Column: Welcome to the Multiverse

Many of you may know that Discover is not only a web site that hosts a diverse collection of entertaining blogs, but also publishes a monthly “magazine” printed on paper. Wild, right? Just ask this baby, who can tell you that a magazine is kind of broken when compared to an iPad.

Nevertheless, people read these things like crazy. I have recently started contributing an occasional column to the print magazine, known as “Out There.” (Our blog neighbor Carl Zimmer has been columnizing about the brain for a while now.) My first column appeared in the October issue (which comes out in September), and is now online — check it out.

The issue I’m tackling, under the draconian word count limit of an actual print magazine, is whether it’s scientific to talk about the multiverse. (Spoiler: it is!) Let me know what you think.

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92 Responses to Column: Welcome to the Multiverse

  1. Gene says:

    I liked it. No doubt at this stage in the evolution of the theory we should look for as much collaborative evidence as is possible. This is the obvious strategy for now, but I’m not certain it ultimately works- given the complexity of the situation. My guess is that whether its in the context of the string landscape, or even the interpretation of QM, we will have to ultimately decide these realities on the basis of personal judgment rather than experiment alone.

  2. Justin says:

    Sean you’re undoubtedly a better physicist than me, but I think there is a mistake in your article: “Everything we see emerged 13.7 billion years ago from the hot, dense state known as the Big Bang, so we cannot observe anything more than 13.7 billion light-years away.”

    The edge of the observable universe is further away than that, owing to continual cosmic expansion during the 13.7 billion years that the light was traveling towards us; the comoving distance to the edge is now 46 billion light-years.

  3. Sean says:

    Hmm, I knew that. Not sure how that got into the column, whether it was my brain fart or an editing snafu… I’ll check.

  4. Joel Rice says:

    string theory would allow lots of possibilities, but it would be nice to have some reason to believe in the necessary supersymmetry that goes along with it. A different approach might be that one algebra defines all the particles and their relationships, which might well be fixed and not allow any adjustments. That would be different from Dirac Algebra defining the electron but not the photon, which has to be put in by hand, and invites fiddling with the coupling. Since one would not want any parameters put in by hand, if the algebra requires the construction of Atoms, there would be increasingly tight constraints on the mass of the electron, etc. In that view, all Bangs would be equivalent, and the ‘laws’ would be the same across all Bangs. Anyway, such an algebra would be a game-changer – rather different kind of critter from Dirac algebra.

  5. maybe, in response to justin (comment 2), you meant that nothing that happened more than 13.7 billion years ago can be observed. looking back in time, not in distance, as it were.

  6. Sean says:

    Upon further review, at one point in the editing process the phrase “so we cannot observe anything more than 13.7 billion light years away” was tacked onto the end of the sentence I wrote. I had a chance to catch it on the final pass, but didn’t. Will try to be more careful next time.

  7. Cosmonut says:

    Am I right in believing that the “diverse multiverse” isn’t really a prediction of either inflation or string theory ?

    If I understand right, inflation generically predicts a huge number of pocket universes where the “inflaton field” (whatever that is) decays. But for all we know, these might be identical to our own in terms of number of dimensions, constants of nature, etc.

    String theory in its current incarnation allows 10^500 solutions, but there is no evidence that any of these correspond to anything in reality.

    It is merely CONJECTURED that one of the 10^500 solutions corresponds to our own universe (not at all clear at the moment) and it is an even bigger conjecture (one which we don’t even know how to verify) that the other solutions might be realized in these other pocket universes.

    I wish the level of speculativeness was made more clear in articles about the multiverse, including this one. You did that very well in the video lecture on cosmic inflation.

    There’s nothing wrong with speculating about other universes, but I get annoyed when the multiverse is invoked as an “explanation”, for, say, why there are 3 dimensions of space.

    To use your analogy, this is like the inhabitants of your cloudy planet claiming that apples fall to the ground because “there are zillions of other worlds where apples move off in all possible directions. We just happen to be on the one where they fall down..”

  8. Bee says:

    I suppose if superluminal information exchange is possible the multiverse increases exponentially in scientification.

    (Our babies also grab and point at printed images and they’ve never seen a touch screen.)

  9. Spinons says:

    As Sean discussed in his Column, the multiverse pictures are mainly driven by two theoretical ideas: Inflation and String theory, both of which remain theoretical speculations at this stage.
    There is no experimental evidence definitely confirming either of these ideas.

    In this sense, I would say that the current multiverse mania is not that different from the approach of Giordano Bruno. By supplementing these ideas with a bunch of mathematical equations doesn’t make it a more scientific theory than pure philosophizing.

    I am not saying that scientists should not think about the possibility of multiverse. But to make it a solid physical science, one still needs experimental or observational results to verify it.

    By the way, at the end of the Column, the example of a tribe of primitive cos­mol­ogists seems to suggest the anthropic argument. Without experiments or observations, it is equally valid to say that their planet is so hospitable by Intelligent Design, which apparently makes sense to many people.

  10. Flagitious Nebulon says:

    You say,
    ” It’s possible that another universe bumped into ours early on and left a detectable signature in the cosmic background radiation…”

    But, as you have explained many times, our universe was initially smooth to a fantastic degree of accuracy — that´s where the arrow of time comes from. If another universe bumped into ours, even gently, wouldn´t that ruin the extreme initial smoothness [absent an extreme fine-tuning]?

  11. Sean says:

    It might, which is why the bumping would have to be extremely gentle indeed, and why the scenario is something of a long shot. But that doesn’t mean we shouldn’t look, which is exactly what people are doing:

  12. Marco Frasca says:

    Hi Sean,

    My view is that also people talking about atoms were considered foolish. So, I cannot say to you: “Please, do not discuss the argument of multiverse being just sci-fi”. I would be foolish my self…



  13. Count Iblis says:

    The funny thing is that if there exists a multiverse, then given that you don’t have precise information about even your own precise state, let alone of your local environment, you cannot locate yourself at precisely one spot in the multiverse. You can be any of a large number of similar copies that are located at a vast distance from each other, that have the same information about their local environments.

    Each has the same consciousness, so it would be wrong to say that out of these copies you are one of them and not some other and that you just don’t know which one. This makes the question of searching for evidence of the multiverse a bit ironic, you are already at multiple locations in the multiverse 🙂

  14. In his latest post, Peter Woit thinks that your argument is circular.

  15. Carleigh says:

    So, The Fried-Egg Cosmologist gets a column with Discover. I think that you will go down in the annals of science right next to Stanton Friedman, aka The Flying Saucer Physicist.


  16. Actually, String Theory and the multiverse are not science, according to the Great Scientists:

    “But before mankind could be ripe for a science which takes in the whole of reality, a second fundamental truth was needed, which only became common property among philosophers with the advent of Kepler and Galileo. Pure logical thinking cannot yield us any knowledge of the empirical world; all knowledge of reality starts from experience and ends in it. Propositions arrived at by purely logical means are completely empty as regards reality. Because Galileo saw this, and particularly because he drummed it into the scientific world, he is the father of modern physics–indeed, of modern science altogether.” -Albert Einstein, Ideas and Opinions. MDT’s dx4/dt=ic honors Galileo and Einstein, as it both “starts and ends” in experience!

    “Once it was recognised that the earth was not the center of the world, but only one of the smaller planets, the illusion of the central significance of man himself became untenable. Hence, Nicolaus Copernicus, through his work and the greatness of his personality, taught man to be honest.” -Albert Einstein, Message on the 410th Anniversary of the Death of Copernicus, 1953

    I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation-a fix-up to say, “Well, it might be true.” For example, the theory requires ten dimensions. Well, maybe there’s a way of wrapping up six of the dimensions. Yes, that’s all possible mathematically, but why not seven? . . . So the fact that it might disagree with experience is very tenuous, it doesn’t produce anything; it has to be excused most of the time. It doesn’t look right.–Nobel Lareate R.P. Feynman

    But superstring physicists have not yet shown that theory really works. They cannot demonstrate that the standard theory is a logical outcome of string theory. They cannot even be sure that their formalism includes a description of such things as protons and electrons. And they have not yet made even one teeny-tiny experimental prediction. Worst of all, superstring theory does not follow as a logical consequence of some appealing set of hypotheses about nature.—Nobel Laureate Sheldon Glashow

  17. Roger says:

    The main point of the article seems to be that Sean has a lot of untestable speculations, but it is all okay if we accept some redefinition of science.

  18. Dear Roger–why would we want to redefine science?

    What is wrong with Einstein’s, Galileo’s, Netwon’s, Bohr’s, Copernicus’s, and Feynman’s definition of science?


  19. Phil says:

    I’m posting this comment because Peter Woit turned off comments for his posting on this topic — something he rarely does, which leads me to think he does not want to see perfectly sensible comments that disagree with his opinion. I will offer such a comment.

    The truth of the matter is that string theory IS testable. Like quantum field theory, string theory has many possible theories. One particular QFT describes our universe pretty well and, therefore, can be regarded as an effective field theory to a more fundamental field theory we don’t know yet. String theory is one such possibility composed of many possible theories. One such theory is that which holds that TeV scale strings should appear at the LHC and that there are large extra dimensions capable of being observed at the LHC. The LHC has observed no such signatures, therefore that particular theory is wrong.

    But it is still in principle possible to test string theory. All you have to do is collide particles with ever increasing energy, all the way up to the Planck scale, and if you observe stringy behavior, extra dimensions, etc., and if you find a string theory that explains those measurements, then you have experimentally validated string theory. The same things is true for QFT. We found a particular QFT that matches with experiment, even though there are possibly an infinite number of possible QFTs. The same things can be done with string theory, only the wait and experimental effort needed will most likely be very very very long!

    So it’s NOT true to say that string theory is untestable because of the multiverse. It is untestable because we do not have the technology to conduct experiments at every energy scale all the way up to the Planck scale. When we do (if we do), we will have the ability to test string theory. But string theory IS in itself testable.

    Is there anything wrong with what I just said?

  20. Dear Phil,

    Actually, Nobel Laureate Physicists disagree with you:

    [String Theory] has no practical utility, however, other than to sustain the myth of the ultimate theory. There is no experimental evidence for the existence of strings in nature, nor does the special mathematics of string theory enable known experimental behavior to be calculated or predicted more easily. . . String theory is, in fact, a textbook case of Deceitful Turkey, a beautiful set of ideas that will always remain just barely out of reach. Far from a wonderful technological hope for a greater tomorrow, it is instead the tragic consequence of an obsolete belief system-in which emergence plays no role and dark law does not exist.[xlviii] —A Different Universe, Nobel Laureate Robert Laughlin

    It is anomalous to replace the four-dimensional continuum by a five-dimensional one and then subsequently to tie up artificially one of those five dimensions in order to account for the fact that it does not manifest itself. -Einstein to Ehrenfest (Imagine doing this for 10-30+ dimensions!)

    String theorists don’t make predictions, they make excuses[xl]. – Feynman, Nobel Laureate

    String theory is like a 50 year old woman wearing too much lipstick.[xli] -Robert Laughlin, Nobel Laureate

    Actually, I would not even be prepared to call string theory a “theory” rather a “model” or not even that: just a hunch. After all, a theory should come together with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions for them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?[xlii] –‘t Hooft, Nobel Laureate

    It is tragic, but now, we have the string theorists, thousands of them, that also dream of explaining all the features of nature. They just celebrated the 20th anniversary of superstring theory. So when one person spends 30 years, it’s a waste, but when thousands waste 20 years in modern day, they celebrate with champagne. I find that curious.[xliii] –Sheldon Glashow, Nobel Laureate


    Dr. E 🙂

  21. Brian Too says:

    @19. Phil,

    Yes, there is something wrong with what you said.

    My understanding is that in order to create experiments that operate at the Planck scale, you need a particle accelerator the size of the universe. One that would consume the entire resources of the universe!

    There is a world of difference between “testable in principle” and “testable by our civilization”. Any theory which cannot, in good faith, produce a viable testing regime within the next 100 years, falls into the realm of philosophy. Scientific dead ends.

    Why 100 years? It falls outside the lifetime of any scientist who would propose the theory needing testing. Worse yet, the passage of 100 years by no means brings the needed resources into reach. There is no visible mechanism or advance that provides hope, let alone assures, that 100 years from now, experimental verification will be possible. All that we know is that 100 years will have passed and very probably, a plausible testing regime will still be so far out of reach as to be invisible.

    Anything wrong with what I said (now watch the fur fly)?

  22. Stephen says:

    Last month I decided not to renew my Discover subscription of 8 years because of the global warming hysteria articles which have become a staple of every issue this year. I find out today that Discover decided to add a string theory/multiverse column that fits right in with the magazine’s pandering to pop culture pseudo-science. Authentic scientific journalism is backed up by experimental results not philosophical musings with circular reasoning. Maybe a new column should be about the fantastic misrepresentations made by the leading climate change evangelicals, oops I mean scientists. Discover was once a trusted science publication, those days have passed.

  23. Phil says:

    @20, Dr. Eliot,

    Do you have any thoughts of your own on this matter? If so, I would love to read them!

    @21 Brian,

    How do you know in 100 years, or in 1000 years, we won’t be technological enough to be able to somehow probe the Planck scale? Many years ago, people like you thought that atoms were forever unobservable. Now, we can manipulate atoms one by one and spell “IBM” with them.

    Maybe it will take a million years, or a billion years, until some species comes up with the technology to find out what happens at the Planck scale. And then we (or they) will know if the theory that describes their observations is string theory or something else.

    In other words, never say never. If string theory is right, there should be signs of it at the Planck scale and, who knows, maybe we’ll get there some day.

  24. Dear Phil,

    One of the reasons we know that String Theory makes no definitive predictions at the Planck scale is that String Theory has no definitive equations, nor solutions. So even when we find out what happens at the Planck scale, we won’t be testing String Theory, as String Theory has no equations. If, Phil, you happen to believe String Theory has definitive equations, please do share them. Thanks! Also please share the definitive masses of the particles ST predicts, while you’re at it.


    I agree with the Greats that Multiverses and Strings are “Cargo Cult Science,” which the Great Feynman warned us of:

    “But this long history of learning how not to fool ourselves–of
    having utter scientific integrity–is, I’m sorry to say, something
    that we haven’t specifically included in any particular course that
    I know of. We just hope you’ve caught on by osmosis.

    The first principle is that you must not fool yourself–and you are
    the easiest person to fool. So you have to be very careful about
    that. After you’ve not fooled yourself, it’s easy not to fool other
    scientists. You just have to be honest in a conventional way after

    I would like to add something that’s not essential to the science,
    but something I kind of believe, which is that you should not fool
    the layman when you’re talking as a scientist. I am not trying to
    tell you what to do about cheating on your wife, or fooling your
    girlfriend, or something like that, when you’re not trying to be
    a scientist, but just trying to be an ordinary human being. We’ll
    leave those problems up to you and your rabbi. I’m talking about
    a specific, extra type of integrity that is not lying, but bending
    over backwards to show how you are maybe wrong, that you ought to
    have when acting as a scientist. And this is our responsibility as
    scientists, certainly to other scientists, and I think to laymen.

    For example, I was a little surprised when I was talking to a
    friend who was going to go on the radio. He does work on cosmology
    and astronomy, and he wondered how he would explain what the
    applications of this work were. “Well,” I said, “there aren’t any.”
    He said, “Yes, but then we won’t get support for more research of
    this kind.” I think that’s kind of dishonest. If you’re
    representing yourself as a scientist, then you should explain to
    the layman what you’re doing–and if they don’t want to support you
    under those circumstances, then that’s their decision.”
    –Nobel Laureate R.P. Feynman

    Nobel Laureate Philip Anderson also recognizes the destructive nature of Cargo Cult Science such as string theory, which takes us on back to pre-Baconian methods:

    “My belief is based on the fact that string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do.

    The sad thing is that, as several young would-be theorists have explained to me, it is so highly developed that it is a full-time job just to keep up with it. That means that other avenues are not being explored by the bright, imaginative young people, and that alternative areer paths are blocked.” —Philip W. Anderson Physicist and Nobel laureate, Princeton

  25. Phil says:

    Dr. McGucken,

    I don’t claim to be able to calculate standard model parameters with string theory. String theory is not my field. But what do you mean by “no definitive equations, nor solutions”? What kind of equations are you talking about? As for solutions, aren’t there something like 10^500 solutions? If someone comes along and finds a solution that allows one to calculate SM parameters and agrees with the SM and GR at low energies, what then?