Sixteen Futures, One Past

In 1948 Claude Shannon, a mathematician at Bell Labs, gave uncertainty a unit. The unit was the bit, a word he credited to his colleague John Tukey. The rule is simple enough to say at dinner: every time the number of live possibilities is cut in half, exactly one bit of uncertainty is gone.

• 16possibilities = 4 bits
• 8possibilities = 3 bits
• 4possibilities = 2 bits
• 2possibilities = 1 bit
• 1possibility = 0 bits

That gives us a clean way to say something that usually only gets said in poetry. The future is the place where every bit is still outstanding. The past is the place where every bit has been paid. I call that second place the Immutable Past: a complete record that no longer contains any uncertainty at all. Not very little. None.

And it gives us something better than a way to say it. It gives us a way to play with it.

Below are sixteen possible futures: every way four coin flips can land. Nothing has been flipped yet. Use the dial to move time forward one flip at a time, and watch what happens to the futures, the bits and the meter.

Go back and forth a few times. Four things show up, and the fourth one is a confession.

1. You turned the clock. You never chose a face.

   Every time you moved the dial, the coin landed the way it landed. You advanced time. You did not pick the outcome. Reload the page and it lands H T T H again. That is not a bug. That is what a past is. In the book I put it this way: She does not choose. She finalizes.

2. The future leaves in bits, not all at once.

   There is no single moment where the future flips into the past. Uncertainty drains out one fact at a time, and most of your life is lived at three bits, two bits, one bit. Partly known. Mostly still open. Already narrowing.

3. The futures that did not happen are part of the one that did.

   Look at the board at 0%. The one bright history only means something because of the fifteen faded ones around it. To become this is to no longer become that. Every outcome carries the shape of everything it ruled out.

4. The toy lies in one place: the dial turns backward.

   Slide it back to 100% and all sixteen futures light up again. Nothing in the world lets you do that. No person, no company, no government can reopen a bit once it has been paid. On the page the road runs both ways. In the world it runs one way.

Here is the part the toy cannot show. You never actually live at 100% or at 0%. You do not experience the Unknowable Future directly; you experience what you expect of it. You do not experience the Immutable Past directly; you experience what it hands you. What you live in is the relation between the two.

That is why the now feels so immediate and so hard to hold. It is not a point on the dial. It is what the whole trip feels like from inside. Stable, because the past underneath it does not move. Open, because the future in front of it has not arrived. Mysterious, because you never touch either end.

The now is not the place where the future turns into the past. It is what that turning feels like.

Quantum theory makes this dial exact and then declines to say how it turns. A quantum state lists the possible outcomes, each with an amplitude. The chance of each outcome is the square of its amplitude. And when you measure, you find one.

There are three serious answers to what that arrow is, and the book walks through all of them.

• CollapseThe dial really goes to zero when a measurement happens. The hard part is saying what counts as a measurement.
• EverettThe dial never reaches zero for the universe as a whole. Every outcome continues in its own branch, and an observer inside any branch sees 0%.
• PenroseGravity sets the clock. Mass in two places at once means two different spacetimes at once, and that may not be able to last.

Penrose’s idea is not just poetry, which is why I like it: it can be tested. In 2020 a team working deep underground at Gran Sasso in Italy looked for the faint radiation the simplest version of the Diósi-Penrose model predicts, did not find it, and ruled that version out. More general versions are still open and still argued over. That is how it should be. A beautiful idea that can lose is worth more than one that cannot.

One honest warning, because the toy invites a mistake. A wave function is not a coin nobody has looked at yet. The coin is classical: it already landed, you just do not know how. A quantum superposition is not ignorance of that kind, and the experiments that prove it are some of the strangest results in science. The coin is a good picture of bits. It is the wrong picture of a wave function. I use it anyway, and I am telling you where it breaks.

This is where my new book begins. I tell the story with two figures. He is the Unknowable Future: every amplitude, every open path, all sixteen futures lit. She is the Immutable Past: complete, nothing missing, nothing left to find out. She does not know Him. He loves Her anyway. In that mythology, quantum gravity is the name for the relation between them: how the language of possibility and the language of completion can belong to one world without one swallowing the other. A bridge, not a blender.

Free PDF · 44 pages · 10 chapters How the Future Becomes the Past A Mythology of Quantum Gravity

Written for philosophy students who suspect beautiful arguments are not enough. You will meet Lemaître, Everett, Feynman, Penrose, Maldacena and Susskind, and you will meet the equations too, there for contact rather than intimidation. It does not solve quantum gravity. It teaches you how to stand near it without lying.

Download the free PDF Free to share, complete and unaltered, for educational and non-commercial use.

I wrote it for the students I teach. Most of them are in their twenties. They love ideas, and many of them flinch at an equation. I wanted them to be able to stand near mathematics without pretending to be mathematicians, near physics without pretending to be physicists, and near mystery without giving up their responsibility to think clearly. That is also why it is free. A book whose whole lesson is posture should not have a gate in front of it.

The prologue ran here in April as She Does Not Know Him. If you have read The Immutable Past or What Is Time, you have met the two figures already. This is where they get their physics.

Load-bearing

Halving the possibilities removes exactly one bit. That is Shannon, and it is exact. The past contains no uncertainty. That is the axiom the whole framework rests on.

Convention

The percentages are bits remaining divided by bits at the start: 4, 3, 2, 1, 0 out of 4. “100%” means fully open relative to this menu of sixteen.

Where the toy lies

The real future has no menu of sixteen; it is not even a list. Coins are classical; wave functions are not. And the dial turns backward, which nothing real does.

Where I am probably wrong

If Everett is right, the universe never reaches 0%. Only each branch does, and “the past” may be a plural noun: one complete past per observer. I do not think that breaks the idea, because 0% is still exactly real from inside every branch that lives it. But I cannot rule it out, and the book does not pretend to.

Go back to Sunday at 11:58. Tomorrow is still sixteen futures, or sixteen thousand. You will not choose which face the coin shows. You will be there when it lands. And once it lands, it will land that way every time anyone ever looks.

Turn the dial once more. It lands the same way. That is what the past is.