Date: 18 August 2002
Subject: Physics/Cosmology
Dr Rodney Holder is a C of E (Episcopalian) minister, who has a PhD in Astrophysics

Introduction

There are numberless earths circling around their suns ... no reasonable mind can assume that heavenly bodies which may be far more magnificent than ours would not bear upon them creatures similar or even superior to those upon our human earth.

Giordano Bruno (I6th century proponent of 'a plurality of worlds').

'I've been searching for some reason why we're here, who are we, what we're doing here. It's worth one human life.'

Jodie Foster in the film Contact.

The interest in extraterrestrial (ET) life, and especially extraterrestrial intelligence (ETI), is enormous if one is to judge by the proliferation of films, TV series, and books on the subject; and by the claims of sightings of alien spacecraft, of aliens themselves, and, even more astonishing, the claims made by many to have been abducted by aliens.

This widespread interest in not confined to the general public. There is considerable interest in the subject in the scientific community - the subject might even lay claim to a degree of respectability these days. As proof of this one might cite numerous books and papers by professional scientists, and of course most especially, one can point to the SETI (search for extraterrestrial intelligence) program, in which massive effort by the world's most powerful radio telescopes is devoted to just this search.

It is clear that behind much of this interest is a quest of a religious kind - a quest for understanding our own place in the universe, a quest for meaning in the light of our perceived loneliness in the universe and our need for relationship. Such a quest is evinced by the above quotation from Contact.

In this article I shall review the evidence for extraterrestrial intelligence, and give a brief theological response.

Extraterrestrials are here! - the claim examined

Some 57% of the public in the USA believe that earth has been visited by aliens, if opinion polls are to be believed (ref.1).

A large number believe in alien abductions of the kind portrayed in The X Files. What are we to make of this?

Of the many sightings of UFOs, unidentified flying objects, the vast majority end up being IFOs - identified flying objects. They are really sightings of Venus, or of an aircraft, a weather balloon, etc. Let us just examine this in a bit more detail for a moment. Let us use the terminology UFO for the subset of flying objects (FOs) which remain unresolved and IFO for the much larger subset of objects which subsequently get identified.

It turns out that the pattern of reporting for each type of object is virtually the same: time of day, duration, age and sex breakdown of the observer are all similar. Very significantly both IFO and UFO observers show a prior interest in UFOs orders of magnitude higher than the general populace.

Now for a really interesting statistic. Year on year the number of FOs fluctuates very considerably. But the proportion of them which remain UFOs does not vary with the overall level of sightings (ref. 2). Just think about this for a minute on the assumption that the UFOs are really alien spacecraft. As an example, in 1966 there were three times as many FOs as 1963, but in each year 3% were UFOs. The question is, Why on earth should a three-fold increase in alien activity cause people also to report Venus and weather balloons as UFOs at three times the previous rate?

The far simpler explanation is that, human beings being fallible eyewitnesses as they are, it is not surprising that there is a small residue of supposedly 'unexplainable' cases. Just because the police do not solve every crime of murder or armed robbery, we do not ascribe the unsolved murders or bank robberies to aliens. As Sheaffer says, why should we ascribe unexplained celestial phenomena to aliens?

The argument from colonization

One of the most powerful arguments against the existence of extraterrestrial intelligence is the one which begins from the question, 'Where are they?' Indeed, even more sharply, 'Why aren't they here?'

There is no evidence that ETs have visited the earth in the historical or geological past. In particular it is certain that the earth has never been 'taken over' by an ET civilization, since this would have put an end to our own civilization.

There are four possible ways of reconciling this lack of evidence with the view that ET civilizations are common in the galaxy (ref 3):

1 Inter-stellar space travel is impossible, so they couldn't have got here even if they had wanted to.

2 Interstellar space travel is possible, but for a variety of reasons ET civilizations do not make use of it, e.g. they destroy themselves before getting advanced enough

3 ETs are exploring the galaxy but haven't reached us yet

4 ETs have reached the vicinity of earth but for a variety of reasons, e.g. sociological, cultural or ethical, do not interfere with us

Interstellar space travel

Space scientists would argue that we ourselves as a species are within at most a couple of hundred years of achieving the necessary technology. We can envisage now some propulsion strategies which might well do the trick, e.g. nuclear rockets, antimatter rockets or laser-pushed light sails, which might take a rocket to within 10% or 20% of the speed of light (ref 4).

Rate of colonization

Given the technology, it is quite easy to show that colonization of the whole galaxy could take place within a time short on the cosmic scale.

Suppose first of all an ET civilization sends out colonists to a few of the planetary systems nearest to it. When these have established themselves, suppose they in turn send out colonizing missions. The number of colonies grows exponentially and it is a simple matter to calculate the time for them to saturate the whole galaxy.

As an example calculation, suppose the distance between colonies is 10 light years, the space ship speed 0.1 c, giving a travel time of 100 years, and the consolidation time on a planet before sending out the next set of missions 400 years. Our galaxy is 100,000 light years across.

To cover the whole galaxy would take 10,000 steps of 10 light years each. Each step would take 500 years in total. Therefore, by a very easy calculation this gives a time to colonize the whole galaxy of a mere 5,000,000 years.

The point is that this is very small in comparison with astronomical and biological timescales. The earth and the solar system is 4.5 billion years old. The galaxy is 10 billion years old. Even if we increase the consolidation time to 4,000 years and reduce the speed to 0.01c we still get a time to colonize the whole galaxy of only 50,000,000 years, still only 1/2% of the age of the galaxy.

What that means is that any technological civilization which had evolved in the 10 billion year history of our galaxy could easily have colonized the whole galaxy. There is no evidence of ETs near earth and no evidence that our planet has ever been colonized.

So why aren't they here?

Several explanations have been offered (ref 5):

l. ET civilizations destroy themselves before they develop the advanced technology for interstellar space flight.

2. They do not want to explore the galaxy.

3. Those who do want to explore the galaxy have strong ethical codes preventing them from interfering with other life forms.

The problem with all of these explanations is that they only work if the number of ET civilizations is small. If there are millions of technological civilizations it would seem highly unlikely that all of them self-destruct or are stay-at-homes or have identical ethical frameworks of non-interference. The point is the stronger when we realise that the only technological society we know about, our own, has not destroyed itself, does seem keen on exploration, and doesn't seem to have ethical qualms about interfering with other life forms.

In fact there are good reasons why a technological civilization might want to colonize other planets. Colonization on earth has occurred in the past for political and religious reasons. Human beings have always been excited by the quest for knowledge, and a spirit of exploration has flourished. The same motivations could apply to interstellar colonization.

Then there is the question of survival. Stars burn out and die. A minimal strategy for survival would be to up-sticks and move to a near neighbour stellar system. But again if there are many ET civilizations, surely not all would adopt this minimalist strategy.

Some scientists have postulated the 'zoo hypothesis', that ET civilizations would only come and look, never interfere and keep themselves hidden. Again, this only works if the total number of civilizations is small. Out of a large number of independently evolved civilizations, surely some would opt for colonization.

This line of argument does not absolutely preclude the existence of highly developed ET civilizations in the galaxy. It shows that if they exist, then they are rare.

Calculating the numbers of ET civilizations: The Drake Equation

'Do you think there's people on other planets?'

'If it is just us, it seems like an awful waste of space.'

- From the film Contact

Suppose we ignore the above argument for a little. What about the detection of civilizations who stay at home and communicate by radio? The early pioneer of radio SETI (search for extraterrestrial intelligence) Frank Drake wrote down an equation for how many communicating civilizations there might be in our galaxy (ref 6):

The notation is as follows:

N = number of detectable civilizations in the galaxy

R = rate of star formation

fp = fraction of stars that have planets

ne = number of planets hospitable to life in a stellar system with planets

fl = fraction of hospitable planets where life emerges

fi = fraction of hospitable planets with life where life evolves into intelligent beings

fc = fraction of planets with intelligent creatures who have the ability to communicate

L = length of time such a civilization remains detectable

The problem with this equation is that very few of the numbers are amenable to experimental determination. For the moment, let's follow (more or less) the line of argument which Frank Drake and his colleagues first developed (ref 7).

R is fairly reliably in the region of 1 to 10. There are something like 100,000 million stars in the galaxy with an average lifetime of about 10,000 million years.

fp is probably in the region of 1/5 to 1/2

ne could be between 1 and 5.

fl is 1 on the assumption that life does emerge where it is possible for it to emerge.

fi is 1 on the assumption that intelligence bestows such an evolutionary advantage that its development is inevitable.

fc is probably between 1/10 and 1/2.

If you take the mid-range of these figures you get a simplified version of the equation. Roughly:

N = L

Drake and his colleagues argued that communicating civilizations would either be relatively short lived (about 1000 years), or very long lived (100s of millions of years). The upshot is then that there should be between 1000 and 100 million civilizations in the galaxy attempting to communicate.

Now I think the holes in this argument are pretty patently obvious.

Most of the numbers are guesses. The astronomical numbers may not be too unreliable, but the real dispute in the equation concerns the biological numbers, fl and fi which involve the probability of the development of life given a habitable planet, and the probability of the development of intelligence, given that life gets going.

This is where astronomers and biologists, by and large, seem to part company. The astronomers assert that it is easy to get fife started, and then intelligence; the biologists think both these things are extremely difficult. Now, just for brevity I'm going to examine only one of these numbers. Both are controversial but I shall concentrate on fl

In 1958 Harold Urey and Stanley Miller took a 'primordial soup' of simple chemicals - hydrogen, water, methane, ammonia, carbon monoxide - and subjected this soup to electric discharges and ultra-violet radiation. They found that more complicated molecules were built up. It is believed that something like this process was responsible for the origin of life on earth.

Now in experiments like that of Urey and Miller some quite complex organic molecules like amino acids have been obtained, and even short chains of amino acids. This looks promising but there is a serious snag, of the chicken and egg variety. The basic characteristic of life is that it is self reproducing. The code for reproduction is in the DNA molecules. DNA codes for the production of proteins. But on the other hand, DNA needs the proteins to get made in the first place.

'The existing translational machinery is at the same time so complex, so universal, and so essential that it is hard to see how it could have come into existence, or how fife could have existed without it': so says pioneering evolutionary biologist John Maynard Smith and his colleague Eors Szathmary (ref 8).

The crucial thing about DNA is the order in which the nucleotides are put on the chain. Unless the order is right, the molecule is biologically useless.

Let's suppose optimistically that we have an environment in which not just proteins but nucleotides readily form and, moreover that the nucleotides readily form into chains. Suppose that the 'seed' DNA we need to get life going is pretty short, say 600 nucleotides (ref 9).

With these assumptions imagine a large number of 600-nucleotide length strands of nucleic acid forming spontaneously.

Let's take some more basic data:

There are about 2 x 10 (to the 44) nitrogen atoms near the surface of the earth or in its atmosphere. A single 600-nucleotide length of DNA contains about 2000 nitrogen atoms.

Hence the maximum number of strands of DNA existing on the primitive earth is about 10 (to the 41).

Suppose every such strand could split up and recombine with other fragments at the rate of 30 times a second.

In 1 year (3 x 10' secs) you would get a maximum of 10 (to the 5) different strands forming. Then in 10 billion years you would get a maximum of 10 (to the 6) strands forming.

The problem is that the number of possible arrangements of the four nucleotides into a strand 600 nucleotides long is 4 (to the 600) , i.e. about 10 (to the 360).

Therefore, the chance that a particular one would be formed during the lifetime of the galaxy is about 1 in 10 (to the 300) – an extremely small probability (ref 10).

Now one can argue about this figure. It increases considerably if you allow that certain permutations on the DNA molecule are equivalent. But then it decreases to a far lower number if you realise that all you have done is produce one gene. Unless other compounds are also present, and indeed many other genes, you will never get even a simple organism.

It is absolutely clear that if you put a figure anything like this into Drake's equation it totally swamps all the other numbers. The probability of getting life anywhere in the universe, let alone our galaxy, is extremely small. The naive but oft repeated argument from the sheer number of stars and planets in the cosmos is defeated.

Now the main argument against this line of thinking is that evolution does not proceed by simultaneous spontaneous organization, but cumulatively. The problem is that until we have got the reproductive mechanism in place, evolution is not even off the ground. Nevertheless, it may be that we can bring this incredibly small number up if we can find some chemical mechanisms which work cumulatively. At the present time it is simply unknown whether we can do this.

SETI

The search for extraterrestrial intelligence (SETI) using radio telescopes has been going on since the late 1950s, with Frank Drake, whose famous equation we discussed above, being one of the pioneers.

To have any hope of success SETI requires there to be millions of civilizations in our galaxy alone. That is to say, the Drake equation needs to come up with a big answer; you cannot allow yourself to side with Michael Hart and others who put the probability of life developing on a planet minute. Moreover, even if you assume this, SETI is immediately faced with two further problems - the enormous number of stars to survey and the wide range of frequencies on which extraterrestrials' signals might be transmitted. It is like looking for a needle in a haystack though many orders of magnitude more difficult.

One problem is that we need a window of frequencies which is relatively open, e.g. not absorbed by the atmosphere. The region between 1 and 3 GHz is suitable, especially as it contains the natural frequency 1.420 GHz characteristic of neutral hydrogen. It has been suggested that aliens might use some natural multiple of such a frequency - 2 or n times it for example. However, whatever frequency they broadcast on might be Doppler shifted due to the motion of the alien planet (ref 11).

Now of course technology has advanced dramatically over the 40 years that searches have been going on. And those who pursue this research seem to remain eternally optimistic. Frank Drake wrote his book in 1991, believing that we were on the threshold of detecting alien signals. But the results so far are still entirely negative.

What if? ... theological reflection

I think I have shown that the probability of there being extraterrestrial intelligence, at least in our galaxy and probably the visible universe as well, is extremely low. Scientifically, the hypothesis 'There is no extraterrestrial intelligence' fits all the observations (contrariwise there are no observations for which we need to postulate ETI), so on the basis of Ockham's razor, this hypothesis ought to be accepted. Nevertheless, clearly people are looking for ETI, and there seems to be a religious motive, at least partially, behind the quest.

What difference would it make to Christian belief if it were shown that extraterrestrial intelligent life does exist? Paul Davies thinks it would have far-reaching consequences for religious, especially Christian belief, yet at the same time he too sees the search for ETI as part of an 'ancient religious quest'.

There is one line of thought that actually sees the existence of ETI as supportive, not undermining of Christian belief. This is because it demonstrates a greater degree of creativity on God's part. A creative God on this view is likely to create a vast cosmos populated with all kinds of intelligent creatures and it is arrogant on our part to see ourselves as special or unique. On the other hand, this is reminiscent of best of all possible worlds' arguments depending on the quantity of goodness. However much there were, you could always add more. Interestingly, Bruno argued that God's infinitude, omnipotence and perfection could only be expressed by creating an infinity of worlds (ref 12).

Perhaps the chief area where there has been perceived to be a problem for orthodox Christianity has been in relation to the incarnation, death and resurrection of Jesus Christ. If there are intelligent creatures besides ourselves who need God's revelation of himself in Christ, and who have sinned and need atonement made for their sins, does that imply that the Son of God would have to be incarnated, die and rise again in many different intelligent life forms?

Some Christians are indeed perfectly happy about this. Yes, he would be incarnate and die for those who needed redemption.

Other Christians, and I count myself among them, are not so happy about this. There seems to be something unique about Christ's suffering and death on the cross. He died 'once for all' we are told in the Scriptures, though of course the possibility of multiple incarnations to minister to aliens was not in the minds of the Biblical writers!

The passage in Colossians 1:15-20 speaks of a cosmic Christ who is 'before all things', in whom 'all things consist', and who 'reconciles all things to himself. Romans 8:18-25 speaks of the whole creation groaning, awaiting redemption. It would seem that Christ is both cosmically pre-eminent and achieves cosmic redemption on the cross (ref 13).

In principle, as Davis (ref 14) argues, the problem of aliens is no different to the problem of those on earth who are redeemed by Christ without ever having heard of him. These would include Old Testament characters - and not just those within the Israelite fold (see, for example, the books of Jonah and Job, plus examples like Naaman the Syrian (2 Kings 5)).

Thinking along these lines leads me to believe that the existence of ETI, even though I regard it as highly improbable, would pose no insuperable problems for the Christian faith. However, I should like to close this paper by endorsing David Wilkinson's thesis (ref 15). The needs expressed through the quest for ETI (e.g. for relationship and meaning) can actually all be met through the much more accessible and rational route of the Christian faith. Unlike ETI, the Christian faith is backed up by a very great deal of evidence: rationally it should be overwhelmingly accepted in preference to ETI. As Wilkinson concludes, 'We are not alone in the Universe' (ref 16).

References

1. Robert Sheaffer (1995) in Zuckerman and Hart (eds.)), Extraterrestrials: Where are they?, 2nd edition, Cambridge University Press, pp 20-28.

2 Robert Sheaffer (1995) in Zuckerman and Hart (eds.)), Extraterrestrials: Where are they?, 2nd edition, Cambridge University Press, p. 26.

3 Ian Crawford (1997), 'How common are technological civilizations?', Astronomy and Geophysics, 38, no. 4, pp 24-26.

4 Ian Crawford (1995) in Zuckerman and Hart (eds.)), Extraterrestrials: Where are they?, pp 50-69.

5 Ian Crawford (1997), 'How common are technological civilizations?', Astronomy and Geophysics, 38, no. 4, pp 24-26.

6 Frank Drake and Dava Sobel (1991), Is Anyone Out There? The Scientific Search for Extraterrestrial Intelligence, Pocket Books edition (Simon and Schuster) 1997, p 52.

7 Frank Drake and Dava Sobel (1991), Is Anyone Out There? The Scientific Search for Extraterrestrial Intelligence, Pocket Books edition (Simon and Schuster) 1997, pp 52-62

8 John Maynard Smith and Eors Szathmary (1995), The Major Transitions in Evolution, Freeman, Oxford and New York, p 81.

9 Michael H Hart (1995) in Zuckerman and Hart (eds.), op. cit., pp 220-222.

10 Michael H Hart (1995) in Zuckerman and Hart (eds.), op. cit., . 222.

11 Paul Davies (1995), Are We Alone? Implications of the Discovery of Extraterrestrial Life, Penguin, pp 92-96.

12 John Hedley Brooke (1991), Science and Religion: Some Historical Perspectives, Cambridge University Press, p 74.

13 John J Davis (1997), 'The Search for Extraterrestrial Intelligence and the Christian Doctrine of Redemption', Science and Christian Belief, 9 (1), pp 21-34.

14 John J Davis (1997), 'The Search for Extraterrestrial Intelligence and the Christian Doctrine of Redemption', Science and Christian Belief, 9 (1), pp 33-4

15 David Wilkinson (1997), Alone in the Universe? The X Files, Aliens and God, Monarch, Crowborough.

16 David Wilkinson (1997), Alone in the Universe? The X Files, Aliens and God, Monarch, Crowborough. p. 147.