"... as each struggled with the concept of a gyroscope space drive, all were forced sooner or later to realize that it would not work. They were beaten by nature's conservation laws."
-- Robert Forward, Introduction to "Spin Drive to the Stars."
The vision of a gyroscopic space drive is admittedly a powerful and fascinating one. And all manner of intelligent people have fallen for it. Variations of the "Dean Drive" (see any popular on-line encyclopedia) crop up all the time, as anyone who has ever attended a fringe "science" conference can attest. These are conferences usually associated with Tesla (a fine man and a great mind who in no ways warrants the sneers he gets), or books and websites with arcane references to UFOs (National Socialist or otherwise). I attended one of those conferences in the '90s and get programs and fliers associated with them to this day. Invariably there is at least one person attending (and hopefully no more lest things get ugly), or maybe just a poster session, devoted to the latest device that claims to transform rotary motion into linear momentum without an intervening medium (rockets of course do not use a medium but are an example of Newton's laws in action -- the business about for every action there is an equal and opposite reaction.)
I even knew an individual at a place I used to work who threatened to kill me (jokingly, I'm sure) if I figured out the secret of his invention that did just that, i.e. transform angular to linear momentum without an intervening medium. From his description, it was clear this was one more device that relied on complicated motions of various masses (and some of these motions get very complicated indeed) to presumably steal rotary motion at one point of the cycle and transform it into linear motion, thereby permitting the thing to take off. Curiously, these devices never take off vertically, but only horizontally. Not a problem. In the new and improved version (we're working on it, coming very soon, please donate!), however, that problem will be solved. It was at that point, not too deep into the discussion with my former co-worker, that I had to ask him to say hello to the work of Emmy Noether.
* * *
Now as everyone knows Emmy Noether was a brilliant mathematician and also one of the homeliest women who ever lived. She definitely encountered sexism in her life, but nobody ever viewed poor Emmy as a sex object. Every writer that touches upon her life mentions and comments upon that lamentable fact, so we might as well get it out of our system. You can look up her picture on one of the popular image search engines if you are curious. You will not be disappointed. What is important to know is that Emmy's genius was to take results implicit in the work of others (in this case Euler) and to greatly expand upon and deepen them. She was to do this feat again for the field of Algebraic Topology. This is not a minor talent. What she saw in the space-time symmetries of her theorem was extremely important: As explained by Victor Stenger in Quantum Gods, three kinds of symmetry (space translation, space rotation, and time translation) imply three conservations laws: linear momentum, angular momentum, and energy. Noether's Theorem shows that symmetry laws and conservation laws go hand in hand. The result is as solid as can be. Huge amounts of physics follows from her theorem. Because an awful lot of contemporary physics is based on identifying and understanding abstract symmetries, physicists then can state explicitly the conservation laws that are entailed. And knowing the conservation laws of a system tells you a great deal about it. Noether's Theorem was the beginning of this profound realization and every modern physicist owes her a lot.
Now the "inventors" would likely say at this point: "Well, that's all very nice, but really its so abstract that who can care? This Noether person could be wrong or missing something. Recall what they did to Galileo." True but irrelevant. To the extent we wish to formulate the laws or models of physics "... in a way that does not depend on the point of view of in space and time of the observer [Victor Stenger]" the burden of proof is on the inventor ("crank," if you are inclined to be impolite) to disprove/break these symmetries. And good luck on that. To date none of these "inventions" have lifted so much as a dust spec a micron off the earth, so we can comfortably say that Noether's theorem and all it implies holds and will continue to do so. There is no way to transform angular moment to linear momentum, unless through the use of an intervening medium, water, air, or the like.
The only way it could happen, of course, is that our knowledge of the underlying space and time of physics were to change . . .
One thought that occurred to me as I was researching this was that perhaps during the heyday of the luminiferous ether (the roughly two generations from the time of Maxwell writing his famous equation to Einstein's discovery of Special Relativity), perhaps some 19th century scientist thought of using the luminiferous ether (the presumption being that such existed) as the medium for transforming rotary to linear motion. Some of the pseudo-science literature I have encountered seems to hint in that direction, but it would have been fascinating if some scientist during the heyday of the ether had actually done some serious research in that direction and published his results. Of course, it would have all come to naught, but still.
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