CAMBRIDGE – Modern physics and cosmology suggest that basic truths about how nature operates, and how our universe arose, are visible only to those who can see events that occur faster than the time it takes for light to cross a proton, and whose vision can resolve sub-nuclear distances. Fortunately, that does not rule out humans, for we can augment the eyes we were born with.
The Large Hadron Collider (LHC) rises to the opportunity. By smashing protons together with unprecedented energy, monitoring the many particles that emerge from the collisions, and reconstructing the primary events that produced them, physicists will in effect have constructed the fastest, highest-resolution microscope ever, with each proton taking a snapshot of the other’s interior.
The LHC is a magnificent engineering project, whose many “gee-whiz’’ features have been widely reported. I will forego all that, and skip to the chase: what can we hope to see?
We will see what the universe was like when it was a thousandth of a second old, in the earliest moments of the Big Bang. The primary events at the LHC are in effect Little Bangs, tiny fireballs that reproduce Big Bang conditions, albeit over very small volumes.
This re-creation of the early universe opens up an exciting possibility. We know that the universe today contains a form of matter, the so-called dark matter, that is different from anything we have ever observed.
The dark matter is actually not dark in the usual sense, but utterly transparent. It neither emits nor absorbs light significantly, which is why astronomers failed to notice it for millennia, even though dark matter contributes five times as much to the total mass of the universe as normal matter. It was only in the late twentieth century that careful study of the motion of normal, visible matter revealed the gravitational influence of lots of otherwise invisible stuff.
Because the original Big Bang produced dark matter, the LHC’s Little Bangs might produce some more. So experimenters will be looking for new particles with the right properties to provide the astronomical dark matter: very long-lived and very feebly interacting with ordinary matter or light. There is a good chance, then, that we will learn what that ubiquitous, abundant, yet elusive substance is.
Imagine a race of intelligent fish that start to think deeply about the world. For millennia, their ancestors took their watery environment for granted; to them, it was “emptiness” as empty as they could conceive. But, after studying some mechanics and using their imaginations, the physicist-fish realize that they could deduce much simpler laws of motion by supposing that they are surrounded by a medium (water!) that complicates the appearance of things.
We are those fish. We have discovered that we can get a much simpler set of equations for fundamental physics by supposing that what we ordinarily perceive as empty space is actually a medium. We have observed the effects of the “water” that we use to simplify our equations – it slows down particles, and makes them heavy – but we do not know what it is made out of.
The LHC will allow us to discern the microscopic structure of the universal medium. The simplest idea is that it is made out of one new kind of particle, the so-called “Higgs particle,” but I suspect that there is more to it. (One gets prettier equations with five new particles, and there might be even more.)
In the 1860’s, James Clerk Maxwell assembled the equations for electricity and magnetism, as they were then known, and discovered an inconsistency. He repaired the inconsistency by adding new terms to the equations.
The augmented equations, today known as the Maxwell equations, described a unified theory of electricity and magnetism. The new equations showed that light is a moving, self-renewing disturbance in electrical and magnetic fields, and they predicted that new kinds of disturbances are possible.
Today we call those disturbances radio waves, microwaves, infrared and ultraviolet radiation, x-rays, and gamma rays. We use them to communicate, cook, and diagnose and cure disease. The unified theory of electromagnetism has led to profound advances across all physical science, from atomic physics (where lasers and masers are essential tools) to cosmology (where the microwave background radiation is our window on the Big Bang).
Our current understanding of physics is powerful and accurate, as far as it goes, but it is not as beautiful and coherent as it should be. We have separate equations for four forces: strong, weak, electromagnetic, and gravitational. This jumble recalls the piecemeal equations of electricity and magnetism before Maxwell.
Some of us have proposed expanded equations that unify the different forces. These expanded equations, which incorporate an idea called supersymmetry, predict many new effects. A couple of the predicted effects have already been observed (for experts: tiny neutrino masses and unification of couplings). But, as Carl Sagan observed, “extraordinary claims require extraordinary evidence,” while here the existing evidence is still circumstantial.
Fortunately, these ideas for a new unification predict that extraordinary things will be seen at the LHC. If so, a whole new world of particles will be discovered: each currently known particle will have a heavier relative – its superpartner – with different, but predictable, properties.
Such are my hopes and expectations for the LHC. Other speculations for what might be seen abound; they include extra dimensions of space, strings instead of particles, and mini-black holes. Very likely, reality will outrun apprehension.