New York, born 1958
Tim Maudlin
Time passes. That is not an illusion or a figure of speech but a fact about the structure of spacetime: an intrinsic direction, built in, in which earlier states produce later ones.
The view
Maudlin is an American philosopher of physics at New York University, best known for his work on quantum non-locality and on the structure of space and time. His essay "On the Passing of Time", in The Metaphysics Within Physics (2007), is the most direct defence in recent philosophy of the claim that time really passes.
His passage is not a moving present. Maudlin is no presentist: past and future events are as real as present ones. What he insists on is direction. Spacetime is not a block that can be read either way. Its temporal dimension is oriented, and that orientation is fundamental, not derived from entropy or from us.
The argument
Take physics at its word. The laws of physics, Maudlin argues, are laws of temporal evolution. They tell us how a state of the world at one time generates the state at later times. That is how physicists use them, and it is how the universe seems to work. Production runs one way.
The direction is not entropy. We use entropy and records to find out which way time points, but that does not make them what the direction consists in. Our evidence for the direction is one thing; the direction is another. Explaining entropy's rise, in fact, requires a direction for it to rise in.
The objections fail. The commonest objection to passage asks how fast time passes. "One second per second" sounds empty. Maudlin replies that it is a perfectly good rate. Rates comparing a quantity with itself are familiar, as when a bet at even odds pays back a dollar for every dollar staked. Being obvious is not the same as being incoherent.
Time's passing is a feature of spacetime, not of our minds. after Maudlin, The Metaphysics Within Physics (2007)
Geometry from direction. In New Foundations for Physical Geometry (2014), Maudlin rebuilds geometry on the notion of a line rather than on sets of points, so that a direction can be part of the basic structure. Time's arrow then sits in the geometry itself.
Where he meets Deutsch
Both are uncompromising realists about physics. Both reject the moving now of presentism: for Maudlin, as for Deutsch, past and future are as real as the present. And both think causation is objective, a matter of how the world is rather than how we describe it, which sets them apart from Price and Carroll.
They also share a style: an impatience with arguments that treat the formalism as a mere instrument, and a demand that a theory say clearly what exists.
Where they part
Does time pass? This is the most direct clash on the site. Deutsch argues that nothing could be called the speed of time, and that a flowing time needs an exterior time to flow in, which needs another, without end. Maudlin answers exactly this kind of objection. One second per second is a rate, and passage needs no second time because it is a direction within the first.
Are the laws directional? For Maudlin, the laws produce later states from earlier ones. For Deutsch, determinism runs both ways: any snapshot, with the laws, fixes the others and their order, and the multiverse's laws are time-reversible. The jigsaw puzzle, in Deutsch's image, was never laid down piece by piece.
Many worlds. Maudlin is a leading critic of the many-worlds interpretation and favours theories in which there is one world with definite outcomes, such as Bohmian mechanics or spontaneous-collapse theories. Deutsch's whole account of time rests on the multiverse.
Where the arrow lives. Maudlin puts it in the geometry of spacetime. Deutsch says causes precede effects because, near us, the variety of snapshots grows: a fact about this region of the multiverse, which might fail elsewhere.
| Maudlin | Deutsch | |
|---|---|---|
| Does time flow? | Yes: passage is a direction built into spacetime. | No. The idea is incoherent. |
| What is real? | All of spacetime, past and future included. | Every moment, in every universe. |
| Where does the arrow come from? | The geometry of time itself. | Growing variety of snapshots in our region. |
| Quantum reality | One world: Bohmian or collapse theories. | A multiverse. |
Further reading
- Tim Maudlin, The Metaphysics Within Physics (Oxford, 2007), chapter 4, "On the Passing of Time".
- Tim Maudlin, Philosophy of Physics: Space and Time (Princeton, 2012).
- Tim Maudlin, Quantum Non-Locality and Relativity (Oxford, 1994).
- Time, Stanford Encyclopedia of Philosophy.