On the edge of the icepack
Now that we might (maybe, possibly, could be, it could go away, let’s be careful
about what we say here lest we put a jinx on it…) be seeing hints of a Higgs, it’s time of
some cautionary tales that a ‘discovery’ is not the end of the story, it’s only the
beginning.
When I was a young graduate student, Martinus Veltman gave a talk at a summer
school. He had yet to share the Nobel Prize in physics with Gerard t’Hooft for work on
the Standard Model. This was 1980. Veltman said, “Right now, theorists are in the
driver’s seat. In fact, for the next 30 years, with the exception of the details of the
masses of some particles, we know what’s going to happen. But in 30 years, we
absolutely are going to need experimental guidance to make any progress in particle
physics whatsoever.”
In point of fact, I don’t think anyone recorded Veltman’s words for posterity, but
it made a deep impression on me in a number of ways. First and foremost to a rookie
experimentalist was the realization that I had to toil in the vineyards for thirty years until
something truly of note would arrive. The second thought was “What on earth is he
talking about?” We were handed the Higgs boson as an article of faith.
In the current publicity about the Higgs boson, I often worry that we simplify the
goals of what we’re doing to the point of trivializing it. Veltman was right: What we call
the “Higgs boson” or the “God particle” is really a surrogate for a strange mechanism that
bestows mass on all particles through an interaction. We have the most precise theory of
anything and, yet, this absolutely crucial piece is missing. We’ve gotten to that point, 30
years later, at which we’ve found almost all of the particles theorists predicted as part of
the Standard Model and are now heading into uncharted territory in higher energy ranges.
What we don’t often talk about are the odd properties that this mysterious particle
is thought to have. Often times, theorists, like Veltman, feel that the current model is
horribly inelegant and must therefore be completely wrong and only a pale approximation
of what nature really does to bestow mass, the most elemental of properties a particle can
possess.
What makes it so inelegant? In the first place, if it is as described in our simplest
model, it would be the only elementary particle we know of that doesn’t possess an
intrinsic property of ‘spin’, which seems to be key in the workings of our theory of
fundamental forces. For more on the inherently quantum mechanical property of
particles known as spin, see this post
<http://www.quantumdiaries.org/2011/06/19/helicity-chirality-mass-and-the-higgs/>
by Flip Tanedo.
Beyond its spin 0, the Higgs has a very odd property: It gives energy to the
vacuum of space. We don’t really know what this means and often just ignore it. Yet, a
kind of vacuum energy has been invoked to describe cosmology on very different energy
scales from the energies we’re exploring at the LHC.
something called the “flatness problem”.
Astrophysicists often talk about
If you took a pot of boiling water just off the stove, and dumped ice into it,
eventually you would see the ice and the hot water come to some equilibrium
temperature. But, in order for this to happen, the ice and hot water have to physically
come in contact with each other. When we look around the universe, the temperature of
everything is the same to a remarkable degree, as if it was all sitting in the same pot and
came to the same temperature. That would all be well and good, but one patch of the
universe cannot possibly have been in contact with another part, because they’re
separated by such a large distance that light itself cannot connect the two. How could the
entire universe be at the same temperature?
The answer is largely thought to lie in a period called ‘inflation’. Initially the
very early universe was so dense and compact that temperatures from one part could
communicate to another part: everything was sitting in the same ‘pot’. Then, a
mysterious vacuum energy appeared that pushed parts of the universe out of contact, but
preserved the uniformity of temperature. This happened within a very early phase of the
universe when temperatures and energy densities were far hotter than the conditions
we’re producing at the LHC. This vacuum energy is about a trillion times larger than
what we associate with the Higgs.
Astrophysicists have also invoked a vacuum energy at another, much weaker
scale. You may have heard of ‘dark energy’. Our best guess is that, like the vacuum
energy of the early universe, this mysterious force that seems to be pushing the universe
apart also seems to be a kind of vacuum energy. Yet, in this case the energy of the
vacuum is exceedingly weaker than the energies we’re exploring at the LHC. So, there’s
a vacuum energy invoked to explain both the very early universe and the very late
universe. At the same time, there’s a vacuum energy associated with the Higgs, but it
just sits there like an orphan, of no consequence.
To deal with some of these strange properties, theorists have come up with other ideas for
how the Higgs might manifest itself:
1.) Supersymmetric Higgs – The energy scale where the three main forces other
than gravity, the strong, weak and electromagnetic- join together is close to
the scale associated with the cosmic inflation. This is often called the ‘Grand
Unification scale.’ The fact that we see two of the fundamental forces - weak
and electromagnetic - joining together at the LHC energies presents a
conundrum. It is very difficult to reconcile the Grand Unification scale with
the LHC scale in a natural way without having some other kinds of matter
arise. The constants of the theory would have to line up just perfectly, finetuned to a level of precision that is equivalent to balancing a pencil on its
point. With Supersymmetry, a number of Higgs-like particles arise.
2.) Composite Higgs – Rather than deal with an inelegant particle with no spin,
theorists have speculated that it’s actually made of multiple objects, possible
pair of top quarks, tightly bound together. The opposite spins of the objects
bound together in a composite Higgs would cancel out to give it zero spin.
3.) No Higgs –According to some models, the Higgs is not a particle at all, but
the result of interactions that create mass. These models are sometimes called
‘technicolor’. Although they aren’t particularly favored by theorists because
they’re difficult to calculate, we cannot rule them out.
Experimentalists are checking the data for all of these possibilities.
But, what if something like our vanilla-Higgs shows up with a high degree of
certainty? Are we done? Hardly! Given all the possibilities and the somewhat inelegant
nature of the vanilla-Higgs model, the work has just begun. We have to ask questions
like: Is there only one? What is its spin? How does it interact with all the other particles?
Are there any variations in its interactions from what we expect, and if so, how does that
relate to other measurements we do. These are the tough questions, the one Veltman
was alluding to and my betting odds are that we’ll find deviations from our vanilla-Higgs,
but it won’t be easy. It may take a decade or more of data taking at the highest beam
intensities and energies before we begin to understand what’s really going on.
Science may begin with blinders and theories may run aground, but eventually we
do manage to figure out what’s going on.
Here’s a cautionary tale from the 19th century. It illustrates how people can be
steered in the direction of one theory, but ultimately can end up with a far more powerful
idea. A German geographer named August Petermann championed a theory of a warm
Polar sea. Some expeditions to the high Arctic reported seeing vast stretches of ice-free
water extending off toward the horizon. An oceanographer named Silas Bent speculated
the that warmth of the Gulf Stream waters flowing north, combined with the waters of a
similar ocean current, called the Kurosiwa (black current) flowing off of the coast of
Japan would be sufficient to warm the Polar Ocean to the point that an expedition, if it
could make it through some part of the ice pack, could sail directly to the Pole.
Petermann was one of the main champions of the idea.
James Gordon Bennett Jr. was the publisher of the New York Herald and tried to
boost publication by underwriting adventurous expeditions. He financed Henry
Morton’s Stanley’s search for David Livingston, garnering a boost in the circulation of
the Herald. Hearing of Petermann’s theory of the warm polar sea, Bennett set about to
finance an expedition and purchased a British gunboat, the HMS Pandora, and refitted it.
He enlisted the US Navy to find a crew. Rechristened the USS Jeanette, it was captained
by Lieutenant Commander George DeLong. Hoping to repeat the publicity of the
famous Stanley-Livingston meeting, Bennett sent the Jeanette north through the Bering
Strait in hopes of reaching the famed open Polar Sea. The Jeanette left San Francisco in
July 1879, and was last heard from in late August of that year.
After crossing the Bering Strait, the Jeanette was soon frozen fast in the icepack.
Trapped there for nearly two years, it slowly drifted northwest from the coast of Siberia
and was ultimately crushed by the icepack. DeLong ordered his crew to abandon ship
and began a trek over the frozen icepack, hauling three lifeboats in hopes of eventually
reaching settlements along the delta of the Lena River in Siberia. DeLong didn’t make it
out alive, perishing in the maze of channels. Some survivors did make it to settlements
and eventually made it back home.
Three years later, the wreckage of the Jeanette washed up on the coast of
Greenland, some three thousand miles away. This prompted many to wonder how the
wreckage could travel so far across the frozen icecap. Theories about ocean current
proliferated. One adventurer, Fridtjof Nansen, constructed a polar exploration vessel,
the Fram. Fram had a rounded hull that allowed it to be frozen into the icepack without
being crushed. Nansen and crew sailed to roughly the point where the Jeanette had been
frozen in and commenced a drift across the Polar Sea. At this point, the theory of the
Open Polar Sea was completely abandoned in the face of the overwhelming data to the
contrary.
Although Nansen never reached the North Pole, during the Fram’s expedition, the
remaining crew made detailed observations of wind patterns, drift, the ocean depths and
temperatures. On its return to Norway, the Fram had a wealth of data that took years to
sift through. Vagn Ekman was a student in physics at the University of Uppsala, Sweden.
He was studying fluid dynamics and heard of the data from the Fram. After exploring
the mathematics of the interactions of air and water flow on the surface of the rotating
earth, he developed the modern theory of surface ocean currents, which bears his name:
Ekman transport.
Ekman’s work remains one of the fundamental underpinnings of oceanography.
What I’m trying to point out is this: We are on a voyage of discovery. As
Veltman said, experimentalists are really now the ones in the drivers seat. The vanillaHiggs is an easy target to fire at, as there are quite specific predictions for how it will be
manifested, but there are good reasons to be suspicious that the Higgs is precisely as it is
described in the simplest version of the Standard Model. Like the long, meandering
progression from the theory of the Open Polar Sea to the modern theory of Ocean
Currents, I suspect that we’ll have many changes and false leads. As it stands now, with
the performance of the LHC, we are just beginning to penetrate the icepack, and we don’t
really know what to expect.