: All of quantum mechanics is based upon Heisenberg's
: Uncertainty Principle. This underlying law of quantum
: mechanics stipulates that it is not possible to
: measure the exact position and exact velocity of a
: particle simultaneously. We can tell one or the other,
: but not both.
: Now, this is derived, not from a necessary law of the
: universe, but from a technological limitation of
: humanity: to "see" a particle, we must
: bounce particles off of it. (Photons are sometimes
: used, but electrons, being higher-energy, have proven
: to be more effective in measuring particle
: attributes.) In any case, when we bounce particles off
: of another particle to collect the reflected particles
: and measure the observed particle, that observed
: particle has been moved by the affectation of our
: observance, it’s velocity and/or position changed.
: Therefore, with our present technology, it is not
: possible to observe both characteristics of a particle
: simultaneously, for our very action of observance
: affects what we observe.
But this isn't the origin of the uncertainty principle...it's only an expression of it. The uncertainty principle--in its infinite forms, of which position versus momentum and time versus energy are only two--actually stems from much more basic principles of quantum mechanics.
Every physical "thing" has an associated wave function. So far as we are concerned, this wave function describes everything about the object. To measure a certain property of the object, you perform the appropriate transformation on the wave function and then take a random sample from the distribution described by the transformed function. That's the value you get. If the transformed function is "heaped" about a point--it spikes there and is almost 0 elsewhere--then you're very likely to get that value. If the transformed function is more spread out, then you can easily get a large range of values. In this way, the shape of the function determines the "uncertainty" level of the property you're measuring.
The uncertainty principle quantifies how different transformation functions affect the uncertainty level of the basic wave function. For instance, the position transformation function is just the identity...it leaves the wave function unchanged. The momentum transformation function is basically a Fourier transform...it returns how much of the original function was made up of sine waves of a given frequency. Now, it's a mathematical fact that if a function is heaped up at a certain point, than its Fourier transform is spread out...and vice versa. This means that the more precise position measurements are, the less precise momentum measurements will be, and vice versa.
To sum up--the uncertainty principle is simply a necessary consequence of the basic belief in an object being describable as a wave function. Arguments like "every time you bounce light off a particle, you change its direction" are used to try to provide a common-sense explanation, but they have *nothing* to do with the basic theory behind the principle. The uncertainty principle is based on quantum theory...not vice versa.
: Alternate examples of the “triumphs” of quantum mechanics
: include “Schrödinger’s Cat”. In this hypothesis, a cat
: is placed in a box which is completely sealed off from
: the outside world. (The cat has ample supply of food,
: water, and air, we just can’t know about it; it’s a
: completely self-contained little world.) Inside the
: box, there is a radioactive trigger which will set off
: a gun and kill the cat. Because of the half life
: nature of radioactive material, the gun has a 50%
: chance of being triggered at any one time. This means
: that there is a 50% chance of the cat being alive or
: dead at any one time. Therefore, the cat is both alive
: and dead at the same time.
: This is absurd! The fact that we can’t see what is going
: on doesn’t denote that both possibilites are right!
: It’s one or the other, not both (I don’t believe God
: plays dice anymore than Einstein did). A simple
: opening of the box will determine if, how, and when
: the cat died. If the cat jumps into the scientist’s
: arms when he opens the box, it can be realized the gun
: never went off and the radioactive material never
: triggered.
Quantum mechanics does not actually say this. It does say the cat exists in a mixed state until a measurement is made, but there's still plenty of argument about what a mixed state means, and what measurement means. If you've heard of the Copenhagen interpretation and the many-worlds interpretation, they come into play here. This is essentially a philosophical question, and has nothing to do with the science of quantum theory.
: Another advancement of quantum mechanics is the
: interpretation of the falling tree in a forest when no
: one’s around. Quantum mechanics says one of the two
: possibilities: the tree made no sound because we
: didn’t hear it; the tree both made a sound and did not
: simultaneously.
I think you may be reading quantum mechanics as described by Deepak Chopra. :-) Actual textbooks on quantum theory have nothing to do with this, nor do actual quantum physicists think this. Believe me, I know; I've been studying the textbooks and talking to the physicists for four years now.
: The answer to anything by quantum mechanics that it
: doesn’t know for sure seems to be that all
: possibilities actually and did occur. (Basically, it’s
: saying that all alternate universes are created by our
: ignorance and then recombine with the rest of the
: universe’s spacetimeline when we learn what really
: happened.) Lol, in a science where there is no wrong
: answer, it is not a science, but a philosphy.
: This anthrocentric view that the universe is governed by
: our very observation of it is the most rediculous,
: contradictory, and unscientific I’ve ever known. It’s
: as absurd as one believing that his point of view is
: entirely correct and that all else is false. We know
: such an interpretation, in reality, to also be a
: fallacy.
Um...if you've worked out a way to actually *know* this, then all the philosophers of the last 2,000 years would be very interested to hear it. Quantum mechanics, like every other scientific theory, merely tells you what you'll see when you make measurement X on system Y. All questions about what's going on in the "real" world are philosophy. Gurus writing popular books may use "quantum" as a buzzword, but that doesn't mean they know anything about it.
.
: “Quantum mechanics is reasonable and a hard science, one
: of the two pillars of modern physics, because it
: describes the world around us,” some will say in
: defense of the “science”. Well, so does the mythology
: of the ancient Greeks, but we don’t follow that
: equally blindly, now do we? A myth describes a world
: just as adiquately as quantum mechanics does (and a
: myth is actually far less contradicted in the real
: world, evidently).
However, Greek myths cannot tell us how to create lasers and microchips.
You may think quantum mechanics absurd, but reality isn't required to fit your system of aesthetics. As far as we know, relativistic quantum theory *works*...it makes predictions that turn out to be right. That's the test of any scientific theory. If we later come up with a deterministic theory that makes all the same predictions and also makes more conceptual sense, physicists will gladly toss quantum aside. (Although Bell showed that a locally deterministic theory--that is, a theory where you can make deterministic predictions without having to know the state of the entire universe first--cannot correctly predict the outcomes of certain "entanglement" experiments--ones which quantum mechanics has predicted correctly.)
--SiliconDream
