“But It Violates The Laws Of Physics!”

     Good morning, Gentle Reader. The news is all bad, except for this bit:

     Interplanetary travel could be a step closer after scientists confirmed that an electromagnetic propulsion drive, which is fast enough to get to the Moon in four hours, actually works.

     The EM Drive was developed by the British inventor Roger Shawyer nearly 15 years ago but was ridiculed at the time as being scientifically impossible.

     It produces thrust by using solar power to generate multiple microwaves that move back and forth in an enclosed chamber. This means that until something fails or wears down, theoretically the engine could keep running forever without the need for rocket fuel.

     Say what? A completely enclosed propulsion system? A device that produces thrust without ejecting matter in the opposite direction? A drive that ignores the sacred Law of Conservation of Momentum?

     Hey, you ain’t seen nothin’ yet:

     The drive, which has been likened to Star Trek’s Impulse Drive, has left scientists scratching their heads because it defies one of the fundamental concepts of physics – the conservation of momentum – which states that if something is propelled forward, something must be pushed in the opposite direction. So the forces inside the chamber should cancel each other out.

     Note the charming use of my favorite word: should.

     However in recent years Nasa has confirmed that they believe it works and this week Martin Tajmar, a professor and chair for Space Systems at Dresden University of Technology in Germany also showed that it produces thrust.

     The drive is capable of producing thrust several thousand times greater than a standard photon rocket and could get to Mars within 70 days or Pluto within 18 months. A trip to Alpha Centauri, which would take tens of thousands of years to reach right now, could be reached in just 100 years.

     While all over the world, physicists and people who fancy themselves scientifically literate are muttering “What’s next, perpetual motion?” “Pons and Fleischman ride again” and “Just wait until someone figures out the scam.”

     But it’s not quite that simple. I’m here to tell you.

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     It’s a commonplace rejoinder – among engineers, at least – to ask a skeptic about some proposition under discussion “Does it violate the laws of physics?” It expresses the conviction, popular among our sort, that “the laws of physics” are the sole serious constraint upon human technology and what it makes possible. In at least one sense, that conviction is a reliable guide to the possible. In another, it’s rather misleading.

     Physics is the name we give to the most fundamental of the sciences: the one that purports to study and elucidate the bedrock rules of existence. And indeed, those we call physicists have propounded marvelous theses over the centuries: “laws” from which they can predict the behavior of objects of specified characteristics within specified contexts. Some of those “laws” have yielded massive technological breakthroughs and consequent improvements to human life.

     But something else has been happening all the while: current physicists have disproved the “laws” propounded by prior physicists by testing them in realms of mass, size, and speed their predecessors could not explore. These supersessions of previously sacred “laws” proceeded under a principle of science sometimes called the Correspondence Principle: The replacement for an existing theory must perform as well or better in all the contexts in which the existing one seemed to function adequately.

     And since we’re talking about science here, perform actually means predict.

     Theory has followed upon theory for centuries, old ones falling by the wayside as new theories, inclusive of a wider range of conditions of mass, size, and speed, have out-predicted them. From this we infer an important limitation upon human knowledge:

We can never be sure we know
what the laws of physics are.

---

     Science fiction writers play along the margins of our physical knowledge all the time. I’ve done so myself:

     “So what did Martin haul us up here to show us?” Patrice said as they settled into seats in her sleeping area.
     “Actually, the showing comes a wee bit later,” Althea said. “First, a lot of telling.” She leaned against the lumpy nickel-iron wall and waved a hand mock-casually. “We think we’ve cracked it.”
     No one spoke, or grunted, or even breathed audibly, yet the spike of surprise that passed through the visitors was impossible to miss.
     “You...think,” Teodor said.
     Althea nodded. “The experimental results from our test crystal are consistent with a fifteen percent increase in the speed of light.” She grinned again. “That’s fifteen percent over the speed of light in a vacuum.”
     A gasp circled the group.
     “What can you do with that?” Teodor asked.
     “With that alone? Not much. But that’s just from the power we have from one eighteen-century-old fission reactor that spends most of its juice keeping us alive up here. If my equations are sound, with a terawatt of power I can get raw space to accept passage at approximately Michelson eighty. Give me a terawatt more, and I can drag a fifty-ton mass up to that speed in about two months.” She pulled a mock innocent face. “Hope to Earth in four months or a little better. That fast enough for you?”
     She swept her eyes over the stunned guests.
     “Rothbard, Rand, and Ringer,” Valerie breathed. “You actually did it.”
     Althea nodded. “We think so, Mom.”
     “Wait a moment,” her mother said. “What about reaction mass?”
     “Don’t need it.”
     “How, then?”
     “Basically, the same technique that allows me to increase the speed of light,” Althea said. “Alteration of the permittivity constant, applied differentially—a front-to-back gradient—over an ovoid volume enclosing the mass to be propelled. A properly distributed effusion of gamma rays and W-plus bosons is all it takes to get the process started. Put a negative charge on the outer surface of the vessel, and you're off. That gives you a reactionless drive and the next best thing to perpetual motion. Only works in a hard vacuum, though, so don't expect to use it for anything groundside.”
     The genesmith appeared near to apoplexy. “You altered a fundamental constant of physics?”
     Althea nodded again. “Should I have asked permission first?” She grinned. “I had to, Granduncle. The only way to breach what we call the lightspeed barrier is to alter the conditions that determine lightspeed. The only way to do that is to increase the permittivity of the vacuum. And the only possibility of doing that lay in Althea's Axiom.”
     “Which is?”
     “Constants...aren't.”

     [From Freedom’s Scion.]

     We regard the “fundamental constants of physics” as constants because we don’t know how to alter them...today. However, it’s merely my fiction-enabling speculation that we’ll eventually learn how to do that. One of the most important of all breakthroughs in physical thought arrived with early high-energy physicist Arthur Compton, who argued that certain interactions of light and “fundamental particles” could not be explained without postulating violations of the Conservation of Mass-Energy. Such violations disturbed many physicists of his time. Isn’t that illegal? they chorused. Werner Heisenberg proved that under certain circumstances it was not – that particles with nonzero mass-energy could spontaneously come into existence for time intervals too short to permit them to be observed. From this and other insights, modern quantum physics was born.

     The deep lesson here is one about the “laws of physics.” We believe there are such laws. At any given time we think we have a decent grip on them, at least for those ranges of mass, size, and speed for which we can perform experiments. But by reason of our inherently limited ability to manipulate reality, we can never know them with complete inclusivity and perfect certainty...if they exist at all.

     The EM Drive appears to have challenged the Conservation of Momentum. No doubt a barrage of tests is being planned for it as we speak. We shall see.

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     What we posit as “the laws of physics” at any given moment are statements about observable regularities that appear to have no exceptions. That’s how all of science is done:

1. Researchers note a regular, reproducible phenomenon;
2. They propose a theoretical structure that would explain it;
3. They use that theory to make predictions about relevant objects in a relevant context;
4. They design experiments to test those predictions:
   1. If the experiments produce results that conform to the predictions, they perform further experiments;
   2. But the first time an experiment produces non-conforming results, they abandon the theory and look for another.

     Should Shawyer’s EM Drive withstand rigorous, worldwide testing, it will compel physicists to look beyond the “classical” Law of Conservation of Momentum for still deeper laws that include the “classical” law but explain the EM Drive as well. Human knowledge will be advanced and refined. But it will still be incorrect to say that we know the laws of physics in some absolute sense. Nature doesn’t permit such arrogance.