Erick Mead

No, not magic -- but physics can be good or bad and remain stuck on mistaken one for a fairly long period of time ... like the sun, you know -- which, plainly, goes around the the earth, right ??? --

Similarly, it was never observations that were in error -- it was the physical interpretation. -- That is really all that is lacking as far as definition goes ... There's only so much one can do with Ptolemaic epicycles, I mean, really. ... one can plot an orbit in those terms ... but for heaven's sake -- why would you want to ..??

Some people eschew the need for any accurate physical description -- (and yet for reasons not readily apparent continue in discussions online). Others rely on things that are simplistic and understandable and suggestive -- but in a key way are fatally flawed as a physical description -- like vectors. Vectors commute. you can easily run them backwards and get where you started from ... except that you can't -- in the real world ...

You cannot trivially reverse the process describing a real world 3d rotation in vector terms. The math will seem right but the result -- to our more refined powers of perception -- will be jerky and artificial and full of gaps. Real world 3d moments, waves, and rotations don't commute -- ask any capable video simulation game designer you may know. Use the word "quaternion."

In a situation involving actual 3d degrees of rotational freedom, using vectors has this naughty problem of creating a situation called "gimbal lock" in control systems. They had to rip out whole suites of control circuitry in the Apollo program because of this problem. Imagine trying to compute time-rate-distance problems on a spherical grid within ten feet of the North pole -- that's the control problem that causes gimbal lock. Not consciously -- but the body has very flexible reference systems for the controls that it uses -- and they can be trained, and in some case substituted -- that is what we are talking about.

In rough terms, once the delicate mechanism is out of alignment, there is no control mode that can accurately take you from the compromised position straight back along the path in reverse to the starting position. The sudden discontinuity of linear reversal creates a non-linearity in the other degrees of freedom that defeats the linearity of the reversal along the line attempted -- "you can't get there from here" -- You can only keep going the long way round on all three axes to get back to the original position -- which of course one is likely to overshoot without a great deal of training in this kind of "navigation" -- instantaneously, of course -- ideally.

This does not require much gross movement, though they certainly can be used (see the aiki taiso) and are the same thing -- but does require, by whatever means, that the same conversion occur, which can be by a wave or pulse (see, again, the aiki taiso) which is equivalent to the gross rotations.

It is hard to see that on video for the same reason -- unless you are attuned to the nature of the problem -- because small changes are disproportionately "folded up" at the cusps or poles of reversal and when unfolded become arbitrarily large.

In case you did not notice your body is a control system -- as well as the machine it controls. The phenomenon of actively using this "gimbal lock" against an opponent whose body and perception is not keyed to the correct perception and whose mode of action is not adapted to the right control scheme is directly presented in applications of aiki -- most typically in aspects of kokyu tanden ho, and in others, the "shudder drops" which are immense fun -- and "pops and drops" (or aiki age and aiki sage, if you prefer) applications of various kinds.

Like at a beach -- any sudden discontinuity (ground, extremity, or the point of uke's bad alignment) breaks the wave -- catastrophically, and yet continuous transitions, even rapid ones, reverses it seamlessly -- like the run-up on a steep beach or the intersection of two waves -- the latter of which is a most useful way of looking at the problem IMO, YMMV.

Aikido is surfing ... people.