The introduction set two rules: look at what is seen, and say what the word is doing. This page takes the first of them. It is an observation page. The conclusion it points toward is argued later.
What is seen is not, in any direct way, time. A clock hand is in one place, then another. A leaf is green, then brown. A stone is on the ledge, then on the ground. Two photographs of the same street are not the same photograph. In every case the later state is not the earlier state. That difference is physical change.
The same difference is going on in us. Life is change. We breathe in, and then out. The heart beats, and beats again. Blood moves. Muscles tense and release. A thought is present, and then another. Hunger arrives, and later it does not. None of this is observed as a substance flowing through the body. It is observed as one state giving way to another.
Nothing in either description, so far, requires an extra object behind the difference. It requires a before and an after, and a difference between them. “Before” and “after” mark the order of the states. They do not, by themselves, name a substance in which the states sit. Whether some further role for time survives that observation is the question the later pages test, not a result this one has earned.
Change is not a special topic reserved for laboratories, and not only something that happens to objects while we watch. Batteries run down, ice melts, people cross a room, faces age, nuclei decay. Inside a living body the same fact holds, continuously: breath, pulse, thought, repair, fatigue. Any case in which a later state is not the earlier state is a case of change. It is the ordinary content of a life, not a rare exception to a static background.
Clocks belong in this picture, not outside it. A clock is an arrangement that changes in a regular way — a pendulum, a balance wheel, a vibrating crystal, a decaying atom — so that other changes can be compared with it. On the evidence of looking, the clock does not detect a hidden entity flowing behind the events. It is one more changing thing, chosen because its change is steady enough to be a measure. A heartbeat can serve the same rough purpose. It is less regular than a crystal, and no more mysterious.
A common reply is that time is what makes the change happen. We age because of time. Things wear out because of time. Leave something long enough and time will have done its work.
Take the cases that can be traced. A cup cools because heat leaves it for the room. A nucleus decays because its internal state is unstable. A stone falls because the gravitational situation is not a balance. A body ages, so far as the biology is understood, because of a long chain of chemical processes, each depending on the one before it. In these cases a physical difference is resolved into a new state, and the clock records how far the resolution has run. It does not push the resolution along. Not every change mentioned on this page has been given its cause here — a thought, a mood — and this argument does not need a single cause for all of them. It needs the narrower point. In the cases we can follow, removing the physical difference stops the change, however long the clock is allowed to run. Nothing in those cases presents a difference made by time rather than by the processes themselves. That is this page’s reading of the examples, not a survey of every theory of causation.
The experience of succession is real. What is misleading, on the account developing here, is the picture we put on top of it.
Watch a clock and the hand moves. Feel a pulse and the beats come one after another. Look back on a day and the events are no longer present, only remembered in order. It is natural to say that time flowed past. The image is of a river, or of a present moment sliding along a line. The river is not observed. What is observed is change: the hand here, then there; one breath, then the next; one event, then a later event.
To call the flow an illusion is not to say that nothing happened. The changes happened. The proposed illusion is the extra picture — a thing called time, moving of itself — laid over a sequence of changes. We see and feel the sequence. We do not see the slide. A reader can grant the sequence and keep the picture. The later pages are what make the picture costly.
A single flowing time also sits badly with what clocks actually do.
Two clocks that start together and later meet again can show different readings, if one has taken a different path: a different speed, or a different height in a gravitational field. The amount of change recorded belongs to the history of that clock. It is not, without further argument, a sample drawn from one stream both clocks were standing in. The same dependence shows up, more roughly, in us. A day of fever, fear or hard effort does not amount to the same bodily change as a day of rest, even when the clock on the wall advances by the same number.
This is the reference-frame point in ordinary language. What counts as “how much has happened” depends on the path taken. A label that is the same for everyone can still be useful for keeping appointments. It is a poor description of the readings, and a poor description of a life, if it is heard as one flow both paths were in.
If what is seen is change, outside us and within us, one question is open rather than shut. The word “time” is not retired. It is doing several jobs at once: naming the succession of change, naming the measure of that change, and sometimes naming a supposed entity that passes on its own. Those jobs are not the same job. Whether any of them requires a further thing is not decided by noticing the jobs.
Words that sit next to it — dimension, period, duration — need the same care. So does the single parameter mathematics writes as t, which physics has often treated as a universal physical thing. Both belong with that sorting, not before it.
