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Thesis Special relativity has refuted presentism, whatever presentists say

Lars Eriksen Fellow
· 5 replies
Physics & cosmologyAnalyticAlbert EinsteinArthur Prior#eternalism#presentism#relativity#simultaneity
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Its coordinates: 1.2 Cosmology (Philosophical) · 1.2.1 Origins and First Cause · 1.2.2 Fine-Tuning and Necessity +1 more

Where it stands

I'd like to argue the strong version, then see how much survives.

Presentism says only the present exists. Past dinosaurs and future grandchildren are not real; only what is happening now is. That requires a fact about which events are happening now, everywhere in the universe. A single, observer-independent present.

Special relativity, in its standard formulation, has no such thing. Two events that are simultaneous in one inertial frame are not simultaneous in another moving relative to it. There's no physical experiment that picks out one frame's simultaneity as the true one. So presentism needs a fact that physics, our most successful theory of space and time, says isn't there.

The presentist can say: there is a privileged frame, we just can't detect it. That's logically possible, but it's exactly the kind of move we'd reject anywhere else in science, positing an undetectable structure to save a metaphysical picture.

So my thesis: standard presentism is refuted, and the right view is eternalism or something like it, where all events are equally real and the "now" is perspectival. Tell me what I'm missing.

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5 replies

For the thesis 1

No replies on this side yet.

Against the thesis 2

  1. Abdulrahman Al-Bassam

    Against Fellow

    Against. You're right about special relativity taken alone. But our best cosmology uses a cosmic time: in an expanding universe that's roughly the same in all directions, there's a natural frame, the one at rest relative to the cosmic microwave background. Neo-Lorentzian and cosmic-time presentists say this frame gives a physically meaningful simultaneity. It isn't required by the local laws, but it isn't an arbitrary add-on either.

    Helpful · 2
    1. Lars Eriksen

      Fellow

      Abdulrahman, I'll grant that cosmic time is real and useful. But it's a feature of the matter distribution, not of spacetime. If the universe had been less uniform, there'd be no such frame. Is presentism true only because the universe happens to be smooth?

      Helpful · 3
  2. Tomasz Szewczak

    Against Fellow

    Against, on behalf of Prior. Prior, as I read him, took the passage of time to be more certain than any physical theory, and he was willing to say that if physics had no place for a privileged present, physics was leaving something out. You can disagree, but it isn't irrational to weigh a datum of experience against a theory's silence. Silence isn't denial: the equations don't mention a present, but nor do they mention colours.

    1. Emeka Anyaoha

      For Fellow

      For. Tomasz, "the theory is silent" undersells it. Relativity isn't silent about simultaneity, it actively relativises it, and has been confirmed in every test we've thrown at it. Positing a hidden absolute frame is like positing an undetectable ether. Possible, but a degenerating research programme in Lakatos's sense.

      Helpful · 1

Other replies

  1. Lars Eriksen

    Fellow

    Revised thesis: special relativity refutes the simple presentism that most people assume, the one with a universal "now" the laws themselves pick out. It doesn't refute every presentism, since cosmic-time and neo-Lorentzian versions are still alive, but they pay a real price. I'd call that a serious wound rather than a refutation.

    Helpful · 2