This week something amazing happened...we think we found the Higgs Boson. I've read many stories in the news this week, even stories from CERN, and I feel that this discovery has not been adequately explained to the public. In order to understand how profound a discovery this is, one must have some context. Up till 1994, I was an experimental physicist. I worked at Fermi Lab in Ill, for the CNRS in France, I worked at DESY in Hamburg Germany, I worked at CERN, and finally, I worked at the SSC in Dallas Tx until it was closed down in late 1993. My primary interest during those years was the Higgs. I have heard the Higgs described in the news this week as just another particle--the Higgs is not just another particle. Nothing like it has ever been seen. I heard it described as the God particle and I've heard that description described as hype. In my opinion, this description is closer to the truth. In the years between 1950 to 1990, physicists had worked hard to establish the two major theories of the objective world that encapsulate the sum total of human knowledge regarding the nature of reality. Those two theories are General Relativity and The Standard Model.
General Relativity was single-handedly developed by Albert Einstein. When Eddington measured the degree to which light bent around the sun, a percise prediction of GR, and delivered a telegram to Einstein with the result, Einstein put the telegram aside. Einstein's wife asked whether he was going to read it or not. To which Einstein replied, "in time." When his wife asked wasn't he curious of the result, Einstein replied, "either I'm right, or God built the Universe wrong." Of course Einstein was right. I consider GR probably the greatest intellectual feat in human history. GR has accurately predicted orbits perturbation around stars, time dilation, black holes, and many other of the bizarre aspects of reality that don't sit well with our experience. But even Einstein was puzzled by Quantum Mechanics, the foundation of the Standard Model, even though Einstein helped create Quantum Mechanics.
Before we talk about the Higgs, we have to know something about the Standard Model (SM). And before we talk about the nature of the Standard Model, it is important to say some things about the beginning of the Universe. This falls under the branch of physics known as Cosmology. We believe the Universe started with the Big Bang. There is compelling evidence for this that we won't talk about now. The Big Bang happened about 13.7 billion years ago--we have compelling evidence for that, but we won't talk about that now. A good argument can be made that before the Big Bang, there was nothing. When I say nothing, I mean nothing: no black, no matter or energy, no space, no time--nothing. It is not possible for people to imagine nothing because, by our nature of being something, nothing is outside of our experience. At the instant of the Big Bang, the Universe was very hot and filled with an opaque soup of energy and subatomic particles. At that time, we believe there was only one force at work in the Universe, not the four we experience today. The Holy Grail of physics is to take the four forces we experience today and discover the formulation that allows us to understand how that primordial single force disentangled into the four we see today. This is called the Grand Unified theory and would unify GR and the Standard Model.
The Standard Model is a theory of how the known particles, on the smallest measurable scales, interact, and in so doing, unifies three of the four forces that comprise the sum total of physical interactions known to humans. The three forces the Standard Model unifies are: the electromagnetic force (EM), which includes light, radio, and the entire spectrum of colors, those we can see and those we can't. EM is the reason that chemistry works the way it does, and it is the force that holds everything together in the macroscopic world we know. The Weak Force is responsible for radioactivity by enabling subatomic particles to decay. And the Strong Force is responsible for holding the nuclei of atoms together. Unifying these forces means that the the SM gives us an understanding that these forces are really only one force beyond a particular energy scale and are differentiated in the world we're familiar with only because our part of the Universe is cold. Cold means that our environment here on earth today is much less energetic than the environment of the Big Bang, or the space around the accretion disk of a Black Hole--or other places and/or times in the Universe where the energetic environment is very hot enabling the forces to unify. This is like saying that all the colors that we see are really a single color, which, before they pass through a prism, is the color white. The Standard Model is probably the most tested theory that humans have ever produced. Some parameters of the model are known to greater precision than any other physical entities. The Standard Model is so good that it predicted, and we found, the three vector exchange bosons of the electroweak part of the theory: the W+, W-, Z0. Seldom do human theories predict something as abstract as the three intermediate vector bosons. Gravity is the only force not unified in the Standard Model.
Now to the Higgs. When I first learned about the Higgs, it was as a mathematical entity in the midst of the architecture of the Standard Model. All the other constituents of the SM arise naturally. That means there is an intuitive arc supported by the structure of the theory on which these entities rely. All particles that comprise the SM have mass. They have mass because they must have mass, because mass is the basis of reality and these theories are constructed to help us understand reality. The problem is that there is no formal mechanism in the SM where by the masses of the particles naturally arise. The embarrassing truth is that masses were put in by hand to reflect what was actually measured in the world. A theory is useless if it doesn't give us a deep understanding of why reality is as it is. This was a strange situation for a model that was good enough to predict never before seen particles that unified the EM, Weak, and Strong forces. The Higgs mechanism is the deep understanding part added to the Standard Model that explains mass--this is a big deal--why? If we remember grade school, we may remember the "definition" of matter: that which has weight and takes up space--remember? Matter is synonymous with reality, and mass is synonymous with matter.
To understand what this really means, let's dig deeper. First, all forces are associated with force fields in space. What is a force field? Imagine the source of a force, then imagine all the space in which that source exists. Let's look at the force. We do this by taking a test particle that feels the force, but is sufficiently weak in emitting the force that it does not greatly disturb the original force. We call this a test particle. Now move the test particle to all the points throughout the space and measure the effect of the force on the test particle. The collection of the strengths and directions of the force at every point in space is called the "force field." Now, the force field is associated with a particle that transmits that force between the source and the test particle. The other thing we must know is something about the nature of particles that transmit forces. As an example, take the photon, a particle of light. The photon is the particle that transmits the EM force. The source of the EM force is any particle with electric charge. All electrical and magnetic forces are transmitted by the photon. The photon is massless. Since the photon is massless, it is never at rest. The photon has no rest mass. The mass of a particle that transmits a force is associated with the lifetime of that particle. That means the heavier an intermediate particle is, the faster it decays to something else because nature likes to be in the lowest possible energy state. Since the photon is massless, it never decays, and the rang of the force it mediates is infinite. So when we "see" EM waves (like light), they can be from sources at the beginning of the Universe and at the beginning of time.
At the time I first learned about the Higgs, I knew that the Higgs, if real, would be the heaviest intermediate particle ever discovered. We now know it's about 125 billion electron volts in mass (it's okay if this means nothing to you, take my word for it, it's heavy). Remember, the Higgs Boson is the intermediate particle that "transmits" the Higgs field. If the Higgs is that heavy, the the range of the Higgs force field is very-very small. If the range of the Higgs force is very short, and it's the Higgs field that gives every particle in the Universe mass forever, then what is the "source" of the field? It can't be far from any particle; in fact, it must be within the size of the particle itself. I was completely confused. I was later told that the Higgs field, unlike any other field, permeates space (apparently without a source) forever. Huh? That was a convenient cop-out reminiscent of the collapse postulate in quantum mechanics. That is to say, when something doesn't make sense, say something that really means nothing.
Currently, there are several theories concerning Grand Unification. There is also an elegant picture as to the nature of the Higgs force field itself and just how it creates mass (this picture is highly mathematical). The most important thing to know about the Higgs field that sets it apart from any other field is this: The Higgs field has something called "a non-zero vacuum expectation value." This basically means that if you look in the vacuum--that is completely empty space (remember, since there is space, there is something) the probability of measuring the Higgs field and finding a Higgs particle is NOT ZERO. This is not true for any other entity--none. This really means that the "source" of the Higgs field/particle is space itself! That means that the Higgs field is an intrinsic property of space itself that bestows mass (or reality) onto otherwise ghostly massless particles. Thus, the God particle. And as of last Wednesday, it seems to really exist! If you're not impressed by this, I have nothing more to say...
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Specfiction |
Let's Talk Higgs
Posted - 07/09/2012 : 09:24:23
