Legacy · Direct Application
Particle Accelerators
Machines like the Large Hadron Collider are special relativity made of steel and magnets, turning energy into new particles exactly as the equation says.
Designing With Relativity
As a particle approaches the speed of light, pushing harder barely increases its speed. The added energy goes into its momentum instead. An accelerator has to be designed with this in mind from the first sketch: the timing of every push and the strength of every steering magnet follow from special relativity.
The Large Hadron Collider at CERN, near Geneva, is a ring 27 kilometers around. At full design energy its protons reach 99.9999991 percent of the speed of light and circle the ring about 11,000 times a second. At that speed each proton carries about 7,000 times the energy it has at rest.
Making Matter From Energy
When two such protons collide, the energy of the collision can turn into particles that were not there before, many of them far heavier than the protons themselves. This is mass–energy equivalence run in the direction opposite to a nuclear reactor: energy becomes mass. The Higgs boson, discovered at the LHC in 2012, was made this way.
Relativity also stretches time for the particles created. Many are unstable and should decay almost instantly, but moving at nearly the speed of light their clocks run slow, and they survive long enough to cross the detectors.
Antimatter
In 1928 Paul Dirac set out to find an equation for the electron that obeyed both quantum mechanics and special relativity. The equation he found had an unexpected extra solution, which he eventually interpreted as a particle identical to the electron but with the opposite charge. The positron was discovered in 1932. Antimatter is Dirac's prediction, and it follows from taking Einstein's relativity seriously.
Synchrotron Light
When electrons moving near the speed of light are bent by magnets, relativity concentrates the radiation they give off into an intense, narrow beam of X-rays, vastly brighter than a hospital X-ray machine. More than fifty of these light sources are operating or being built around the world. They are used to work out the structures of proteins and viruses, to design drugs, and to study new materials for batteries and electronics.
How Direct Is the Link?
Direct. Special relativity is the mechanics of every high-energy accelerator, and every collision that produces a new particle is a demonstration of . Antimatter is one step removed: Dirac's achievement, built on Einstein's foundation.