Recent content by jeblack3

In QED it works the other way around. You start from the electromagnetic field. Then you treat waves of each wavelength as independent harmonic oscillators. By applying quantum mechanics, we find that each oscillator has a discrete set of energy states, and the difference between any two...

Here's a very easy method: http://groups.google.com/group/alt.sci.physics/msg/a53fbd5a66f9ba15 Below is some pictures I have of doing it with a padlock. The shackles on the padlock work nicely if you want to do precise measurements because they come pre-aligned. But you can get it to work...

First, don't forget about logic. Your problem is not "Aristotelian thought." The problem isn't quantum mechanics, either. It's that you're taking quantum mechanics too literally. You say: No one knows that. We don't even know if objects have positions and momentums. These are...

That's incorrect. "At the same position at the same time" is a frame-invariant concept. Simultaneity is relative, but when two events are simultaneous in frame K, the time difference between the events in another frame k is proportional to the distance between the events. If two events occur...

I think it just means 0 < \theta_{12} < \pi/4.

There's an argument called the "WIMP miracle" that can explain the amount of dark matter present in the universe today if dark matter particles and their antiparticles were produced in equal numbers and have been annihilating ever since, provided the particles have a weak-scale mass and cross...

Consider the probability amplitude for the electron to go through the hole and hit a particular point on the screen. The phase of that probability amplitude depends on where the hole is. So the wavefunction of the object with the hole in it gets multiplied by a phase that depends on its...

This can be made a lot easier by employing spinor indices. We write a spin-1/2 object as X_a, where the index a can be 1 or 2. A spin-n object is a fully symmetric object with 2n indices: A_{abc} = A_{acb} = A_{bac} = A_{bca} = A_{cab} = A_{cba} A_{111} is the s_z = +3/2 spin component...

Spin is not the angular momentum of a particle. The total angular momentum of a particle is spin plus orbital angular momentum. The orbital component doesn't commute with momentum, but the spin component does.

I was looking for that link, but couldn't find it. You don't have to go into momentum space to understand this, though. You can do it in ordinary position space. Consider an electron some distance from a proton. The probability amplitude to absorb a photon is larger on the side of the...

Consider an electron some distance, much more than the size of an atom, from a proton. (Let's not worry for the moment about what happens at the atomic scale.) The reason the electron accelerates is because of interference between the case where a photon is exchanged, and the case where it...

If flavor SU(3) was a perfect symmetry of the world, then all of the baryons in the baryon octet would be indistinguishable. They would all have the same mass, charge, etc. But it isn't. It's broken by the mass and charge differences of the up, down and strange quarks. It's these...

Okay, bras and kets. This is better because it strips out my hand-waving, and let's you interpret what's going on as you please. As the electron is passing through either slit A or slit B, it is described by the state vector a|A\rangle + b|B\rangle . Without the light, the electron is...

Yes, there is a reason. Their coefficients have dimensions of (mass)^{-n} (with n \geq 1). We usually work with effective theories, which are presumed to reduce to some more accurate theory at some very high energy scale. When a coupling constant has units of some power of mass, that mass...

The disappearance of the interference pattern is due to "decoherence." To try to put it simply, once the electron interacts with the light, you have to consider the joint quantum state of the electron and the light. Without the light, interference requires that possible paths through each hole...