Books: Through Two Doors At Once By Anil Ananthaswamy

 (Drivebycuriosity) - "Quantum mechanics is spooky", said Einstein, even though the genius belonged to the fathers of quantum physics. Indeed quantum mechanics, the behavior of infinitesimal small particles like electrons and photons (light), has a lot spooky phenomena. One of them is them is the result of the famous double-slit experiment. Sorry, no threesome. 

Since the 1920s physicists have been shooting a single photon through a barrier that has two slits. They noticed that - when the photon has passed the barrier - on the other side the photon created not just one impact but two or more. Can a photon exist on more than one place? 

Since the 1920s physicists have been discussing this phenomena and created more and more elaborated experiments and theories. Anil Ananthaswamy`s book "Through Two Doors At Once" sketches the basics of quantum physics and describes how physicists have been developing more and more complex experiments and theories over around 100 years  (amazon). 

Already in the 19th century started a controversy about the behavior of elementary particles, the basics of our world. Physicists stated that light is an electromagnetic wave, comparable to radio waves. But Einstein disagreed. He noticed that when a photon, a particle of light, hits an atom, the impact kicks an electron out of this atom, like a pebble causes a splash, when it hits water. According to Einstein this photoelectric effect proves that light consists of particles (photons) and not of waves.

 

                 Collapsing Wave-Function 

Unfortunately the double-slit experiments show multiple impacts on the other side of the barrier that fit to the wave theory. Einstein`s observation started a controversy about whether our universe is based on particles like photons and electrons or is based on waves. Some physicists believe that photons and electrons behave as waves when they are unobserved and turn only into particles after observation - the famous collapse of the wave-function. Schrödinger`s cat is either dead or alive as long it is hidden in a experimental box (unobserved), only when the box gets opened (observation) the state of the feline is decided. 

 Ananthaswamy presents over almost 300 pages the more and more esoteric theories that ambitious quantum physicists, many of them Nobel Prize winners, developed over the times and describes their more and more ridiculously sophisticated double-slit experiments, some of them cost meanwhile millions of dollars.

"Through Two Doors At Once" reminds of medieval philosophers who asked "can multiple angels occupy the exact same space simultaneously". Later authors mocked them with the infamous satire: How many angels can dance on the head of a pin?