# Meir Achuz

Senior Members

147

1. ## forces

Forces are useful concepts in statics problems and were historically important in Newtonian mechanics, but using force in relativistic or quantum mechnics is confusing, and generally avoided. The concept of force is ambiguous in relativity and QM, often being used incorrectly if tried.
2. ## books

I would read a number of standard QM books before looking at that one.
3. ## does EM energy decrease with red-shifting?

"Therefore, does the minimum energy of the radiation decrease when it red-shifts?" Yes.
4. ## Energy expression for an Electron

It seems that you mean the energy of an electron bound to a nucleus. For that case, E=-Zme^4/2n^2 in Gaussian units. Since E~-1/n^2, the electron energy becomes more negative if it moves closer to the nucleus (lower n). The "energy of the energy shell" is just a formula used to calculate the electorn energy, so they are equal.
5. ## Using a sweater as a corrective lens

The pinhole in front of your eye makes your eye into a pinhole camera I do the same thing by folding my forefinger, leaving only a small hole to look through.
6. ## A question about Superstrings

"I've been searching in the books that I have, such as a Brief History of Time and Elegant Universe, and they never really talk in great detail". That's how they sell so well.
7. ## Is alpha a constant (split from cosmological constant)

The dependence of alpha on 4-momentum transfer Q^2 does not change the meaning of alpha(Q^2=0) being constant.
8. ## electrodynamics puzzle

But Max could not find the field of a moving charge, until Einstein and Lienard-Wiechert.
9. ## Is alpha a constant (split from cosmological constant)

http://arxiv.org/abs/0705.3704
10. ## electrodynamics puzzle

I am not sure what you mean by "look so much like relativity,". Only relativity can give the fields of a moving charge. There is no other way.
11. ## What is Retarding Voltage?

You are basicly correct. The retarding voltage V that stops any photo-electric current gives a measure of the maximum energy of the emitted electrons in eV.
12. ## Shm

In the cm of the two blocks, the center of the spring does not move. This is the same as each block oscillating with a spring of length L/2, which changes the effective k.
13. ## Young's Modulus

Y by itself doesn't so imply. It could be that there are molecular calculations that give a reasonable value for Y for a particular material. This would imply that the molecualr hypothesis was correct.
14. ## QM Question.

It did that fifty years ago.
15. ## Can a quark be compressed?

The elementary quark is pointlike. A point is beyond compression.
16. ## Fast, Slow and Backwards Light

It's smoke and mirrors. The animation on the webpage is a computer animation, not an experiment. In the experiment a short pulse is distorted by anomalous dispersion so that the maximum of the pulse drifts a bit backward, while the pulse moves forward. If they define speed as the movement of the peak, they call it backward.
17. ## Stern Gerlach Magnet

What is needed is a magnetic field that increases in the direction of the field lines. The simple shape does this.
18. ## Do tachyons have negative mass?

They have m^2<0.
19. ## Stern Gerlach Magnet

The Stern-Gerlach setup is only effecctive for neutral particles.
20. ## What is the formula?

$$v=at/\sqrt{1+a^2t^2}$$ for an object with a constant acceleration a in its rest frame.
21. ## newton rings!

They are interference bands that are seen when a large plano-convex lense (That is one side flat, the other spherical with a large radius) is placed on a flat glass plate, and a light of definite wave length is shone directly onto it. Destructive interference at every thickness of air space equal to (n+1/2)lambda produces dark rings. This is described in many physics texts, which still are available off line.
22. ## The magic sausage.

Please don't quote me, but maybe the frozen sausage was frozen. When it thawed, it could become softer and the pressure of the bag could squeeze it. This is hardly rocket science.
23. ## Septenary Units (split from Different Planck Units)

Neither the P mass nor the P length is the smallest. They are just sizes that are convenient unitgs for some applications.
24. ## Are "virtual particles" a fact?

Virtual particle are mathematical constructs in momentum space in a perturbation calculation, usually of scattering. They don't exist in any real physical sense.
25. ## Electroweak Force and Unification

The EM photon is a linear combination of the W_3 and B. Yes. It is this particular breaking of the symmetry that unifies the U(1) and SU(2) groups. They can no longer be disjoint. In a similar way, 100 years earlier, the E and B had to be in the same tensor, and could no longer be disjoint. A similar unification has been conjectured for the SI with the EW, but that conjecture has not worked out yet, if ever.
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