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A PHYSICIST WRITES . . .

(September 2015)

Sixty-plus years ago, my parents suddenly started encouraging my young curiosity about astronomy. I was about to face an interview at a secondary school, and their idea was that I would have useful answers when asked about my interests. It seemed to do the trick! And if I had taken any different path though life, certainly I would not have met Mrs S at an astronomy Ďgatheringí 30 years later...

From time to time we find ourselves driving at night through counties like Sussex, under a clear dark sky. You donít realize itís clear, though, until you notice the stars. The temptation then is to look upwards or sideways at them, which is not a good idea if youíre the driver. Instead you should concentrate on the road ahead and find a safe place to stop. Then turn off the lights, get out, let your eyes become more adjusted to the darkness, and just gaze at the heavens Ė with the aid of binoculars if you happen to have a pair in the car.

Even unaided, in the absence of town light and the Moon you should be able to see thousands of stars, each of which is of course a sun something like our own. And if you are lucky or you choose a good time (near midnight in July is said to be the most favourable), the Milky Way too will be visible, stretching across the night sky as an irregular band of light from countless stars much further away: as you look at it, remind yourself that what youíre actually viewing, from the inside, is the flat spiral galaxy in which our solar system sits.

And if the stars in our own galaxy are Ďcountlessí, so are all the galaxies in the universe. In reality, the count for each item is at least 100,000,000,000. Iíll leave you to multiply this figure by itself, for a guess at the total quantity of stars!

In recent years nearly 2000 planets have been detected in orbit around the nearest stars, and this number is steadily growing. Incredible techniques are used to demonstrate their existence, for example looking for the tiny drop in a starís brightness when a planet passes in front. Itís now thought that on average, there is a minimum of one planet for every star, out there...

...Which brings us to the Big Question: does Ďintelligentí life exist elsewhere in the universe? Well, already (in the last two paragraphs) Iíve encouraged you to guess how many stars Ė and hence at least how many planets Ė there are in the universe. Letís call this huge number N. Next, what are the chances that any one of these planets happened to go through just the right sequence of circumstances for life to spark into existence, and then evolve into some form of intelligence?

You canít just argue that because we have evolved on Earth, there must be other civilizations. Our existence arose from a quite extraordinary combination of chance factors. For example, this is an ideal planet for size, rotation speed, temperature, surface structure (water and land) and surface chemistry. Itís in a stable solar system, with big planets to deflect asteroids away from us. At times conditions here changed greatly, first encouraging chemicals to form self-replicating molecules and later allowing the evolution of life in all its forms.

And then 65 million years ago an object collided with the Earth, doing for the dinosaurs and clearing the way for the rise of mammals. But itís not obvious why this should have now resulted in animals as brainy as us! Anyway, letís say that the tiny probability of enough vital factors occurring (at the right time and in the right sequence) on any given planet is 1-in-F, where F will be another large number.

Lastly, how long might such a bright civilization as ours last, in comparison to the lifetime of its planet? (It does rather seem that the more we advance technologically, the more vulnerable we become both to natural and to man-made disasters.) Dividing the likely duration of a clever society by that of its planet gives us a fraction 1/D, where D is enormous too.

Weíre there! The Soul Formula for how many other planets (in the whole universe) carry intelligent life is N ų (F D), in other words one big number divided by two others. But is the result large, or small, or less than one (which means probably zero)? That depends on the relative sizes of N, F and D, which I donít know nor does anyone. I do claim, however, that my formula is simpler than any of the others that you may come across for attempting to answer the Big Question.

Itís just conceivable that radio signals will be detected from far-off beings one day, but we shall surely never meet them, because of the distances involved. A journey to or from even the nearest star by any possible means would take thousands of years (during which time, collisions with interstellar debris would in any case be likely to destroy the spacecraft). Effectively, therefore, we are living our lives alone in space...

Allow me now to focus on one particular life: my mother was born in the same year as the Model T Ford, when the Titanic was still on its drawing-board. From her (and equally from my father) I inherited a love of music. Long ago she sang in a choir conducted by the composer Gustav Holst. Later she was the secretary of a committee whose chairman was Ralph Vaughan Williams: she told us that as he arrived for one meeting, she realized that the only vacant chair wouldnít be wide enough for his, er, chairmanship Ė so she had to engineer a hurried swap!

In her sixties she briefly took up driving and after several attempts actually passed the test, but with little enthusiasm. She was quite content to sit and be driven by others, while perhaps quietly working out how to motivate them in what she would like them to do.

When my mother died in Littlehampton last month, the world had advanced 107 years (all but a few days). Maybe she didnít quite keep up with it near the end, but she stayed happy and well. Alas, though, we have lost a link with times long gone Ė and we shall have fewer opportunities now to stop in Sussex and gaze at the stars...

Peter Soul

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