✱The second essay in the series
This text is the second part of the series The Written and the Unwritten; the first is The Two Causalities — Why Perfect Explanations Make Terrible Predictions on this site. The author announces a continuation (the “loose thread” in the closing section) but does not state a total number of parts — hence no numbered ending is shown here.
⚠ A note on language — the direction is reversed here: In most reflection essays on this site the Turkish is the author's own pen. This text was written originally in English; the Turkish version here is a translation.
There are photographs of yesterday and none of tomorrow. Put that way, the fact sounds too obvious to deserve a second look, which is usually the sign that it deserves several. Nothing in the microscopic laws of physics explains it: those laws run equally well in both directions, and a film of two colliding particles played backward shows another perfectly legal collision. Yet the universe is littered with traces of one temporal direction and utterly silent about the other. Craters, tree rings, ice cores, memories, this sentence. All of them point backward. Nothing points forward.
The same laws, two directions — yet only one side bears traces
The universe is littered with traces of this direction.
Craters · tree rings · ice cores
Memories · documents · starlight
This sentence — itself a record
→The microscopic laws do not produce this difference — the film of a collision played backward shows another legal collision. So the difference lies not in the laws but in the records.
The side that looks forward
The universe is utterly silent about this direction.
There is no photograph of tomorrow
Nothing points forward
The previous essay traced this asymmetry logically. Backward from a leaf, a tree is a corridor; forward from the trunk, it is a hall of open doors. But logic only describes the asymmetry; it does not explain why the universe should contain corridors at all. That explanation is physics, and it is stranger than the tree suggests. The past and the future do not merely differ in how much we happen to know about them. They differ in what exists.
❝
The past is classical. The future is quantum mechanical.
— Felsufi
You Have Never Seen the Past
Start with an uncomfortable inventory. Everything you know about the past, you know from records. A memory is a record kept in neurons. A document is a record kept in ink. Starlight is a record kept in photons that left their source before you were born. A crater is a record kept in rock, a tree ring in wood, an ash layer in sediment.
Where the past is kept
The past is not a place but the sum of the records
Inanimate carrier
Crater → in rock, ash layer → in sediment
Cosmic carrier
Starlight → in photons that left before you were born
✱Remove the records — the past does not blur, it becomes inaccessible
Remove the records and the past does not become hazy; it becomes inaccessible in principle, because retrodiction is record-reading. There is no other kind.
This places the corridor of the first essay exactly where records exist. And it turns the question around: the mystery is no longer how we trace the leaf back to the trunk, but why the pen of the universe writes at all, and why in only one direction.
The Experiment That Draws the Line
Physics has an experiment whose entire job is to locate the boundary between the written and the unwritten, and it is famous for other reasons: the double slit.
The double slit — the existence of a record kills the pattern
TRIGGER
Electrons one at a time
Electrons are sent one at a time toward a barrier with two slits.
STATE
Single flashes
Each electron arrives at the screen as a single flash — like a particle.
STATE
Interference pattern
The flashes accumulate into an interference pattern: the signature of a wave that passed through both slits and recombined. Each electron, in a serviceable sense, interferes with itself.
STATE
A detector is added
A detector is added that registers which slit each electron used.
OUTCOME
The pattern vanishes
The interference vanishes. The electrons begin behaving like little stones, and the pattern becomes two plain heaps.
✱No one needs to look
The standard moral concerns measurement, but the sharp version of the result is more specific: no one needs to look at the which-way detector. It is enough that the universe holds a record of the path, read or unread. Interference survives exactly as long as no such record exists anywhere in the world.
And the converse is just as strict. Imagine a being in the style of Laplace's demon that arrives one instant after the flash on the screen and takes stock of every particle in the universe. It cannot tell you which slit that electron used. Not because the computation is hard, but because no measurement, however complete, could recover the route. The universe kept no record of it.
Some interpretations of quantum mechanics insist there was nonetheless a fact of the matter, a definite path the electron secretly took; they purchase that fact at the price of making it unrecoverable in principle — and for everything this series needs, that is the same thing. Where no record exists and none can be reconstructed, the past offers nothing to read.
Electron and baseball — the difference is not size but trace
Nothing inside the apparatus took notes.
The record of the path exists nowhere
It can hold several histories open at once
This is why it is quantum
→What decides whether a thing behaves classically or quantum mechanically is not whether its path was measured, but whether its path could later be recovered. What makes the baseball classical is not its size as such — it is its inability to go anywhere without leaving a record.
It cannot go anywhere without leaving a record.
Every air molecule it shoves aside, every photon that scatters off its seams, carries away where it flew
The which-way record is written into the world in a billion redundant copies
A sufficiently patient detective could reconstruct the path a day later from the testimony of the air
❝
Classical means: the record exists. Quantum means: it does not.
— Felsufi
Physicists call the baseball's condition decoherence, and the mechanism deserves a moment, because it is the hinge of this whole series. A macroscopic object cannot stop publishing. Air molecules bounce off it, photons scatter off its surface, and every one leaves carrying a copy of its position. The environment is a witness that never blinks — and against such a witness the electron's trick (holding several possible histories open at once) is impossible.
✱The writing does double duty
The alternatives are not merely unobserved; they are contradicted by records already distributed across half the room. Classical behavior is what remains when every alternative history has been written out of existence.
The writing does double duty: it erases the alternative paths even as it commits the surviving one to consistency with everything already written. Why the pen writes this line rather than that one is a question physics still argues about; what matters here is only that once written, it is written for everyone.
This gives the tree its physical explanation. The backward corridor is unique because a record of it exists: the past is the part of the universe that has been written. The forward doors stand open because nothing about them has been written yet; the future is not hidden, it is unwritten. The asymmetry of the two causalities is the asymmetry of a ledger: dense with entries on one side of the bookmark, blank on the other.
❝
That is also where this series takes its name. The written and the unwritten are not two regions of time. They are two different kinds of thing.
— Felsufi
It would be natural to hear all this as a statement about our limitations: the future is “uncertain” the way next week's weather is uncertain, a matter of missing data. The physicists who built quantum mechanics were unusually insistent that this is the wrong reading.
❝
“This formulation makes it clear that the uncertainty relation does not refer to the past.”
— Werner Heisenberg — The Physical Principles of the Quantum Theory (1930), s. 20
✱Uncertainty is a property of the unwritten side only
Heisenberg's sentence is subtle but decisive: uncertainty casts no fog backward. It does not blur what has already happened. Uncertainty belongs to the blank page of the ledger — not to the written one.
❝
We can write a wave function for a uranium nucleus that may decay tomorrow, a distribution over possibilities. But no wave function expresses the statement “this nucleus decayed yesterday at 9 a.m.” — “Knowledge about the past can only be expressed in classical terms.”
— Freeman J. Dyson — Thought-Experiments in Honor of John Archibald Wheeler (2004), böl. 4
✱Dyson's second conclusion, easy to miss
The two directions of time are not written in the same language: facts on one side, amplitudes on the other, and no translation between them.
Dyson drew a second conclusion that is easy to miss and worth keeping: the observer's role in quantum mechanics is not to cause some abrupt collapse of the wave. It is “solely to make the distinction between past and future” — to stand at the point of reference that separates facts from probabilities.
❝
Past, present and future are not fundamental at all, but derived from the more basic distinction between definite and indefinite. An event is the transition from one to the other, and “when we observe something we do so as spectators to the transition between indefinite and definite.”
— Lee Smolin & Clelia Verde — The Quantum Mechanics of the Present, arXiv:2104.09945 (2021)
✱The present is not a place but the writing head
On this view the present is not a location in time. It is the writing head — the moving edge where the unwritten becomes the written.
One more piece completes the picture: why must the written side be single? The tree branches forward; why does it never branch backward?
What if the past branched
A branching past (hypothetical)
If the past were like the future, a distribution of alternatives.
Records could disagree
Your yesterday and mine could be different yet both correct
“What happened” would be a property of the person asked, not of the world
→Objective reality is, at bottom, the requirement that all records be reconcilable. A universe whose observers compare notes can afford many futures, but only one past.
Records are written in a billion redundant copies.
Many observers reading many copies of the same entry cannot help but agree
Objectivity is not an extra assumption — it is what redundancy looks like from inside
✱A consistency condition, not an accident of geometry
The uniqueness of the backward corridor is not an accident of geometry. It is a consistency condition. Even relativity, which cheerfully relativizes simultaneity, is built on the postulate that the order of cause and effect — of events close enough to influence one another — is the same for every observer.
The universe permits enormous freedom about what to write next. It never contradicts what it has already written.
Information diffusion — two results in one stroke
TRIGGER
The system scatters its information
A record is made by information diffusion: the system scatters information about itself into the environment. That is the writing.
STATE
Backward: a record is born
The environment now holds a record; record-reading becomes possible → retrospective causality.
STATE
Forward: determinism dies
The fine details that diffused into a billion air molecules are exactly the details a perfect forward prediction would have needed.
OUTCOME
One stroke, two characters
Openness does more than separate the two causalities — it manufactures both of their characters at once: a definite past, an open future.
❝
Entropy is, at bottom, a count of how widely a system's information has spread, and the second law is the statement that the universe keeps writing and never unwrites. The arrow of time and the arrow of records are not two mysteries; they are the same arrow.
— Felsufi
✱And the writing is lossy
The air remembers that the baseball passed, not every molecular nuance of its passage. Records are compressions: coarse-grained summaries of what the system gave up.
This is the promised answer to why records must be incomplete. The first essay conceded that several incompatible narratives can fit the surviving evidence, and here is the reason: the register was never a transcript. It was written by the same diffusive process that erased the details.
The two causalities — not one relation read two ways
Defined on the register.
Facts · classical statements · the written
→They are not one relation read in two directions, because they are not about the same kind of object at all. The pundit of the first essay reads the register fluently, then quotes it as a description of the unwritten, in a language the unwritten does not speak.
Defined on the distribution.
Possibility · amplitude · the unwritten
But a detail has been quietly load-bearing throughout. The baseball was classical because we let the air testify. The electron was quantum because nothing inside the apparatus took notes. Written and unwritten, it turns out, were judged relative to a boundary — to where we drew the box around “the system” and declared everything else environment.
❝
Draw the box differently and the verdict changes: a die whose throw is governed by a hidden mechanism just outside your box looks random from inside and clockwork from one step back. Whether a thing is random, it seems, is not a fact about the thing.
— Felsufi
Sources
Werner Heisenberg — The Physical Principles of the Quantum TheoryTrans. Carl Eckart and F. C. Hoyt (University of Chicago Press, 1930), p. 20. The statement that the uncertainty relation does not refer to the past. Freeman J. Dyson — Thought-Experiments in Honor of John Archibald WheelerIn Science and Ultimate Reality: Quantum Theory, Cosmology, and Complexity, eds. John D. Barrow, Paul C. W. Davies and Charles L. Harper Jr. (Cambridge University Press, 2004), ch. 4. Lee Smolin & Clelia Verde — The Quantum Mechanics of the PresentarXiv:2104.09945 (2021). The thesis that past/present/future derive from the distinction between definite and indefinite. ✱What follows, and about this text
The author leaves the question of where the box is drawn — the relativity of randomness to the observer's boundary — to the next essay.
This text was written originally in English; the Turkish version here is a translation. In most reflection essays on this site the direction is reversed (Turkish original, English translation) — not in this one, nor in the first part of the series. The original text is published on Substack.