Entangled Photons Act as One

Scientists are one step closer to etching smaller computer chips, imaging ever-smaller objects, and detecting gravitational waves, thanks to a recent experiment reported in the May 14th issue of Science.  Yaron Silberberg and his “Ultrafast Optics Group” at the Wiezmann Institute of Science were able to put five photons into an entangled state, called a “N00N” state which is a superposition of two other states, one with all N photons taking path A, the other with every photon taking path B, |N,0>+|0,N>.  Thus, while it is uncertain which path any particular photon will take, it is 100% certain that they will all take the same path.  This experiment demonstrates how quantum entanglement, a correlation between distant particles, can exist between many different photons as well.

That such non-local correlations exist was proved by John Bell in 1964, and accounting for the mechanism by which distant particles or photons are correlated remains one of the biggest puzzles in quantum mechanics to this day.  In the literature on causation, most philosophers assume Continue reading “Entangled Photons Act as One”

The Kilogram is not a Kilogram!

Though it may sound paradoxical, physicists have known for decades that a kilogram just isn’t what it used to be. That’s because it’s lighter—or at least lighter than its copies—by fifty micrograms. After all, worldwide agreement on experimental results is only possible because there are standardized (SI) units like the meter, the second, and the kilogram. But when the standard kilogram, a cylinder of metal alloy (platinum and iridium), is compared to manufactured copies (with the same composition and size), the scale tips, very slightly, toward the copy. Thus, the original has lost mass (perhaps to polishing) or the copies have gained mass (perhaps by absorbing air), but of course, there’s no way to tell which; they are the standards by which scientists would make such a judgment.

Philosophers should take note. Does the standard cylinder weigh one kilogram because scientists were careful when they made it or because it was defined that way? According to National Public Radio, Continue reading “The Kilogram is not a Kilogram!”