COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	.bottom←58
C00006 ENDMK
C⊗;
.bottom←58;
.page frame bottom high 85 wide
.area text lines 1 to bottom char 1 to 80;
.require "let.pub" source file
.<<
.FONT 1 "basl30"; TURN ON "%";
.FONT 2 "BASI30";
.FONT 3 "basb30";
.FONT 4 "sta200";
.FONT 5 "ngb25";
.>>
.FONT 6 "sup";
∂AIL↓Engineering and Science↓Caltech↓1201 E. California St.↓Pasadena, Calif. 91125
$John McCarthy↓BS '48∞

To the editor:

	Fred Hoyle is indulging in wishful thinking in constructing
a model of intelligent life in the universe in which interstellar
travel is impossible.  Why he wishes it to be impossible is beyond
me despite his explanation, but here are some facts:

	1. There is no scientifically plausible way of travelling
at speeds close to that of light - let alone close enough to get
significant time dilation.

	2. Using a nuclear reactor like those used today in submarines
to expel a working fluid electrically at the optimal velocity (energy
and mass flow have to be compromised and the best velocity varies
during the journey) leads to times between several hundred and several
thousand years to nearby stars.

	3. The time required for the journey is proportional to
%2p%61/3%2s%62/3%1, where %2p%1 is the power per per unit mass of
the system and %2s%1 is the distance to be travelled.  The derivation
can be supplied if wanted.  The %2p%61/3%1 factor means that the
performance is not very sensitive to improvements in the power system.
The %2s%62/3%1 factor means that long distances are covered in less
than proportional time.

	4. The galaxy can be occupied in less than a million years.

	These times look very long to us - only a couple hundred years
into the technological age.  However, our solar system can support
life for a few billion years, and after man has had space technology
for 10000 years, surely the nearer stars will be explored, and unless
colonies are prevented from seceding by some very effective dictatorship,
the expansion process will start.

	My own guess is that if the bureaucratic ethic of present liberal
thought continues for even a few tens of years, there will develop a
very strong desire among small groups to escape into space from
the welfare state.

.sgn