Another Book on the Higgs
I'm just about
done with my first book of the summer and felt like sharing a few tidbits.
It's always
interesting to me to see the historical/human aspects of science that I don't deal
with much in my classroom (maybe I should address them more).
- Physicist Murray Gell-Mann had succeeded in
fitting a group of known particles (proton, neutron, kaon, and others) to
a mathematical system known as a symmetry group. The math suggested
that these known particles were actually composites of three more fundamental
particles for which there was no experimental evidence. Most
physicists felt the were just artifacts of the mathematics without any
physical reality, but a few had their curiosity piqued. Gell-Mann
originally called these theoretical particles quorks, a derivative of the
word quirk, to emphasize the absurdity of the likelihood that they actually
existed. Over time he warmed to the idea of their existance and also happened across a
line from James Joyce that read,
Three quarks for Muster Mark!
Sure he hasn't got much of a bark.
And sure any he has it's all beside the mark.
So he changed the name to quark. Said
Gell-Mann, "The whole thing is just a gag. It's a reaction against pretentious
scientific language" (p 80). With
names of specific types of quarks like “strange” and “charm,” it looks like the
naming tradition caught on.
- In 1974 two separate research groups discovered
the same new particle at essentially the same time. One group named
it the J particle and the other the Ψ. Neither could convince the
other to switch and the particle is still called the J/Ψ particle today.
Now to some of the
meat of the material…The Higgs field is actually the important theoretical idea
for which confirmation was being sought.
The Higgs boson is simply the most direct way to confirm the existence
of the Higgs field.
Without the Higgs field there could be no electro-weak
symmery-breaking. Without
symmetry-breaking the W and Z particles would be massless, like the photon, and
the electro-weak force would still be unified.
Without interactions between elementary particles and the Higgs field,
there would be no mass: no material
substance, no stars, no planets, no life.
And the direct evidence for the existence of this field could only come
from finding its field particle, the Higgs boson. Find the Higgs boson, and suddenly we would
understand a lot more about the true nature of the material world (p 171).
So how does the
Higgs field impart mass to otherwise massless particles? Well the following explanation is a little technical,
but I prefer it to the oft quoted snowball in a snowstorm analogy.
A massless field particle…moves at the speed of light and has two ‘degrees
of freedom’, meaning that its wave amplitude can oscillate in two dimensions
that are perpendicular (that is, transverse) to the direction in which it is traveling.
[A photon for instance can have vertical and horizontal polarization]…but there
is no polarization in the third dimension.
To change this state it is necessary to introduce a background
quantum field, often called the Higgs field to break the symmetry [the fact
that all particles are (or would be) massless is considered a symmetry]…Breaking
the symmetry creates a massless…boson.
This may now be ‘absorbed’ by the massless…field boson [the original
particle we were considering] to create a third degree of freedom
(forward/back). The wave amplitude of
the field particle can now oscillate in all three dimensions, including the
direction in which it is traveling.
The particle’s interactions with the field are manifested as a
resistance to the particles acceleration…We
now interpret the extent to which the particle’s acceleration is resisted by
the Higgs field as the particle’s (inertial) mass (p 85-89).
There you have it
folks. Mass redefined.
One other nugget since we’re on the topic of
mass. If you take the mass of the three
quarks that compose a proton (two ups and a down), it only adds up to about 1%
of the mass of an actual proton. The rest
of the mass comes from the energy of the gluon field (yes, it is all about
fields). Mass and energy are two
manifestations of the same thing, just like Einstein told us.
Lastly, aside
from having a better understanding of how the universe works, this book left me
amazed at the interplay between math and nature. Here we had these seemingly utterly abstract
mathematical structures (symmetry groups) that essentially take a given number
of input parameters and show how they are interrelated through “rotations” and
how they can lead to higher structures of interrelated parameters. Then the physicists saw that fitting some parameters
(mass, charge, spin) of known particles into these symmetry groups allowed them
to predict the existence and properties of new particles…and it worked. Craziness!
Comments
Not that you asked for it, but let me try one more explanation.
You might have heard of the 4 fundamental forces (gravity, electromagnetic, nuclear strong and nuclear weak). These forces can be used to explain every interaction we observe in the physical world (e.g. you're not falling through your chair right now because the electrons in your rear are repelled by the electrons in your chair).
These forces generally appear to be very different phenomena (the gravitational force between an electron and a proton in a hydrogen atom is nothing compared to their electromagnetic attraction), but at sufficiently high energies (i.e. temperatures) all 4 forces behave identically. They are indistinguishable. There is only one force.
If we start from a high energy state and cool things off, the 4 forces will separate out (not all at the same temperature) from the unified single force. But physicists want to explain why this happens. What is the mechanism that causes one force to become distinct from the others. One way to do this is to invoke what's called the Higgs mechanism. We say there is this Higgs field (like a gravitational field) that exists everywhere in space and which interacts to differing extents with different particles (as long as the energies of these particles aren't too large). The fact that neutrons interact with the Higgs field more than photons do helps make the two particles distinct (and since forces are mediated by exchanging particles, this mechanism can explain how the forces become distinct). We call this introduction of distinguishing features "symmetry breaking".
The Higgs boson (a confirmation of the Higgs field) was the last piece of this puzzle that explains the particles and forces we observe.
The Higgs field is not considered a force, though it is intimately related in that it influences the effects of forces.
It's not considered a force because by itself it can's cause particles (or anything) to speed up or slow down. But it does affect how much a particle speeds up or slows down when a force acts on it.