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Author Topic: Are you uncertain about Heisenberg's Uncertainty Principle?  (Read 2950 times)

Offline tychobrahe

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  Ok I'm not disputing the truth in Heisenberg's Uncertainty Principle whatsoever.  I'm wondering how the gap is bridged between our inability to observe something and the inherent truth of the universe, i.e. how being unable to observe electrons and smaller particles without affecting their position or momentum means that they have no true position or momentum.  The principle works and has to be used to model things at a subatomic level, but it seems really anthropocentric when actual physical observation by observers determines the state of the universe.
  I guess my main problem is with the idea of the multiverse that uses HUP as a starting point.  1) What is the basis for this extrapolation?  I understand the need for these equations to understand things at a subatomic level, but 2) Aren't they a tool, like a set of rules to follow to play a game effectively as an observer, but not a statement about the observer's importance?
  There was a time that there was no life in the universe, and thus no observers, and we we can even see some of those times in the light from far off galaxies.  3) Are we just now by observing them solidifying their existence, even though they existed billions of years ago, even though it is impossible under general relativity for us at present to affect them in the past?  There probably were or are universes that were completely inhospitable to life.  4) Does their exclusion of observers exclude them from being real?
  Heisenberg's Uncertainty Principle and the rest of of quantum physics seem like a way to get an answer without asking a question, a way to win a game of blind man's bluff without moving around or touching anyone.  It's incredibly useful for working on problems at this subatomic level, but 5) How did something that seems like a new set of rules to get around our limitations become a great smokey dragon that creeps around when our eyes are closed?
  I know that's a lot of questions, but I'd appreciate some help, or more questions.  If I'm way off let me know too, its been 2 years since I read any textbook physics.
« Last Edit: 20/07/2009 14:23:15 by chris »


 

lyner

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You don't need an 'observer' as such. All you need is something to react. So an atom is an observer, effectively, when a photon interacts with it.

It is not very fruitful to try to constrain 'the rules' to be something which you can understand in the terms you started off with. People who do that are constantly asking the same questions of Science and never get a satisfactory answer. The fact is that you have to go with the flow and to be prepared to accept things like duality as a help not a hurdle in your parth of understanding.
Some of the Eastern Mystic paradoxes can useful for getting you in the right state of mind to step out of your box.
Text books are not always the best way of getting into a subject; they get you through Exams, which is important. You may need to refer to them for the occasional bit of rigour but there are some better ways of getting a feel for the subject.
I would recommend "The Human Touch" by Michael Frayne. He's not a Scientist but he is very well informed, right across the board from Psychology, Physics and Philosophy - good value and excellent for sounding knowledgeable in conversation. His book is chock full of references, too.
 

Offline exton

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Don't get caught up on the term "observation"; in the context of quantum physics, it's more equivilant to the term "interaction". There is no requirement that there be an actual thinking, feeling observer involved. In real life, an observer always IS involved somewhere along the line, of course - otherwise, how would the rest of us ever know what happened? - but the thinking observer doesn't play any role in the actual physics.

The heisenberg uncertainty principle states that (for example) the better you know a particle's position, the less well know know its momentum.
The reason for this is the manner in which momentum is determined in quantum physics; a particle's state is represented by its 'wave function', and its momentume is related to the frequency of its wave. If your particle's wave function is nonzero only for a particular small region of space, then you know that the particle has to be somewhere in that region; however, due to the way these things work mathematically, you need *multiple* waves of different frequencies added together in order to get a wave function that is nonzero for only a particular region of space. Since the momentum of the particle is related to its frequency, and the particle has multiple frequencies, the particle's momentum could be any one of the momenta that correspond to the frequencies of which the wave function is made.

That's more or less where the heisenberg uncertainty principle comes from; it's just a bunch of math. What it actually *means*, however, is unclear. Are the particle's position and momentum undetermined until something interacts with it? Or does it have *multiple* positions and momenta at any given moment? Or maybe some wierd nonsense involving parrallel universes?

If anyone claims to know that one such interpretation is true, he is a liar. Nobody knows. A lot of people have their pet theories, but none of them have been experimentally verified, and most of them amount to nothing more than intellectual masturbation. All anyone knows for the moment is that the math associated with quantum physics yields results that are consistent with experiment.
« Last Edit: 19/07/2009 17:24:16 by exton »
 

Offline tychobrahe

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Thanks exton for the breakdown, I didn't know the stuff about needing waves more than one frequency to get a nonzero wave function.  My main problem is with the theories of the multiverse and string theory which don't explain why this model should affect the universe on a large scale in the way they say it does.  It's kind of like when people using a catch phrase of evolution, 'survival of the fittest', to justify zany social theories without looking at the bigger picture and other contributing factors.
 

Offline exton

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The real trouble with quantum physics is that it's all ultimately math, but when people try to explain it in words in popular literature, they end up trying to use metaphors and over-simplifications. That, more often than not, fails to convey the true meaning of what's going on, and it often gives a deceptive and unfortunate impression of hand-wavy mysticism.

I couldn't tell you much about string theory or any ideas on multiverses; i generally discount them both as currently being too divorced from reality to be of great interest to me.
 

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