Full transcript of the episode (it gives away every surprise)
Interactive experiment
Ten seconds
Without looking at a clock: press to start, count ten seconds in your head, then press to stop.
The reader estimates ten seconds without a clock; they are then told how long they actually counted.
Your inner clock is not a metronome.
It speeds up with excitement and fever, and slows down with boredom. In the 1930s, the physiologist Hudson Hoagland noticed that his wife, who had a fever, felt he had taken forever to come back from the pharmacy. He had her count out a minute: the higher her fever, the shorter her minute.
Elastic Time
Your inner clock cheats, and so does the universe’s.
Interactive experiment
The stopped clock
Stare at the cross. When the clock appears to the side, move your eyes to it quickly, and watch its first second.
A clock with a second hand appears at the side of the screen. When they suddenly look at it, many people feel that the first second lasts longer than the following ones: this is chronostasis.
The first second lasts longer.
This is chronostasis. While your eyes are jumping, you see nothing; to fill that gap, your brain backdates the image of the clock to the start of the jump. So the first second seems longer than the others.
People say that in an accident, “everything happens in slow motion.” The neuroscientist David Eagleman wanted to know whether that is true. He had volunteers free-fall about 100 feet (31 meters) into a net.
On their wrists, a display flashed numbers too fast to be read. If time really slowed down in fear, they would have been able to read them. Nobody managed to. But afterward, they all estimated that their own fall had lasted a third longer than other people’s.
Fear doesn’t slow time down. It fills up memory.
The more memories a moment leaves behind, the longer it seems afterward.
That is why a vacation full of new things goes by fast… but seems long when you remember it. And, according to a widespread hypothesis, why the years seem to speed up as we get older: fewer firsts, fewer memories, less time felt.
To lengthen your life, at least in your memory, have more firsts.
On July 16, 1962, a 23-year-old geologist from Nice, Michel Siffre, went down into the Scarasson chasm, in the Alps, to live there with no watch and no daylight. Every time he woke up and every time he ate, he phoned the surface.
When his team came to get him, on September 14, he thought it was August 20. He had “lost” twenty-five days.
Question for the reader
Two twins are 30 years old. One of them travels to a distant star at 99.5% of the speed of light, then comes back. For the traveler, the trip lasted ten years. How old is the twin who stayed on Earth?
- 40, the same age
- 50
- About 130 (correct answer)
If you answer “40, the same age”:
About 130. The twin who stayed behind is almost certainly no longer there to welcome the traveler home.
If you answer “About 130”:
Yes: about 130. The twin who stayed behind is almost certainly no longer there to welcome the traveler home.
Interactive experiment
The traveler and the stay-at-home
Set the speed of the trip: the closer it gets to the speed of light, the more the traveler’s time slows down compared with Earth’s.
A calculator compares the time that passes for a traveler and for Earth depending on the speed of the trip: at 99.5% of the speed of light, ten years of travel correspond to a century on Earth.
This isn’t science fiction. The clocks on GPS satellites gain 38 microseconds a day compared with ours: their speed slows them down a little, and the weaker gravity up there speeds them up even more.
Without correction, your GPS would drift by more than six miles a day. Einstein is in your pocket.
Time is not the same for everyone.
It depends on your speed and on the gravity around you. Your head, slightly farther from the center of the Earth than your feet, ages a tiny bit faster than they do.
Interactive experiment
The cosmic calendar
Let’s squeeze the universe’s 13.8 billion years into a single year. The Big Bang happens on January 1 at midnight; today is December 31 at midnight. Scroll through the year.
On a year that sums up the whole history of the universe, the Sun is born in early September, life appears in late September, the dinosaurs die out on December 30, the first modern humans arrive on December 31 around 11:48 PM, and writing twelve seconds before midnight.
All of human history fits into the last seconds of the year.
Writing appeared twelve seconds ago. An entire human life lasts barely two tenths of a second.
Time dilation. Time flows more slowly for a clock that moves fast, or that sits in strong gravity, than for a clock at rest far from any mass. The effect is tiny at our scale, but measurable, and essential to GPS.
Thirteen billion years to reach you. Time to step back. A long way back: 3.7 billion miles.
Sources
- Hudson Hoagland, “The physiological control of judgments of duration,” Journal of General Psychology, 1933.
- Kielan Yarrow et al., “Illusory perceptions of space and time preserve cross-saccadic perceptual continuity,” Nature, 2001.
- Chess Stetson, Matthew Fiesta and David Eagleman, “Does time really slow down during a frightening event?,” PLoS ONE, 2007.
- Claudia Hammond, Time Warped, 2012.
- Michel Siffre, Beyond Time, 1964 (Hors du temps, 1963).
- Neil Ashby, “Relativity in the Global Positioning System,” Living Reviews in Relativity, 2003; James Chin-Wen Chou et al., “Optical clocks and relativity,” Science, 2010.
- Carl Sagan, The Dragons of Eden, 1977 (the cosmic calendar).