Why Nothing Can Go Faster Than the Speed of Light

Einstein's equation gives us the most concrete explanation for the central fact that nothing can travel faster than light speed. You may have wondered, for instance, why we can't take some object, a muon say, that an accelerator has boosted up to 667 million miles per hour—99.5 percent of light speed—and "push it a bit harder," getting it to 99.9 percent of light speed, and then "really push it harder" impelling it to cross the light-speed barrier. Einstein's formula explains why such eff...

 How to Disguise a Helium Atom as a Hydrogen Atom

Donald Fleming of the University of British Columbia in Vancouver, Canada, and colleagues managed to disguise a helium atom as a hydrogen atom byreplacing one of its orbiting electrons with a muon, which is far heavier than an electron. Because it is so heavy, the muon sits 200 times closer to the helium nucleus than the electron it replaces and cancels out one of the nucleus's positive charges. The remaining electron then behaves as if it were orbiting a nucleus with just one positive ch...