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View Full Version : Quantum Mehanics: Cat wanted: Dead or Alive.


Zybraxia
04-11-2009, 04:08 PM
Quantum mechanics is a now well established theory of physics which describes what goes on at a sub-atomic scale. It explains for one thing how atoms themselves hold together, (which classical Newtons mechanics cannot), and certainly has practical application since it is the underlying principal of semiconductors, (transistors and silicon chips)

The trouble is it doesn't make sense on the much bigger scale of things in which we live. To us everything seems to be cause and effect, but on a quantum level cause and effect do not exist, only probabilities exist. Events are like a huge cosmic casino and we don't know the outcome of anything until we actually 'see' it. (although the probabilties of various outcomes can be assessed.)

The classic 'thought experiment' which describes this is 'schrodinger's cat '. In this senario, a cat is placed in a closed box for an hour. Also in the box is an atom of a radioactive substance with a half-life one hour. It stands a 50/50,chance that it will spontaneously decay within the hour. If it does so the cat dies, if it does not the cat lives. The question is: what state is the cat in before we open the box and check it's condition. Acording to Quantum Mechanics the cat is both alive and dead until we actually open the box, and that point it will spontaniously be either alive or dead but not both.

What do you make of this?, after all a huge amount of modern physics and engineering is based on Quantum Mechanics being real.

BTW, In case you didn't know, Isaac Newton whose classical mechanics was replaced by QM, was the inventor of the cat-flap. Maybe he would have somethig to say about this ....... 'Z'

crawfish
04-12-2009, 12:50 PM
I understand it's all about weighing probabilities and not holding anything true or false until you can observe it...but a cat can't be dead and alive at the same time...unless it's a zombie cat!

Seriously though...from what you described about quantum mechanics it sounds like physicists trying to cover all their bases before they put their wingtips in their mouths.

That's like in metaphysics nothing is absolutely true, only highly probable of being true. For example if we throw a hundred bricks at a hundred windows and they break a hundred times, we can't prove that the next brick will break the next window 100%, only 99.999 ad infinitum %...we can only hypothesize it will by saying it is very likely.

Zybraxia
04-12-2009, 01:23 PM
I don't know much about metaphysics, but it does sound like the idea is very much related.
In quantum physics the state of everything is indeterminate until it is observed. So to be more correct about the cat, it's not both 'dead and alive', but is in an indeterminate state and it's fate is decided only when the box is opened. It is a tricky and paradoxical subject, but despite being completely counter-intuitive it does seem to explain what 'reality' is on a subatomic scale. Nothing actually 'exists', Things all 'virtually' exist with different probabilities.

A bit more here:
http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat