William Whewell was an English philosopher and Master of Trinity College, Cambridge (1841–1866), renowned as the last polymath. His interests ranged from mineralogy to moral philosophy, but he is chiefly remembered for his Philosophy of the Inductive Sciences (1840), which reflected his study of Kant and led to a famous controversy with John Stuart Mill.

 

In his On Plurality of Worlds: An Essay, published anonymously in 1853, Whewell sparked off one of the most intense periods of debate on the issue of life on other worlds. Whewell who, until this time, had argued in favor of pluralism, suddenly presented a range of scientific and theological arguments against it.

 

Whewell's early support for the pluralist position is reflected in a sermon he delivered in 1827:

 

[T]he earth ... is one among a multitude of worlds ... with resemblances and subordinations among them suggesting ... that [they may be inhabited by] crowds of sentient ... beings ...

 

He employed the microscope argument of Thomas Chalmers:

 

Does not even science herself compel us to expand our notion of God's vivifying and cherishing care, when she ... shews us the myriads of animals that live in ... the drop of water?

 

His acceptance of extraterrestrial life at this stage is also clear from passages in his Astronomy and General Physics (1833):

 

[The stars] ... may ... have planets revolving around them; and these may, like our planet, be the seats of vegetable and animal and rational life: - we may thus have in the universe worlds, no one knows how many, no one can guess how varied ...

 

By 1850, however, Whewell's difficulties in reconciling traditional Christian doctrines, especially the incarnation and redemption, with pluralism and also with Laplace's nebular hypothesis were beginning to emerge. In an unpublished manuscript, "Astronomy and Religion," he writes:

 

God has interposed in the history of mankind in a special and personal manner; ... that one, having a special relation to God, came from God to men in the form of a man ... [Consequently] what are we to suppose concerning the other worlds which science discloses to us? Is there a like scheme of salvation provided for all of them? Our view of the saviour of man will not allow us to suppose that there can be more than one saviour. And the saviour coming as a man to men is so essential a part of the scheme ... that to endeavour to transfer it to other worlds and to imagine there something analogous as existing, is more repugnant to our feeling than to imagine those other worlds not to be provided with any divine scheme of salvation ...

 

Later in the same manuscript, he introduces an argument which in subsequent years he applied against pluralism. Whewell points to the vast eras of time which preceded the appearance of human beings on Earth. Such a hiatus without intelligent life might appear problematic if the world were designed by God specifically for man. But Whewell stresses that wastage in nature is common: many seeds must fall, for example, in order that a few might germinate. If, Whewell argues, God has placed man on Earth for only a tiny fraction of our planets' history, is it not possible that intelligent life may exist on only a proportionately small number of other worlds?

 

Although Whewell's emergent antipluralist stance was firmly rooted in theological concerns, he was aware that religious arguments alone would not win the day against his critics. Consequently, he marshaled an array of often impressive scientific and philosophical objections against the view that intelligence (as distinct from lower life-forms) was common throughout the universe. In addition to the geological argument mentioned above, Whewell called into question the hypothesis, gaining ground at the time, that some nebulas were "island universes," or external galaxies. He also doubted that "star clusters" were really made of separate stars rather than pieces of a single star in the process of formation. Regarding the nature of stars themselves, he pointed out that some were variable, while others, such as the 61 Cygni pair, were known to be much less massive than the Sun. What assurance did we have, then, that most stars were similar to the Sun and therefore attended by planets, let alone by planets capable of supporting intelligent life? Some of his arguments are still relevant today. For example, he questioned whether the gravitational field around binary stars would be suited to providing stable conditions for planets. He also raised a valid objection concerning Algol, the light variations of which had been interpreted as due to eclipses of the star by a planetary companion. Turning to the solar system, he dismissed the outer planets as possible habitats of intelligent life on account either of their low temperature (Uranus and Neptune) or low density (Jupiter and Saturn). Jupiter, he thought, perhaps "a mere sphere of water," home at best to "boneless, watery, pulpy creatures." Mercury and Venus were too hot, though he allowed Venus might harbor heat-resistant "microscopic creatures, with siliceous coverings." The Moon he considered uninhabitable because of evidence (for example, from Bessel's research) that it lacked both water and an atmosphere. Only Mars caused him some doubt. He suggested it might resemble the primordial Earth and be populated by dinosaurs.

 

Although Whewell's objections to pluralism were grounded in theology, it is just as true to say that those in favor of pluralism looked to support their cause with their own special interpretations of Christian doctrine. Science and religion were called upon to give evidence on both sides of the extraterrestrial life debate. But it was only with Whewell that the full strength of the scientific case against pluralism, as it stood in the mid-19th century, was brought to bear. Whewell was successful in showing that the limited observational evidence to hand could be used just as effectively to dispute the view that (a) planets, and (b) intelligent life, were ubiquitous. In some cases, his scientific arguments (for example, regarding the nature of stars and external galaxies) came to be rejected, while in other cases (such as his caution about the habitability of other planets in the solar system and his suggestion of the non-solidity of Jupiter and Saturn) he was eventually vindicated. Whewell was an important figure in the field, not because he was always right, but because his Essay and subsequent Dialogue on the Plurality of Worlds (1854) led to a much-needed period of re-evaluation on the question of extraterrestrial life and intelligence.¹

 

Reference

1. Whewell, William. The Plurality of Worlds. Boston: Gould and Lincoln (1854).