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Friday, August 5, 2016

Pratfalls of the Physicists: Lessons of the SUSY and Diphoton Blunders

Ever since the atomic bomb was invented, some people have regarded physicists as almost godlike figures. But two examples I will discuss below show that large number of physicists are capable of falling flat on their faces.

What is called the 750 GeV diphoton excess is an observational blip reported in 2015 by scientists working with the Large Hadron Collider, the world's largest particle accelerator. When the diphoton excess was reported in 2015, scientists began to speculate that it might be a sign of physics beyond the Standard Model of physics.

But today scientists poured cold water on such thinking. As discussed here, they reported that the diphoton excess is just a random data blip that doesn't indicate anything important. David Charlton, leader of the ATLAS experiment at the Large Hadron Collider, reported the following:

There was a lot of excitement when we started to collect data. But in the [latest results] we see no sign of a bump, there's nothing. It is a pity because it would have been a really fantastic thing if there had been a new particle.

But (as mentioned here) our impatient theoretical physicists have already written 500 scientific papers pontificating on the deep significance of the diphoton excess. Today's announcement makes all such papers into laughable jokes. Such papers are now like some paper claiming to find some deep significance in an arrangement of objects on a road, with someone later announcing that the objects ended up in such a way because they fell out of a passing truck at random intervals.

You can call it the Diphoton Fiasco. But such a fiasco only has lasted for about 8 months. A much larger fiasco is what we may call the SUSY Fiasco. This embarrassing physicist's debacle has been dragging on for 30 years. 

It's "OOPS" time for our physicists 

SUSY is a shorter name for the theory known as supersymmetry. The theory is an extremely complicated speculation. The Standard Model of physics has less than 30 independent parameters. But according to one scientific web site, supersymmetry has more than 100 independent parameters. According to another page at the same web site, more than 10,000 scientific papers “reference” the theory of supersymmetry.

With all that work by physicists, you would think that there must be some evidence for supersymmetry. But efforts to find evidence for the theory have been a complete failure. The Large Hadron Collider has completely failed to support the theory.

Why have physicists spent so much time on such a theory? It seems they were troubled by something called the hierarchy problem or the naturalness problem. The problem is hard to explain, but some excerpts from the Wikipedia article on the hierarchy problem may give you a little scent of it.

It appears that Fermi's constant is surprisingly large and is expected to be closer to Newton's constant, unless there is a delicate cancellation between the bare value of Fermi's constant and the quantum corrections to it. More technically, the question is why the Higgs boson is so much lighter than the Planck mass (or the grand unification energy, or a heavy neutrino mass scale): one would expect that the large quantum contributions to the square of the Higgs boson mass would inevitably make the mass huge, comparable to the scale at which new physics appears, unless there is an incredible fine-tuning cancellation between the quadratic radiative corrections and the bare mass.

The “incredible fine-tuning cancellation” being talked about here is a kind of matching of two unrelated numbers so that they end up canceling each other out – rather like what you might have if you had to pay on Friday a $5000 payment to save your house from foreclosure, and you coincidentally won $5000 in the lottery on Friday morning.

But it's actually much more of a coincidence. Because according to this scientific web site, “one has to hypothesize that the several correction terms cancel out to a part in 10^34 (a hundred billionths of a billionth of a billionth of a billionth), if one is to make the Higgs mass smaller than a lead brick.” So maybe our analogy should be that you own 6 houses that are each behind $5000 on the mortgage, with Friday being the last day for you to save them; and you coincidentally on Friday morning buy 6 different lottery tickets that each win $5000. That's the kind of fine-tuning that seems to be involved in the case of the Higgs mass.

Supersymmetry (also known as SUSY) is an attempt to offer an explanation for this fine-tuning, or to explain it away. But supersymmetry has always been a ridiculously ornate contrivance. For example, it imagines that almost every known type of particle has a corresponding “superpartner.” It would be quite the fantastic coincidence if nature was set up in such a way. So supersymmetry is basically a kind of gigantic case of “robbing Peter to pay Paul.” It tries to get rid of one fine-tuned coincidence (the hierarchy problem) by introducing a whole bunch of other fine-tuned coincidences, involving all these cases in which a known type of particle happens to have a matching “superpartner” particle.

Why do I use the term “the SUSY Fiasco”? It's because supersymmetry has been a gigantic waste of time. For years scientists were hoping that the Large Hadron Collider would produce some evidence for supersymmetry. But no evidence has been produced. The chance of supersymmetry being confirmed in our lifetimes now seems almost zero.

Below are some lessons we might learn from these blundering fiascoes. The first lesson is: avoid the hero-worship pitfall, and remember that physicists are just fallible humans like the rest of us. The second lesson is: remember that many of our scientists have an unfortunate tendency to “jump the gun” – they often get overexcited about some theoretical idea before there is good evidence for it. This tendency is abundantly evident in the field of biology as well as the field of physics. The third lesson is: when nature presents you with a dramatic case of apparent fine-tuning, don't waste tons of time twisting yourself into knots trying to explain it away. Just live with it. 

Postscript: Engaging in some morose commentary triggered by Friday's announcement, physicist Sabine Hossenfelder writes this (perhaps using hyperbole) at her blog Backreaction:  

During my professional career, all I have seen is failure. A failure of particle physicists to uncover a more powerful mathematical framework to improve upon the theories we already have...What worries me much more is our failure to learn from failure. Rather than trying something new, we’ve been trying the same thing over and over again, expecting different results. When I look at the data what I see is that our reliance on gauge-symmetry and the attempt at unification, the use of naturalness as guidance, and the trust in beauty and simplicity aren’t working. The cosmological constant isn’t natural. The Higgs mass isn’t natural. 


She refers to the cosmological constant, because it has the same type of fine-tuning problem as the Higgs mass (as discussed here).