There are a few. They’ve been the subject of several emails I’ve received since I posted this piece.
What we call natural laws are observable regularities in the behavior of mass, energy, and spacetime. Jokes to the contrary notwithstanding, Congress can’t modify or repeal them. If there’s a “legislator” behind them, it’s Almighty God. That irritates a lot of people who like to dream of convenient interplanetary and interstellar travel. The linked piece is about one such law: the conservation of momentum.
That law, not the availability of energy, is what limits Mankind’s ability to leave Earth for other destinations. We live in a relatively deep gravity well that imposes certain conditions upon us. One of those conditions is the velocity required to propel an object free of Earth’s gravity. If the conservation of momentum is an inviolable natural law – and for macroscopic objects, it appears to be so – then to accelerate something upward, you must throw something downward.
The problem many laymen have in understanding this arises from what’s visible around us. We travel routinely in cars and trains that accelerate forward without visibly throwing something backward. We ride airliners that appear to do the same. Yet in both cases there is momentum transfer to a conveniently situated medium. Cars transfer momentum to the road; airplanes transfer momentum to the air. It doesn’t matter that we can’t see it happen.
That’s the “sad” part of this piece. The “hopeful” part comes now, though the amount of hope it actually offers is small.
Various inventors and tinkerers have tried to develop “reactionless” or “inertialess” space drives that violate the law of conservation of momentum. So far none have succeeded. But you’ll notice that it’s not because “enforcers” come to their labs and issue them tickets for trying to do so. Natural laws enforce themselves. If they’re truly embedded in the nature of mass/energy and spacetime, they express God’s will.
But as I said above, what we call natural laws are really estimates. They’re based on observations and measurements made repeatedly, century after century, of how objects behave. We might not have performed enough experiments under a wide enough variety of conditions to encounter an exception that would prove that the conservation of momentum isn’t inviolable. As it happens, experiments suggest that at the quantum level, momentum is not always conserved. Further experimentation might teach us how to circumvent the law at the macroscopic level, though I doubt it.
Science fiction, like all fiction, is about entertainment. It provides us a way to “experiment” with our natures, by contriving situations in which individuals and societies are tested in novel ways. It stimulates our thinking about another set of laws: those built into human consciousness. That can be highly refreshing. But it doesn’t free would-be space travelers in the real world from the laws their science-fictional colleagues blithely disregard.
I’m a fan of Elon Musk’s desire to establish Mankind as an interplanetary species. I want to see him succeed. But I have a feeling that it will take a slow evolution: first to persistent orbital stations capable of “servicing” spacecraft that intend to go further; then to a persistent lunar presence where large quantities of the necessary fuels can be manufactured and stored; and only then to Mars. I could be wrong about any of that, but just now the laws of mechanics appear to favor my approach.
All that having been said, I will go on writing science fiction. It’s not really about space travel, you know. It’s about fun!
1 comments
I must admit that I was unfamiliar with the law of conservation of momentum. So sue me. But thanks for filling in one of my many knowledge lacunae. And it got me to thinking how the left is constantly attempting to thwart, deny or avoid natural law by the expedient of passing some legislative pronouncement. You know, a “law,” such as the ones that allege to confirm a man’s inalienable right to become a woman, the ones that declare that two men can form a “marriage” or the ones that deny that there are quantifiable differences in individuals which account for differences in outcomes, viz., nearly all of the so-called “civil rights” laws. These are what pass for suitable subjects of legislation in the clown congresses that sit in every state and Washington, DC.