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The Rise and Fall of Supersymmetry 138

Posted by Soulskill
from the who-needs-experimental-evidence-anyway dept.
Ethan Siegel at the StartsWithABang blog writes: "Have you ever wondered why the masses of the fundamental particles have the small values that they do, compared to, say, the Planck scale? Whether the fundamental forces all unify at some high energy? And whether there's a natural, compelling particle candidate for dark matter? Well, in theory supersymmetry (or SUSY, for short) could have solve all three of these problems. In fact, if it solves the first one alone, there will be definitive experimental signatures for it at the Large Hadron Collider. Well, the LHC has completed its first run, and found nothing. What does this mean for theoretical physics, for SUSY in particular, and what are the implications for string theory? A very clear explanation is given here; it might be time to start hammering in those coffin nails."
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The Rise and Fall of Supersymmetry

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  • by schlachter (862210) on Tuesday March 04, 2014 @11:18PM (#46404703)

    Is there an xkcd comic that explains this at the level that most of us can understand? Something with an exacerbated physicist trying desperately to explain the experiment with analogies and gestures would be ideal?

    • by flaming error (1041742) on Tuesday March 04, 2014 @11:28PM (#46404767) Journal

      I'll try. Supersymmetry predicted the existence of subatomic particles which the LHC would detect. The LHC hasn't detected them.

    • by dreamchaser (49529) on Tuesday March 04, 2014 @11:31PM (#46404791) Homepage Journal

      I don't think there is one. Simply but probably poorly put, supersymmetry postulates that each particle that we know of and have observed has a heavier 'super-symmetric' partner particle. The significance of this is that if true it explains a whole bunch of how the observed Universe works. If it is not true it's almost as exciting really, at least to me, because it means there are some big missing pieces to our current models and a lot of new and exciting work will need to be done.

      The short version of the article is that the LHC should have detected supersymmetric particles by now. There's still a slight chance that the next run will, but the energies that fit the current theories are running out. If they are not detected soon physicists might just have to move on to new theoretical models. For one thing, string theory will probably need to be scrapped.

      • by QQBoss (2527196)

        For one thing, string theory will probably need to be scrapped.

        I felt a minor disturbance (you know, like quark-sized) in the force, as if a few hundred physics grad students had their thesis hopes suddenly ended.

        That said, I am not a physicist, but I would like to add a hearty 'Huzzah!' to what I am sure is a chorus of many other physicists not present, at least based on my trying to keep up modestly with the goings on.

      • by Alomex (148003) on Wednesday March 05, 2014 @03:23AM (#46405793) Homepage

        For one thing, string theory will probably need to be scrapped.

        This much has been obvious for quite a while. Too much time has gone by without string theory being able to produce a falsifiable statement and now that finally we have one for SUSY, it failed.

        It's been around for about 35 years in its current form and even its best proponent, the distinguished Juan Maldacena, thinks it is still 20 to 30 years before it can be tested experimentally.

        p.s. you can count Richard Feynman among the superstring skeptics.

        • by Kjella (173770) on Wednesday March 05, 2014 @05:31AM (#46406221) Homepage

          Just because it's ridiculously hard to prove doesn't mean that it's false. For example, most physists believe gravity needs a force carrier which they've called a "graviton", the same way light (electromagnetic radiation) consists of photons. That theory is 80 years old and still totally unproven but as long as nobody has a good competing theory we still kind of assume that's how it works. Not that we're not trying to look for gravitational waves and other clues, but most of it is so far off the scale of what we can experimentally detect that it'll probably still be unproven in a thousand years.

          • by negablade (2745981) on Wednesday March 05, 2014 @06:54AM (#46406527)

            Just because it's ridiculously hard to prove doesn't mean that it's false. For example, most physists believe gravity needs a force carrier which they've called a "graviton", the same way light (electromagnetic radiation) consists of photons. That theory is 80 years old and still totally unproven but as long as nobody has a good competing theory we still kind of assume that's how it works.

            Gravity waves have already been proven to exist. The 1993 Nobel Prize in physics was awarded for the study of the Hulse-Taylor binary pulsar that showed indirect confirmation of the existence of gravity waves http://en.wikipedia.org/wiki/H... [wikipedia.org].

            Not that we're not trying to look for gravitational waves and other clues, but most of it is so far off the scale of what we can experimentally detect that it'll probably still be unproven in a thousand years.

            Gravity wave detection is expected within the next 20 years from the LIGO programme http://en.wikipedia.org/wiki/G... [wikipedia.org], http://www.ligo.caltech.edu/ [caltech.edu] and http://en.wikipedia.org/wiki/L... [wikipedia.org]. It won't require a thousand years, nor is it beyond existing technology. LIGO is already taking measurements in the US, at Hanford and Livingston, and advanced LIGO will increase the sensitivity of the LIGO interferometers by a an order of magnitude, and is expected to increase detection rates from a few per year to 100s per year by increasing the detection volume a thousand fold. If advanced LIGO doesn't detect anything, then it will be time to review the theory.

            (I worked for ~6 years at the University of Western Australia in the physics department in collaboration with the Australian LIGO research group)

          • by Alomex (148003)

            I didn't say it was false. However a theory that can produce no predictions is useless and needs to be scrapped. People working on it need to be repositioned to more useful pursuits within theoretical physics.

            • by microbox (704317)
              String theory did produce predictions... like a graviton leaving the brane [unige.ch].

              In my experience, most of the anti-physics, anti-string-theory sentiment is based on "look, those really smart guys aren't so smart, so I must be smart too, or at least smart sounding."
              • Actually those are physicists that have been saying string theory is all hat. Just because you don't like that doesn't make it not true. String theory is dead. Data after data being collected from experiments have been proving String Theories claims as false.
                • by microbox (704317)

                  Just because you don't like that doesn't make it not true.

                  Actually I *do* like the idea that string theory gets buried. My point still stands. Science deniers everywhere (esp. in the social sciences) will have to find a new branch of physics to rail against in order to rationalize their motivated reasoning.

              • by Alomex (148003)

                You are far off the mark dude. In fact I don't know any professional physicist whose criticism of string theory is motivated by such childish considerations. Personally, I've been following string theory since the early 80s and I was initially very enthusiastic about it.

                By the late 80s, however there were already more patches than one usually sees in such theories, and by the late 90s things were looking rather bad. The last 15 years have done nothing to reverse that assessment.

                • by microbox (704317)

                  In fact I don't know any professional physicist whose criticism of string theory is motivated by such childish considerations.

                  Not physicists... I'm talking about wingnuts in the social sciences, and science deniers of other kinds as well. Sorry for not being clear.

          • Actually there has been other published data from experiments that say it's false. Time to give up zippy.
        • you can count Richard Feynman among the superstring skeptics.

          Appeal to authority.

      • by stevelinton (4044)

        . For one thing, string theory will probably need to be scrapped.

        Not because of this. Supersymmetry and string theory address different problems and are more or less independent.

        • by Warbothong (905464) on Wednesday March 05, 2014 @06:10AM (#46406359) Homepage

          . For one thing, string theory will probably need to be scrapped.

          Not because of this. Supersymmetry and string theory address different problems and are more or less independent.

          String theory builds on supersymmetry, so evidence of string theory would imply supersymmetry, but evidence of supersymmetry wouldn't imply string theory. Dually, evidence against string theory wouldn't kill supersymmetry, but evidence against supersymmetry would kill string theory.

          Until, of course, some string theorist fudges the numbers to make it unfalsifiable again ;)

      • by Nutria (679911)

        For one thing, string theory will probably need to be scrapped.

        Electric Universe FTW!!!

      • If we get a new theory, hopefully it will explain how fucking magnets work.

      • https://www.youtube.com/watch?... [youtube.com]

        The Higgs Boson was supposed to have an Earth-shattering Kaboom.

        They found something that they called a Higgs Boson, but what they found doesn't have the earth-shattering kaboom the Mathematical Physicists predicted it would.

        Where's the kaboom?!?

    • by Roger W Moore (538166) on Wednesday March 05, 2014 @01:51AM (#46405491) Journal
      Not that I know of but since I am an exacerbated physicist how about I try to explain our experiment with analogies and you can just imagine appropriate gestures to go with them? First though I should say that while SUSY is in trouble the article paints an overly pessimistic picture and gets a few things wrong.

      The problem SUSY is trying to solve is that nature seems to be performing an amazing balancing act with the Higgs field. Now this is not just some ordinary balancing act that generates a few "oohs" and "aahs" from the audience like Idol Rock [wikipedia.org]. According to the physics we know the chance of the Higgs boson having the mass is does is about one in 10^30. Those are about the same odds as some person winning a national lottery 5 times in a row and getting a lesser prize in the 6th week. By about the third or fourth win the "oohs" and "aahs" are replaced by a call to the serious fraud squad of the local police force with a request to figure out how the person is fixing the results of the lottery because the chance that this person is just "really lucky" are so astronomically small that nobody will believe it is just chance.

      This is the situation we are in now with physics and the usual way nature solves balancing problems like this is with a symmetry that requires the balance be perfect. For example it is not just dumb luck that the electrical charge in the universe happens to cancel out so precisely - we were not just "really lucky" with our Big Bang! - there is a symmetry which gives conservation of electric charge which requires that the balance be exact. To solve the problem with the Higgs mass being so tiny the symmetry is called "Supersymmetry" - not because it flies around with a big S on its chest saving us from bad symmetries but because it is an extremely high level symmetry, perhaps even the highest possible in nature. In very simple terms you could describe it as a symmetry between force and matter.

      This is also why I would disagree with the article when it says that the LHC must see supersymmtery or else it cannot solve our balance problem. This would be like saying that if you win the lottery twice that's ok but win it a third time and you are automatically guilty of a crime. Winning it 3 times in a row might be very, very unlikely but this is a continuous scale. 10TeV SUSY may be less natural than 1TeV but it is not so incredibly less likely that you know it cannot be right - sometimes 0.1% chances happen e.g. the angular size of the moon being almost exactly the same as the sun on Earth.

      Supersymmetry is not a perfect symmetry because otherwise all the super-particles (which have fun names likes squarks, winos and sleptons) would then have the same mass as our Standard Model particles and we would have already seen them. So it has to be broken by some unknown mechanism which gives all the super particles higher masses which is why we have not yet seen them - our colliders do not yet have enough energy.

      Another possibility is that the lightest super particle cannot decay. This would give us a high mass, stable particle which is an excellent candidate for dark matter. However this where the article is not correct in saying that the particle should have been seen by direct search experiments because one possibility is that it is a gravitino (a super partner of the graviton). This would mean that it only interacts via gravity and will not be seen in direct search experiments. This would be a real pain for physics because while we would know that we had produced them in the detector (because the other particles we can see will rebound from it) it will be very hard to prove that these were the Dark Matter astronomers see.

      Probably out best chance to see supersymmetry, or indeed any new physics, will be the next three year run of the LHC. We will get almost twice the energy and about 5 times the luminosity. Certainly if we do not find supersymmetry or something else then the chances of us every seeing it with the LHC are dramatically lower after this point because increasing numbers of events at the same energy only slowing increase the regions you can search. So fingers crossed!
      • I am an exacerbated physicist

        My condolences. I hope you'll get better!

      • by selectspec (74651)

        Thank you for the informative rebuttal and for not quoting Che Guevara.

      • I've always liked the "infinite universes" theory that explains improbable physical constants with the observation that: "if this physical constant were not what it is, we would not be here..." In so many other universes where that physical constant did happen to be something other than what it is here, there is nobody there to observe it.

      • by PvtVoid (1252388)

        According to the physics we know the chance of the Higgs boson having the mass is does is about one in 10^30.

        Only if you know the measure on the space of parameters for the Higgs. Which you don't.

        The question isn't "is there SUSY or not?" That question cannot be answered, because you can always push the SUSY breaking scale up to a little higher than the energy of your collider. SUSY will be a part of quantum gravity for the foreseeable future, since String Theory is not consistent without it as far as anybody can tell.

        The real question is: "Does SUSY make useful predictions for detecting physics beyond the S

        • by Zalbik (308903)

          The real question is: "Does SUSY make useful predictions for detecting physics beyond the Standard Model?" The answer to that seems to be tending very strongly toward "No."

          Of course SUSY makes useful predictions. SUSY makes predictions about super-particles.

          The problem is, it's starting to look like those super-particles do not exist.

    • by Nutria (679911)

      exacerbated physicist

      I think you meant "exasperated physicist".

    • Experiments are real but the results aren't pretty. SUSY is pretty but the results aren't real.

      When we look at the tables of known particles, it is tempting to think of the periodic table. We might hope to see patterns in the particles, and then guess at the missing parts of the grid. Unfortunately, we don't have nice families of halogens, alkaline earths, and so on. We started off with electrons, protons, and neutrons which all had sensible masses even if the electron was less than a thousandth of the m

    • by Kelbear (870538)

      If you replace the "en." in a wikipedia like with "simple.", it takes you to a more digestible version of most pages.

      http://simple.wikipedia.org/wi... [wikipedia.org]

      The regular wikipedia article was mostly gibberish to me, so I had to consult this link to get a basic idea of what SUSY is.

    • by sjames (1099)

      How about a song?

      Wake up, little SUSY, wake up
      The movie wasn't so hot
      It didn't have much of a plot
      We fell asleep, our goose is cooked
      Our reputation is shot
      Wake up, little SUSY, It's time to go home

  • Bad web design (Score:2, Flamebait)

    by Carnildo (712617)

    I'm sure a "very clear explanation" is given, but I'm not going to read something that presents it to me at a rate of one sentence per page.

    • It's all on one page, and it's paragraphs separated by useful, illustrative graphics. ADHD much?

    • by sk999 (846068)

      Web design was copied from /. beta. Surely you only read /. from an iPhone?

  • by mmell (832646) <mmell@hotmail.com> on Tuesday March 04, 2014 @11:29PM (#46404779)
    into M/String theory, when particles and wavicles fell out of favor in place of open- or closed-loops on the brane?

    Never mind - the presence of empirical data which tends to place supersymmetry in doubt is enough to convince me that either we need a better theory, or the existing theory needs a major overhaul.

  • by Anonymous Coward on Wednesday March 05, 2014 @12:01AM (#46404935)

    ...is disconfirm our beliefs.

  • SUSY isn't dead yet. (Score:5, Interesting)

    by ITEM-3 (3348273) on Wednesday March 05, 2014 @12:37AM (#46405103)
    In SUSY, there is no way to predict the masses of supersymmetric particles, but there is a way to predict a range of values that the mass of the lightest SUSY particle must fall within in order for SUSY to be a valid theory. The range is determined by the mass of the Higgs boson. For small Higgs masses (less than ~100GeV, don't quote me on these numbers as it's been a while) and large Higgs masses ( greater than ~140GeV), the range is very small, and our current colliders would have already disproven SUSY. However, the observed Higgs mass of 126GeV is a sweet spot which allows the mass of the lightest SUSY particle to be far greater than the LHC can produce. It'll take a few more colliders before we can dismiss SUSY completely.
    • by hweimer (709734) on Wednesday March 05, 2014 @03:56AM (#46405913) Homepage

      However, the observed Higgs mass of 126GeV is a sweet spot which allows the mass of the lightest SUSY particle to be far greater than the LHC can produce. It'll take a few more colliders before we can dismiss SUSY completely.

      The main motivation behind SUSY is that it solves the fine-tuning problem associated with electroweak symmetry breaking. But if SUSY itself is fine-tuned, this solution creates the same problems that it was intended to solve.

      BTW: The largest constraint on SUSY partner masses does not come from the $9bn LHC, but from the ACME collaboration's measurement of the electron electric dipole moment, a $6M tabletop atomic physics experiment.

      • BTW: The largest constraint on SUSY partner masses does not come from the $9bn LHC, but from the ACME collaboration's measurement of the electron electric dipole moment, a $6M tabletop atomic physics experiment.

        Gasp! You mean maybe, just maybe, CERN might want to hold off on those grandiose plans for a bigger, better LHC and think if it might be able to toss that cash around and get better bang for the..um..Euro?

  • hrm... (Score:4, Insightful)

    by Charliemopps (1157495) on Wednesday March 05, 2014 @12:38AM (#46405111)

    I liked this article. The author did a good job of dumbing things down for us mortals. Super symmetry has been dieing since the day the LHC came online. But I have a problem with:

    A lot of people have invested their entire careers in SUSY, and if it’s not a part of nature, then a lot of what they’ve invested in is nothing more than a blind alley. For example, if there is no SUSY in nature, at any energy scale (including the Planck Scale, although this will be a challenge to test), then string theory cannot describe our Universe. Plain and simple.

    I seriously doubt many of the geniuses that dedicated their entire lives with Super Symmetry would consider it a blind alley. There's been some amazing math, and amazing theoretical work on it. It's a very very good theory. It's rather clear that this point that it's not correct, but whatever the truth really is (something we clearly haven't even imagined yet) will be helped greatly by the work done by those investigating super symmetry. The Wright Bothers didn't just hop in a plane and fly off... There were mountains of work by thousands of failures that they built their success on.

    • "will be helped greatly" - You know this how? The Wright Brothers designed their plane using very well established and tested principles. They didn't manufacture a bunch of math and then set out to build a machine to prove it. And unless you're counting the people who figured out how to make screws and such, I believe you're vastly overrating the preceding contributions. Meaningful ones anyway.
      • The Wright Brothers designed their plane using very well established and tested principles.

        You're proving my point for me.

        • Principles that were unknown to Simon Newcombe and Lord Kelvin, both of whom predicted machines heavier than air would not fly for a very long time before the Wright brothers did it within a few years?

    • Science progresses one funeral at a time. - Max Planck
  • I don't know about you, but that link goes to an article that has been very cleanly written, no information overload, very well planned. I was surprised that people can write scientific stuffs using such clarity.
  • by ferrisoxide.com (1935296) on Wednesday March 05, 2014 @04:15AM (#46405977) Homepage
    By explaining that those extra supersymmetrical particles are actually packed away in really tiny dimensions that the LHC can't touch. Prove it aint so!
  • Sorry, I have trouble with these big letters, a handful short lines shown at a time, and huge images that take up a lot of the screen. Feels like an oversized mobile site or a powerpoint with vertical scrolling. I'm reading this at a low res desktop not on a 2048x1536 tablet. Thanks.

  • Perhaps it's time to reexamine Coleman-Mandula and see if there are some conditions that can be relaxed and thus create a variation of supersymmetry.

  • it might be time to start hammering in those coffin nails.

    this makes me happy, and the researchers should be happy as well...so another theory is proven wrong...*that's science*

  • "it might be time to start hammering in those coffin nails."

    Quite clearly you are a SUSY denier. Have you not seen the models? The many papers? To deny the existence of SUSY is to deny all but certain fact! And do not resort to quoting LHC "results" as that is just chery picking from the very large parameter space SUSY occupies!

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