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108 Nanoseconds

Annika Ewigleben, PhD Student

Lehigh University


Every 108 nanoseconds at the Relativistic Heavy Ion Collider (RHIC), two ion beams pass by one another at 99.999% the speed of light, in the hopes that two out of trillions of them will collide in just the right spot, and we will be able to measure what happens. For 24 hours a day, 7 days a week (yes, including holidays), for 4 months every year, for the past 2 decades; every 108 nanoseconds.

There is some truth in this, but the reality is much messier. Things break, alarms go off, objects are thrown. Getting the timing just right is very hard; 108 nanoseconds is a very, very small amount of time, and the timing changes based on the energy! Particle detectors turn on, ions collide; oh no the machine is out of ions, particle detectors down, more ions please! Feed the machine of physics more data in the hopes that this will culminate in a deeper understanding of the physical world around us.

From the gold foil scattering experiments in the early 1900s (what is now called a fixed target experiment), to the first collider accelerators in the 1960s (where two beams are collided with one another, providing more total energy than if one collides a single beam with a stationary target), to the future Electron Ion Collider (EIC), which will be built where RHIC is now running at Brookhaven National Lab; each machine is built on the learned knowledge of past experiments. Many machines are also literally built with the physical remains of previous experiments. The sPHENIX detector currently being built at RHIC reuses the solenoidal magnet from the BaBar experiment at SLAC National Accelerator Laboratory —electronics are saved whenever possible in order to be used in the next big experiment—and, as previously mentioned, RHIC will eventually become the EIC. All things, in time, run their course and are torn asunder, providing the soil for the next season's growth.

As we build ever greater machines—built on ever growing contours of understanding—we probe more precisely and more deeply, trying to understand: what is it? What we've learned is that reality is far more richly textured than earlier mechanistic models in physics would lead one to believe. A proton is not simply a hard ball of matter, but a swirling mix of various, varying intensities of quantum fields, constantly tugging, pushing and pulling one another about, only existing through constant interaction, lest the entire thing come apart. In fact, a proton is the only stable single-baryon that we know of, all other bound states decaying back into a proton and/or other forms of matter and energy.*

We've also learned that no matter how hard we try, we cannot escape the subjective element. From the beginning, the modern field of physics has been the attempt of humanity to create, through objective observation and experimentation, a mathematically rigorous, physical model that maps directly to the reality around us. In essence, not just experimenting and observing, but formulating these observations into objective, mathematical models that can be used to accurately predict the results of future experiments. Eventually, as these experiments grew more and more complex, a fracture was introduced. Humanity had come face to face with the quantum reality of our existence. No longer was our beautiful idealistic world apart from us, where we could merely observe objectively and without interaction. Gone were the days of taking notes as impartial judges and using these to develop our objective models. No, this was a world where the particles changed their behavior depending on whether we tried to measure them or not.

To compensate, the mathematics has become ever more complex. In particular, we can't simply calculate the path from point A to point B; we must consider all of the different ways one could possibly travel from A to B and weigh each path accordingly. How are we to know our particle didn't simply go on a stroll in the middle of our experiment? We only measured it at the beginning and the end, what happened in the meantime is anybody's guess.

So what are we to do? Is it all for naught? In our attempts to build a purely objective model of the universe, we have found that some element of subjectivity is required. Freed from our role as impartial, objective observers, we now must jump in and fully immerse ourselves as subjects in the web of reality, fully aware that our actions and observations are part of the system we are trying to understand. And personally, I find that to be a much richer and more beautiful world than a cold mechanistic one, where going from point A to point B is done in the strictest linear fashion possible, objects merely tracing out a predetermined path, no detours allowed.

*If the proton can decay, it is thought to have a half-life that is stable to ~10^33 years, which is much much older than the current age of the universe. The deuteron (bound state of a proton and neutron) is itself stable, but an isolated neutron only has a half life of about 15 minutes.


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