Concepts explained
Where Does a Person's Information Go When They Die? — It Spreads and Fades, but Is Not Lost
The first question behind the film The Olive Tree Below. A voice and a face really do leave on waves, and radio broadcasts from a century ago are still crossing space. But waves fade as they spread, and memories do not leak out as waves. Even so, physics holds that information scatters rather than disappears. The story runs all the way to the bet Stephen Hawking lost.
The director's question
A face and a voice, a turn of phrase, the way someone said a name. It was hard to believe that all this vanishes at once along with the body. If sound is a trembling of the air and light is a wave too, might a person's traces also be spreading out somewhere as ripples? And if so, could those ripples be gathered again? The wave-gathering device in the film came from this imagining.
Science's answer, one — information really does leave on waves
This part is not imagination. A voice is a of air trembling back and forth as it spreads. We see a face because bouncing off it reaches our eyes, and light is a wave too. Information always travels this way, riding on ripples.
There is something more remarkable. Radio and television broadcasts, made for about a century now, have leaked out beyond the Earth. Radio is an like light, moving 300,000 km every second. So a voice from a hundred years ago is now a hundred from Earth. The Earth is wrapped in a great bubble made of our voices.
Marconi sent a signal across the Atlantic without wires in 1901. From that day, human signals began leaking into the sky.
Science's answer, two — but the farther they spread, the fainter they grow
The trouble is that waves spread. Ripples from one point swell outward like a balloon, and the same strength is shared over an ever larger surface. Double the distance and the strength drops to a quarter; ten times the distance, to a hundredth. This is the . So Earth's broadcasts, a few light-years out, are already weaker than the radio noise of stars and galaxies, too faint for today's technology to make out. They left, but they faded past the point where anyone could write them down.
Sound vanishes even faster. Words spoken in a room die away in a little over a second, striking walls and air. The trembling is not lost; it turns into the random jostling of air particles, which is . This one-way street, from orderly trembling to scrambled trembling, is the same story as in Part 6, Why Doesn't Time Run Backwards?
Science's answer, three — even so, it is not lost
Then is scattered information gone? Physics, surprisingly, comes close to saying no. By the laws of quantum mechanics, information cannot in principle be destroyed. It only scatters and mixes until it cannot be read. The letters of a burnt book are all still out there in the smoke, ash and heat, but there is no way to gather them and read them again.
Physicists once made an actual bet over this answer. Stephen Hawking argued that information falling into a at least was lost forever, and in 1997 he bet on it against his colleague John Preskill. The terms said the loser would give the winner an encyclopaedia of the winner's choice, from which information can be recovered at will.
In 2004, nearly thirty years after he first made the claim, Hawking stood up at a conference, admitted he had been wrong, and handed over a baseball encyclopaedia as promised. Exactly how information gets out of a black hole is still being worked out, but many physicists now stand on the side of information not being lost.
A little further in
What we don't know yet
That information remains in principle, and that it could actually be gathered again, are entirely different matters. To gather scattered information you would need to know the motion of every particle spread through the universe and retrace it all backwards. That is science in principle, and something no one could ever actually do. How information escapes a black hole, and how that fits the laws of physics we know, is also still unsolved.
In the film
The wave-gathering device in the film tries to gather scattered ripples and call a departed person back. Drawing this piece's line: that information leaves on waves is science; that information is not lost is science in principle; gathering those ripples to meet a person again is imagination.
While the film was being made, this imagining changed shape once more. The device that gathered scattered waves became a device that gathers an undying atom of life. That story runs from Part 1 onwards and closes in Part 7, Is There a Special Atom of Life?
The question that remainsAfter I am gone, what ripple would I want to leave clear enough for someone to write down?