Right round, like a record babyPosted: October 5, 2012
Yesterday I was reading the lovely blog of Mr Lawrence Miles, because he’s always good for a laugh or a crossly-worded diatribe.
For those of you who are not ming mongs, Mr Miles is a gentleman of the crabby and outspoken persuasion who has written some rather excellent Doctor Who novels, and who co-authored About Time, a Doctor Who guide so compendious that it makes The History of the Decline and Fall of the Roman Empire look like Listverse’s Top Ten Whacky Romans.
I found Mr Miles musing about wormholes and perpetual motion machines. Now, dear Lawrence does like to hear the sound of his own fingers typing, but I can’t criticise him for that, particularly when he muses so charmingly about the history of scientific thought and entropy. As I often do, I suggest you may wish to read the whole thing.
We can be sure, at least, that wormholes work. Which is to say, we can be sure we won’t look stupid if we bring them up in conversation. We know this because Carl Sagan told us so. Needing a way to bring humans and aliens into Contact, and not wanting to resort to anything silly like spaceships travelling faster than light in real-space, he concluded that the most feasible method of travelling bbbillions and bbbillions of miles in order to meet one’s own dead dad was to interpret General Relativity in a rather dynamic way. This idea wasn’t new, and the w-word had been used by a rather apologetic John Wheeler in the ’50s, but it’s informed every generation of nuts-and-bolts sci-fi since 1985. Nobody has yet proved wormholes impossible. In theory, they’re still the fastest way to get from A to A-but-on-the-other-side-of-space.
Note the sentiment buried in that logic, though. It’s a sentiment – perhaps in more than one sense of the word – that’s found even in Sagan’s own musings. Not wanting to resort to anything silly like faster-than-light travel. Current Scientific Thinking is an awkward, chimerical thing, always slippery, always mutable, but mutable in surprising ways. Thankfully, and despite the best attempts of creationists to suggest otherwise, it’s well aware of its own nature: yet even so, there are principles for which even the most flagellantly self-analytical physicist feels an attraction stronger than reason. You don’t mess with the speed of light, even if the Standard Model is incomplete. And you don’t try to outwit the Laws of Thermodynamics, especially not the second one.
The thing I particularly wanted to point out, because I suspect you lot would enjoy it, is Mr Miles’ proposal for a perpetual motion machine.
It’s really very simple. The core of the device is a vertical tube, within the gravitational field of a planet (or any other sizeable body). A projectile, let’s just call it a metal ball, is dropped into the tube. It turns the “water wheel”, and the energy is stored in whatever medium suits you. After that, the ball falls to the bottom of the tube and enters your wormhole. The wormhole has been arranged, and space-time carefully folded, so that the “exit” of the wormhole is at the top of the tube. Travelling from bottom to top without actually being lifted, the ball begins its journey again. The wheel keeps turning. Infinite energy is produced.
No, I couldn’t see the problem either. But I’m one of the half-learned.
The obvious difficulty – I say difficulty, not flaw – is that entropy strikes at the heart of the machine. The ball will wear down the wheel; the machinery will fall apart. But this ceases to be a problem when you realise the vast amounts of energy being produced out of nowhere, more than enough to fuel a self-repair system. Vast energy permits the replacement of matter, so it’s an engineering problem, not a problem with the physics. (And if you’re prepared to countenance the wormholes, then something clever involving nanites is probably going to be on the cards.) This aside, it all looked moderately rational.
Given my background, however, it seemed… a little unlikely that I’d found a way of punching entropy in the face.
Have at it. My immediate thought (and I stress that my book learning on science is pretty much restricted to what you get from Doctor Who novels and Buffy, so I believe all sorts of weird shit) was that the machine works (if it works) because it is not, in fact, a perpetual motion machine (assuming we define perpetual motion as motion that continues indefinitely without any external source of energy) so much as a way to harness gravity on an ongoing basis.
The ball is in free fall and continues to accelerate at a constant rate due to gravity (assuming (again) a uniform gravitational field). The machine captures energy from the ball roughly equal to the amount of the acceleration when hits the waterwheel, and siphons it off to run flying cars and time machines.
So while the machine might run until gravity runs out, it can’t run perpetually and would be extinguished, as us all, in the final heat death of the universe.
[Image copyright: Lawrence Miles]