296 



KNOWLEDGE 



[April 10, 1885. 



aoainst such a coincidence 1 If, as Helmlioltz has well 

 said, the duration of life ou our earth is but the minutest 

 " npple in the infinite ocean of time," and the duration of 

 life on any other planet of like minuteness, what reason 

 can we have lor supposing that those remote, min\ite, 

 and no way associated waves of life must needs be abreast 

 of each other on the infinite ocean whose surface they 

 scarcely ripple 1 



But let us consider the consequences to which we are 

 thus led. Apart from theoretical considerations or observed 

 facts, it is antecedently imi>robable that any planet selected 

 at random, whether planet of our own system, or planet 

 attending on another sun than ours, is at tliis present time 

 the abode of life. The degree of improbability corresponds 

 to the proportion between the duration of life on a planet, 

 and the duration of the planet's independent existence. We 

 may compare this proportion to that existing between the 

 average lifetime of a man and the duration of the human 

 race. 



If one person were to select at random the period of 

 a man's life, whether in historic, prehistoric, or future 

 time, and another were to select an epoch equally at 

 random, save only that it fell somewhere within the period 

 of the duration of the human race, we know how exceed- 

 ingly minute would be the probability that the epoch 

 selected by the second person would fall within the period 

 selected by the first. Correspondingly minute is the 

 ft priori probability that at this present epoch any planet 

 selected at random is the abode of life. This is not a 

 mere speculation, but an absolute certainty, if we admit as 

 certain the fact, which few now question, that the period 

 durino which organic existence is possible on any planet 

 is altogether minute compared with the duration of that 

 planet's existence. 



The same relation is probably true when we pass to 

 higher systems. Regarding the suns we call " the stars " 

 as members of a siderial system of unknown extent 

 (one of innumerable systems of the same order), 

 the chance that any sun selected at random is, like 

 our own sun at the present time, attended by a 

 planetary system in one member of which at least life 

 exists, is exceedingly small, if, as is probable, the life- 

 suppovting era of a solar system's existence is very short 

 compared with the independent existence of the system. 

 It the disproportion is of the same order as in the case 

 of a single planet, the probability is of the same order 

 of minuteness. In other words, if we select any star 

 at random, it is as unlikely that the .system attending 

 on that sun is at present in the life-bearing stage as a 

 system, as it is that any planet selected at random is at 

 present in the life-bearing stage as a planet. This conclu- 

 sion, indeed, may be regarded as scarcely less certain than 

 the former, seeing that we as little doubt the relative vast- 

 ness i)f the periods of our sun's existence before and after 

 his existence as a supporter of life, as we doubt the relative 

 vastness of the periods before and after the life-.'^upporting 

 era of any given planet. There is, however, one element 

 of doubt in the case of the star. The very fact of the 

 star's existence as a steady source of light and heat implies 

 that the star is in a stage resembling that through which 

 our own sun is now passing. It may be, for instance, that 

 the prior stages of solar life are indicated by some degree 

 of nebulosity, and the later stages by irregular variations, 

 or by such rapid dying out in brightness as has been 

 observed in many stars. Yet a sun must be very nebulous 

 indeed — that is, must bo at a very early stage in its history 

 — for astronomers to be al)le to detect its nebulosity ; and, 

 again, a sun must long have ceased to be a life supporter 

 before any signs of decadence measurable at our remote 



station, and with our insignificant available time-intervals 

 for comparison, are manifested. 



As to higher orders than systems of suns we cannot 

 speculate, because we have no means of determining the 

 nature of such orders. For instance, the arrangement and 

 motions of the only system of suns we know of, the galaxy, 

 are utterly unlike the arrangement and motions of the 

 only system of planets we know of. Quite possibly 

 systems of sun-sjstems are unlike either galaxies or solar 

 systems in arrangement and motions. But if, by some 

 wonderful extension of our perceptive powers, we could 

 recognise the countless millions of sy.stems of galaxies 

 doubtless existing in infinite space, without, however, being 

 able to ascertain whether the stage through which any one 

 of those systems was passing corresponded to the stage 

 through which our galaxy is at present passing, the proba- 

 bility of life existing anywhere within the limits of a 

 galaxy so selected at random would be of the same order as 

 the probability that life exists either in a planet taken at 

 random, or in a solar system taken at random. For though 

 the number of the suns is enoi-mously increased, and still 

 more the number of subordinate orbs like planets (i)i ^;oss« 

 or in esse), the magnitude of the time-intervals concerned 

 is correspondingly increased. One chance out of a thou- 

 sand is as good as a thousand chances out of a million, or 

 as a million out of a thousand millions. Whether we turn 

 our thoughts to planet, sue, or galaxy, the law of Natui'e 

 (recognised as universal within the domain as yet 

 examined), that the duration of life in the individual is in- 

 definitely short compared with the duration of the tyjie to 

 which the individual belongs, assures us, or at least renders 

 it highly probable, that in any member of any of these 

 orders taken at random, it is more probable that life is 

 iratitinij than that life exists at this present time. Never- 

 theless, it is at least as probable that everi/ member of every 

 order — planet, smi, gala.i-y, and so onirard to higher and 

 higher orders endlesshj — has been, is now, or vnll hereafter 

 be, life supporting " after its kind." 



In what degree life-supporting worlds, or suns, or systems 

 are at this or any other epoch surpassed in number by those 

 which as yet fulfil no such functions or have long since 

 ceased to fulfil them, it would only be possible to pronounce 

 if we could determine the average degree in which the life- 

 sustaining era of given orbs or systems is surpassed in 

 length by the preceding and following stages. The life-sus- 

 taining orbs or systems may be surpassed many thousand- 

 fold or many millionfold in number by those as yet lifeless 

 or long since dead, or the disproportion may be much less 

 or much greater. As yet we only know that it must be 

 very great indeed. 



But at first sight the views here advanced may appear as 

 repugnant to our ordinary ideas as Whewell's belief that 

 perhaps our earth is the only inhabited orl) in the universe. 

 Millions of uninhabited worlds for each orb which sustains 

 life ! surely that implies inci-edible waste ! If not waste 

 of matter, since according to the theory every orb sustains 

 life in its turn, yet still a fearful waste of time. To this it 

 may be replied, first that we must take facts as we find 

 them. And secondly, whether space or matter or time or 

 energy appear to be wasted, we must consider that, after 

 all, space and matter and time and energy are necessarily 

 infinite, so that the portion utilised (according to our con- 

 ceptions) being a finite portion of the infinite is itself also 

 infinite. Speaking, however, of the subject we are upon, 

 if one only of each million of the orbs in the universe is 

 inhabited, the number of inhabited orbs is nevertheless 

 infinite. Moreover, it must be remembered that our 

 knowledge is far too imperfect for us to be able to assert 

 confidently that space, time, matter, and force, though not 



