Inertialess drive

The inertialess drive is a fictional means of accelerating to close to the speed of light or faster-than-light travel, originally used in Triplanetary and the Lensman series by E.E. "Doc" Smith, and later by Robert A. Heinlein, Larry Niven, and Alastair Reynolds.

The Concept of Inertia

Inertia is the measure of the resistance of a material body to a change in state of motion (acceleration) under the effect of an applied force. This resistance is proportional to the mass of the body, and is usually expressed (in simplest form) as F = ma.

For a body to be rendered inertialess thus means that, in principle, its mass should be reduced to zero. In classical special and general relativity, massless bodies are constrained to always move at exactly the speed of light (the speed of photons in a vacuum), and the term relativity in this context in fact implies that light is always measured to move at the same speed by an observer, no matter how rapidly the observer is moving relative to any body defined as fixed. This aspect of inertialessness is explored by the more exacting authors who have adopted the term after Smith's groundbreaking use.

In classical special relativity, in order to move faster than the speed of light, a particle must have not zero mass -- and inertia -- but mathematically imaginary mass. This is, of course, as viewed by an external observer, and one can postulate that Smith's inertialess field is thus similar in form to a space warp that acts as a tachyon when viewed by an observer in the external universe. Whether this formulation can be expressed self-sufficiently in the context of Smith's fiction is, of course, irrelevant to the enjoyment of it.

Triplanetary Universe

The possibility of inertialess travel was first suggested in Theoretical and Physical Chemistry, published in 1912 by the Tellurian chemist Samuel Lawrence Bigelow, an alumnus of Harvard. The first faster-than-light drive, which achieved only partial neutralization of inertia, was developed on the planet Nevia. Soon thereafter, two Tellurian scientists, Lyman Cleveland and Frederick Rodebush developed the one-hundred-percent inertialess Rodebush-Cleveland drive, which traveled (and decelerated) much faster. (In contrast to accounts in later versions, there were no critical flaws with this drive, and no contribution by any scientist named Bergenholm or by Arisians.)

Physiological Effects

• The Nevian faster-than-light drive apparently had no noticeable physiological effects even to an observer as well-trained as Conway Costigan. An alternative explanation is possible, however. There is no mention of the neutralization of inertia until the third installment; the physics in the first two installments seems consistent with that of the Skylark universe, in which faster-than-light travel is possible without even partial neutralization of inertia. So it is possible that Dr. Smith did not come up with the inertialess drive until writing the third installment.
• The Rodebush-Cleveland drive, in contrast, causes “a sensation akin to a tremendously intensified vertigo” which was completely incapacitating until Cleveland’s “indomitable force of will” overcame it.

Lensman Universe

Galactic Civilization developed for a long period using only the semi-inert drive, which was presumably similar to Nevian partially-inertialess drive discussed above. The exact duration is not known, but even as late as the Third Galactic Survey it still “took years to cross the galaxy.” Because the key piece of inertialess technology is known as the Bergenholm, it seems likely that an engineer by that name was responsible for a key advance, but little is known for certain. Dr. Bergenholm is referred to as the “late Dr. Bergenholm himself” in the original, which suggests that he was a more recent figure than in the ret-con version, below.

Physiological Effects

• The fully inertialess drive in Galactic Patrol, even for Worsel, who had never experienced it before, apparently has no noteworthy ill effects.

Triplanetary/Lensman Ret-con Universe

In the revised book versions of Triplanetary and the core Lensman novels, the partially-inertialess drive was given by Arisia to Nevia, and the fully inertialess drive was developed by Rodebush and Cleveland, but these achievements are apparently forgotten, and the semi-inert drive is never mentioned. All apparent credit, and the name of the principal component of the fully inertialess drive, is due to the Tellurian scientist Nels Bergenholm, activated by the Arisian Drounli, who “made the drive safe and commercially practical.”

Other Authors’ Universes

Inertialessness, though not for faster-than-light travel, is discussed in Robert A. Heinlein’s Methuselah's Children,, Isaac Asimov's short story The Billiard Ball, Larry Niven’s “ARM,” Orson Scott Card's Speaker for the Dead, Arthur C. Clarke's 3001: The Final Odyssey, and Alastair Reynolds’ Redemption Ark. See the Lensman Technology article for details.

References