## Particle Physics for Everyday Life

Just last week one of the most sophisticated physics labs, CERN announced that as part of its research into particles smaller than a single atom it had clocked a neutrino traveling faster than light. Truly amazing stuff as the speed of light is the galactic speed limit. Nothing can travel faster than light, nothing in the entire universe. None other than Albert Einstein in his famous special theory of relativity, you know the E=mc2 equation you have seen but don’t remember from physics class, more than one hundred years ago. As a refresher, E (Energy) = m (mass) * c (speed of light) squared. Energy and mass are equivalents. Einstein’s theory has been so profound and reliable that more than academics and particle physicists pay attention to it.

So, what are some of the ways that Einstein’s theory of relativity impact our everyday lives?

Consider the effect of the ticking clock. One of the consequences of the theory of relativity is the effect of motion on a ticking clock. If you watch a stationary clock ticking, and simultaneously compare it to a moving clock, the moving clock will tick more slowly. It does just appear to tick more slowly, it is measurably ticking more slowly than the stationary clock. Time does not slow down for the moving clock, except as measured from the vantage point of the stationary observer, you.

Because we can actually measure this effect, you can find the nearest gas station or espresso shop using a GPS enabled smart phone. GPS (global positioning system) uses satellites to triangulate and find your location within a few feet. Signals from multiple GPS satellites are received by your phone and based on the known location of the satellites, the exact location of the phone can be determined by measuring the time it takes the signals to travel from the satellite to Earth. Due to relativity, the highly accurate atomic clock on the satellite will appear to you, standing on the Earth, to tick more slowly because of the speed at which they travel around the planet. (Interestingly, the satellite’s clock will also appear to tick faster due to differing gravitational force, but that is general relativity.) In order to accurately measure your location, the effects described by the theory of special relativity have to be taken into account. If not, the accuracy of GPS navigation would be off by as much as 10 km after one day and continue to accumulate.

Perhaps the most interesting part of the application of Einstein’s theory to GPS is how scientists fixed the impact of relativity. Knowing how high above the Earth and at what speed the satellite would eventually operate, they slowed down the satellite’s clock before launching it into space. So far, my GPS still finds me at home in the basement - so, I’m guessing the neutrinos have not altered the accuracy of the GPS satellite’s, yet.

Nuclear Energy and The Bomb. Einstein’s theory of relativity is the essential science behind our understanding of the tremendous energy released during nuclear fission that occurs in a nuclear reaction chamber at a power plant. A small mass of material - in these cases uranium, plutonium for example - are capable of producing massive amounts of energy. It took Einstein’s theory of relativity to effectively inspire the use of nuclear fission as an energy source and a destructive force. Likewise, the theory of relatively helps explain the energy output of the Sun, which produces energy by nuclear fusion - joining atoms rather than splitting them.

Moving Objects with Light. Light, which is made up of photons, lacks mass, but travels at the extreme speed. One of the unique implications of Einstein’s theory is that because light has energy, it could exert pressure on solid objects. The energy of light can be converted to perform work. One of the more visually stunning examples is spacecraft propulsion based on nothing more than light from the Sun using solar sails. Much as a sailboat gathers wind for propulsion, these spacecraft use large sails to gather photons. Each photon that impacts the sail imparts a tiny amount of energy from the photon to the spacecraft, but the Sun fires our billions in a constant stream allowing the spacecraft to enjoy constant acceleration. The first spacecraft designed to use solar sail propulsion was the IKAROS launched in 2010 and it successfully completed its mission.

Alright, so maybe the practical applications of Einstein’s theory of special relativity are a bit difficult to come by, but the fantastical implications are not. Amazingly, the theory of relativity, if true, absolutely precludes both travel at faster than light speed and time travel. Staples of science fiction and my favorite childhood movies, but relegated to fiction nonetheless. What if, Einstein was wrong - or at least only mostly right - and a neutrino can travel faster than the speed of light. Normal objects with mass cannot accelerate past the speed of light because as their speed increases so does the energy needed to continue to accelerate and the amount of energy needed reached infinity. But, if the CERN measurements were right, and a neutrino traveled faster than light, the implications truly are revolutionary. Neutrinos have mass. A mind-boggling tiny amount of mass, but just the same, they have mass and have now been measured to exceed the cosmic speed limit. That fact alone blows the lid off of our assumptions and requires us to re-examine the possibilities of space travel beyond light speed and perhaps travel that can break free of the bond of space and time itself.

Before you get too starry eyed, the CERN results have yet to confirmed and almost no one in the scientific community believes that that experiment will hold up. Put your time travel plans on hold for now. Stay tuned....