Is there a physicist in the house?

Comments below... Ron Hudson wrote: Correct. For <thing> small enough to show quantum effects, locating <thing> once will change it's speed (momentum)... For quantum-sized <thing>, there would be no way to know the <thing> at 35 was the same <thing> at 5... Measuring <thing> at 5 disturbs <thing> -- see below Not meaningless... In fact, the basis of QM. Usually stated, you can't know the momentum of a particle (p = mv, m = mass, v = veloicty, p = momentum) and the position of a particle more accurately than the uncertainty introduced by Planck's constant h = 6.626068 ? 10-34 m2 kg / s You usually talk about momentum because at relativistic speeds the mass is not a constant... This is usually explained as uncertainty introduced by measuring one or the other of the two quantities momentum or position. A simple view is an electron -- if you shoot it at a phosphor screen, it illuminates a spot, and you know exactly where it is, but you no longer know how fast it is travelling, as it gives up some of it's energy to light the phosphor. On the other hand, if you accelerate electrons between two charged plates, you can have a very good idea of the speed (therefore the momentum) of the electrons (or think of them in a cyclotron) but you have no idea of the actual position of them. The act of measuring one item affects the other... No one has come up with a way of measuring a particles position that doesn't cloud the knowlege of the particles momentum, and the reverse. Plank's constant is so small that these effects are only noticable on the scale of atomic particles, atoms, molecules, etc. and not on normal objects that we look at (the classical limit, where Newtonian mechanics is usually used...), so there is no problem with the fact that you can know the position and momentum of a billiard ball fairly accurately... There is usually a good (math) expanation of this in textbooks with the title Modern Physics (2nd year college physics texts...) -- they usually also have a good explanation of Relativity for someone who has had first year college physics using Calculus. A good explanation for non-math types is in a book called "Mr. Tompkins in Paperback" by George Gamov -- has relatively clear explanations of both QM and Relativity by writing a story where the speed of light is low enough and Planck's constant large enough to make the effects visible on "normal" objects... Bill