Schroedinger's Bird ???????

 Quantum Mechanics is weird. In a quantum world of photons and sub-atomic particles, things behave very differently from the world that we can observe and know. It’s extremely difficult to understand that light is both a photon particle and a wave. It’s very hard to believe that a particle doesn’t have a specific property until you measure it. And until then it has all the possible properties you might measure. Famously, Einstein himself didn’t believe this, saying “God doesn’t play dice with the universe”. 

 

Courtesy: Jadvani_Sharad at Pixabay.com

 

Equally famous is the argument that Erwin Schroedinger used to illustrate this apparent impossibility. Schroedinger described a “thought experiment”, where there is a cat and a radioactive atom sealed inside a box. There is also a Geiger counter, which will detect radiation if and when the atom decays. If it detects radiation, it breaks a flask of poison which kills the cat.  The only way to find out if radiation has been detected is to open the box. According to quantum theory, until that is done, the radiation both has and hasn’t occurred, and therefore the cat is both alive and dead until the box is opened.

Diagram of Schrödinger's cat thought experiment.
Roughly based on Schroedingerscat3.jpg. Dhatfield-own work. CC Creative Commons.

Einstein, with Boris Podolsky and Nathan Rosen, published another thought experiment (called the EPR paper) which demonstrated another paradox. This thought experiment showed another seemingly ridiculous outcome of quantum mechanics math. It went (more or less) like this:

• ·         Two particles are set in motion towards each other with the same momentum. They interact with each other briefly at a known position.
• ·         This relationship between the two particles is called “entanglement”.
• ·         These particles have a range of momentum and location. Until you measure them, they have all of those with some probability. (Yes, hard to believe, but that's what quantum mechanics math says).
• ·         When you measure, say, the momentum of one of the two articles it resolves to have only the one measured momentum.
• ·         But magically, as you do that, the second particle, which may have travelled anywhere in the universe, resolves its momentum to the same value.(How it know to do this, and at the same instant?)
  

It seemed clear to Einstein that this kind of action-at-a-distance was impossible. He said it therefore followed that quantum mechanics was incomplete. There must be some additional factor that was being overlooked and which could explain this paradox.

Shockingly, experiments in the 1970’s and 80’s showed that entanglement is not impossible, but a real phenomenon. Hard to believe, but true.

And now to birds. No, Schroedinger didn’t really do any thought experiments on birds. Sorry.

Birds are astonishingly good at finding their way over vast distances. Homing pigeons have been used for centuries to carry messages back to their homes from hundreds of kilometers away. Some species of birds migrate thousands of kilometers each season, and find their way back to the nest that used in the previous season.

Some slightly nasty scientists have tested migrating abilities. They captured 30 white-crowned sparrows near Seattle migrating South from Alaska to Southern California. They packed the birds into crates and flew them 2,300 miles to Princeton, New Jersey. When they released them, the adult sparrows set off in a direct course South-West toward Southern California. 

 

White-crowned Sparrow. Photo: Steve Ryan, CC BY-SA 2.0, via Wikimedia Commons

Even hummingbirds, with brains the size of a pea, put human navigation abilities to shame. A researcher described finding a hummingbird hovering opposite the hook where he hung a feeder each year. He was planning to put it out in a few days' time. The hummingbird showed up earlier than expected, and remembered exactly where the feeder was supposed to be. 

Photo: Simon Shapiro

 We don’t know exactly how birds are able to navigate so well. It’s clear that they use multiple strategies, including:

• ·         Following rivers, mountains or the seashore
• ·         Using senses of smell and sound, both of which are far more acute than humans’.
• ·         Navigating using the sun and stars. Like ancient mariners they might be using these to identify their latitude and longitude. 
  

But the really mysterious ability is that birds are able to sense the earth’s magnetic field. This requires exquisite sensitivity. Scientists have been working for decades to figure out how the mechanism works.

Birds need some light to do it. Not much, because even the dim light of stars at night is enough. But total darkness inhibits the ability.

Enter Entanglement

There is growing consensus that the ability involves crytochrome, a light-sensing protein that exists in birds’ eyes. A photon colliding with crytochrome can disturb electrons in two molecules, creating an entangled radical pair of molecules, each with an odd number of electrons. They return to equilibrium very quickly – about 100 microseconds. During that time, they can flip-flop between two states of electron spins – each molecule changing at exactly the same time, because of the entanglement. The relative time spent in each of the two states can be influenced by the earth’s magnetism. And each state can participate in different chemical reactions, producing different chemicals. These product chemicals – as yet unidentified – could be the mechanism for the bird’s brain to sense magnetism. 

 Scientists are working on harnessing entanglement to build quantum computers. It seems that birds (and evolution) beat us in the race to make practical use of quantum entanglement.