J.C.MacSwell

Can comeone explain the difference between spin 1/2, spin 1 and spin 2 in such a way that the numbers make sense. I realize they mean quantum spin and relate to classic spin by analogy only but in what sense is spin 2 "twice" spin 1, or spin 1 "twice" spin 1/2. I realize also that spin 1 and 2 are in a different "family" than spin 1/2.

Is that your conclusion/you agree fully with it?

If equally hard means equal force... I said if we were equally powerful.

Maybe this will help: Assuming the force does not act through the centre of mass. All of the force will also go into rotation. The moment will depend on the magnitude of the force and the "lever" due to the alignment of the force wrt the centre of mass.

It takes more energy to maintain the force. If you and I were in outer space with bars and we were equally powerful and I pushed with all my might through the centre of mass and you pushed with all your might on the end as described on an equivalent bar then I would exert more force.

All of it will go into translation.

It will spin and translate (wave good-bye to it) It will move away in the direction of the force and you will move in the opposite direction. Depending on the alignment of the force with respect to your centre of mass you may spin also.

What I was trying to show here is that any force acting on a rigid body that is not acting through the centre of mass is equivalent to an equal force in the same direction acting through the centre of mass plus a rotational moment.

I think this is where you are going wrong. ALL of the force acts to translate the centre of mass. F=X, if X+Y=F then Y=0 Picture 100 particles. Any configuration. Some glued together rigidly. Some totally detached. Some attached by elastics. Now apply a force upwards on any particle or particle group. Call that force F. F will equal ma, where a will be the acceleration upwards and m will be the mass of the system.(elastics and all) Redo the math for the same thing adding a mass the size of Jupiter to the system where Jupiter is 100 miles away and is totally unaffected. F will equal ma, where a will be the acceleration upwards and m will be the mass of the system including Jupiter. Redo the math for the same thing adding a mass the size of Jupiter to the system where Jupiter is 100 miles away and is the only body affected by the force (upwards again whatever that means in the reference frame you are using) F will equal ma, where a will be the acceleration upwards and m will be the mass of the system including Jupiter. If F accelerates the mass in translation and in rotation it doesn't matter. F will equal ma. (if you sum the "rotational accelerations in the upward, or any direction they will cancel out) If this seems odd it is probably because you intuitively feel that since F may be doing work to stretch elastics or cause rotations etc that maybe some of F is "used up" in this regard. It is not. What is different and does need to be divided up is the energy or work done by the force F. The work done by F is very different in each of the above cases.

I'm thinking in terms of the masses themselves. Their receding velocities (regardless of why) would require the same change in momentum to slow down or speed up??

I think that's right (the second part, not so sure about my armchair cosmology ).

Why does the expansion OF space have MOMENTUM? Is it assumed to hold to the same equations as an explosion IN space?

I like it already! I would like to see a few more competing theories but you have to adapt them when you have a contradiction or you can add/remove assumptions until they collapse under their own "weight". I read a book by British astronomer Martin Reese "Just 6 numbers" where he says he was originally against the Big Bang Theory, then converted by the evidence to being 90% certain 10 or 15 years ago, and now is 99% certain. seems rather high considering all the basic things we don't know. What are your odds? I'm a Steady State Theorist at heart but I'll go with 50% for some form of the Big Bang, 25% for some form of the Steady State Theory and 25% for "something else". Be interesting to see if people who are really knowledgable about these things would be committed in the 90+ percent range. Edit: I think a universe based on the 3Dsurface of a 4D hypersphere that slowed in expansion forever but never stopped and reversed would be considered "FLAT" (mathematically) no pancake necessary.

Conservation of momentum