The “Unnatural” Standard Model

The Standard Model is a physical theory of a spectacularly successful sort. It is built on beautiful and deep mathematics, covers almost all known physical phenomena, and agrees precisely with the result of every single experiment ever done to test it. It leaves open a very small number of questions: why this specific combination of small symmetry groups and their representations? What determines the parameters of the model (18 if you ignore neutrino masses, 7 more if you include them)? What about gravity? Does it need to be extended to account for dark matter?

For several decades now, there has been a very active and heavily advertised field of “Beyond Standard Model” physics, the study of extensions of the standard model that remain consistent with experimental bounds. While BSM models have played a role in guiding experimentalists towards things to look for that are not already ruled out by what is known, they have never come anywhere near fulfilling the hope that they might provide some insight into the SM itself. They provide no explanation of the unexplained aspects of the Standard Model, instead adding a great deal of additional unexplained structure. Perhaps the simplest and most widely studied example is the minimal supersymmetric extension of the SM, which not only explains none of the 25 undetermined SM parameters, but adds more than 100 additional such parameters to the list.

Theorists have traditionally followed what has been described as “Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained”, and the SM is our closest approach so far to Einstein’s dream. If you shared this dream, the known BSM models would never have much appealed to you, since they just added complexity and extra unexplained parameters. You also would not have been at all surprised by the strong negative results about such models that are one of the two major achievements so far of the LHC (the other is the Higgs discovery). If you’re a follower of Einstein’s dream, the obvious reaction to the LHC results so far would be to rejoice in the vindication of this dream, welcome the triumph of the simplicity of the SM, and hope that further study of the Higgs sector will somehow provide a hint of a better idea about where the SM parameters come from (almost all of them are Higgs couplings).

Remarkably, a very different story is being sold to the public by those who had a great deal invested in now failed BSM models. In this story, the BSM models were the ones of Einstein’s dream: they were “natural”, and their failure leaves us with the “unnatural” Standard Model.

An article entitled Is Nature Unnatural? is the source of the above quote about Einstein, and it tells us that

Decades of confounding experiments have physicists considering a startling possibility: The universe might not make sense…

In peril is the notion of “naturalness,” Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained. Without it, physicists face the harsh prospect that those laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time…

“The universe is impossible,” said Nima Arkani-Hamed, 41, of the Institute for Advanced Study, during a recent talk at Columbia University [more about this talk here].

What is behind this sort of claim that down is up is abuse of the English word “naturalness”, which in this particular case has been adopted by theorists to refer a technical property better described as “not quadratically sensitive to the cut-off scale”. There’s a lot to be said (and a lot that has been said on this blog) about the precise technical issue here. It’s a real one, and likely an important hint about the true nature of the Higgs sector of the SM and where all those undetermined parameters come from. Getting rid though of this technical problem by invoking hundreds of new undetermined parameters is not the sort of thing Einstein was dreaming about. He would see the LHC results as vindication and encouragement: as we investigate new energy scales we find the universe to be as simple as possible. It’s remarkable to see this great discovery being promoted as telling us that we have to give up on Einstein’s dream and adopt a pseudo-scientific research program based on the idea that physical “laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time”.

Update: The Science News story has now appeared at Scientific American, with the title New Physics Complications Lend Support to Multiverse Hypothesis. The “New Physics Complications” are the LHC only seeing pure SM behavior. If the LHC had seen a complicated SUSY spectrum, that would have been “natural”, but somehow seeing the simplest possibility has become a new “Complication”. It is a “complication”, but a sociological not physics one. SUSY theorists do have an answer for the complication of their ideas failing: the Multiverse did it.

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58 Responses to The “Unnatural” Standard Model

  1. pissantz34 says:

    What a fascinating debate. If only the professionals in my field were able to debate so eloquently – indeed, I work in a field universally despised by yours: politics. Worse still, I’m a Republican. It’s amusing to hear Matt decry the negativity. You guys sound like choir boys compared to some in my line of work!

    Just wanted to drop a note and provide a bit of encouragement from the outside world. Please, keep doing what you all are doing. I have not taken a physics class in my entire life, so it’s hard for me to follow the specifics of your arguments, but I keep my eye on science nonetheless. I believe you and others across so many disciplines are on the verge breathtaking breakthroughs ahead in the next 30 years.

    Groupthink is a major problem in politics as well. The journalists who are supposed to hold the powerful accountable attend the same Georgetown parties as the politicians and Joe Biden’s water gun fight parties every summer.

    If it weren’t for the Peter Woits of the political world, the hubris inherent in any political system would go unchecked. I applaud Peter and Matt and anyone else working their butts off to advance science. Peter, continue to question the status quo.

    If I ever get to the point in my career where I can sway national policy in any significant way, I will defend science to the hilt. Whether major advancements come from String Theory that Matt is working on, or groundbreaking mathematics Peter is, it doesn’t matter from my perspective. All of this work needs to be consistently and concisely explained and defended to policymakers and the public. That’s one reason why I think String is succeeding to the extent it is: Green, Hawking, Kaku are fantastic, engaging ambassadors for your profession. The public needs more.

  2. Mark Israelit says:

    I don’t understand why the connection is DENIED.
    I wanted to see the paper submitted by myself, , and received even in this case the DENY answer.

  3. Hugh says:

    @Mark, you’re missing a period from the url. It should be

  4. Haim says:


    This is pseudo-science indeed: “laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time”.

    But this would not be pseudo-science: “The standard model and general relativity are the direct, obvious, and natural outcome of random fluctuations in the fabric of space and time.” A number of people are trying this approach, which clearly follows Einstein’s dream.

    After all we know that space-time is randomly fluctuating. Or do you disagree? Are you implying that there is something wrong in trying to find the correct fabric of space-time? We all know that nobody has found the correct fabric yet. Connes did not succeed. Bilson-Thompson did not succeed. String people did not succeed. Spin network and many more did not. But some day somebody will succeed! Or are you proposing something else? Are you implying that space-time has no “fabric”?

    My impression from reading your blog is that you are only arguing against the epithets “arbitrary” and “messy” in the quotation. Or are you arguing something different?

  5. Jack says:


    Peter was arguing against the multiverse. To get to your point, there is little hope that some microstructure of space-time will lead to the standard model.

  6. Peter Woit says:


    If your ideas are so vague that you can’t extract any information about the way nature behaves out of them, then you’re in danger of doing pseudo-science. Multiverse theories typically not only don’t predict anything, but their who motivation is to construct an excuse for failure, an argument that it is impossible to predict anything. This is true pseudo-science.

    The problem with discussing “random fluctuations in the fabric of space and time” is that this is also too vague to be very meaningful. Replace “random fluctuations” by some specific notion of quantization, and “fabric of space and time” by a specific notion of exactly what the fundamental variables describing space-time are and then you start to have something. To have something convincing and testable though, I think you need to do this in a way that unifies with our understanding of quantization and the fundamental fields of the SM.

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