lesson 54, new concept english, book 4-ag真人试玩平台

we must conclude from the work of those who have the origin of life,

that given a planet only like our own, life is almost certain to

start. of all the planets in our own solar system we arc now pretty certain the

earth is the only one on which life can survive. mars is too dry and poor in

oxygen, venus far too hot, and so is mercury, and the outer planets have tem-

peratures near absolute zero and -dominated atmospheres. but other

suns, stars as the astronomers call them, are bound to have planets like our own,

and as the number of stars in the is so vast, this possibility becomes

virtual . there are one hundred thousand million stars in our own

milky way alone, and then there are three thousand million other milky ways,

or galaxies, in the . so the number of stars that we know exist is

estimated at about 300 million million million.

although perhaps only 1 per cent of the life that has started somewhere will

develop into highly complex and intelligent patterns, so vast is the number of

planets that intelligent life is bound to be a natural part of the .

if then we are so certain that other intelligent life exists in the , why

have we had no visitors from outer space yet ? first of all, they may have come to

this planet of ours thousands or millions of years ago, and found our then pre-

vailing primitive state completely uninteresting to their own advanced knowledge.

professor ronald bracewell, a leading american radio-astronomer, argued in

nature that such a superior civilization, on a visit to our own solar system, may-

have left an messenger behind to await the possible of an

advanced civilization. such a messenger, receiving our radio and television sig-

nals, might well re-transmit them back to its home-planet, although what im-

pression any other civilization would thus get from us is best left unsaid.

but here we come up against the most difficult of all obstacles to contact with

people on other planets--the astronomical distances which separate us. as a

reasonable guess, they might, on an average, be 100 light years away. (a light

year is the distance which light travels at 186,000 miles per second in one year,

namely 6 million million miles.) radio waves also travel at the speed of light,

and assuming such an messenger picked up our first broadcasts of the

1920's, the message to its home planet is barely halfway there. similarly, our

own present primitive chemical rockets, though good enough to orbit men, have

no chance of transporting us to the nearest other star, four light years away, let

alone distances of tens or hundreds of light years.

fortunately, there is a 'uniquely way' for us to with

other intelligent beings, as walter sullivan has put it in his excellent recent book,

we are not alone. this depends on the radio- of the 21-cm

wavelength, or 1420 megacycles per second. it is the natural of emis-

sion of the atoms in space and was discovered by us in 1951; it must

be known to any kind of radio-astronomer in the .

once the existence of this wave-length had been discovered, it was not long

before its use as the uniquely recognizable broadcasting for interstellar

communication was suggested. without something of this kind, searching for

intelligences on other planets would be like to meet a friend in london

without a pre-arranged rendezvous and absurdly wandering the streets in the

hope of a chance encounter.

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