Of Particular Significance

It’s (not) The End of the World

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 12/21/2012

The December solstice has come and gone at 11:11 a.m. London time (6:11 a.m New York time). That’s the moment when the north pole of the Earth points most away from the sun, and the south pole points most toward it. Because it’s followed by a weekend and then Christmas Eve, it marks the end of the 2012 blogging season, barring a major event between now and year’s end. But although 11:11 London time is the only moment of astronomical significance during this day (clearly the universe does not care where humans set our international date line and exactly how we set our time zones, so destruction was never going to be at local midnight — something the media doesn’t seem to get) it obviously wasn’t the end of the world.

A lot of people do put a lot of stock in prophecy, including prophecies of the end of the world that nobody ever made (such as the one not made for today by the Mayans, through their calendar) and others that people made but were wrong (such as those made by Harold Camping last year and by many throughout history who preceded him.) If anyone were any good at prophecy they’d be able to use their special knowledge to become billionaires, so maybe we should be watching Bill Gates and Michael Bloomberg and the Koch brothers and people like that. I haven’t heard any rumors of them building bunkers or spaceships yet. Of course at the end of the year they may get a small tax hike, but that wouldn’t be the end of the world.

The Large Hadron Collider [LHC], meanwhile, has triumphantly reached the end of its first run of proton-proton collisions. Goal #1 of the LHC was to allow physicists at the ATLAS and CMS experiments to discover the Higgs particle, or particles, or whatever took their place in nature; and it would appear that, in a smashing success, they have co-discovered one.  But no Higgs particles, or anything like them, will be produced again until 2015. Although the LHC will run for a short while in early 2013, it will do so in a different mode, smashing not protons but the nuclei of lead atoms together, in order to study the properties of extremely hot and dense matter, under conditions the universe hasn’t seen since the earliest stages of the Big Bang that launched the current era of our universe.  Then it will be closed down for repairs and upgrades.  So until 2015, any additional information we’re going to learn about the Higgs particle, or any other unknown particle that might have been produced at the LHC, is going to be obtained by analyzing the data that has been collected in 2011 and 2012. The total amount of data is huge; what was collected in 2012 was about 4.5 times as much as in 2011, and it was taken at 8 TeV of energy per proton-proton collision rather than 7 TeV as in 2011. I can assure you there will be many new things learned from analyzing that data throughout 2013 and 2014.

Of course a lot of people prophesied confidently that we’d discover supersymmetry, or something else dramatic, very early on at the LHC. Boy, were they wrong! Those of us who were cautioning against such optimistic statements are not sure whether to laugh or cry, because of course it would have been great to have such a discovery early in the LHC program. But there was ample reason to believe (despite what other bloggers sometimes say) that even if supersymmetry exists and is accessible to the LHC experiments, discovering it could take a lot longer than just two years!  For instance, see this paper written in 2006 pointing out that the search strategies being planned for seeking supersymmetry might fail in the presence of a few extra lightweight particles not predicted in the minimal variants of supersymmetry. As far as I can tell at present, this very big loophole has only partly been closed by the LHC studies done up to now. The same loophole applies for other speculative ideas, including certain variants of LHC-accessible extra dimensions. I am hopeful that these loopholes can be closed in 2013 and 2014, with additional analysis on the current data, but until they are, you should be very cautious believing those who claim that reasonable variants of LHC-accessible supersymmetry (meaning “natural variants of supersymmetry that resolve the hierarchy problem”) are ruled out by the LHC experiments. It’s just not true. Not yet. The only classes of theories that have been almost thoroughly ruled out by LHC data are those predict on general grounds that there should be no observable Higgs particle at all (e.g. classic technicolor).

While we’re on the subject, I’ve been looking back at how I did on prophecy this year. It’s been a remarkably good year, probably my best ever — though admittedly I only made very easy (though not necessarily common) predictions. First, the really easy one:  I assured you, as did most of my colleagues, that 2012 would be the Year of the Higgs — at least, the Year of the Simplest Possible Higgs particle, called the “Standard Model Higgs”. It would be the year when Phase 1 of the Higgs Search would end — when we’d either find a Higgs particle of Standard Model type (or something looking vaguely like it), or, if not, we’d know we’d have to move to a more aggressive search in Phase 2, in which we’d look for more complicated versions of the Higgs particle that would have been much harder to find. We started the year with ambiguous hints of the Higgs particle, too flimsy to be sure of, but certainly tantalizing, at around a mass of 125 GeV/c2. In July the hints turned into a discovery — somewhat faster than expected for a Standard Model Higgs particle, because the rate for this particle to appear in collisions that produce two photons was higher than anticipated. The excess in the photon signal means either the probability for the Higgs particle to decay to photons is larger than predicted for a Higgs of Standard Model type, or both CMS and ATLAS experienced a fortunate statistical fluctuation that made the discovery easier. We still don’t know which it was; though we’ll know more by March, this ambiguity may remain with us until 2015.

One prophecy I made all the way back at the beginning of this blog, July 2011, was that the earliest search strategy for the Higgs, through its decays to a lepton, anti-lepton, neutrino and anti-neutrino, wouldn’t end up being crucial in the discovery; it was just too difficult. (In this experimental context, “lepton” refers only to “electron” or “muon”; taus don’t count, for technical reasons.) In the end, I said, it would be decays of the Higgs to two photons and to two lepton/anti-lepton pairs that would be the critical ones, because they would provide a clean signal that would be uncontroversial. And that prophesy was correct; the photon-based and lepton-based searches were the signals that led to discovery.

Now we’ve reached December, and the data seems to imply that except possibly for this overabundance of photons, which still tantalizes us, the various measurements of how the Higgs-like particle is produced and decays are starting to agree, to a precision which is still only moderate, with the predictions of the Standard Model for a Higgs of this mass. Fewer and fewer experts are still suggesting that this is not a Higgs particle. But it will be some years yet — 2018 or later — before measurements are precise enough to start convincing people that this Higgs particle is really of Standard Model type. Many variants of the Standard Model, with new particles and forces, predict that the difference of the real Higgs from a Standard Model Higgs may be subtle, with deviations at the ten percent level or even less. Meanwhile, other Higgs-like particles, with different masses and different properties, might be hiding in the data, and it may take quite a while to track them down. Many years of data collecting and data analysis lie ahead, in Phase 2 of the Higgs search.

Another prophecy I made at the beginning of the year was that Exotic Decays of the Higgs would be a high priority for 2012. You might think this prophesy was wrong, because in fact, so far, there have been very few searches at ATLAS, CMS and LHCb for such decays. But the challenge that required prioritizing these decays wasn’t data analysis; it was the problem of even collecting the data. The problem is that many exotic decays of the Higgs would lead to events that might not be selected by the all-important trigger system that determines which tiny fraction of the LHC’s collisions to store permanently for analysis! At the beginning of 2012 there was a risk that some of these processes would have been dumped by the trigger and irretrievably lost from the 2012 data, making future searches for such decays impossible or greatly degraded. At a hadron collider like the LHC, you have to think ahead! If you don’t consider carefully the analyses you’ll want to do a year or two from now, you may not set the trigger properly today. So although the priority for data analysis in 2012 was to find the Higgs particle and measure its bread-and-butter properties, the fact that the Higgs has come out looking more or less Standard Model-like in 2012 means that focusing on exotic possibilities, including exotic decays, will be one of the obvious places to look for something new, and thus a very high priority for data analysis, in 2013 and 2014. And that’s why, for the trigger — for the collection of the data — exotic decays were a very high priority for 2012. Indeed, one significant use of the new strategy of delayed data streaming at ATLAS and of data parking at CMS (two names for the same thing) was to address this priority. [My participation in this effort, working with experimentalists and with several young theorists, was my most rewarding project of 2012.]  As I explained to you, a Higgs particle with a low mass, such as 125 GeV/c2, is very sensitive to the presence of new particles and forces that are otherwise very difficult to detect, and it easily could exhibit one or more types of exotic decays.  So there will be a lot of effort put into looking for signs of exotic decays in 2013 and 2014! I’m very excited about all the work that lies ahead of us.

Now, the prophecy I’d like to make, but cannot — because I do not have any special insight into the answer — is on the question of whether the LHC will make great new discoveries in the future, or whether the LHC has already made its last discovery: a Higgs particle of Standard Model type. Even if the latter is the case, we will need years of data from the LHC in order to distinguish these two possibilities; there’s no way for us to guess. It’s clear that Nature’s holding secrets from us.  We know the Standard Model (the equations we use to describe all the known particles and forces) is not a complete theory of nature, because it doesn’t explain things like dark matter (hey, were dark matter particles perhaps discovered in 2012?), and it doesn’t tell us why, for example, there are six types of quarks, or why the heaviest quark has a mass that is more than 10,000 times larger than the mass of the lightest quarks, etc. What we don’t know is whether the answers to those secrets are accessible to the LHC; does it have enough energy per collision, and enough collisions, for the job?  The only way to find out is to run the LHC, and to dig thoroughly through its data for any sign of anything amiss with the predictions of the Standard Model. This is very hard work, and it will take the rest of the decade (but not until the end of the world.)

In the meantime, please do not fret about the quiet in the tunnel outside Geneva, Switzerland. The LHC will be back, bigger and better (well, at least with more energy per collision) in 2015. And while we wait during the two year shutdown, the experimentalists at ATLAS, CMS, and LHCb will be hard at work, producing many new results from the 2011 and 2012 proton collision data! Even the experiments CDF and DZero from the terminated Tevatron are still writing new papers. In short, fear not: not only isn’t the December solstice of 2012 the end of the world, it doesn’t even signal a temporary stop to the news about the Higgs particle!


One last personal note (just for those with some interest in my future.)

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31 Responses

  1. WMAP Team Releases Final Results, Based on Nine Years of Observations:
    WMAP observations also support an add-on to the big bang framework to account for the earliest moments of the universe. Called “inflation,” the theory says that the universe underwent a dramatic early period of expansion, growing by more than a trillion trillion-fold in less than a trillionth of a trillionth of a second. Tiny fluctuations were generated during this expansion that eventually grew to form galaxies.
    Remarkably, WMAP’s precision measurement of the properties of the fluctuations has confirmed specific predictions of the simplest version of inflation: the fluctuations follow a bell curve with the same properties across the sky, and there are equal numbers of hot and cold spots on the map. WMAP also confirms the predictions that the amplitude of the variations in the density of the universe on big scales should be slightly larger than smaller scales, and that the universe should obey the rules of Euclidean geometry so the sum of the interior angles of a triangle add to 180 degrees- ie… the universe is three dimensional.

    Where there is matter, there is dark matter, that has gravity but does not emit any light. So light(photons) also locked inside closed system of dark matter(during inflation)- like, Gold stone bosons locked inside matter, creating rest mass?

    Higgs boson(h) create graviton at lower energy level, outside the closed system of matter(for a while). We cannot differentiate this with Neutrino oscillation- while it behave as Higgs boson of dark matter, acquire it mass from “dark energy”- thus neutralizing the effect of expansion of the space, from matter explosion?.
    Analogy: When baking a cake, the distance between raisins go apart. If raisins were replaced by small stones, will be more intact(matter not the space) during baking(from acceleration of the expansion of the universe)???

  2. Actually, Harold Camping did use his prophesy to make lots of money — by convincing thousands of people to donate money to him and his radio program by convincing them that the world would end so their earthly posessions were of no value (some gullible ppl actually sold their house and everything and gave it to him).

  3. The world did not end, as was fully expected by rational people 🙂
    so let’s celebrate the Season …

    * _██_*。*. / .˛* .˛.*.★* *★ 。*
    ˛. (´• ̮•)*˛°* /.♫.*˛.* ˛_Π_____. * ˛*
    .°( . • . ) ˛°. /• ‘♫ ‘.˛*. /______/~\*. ˛*.。˛* ˛. *。
    *(…’•’.. ) *˛╬╬╬╬╬˛°.|田田 |門|╬╬╬╬ .
    ¯˜”*°••°*”˜¯`´¯˜”*°••°*”˜¯` ´¯˜”*°´¯˜”*°••°*”˜¯`´¯

    Merry Christmas and all the best for 2013 ! Joseph

    1. Yeah, I noticed that too and checked a dictionary to be sure, but since English isn’t my first language I decided to remain silent 😉

        1. 1) I wasn’t referring to you (as should be obvious if you read closely.) I was referring to informal proof-readers, not to standard readers like yourself.

          2) You do not do a writer any favors by failing to point out even minor errors. Editing is generally appreciated. It is extremely difficult, when writing several thousand words a week, to avoid errors, and no one gains if errors remain in the text.

          3) There are no “minor” spelling mistakes.

  4. “This image maps the temperature of the radiation left over from the Big Bang, at a time when the universe was only 375,000 years old. It shows a temperature range of plus-or-minus 200 microKelvin, with fluctuations in the so-called cosmic microwave background radiation appearing here as color differences.” … Space.com

    +/- 200 micro Kelvin at T = 375,000 years?

    1. Does this rapid decrease in temperature suggests that the rate (speed) of expansion of space-time due to the Big Bang far exceeded the universal constant speed of light?

    2. Or maybe the Big Bang theory is just invalid?

    “Among other revelations, the data from WMAP revealed a much more precise estimate for the age of the universe — 13.7 billion years — and confirmed that about 95 percent of it is composed of mind-boggling stuff called dark matter and dark energy. WMAP data also helped scientists nail down the curvature of space to within 0.4 percent of “flat,” and pinpoint the time when the universe began to emerge from the cosmic dark ages (about 400 million years after the Big Bang.)” … Space.com

    3. Flat? … Could we be looking at the “horizon” of the spherical (closed) universe and mistaken it as flat. Remember we made the same mistake about the Earth being flat as well, because we could not see past the horizon.

    4. As far as the idea that if it was closed we should be able to see the back of our heads, well not if space-time was expanding faster the speed of light.

  5. ‘ If anyone were any good at prophesy’ should read ‘ If anyone were any good at prophecy’; unless my using English spelling misleads me, the first is the act of predicting while the second is the practice of prediction itself. Of course this is a minor point, it’s not the end of the world or anything.

  6. Professor Strassler,

    One last silly question. Perhaps I should study physics rather than ask, but here it is: What is the relationship between the Higgs field effect on a particle and one that is acquiring more mass as it approaches the speed of light. Thank you sir.

    Matt Chambers

    1. The Higgs field gives most particles a ‘rest mass’, a minimum mass present even when the particle is not moving. This increases in a predictable way as the particle’s speed approaches c.

      Without the Higgs many particles would have no ‘rest mass’ and be massless like the photon. They would travel at light speed all the time.

  7. Dear Prof. Strassler,

    thanks for this nice end of the year article summarizing the particle physis year 2012 🙂

    Can you say a bit more about what this hidden valley sector is, how it expands the minimal supersymmetry variants (I know only a little bit about the MSSM). Is this just a random ad hoc expansion or is it derived from some higher energy theory?

  8. Professor Strassler,

    I apologize for raising a question off-topic, and perhaps it’s a silly one at that. My question is: If it was possible to cool particles to absolute zero such that they would be in a state of suspended animation, would they no longer move through space and no longer be able to acquire mass from the Higgs field? If this is true, then wouldn’t that make a particle that would otherwise have mass massless? Thank you sir.

    Matt Chambers

    1. A particle does not need to move through space to gain mass from the Higgs field. Think of the Earth’s gravitational field, we feel gravity constantly, even when not moving. The same is true of other fields like air pressure.

      A particle cooled to absolute zero (An impossible task.) still moves; this is due to the uncertainty principle, which states we can never know the speed and the location of an object exactly. (A particle not moving at all and thus in one spot exactly would have both its position and speed known exactly.) Thus particles still jiggle at zero kelvin. For helium this jiggling is enough to keep it a liquid no matter how cold it gets.

      1. Kudzu,
        I appreciate the feedback. Obviously, I didn’t study physics but I’ve always been interested. Thanks.

  9. I personally found the measurement by LHCb of the small branching ratio of the Bs to two muons also a mayor event in 2012.
    Talking of which: does anyone know the EXPERIMENTAL value (plus reference) of the decay rate of the 2p -> 1s transition in hydrogen. I get the impression it has never been measured, at least I can’t find it anywhere on the internet. Thanks in advance.

    1. I just do not understand why people are so excited by the fact that LHCb found a small branching ratio for Bs to two muons.

      If they had found a big branching ratio, that would have been hugely exciting, because that would have told us the Standard Model is wrong.

      But finding a small branching ratio, as is true both for the Standard Model and for many other speculative theories, does NOT (despite all the press reports and mistaken blog articles) tell you that supersymmetry is ruled out. Absolute rubbish. You can just look at the formulas for the supersymmetry prediction for this process yourself, and you’ll see — it’s rubbish. I confirmed this with a theorist who specializes in this type of measurement. You can see that there is lots of room left for supersymmetry after this measurement in http://profmattstrassler.com/2012/11/16/remember-that-blow-to-supersymmetry-and-other-theories/

      The Higgs mass of 125 GeV/c^2 is MUCH more important in constraining supersymmetry. Entire classes of supersymmetric models are inconsistent with this number.

      And the most important measurements of all are the absence of any signs of new particles other than the Higgs. However, exactly which sets of supersymmetric variants are excluded by the non-observation of superpartner particles is still being worked out at this time (and it is very complicated work). It’s also a moving target, since much more will be done throughout 2013 with the current data set. The same is true for other speculative theories.

      1. It tells us that the Standard Model is all we need up to that level, that’s why I’m so excited! I don’t want to see a glimpse of some new theory with even more free parameters that is not able to explain why there are three generations of quark and leptons. I prefer the Standard Model up to around the Planck scale. Just a personal preference (and expectation), nothing more. Because my prophesy is that the Standard Model will never be replaced by anything else by the human race. So for me 2012 has been a great year.

        1. Well, Marcel — if you read this blog carefully, you’ll see your excitement is misplaced. Indeed, even if you read my previous comment.

          The LHCb measurement is also what would occur in MANY MANY MANY MANY theories that are not the Standard Model. It is a good way to discover new phenomena; it is not a very good way to rule out new phenomena. It gives very little evidence in favor of the Standard Model.

          By contrast, the absence of discoveries in the now vast array of the ATLAS and CMS measurements gives MUCH STRONGER (but still relatively weak) evidence in favor of the Standard Model, because MANY MANY MANY MANY variants of many different theories would have shown up by now.

          You’re putting way too much weight on the LHCb measurement, which is rather weak (though important), and far too little on all the measurements that were done by others.

          In any case, if the current situation makes you happy, fine with me. I don’t really get happy or unhappy about such things, as long as we learn the correct answers and aren’t led by our biases into making an error in interpreting or analyzing data.

          1. “as long as we learn the correct answers and aren’t led by our biases into making an error in interpreting or analyzing data.” I absolutely agree with that and it can’t be repeated enough! That’s why I want the EXPERIMENTAL value of the decay rate of the 2p->1s transition in hydrogen to check the outcome of a standard quantum mechanical calculation everybody says agrees so well with experiment 🙂

          2. Thanks Matt.
            Impressive work but I don’t think it’s there. It’s all about energy levels.It has a chapter called “Theory of Spontaneous Transition” and that was not what I was looking for 🙁

  10. I confess to not reading this article all the way through because I am in Spain with a very sick friend. But I did want to point out a trivial error in the part that I did read – the man who predicted the end of the world last year was Harold Camping, not Howard Camping.

    Happy New year!

  11. I am going to take the Mayans side. Even Townhall states they are wrong. You see TIME will stop, they just missed the date. Now lets see about physics. General Relativity, wrong; Quantum Mechanics, wrong; Expansion, wrong; Dark Matter, wrong; Multiverses, wrong. Given that, if you have a degree in Physics, you should ask for your tuition back. Why ? Time is discrete , not continuous. Even the Mayans missed that. Prophesy: In 40 years this will all be corrected. No need to reply, every one is sure this is wrong.

    1. Actually there are physics theories that attempt to quantize time. We haven’t been able to detect it (can’t measure time scales short enough yet,) but it seems likely (To me, a non-physicist, and some, but not all, physicists,) that a “Grand Unified Theory” will require quantization of space-time.

      Now, people will be sure you are wrong because of your flippant tone and your lack of evidence for your dismissal of very successful theories. Sure, we know quantum mechanics and general relativity are incompatible, and thus incomplete, but they’re both fantastically accurate. Any complete theory will have to reduce to them at the scales we can measure (just as Relativity reduces to Newtonian mechanics in many conditions.) “Wrong” is thus a misleading term.

      Also, if the Mayans were so good at seeing the future, why didn’t they prepare for the coming of the Spanish? Likewise with every other “wisdom of the ancients” philosophy: If the ancients were so wise, why are they all dead and their civilizations gone?

      I feel the scientific mindset is very important. You seem to think you have the answers already. I know I don’t have the answers, and I have reason to think no one else does either. But I’ll keep looking at the evidence, and the reasoning of others who look at the evidence, and hope to eventually find more of the answers. To me the concept of a world with nothing left to discover is disturbing, it’s far more comforting to be able to wonder at the vastness and complexity of the unknown than to sit in smug assurance that all is known.

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