Hard Evidence for the Multiverse Found, but String Theory Limits the Space Brain Threat


“The Planck team’s paper appears to rule out the claims of Kashlinsky and collaborators,” says David Spergel of Princeton University, who was not involved in the work. If there is no dark flow, there is no need for exotic explanations for it, such as other universes, says Planck team member Elena Pierpaoli at the University of Southern California, Los Angeles. “You don’t have to think of alternatives.”

One of those promoting the idea that “dark flow” was evidence for a multiverse was Mersini-Houghton, who in a 2008 paper with Holman wrote:

Our contention, then, is that these observations of bulk flow can be construed as evidence for the birth of the universe from the landscape multiverse imprinted on the superhorizon sized nonlocal quantum entanglement between our horizon patch and others that began from the landscape. When we calculate the size of the induced dipole in our theory and convert it into a bulk velocity dispersion, we will see that for the constrained values of our parameters we arrive at a velocity dispersion of order 670 km/sec, remarkably close to the observed value of 700 km/sec.

One might think that the refutation of their prediction by the Planck data would be a problem. Instead though, the Sunday Times reported a few days ago that Scientists believe they have found the first evidence that other universes exist. The story got picked up by other news outlets, and appeared in the Daily Mail as “The first ‘hard evidence’ that other universes exist has been found by scientists”. The source for the story was Mersini-Houghton:

Now that she has studied the Planck data, Dr Mersini-Houghton believes her hypothesis has been proven.
Her findings imply there could be an infinite number of universes outside of our own.
She said: ‘These anomalies were caused by other universes pulling on our universe as it formed during the Big Bang.
‘They are the first hard evidence for the existence of other universes that we have seen.’

She will be in Britain soon promoting this at the Hay Festival on May 31 and at Oxford on June 11.

According to a New Scientist story just out, this hard evidence for the multiverse should be welcomed, since it (together with string theory) has just been shown to have the power to save us from “Legions of disembodied brains floating in deep space”. The story, which appeared in print as String Theory Limits Space Brain Threat starts with

LEGIONS of disembodied brains floating in deep space threaten to undermine our understanding of the universe. New mathematical modelling suggests string theory and its multiple universes may just provide our salvation – and that could win the controversial theory a few more backers.

It goes on to explain about Boltzmann brains and a recent paper by Bousso and Zukowski, and ends with news of yet another experimental success for string theory:

“This is potentially an added experimental success for string theory and eternal inflation,” says Daniel Harlow, a physicist at Princeton University. “We need to understand it better – [but] the fact that it potentially explains something is motivation to understand it better.”

Update: More here on how string theory will save us from the space brains.

Update: I’ve appended a response from Laura Mersini-Houghton and Richard Holman about this to a later posting, see here.


34 Responses to Hard Evidence for the Multiverse Found, but String Theory Limits the Space Brain Threat

  1. Adam Treat says:

    Can you provide a link to the New Scientist article that you quote above? Also, it is unclear if Mersini-Houghton and others are talking to the press about a new paper where they discuss their analysis of the planck data. Is this the case or are they talking to the press in anticipation of a new paper?

    I am also looking forward to a follow-up on the claims by Penrose and Gurzadyan regarding evidence for Conformal Cyclic Cosmology found in CMB data. I wonder if the planck data will be used to bolster or refute these claims that seem to be still alive and kicking.

  2. Peter Woit says:


    I forgot to put in the link, it’s there now. As far as I know there is no new Mersini-Houghton paper providing her own analysis of the Planck data. The Gurzadyan/Penrose claims about the CMB may also be in the category of things the Planck found too implausible to investigate themselves.

  3. Bob says:

    I just can’t stop laughing at the headline . . .

  4. dark flow says:

    I thought that the dark flow was convincingly debunked already in 2011:
    “Measuring the cosmological bulk flow using the peculiar velocities of supernovae”
    De-Chang Dai, William H. Kinney, Dejan Stojkovic, JCAP 1104 (2011) 015 .

  5. Charles Wilson says:

    “LEGIONS of disembodied brains floating in deep space threaten to undermine our understanding of the universe.”
    Ed Wood, Director of “Plan Nine from Outer Space”, just rolled over in his grave.
    Ed, you were born 60 years too soon.

  6. Eric says:

    I am confused…. So is it hard evidence for the multiverse or not?

  7. Peter Woit says:


    Well, the Daily Mail and Mersini-Houghton say there’s hard evidence, and they don’t quote anyone contradicting this. Other reporters might turn up someone who would disagree.

    I assume the “hard evidence” is not the “dark flow” prediction that didn’t work out, but something else (probably the CMB “cold spot” that WMAP found, which Planck says is still there).

  8. Student says:


    Here’s a picture of string theory saving the Empire from the Boltzmann brains:


  9. paddy says:

    oops…I clicked a link for NEW though ended up in xkcd

  10. nasren says:

    My first thought on reading this was: O dear God what will Matt Strassler say about this kind of journalism. So far he seems to be ignoring it.

  11. Peter Woit says:


    I don’t think the problem here is the journalists, who are just reporting the exciting news about hard evidence for other universes and great progress on the disembodied brain front that they are hearing from physicists. Michio Kaku did seem to once get to Strassler, but in general he doesn’t appear to think this kind of behavior by scientists is worth commenting on.

    It’s a plausible idea that if most prominent theorists just ignore it, Multiverse-mania might go away on its own. My suspicion is that most physicists subscribe to this. Unfortunately, that doesn’t seem to be happening.

  12. Maciej says:

    “This is potentially an added experimental success for string theory and eternal inflation”

    Wow! Experimental? Seriously?
    Forget experimental. I am not sure if this is mental success at all…

  13. physicsphile says:

    I think it is a bit unfair to tar all multiverse work as being garbage because of this. There certainly is a lot of bad research being done on the multiverse but I think there is also interesting stuff like Weinberg’s original claim that it may be how the cosmological constant problem is solved.

  14. mult says:

    There will always be something to laugh at other people. Do some better work of your own which captures the headlines. One never knows, this may inspire young people to get interested in science, and they will produce the ‘correct’ Theory of Everything, whatever that might be.

  15. Visitor says:


    Strassler might want to rethink things because the house of physics is becoming an Augean stable and if the interested and responsible parties can’t or, possibly worse, won’t clean up the mess, eventually the government is going to *seriously* curtail its funding. And then you’ll see see how far some noveau-riche Russian oligarch’s money is going to get a very few of you – with the rest of you driving taxis or teaching algebra and geometry in high schools across the land.

  16. M says:

    Boltzmann Brains are great, but can String Theory explain why chicken with cut head can survive for years? This phenomenon probably is related to the survival of theories found to be (not even) wrong.

  17. David Nataf says:


    Your criticisms of the Dark Flow are quite unfair. Just because it could be explained by a multiverse, does not mean it would need to be explained that way.

    The idea of the dark flow was that galaxies have a preferred vector of peculiar motion, which would break the anisotropy assumption that is fundamental to cosmology. There is definitely a coherent linear flow in the nearby universe up to several dozen megaparsecs, and people have debated whether this is due to a “great attractor” (a nearby supercluster), statistical coincidence, or a dark flow. If Planck is correct then it may just be a 1 in 20 statistical coincidence or so that affects the local volume.

    Regardless of whether a preferred peculiar direction of motion for matter would be due to a multiverse or not, it is a legitimate scientific test to conduct, to investigate, to write papers about, et cetera. It doesn’t need to exist, but it could have existed as dark matter and dark energy (for example), certainly exist, and dark radiation is now a 2-sigma phenomenon. The Friedman-Robertson-Walker-Lemaitre metric from General Relativity, that is the foundation of cosmology, predicts that there should be zero dark flow, similarly to how the standard model of particle physics predicts zero dark matter and zero dark energy. It is good and valid to test these things.

    I do however apologize for astronomers’ lack of imagination in naming mysterious phenomena. As such, please don’t turn into Dark Peter.

  18. Peter Woit says:

    David Nataf,

    I’m sorry if this was unclear, but I had no intention of in any way criticizing people for studying “dark flow” or for calling it that.

  19. dark flow says:


    There is no bulk flow as initially claimed. The paper I mentioned indicates that while the direction of the “bulk flow” was correctly measured, its magnitude is much smaller than initially thought (200 km/s instead of 1000 km/s). This magnitude is consistent with Lambda CDM, so there is no need for any unusual physics, certainly not multiverses which are tugging on us. These findings were now confirmed by Planck.

  20. Dom says:

    A good day for solving all known problems, in The Guardian we have
    Roll over Einstein: meet Weinstein

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  22. Luis says:

    It should be noted that the usual “piece of evidence” claimed for “other universes” comes not that much from the dark flow but from a rather large cold spot in the CMB. Apparently, the consensus as of now is that the spot is simply an artefact of the analysis: http://arxiv.org/abs/0908.3988

  23. Avattoir says:

    The Daily Mail you say?


  24. Peter Woit says:


    Thanks. I added a new posting about that topic.

  25. Nick M. says:


    I think you may have meant May 31, and not June 31, for the date of the Laura Mersini-Houghton appearance at the 2013 Hay Festival in London; i.e., see here, and scroll down the page to see the appropriate listing.


  26. Peter Woit says:

    Thanks Nick, fixed.

  27. Stephen Heyer says:

    To me, the strange thing is the very odd and unlikely model of a Boltzmann brain that always seems to be discussed: In short, a complex, fully formed, self-aware being appearing out of nothing. Oh! And the life support system capable of supporting the brain from local resources (wisps of left over hydrogen?) is never mentioned, despite the fact that without it the brain’s existence would be momentary.

    Far, far more likely would be the Boltzmann equivalent of a bacteria with a built in tendency to survive, reproduce and become more intelligent, much the way we current Boltzmann brains did it. The only real difference being that Boltzmann brains are usually imagined as existing much later in the universe’s history when resources are much more diffuse.

    In fact, looked at like that, they become both familiar and very likely. All we are really saying is that life and probably intelligence will arise anywhere there are the resources to support it, even if those resources are very different to those we are currently used to.

    A final thought, given the fascination these discussions always have with a late stage universe with mostly burned out stars, that universe is probably going to be already fully populated and it’s resources carefully husbanded so there might not be much opportunity for late comers.

    All it takes is for one high technology society from our period of the universe to not destroy itself during adolescence and stabilize and, it, or something derived from it, will be still there thousands of billions of years later using increasingly clever ways of living off the available resources (unless, of course, its cracked ways of making entirely new ones).

    So you see, for almost all of its existence, the universe will be mostly observed by something like us, or something distantly derived from something like us. No problem!

    Stephen Heyer

  28. Michael R says:

    Does anyone know how the proponents of the Dark Flow Multiverse concept explain how it is that light may not escape a universe but that the gravitational force of one universe acts on another neighboring universe?

  29. chris says:


    the horizon was not always as small as today. all these proposed effects would be primordial remnants.

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  31. Bob Hope says:

    No. Seriously, if there is a Boltzmann brain, then there must be a corresponding Boltzmann brane or a class or category of them which embed the Boltzmann brain. And yet I couldn’t find any. Is not there any? Are these just Riemann surfaces too? Or are they higher dimensional branes?

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