The Search for New Particles — anticipating a new Golden Age
By Frank Wilczek (MIT)
On 24 - 25 May 2010, theoretical physics Frank Wilczek (Nobel Prize in Physics, 2004) gave a morning general lecture on the search for new subatomic particles at the Large Hadron Collider at CERN. Then, on Monday and Tuesday afternoons, he taught the physics class, giving an overview of the history of discoveries in the study of particle physics and a review of the chapter on fields, which the students had just finished studying.
In his general lecture, Frank first explained that there has been three Golden Ages in particle physics: The period in 1910s, when the theories of relativity were developed; the period around 1925, when the theories of quantum mechanics were developed; and a period in the 1970s, when the theories of the Standard Model were developed, which are beautiful and economical laws based on symmetry and are very precise.
Although the Standard Model (a theory concerning the electromagnetic, weak, and strong nuclear interactions, as well as classifying all the subatomic particles known) is beautiful, it is not the last word — it is based on the world as having four distinct forces. But four is more than one and we’d like to have a unified, coherent description of all the interactions.
The LHC as a Physical Machine
Now we have a new tool to probe the deep secrets of nature — the Large Hadron Collider at CERN in Geneva which, in the first instance, Frank referred to as an engineering wonder that can accelerate protons to within one-billionth of the speed of light and collide them with one another. Giant superconducting magnets, cooled to just 2 degrees above absolute zero, guide the beams of protons through the ring of the accelerator. The temperature in the ring is actually colder than the temperature in outer space.
To collect all the data streaming from the detectors, massive banks of computers are required, which operate on a distributive basis with other computers at 100 sites around the world, all working together, which Frank called the “grid.” He explained that it generates 15 petabytes of data a year and compared this to the same as monitoring all the telephone traffic of all the people in a city of 500,000.
Frank said that many of the chips in the computers are actually chips from video games because they are very fast and that the computer system is something like the Internet on steroids. He commented that he finds it poetic that, at the end of the day, all of the information from the thousands of linked computers gets fed into a single computer screen where a human being looks at it and decides what it all means.
The LHC as a Scientific Tool
Next, Frank described the LHC conceptually, or as a scientific tool. It is an —
ultra stroboscopic nano microscope for studying deep inner space.
The LHC is the latest and greatest microscope, or aid to vision, that has ever been. Its resolving power is so great that when the protons collide each takes a snapshot of what’s inside the other, and then the encoded information is reconstructed using massive computing power.
The image above is a static picture in two dimensions that gives an idea of how complex it is to capture the collisions at high energies. In reality, the particles come out in many different directions and are moving close to the speed of light, and how fast they are moving is very important to the amount of energy they carry and must be measured very precisely.
He also explained that “empty” space is no so empty at all, but rather is a bubbling soup of virtual particles and antiparticles (a concept that is found in mathematical calculations about quantum field theory) popping in and out of existence and which can travel backwards in time and faster than the speed of light.
Our eyes can’t resolve small enough to see the quantum fluctuations of empty space, or evanescent quantum activity. But, by way of analogy, Frank explained that quantum activity is like a subsidence thought — a dormant thought — or magma sealed beneath the surface of the earth.
Knowing the equations for what goes on in empty space, we can do image processing of what we would see if our eyes were capable of resolving to the small times and distances necessary to see the fluctuations that go on everywhere in the universe.
Behold, Frank exclaimed, the deep structure of reality is akin to a lava lamp!!
Watch Visualization of Quantum Chromodynamics
This video is based on actual calculations of the fluctuations in energy in gluon fields (the glue that holds quarks, neutron and protons together) and how they fluctuate in space and time on very small scales.
In venturing into the deep quantum world, seeing is not only an invasive process, but to see something you must first create it by giving particles a great deal of energy. In this way, seeing is a creative process.
Thus, the reason the LHC is so big and complex is because that is what is necessary to produce the massive level of energy to create new subatomic particles.
Anticipating a New Golden Age
Frank shared his vision of what will be the next most profound discovery at the LHC.
First, by way of introduction, he described a puzzle — based on concepts of symmetry — but with some of the pieces missing. If you had some idea of what the completed puzzle is supposed to look like, and have some imagination and knowledge about the mathematics of symmetry, you could complete the puzzle below.
That is the situation we now face in the Standard Model. It contains patterns that seem to point in the direction of unification, but some of the pieces are missing. It has different pieces and three interactions (strong, weak and electromagnetic), which at the level of the Standard Model seem to be disconnected, and the interactions mix up the particles in different ways.
It is important that although many of the particles are related, they still fall into six disconnected pieces. Thus, although the Standard Model is extremely powerful, precise and economical — it essentially represents all of known physics on a single page — it still has room for improvement. It looks like the puzzle with some of the pieces removed.
But, if you study the mathematics of the symmetry that are appropriate to the particles and interactions, it can be found, if you make the bold guess that the sub-symmetries that are actually observed, that they fit into a larger symmetry that includes them all — the different pieces should actually fit into one unified, beautiful figure.
But there is a difficulty with this idea. If the different interactions (forces) were really different aspects of one more basic interaction, we should expect that they have the same strength. But in reality, observations show that they do not.
There are efforts underway to overcome this difficulty. When we examine particles and their properties, we don't see them directly or with completely accurate focus. Rather, we see them through the distortion of all the fluctuations of empty space — like the way fish might see things in turbulent water. But if we correct for these distortions, by going to really short distances and high energies, we can penetrate to see if the strength of the different interactions are really equal. We can calculate this mathematically but the LHC will have to be souped-up to even higher energies in order to validate the theory experimentally.
Frank said that we should not give up on unification, and that we should be bold and not toss aside beautiful ideas. He recalled that earlier electrons and quarks seemed to be very different types of particle with different behaviors, but that our unification theories have brought into the same structure and are interchangeable. And photons and gluons also seemed to different types of particles, but they also were unified.
Yet, can those two unifications be merged into one? — as one is more beautiful than two.
To achieve this, Frank explained a further bold idea in physics — not just unifying the different types of particles but also the different types of interactions. This is the idea called supersymmetry, which postulates that there is an extra dimension of space-time that is very different than the normal dimension in which we live. Instead, it’s a quantum dimension.
What happens when you move in the quantum dimension, it’s not that your position changes but rather you change. If you were a particle, your mass and spin would change, although some things would stay the same, such as electric and color charges.
We can expand the physics that we know to describe this extra dimension, and in doing so we find that there must be many new particles — every particle that we know of must have a partner that it changes into when it moves into the extra dimension. Figuratively, supersymmetry enables us to changes apples into oranges and visa versa.
All of the new super symmetrical particles also exist in fluctuating form, contributing to the distortion of the power of the different interactions (forces), and thus must be corrected for when we extrapolate to short distances or high energy — the properties of the fluctuating medium must be recalibrated. When this is done, the different strengths of the interactions do meet.
Unification of forces
Even gravity, which is trillions of times more feeble than the other forces, fits into the theory, as well, because it responds directly to energy.
In conclusion, Frank likened Nature as singing a Siren’s song and posed the question: is She teaching or teasing. Only the LHC can answer this question.
Frank is considered one of the world's most eminent theoretical physicists. He is known for the discovery of asymptotic freedom, the development of quantum chromodynamics, the invention of axions, and the discovery and exploitation of new forms of quantum statistics (anyons).
The inside of the proton when seen with the HERA accelerator - a dense soup of quarks and gluons.
The most dramatic of these tests, that protons viewed at ever higher resolution would appear more and
more as field energy (soft glue), was only clearly verified at HERA twenty years after Dr. Wilczek's prediction.
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