A First Stab at Explaining “Naturalness”

Arguably the two greatest problems facing particle physicists, cosmologists, string theorists, and the like are both associated with an apparent failure of a notion called “naturalness”.  Until now, I’ve mostly avoided this term on this site, because to utter the word demands an extended explanation.  After all, how could nature be unnatural, by definition?

Well, the answer is that the word “natural” has multiple meanings.  The one that scientists are using in this context isn’t “having to do with nature” but rather “typical” or “as expected” or “generic”, as in, “naturally the baby started screaming when she bumped her head”, or “naturally it costs more to live near the city center”, or “I hadn’t worn those glasses in months, so naturally they were dusty.”  And unnatural is when the baby doesn’t scream, when the city center is cheap, and when the glasses are pristine. Usually, when something unnatural happens, there’s a good reason.

I’ve started writing an article about naturalness and unnaturalness, and how there are two great mysteries about how unnatural our universe is, one of which lies at the heart of the Large Hadron Collider‘s [LHC’s] research program.  What I’ve written so far explains what naturalness means and (in part) how it applies to the Standard Model (the equations we use to describe the known elementary particles and forces).  I’ll be extending the article to explain this in more detail, and to explain the scientific argument as to why it is so unnatural to have a Higgs particle that is “lonely” — with no other associated particles (beyond the ones we already know) of roughly similar mass.  This in turn is why so many particle physicists have long expected the LHC to discover more than just a single Higgs particle and nothing else… more than just the Standard Model’s one and only missing piece… and why it will be a profound discovery with far-reaching implications if, during the next five years or so, the LHC experts sweep the floor clean and find nothing more in the LHC’s data than the Higgs particle that was found in 2012.

30 responses to “A First Stab at Explaining “Naturalness”

  1. I think you’re looking at this the wrong way, Matt. Look at it the right way, and these problems go away. And to do that all you have to is have a shot at explaining how gamma-gamma pair production actually works. IMHO it’s like pulling a thread, and out comes a string of pearls.

  2. Richard Bauman

    I think you are right on. Nature is simple ! Simple example without physics or math. The neutrino is the simplest fermion. If nature gives the three neurtinos mass it would do it simplely in units 1,2,3. Look up best values now and that would be 04ev, .08ev, .12ev. Not sure here but these appear to fit the given data BETTER than any other guess. And rather interesting idea if you add one unit of mass to one you get the next, or neurtino oscilllation

  3. Richard Bauman

    Sorry about the spelling. There are about 7-8 other simple examples. They all go in the opposite direction from wave equations and fields. If your question is how to fit the two concepts together, you don’t. However, it may be of some interest, as above, to see what simple physics predicts.

  4. DJ Williamson

    Stop sending emails

    Sent from my iPhone

    • If you’re receiving unwanted emails, it is because of something *you* did (on your twitter or facebook or RSS account or whatever.) I do not send emails to anyone; all emails are sent by intermediate parties, so you’ll have to talk to them.

  5. Tienzen (Jeh-Tween) Gong

    Nature is nature. The un-naturalness of the current usage is referring to some particular theories while their frameworks do not work well with the data (the nature). Instead of fine-tuning their theories, they claim that the Nature is fine-tuned. In the old time, the un-nature theory was deemed wrong. Today, the un-nature theory declares that Nature is unnatural.

    • I have no idea what your use of the world “natural” and “unnatural” are in this paragraph. In general, without careful definition of subtle terms, no communication is possible.

  6. Matt, as a person with a 45-year interest in physics, I can’t figure out what you are talking about. When referring to “naturalness,” do you mean something like intuitive expectations? Well (pondering), my intuitive expectations about fundamental particles are… wait, let me check… nonexistent. Ditto with atoms — wait, not true. My personal image of gold atoms is that they look like tiny little itsy bitsy specs of… gold. Alternatively, like all atoms, they are grey in color, since there was no color television when I was introduced to the concept of an atom — on a Sunday evening in 1956, watching Walt Disney’s weekly TV show.

    Probably my blathering is irrelevant to what you are discussing, but still, how can you expect to expect anything accurate about phenomena that are so far removed from our daily experiences? We might just as well be exploring someone else’s universe as our own, for all the familiarity we run into while trying to figure out what is really happening.

  7. It seems to me that naturalness is the probability of something being true, independent of an instance of that ‘something’. If you flip a coin 100 times, it would be highly unnatural for it to land on its edge 100 times. If you flip a coin 100 times and it lands on its edge 100 times then it’s certain that this has just happened – this doesn’t change it’s “naturalness”.

    For physics it’s similar. Given what we know, some things appear highly unnatural. If we observed our universe (the ‘instance’) and saw that these unnatural things were true, they would still be unnatural.

    • Naturalness is a measure of expectation versus actuality. If something appears unnatural in NATURE, your expectation is wrong. That means your model is wrong, and you have to look within that model to fix it. If you have to roll it all the way back to gamma-gamma pair production and the photon field being the Higgs field and mass being the flip side of momentum for a standing wave, so be it. But some guys just won’t listen. So they’ll have to find out the hard way. And then when they bleat about funding cuts it’s going to be just too bad, because I’d like to go large, and I’ll have a strawberry shake please Matt.

      • Have you noticed that many of these people whom you say “won’t listen” and “will find out the hard way” have been seriously considering the possibility that their expectation is wrong?

        You must really think that we’re all a bunch of idiots. I’m getting very tired of the fact that almost every comment you leave is a personal insult to me and to all of my colleagues. Remember you’re a guest on this website. If you can’t be more polite, you’ll be banned.

        • I don’t mean to be insulting Matt, I’m just trying to get your attention and get you (and your colleagues) to look within the standard model instead of beyond it. Maybe somebody at SEARCH was saying that, but I couldn’t see it in your reportage. I’m confident that it will pay dividends.

          • Matt Strassler and his colleagues are well capable physicists who know what they are doing and why, they dont need you to tell them what is worth looking at, how they should do their job, etc … 😉

    • The point here is a heuristic one. If you flipped a coin 100 times and it landed on its edge each time, wouldn’t you go looking for an explanation? Or would you just accept it as one more unusual event in a long life filled with unusual events?

      When I see something apparently unnatural (like the unbalanced vase), I, as a rational being, make a judgment call. I decide whether to investigate a possible cause, or simply accept it as “one of those things”. Well, when the universe as a whole is doing something unnatural, it’s my responsibility as a scientist to investigate possible causes — even if in the end it turns out it *is* just “one of those things.”

      I quote:

      “Is there any point to which you would wish to draw my attention?”

      “To the curious incident of the dog in the night-time.”

      “The dog did nothing in the night-time.”

      “That was the curious incident,” remarked Sherlock Holmes.

  8. The book of Nature ( esp. of Physics ) is written in the language of Math,
    This principle has worked up to now. The “right” math of the searched physical reality can be either found among existing math formalisms (ex: Einstein’s interpretation of Lorenz transformation formula), or (more difficult case) – a new math should be created from scratch ( Example: how Newton created calculus, or string theorists now try to unite general relativity and quantum mechanics ) . In either way one can’t bypass math today. And it’s very difficult. Einstein, e.g. had great intuition, but he was “given” as helps 2
    professional mathematicians to connect his intuition to “correct” math.
    I see the importance of today’s discussion of the meaning of naturalness and un-naturalness as an attempt to find the right math in solving current problems in physics.

    • Richard Bauman

      Sorry Bob, but math leads us to the Big Bang was an accident. No math tells me this is the 8th bang, which leads to this near perfect universe and why we had a bang in the first place. Nature is simple is a better logic.

  9. All of these usual and familiar intuitions about naturalness occur within a universe within which we have a large number of warranted expectations. When it comes to intuitions about the entire universe, what basis can their possibly be for entertaining presumed intuitions as to how it’s “expected” to go. There’s a universe, and it is what it is. In short, it seems absurd to apply the same intuitions applicable within the world to the world itself. Of course you are veering into philosophical territory here….

    • Torbjörn Larsson, OM

      It would be very unnatural for a process to produce only one object. So we can’t be sure what “what it is” is.

      This is before you veer into philosophy of course, where you can imagine anything, even that you have only one universe out of inflation. (To name the first process which naturally creates many universes.)

  10. Thank you Matt for explaining some of these concepts. It is really disheartening reading internet discussions about some of these particle physics topics where it is construed as if the whole field is filled with simpletons..

    Perhaps going over some of the old objections to naturalness that are manifestly wrong.. Like the usual nonsequiturs, eg dimensional regularzation and the concepts where people simply claim that any old naive UV theory can fix everything no problem.

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  12. Thanks for enlightening us, Matt on the problems of ‘unnaturalness’ of the universe. I’m sure you know where the problem lays. I only hope that you will share it with us, such an ungrateful audience. I have a ‘need’ to understand what this universe is like and the nuts and bolts of everything, and could not be possibly happy with closing the doors to these unanswered questions that are pestering my mind. Since we can’t do the field tests to find out what really is out there, we rely on examining the micro world and pasting things together into a wider picture of the universe. So far this approach has paid us good dividends, but all is not sticking nicely together. Just as when a broken vase that has been hastily glued together, can never look right any more, especially if we missed couple of smaller pieces of glass or ceramics. The finished product will be aesthetically unpleasing. likewise, something is not adding up to our expectations of the nature of the universe that it has to be 100% balanced. If universe is functioning on the edge of a knife it is disconcerting because
    not only is our future at stake, but also our sanity. So, I fully trust that you Matt have needed qualifications and abilities to solve this problem. I know you can do it.

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  14. Reblogged this on Dialogos of Eide and commented:
    The Need for Understanding Naturalness

  15. De verdad que estaba buscando esto, la verdad que es bueno conseguir sitios web como este, ahora mismo iniciaré un trabajo del cual este tema me va como anillo al dedo.