stealthmongoose
Is it demonstrable as fact? I always thought Quantum Mechanics was untestable, that and i can't get my head around it.
Y u raep mah braens?
The uncertainty principle has several manifestations, the most popular being the momentum-position one. This one is easily demonstrable, but probably not in a very convincing way to a layman. The way you demonstrate it is true is perform a large set of experiments where you measure the location or momentum of a particle that behaves quantum mechanically. Since each experiment should have identical initial conditions, you will get a momentum and position distribution function. From this, you can calculate standard deviations and then test the uncertainty condition.
Another form of the uncertainty principle is the time-energy uncertainty principle. This one is a tad easier to see as satisfied in that it allows us to predict the half lives of particle states based upon their energy and it works out rather well.
As for the "testability" of quantum mechanics in general, it is incredibly easy to test. Your computer operates using quantum mechanical principles, as does a rather large amount of current, mundane technology [like microwave ovens, laser pointers, neon lights, florescent lights, street lamps, etc]. More advanced tests of the theory have also been performed, such as double slit experiment with a very small number of particles at a time.
Tuah
It is quite demonstrable, albeit I don't know how it's done. But that is the entire point of the Large Hadron Collider. All the other particles' behavior has been demonstrated, and they are working to discover the last, and most important, one necessary to complete their equations.
Actually, the LHC is meant to be a further test of the standard model [by finding the Higgs boson], of several "exotic matter' hypotheses of dark matter and a test of "supersymmetry." Basic quantum mechanics [and a good deal of the advanced stuff] is very well established by much less...expensive testing.
Xion0101
There is a problem as to why quantum mechanics and relativity cant be united, one explains the atomic world of particles, the other with the cosmic world of celestial bodies. Each theory attempts to explain how each part acts according to the whole, but neither tries to explain how the whole results fromthe individual proerties of the parts functioning with one another acvording to a single natural law of interaction.
The issue with quantum mechanics and the general theory of relativity is that quantum mechanics, on microscopic scales, destroys the space-time curvature required for the general relativistic description of gravity. So, the two theories are mutually exclusive. A descent amount of research is going into coming up with a quantum mechanical description of gravity [beyond the standard model's tacked on "graviton"].
Xion0101
Interestingly that can be easily explained, matter is a result of colliding waves of energy. For example the existence of the electron is only temporary, its not that its moving in and out of dimensions, its actually being recreated by the interaction of the proton and neutron, which was originall two neutrons that were set in motion, consider the n>p+e, but could b n=p+e+E, so m1>m2, m1=n and m2=p+e, so m1=m2+E, m1 is inactive state and m2 is active state.
This is a rather...inaccurate description. For one, your example, would imply that there is some measurable life time to protons and electrons when neither has ever been observed to decay. Additionally, your neutron decay is missing out on the anti-neutrino required to conserve lepton number.
This aside, what quantum mechanics "says" depends upon the interpretation used. The easiest way to think of it is that the particles are the wave functions. They exist over extended areas of space and that interaction between particles alters these wave functions.
To show what this means, let's look at a simple example: the single particle-double slit experiment. Let's consider two simple cases before going into the quantum mechanical one. So, the first case is classical particles. These are well localized and I know where they are and where they are going. I shoot a bunch at a screen with two slits and they stick to another screen further away. What I get is two piles of particles on the screen, one behind each slit. I now do the same thing, but instead of classical particles, I use light waves. The light, being a wave instead of a classical particle, interferes with itself and produces a pattern of light and dark spots instead of just two bright spots behind each slit. So, these are the two outcomes we might see. One is for "waves" which occupy some area of space and the other is for "particles" which occupy a single point in space.
Now, let's try some electrons [normally it is photons, but I like electrons more]. What would be expected classically is the two piles of particles, instead we get a diffraction pattern [see
electron diffraction]. So, a large number of electrons have the "wave" behavior. Well, maybe that is a result of their being a lot of them. So, let's try one at a time. We get the same result. So, what is generally thought of as a "particle" behaves like a wave. Why is this? Well, electrons are quantum mechanical objects. So, they exist over an extended area of space, much like a wave. When the electron reaches the two slits, it passes through both and interferes with itself as it is in a superposition state of going through slit A or through slit B. When it reaches the screen, the electron seems to collapse into a point [if we are shooting one electron at a time, we only get 1 dot of our diffraction pattern at a time, but if we shoot enough, we get the whole thing]. Why is this? Well, the screen it is hitting is a classical object. So, the electron, while being in a superposition of two states, has to pick a single point to be on the screen as the screen cannot be in a superposistion [a property of classical objects that can actually be derived form purely quantum mechanical considerations]. Now, since the electron exists over an extended area, we can say that it exists "more" in some spots than in others due to the interference pattern. At the screen, it has to pick one of these allowed locations.
The next step in the experiment is to try and figure out where the electrons are going before reaching the screen. So, we stick some sort of detector on one of the slits and start shooting electrons again. What we end up with is 2 piles of electrons as we would expect from particles. Now, why is this? The detector, again, is a classical object. So, it cannot be in a superposition. This means that the electron can only be in a state that passes through one slit, not two. Therefore, the electron cannot interfere with itself on the other side of the slits as all of it goes through one slit or all of it goes through the other.
[All of this is derived in the Copenhagen interpretation. There are other interpretations, but they have rather different descriptions of what happens and are a bit more complex to describe in layman's terms.]
