Contact — Why the Message Begins with Prime Numbers

This series does not check a film's homework. A film is a film. It asks instead: which scientific theory did this film take up, and how was that theory turned into a story?

Contact is a good place to start, because the novel was written by an astronomer and the skeleton of the story came out of the theory itself.

First theory — is mathematics a common tongue

The film's founding idea is that you can speak in numbers to someone with whom you share no language.

A prime divides by nothing but one and itself: 2, 3, 5, 7, 11, 13, 17.

The universe is full of regular signals. Stars brighten and dim on schedule; some objects pulse with the accuracy of a clock. Regularity by itself means nothing.

The film did not invent this. The message beamed from the Arecibo telescope in 1974 consists of 1,679 pulses, which is 73 times 23. Both are prime, so there is no other way to divide it, and laid out 23 across and 73 down it becomes a picture.

How the theory becomes a story

The film stacks the idea in three layers, and those three layers are the structure of the plot.

1. Primes — someone is here. No content, only presence.
2. An old television broadcast — we know you. Here is what you sent, returned.
3. A blueprint — now we have something to say.

Greeting, proof of good faith, then business — the order in which you address a stranger. Rather than stopping to explain the theory, the film lets the plot advance in that order. That is the craft of it.

Second theory — listening to the sky

A radio telescope receives long wavelengths rather than visible light. Stars, gas clouds and galaxies all emit radio, so the sky can be drawn again in it.

But which frequency should you listen to? The sky is wide and frequencies are endless.

In the film Ellie listens on headphones. Radio is not sound and cannot be heard directly; in practice computers sweep millions of frequencies at once.

But the scene is a translation rather than an error. Instead of numbers pouring down a screen, the film renders the search in a sense the audience grasps immediately — and early researchers did wire signals to loudspeakers, so it has a basis.

A night that really happened

Something like the film's opening did occur.

In 1967 Jocelyn Bell Burnell, a graduate student at Cambridge, found an odd trace on the chart paper of a radio telescope she had helped build: a pulse repeating every 1.337 seconds, too regular to look natural.

The group labelled it LGM-1 — for Little Green Men.

A little further in

The novel was written by Carl Sagan, an astronomer of planetary atmospheres who showed early that Venus is hot because of a runaway greenhouse effect.

He spent his life on the search for other civilisations. He designed the Arecibo message and chose the contents of the gold record carried out of the solar system aboard Voyager. The novel is close to a retelling of his life's subject as a story.

Third theory — curved space

Sending the protagonist twenty-six light years away needs a method, since not outrunning light is not negotiable.

The film's answer is general relativity.

The film does not deliver this in dialogue. It shows a sheet of paper being folded and pierced with a pencil — the hardest part of the theory carried over into one action of the hands.

The film handles one more thing quietly well. The blueprint is received from elsewhere; we do not work out how to build it. Rather than forcing us to make what we cannot make, it assumes only that someone else might know how.

Fourth theory — what counts as evidence

What the film treats most deeply is not the wormhole but the method of science. The last half hour is given to it.

Ellie goes through something and comes back. From the outside nothing happened, and the recorder captured nothing. What she experienced has no evidence.

At the hearing she finds herself asking to be believed — she, who has refused belief without evidence throughout.

The film takes neither side. It tells the audience one thing only: the recorder held no images, but eighteen hours of static.

Sixty years of silence

Since Frank Drake turned an antenna towards two stars in 1960, people have gone on listening. Nothing has been heard.

Once, in 1977, an Ohio telescope caught a very strong signal for seventy-two seconds. The researcher reading the printout wrote Wow! in the margin, and the name stuck. The same patch of sky has been searched countless times since. It has never returned.

1. 1960Drake — an antenna turned towards a star for the first time
2. 1961The Drake equation — the unknowns broken into terms
3. 1967Bell Burnell — LGM-1, which turned out to be a pulsar
4. 1974The Arecibo message — 1,679 pulses (73 × 23) sent
5. 1977The Wow! signal — 72 seconds, never seen again
6. 1985Sagan publishes Contact
7. 1988Kip Thorne — the traversable wormhole paper, prompted by the novel
8. 1995The first exoplanet confirmed — one blank in Drake's equation filled

One thing has changed greatly since the film. The era of not knowing whether stars have planets at all is over. Thousands of exoplanets are now confirmed, and a fair number sit at distances where water could be liquid.

That is one blank in the Drake equation filled. The rest — the chance life begins, the chance it becomes intelligent, how long a civilisation lasts — remain empty. The last especially, since we do not know how long our own will last (the Fermi paradox).

The question that remainsPrimes are the same primes to anything that can count, which is why we made them our common tongue. But if whoever is out there thinks in a way quite unlike ours, what would our chosen greeting sound like to them?