Hints of ‘time before Big Bang’

The BBC is running a story entitled Hints of ‘time before Big Bang’ based on Sean Carroll’s latest efforts to promote the multiverse. The writer attended Sean’s talk at the recent AAS meeting and presumably also read Sean’s new Scientific American article, and here’s what he got out of them:

A team of physicists has claimed that our view of the early Universe may contain the signature of a time before the Big Bang…

Their model may help explain why we experience time moving in a straight line from yesterday into tomorrow…

Their model suggests that new universes could be created spontaneously from apparently empty space. From inside the parent universe, the event would be surprisingly unspectacular.

Describing the team’s work at a meeting of the American Astronomical Society (AAS) in St Louis, Missouri, co-author Professor Sean Carroll explained that “a universe could form inside this room and we’d never know”.

The inspiration for their theory isn’t just an explanation for the Big Bang our Universe experienced 13.7 billion years ago, but lies in an attempt to explain one of the largest mysteries in physics – why time seems to move in one direction…

“Every time you break an egg or spill a glass of water you’re learning about the Big Bang,” Professor Carroll explained…

If the Caltech team’s work is correct, we may already have the first information about what came before our own Universe.

Besides the “Does Time Run Backwards in Other Universes?” material from his paper with Jennifer Chen discussed in Scientific American, what’s new here is his recent paper with two Caltech collaborators about the possibility of explaining an asymmetry of marginal statistical significance observed in the CMB by invoking a more complicated version of inflation, adding a “curvaton” field to the usual inflaton. In their model, this asymmetry comes from a perturbation to the curvaton field of size larger than the horizon. Such a thing could in principle make testable predictions, but doesn’t necessarily come from the existence of a multiverse or tell us anything about it. The authors throw in one clause of a sentence about how it might occur as

a remnant of the pre-inflationary epoch or as a signature of superhorizon curvaton-web structures.

and that’s the basis of the BBC article. I have no idea what’s going on with the business about universes forming inside of rooms and us not knowing anything about this.

Sean gives more details about this in a new blog posting.

Update: The author of the piece, Chris Lintott, has a blog, and a posting about the article, where he writes:

What made me want to write the story in the first place, though, was exactly what Sean said above – to an outsider to the field the idea that it is even imaginable that we might be able to make concrete predictions from ideas about multiverses which have haunted the pages of New Scientist and its ilk for decades is stunning. That’s what I wanted to get across.

He doesn’t seem to realize that there’s nothing here different than the things he’s thinking of that “have haunted the pages of New Scientist and its ilk for decades.”

Update: This story is getting the full media treatment, including haunting the pages of New Scientist, which has the sense to strip out the nonsense and hype about the multiverse and the arrow of time. Slashdot emphasizes the part about:

Describing the team’s work at a meeting of the American Astronomical Society (AAS) in St Louis, Missouri, co-author Professor Sean Carroll explained that ‘a universe could form inside this room and we’d never know.'”

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57 Responses to Hints of ‘time before Big Bang’

  1. anon. says:

    ‘I have no idea what’s going on with the business about universes forming inside of rooms and us not knowing anything about this.’

    If time is going backwards in the universes that form in your room, they will instantly disappear into the past, so you can’t see them.

  2. Peter Woit says:


    Thanks, I was having trouble figuring that one out.

  3. hmmm says:

    I wonder how many unobservable universes will be produced at CERN.

  4. Chris says:

    Thanks for the link. Sean in his talk made a possible connection between pre-inflationary structure and the observations contained in the paper. As you say

    “Such a thing could in principle make testable predictions, but doesn’t necessarily come from the existence of a multiverse or tell us anything about it.”

    The ‘could in principle’ was new to me as an astronomer, not a cosmologist, and I thought that was worth writing about. Perhaps these ideas have been floating for a while, but it was the first time I’ve heard a talk that directly suggested we could – even in principle – hope to probe pre-inflationary structure. That’s a better and more interesting story than the classic multiverse with no observable consequences which I was unfairly throwing at New Scientist.

    If that’s common knowledge among those who work in this field, then you should all shout louder.

  5. Jayvee says:

    According to this week’s New Scientist, Benjamin Wandelt has discovered the non-gaussianities that Sean is looking for in the cosmic microwave background.

  6. Peter Shor says:

    anon says “If time is going backwards in the universes that form in your room, they will instantly disappear into the past, so you can’t see them.”

    I don’t understand. If there are backwards-going universes that are currently forming in my room, won’t I remember them having been there yesterday?

  7. wolfgang says:

    > If there are backwards-going universes that are currently forming in my room, won’t I remember them having been there yesterday?

    No. you would remember that they have been there tomorrow 😎

  8. jpd says:

    i think the tense you want is “will have been”

  9. Thor says:

    Perhaps there are many universes, each with it’s own point of origin or big bang like expanding soap bubbles. And spots inbetween where matter from different big bangs gather in massive black holes. Then when each of those black holes reaches some critical point or some other criteria it explodes with a big bang, forming a new universe. That’s my theory at lest.
    Note that scientists can only inspect the universe to the degree their equipment allows, and the universe is hugenormous.

  10. Amos says:

    “If time is going backwards in the universes that form in your room, they will instantly disappear into the past, so you can’t see them.”

    Wouldn’t this violate the conservation of… like everything?

  11. M.Wang says:

    The host really makes the paper sound like lame beyond belief. Does anyone have a rational retort, i.e. an argument why this line of research should not be dismissed off-hand as meaningless mumble-jumble?

  12. Sakura-chan says:

    This story has reached the heady depths of the Xbox forum I frequent. http://forum.teamxbox.com/showthread.php?t=583146

  13. “Never understimate the power of Human Stupidity in large groups [ science challenged journalists ]”
    — anonymous

    A good example is a post by Joanne @Cosmicvariance

    My senior science teacher summed it up best by saying `What you said was probably correct, but it’s not what you say to a newspaper reporter.’ That’s when I should have learned to be careful with reporters.

    Two weeks ago, it happened again. The good folks in the SLAC publicity office are starting a feature where every few weeks a piece of work from the SLAC theory group will be highlighted. Great idea, I thought! I was the first guinea pig and was asked to do an interview for an article on a paper I wrote last Spring. The work was cute, has a catchy title, and is published in Physical Review Letters, but is not going to change life on earth as we know it. The article was to be for the internal SLAC newsletter TIP (The Interaction Point) and would also make a brief appearance on SLAC Today, the daily newsboard for the SLAC community.

    Next thing I knew, the headline

    SLAC Physicists Develop Test for String Theory

    was emblazened on the main SLAC homepage! Then Peter Woit of Not Even Wrong lashed onto it. Then it was picked up by PhysOrg.com, which was subsequently featured by Slashdot. All with a smiling picture of yours truly, supposedly devising a definitive test for all of string theory. AARGH!!!!

    The entire article was misrepresented, blown up out of proportion, and I could not have been more upset. Nothing against the good folks at the communications office at SLAC – we worked on this together and none of us saw this coming. Nonetheless, I did not have a good week.

    The remedy? We posted comments on all the blogs and revised the article to include the scientific details which then put our work into proper context.

    I recall P. Woit & Bee complaining (rightfully) about poor Science coverage in media, e.g. New Scientist.

    Why do you keep pandering to these idiots?

    The physics blogosphere needs to realize that blogs can be used for Journalism (Content/Distribution model). You no longer have to use a [ science-challenged ] journalist as an intermediary to the Media (Standard Model of TV, newspaper, etc). You Can Do It Yourself.

    It’s trivial to setup an RSS feed to iTunes (from WordPress, Blogger blog), & blog with video. There are solutions out there which will automatically set you up with an iTunes video-podcast. Presto..YOU are a scientist reporting the Science News as It Should!! Over the iTunes portal (with its powerful search engine), which has numerous distribution points: iPod/iPhone (mobile media device..over a hundred million units), AppleTV (living room set top box, reaching the public in the comfort of their living room), Internet (embedded Flash or Quicktime videos, i.e. Internet website). See for example:

    [ search in iTunes using “physics”, “string theory”, “lisa randall”, etc ]

    Based on my multimedia project, I’ve tried to encourage physicists to video-blog, to no avail (here, Backreaction, Arcadian Functor, CV). I know the mentality (since I am guilty of it myself): “It is illogical for Technical types to use an emotional argument”.

    “Facts Tell, Stories SELL”
    — marketing pots&pans, auto-racing, etc

    Scientists fall into the trap of using Facts to “sell” to the public, when in fact they should be “telling a story”. In a sense, this is what S. Carroll is doing: he’s “weaving a [ fairy ] tale”. The G. Lisi publicity (Next Einstein, surfer dude, et al) is the correct strategy..which is widely criticized in the Physics community!! Take the JPL Rover mission, geophysicist Dr. M. Golembeck was considered “the story” (because of his personality: boyish looks & enthusiasm).

    At least L. Motl/TRF embraces extensive use of Youtube videos in his blogging (Youtube is a video-sharing service).

    L. Motl/TRF (“End of Science”):

    Nevertheless, the author of the stupidity from 1997, after those ten years that have demonstrated that his stupidity is among the greatest stupidities that have ever been pronounced by homo sapiens, has the stomach to come in front of a conference in Portugal and repeat the same stupidity.

    How is it possible? Well, it is because there are almost no people who would be pointing their fingers at this – very politely speaking – intellectual shit that keeps on contaminating the public sphere. That’s why the likes of Horgan keep on thriving. If we allow them to thrive, they can indeed force science to end on a sunny day in the future. This is the only way how science could possible end. Let’s not allow it.

    Lumo is 1 of the few physicists “starring” in their own Youtube productions, a Tom & Jerry rendition (entertainment). Max Tegmark recently did a musical skit for his MIT class.

    A) Information
    physics, etc

    B) Entertainment
    “the sizzle sells the steak” as the saying goes. Looks, musical ability, personality (incl strange behavior), etc.

    The flawed reasoning by HEP community (which is the cause of the Fiscal 2008 crisis) is that they are selling A), instead of A+B. I.e., they need a mult-dimensional model (call it a “multiverse” of solutions) for marketing to the masses. That’s how NASCAR (a geographically niche, gear-head techno thing) made their breakthrough to the masses (leapt past Baseball as the No 2 sport in USA!!??). There are enough physicist baseball fans (Joanne, et al) to understand the enormity of this. Simlarly, Formula 1 (auto racing) is the No 1 watched sport in the World (exceeding Soccer).

    “Life’s a Stage”
    — Shakespeare

    S. Carroll/CV understands this, & that is exactly what he’s doing: “pulling an act” (marketing his research) for the Media. He had a long post about how to “play the game” in Academia: “suck it up” (Bee & others found it somewhat offensive)

    “People don’t buy Good Products [ research ], they buy GOOD MARKETING”
    — business saying

    Physics is not that different from the Business World. You have a product, you have to sell it, you have to get funding. “You have to learn to sell yourself” (advice given to Bee by her advisor). Here’s an example from Caltech/IPAC:

    from Kip Thorne’s PhD student (who works at IPAC):

    1) He who has the Gold..rules
    funding issues

    2) Schmoozing & Salesmanship are important
    marketing/sales, aka “kissing a**” as per M. Franklin/Harvard

    3) Dealing with Difficult people
    “Suppose you were an idiot, suppose you were a Congressman..but I repeat myself”/Mark Twain

    Face it, we live in an Imperfect World. Deal with it (or not).

    Guess what? There is a “sleeping giant” & it’s Kea..she’s the key to a Physics marketing breakthrough. L. Randall is 2nd. Hint: extreme outdoorsmanship & survival. Perfect subject matter for media coverage: TV, movie, etc. I’ve recently been contacted by National Geographic documentary (I know the chief illustrations editor), chief of ABC prime-time programming, BBC Documentary. Hit them up with proposals.

  14. Eric H says:

    Your comments about becoming a better showman put me into a cold sweat. I don’t think the answer to the ignoramuses promoting multiverses inside a coffee cup is to fight fire with fire. For one thing, many of the best minds that go into science fields go there because because they have a basically reflective temperament. They don’t want to stir up the atmosphere around them so much that they can no longer be objective in their own thinking. This problem always comes with being too publicly pushy in one’s ideas. Once your name is firmly established in the public mind with a specific point of view, it is very difficult to unwed yourself from it. People with a more humble and denigrating temperament – i.e. the best people in science – know this. They know that, even with a great preponderance of evidence in their favor, that the future can be somewhat unpenatrable.

    The problem is that the worst people in science, and for that matter in general, have no such problem. They go along quite swimmingly with any change that proves they have been alarmingly wrong. And like politicians and neo-conservatives declare that they secretly suspected the new information all along – no shame and no regret to their prior public declarations. Maybe you want to try to compete with those kind of people in that kind of salesmanship but I sure wouldn’t attempt it. I’d feel sort of dirty.

  15. ProfM says:


    Why do you allow this meaningless, offensive and irrelevant exchange of opinions to take place on your blog? The last two entries are good examples. These pathetic conversations have nothing to do at all with the issue of testability in String Theory!
    People enter your blog to be educated but they are turned away by significant loud noise and mumble-jumble.

    I know that you are going to delete my message right away. But you cannot hide the truth!

  16. Tony Smith says:

    Adrienne Erickcek, Marc Kamionkowski, and Sean Carroll (all of Caltech)
    in arXiv 0806.0377 astro-ph said:
    “… there is an anomaly in the CMB: measurements from the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the temperature-fluctuation amplitude is larger, by roughly 10%, in one hemisphere than in the other. This power asymmetry occurs at the 99% C.L. …
    the observed CMB fluctuations … appear to be modulated by a dipole …
    More precisely, the fluctuation amplitude in one half of the Universe is higher, by about 10%, than in the other half …
    it cannot be attributed to any known astrophysical foreground or experimental artifact.
    This asymmetry has gone largely unnoticed
    (as opposed to the “axis of evil”, an apparent alignment of only the lowest multipole moments) …”.

    in a 2006 Physics Nobel Prize powerpoint (slide 17) at
    Piet Mulders said, about the work of Mather and Smoot:

    “… COBE and WMAP … A dipole effect corresponding to the motion of Earth with respect to CMB rest frame (about 600 km/s) …”.

    Is there any reason to reject the explanation of such a dipole asymmetry by “the motion of Earth with respect to the CMB rest frame”?

    Tony Smith

  17. Christine says:

    Tony Smith,

    I could be mistaken, but Isn’t the CMB dipole anisotropy about two orders of magnitude above the other CMB anisotropies? Those authors do not appear to be talking about the amplitude of CMB dipole per se, but a 10% fluctuation of it.

  18. Tony Smith says:

    Christine, thanks for explaining to me that “Those authors … appear to be talking … about a 10% fluctuation of … CMB dipole …”.

    Does that mean that there are 3 relevant axes ?

    dipole axis of amplitude – due to motion with respect to the Cosmic Microwave Background. – according to astro-ph/0302207 (First Year WMAP) “… COBE determined the dipole amplitude is 3.353 +/- 0.024 mK in the direction (l, b) = (264.26 degrees +/- 0.33 degrees, 48.22 degrees +/- 0.13 degrees),
    where l is Galactic longitude and b is Galactic latitude …”.

    dipole axis of fluctuations – according to astro-ph/0701089 (Hemispherical power asymmetry) “… in Bayesian terms, the log-evidence difference is about 1.5 to 1.8, corresponding to odds of one to five or six. … Thus, there is still a chance that the effect may be a fluke, and most likely, this will remain the situation until Planck provides new data in some five years …
    The best-fit modulation dipole axis points toward (l, b) = (225 degrees, −27 degrees) …
    much effort has been spent by theorists on providing possible
    physical explanations …
    second order gravitational effects from local inhomogeneities – Tomita 2005;
    the presence of local voids – Inoue and Silk 2006 …”,

    quadrupole/octupole axis (axis of evil) – according to astro-ph/0302496 (cleaned CMB map from WMAP) “… The preferred axes … for the quadrupole and octopole … are … both roughly in the direction of (l, b) = (−110 degrees, 60 degrees) in Virgo …”.

    So, is it fair to say that:
    the dipole axis of fluctuation as of now is hard to distinguish from an irrelevant fluke;
    even if it might turn out to be real,
    it might be explainable in conventional physics terms, including but not necessarily limited to those described by:

    Tomita (astro-ph/0505157) “… The present state of our universe is … locally complicated and associated with nonlinear behavior on various scales, and so the observed quantities of CMB anisotropies may include some small effects caused by large-scale local inhomogeneities through nonlinear process. … there is a non-trivial north-south asymmetry in various quantities about CMB anisotropies … based on the relativistic second-order theory of perturbations in nonzero-/\ flat cosmological models … and on the second-order formula of CMB anisotropies … it is found that there is a possibility to explain the small north-south asymmetry of CMB anisotropies …”.

    Inoue (0710.2404 (astro-ph)) “… various types of anomalies have been reported after the release the WMAP data … an asymmetry in the large-angle power between opposite hemispheres … Inoue and Silk 2006 … explored the possibility that the CMB is affected by a small number
    of compensated local dust-filled voids … The Shapley supercluster
    (SCC) is near the tangential point of the two local large voids. The mysterious correlation with the ecliptic plane can be explained naturally because the ecliptic plane is by chance tangential to the CMB dipole that originates from a mass concentration around the SCC …”.

    Tony Smith

  19. anon. says:

    “… dipole axis of amplitude – due to motion with respect to the Cosmic Microwave Background. – according to astro-ph/0302207 (First Year WMAP) “… COBE determined the dipole amplitude is 3.353 +/- 0.024 mK in the direction …”.”

    ‘Dipole axis of amplitude’ is a very polite euphemism for this massive +/- 3mK cosine anistrophy in the CBR, compared to the original name given by discoverer R. A. Muller in his Scientific American article (v238, May 1978, pp. 64-74): see http://adsabs.harvard.edu/abs/1978SciAm.238…64M

    (If the CMB is used to establish a reference frame for motion, this anistrophy indicates absolute motion with respect to that frame.)

  20. Peter Woit says:

    Tony et. al.

    Please, a much better place to discuss the technical details of Sean’s paper would be at his blog posting on the topic.

  21. Pradeep says:

    “a universe could form inside this room and we’d never know”

    I am an engineer by profession and working towards a PhD. My advisor would throw me out if I propose any explanation of any experiment and not substantiate it with numbers/logical arguments/predictions about how to go further about the experiment.

    I have an avid interest in the way physics (I don’t say “theoretical”..after all, this distinction of subject into theory and experiment is really meaningless…both have to go hand in hand) is going. The way I look at the claims and hype about stuff like multiverse, string theory, brane world and so on… is getting really disgusting.

    If I had made a statement as the one quoted above, my advisor would throw me out of PhD programme telling me I am a crackpot.
    And string theory and its ilk has continued to occupy center stage for ~30 years without someone calling them crackpots baffles me!

    I think Feynman’s dictum that the experiment is the only test of theories summarizes all that is wrong with string theory and it’s variants.

    PS: I was made aware of the “dark side” of string theorists by this blog and I thank Peter for calling spade a spade (or crackpot theory as crackpot theory)!

  22. Christine says:

    “a universe could form inside this room and we’d never know”

    When I read this I thought: this only deserves a cartoon. What else?? That’s why I draw it in 5 minutes in my paintbrush and posted on my blog as a comedy. Reminds me of when kids swear that they saw things that don’t exist. Actually, I was not really very fair to it. My kid asks far more relevant scientific questions than that silly statement.

    I don’t have the willingness or energy to debate that claim scientifically, even because it’s not scientific to start with. It’s difficult to understand how a scientist would ever think this is scientific and spend his/her time with it. And having it published, if that is/will be the case, is beyond my comprehension.

    I usually am not so harsh and try to have an open mind. But everything has limits and I’m really getting tired of these multiverses & co.

  23. Peter Woit says:


    “string theory” is a very big subject, and it’s extremely unfair to dismiss it all as “crackpot”. Unfortunately some parts of string theory (and parts of cosmology having little to do with string theory) have taken a turn towards pseudo-science, but I think the people promoting this are very much a minority in the subject. It would be in the interest of serious physicists working in string theory and cosmology to take a more active role in making it clear to the public what is pseudo-science and what isn’t. By not doing this, I think they are damaging the credibility of their field, with the whole thing getting tarred as “crackpot”.

  24. Eric H says:


    I agree with your assessment of the need for pointing out more publicly what is pseudoscience and what is not. There is a definite need to call out publicly the wackiness of some of these ideas. I hope you and others understand that what I was saying earlier about the problem with public promotion refered to excessive pushing of “one’s own theories”. I think a lot of the problem with string theory and multiverses originated from that human frailty of need for recognition at the expense of truth and logic. In a way you could say that kind of human sociology produced string theory and the trendiness in physics that went with it, and not the other way around.

  25. somebody says:

    Pradeep says:
    “I think Feynman’s dictum that the experiment is the only test of theories summarizes all that is wrong with string theory and it’s variants.”

    The tragedy of string theory (and in fact theoretical physics in general today) is that the really interesting questions that we want answers for, are currently way outside our experimental capabilities. To answer essentially all the questions to which we have experimental access, standard model plus Einstein gravity is perfectly enough. But unfortunately(?) human curiosity does not end where our experimental capabilities end. The difficult question is where does the deadly combination of curiosity + lack of experiments turn into mathematical masturbation.

    When you attack a caricature of this problem (like “no experiments yet, so kill strings”), it is easy to come up with simple answers to this difficult question like you did. But on the other hand, if we take the hints from particle physics and gravity seriously, we are lead to an enormous and (surprisingly) consistent mathematical structure called string theory. Should we take this structure seriously in the interim, or should we not do anything because we have no experiments (yet)?

    Of course, most of the criticisms against string theory come from people like you who are (admittedly) ignorant about these hints. So any debate of this form almost always degenerates to frustration for the defender of string theory. I see no way even in principle to show you my side of the argument. And when I say this, I am called arrogant.

    Incidentally, your advisor is perfectly right to kick you out of the department if your model does not tie up with experiments. Because you HAVE experiments. Everything you ever do (if you are anything other than a reactor engineer or something) MUST be prefectly understood within the context of electromagnetism. This does not mean that what you are interested in is useless, but it does mean that what you are interested in is merely a detail from the perspective of someone interested in more fundamental things. But there are people who want to see beyond E&M, the standard model and all the way to gravity. I am sorry to be rough, but I see no way but to point out the difference in perspective when faced with such hostility.

    In any event, as everyone knows, we string theorists do face the possibility that we are victims in an unfortunate age trying to delude ourselves. But even then, I see no reason for your hostility. If you do not like what we are trying to do, think of us as something like half-mathematicians. We only take up as much academic resources as them.

    The fact of the matter is that string theory IS fascinating. That is the bottomline at the moment.

  26. somebody says:

    Just to point out one historical fact: the whole idea of the multiverse in the sense of eternal inflation has been there long before string theorists stumbled across it via independent arguments. And Sean is a cosmologist.

    So even if the idea was flack-worthy, …

  27. Chip Neville says:


    You are right when you say in your June 14th reply to Pradeep, “It would be in the interest of serious physicists working in string theory and cosmology to take a more active role in making it clear to the public what is pseudo-science and what isn’t”, and you are right when you criticize Scientific American and other popular science publications for hyping speculative ideas without warning readers of their speculative nature. But perhaps you will be cheered up by the Letters section of the June issue of Scientific American, the very same one containing Sean’s article, where a reader asks: “Are any experiments planned for the LHC that could either support or falsify theory’s claims, expectations or predictions?”, and Quigg replies: “String theory is not at the point of making specific predictions for the LHC. … The LHC has influenced some prominent string theorists to put the theory aside, for the moment, to concentrate on theoretical problems that promise a more immediate dialogue with LHC experiments.”

    Do you have any idea to which prominent string theorists Quigg is referring?

  28. Peter Woit says:


    Quigg’s description of

    “a conversation between an experiment and threads in the string theory worldview”

    just sounds like obfuscation to me. I don’t see why he can’t just straightforwardly say that string theory predicts nothing about what the LHC will see, and that the interest in the LHC has to do with physics (electroweak symmetry breaking) which has nothing at all to do with string theory.

    I don’t know who he is thinking of in claiming string theorists have abandoned string theory for LHC physics. LHC phenomenology is a very different subject than string theory, and few people can move from one to the other. One example might be Arkani-Hamed, but he was never much of a string theorist. Some string theorists have gotten involved in the “LHC Olympics”, but it’s unclear whether that counts as a change in research direction. There are a few other examples of people doing AdS/CFT stuff that is supposed to be related to the LHC, see, e.g. recent paper by Maldacena.

  29. Thomas Larsson says:

    The tragedy of string theory (and in fact theoretical physics in general today) is that the really interesting questions that we want answers for, are currently way outside our experimental capabilities.

    I want to know why m_p/m_e = 1836 or why 1/alpha = 137.036. It seems to me that it is theory rather than experiment that is the problem.

  30. Chris Austin says:

    Hi somebody,

    “To answer essentially all the questions to which we have experimental access, standard model plus Einstein gravity is perfectly enough.”

    Three independent approaches to making sense of the quantization of Einstein gravity in 3 + 1 dimensions have had a substantial amount of success recently:

    1) Bennie F. L. Ward’s technique of resumming Feynman diagrams, e.g. arXiv:hep-ph/0610232

    2) Asymptotic safety, e.g. arXiv:0708.1317, arXiv:gr-qc/0610018

    3) Causal dynamical triangulations, e.g. arXiv:0712.2485

    All three of these approaches appear to lead to the conclusion that the strong / electroweak Standard Model plus quantum Einstein gravity in 3 + 1 dimensions predict that the universe has a radius of curvature around 10^{-35} metres, i.e. the Planck length, in gross contradiction with observation.

    On the other hand, if we choose not to quantize gravity, but accept the existence of gravitational radiation, for which there is experimental evidence from binary pulsar timing studies, see http://nobelprize.org/nobel_prizes/physics/laureates/1993/press.html then we meet the equipartition theorem of classical statistical mechanics, namely that in thermal equilibrium at temperature T, every quadratic degree of freedom has mean energy (1/2)kT, where k is Boltzmann’s constant. The gravitational radiation field has an infinite number of quadratic degrees of freedom per unit volume, since the frequency of gravitational radiation can be arbitrarily high, hence we must conclude that the gravitational radiation field is either not in thermal equilibrium, or has exactly zero temperature, or has infinite energy per unit volume. This is precisely analogous to the corresponding paradox for the electromagnetic field, that led Planck to the introduction of quantum theory, so that the equipartition theorem is only valid for frequencies \nu such that h \nu is small compared to kT.

    Best regards,

  31. Observer says:

    Somebody says:

    “The tragedy of string theory (and in fact theoretical physics in general today) is that the really interesting questions that we want answers for, are currently way outside our experimental capabilities”

    Since the complaint is testability of String Theory, I am interested to know if there are any thought-experiments that can reasonably substitute experiments.

  32. Aaron Bergman says:

    Since the complaint is testability of String Theory, I am interested to know if there are any thought-experiments that can reasonably substitute experiments.

    Of course not. But, when you don’t have any real experiments, you make do with what you have.

  33. Peter Orland says:

    Somebody says:

    “The tragedy of string theory (and in fact theoretical physics in general today) is that the really interesting questions that we want answers for, are currently way outside our experimental capabilities”

    I don’t understand why some people think that the only really interesting questions are quantum gravity and unification.

    What about confinement? What about the soft Pomeron in QCD? What about chiral symmetry breaking? What about High-T_{c} superconductivity? What about turbulence? What about the Hubbard model in two or three dimensions? What about dark energy? What about inflation? Etc., etc., etc. All of these questions are related to experiments or observations. The people who work on them have as much talent as anyone (with the exception of yours truly).

  34. Tom W. says:

    Peter, you say:
    >Unfortunately some parts of string theory (and parts of cosmology >having little to do with string theory) have taken a turn towards >pseudo-science, but I think the people promoting this are very >much a minority in the subject. It would be in the interest of >serious physicists working in string theory and cosmology to take >a more active role in making it clear to the public what is pseudo->science and what isn’t.

    Anyone claiming the existence of extra dimensions is talking pseudo-science, so this would seem to include a majority of string theorists. If this is not the case, then can you (as a serious physicist) make it clear to me ( the public) where the scientific basis for extra dimensions can be found?

  35. Christine says:

    I philosophically oppose to extra-dimensions and multiverses.

    Scientifically, the only way to address them is to experimentally test the various hypotheses for their existence. In this case, extra-dimensions can be scientifically tested, but not multiverses. By definition, the universe is *all* that exists. There is no intrinsic meaning to talk about *other* universes. It is not scientific because to begin with, it has no meaning. I don’t understand why people cannot see the logic of this simple argument.

    Sometimes I find interesting to read about ideas like the quantum creation of the universe from nothing, like Vilenkin’s attempt, but when it comes to other universes, the line between science and pure imagination/illogic is crossed. Since I have a science-fiction vein, these ideas can serve as some inspiration. But even then, since they are already so much explored (and since I dislike them), I avoid them and look for other more interesting ideas that abound in other areas of science.

  36. Peter Woit says:

    Christine and Tom,

    I don’t think a generalized denunciation of multiverse and extra dimensions research is at all helpful. All it does is convince string theorists that their critics are completely close-minded and don’t understand what they are trying to do. You have to look at exactly what the research in these fields is, it’s not so easily dismissed without considering exactly what is going on.

    In the case of extra dimensions, first of all there are successful uses of the idea (see AdS/CFT). Mostly though, it’s not pseudo-science, just unsuccessful science. Multi-dimensional models in principle typically make predictions, the problem is that they don’t agree with observation. You end up having to adjust your model so as to not violate known experimental results, making it untestable and not explaining anything.

    In the case of the multiverse, one can imagine testable versions of the idea, but one often sees people pushing research programs that all evidence shows are inherently untestable. This deserves to be called pseudo-science.

  37. anon. says:

    “… it’s not pseudo-science, just unsuccessful science. …”

    It’s financially successful in being marketed. So it gets citations and research grants. The number of researchers exceeds the critical mass for a growing discipline: reading, peer-reviewing and citing one another. From these criteria, it is a scientific success.

  38. Christine says:

    Peter Woit,

    It may appear to others that my “generalized denunciation” of these issues are closed-minded. Well, I don’t care to be judged that way, simply because I know how I am better than anyone else, and I know that I am an open-minded person. I have run and run blogs that widely accept any civilized comments on all these issues, even if I strongly oppose one concept or another.

    As I mentioned, I am not philosophically inclined to the extra-dimensional programme, although I was much more interested in the past. And I never said that it cannot be tested. My general remarks about extra dimensions were purely philosophical.

    Concerning multiverses, as I wrote, I see it clearly untestable by definition, because by definition there is only one universe, which encompasses all nature. I see no logic in talking about multiverses poping in and out of “existence” “elsewhere”. This is my starting point, but it does not mean that I don’t want to hear anything about it or that I am not interested in understanding the arguments further.

    String theory is testable and should be tested, and it is scientific as far as I understand it. But I presently am interested in other ideas. I don’t really care whether other people want to work on this subject as far as they act as honest scientists and face the problems of their discipline with dignity. (I am *not* saying that string theorists are dishonest or lack dignity. This should be applied to any scientist, or any person for that matter).

    Yes, I do have a strong philosophical position that multiverses are things of the imagination, and hence one will have to convince me that it is a scientific problem. Since up to this moment I have not seen any convincing argument, I keep my position. If people want to try to convince me, they are invited to post on my blog; I have specific entries on these matters. Search for, e.g., “the universe” and “what is science”, etc. But I strongly advise that if you don’t have a really sound argument, never mind, I’d rather run a low traffic blog.

  39. Peter Woit says:


    I’m sorry if my comment came off as hostile, I’m well aware that you are a quite open-minded person, well-informed about these issues, and that your blog does a good job of reflecting this.

    You’re right that the overriding problem with the multiverse idea is that the other “universes” are by definition not directly observable to us. So anyone who wants to talk about them has to come up with an explanation of how multiverse research is going to lead to an experimental test. My point is just that multiverse proponents do have answers to this, and one needs to look at them and address them. I think when one does, one finds that they are completely unconvincing. The kinds of answers they have are:

    1. A version of string theory will be found that explains the standard model convincingly, while at the same time also implying the existence of other universes corresponding to other states of the the theory. Knowing one ground state of the theory will tell us what the theory is, and indirectly evidence for the other ground states. Problem with this of course is that, after a quarter century string theory has failed completely to explain anything about the standard model.

    2. Statistical analysis of string vacua will make testable predictions, again giving indirect evidence that the other states in the statistical ensemble exist. Again, this is a research program that has gone no where, and has zero evidence supporting it, or giving any encouragement that anything can come of it.

    3. Construction of models with observable effects of pre-inflationary times. Such models typically are rather contrived, and involve an extremely small amount of information about this pre-inflationary “other universe”, such as one number, the only thing surviving from some very complex earlier state. Actually I don’t think this really works, since you’re talking about the earlier history of this universe, not another one. Again, you can claim that finding evidence of a pre-big-bang state consistent with multiverse ideas of existence of lots of baby universes is indirect evidence for them, but at this point this just seems to me to be wishful thinking.

  40. Chris Austin says:

    Hi Tom W.,

    ” … can you (as a serious physicist) make it clear to me ( the public) where the scientific basis for extra dimensions can be found?”

    I hope Peter won’t mind if I try.

    Experimental evidence has been steadily mounting since 1915, when Einstein proposed his General Theory of Relativity, that gravitational fields are properly described as a curvature of space and time. A logical consequence of this description, already recognized by Theodor Kaluza in 1919, is that there could be extra dimensions of space, curled up too small for us to see them.

    To see something small, it is necessary to look at it with something – photons, electrons, neutrons – whose wavelength is smaller than the thing we are trying to look at. From Planck’s relation E = h \nu, where E means energy, h is Planck’s constant, and \nu means frequency, and the relation between frequency and wavelength, which for photons, and also for massive particles, when their energy is sufficiently high, is \nu = c / L, where c is the speed of light and L means wavelength, it follows that to see very small things we need very high energies.

    The Large Hadron Collider, due to start up at CERN in the next few months, will enable us to see smaller things than ever before, down to around 10^{-19} metres, by looking at them with the quarks and gluons in protons colliding at extremely high energy. This does not mean that we will see such small things immediately. Rather it will be like gradually increasing the level of illumination in a room that was initially completely dark: things will gradually appear out of the murk as the accumulated data increases. There is a significant possibility that the LHC will eventually see small extra dimensions of space, curled up to a size of around 10^{-19} metres, that are too small to have been detected up to now, and I will try to explain why this is.

    The two most fundamental experimentally established theories of physics that we have at present are the Standard Model of the strong / electroweak interactions, which describes everything that we observe except the gravitational field, and Einstein’s theory of gravity, which describes the gravitational field and its interactions with the energy and momentum of matter. As I tried to summarize in my comment above, when we work out the logical consequences of the two theories together, they make a prediction that is disastrously wrong, namely that the universe curls up so that its radius of curvature is around 10^{-35} metres, which is roughly as small in comparison to the smallest specks of dust we can see with the naked eye, as those specks of dust are in comparison to the actual size of the universe. This means that the two established theories must be part of a larger picture, and a very important part of the larger picture is missing.

    The reason the two established theories make this wrong prediction, is that the fields associated with the particles of the strong / electroweak Standard Model, in the same way that the electromagnetic field is associated with the photon, have nonvanishing fluctuations even in empty space, and these fluctuations have nonvanishing energy. The energy of these fluctuations acts as a source for the gravitational field in the same way as massive objects do, and this results in the universe curling up to a size around the square root of G h / c^3, where G is Newton’s constant. This size is around 10^{-35} metres, which is roughly what is known as the Planck length.

    For particles like the photon, the W and Z particles that transmit the weak interactions, the gluons that transmit the strong interactions, and the graviton, which are collectively called bosons, the leading contribution to the energy of their fluctuations in empty space is always positive, while for particles like the electron, the muon, neutrinos, and quarks, which are collectively called fermions, the leading contribution is always negative, so there is in principle the possibility of a cancellation between the two, but this does not happen for the strong / electroweak Standard Model, nor for the Standard Model plus gravity. However in 1974, Bruno Zumino demonstrated that in field theories with a special property called supersymmetry, the contributions to the energy of fluctuations in empty space cancelled between bosons and fermions exactly, for the leading contributions, and also for all further contributions from more and more complicated processes. Supersymmetry means that the formula for the energy density of the fields, averaged over space and time, which is called the action, is unchanged when certain small multiples of the fermion fields are added to the boson fields and conversely. Because of Zumino’s proof, it seems reasonable to expect that supersymmetry is part of the missing part of the larger picture.

    Zumino’s proof does not apply, however, to field theories with supersymmetry that involve the graviton, which are called supergravity theories, and with one single exception, whose fluctuations in empty space can only have exactly zero total energy, supergravity theories can have zero or negative total energy of their fluctuations in empty space, so that the energy of their empty space fluctuations is not much better controlled than for theories without supersymmetry. The single exception is supergravity in eleven dimensions, that is ten space dimensions and one time dimension, which is the largest number of dimensions in which supergravity can occur. Supergravity cannot occur in more than eleven dimensions, because the number of degrees of freedom of the gravitino, which is the fermion field of which a certain small multiple gets added to the gravitational field in a supersymmetry operation, increases much more rapidly than the number of degrees of freedom of the graviton, as the dimension of spacetime increases. The result of this is that while supergravity in four spacetime dimensions can involve up to eight gravitinos, in ten dimensions it can only involve either one or two gravitinos, in eleven dimensions it involves exactly one gravitino, and in more than eleven dimensions supergravity cannot occur at all, because the gravitino has too many degrees of freedom.

    In consequence of being an extreme case, supergravity in eleven dimensions has completely exceptional properties. Its action is unique, and the pieces fit together like a perfect Chinese puzzle. It is the only field theory involving gravity whose fluctuations in empty space necessarily have exactly zero total energy. When one of its ten space dimensions is curled up into a very small circle, and a certain solution of its field equations, which looks like a membrane, is wrapped around this circle, it becomes the type IIA superstring in ten spacetime dimensions, and it can also become each of the other four superstring theories when one or more of its ten space dimensions are curled up or folded in appropriate ways, and certain modifications fixed by self-consistency on any folds are made. Its quantum theory, which is called M-theory, has a vast array of consistent solutions in which seven of the space dimensions are curled or folded up into a very small size, while the remaining three space dimensions and the time dimension are very large and nearly flat, like the familiar dimensions of space and time that we know.

    In many of these consistent solutions, there are fermions and bosons on the four large spacetime dimensions that look very similar to those in the strong / electroweak Standard Model, in the sense that exactly the same fields occur as in the Standard Model, and they have exactly the same types of interactions as in the Standard Model, but the masses of the particles, and the strengths of interactions, defined by numbers such as Newton’s constant and the fine structure constant, are generally different from those in the Standard Model. However only a tiny fraction of the possible consistent solutions of this type have been examined so far, so it seems reasonable to expect that the larger picture, of which the strong / electroweak Standard Model and Einstein’s theory of gravity are the two parts that have been established experimentally up to now, will be a consistent solution of M-theory of this type.

    The vast number of consistent solutions of M-theory which, for everything larger than around 10^{-19} metres in size, look similar to the strong / electroweak Standard Model plus Einstein gravity in 3 + 1 dimensions, but differ in detail, have been characterized as a “landscape”, and leave us with the practical problem of finding out where in that “landscape” we live. The parts of the “landscape” that have been investigated up to now fall into some ten or so broad families, that differ very greatly from one another for things smaller than around 10^{-19} metres in size. It will thus be possible to distinguish between some of these broad families at the Large Hadron Collider, and exclude some of them in favour of others.

    The reason it is certain that the Large Hadron Collider will be able to distinguish between some of the broad families of solutions is that the strong / electroweak Standard Model becomes very stressed at the energies that will be studied at the LHC. One of the particles predicted by the Standard Model, called the Higgs boson, has never been discovered, and the logical consistency of the parts of the Standard Model that have been confirmed experimentally, requires that the Higgs boson, or something more complicated to serve in its place, must be light enough to be discovered at the LHC. Furthermore, the mass of the Higgs boson in the Standard Model is unstable to quantum corrections that tend to increase it greatly, so if the Higgs boson is discovered, then something more complicated must also be discovered that stabilizes its mass.

    Whatever more complicated things are discovered, either together with the Higgs boson or in place of it, will distinguish between some of the broad families of solutions. In some of the broad families, the seven extra dimensions are large enough to be seen at the LHC, while in others they are not. In some of the families, there will be string-like excitations similar to the Regge recurrences observed at much lower energies in the strong interactions, while in others there will be none. In some of the families, the size of the extra dimensions is much larger than 10^{-19} metres, in fact up to a millimetre, but the Standard Model particles can only move in a small part of them, of size around 10^{-19} metres, which is why the large extra dimensions have not yet been detected, whereas the graviton and gravitino can move in their full extent. This would explain why the force of gravity is so much weaker than the other forces, for example the gravitational attraction between two protons is around 10^{-40} times weaker than the electrostatic repulsion between them, due to the gravitational force being diluted by the larger volume in which the graviton can move. In these families, the strength of the gravitational force increases extremely rapidly with energy as the LHC energy is approached, becoming comparable in strength to the other forces at around the LHC energy, and loss of part of the collision energy due to radiation of gravitons into the large parts of the extra dimensions will be observed at the LHC.

    Best regards,

  41. Christine says:

    Peter Woit,

    No, your comment did not came off as hostile, perhaps I was a little too defensive.

    I appreciate that you have itemized your main criticisms to the “multiversism”. If I may, I suggest that you produce a FAQ to your arguments. It would avoid that you keep repeating yourself. There is a lot of information in your blog that deserves to be assembled into one place for easy access.

    What concerns me is the recent edifice of joining string theory and multiverse scenarios (in addition to the intrusive anthropic arguments). I think this is a major shortcoming, but my discomfort is purely philosophical, because, as I mentioned previously, the multiverse idea does not convince me as scientific to begin with. I wonder whether only a minority of string theorists are willing to embrace such an edifice, or whether in fact this is a major trend.

  42. Eric H says:

    Your latest comment explains where you are coming from theoretically. However, it seems to me you are just repeating standard theory from certain books, some of which are right and some of which are probably wrong.

    While I agree that supersymmetry explains some things in particle physics it seems to do a lot more damage at theories of large scales, i.e.,gravity. It also must be remembered that general relativity can be considered proven while supersymmetry cannot. This isn’t to say that general relativity won’t probably be eventually enfolded into a larger theory that explains things such as the acceleration due to dark energy, (not to be confused with the vacuum energy or zpf). But my view is that supersymmetry directly contradicts GR and thus can’t enfold GR within it. In this way supersymmetry can be considered a good, but very flawed theory for certain interactions. Let me say it again: supersymmetry has not been proven.

    Finally, the basic problem seems to come down to the problem of the universe being nearly “flat” but not quite. Supersymmetry addresses the problem by assuming “anti” particles and forces to everything. That ball got rolling because there actually are anti-particles with the same mass but opposite spin in all their internal components. But you are basically extrapolating an “anti” universe from the tinyest bit of evidence. And even then it doesn’t explain the small bit of “material” remaining that makes the combined positive and negative universes flat. It’s not good science but just a supposition that actually creates more questions than answers. Good science is when after given suffient time what remains in the wake of a new theory are “less” unanswered questions from the original questions, not more.

  43. Eric H says:

    “And even then it doesn’t explain the small bit of “material” remaining that makes the combined positive and negative universes flat.”

    make that not quite flat.

  44. Eric says:

    Eric H.,
    You apparently have a misunderstanding about what supersymmetry is about. Supersymmetry does not assign an anti-particle to every other particle. Supersymmetry is a symmetry which relates bosons to fermions. Thus, for the case of N=1 supersymmetry every fermion has a scalar partner, while every boson has a fermionic partner. In the case of supergravity, the spin 2 graviton is paired with a spin 1/2 gravitino, and gravity emerges from elevating supersymmetry to a local gauge symmetry. Your statement that supersymmetry contradicts general relativity is completely wrong.

  45. Eric H says:


    Have they found any of these superpartners experimentally?

  46. Eric says:

    Give LHC a couple of years….

  47. woit says:

    Enough unenlightening supersymmetry warfare.

    Chris laid out some of the standard lines of speculation that lead to the theoretical picture that string theorists are trying to sell today. The problem is that it’s a long line of speculation, which could be wrong at many places, which has never managed to make contact with the real world. There’s no particular reason to believe that extra dimensions explain electroweak symmetry breaking, they don’t explain any of its known features, or predict what the LHC will see.

    So, I still maintain that extra dimensions are science, just (scientifically) unsuccessful science. We’ll see what happens at the LHC, I just hope that if extra dimensions or supersymmetry don’t turn up there, we can finally stop having the field of particle theory dominated by these ideas.

  48. Eric says:

    I hope that whenever supersymmetry is found at LHC that you will disappear.

  49. Observer says:


    In a previous comment you say: “In the case of extra dimensions, first of all there are successful uses of the idea (see AdS/CFT). Mostly though, it’s not pseudo-science, just unsuccessful science”

    Is there any empirical evidence in support of the AdS/CFT correspondence to promote it at the level of a successful theory?

    Best regards,


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