swansont

Start by drawing a free-body diagram.

How would spinning mercury make a mirror, in space?

It's not so much about whether or not the lifter technology works - it appears to. The question is how useful it is (thrust/mass, and whether it requires an atmosphere to work) and why some people tout it as "antigravity."

(emphasis added) Two issues jump to mind: 1. Lasers don't give you a parallel beam - they do diverge. 2. How do you aim the weapon? The image you see is where the target was when the light left, not where it is now, and how do you figure out how to aim where the target will be, at large distances?

Not easily deflected. Neutron magnetic moment = 9.6623707e-27 ± 4.0e-33 J/T It's not zero.

How so? Especially once you've accepted the term "real numbers."

OK, now we're in the "speed of thought" thread, but that's...OK. I actually was thinking of this thread when I said I gave some examples.

I'm talking about transmission, not reflection. I don't think reflection is involved.

I don't think it's reflection. It's light that enters through other edges.

For light to have come out the edge, it basically has to have entered through another edge* so you get total internal reflection. So it travels a large distance through the glass, which is acting like a waveguide. Absorption. *it's possible a small amount scatters off of some impurity, or some other medium on the surface allows coupling into the glass at some angle.

Consumer grade soda-lime-silicate glass absorbs and/or scatters light just a little unevenly across the visible spectrum, so you lose some red and blue relative to the green. You can also see this effect in a room with mirrors on both walls (like a large public restroom/lavatory) When you look into the mirror and see the multiple reflections, they will often look increasingly green.

It's not you. All definitions are, at some point, circularly dependent.

Well, I did one better. I went to a talk by Kopeikin on Friday - he did the measurement with a quasar almost being occulted by Jupiter, and the experiment was part of the talk. I don't have the expertise in GR to evaluate or give details, but he did present his explanation why the bending of the quasar light would be different if gravity were instantaneous vs. c. However, he presented it in terms of the angle of deflection, and not as speed of propagation, as reported in some of the popular-press articles.

Why? You have it basically right.

If they floating, i.e. weren't moving relative to the bulkhead (in r or [math] \theta [/math]) then they won't smash into anything. (assuming a vacuum. with an atmosphere, eventually the air will start moving and exert a force)

No, actually, it's not called centrifugal force. The floor pushes the astronauts inward; it's called centripetal force. If the astronauts were floating, and you turned such a mechanism on, nothing would happen. If they were touching the floor, and thus moving, they would feel a force, because the floor's path is curved and the astronaust would have the tendency to move in a straight line (as per Newton's first law). The floor pushing inward is what gives the appearance of gravity in this case. There is no outward-directed force.

You're right - all dates are approximate.

Planck's constant is also the unit of angular momentum, so it tells you the minimum change there can be in a system's tendence to rotate (or in some other way behave like it is doing some kind of circular motion)

When did I say that I was? Not a whole lot. But I didn't set out to point out a whole lot. 5614 asked a question. I gave a quick answer that I thought would help. When I mentioned F=ma' date=' I thought it was implied that I wasn't considering a system where mass was changing. When I mentioned F=GMm/r[sup']2[/sup] I though it was clear that I was looking at things from a classical standpoint. Obviously I was wrong. You want to add to the conversation, great! But there are more constructive ways to do it than to say "that's incorrect" when, in the context I was using, it wasn't incorrect. I also suggest that giving the technically correct answers in terms of tensors and four-vectors isn't going to help as much as you might hope. And when I say that terms like "relativistic mass" aren't generally used, I am basing that on my experience of being a research physicist, because, in my experience, the term isn't used much. If you asked the people with whom I do research what the mass of a photon, is, they'd say, "Zero." Because they take "mass" to be "rest mass" And I see no point in discussing this further.

Yes, as JaKiri surmised, my quick answers were watered down for a mostly non-physicist crowd. But I don't see how you can contend that you are presenting the viewpoint of the "relativity community" with a list of college intro courses, beginner's textbooks and the above list of journal articles - the American Journal of Physics is not a research journal, it is a teaching journal. All you've shown, really, is that some people use it as a teaching tool, or to explain it to the public (e.g the www).

Humans (Homo sapiens) have been around a tad longer than that; ~50k years. Agriculture has been around for ~10k years.

In a sense they are undefined - science doesn't use the terms anymore. mass is the invariant mass (aka rest mass) - that's the only term you can really discuss, because it's reference-frame independent. for the people that still refer to relativistic mass, it's E/c2, but it's not a useful quantity since it's not invariant. So it's not generally used. inertial mass is even more problematic, because if you look at it from point of view of resistance to acceleration (i.e. m=F/a), you have to see that for a massive object moving at a reasonable fraction of c, it's easier to accelerate it perpendicular to the direction of motion than in the direction of motion. Which means inertial mass isn't a scalar, and that's a problem. It's a purely classical phenomenon that loses meaning in QM and relativity. more on the topic.