Knocking on Heaven's Door - Lisa Randall [47]
Then—and here’s where all the action happens—magnets guide the two proton beams around the ring in a precise path so that they collide in a region smaller across than the width of a human hair. When this collision occurs, some of the energy of the accelerated protons will be converted to mass—as Einstein’s famous formula, E = mc2, tells us. And with these collisions and the energy they release, new elementary particles, heavier than any seen before, could be created.
When the protons meet, quarks and gluons occasionally collide with a great deal of energy in a very concentrated region—much as if you had pebbles hidden inside balloons that were smashed together. The LHC provides such high energy that in the events of interest, individual components of the colliding protons crash together. These include the two up quarks and the down quark responsible for the proton’s charge. But at LHC energies, virtual particles carry a sizable fraction of the proton’s energy as well. At the LHC, along with the three quarks contributing to the proton’s charge, the virtual “sea” of particles also collide.
And when that happens—and here is the key to all of particle physics—the numbers and types of particles can change. New results from the LHC should teach us more about smaller distances and sizes. In addition to telling us about possible substructure, it should tell us about other aspects of physical processes that could be relevant at smaller distances. LHC energies are the final short-distance experimental frontier, at least for quite some time.
BEYOND TECHNOLOGY
We’ve now finished our introductory journey to the smaller scales accessible with current or even imagined technology. However, current human limitations on our ability to explore do not constrain the nature of reality. Even if it seems that we will have a tough time developing technology to explore much smaller scales, we can still try to deduce structure and interactions at those distances through theoretical and mathematical arguments.
We’ve come a long way since the time of the Greeks. We now recognize that without experimental evidence it is impossible to be certain of what exists at these minuscule scales we would also like to understand. Nonetheless, even in the absence of measurements, theoretical clues can guide our explorations and suggest how matter and forces could behave at tinier length scales. We can investigate possibilities that could help explain and relate the phenomena that occur at measurable scales, even if the fundamental components are not accessible directly.
We don’t yet know which, if any, of our theoretical speculative ideas will turn out to be right. Yet even without direct experimental access to very small distances, the scales we have observed constrain what can consistently exist—since it is the underlying theory that has to ultimately account for what we see. That is, experimental results, even on larger distance scales, limit the possibilities and motivate us to speculate in certain specific directions.
Because we haven’t yet explored these energies, we don’t know much about them. People even speculate the existence of a desert, a paucity of interesting lengths or energies, between those of the LHC and those applying to much shorter distances or higher