A Quantum Test

Credit: Ellie Hammack

The late UT Austin physicist Steven Weinberg grappled with aspects of quantum mechanics. The Nobel laureate even envisioned having an experiment to poke holes in it. Now his UT colleague Mark Raizen has proposed pairing an atomic clock with the element ytterbium to bring Weinberg’s experiment idea to life. 

The experiment calls for hitting ytterbium with a laser at just the right frequency, so that an atom jumps from a resting energy level (A) to some higher level (B). Hit it with a laser at a second frequency, and it then jumps from B to a third level (C). 

According to quantum mechanics, you can also go straight from A to C with just one laser at the frequency of the other two lasers combined. And that's the crux of the experiment: if quantum mechanics is correct and complete, you should be able to measure the laser frequencies it takes to go from A to B and from B to C and those should add up to the frequency of a third laser for A to C. Raizen calls this the "Does 1 plus 2 equal 3?" experiment. Now labs around the world are in a race to give the experiment a try – and find out once and for all if quantum mechanics needs a revision.

Read the full feature story and hear audio tributes to Steven Weinberg.