QuestionsDoes time really exist?There is an absolute time that flows by itself, and our clocks only measure it approximately
Does time really exist?Time really passes

There is an absolute time that flows by itself, and our clocks only measure it approximately

Newton's absolute time

Isaac Newton 1643 · 1727A physicist and mathematician who founds mechanics on an absolute, true and mathematical time and space.
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What it claims

There exists an absolute, true and mathematical time which, of itself and from its own nature, flows uniformly without relation to anything external, and which is also called duration.

Why

No motion measures time exactly, yet the duration of things stays the same: so there must be a true time behind our clocks.

The same idea through history
Isaac Newton1687Newton distinguishes absolute, true and mathematical time from the relative, apparent and common time that clocks, days and years measure.
In short

"There is an absolute time that flows by itself, and our clocks only measure it approximately" is an argument by Isaac Newton (Mathematical Principles of Natural Philosophy (Principia), 1687, scholium to the definitions, 1687) on the question "Does time really exist?" (answer: time really passes). Its claim: There exists an absolute, true and mathematical time which, of itself and from its own nature, flows uniformly without relation to anything external, and which is also called duration. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P5). AskPhilosophy presents 3 objections, 2 of them with a documented reply, and the original text behind each premise, checked word for word.

Mathematical Principles of Natural Philosophy (Principia), 1687, scholium to the definitions
Valid with an implicit premise

A clock can run fast or slow. How do we know? Because we compare it with another clock, or with the motion of the stars. But those motions can vary a little too. Newton draws a bold conclusion: for astronomers' corrections to make sense, there must be a true time that depends on no motion, which all motions measure more or less well. All the mechanics of the Principia rests on this idea.

P1The time we use every day (hour, day, month, year) is only a sensible and external measure of duration, taken from motions.
P2Every motion can be sped up or slowed down, and it may be that no motion is perfectly equable. So no motion measures time with guaranteed accuracy.
P3Yet the duration of things stays the same, whether motions are fast, slow or none.
P4Astronomers nevertheless correct common time by an 'equation', and this correction is confirmed by experience (pendulum clocks, eclipses of Jupiter's satellites).
P5 · implicit premiseA correction is possible and justified only if there is a reference that is itself no motion: a uniform flow, against which a motion is said to be too fast or too slow.
So there exists an absolute, true and mathematical time which, of itself and from its own nature, flows uniformly without relation to anything external, and which is also called duration.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, one could accept everything else and say: when we correct a clock we simply compare it with a better clock, and so on, never reaching a pure time. Corrections would then be mere conventions that become more and more precise. This is exactly what Leibniz and Mach will say.
The argument is valid. P1 to P4 describe the situation: common time is measured by motions, those motions vary, the duration of things does not, and yet measures are successfully corrected. P5 adds the bridge: to correct, you need a standard that is not a motion. Then this standard, absolute time, exists.
Analogy. A thermometer can be badly graduated. To find out, we compare it with other thermometers. But if all thermometers were a little off, we would still say there is a true temperature that they all measure badly. Newton reasons in the same way about time.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Gottfried Wilhelm Leibniz 1716 · attacks the conclusion

Leibniz holds that time is only the order of successions, as space is the order of coexistences. If time were something over and above things, nothing could explain why God placed things at one instant rather than a year earlier. But this shows that instants, taken without the things, are nothing.

a defender replies
Samuel Clarke defender of the argument · 1716
Clarke, who defends Newton, replies that the order of things succeeding each other in time is not time itself: the same events, in the same order, may succeed each other faster or slower, but not in the same time.
Gottfried Wilhelm Leibniz 1716
Leibniz maintains that instants, considered without the things, are nothing at all and consist only in the successive order of things. If this order remained the same, the state where everything had been created earlier would not differ at all from the present state, nor could it be told apart.
Where the debate stands (our summary)The disagreement is about speed: for Clarke, we can speak of things succeeding each other faster or slower, which supposes a time distinct from the order; for Leibniz, two worlds that differ only in the date of their beginning are one and the same world. The question is still debated, but takes another form with relativity.
Albert Einstein 1905 · attacks the conclusion

Einstein shows that two events that are simultaneous for one observer are not necessarily so for another who moves relative to the first. Simultaneity depends on the observer: so there is no single, universal time flowing in the same way everywhere, as Newton wanted.

a defender replies
see the argument
No reply possible: objection raised in 1905, after the author's death (1727).
J
John Stewart Bell defender of the argument · 1976
Bell argues that relativity can be presented in Lorentz's way, with an unobservable preferred frame: the predictions of physics stay the same. Physics therefore does not force us to give up all absolute time, even if it does not need it.
Where the debate stands (our summary)Most physicists give up absolute time because relativity has no need of it. A minority, including Bell, notes that the theory remains compatible with a hidden preferred frame. The disagreement is about the value of an entity that no experiment can detect.
E
Ernst Mach 1883 · attacks premise 5

Mach judges that speaking of an absolute time, independent of change, makes no sense: this time can be measured by comparison with no motion, so it has no practical or scientific value, and no one is entitled to say that he knows anything about it. Time is an abstraction we draw from the changes of things.

no reply
No reply possible: objection raised in 1883, after the author's death (1727).
The debate goes on (our summary) Newton died in 1727 and could not reply. A Newtonian would say that absolute time is not measured directly but is accepted because it explains inertial forces and the correction of clocks (P3, P4). This is how physics reasons: we accept what we do not see when it explains what we see.