02 July, 2010

The Copenhagen Interpretation vs. The Many-Worlds Interpretation

Now, in quantum physics, there is such a thing as superposition. Basically, it means that if something goes unmeasured, then its position can be in many places at once, and is therefore in several places at once. Take Chad Orzel's example:

If there are two boxes, then there is the probability that a treat is either in the left box, or the right box. (Please ignore the doggy examples; the book is based on them) Therefore, until you go over and actually check the box, then it is in both boxes at the same time.

Now, the Copenhagen Interpretation says that something called "collapse" happens when something "measures" the position of the object, in this case, a treat. Collapse is when the object lands in one of the allowed states, in this case, either the right box or the left box. Now, people argue over what counts as an "observer"; humans, dogs, insects? They argue over why an "observer" should have any effect at all over a quantum object.

The quantum-mechanical "Schrödinger's cat...Image via Wikipedia
The other explanation for this phenomenon is the "many-worlds" interpretation; basically, the wavefunctions of the objects turn "decoherent" and the two wavefunctions are no longer "interfering." Basically, a new branch of the universe is created for every possible outcome, if you want it in a nutshell. This is the basis for many fiction books, where universes branch off from one another.

One example of this occurences is the Shroedingers Cat thought experiment. A cat is placed in a box with uranium that has a 50% chance of decaying. If it decays, then gas is released, killing the poor kitty. If no decay occurs, then no gas is released and the cat lives. Shroedinger proposed that a different universe was created in that instant, one where the cat lived, and one where the cat died. We exist in both.

Both of these theories--the Copenhagen Interpretation and the Many-Worlds theory--give you the same result: the object is either there, or it isn't there, and that's the end of it. We have no control over the probability or what wavefunction our lives work in. That's the basis of the "shut up and calculate" theory, possibly said by the well-known physicist Richard Feynman.

Feynman (center) with Robert Oppenheimer (righ...Image via Wikipedia
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-----The Golden Eagle

P.S. I took the advice, and yes, Zemanta was helpful! :)


laughingwolf said...

cool stuff!

robert a. heinlein wrote a book you may want to read: the cat who walks though walls

laughingwolf said...

THROUGH walls... grrrrrrrrrr

The Golden Eagle said...

Through walls? Sounds interesting! :)

laughingwolf said...

it's sf, but a fun read :)