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Could the Higgs Nobel be the end of particle physics?

The 2013 Nobel Prize in Physics has been awarded to François Englert and Peter Higgs for their work that explains why subatomic particles have mass. They predicted the existence of the Higgs boson, a fundamental…

Spelling out the end? Claudia Marcelloni/CERN

The 2013 Nobel Prize in Physics has been awarded to François Englert and Peter Higgs for their work that explains why subatomic particles have mass. They predicted the existence of the Higgs boson, a fundamental particle, which was confirmed last year by experiments conducted at CERN’s Large Hadron Collider.

But today’s celebrations mask a growing anxiety among physicists. The discovery of the Higgs boson is an undoubted triumph, but many note that it hasn’t brought us any closer to answering some of the most troubling problems in fundamental science.

A senior physicist went so far as to tell me that he was “totally unexcited by the discovery of the Higgs boson”. Though not the typical reaction, this discovery threatens to close a chapter of 20th century physics without a hint of how to start writing the next page.

Until July last year, when physicists at the Large Hadron Collider (LHC) announced its discovery, the Higgs boson remained the last missing piece of the Standard Model of particle physics, a theory that describes all the particles that make up the world we live in with stunning accuracy. The Standard Model has passed every experimental test thrown at it with flying colours, and yet has some rather embarrassing holes.

According to astronomical measurements, the matter described by the Standard Model that makes up the stars, planets and ultimately us, only accounts for a tiny fraction of the universe. We appear to be a thin layer of froth, floating on top of an invisible ocean of dark matter and dark energy, about which we know almost nothing.

Worse still, according to the Standard Model, we shouldn’t exist at all. The theory predicts that, after the Big Bang, equal quantities of matter and antimatter should have obliterated each other, leaving an empty universe.

Both of these are good scientific reasons to doubt that the Standard Model is the end of the story when it comes to the laws of physics. But there is another, aesthetic principle that has led many physicists to doubt its completeness – the principle of “naturalness”.

The Standard Model is regarded as a highly “unnatural” theory. Aside from having a large number of different particles and forces, many of which seem surplus to requirement, it is also very precariously balanced. If you change any of the 20+ numbers that have to be put into the theory even a little, you rapidly find yourself living in a universe without atoms. This spooky fine-tuning worries many physicists, leaving the universe looking as though it has been set up in just the right way for life to exist.

The Higgs’s boson provides us with one of the worst cases of unnatural fine-tuning. A surprising discovery of the 20th century was the realisation that empty space is far from empty. The vacuum is, in fact, a broiling soup of invisible “virtual” particles, constantly popping in and out of existence.

The conventional wisdom states that as the Higgs boson passes through the vacuum it interacts with this soup of virtual particles and this interaction drives its mass to an absolutely enormous value – potentially up to a hundred million billion times larger than the one measured at the LHC.

Theorists have attempted to tame the unruly Higgs mass by proposing extensions of the Standard Model. The most popular of which is “supersymmetry”, which introduces a heavier super-particle or “sparticle” for every particle in the Standard Model. These sparticles cancel out the effect of the virtual particles in the vacuum, reducing the Higgs mass to a reasonable value and eliminating the need for any unpleasant fine-tuning.

Supersymmetry has other features that have made it popular with physicists. Perhaps its best selling point is that one of these sparticles provides a neat explanation for the mysterious dark matter that makes up about a quarter of the universe.

Although discovering the Higgs boson may have been put forward as the main reason for building the 27km Large Hadron Collider (LHC), what most physicists have really been waiting for is a sign of something new. As Higgs himself said shortly after the discovery last year, “[The Higgs boson] is not the most interesting thing that the LHC is looking for”.

So far however, the LHC has turned up nothing.

If supersymmetry is really responsible for keeping the Higgs boson’s mass low, then sparticles should show up at energies not much higher than where the LHC found the Higgs. The fact that nothing has been found has already ruled out many popular forms of supersymmetry.

This has led some theorists to abandon naturalness altogether. One relatively new idea known as “split-supersymmetry” accepts fine-tuning in the Higgs mass, but keeps the other nice features of supersymmetry, like a dark matter particle.

This may sound like a technical difference, but the implications for the nature of our universe are profound. The argument is that we live in a fine-tuned universe because it happens to be one among an effectively infinite number of different universes, each with different laws of physics. The constants of nature are what they are because if they were different atoms could not form, and hence we wouldn’t be around to wonder about them.

This anthropic argument is in part motivated by developments in string theory, a potential “theory of everything”, for which there are a vast number (roughly 10500) different possible universes with different laws of physics. (This huge number of universes is often used as a criticism of string theory, sometimes derided as a “theory of everything else” as no one has so far found a solution that corresponds to the universe we live in.) However, if split-supersymmetry is right, the lack of new physics at the LHC could be indirect evidence for the existence of the very multiverse anticipated by string theory.

All of this could be rather bad news for the LHC. If the battle for naturalness is lost, then there is no reason why new particles must appear in the next few years. Some physicists are campaigning for an even larger collider, four times longer and seven times more powerful than the LHC.

This monster collider could be used to settle the question once and for all, but it’s hard to imagine that such a machine will get the go ahead, especially if the LHC fails to find anything beyond the Higgs.

We are at a critical juncture in particle physics. Perhaps after it restarts the LHC in 2015, it will uncover new particles, naturalness will survive and particle physicists will stay in business. There are reasons to be optimistic. After all, we know that there must be something new that explains dark matter, and there remains a good chance that the LHC will find it.

But perhaps, just perhaps, the LHC will find nothing. The Higgs boson could be particle physics’ swansong, the last particle of the accelerator age. Though a worrying possibility for experimentalists, such a result could lead to a profound shift in our understanding of the universe, and our place in it.

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20 Comments sorted by

  1. Prasad Sudhakar

    logged in via Twitter

    First line, you surely meant Physics and not Medicine! :-)

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  2. Khalil A. Cassimally

    Community Coordinator at The Conversation

    But then again, if the LHC finds nothing, that's something. It disproves hypothesis and contributes to the advancement of science. Surely worth it.

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    1. Akshat Rathi

      Science and Data Editor at The Conversation

      In reply to Khalil A. Cassimally

      Yeah. The question is not about the value of the LHC. Instead, Harry's point is that there is very little clue about what to do next. If they don't come up with a good solution, LHC funding might run out. And if the answer is bigger accelerators, that's not a good one to hear either.

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    2. Khalil A. Cassimally

      Community Coordinator at The Conversation

      In reply to Akshat Rathi

      Absolutely. Harry's point was quite illuminating. Just pointing out that a negative result by the LHC may condemn the field of particle physics but will still push the frontiers of science forward.

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  3. Mark D. Roberts

    failure

    no, not the end of particle physics, what will happen is data from satalites will become more important than that from accelorators. I think that it was awarded to the wrong people...

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  4. Jack Nagy

    logged in via Facebook

    "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" - Lord Kelvin, 1900

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    1. Robert Tony Brklje
      Robert Tony Brklje is a Friend of The Conversation.

      retired

      In reply to Jack Nagy

      Of course the most obvious particle to be discovered or not is the gravity particle or not. Now that particle if it exists would transform society as much as the discovery and use of the electron.
      It's discovery would open the universe up to us.

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  5. Stephen Nicholson

    Town Planner

    Thanks for a well written article that I could (generally) follow, even if some of the terms are jargon to me. But it is a good basis for further reading.
    Only one puzzle to me:
    "However, if split-supersymmetry is right, the lack of new physics at the LHC could be indirect evidence for the existence of the very multiverse anticipated by string theory."
    This indirect evidence could be problematic - something is proven because you don't find evidence of something else? Are the choices really that binary?

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    1. Harry Cliff

      Particle physicist and Science Museum fellow at University of Cambridge

      In reply to Stephen Nicholson

      It certainly wouldn't be proof of the existence of other universes, but it would at least be suggestive.

      Of course, there could be some other, larger theory that makes the Higgs mass natural, which has yet to be discovered. Some theorists even suggest that the Standard Model on its own it sufficient to keep the Higgs mass low, so really there are many possibilities!

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    2. Yoron Hamber

      Thinking

      In reply to Harry Cliff

      Heh, the particle is a field :) And the field is either without Lorentz contractions and time dilations, or it is with both? Don't think particle physics is finished in any way, it all depends on what you define as particles it seems. And the Standard theory isn't finished either.

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  6. Leslie Shaw

    Retired

    So why is an alternative theory such as the "Electric Universe" which postulates electro magnetism as the prime driver rather than gravity and leaves no room for the big bang, black holes, dark matter and energy, and other mathematically constructed wraiths, not even considered but actively condemned?

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    1. Yoron Hamber

      Thinking

      In reply to Leslie Shaw

      Because it is wrong. If it was viable it would have been interesting, although slightly boring.

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    2. Caroline Copley

      student

      In reply to Yoron Hamber

      Although I don't know much about the Electric Universe theory I have read a fair few criticisms of it. However that theory having no validity doesn't preclude a different sort of role for EM as discussed in my post. There are some rather interesting thermodynamic perspectives floating around too which relate gravity and thermodynamics together (e.g. Peter Ford) or stand on their own.
      I think it is important to accept the standard model but also understand that it has flaws which further investigations may expand on. These may indeed involve EM or a very similar force to it, or some aspect of thermodynamism, and therefore ideas involving these should not be dismissed outright, even though it is generally accepted the Electric Universe is not correct.

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  7. Caroline Copley

    student

    From a biological point of view the argument is turned around, I can probably give a qualified opinion on that but my stuff on the physics is unfortunately just guesses based on first year physics and online stuff.
    My guess on the Big Bang and the subsequent result is that the Universe was created in response to an error in a background (eternal) field and that there were indeed many possibilities, some of which were probabilities and one of which worked. The coincidental and elegant nature of…

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  8. Jonathan Shearman

    Global Document Specialist

    'Some physicists are campaigning for an even larger collider, four times longer and seven times more powerful than the LHC.'

    My feeling is we could build a collider the size of the moon's orbit, and we'd still never get to the bottom - because there isn't one.

    'Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are part of nature and therefore part of the mystery that we are trying to solve.' - Max Planck

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  9. Adam Smith

    Psychologist & part-time astro-physicist

    The Cryogenic Dark Matter Search (CDMS) collaboration reported earlier this year that they have found three dark matter WIMP (Weakly Interacting Massive Particle) signatures in their data, which was collected using detectors filled with silicon atoms stored deep underground in the Soudan mine in Minnesota, USA. The three events are consistent with a dark matter WIMP sub-atomic particle of mass 8.6 GeV, roughly nine times heavier than a proton. The CDMS collaboration scientists estimated that there…

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