological constant might arise. This is, as many blogosphere readers will be aware, a controversial issue, and one that often gives rise to strong emotions. But Vilenkin confines his discussion of it to a chapter (and a few other comments here and there), and presents his central thesis without relying on the landscape. I found this very positive, not because I’m trying to make a deep point about the landscape, but because it makes Alex’s treatment more general, and hopefully will allow a wider interested readership access to the ideas without getting caught up in that particularly heated debate.

Many Worlds in One is a tour through one of the most exciting areas in modern physics, led by a modest guide, who most certainly has his own firm opinions, but who is much more interested in a serious discussion of the physics than in self-aggrandizement and evangelizing for a particular area. Vilenkin’s credentials in particle cosmology are unquestionable, and the book is fascinating as a selected review of his own contributions to the field.

Nevertheless, there are a number of comments in the book that I had problems with at one level or another. When Vilenkin first talks about the multiverse implications of eternal inflation he writes (on p.83)

The response I got from other colleagues was also less than enthusiastic. Physics is an observational science, they said, so we should refrain from making claims that cannot be observationally confirmed. We cannot observe other big bangs, nor can we observe distant inflating regions. They are all beyond our horizon, so how can we verify that they really exist? I was disheartened by such a cool reception…

I was a little surprised by this, since it seems to me to be merely a plain statement of what science really means. We get a better idea of what he means on p.91 when he writes

The main objection against it was that it was concerned with the universe beyond our horizon, which is not accessible to observation. But if the theory of inflation is supported by the data in the observable part of the universe, shouldn’t we also believe its conclusions about the parts that we cannot observe?

But again, I can’t really sign on to this way of looking at it, since I feel that one of the great strengths of science is the willingness to say “we don’t know” about things that are untestable, and to have to live with that.

Another criticism is that I would have liked to see a more detailed and complete discussion of the assumptions behind the conclusions Alex draws, and what needs to be done to put them on firmer ground or, in fact, refute them. What we have is a section, starting on p.116

SOME WAYS OUT: Many readers are, no doubt, wondering. … Is there any way to avoid these bizarre conclusions? … if you are willing to clutch at any straw at all to avoid it, let me offer you a couple of straws.

which is then followed by three short paragraphs – eight sentences – in which loopholes are briefly mentioned.

There are certainly other examples of individual comments with which I don’t agree, such as (p.151)

The observed value of the cosmological constant gives a strong indication that there is indeed a huge multiverse out there.

but these are small points.

I have gone into a little detail about some of the places where I take issue with Alex’s claims precisely because I want to be clear about my problems before stating that I actually liked this book very much and would most definitely recommend it to others. The writing is clear, the tone is appealing, and the science is discussed in an honest way, by a master who loves the subject. Vilenkin provides us not only with a fascinating account of the physics, but also with a fun and, in places, humorous picture of life as a scientist. (As a former MIT postdoc, the description of Alan Guth’s office had me smiling for a while)

In the end, I remain relatively unemotional about, but unconvinced by the arguments for an anthropic understanding of the cosmological constant. Of course, with significantly more theoretical progress that might change, as should always be the case. But whatever one thinks about this issue, Vilenkin’s book is a wonderful, likeable and refreshingly ego-free contribution to the popular discussion (there is plenty in there for experts to learn from as well). Even if you want nothing else but an excellent discussion of modern cosmology, it is well worth a read.

CATEGORIZED UNDER: Science, Science and Society, Words
  • Jack

    “but these are small points.”

    I’m afraid I don’t agree with this. I find it very disturbing when people present things like eternal inflation as just-about-certain when they are nothing of the sort. In particular, we have no idea whether string theory really allows things like nucleation of baby universes, etc. To take another example that has often been discussed here, we have a very poor understanding of the arrow of time, so how do we know how many baby universes have such arrows? But without that, how can we possibly assess *any* kind of anthropic claim? Again, I have seen Vilenkin talking about the “fact” that the universe is infinite as if that were something everyone knows, which is nonsense. Again, I, and I think many people, are very very suspicious of all arguments of the form, “yes, this process is unbelievably rare, but in an infinite universe it is bound to happen”. There used to be a time when finding that something was unbelievably rare was regarded as good reason for ignoring that possibility…..

    What I am trying to say is that there are a *lot* of good scientific reasons to be very skeptical indeed about eternal inflation and the claims made on its basis, and these are *not* the result of people droning on about Popperian falsificationism etc.

    I agree that Vilenkin seems like a nice guy, but I have to admit that I did not feel very sorry for him when, at a conference where he [bravely] described his anthropic stuff, the following speaker began by saying that it was fortunate for us all that the early universe was so good at generating monkeys, “and the rest is history!”

  • Louise

    From Mark’s description, there is plenty to disagree with. Although Alan is a nice person, the inflationary paradigm is leaking. It is similiar to strings in that 25 years of work have not turned it into a complete theory. Linking it to the landscape is like tieing your boat to the Titanic.

    Re Joanne’s post: The “toy model” in this paper is even less complete. It posits solely from observation that we live between periods of accelerated expansion, just as Earth is the centre of the Universe. GM=tc^3, people.

  • amanda

    “…, led by a modest guide, who most certainly has his own firm opinions, but who is much more interested in a serious discussion of the physics than in self-aggrandizement and evangelizing for a particular area.”

    Now that was quite an unfair dig at Professor Susskind!

  • Carl Brannen

    The best use for the anthropic principle is to keep us from assuming that an apparent symmetry is exact. The classic example is the orbit of the earth. The ancients thought it was exactly a circle. But the anthropic princple tells us that the earth’s orbit must not be very eccentric because life requires stability.

    Along that line, since life requires stability, shouldn’t we expect that the laws of physics (and chemistry) will not depend much on velocity or gravitational potential? Thus we have relativity theory derived as an anthropic principle, which leads to the question, is relativity exact.

  • Eugene

    There seems to be a hurry among many people to connect “eternal inflation” or “multiverse” to “anthropic arguments”.

    I don’t see what is so distasteful about the “unobservability” of the multiverse. Like Sean like to say, the multiverse is not a theory, it’s a framework. Eternal inflation is a mechanism which you can use to generate a multiverse, i.e. you can write down the Lagrangian for some eternal inflation model and use it to actually “compute” the structure of the multiverse. (Ok the computation is hard and difficult and nowhere near complete, but it’s a question we can try to answer.)

    Sure, you can’t observe the “rest” of the multiverse save the universe we are in. But eternal inflation is a statistical process : it makes statistical predictions on the probability distribution of the various parameters of the multiverse. You have one such measurement….or perhaps you have many if you count different “fundamental” parameters as different measurements of the multiverse (insert philosophical arguments either-or here).

    This is no different from the problem of the cosmic variance problem , the namesake of this blog. There you have 2l+1 measurements of some probability distribution (the fluctuations of the inflaton at large scale). In the multiverse, you have N number of measurements (N=1 if you subscribe to the “one universe = one measurement” camp, extreme cosmic variance!).

    Now, we all know the low multipole of the CMB is underpowered…people write tons of papers trying to come up with alternative theories to explain it. But there is nothing *wrong* philosophically with the standard inflation theory….we could just be living in an atypical realization of the universe. So if Dr XXX comes up with a theory that predicts a low multipole, which one would you believe? Of course science provides a way to answer that : you measure believability by confidence levels, 3sigma, 4sigma etc…

    If we are all comfortable with cosmic variance, then why do we instinctively react differently when we think about the “unobservability of the multiverse”? A model of eternal inflation (there are as many models as there are Lagrangians you can write down) makes some statistcal predictions about the universe we live in, we can make measurements, and then draw conclusions whether this model is believable or not. That sounds like science to me, and nowhere does the word “anthropic” appear.

  • another amanda

    I agree with Eugene, there is nothing wrong with talk about what lies beyond the horizon. But I also agree with Jack, that eternal inflation is heavily oversold. Too many people are trying to portray it as an “inevitable” consequence of believing in inflation. If somebody can come up with a really convincing version of inflation in string theory, plus a proof that that particular version is eternal, then I think we would have good reason to take the whole idea seriously, including what it says about what lies beyond the horizon. But we are a long, long way from that point. Sadly, Vilenkin seems to have a bad case of Susskindosis — the tendency to proclaim that one’s favourite wild speculation is believed by everyone. Wild speculation is fine and necessary. Just don’t tell the world that it’s a done deal. It ain’t.

  • Count Iblis

    You can also take this perspective. Compared to the Bible, the Multiverse makes more sense scientifically. So, one could promote the philosphical aspects of this as an alternative to traditional religion.

    All posible histories are realized. There is no need to worry too much about death, because you “always exist” somewhere in the multiverse.

    Can we prove this? No, but at least it is compatible with current scientific knowledge, no conflict with evolution etc.

  • http://www.anthropic-principle.ORG island

    The best use for the anthropic principle is to keep us from assuming that an apparent symmetry is exact.

    The best use for the anthropic principle is to let is know that asymmetry/traits/characteristics, are perpetually convolved inherently forth.


  • http://www.anthropic-principle.ORG island

    I see that Christine Dantas also has a review of this book:

    And I see that she doesn’t buy into the many worlds hype either…

    Like… it’s a mighty cold day in science when evidence that we’re not here by accident gets twisted into evidence that we are by adding an infinite number of extra entities, while the strongest MOST APPARENT implication doesn’t even receive equal time:

    The actual structure of the universe is in “dramatic contrast” to the “expectation”, so many fixed balance points that are all commonly/coincidentally pointing directly toward carbon-based life indicate that there is some good physical reason for it that is somehow “specially” related to the existence of carbon-based life.

    The clear implication is that WE ARE the freaking stability mechanism.


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  • Mark

    Just to be clear, in reference to comment #3; I don’t necessarily compare the book to any specific other piece of work by anyone else, and I merely comment on Vilenkin’s attitude, not on other people’s.

  • Thomas Dent

    You can’t have eternal inflation without inflation, so the theory has done fairly well already by passing the WMAP tests.

    And not all forms of inflation are compatible with eternal-ness. So it is conceivable that with better information about the inflationary potential from CMB etc. one could rule out some possibilities of eternal inflation.

    Conversely, if the universe does happen to be descibed by a model that eternally inflates then, so as to say, there is no stopping it, just as if you drop a coin down a mineshaft you can be pretty sure it will carry on going down beyond any point where you can see or hear it.

    So no crises appear with eternal inflation – *until* you start making some untestable assumptions about the properties of other unobservable universes, and start using their existence as an explanatory mechanism for things we see in ours.

    But it is *not true* that anthropic-like argumentation is untestable or unfalsifiable. Simply show that life could arise in another form which was not apparently fine-tuned, and you have buried the anthropoids once and for all.


    for the latest update in a – slightly silly because carbon-chauvinist – story along these lines.

    My favourite along these lines is to show that a Turing machine can be constructed out of black holes. So if the only thing in the Universe were black holes, it is still not impossible that some configuration could evolve with the intelligence to ask about its own origins…

    Only thing we really need for ‘life’ is a Universe that is big, lasts long and has sufficiently much stuff in it such that chaotic or complex dynamics can arise. Galaxies? stars? molecules? atoms? protons? … maybe not.

    *At most* the cosmological constant is somewhat susceptible to anthropics, with our current level of understanding of ‘life’.

  • http://www.anthropic-principle.ORG island

    But it is *not true* that anthropic-like argumentation is untestable or unfalsifiable.

    I don’t know whether to laugh or cry at the complete utter ignorance of the facts that people who also have an opinion about the AP commonly express.


    So I was just wondering how many theorists are giving equal time to investigating the OBVIOUS implication of this direct observational evidence that “the rest” are so desparately STILL trying to “explain-away”?
    Direct observational evidence in support of the Anthropic Principle includes the Cosmic microwave background radiation, whose anthropic relevance has only been partially “explained-away”:

    CERN Courier “Does the motion of the solar system affect the microwave sky?”

    “On the large-angle anomalies of the microwave sky.”

    “The Energy of Space That Isn’t Zero.”

    In this article, Lawrence Krauss is quoted as follows:
    “But when you look at CMB map, you also see that the structure that is observed, is in fact, in a weird way, correlated with the plane of the earth around the sun. Is this Copernicus coming back to haunt us? That’s crazy. We’re looking out at the whole universe. There’s no way there should be a correlation of structure with our motion of the earth around the sun — the plane of the earth around the sun — the ecliptic. That would say we are truly the center of the universe.”

    Remember, I didn’t ask about progress by those pre-motivated to “explain-away” this direct observational evidence, my question was more about the honest recognition of the smoking gun… that doesn’t appear to exist in science.

    The new results are either telling us that all of science is wrong and we’re the center of the universe, or maybe the data is imply incorrect, or maybe it’s telling us there’s something weird about the microwave background results and that maybe, maybe there’s something wrong with our theories on the larger scales. And of course as a theorist I’m certainly hoping it’s the latter, because I want theory to be wrong, not right, because if it’s wrong there’s still work left for the rest of us.
    -Lawrence Krauss

    The astro-ph/0508047 anomaly might soon be explained away if CMB radiation has a positive effect on the formation of planetary systems).

    No, that’s false, but do you have a clue why?… I didn’ think so…

  • Thomas Dent

    Dear Island,
    please either explain what in the Hoyle you are talking about, or cease and desist from insulting the understanding of your fellow commenters.

    You said, for one:

    … symmetry/traits/characteristics, are perpetually convolved inherently forth.

    Now, what does it mean for something to be ‘convolved forth’?

    And just what is it you are asking for ‘equal time’ to be given to?

    Be explicit.

  • http://www.anthropic-principle.ORG island

    Dear Island,
    please either explain what in the Hoyle you are talking about, or cease and desist from insulting the understanding of your fellow commenters.

    Dear Thomas, it isn’t me that is doing the insulting:

    Simply show that life could arise in another form which was not apparently fine-tuned, and you have buried the anthropoids once and for all.


    for the latest update in a – slightly silly because carbon-chauvinist – story along these lines.

    Okay, in the first place, the observed universe is carbon-rich by a ratio of approximately 10:1, but carbon based molecules and chains also form more readily when the ratio is reversed, (as is the case on Earth!), 10:1 in favor of the next most plausible life-form that we have been able to imagine, (silicon based life), so there is absolutely no justification for speculation about other forms of life in context with the known physics.

    2) The anthropic coincidences are near perfectly balanced between diameterically-opposing cumulatively-runway tendencies, (like the near-perfectly flat structuring of the universe), where any sustained deviation from “fine-tuning” sends conditions racing so far from your wildest dreams for what constitutes conditions for life, (at a expeonentially accelarating rate), that it would make your head swim.

    Those silly kids:

  • LambchopofGod

    Thomas D said: “And not all forms of inflation are compatible with eternal-ness. So it is conceivable that with better information about the inflationary potential from CMB etc. one could rule out some possibilities of eternal inflation.”

    Quite. Vilenkin et al have the attitude that there are *more* inflationary models that are eternal than there non-eternal models, *therefore* eternal inflation is all-but-inevitable. Likewise of course there are *more* wrong physical theories than there are right ones, so we should search for new theories of physics among those that we know to be wrong! This is perhaps an extension of the Popperian dogma that the best theories are those which are most easily falsified, so wrong theories are the best, since they are the most easily falsified of all…..

  • Count Iblis

    Even without eternal inflation you can have a multiverse. I haven’t read Vilenkin’s book yet, but from the reviews I’ve read, he seems to ignore other ways that lead to the multiverse.

    An alternative idea was postulated by Max Tegmark some time ago: The multiverse is just the set of all possible mathematical models. There is no “real physical world” that singles out one element of this ensemble. All the members of the ensemble are purely mathematical in nature. What we call “physical existence” is just how we (and “we” are nothing more than mathematical structures) find ourselves living embedded in a larger mathematical structure.

    Tegmark claimed that this theory has no free paramters whatsoever. This is not entirely true, because you need to define a probability distribution over this multiverse. You regain a single universe theory by assuming that the probability distribution is a delta function. For consistence, one has to assume that the probability distribution favors simpler models and decays exponentially as a function of the Kolmogorov complexity. So, in this setting one can actually derive the principle of Occam’s Razor.

  • http://www.anthropic-principle.ORG island

    Speaking of Occam, you’ll get the correct information from the CMB if we have a big bang right now, and this information, including structuring, will be “convolved” forth into the next universe, since there is no need for pre-inflation, nor an absolute cosmic singularity if this happens.

    You’d have to actually think about it without false dogmatic preconceived prejudice concerning what is wrongly assumed to be, “geocentric arrogance”, but a literal anthropic constraint on the forces demands that traits are inherent, which is all that we actually know without projecting to an unobserved idealization, so ad-hoc assumptions about multiverses aren’t warrented in lieu of a stability mechanism when there is no theoretical need for these extra entities.

    An anthropic constraint on the forces says that the universe will “evolve” its characteristics to higher orders of entropic efficiency, as proven by our leap from apes, to harness fire, and beyond…

    The *near*-perfectly symmetrical effort of our big bang is quite apparently made *toward* absolute symmetry.

    That’s what an anthropic constraint on the forces indicates, not a bunch of hokie-mokie “hype” assumptions about unnecessary additional entities that can’t be verified.

  • Count Iblis

    Island, I agree that one shouldn’t make unnecessary unverifiable assumptions. So, why not then dump the concept of a physical universe? That’s what I’ve written about on my blog.

  • http://www.anthropic-principle.ORG island

    Math killed physics, huh… ?

    I think that the idea that more than one universal configuration is even possible is one of the biggest cop-outs on first principles in the history of science, and I don’t buy dogmatic anticentrist disbelief as an excuse to reject anthropic specialness out of hand, especially when a true antropic cosmolgical principle has the potential to define a causally responsible ToE, (not to mention the stability mechanism that leads to insanity in science… *monkey picture of Alan Guth goes here*).

    … 😉

    I don’t buy the copout on first principles, and if you follow the timeline of cosmology you’ll find that something like what I described was what we were most naturally guided toward.

    Surely the structure of our universe follows the least action principle within the limitations of the restrictions that are placed by inherent asymmetry.

    Surely energy and mass are conserved.

    This is reality.

  • Jack

    Sigh….Gresham’s Law of Blogs: crackpot comments drive out non-crackpot comments…

  • http://www.anthropic-principle.ORG island

    Yeah, but what’s even worse is that law of morons: People that don’t know didley squat about whtat they’re looking at, but think that they can differentiate a crackpot from adam, without any support whatsoever for their lame statements.

    I think it’s about numer 2 in the crackpot index.

  • simoshka

    Dear Mark and blog participants,
    I’ve never written anything on the Internet, never mind to a blog. In fact, this is the first blog, I’ve ever READ in my life. I can’t evaluate physics in the book and participate in the discussion whether the author’s scientific theories are right, or his assumptions are correct, etc. – I am not qualified… I am simply trying to decide whether to BUY this book, whether it’s interesting to read, and will I learn something new without being BORED to death (I was with Brian Greene’s greatest bestseller on Earth).
    I’ve noticed a strange phenomenon that I want to offer for discussion and get some of your feedback. Here are my observations.
    On one hand:
    1) All 8 ‘Readers’ Reviews’ on Amazon gave it 5 stars – 100% rating. You don’t see that very often. 2) Mark, who wrote this thorough and very interesting review, ‘liked this book very much’. 3) Christine Dantas (thanks for the link, island!) found it a ‘fascinating reading’. (She also thinks that the front cover is ‘outstanding’ which is kind of funny).
    But on the other hand:
    1) It looks like other blog participants never read it — not a good sign; 2) Very few people read ‘Readers’ Reviews’ on Amazon as well; 3) Amazon Sales Rank is next to zero — nobody buys it; 4) This book does not have any reviews in the news media, not even one — forget about New York Times, Washington Post, Times, Newsweek, any other major paper or magazine. But where are reviews in Scientific American, Discover Magazine, Physics Today, at least?
    I read Lisa Randall’s book several months ago. It’s a good, well-written book. Before I bought it I researched it on the Internet as well. It has plenty of coverage in the press: reviews in New York Times, New Yorker, Newsweek and Boston Globe, to mention a few; over 3 HUNDRED clicks on readers’ ‘Spotlight Reviews’ on Amazon. I can and Boston Globe, to mention a few; over 3 HUNDRED clicks on readers’ ‘Spotlight Reviews’ on Amazon. I can go on… If Vilenkin’s book is so interesting, why nobody even mentions it or talks about it? How can a layman decide if he is like me interested in science? I don’t understand this phenomenon but may be you do. I found plenty of coverage for other physics books, e.g. Smolin’s “The Trouble With Physics”, Woit’s “Not Even Wrong” or Primack’s “The View from the Center of the Universe”. Shall I buy one of them instead? What do you think?

  • http://www.anthropic-principle.ORG island

    I personally think that you can learn a lot from Alexander Vilenkin, so a popular book should be good. As far as which *cosmology* is “right” or wrong, this is yet to be determined, possibly to be decided by a complete theory of quantum gravity or a theory of everything.

    Until that happens, all assumptions are supposed to be subject to suspect review, given new physics, and regardless of popular opinion. Even then, a less complex or more accurate representation will be, more-“right”.

  • Count Iblis


    Many posters here are insiders who regularly read scientific articles. By the time some scientist writes a popular book, the contents are “old news”. If you’ve read the reviews you can pretty much guess what’s in the book.

    There are actually two articles by Vilenkin that are accessible to lay people:

  • simoshka

    I think I did a poor job explaining myself.
    Apart from general subject of particle physics/cosmology, I don’t care much about book’s specific contents, and since I don’t (and won’t) read scientific articles, “old news” for you are “new news” for me. I wasn’t trying to find out what is in the book but rather if it’s a GOOD book, an INTERESTING book, a book that is enjoyable reading. I failed because of ‘on one hand’ vs. ‘on the other hand’ problem. So, I am asking a slightly more general question: if the book is really good, why there is not a SINGLE review and nobody even mentions it in the media? I read only few pop science books but they all had reviews, radio shows, etc., and they were not particularly good or well written. Does anybody have an explanation or a clue? What does Mark think? After all, he read it. Thank you.

  • Mark

    I don’t have much time to answer today, but I would say it is pretty well written, and that it is enjoyable because the writing is succinct, explaining the concepts in a clear and economical way. I enjoyed it and think you might.

    I think review have just been slow coming out – I know a number are in the works at various publications.

  • Delia

    Speaking of reviews, I thought Lubos Motl’s review on was very interesting and quite funny too. Although Motl is a strong opponent of anthropic reasoning, he says that Vilenkin’s book is clearly written, very entertaining and worthy of a 5 star rating!

  • simoshka

    Thank you very much, Mark. You’ve convinced me 100%, I am getting the book. I do appreciate you taking time to respond. After all it’s a totally trivial and insignificant issue.

  • Jeffsan

    Re Euguene’s and Another Amanda’s posts (# 5 & 6) on making conclusions re the unobservable from the observable, Einstein made an insightful and amusing comment in a letter to Willem de Sitter in 1917. It was at the time when Einstein had just developed his cosmological solution to the GR field equations and had introduced his cosmological constant to keep his model universe static. He admitted to de Sitter “I have erected but a lofty castle in the air”, noting that his model was untestable by observation. He wrote: “I compare the space to a cloth floating (at rest) in the air, a certain part of which we can observe. This part is slightly curved similarly to a small section of a sphere’s surface. We philosophize on how we must construe the continuation of the cloth so that an equilibrium is reached in its tangential tension, whether it is fastened in position at the edges, extends infinitely, or has a finite size and is a closed unit. Heine has provided the answer in a poem: ‘And a fool waits for an answer.’ So let us be satisfied and not expect an answer…” De Sitter replied “Well, if you do not want to impose your conception on reality, then we are in agreement.” But he ended up arguing with Einstein and hated the cosmological constant. Thought you’d enjoy this historical tidbit.

  • Don Severs

    I don’t see any difference between extrapolating from the observable universe to the multiverse and extrapolating from the observed universe to the observable universe. Both involve guesswork and are still valuable. I admired Vilenkin’s courage in going so far afield from empirical physics, just to see what he could learn. I think his investigations are extremely fruitful, particularly in identifying limiting cases and flaws in prevalent ideas.

  • Don Severs

    Can anyone elucidate this key point that Vilenkin doesn’t explain: Why are his O-regions spatially infinite? How can there be an infinite amount of matter in them? These traits are central to his claim that there are a finite number of histories, thus an infinite number of copies of those histories.

  • simoshka

    O-regions are NOT spatially infinite. It’s just a sphere with radius equal to the cosmic horizon. It’s finite by definition but each “island universe” contains an infinite number of them. I recently found a very clear explanation by Vilenkin himself on Here is the link: You might also find it helpful.

  • Plato

    While I have not read the book either I am still “drawn to the debate” about what the “anthropic reasoning” is talking about at a fundamental level?

    So as a layman I am curious too ,about views here and what the basis could lead too, in terms of what our universe had become?

    If “carbon” wasn’t present at the beginning, then how would you explain “our universe?”

  • Plato

    By implcation, we can say a lot?

  • simoshka

    I did buy the book and almost finished it already. I would strongly recommend you to do the same. It’s a wonderful book, a delight to read, it is very different from all other pop-physics books I ever read. Vilenkin is a very good writer, he writes in a literary language which is normally reserved for fiction. He does not give you all the answers immediately, so you are interested in what is coming next. He is also witty and illustrates his text with great cartoons. His book presents the whole picture of the Universe, not just Anthropic arguments, and all pieces of the puzzle fit remarkably well. (If you are specifically interested in anthropic discussion, there is a great piece from the book on, I put the link in my previous post).
    For some unknown reason (to me!) the book didn’t attract a lot of attention; it doesn’t get exposure and publicity it deserves in my view, it has practically no reviews in the press. There are 8 reviews from readers on Amazon, all gave the book 5 stars, well justified. In short you will never regret spending 15 bucks for such a wonderful reading, it’s truly a BARGAIN!

  • Plato


    Yes I did indeed copy your link, to the book on “your reference” to Vilenken.

    I just purchased Lee Smolins “What’s the troube with physics” so I am going through that slowly. I will definitiely have a look. Yours and others who gave good comments, are encouraging.

    Thank you

  • Pingback: The Trouble With Physics | Cosmic Variance()

  • simoshka

    There is a recent review of Vilenkin’s book written by the founder of Autodesk, Inc. John Walker and posted in Switzerland. I found this review EXTREMELY INTERESTING and informative. Here is the link:
    Fourmilog: None Dare Call It Reason: Reading List: Many Worlds in One

  • simoshka

    Oops, the link didn’t work. Here it is again if anybody still cares:

  • Pingback: Coast to Coast | Cosmic Variance()


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Cosmic Variance

Random samplings from a universe of ideas.

About Mark Trodden

Mark Trodden holds the Fay R. and Eugene L. Langberg Endowed Chair in Physics and is co-director of the Center for Particle Cosmology at the University of Pennsylvania. He is a theoretical physicist working on particle physics and gravity— in particular on the roles they play in the evolution and structure of the universe. When asked for a short phrase to describe his research area, he says he is a particle cosmologist.


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