**Xenology:
An
Introduction to the Scientific Study of Extraterrestrial Life, Intelligence,
and Civilization**

**
First Edition**

**©
1975-1979, 2008 Robert A. Freitas Jr.
All Rights Reserved.**

Robert A. Freitas Jr., **Xenology: An Introduction to the Scientific
Study of Extraterrestrial Life, Intelligence, and Civilization**, First
Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

**17.4.4
Momentum Interconversion Drives**

Terran scientists already know that electricity and magnetism are inter changeable, based on the work of James Clerk Maxwell in the 19th century. Mass and energy are too, according to Albert Einstein, as well as space and time. It is not unreasonable to hypothesize that angular and linear momentum may be similarly related.

If such interconversion were possible, theory has it that
some fundamental physical constant would be required, having the dimensions
of length, to balance the mathematical equation involved. According to John
Wheeler,^{2741} one of the fundamental constants of nature is the Planck
length, written L, based on the Planck constant (h), the universal gravitation
constant (G), and the speed of light (c).*

Robert Forward suggests that if we use the Planck length a suitable interconversion formula may be derived: Angular momentum (L) equals linear momentum (p) times the Planck length, or L = pL. Using this purely hypothetical relationship, it is simple to calculate that the destruction of a unit spin from a single tiny atom (about 10-34 kg-m2/sec) would yield 6.6 kg-m/sec of linear momentum. This means 6.6 kilograms of mass moving at 1 meter/second. The interconversion of only 45 billion atoms -- about 0.1 picograms of hydrogen -- would thus be sufficient to propel a 100-ton starship at l%c.

The above scheme, of course, requires the violation of conservation of linear and angular momentum. This difficulty may be made somewhat more palatable in the following way. Physicists recognize that the source of gravity in General Relativity theory is what is called the "stress-energy-momentum-mass tensor." That is, mass alone isn’t the only source of gravity. Kinetic energy, stress energy, linear and angular momentum also contribute to the field.

We already know that mass and energy can be interconverted,
according to the relation E = mc^{2}. It may turn out to be possible
to interconvert everything in the stress-energy tensor, perhaps according to
an equation like E = mc^{2} = pc = Lc/A. Vast amounts of propulsive
energy would become available. Says Forward: "If we took one unit of spin
which is 10^{-34} units of angular momentum (very small), we would get
6.6 kg-m/sec of linear momentum or 10^{-8} kg of mass or, equivalently,
10^{9} joules of energy -- all from one atom."^{2014}

* The formula Wheeler gives is: L = (hG/2pc^{3})^{1/2}
= 1.6 x 10^{-35} meters.

Last updated on 6 December 2008