Physics

George Gollin
Department of Physics
University of Illinois
February 25, 2000

Introduction

Think of madness.

Think of something profoundly alien, unfathomable, unknowable.

Think of crushed stars, whose mirror-surfaces emit no light of their own, but reflect light from elsewhere more perfectly than colossal spheres of liquid mercury.

Think of a world where the sequence of events can be meaningless: where THIS [snap fingers of one hand] has happened before THIS [snap fingers of other hand], and also-- and instead-- but certainly also-- this [raise first hand] had happened after this [raise other hand]...

...where stars (such as our own) should be flung free of spinning galaxies, but aren't, because almost "everything that there is" is unknown to us: not atoms, not protons, not electrons...

...where the night sky is still filled with the flash of creation, the light from the beginning of the universe fifteen billion years ago...

...where every cell in our bodies is built from the nuclear ash of exploded stars...

...where time and space are built from something else, something more fundamental, more real...

...where the boundaries between a thing and its environment have little meaning.

This is where we live. We experience almost none of our world directly: we move through it oblivious to all but a miniscule fraction of that which surrounds us.

Let's talk about two aspects of physics (of reality) and then about antimatter.
 
 

Scales of size

The smallest things that are "real" to us, that we experience with some of our senses, are visible, and are a fraction of an inch in size. Perhaps the largest (and perhaps the most annoying!) thing we can "know" is the 10,000 mile plane ride in a cramped seat to Japan.

The Japan trip is about a trillion times longer than the smallest objects we can comfortably see.

We have heard about larger and smaller things- the sun is 93 million miles away- but what does that actually mean to us? If I said "well, astronomers have actually determined that the sun is 120 million miles away, sorry about that" we wouldn't all think "oh, yeah, I always thought it looked further away than they told me in Earth Science class."

In physics, we deal with inconceivably large and small objects.

In our cosmic backyard, the closest star (besides the sun) is the triple star system a, b, Proxima Centauri. It's 25 trillion miles away. (That's 4.3 light years.) Our galaxy, the Milky Way, is about 100,000 light years in diameter. That's about six hundred thousand trillion miles in size, or about 60 trillion times farther than Japan.

The numbers are so big that they're meaningless to us!

We think our universe contains over a hundred billion galaxies, each with billions of stars.

As far as we can tell, the universe is roughly ten billion light years in diameter (but it's expanding, so the number will change). This is 6´ 1018 times the distance to Japan. (That's a 6 followed by 18 zeroes or, if you like, six million multiplied by a trillion.)

People who do cosmology (a branch of physics, or astronomy) work at describing the dynamics of stuff this big.

Going the other way now- we understand how atoms and nuclei work, why they do the things they do. We have a great deal of confidence in our ability to describe, predict, calculate- to "understand" in an abstract sense- phenomena happening at distances as small as a thousandth the size of an atomic nucleus.

That's really small- about ten trillion times smaller than the smallest thing we can see without instruments. This ratio is a factor of ten larger than the ratio of sizes for the Japan trip and the smallest thing we can see.

This is where one of the frontiers of physics lies- high energy physics experiments currently under construction will provide insight into "smaller" phenomena. We want to know about this because something crazy, something completely bonkers, happens at distances just a bit smaller than what we've already probed. More on this shortly.

How small can we go? Some of my colleagues work with a theory in which the universe has ten dimensions, all but three of which are unobservable. It sounds wacko, but it appears likely that the universe must be this way: that it is inevitable, and that it is impossible for it to be different.

This "string theory" business describes physics at distances which are a hundred million trillion times smaller than atomic nuclei. At such small scales, it is likely that our very notions of space and time no longer apply- that we'll learn that space and time are built from something else, something more fundamental.

So- our reality includes things six million trillion times larger than our flight to Japan, and a million trillion trillion times smaller than the smallest thing we can see. We don't even have proper names for numbers this big.
 

The Higgs sector and the blurring of boundaries

I mentioned that we're about to start "seeing" things which are completely nuts in the next generation of experiments.

Here's the story. We think that all the stuff we're made from- electrons, quarks (the protons and neutrons in atomic nuclei are made of quarks), and so forth- is "really" massless. In its heart of hearts, an electron "weighs" nothing. A quark "weighs" nothing. They're all massless, just as photons (particles of light) are massless.

It's only because we don't get to ask the right question- that we don't make the right measurement- that we think that an electron "weighs" anything at all.

Imagine that we did an experiment to determine the answer to the question "How many hamburgers does it take to feed lunch to the President?" We keep pushing Big Macs through a mail slot in the Oval Office door until they start coming back uneaten. Now, the President (usually) has an entourage of accompanying secret service agents, so we're unlikely to find him alone at the Office. It's hard work keeping the President out of trouble, and our hamburger count invariably will include the effects of the unobserved, but hungry, staff around him.

It's kind of like this with electrons: deep down, they're massless. If they weren't, all the predictions of our highly successful theory- what we call "The Standard Model" would be junk. It's not that they might be off by a factor of ten: it's quite a bit more extreme. Everything comes out infinite. Complete gibberish. Nonsense.

What the Model says is that all of space is filled with a peculiar goo called the Higgs scalar field. Most everything there is interacts with this omnipresent Higgs field, is constantly surrounded and buffeted and jostled by Higgs scalars. It's difficult to "clean out" a region of space, to empty it of Higgs particles, since it takes too much energy. All the experiments we've done so far have been unable to get close enough to the electron (haven't made it far enough into the Oval Office) to see a bare electron inside its accompanying cloud of Higgs particles. We're getting close (thus the next generation of experiments), but we need to look a little deeper.

When we measure the electron mass, we're seeing it plus its entourage. When we measure the president's appetite, we're really determining the total hamburger consumption of everyone inside the Oval Office.

We need to enter the Office to determine his hamburger consumption independently of his intern's.

It's the presence of all those Higgs particles which makes an electron (a quark, a whatever) appear to have mass. But- really, they're all massless. It is, at some level, an illusion carried forth by physics at small distances.

Now, all the properties of an electron that make it what it is, that let it do chemistry in atoms, that let it flow through metal wires and doped silicon crystals, evaporate if we insist on viewing an electron as a massless object. Sure, it really is massless, but still... it's just not really an electron any more if it can't do electron-like stuff. It's missing the point to talk about what flows through the filament of an electric light as a massless electron plus its accompanying Higgs scalar field.

Imagine ECE courses: "one ampere of electrons (accompanied by the requisite swarm of Higgs scalars) flows through a 1000 ohm carbon (um, oh yeah, plus a bazillion Higgs scalars) resistor. Calculate the voltage drop across the carbon + Higgs resistor." Yeah, right.

The idea is this: when removed from its context, the idea of an electron, what it really is, how it behaves, its "electronness"... vanishes. It doesn't make any sense to talk about bare electrons (except in a certain mathematical way), because they're just not electrons anymore. Things removed from their contexts, at least in high energy physics, lose their identities. The boundaries between a thing and its environment have little meaning.

Modern physics doesn't deal in distinct, well-separated particles which occasionally interact. Fundamental physics describes everything as more like a crowded, gigantic summer block party. This sense of the indistinctness of boundaries is inextricably bound up in how we think about physical reality.

It is interesting to me to see similar ideas in the arts- how the separations between the static and the dynamic, between structure and movement, between audience and performer are being blurred in a variety of investigations.
 

CLEO event displays

Let me tell you about the CLEO event displays you'll be "interpreting."

We make our own antimatter.

Positrons are anti-electrons. We make several trillion of them, and steer (and focus) them into a particle beam moving at nearly the speed of light. The beam orbits inside a vacuum pipe which is bent into a circle 800 feet in diameter.

We inject a beam of electrons into the same vacuum pipe, but traveling in the opposite direction. Thousands of times per second, an electron in one beam is annihilated by a positron in the other beam in a brief, violent, head-on collision.

The collision is so violent that objects as massive as ten protons can emerge from this flash of matter-antimatter annihilation.

As the quarks, antiquarks, and photons emerge from the explosion, they yank other quarks and antiquarks into existence, turning their kinetic energy into new matter.

By the time the newly formed plasma of stuff is the size of a proton, it has jelled into particles which may live for picoseconds, nanoseconds, or microseconds, (or for billions of trillions of trillions of years) before decaying.

Usually, nearly everything leaving the annihilation is traveling close to the speed of light.

A tenth of a billionth of a second later, the debris from the collision (a variety of stable and unstable particles) passes through the walls of the vacuum pipe, entering the CLEO detector.

Instrumentation registers the ionization trails left by charged particles as they travel through the magnetic field of the apparatus.

A few billionths of a second later, particles leave (or are stopped in) the detector.

Information, recorded on tape, is processed later to learn the identities and kinematic properties of the objects produced in the collisions.

By studying the relative rates at which different interactions are found to occur, we can test our understanding of the dynamics of physics at very small distances.