The Is: The Many Worlds Interpretation of Quantum Physics

This series of posts is based on Brian Greene's The Hidden Reality, and I highly recommend buying it if you are interested in exploring the subject further.

Quantum physics came about at a time when people were wondering if they had reached the End of Science at the end of the 1800s.  Newton's concept of gravity had ideally described motion for hundreds of years.  Maxwell and others developed Maxwell's Equations which seemed to completely explain the nature of light and electromagnetism.  All was good with the world.  Lord Kelvin's indicates the general notion at the time:

"There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" - Lord Kelvin, 1900

Little did they know that an obscure worker at the Swiss patent office, Albert Einstein, was spending his evenings developing his Special Theory of Relativity which would be published in 1905.  That would lead to a tectonic shift in the way all of us perceive the universe, would meld space and time, and would climax with two giant mushroom clouds over Japan in 1945.  But we're here to talk about another breakthrough round about the same time.

Quantum physics all came about because someone wondered why things glowed red hot.  Or more particularly why things glowed a certain colour based on their temperature regardless of the material.  Classical physics was having a hard time explaining this until a fellow named Max Planck offered that you could get the math to work if you made it so that electromagnetic could only be emitted in multiples of a certain of a certain package size, called a "quantum."  Electromagnetism, at small scales, was not continuous, but discrete, made up of bits, like a digital computer.

Well, like any good physicist, Planck and other physics luminaries kept going, and it was one of those extremely satisfying moments like when you get your fingers under a corner of wallpaper and a whole huge swath of it rips up in one piece.  Several groundbreaking findings followed that laid the basis for quantum physics.

Heisenberg's Uncertainty Principle showed that you couldn't know both the position and the velocity of a particle exactly.  You could know exactly where it was, but nothing about its velocity, or vice versa.  But not both.  Not just because they didn't have machines sophisticated enough to measure them, but because, at the tiny subatomic scale, reality itself became smeared.  At this scale, an electron or a photon could not be thought of as a particle or a wave, but a particle and a wave.

Erwin Shrodinger developed an equation to predict the probable location of subatomic particles.  Again, because of Heisenberg's Uncertainty Principle and the mathematics involved, you never knew exactly where the little buggers were hiding, but with Shrodinger's equation you could say "I'll lay two to one odds the electron is over there" and come out a winner at the end of the night.

So in twenty years they went from the End of Science to black holes, the gravity-warped space-time continuum and the idea that the stuff of nature, at the subatomic substrate doesn’t really exist per se, but just kind of exists.  This is what caused Reginald Bottomsley III  to remark, at the 1927 World Physics Conference, "What f%@kery is this?"  OK, I made that last part up.  But they were all thinking it.

But was this "probability wave" of Shrodinger's real or just a mathematically convenient description of what was happening?  The famous double-slit experiments of the 1920s showed that the electrons behaved, in reality, like both particles and probability waves.  If you're interested in the double-slit experiment, here's  a good little youtube video on it.

Now if your head is spinning, don't worry.  That's pretty much everyone's reaction upon exposure to the double-slit experiment.  An electron exists as a probability wave, harbouring within in it every possible future.  But when you point a machine to look, an electron jumps out at you singing Here I am / The one that you love.  It's only a probability wave when you're not looking,  but when you look at it, it becomes a particle at a point in space.  Like little children, the electrons behave completely different when people are watching.  What the heck is that all about?

View of electrons through microscope.  Note the remarkable similarity to 80s cheezerock band Air Supply.

 Well all the eggheads got together, led by Neils Bohr, the father of quantum physics, and came out with something called the Copenhagen Interpretation.  The Copenhagen Interpretation of quantum physics is that matter and energy exist as probability waves until such time as we decide to take a peek at what is going on.  It is this act of observation itself that causes the collapse of the probability wave, forcing one probability to actually happen (P=100%) and all the others to not happen (P=0%).

This remains, probably, the most popular interpretation, but it has some problems.  Why, for example, should an electron care if someone is watching it?  What does "observation" mean?  Does a sentient being need to be involved?  Will an electron show up singing the Greatest Hits of Air Supply if the measuring machine is on but the grad student whose supposed to be watching it is playing Second Life? Who or what chooses which probability actually happens?  And then there's the niggling detail that Shrodinger's Equation doesn't really allow for a sudden collapse like that.

So another interpretation of quantum mechanics was proposed. In this one, the probabilities of the events that didn't happen didn't collapse to zero.  All possible events happened, each in a co-existing universe.  The universe splits for each outcome.  A different parallel universe is created for each possibility.  To use a not-completely-accurate "macro" analogy, when you roll a pair of dice, eleven universes are created, one for each outcome.  We are part of a vast, complex probability wave function containing every possible future of every subatomic event within it.  Anything that ever could have happened did happen—not necessarily in the universe we experience but in other, parallel, universes that are being instantiated by the trillions every microsecond from all the probability waves of the subatomic particles in our universe.

This is the Many Worlds Interpretation of quantum physics.  It's got it's issues too, but it's preferred by many of the great minds of quantum physics, not the least of whom is Stephen Hawking.  Many Worlds or the Copenhagen Interpretation?   It's somewhat of an academic question right now.  Since the various probability waves decohere, it doesn't seem that we can actually communicate with any of these parallel universes.  And no one has thought of a way to feasibly test the Many Worlds Interpretation (though there are some ideas).

But like the infinite universe and the bubble universes of the last column, the Many Worlds Interpretation is completely mathematically consistent.

So now we've got The Is containing, potentially, an infinite number of infinite universes and a parallel universe for every possibility of every subatomic event that ever happened or ever will happen in all those universes.  But we're not done yet.

Next up:  Simulated Universes.