Philosopher of physics, contemporary

Jenann Ismael

Grant the block universe. The feeling that time passes, and that the future is ours to make, can still be explained, from the inside, by how creatures embedded in time gather information and act.

The view

Ismael is a philosopher of physics whose books include The Situated Self (2007), How Physics Makes Us Free (2016) and Time: A Very Short Introduction (2021). Her central theme is the difference between describing the world from outside, as physics does, and living in it, as we do.

Physics gives the view from nowhere: a block of events, related by laws, with no privileged now. We never occupy that view. Each of us is a system inside the block, receiving information from some events and not others. Ismael's project is to show how the features of lived time follow from that situation, without adding anything to the physics.

The argument

Memory runs one way. We have records of the past and none of the future. That asymmetry, itself grounded in the thermodynamic asymmetry of the world, means that each moment of a life has a remembered past and an open, unknown future.

Passage is a changing perspective. At each moment, I have records of the earlier moments of my life. A later stage of me holds everything the earlier one did, and more. Strung together, these perspectives make a self that seems to move through time. Nothing moves. What changes from stage to stage is what the stage knows.

Passage is how a fixed history looks from a position inside it. after Ismael, Time: A Very Short Introduction (2021)

The future is open to us. When I deliberate, my decision is among the causes of what happens next, and I cannot know it until I have made it. From the inside, then, the future really does depend on me, even if, seen from outside, the whole history is fixed. The laws describe patterns in the block. They do not push us around.

This is freedom enough. In How Physics Makes Us Free, Ismael argues that complex, self-governing systems like us are the authors of their actions in every sense that matters, determinism notwithstanding.

Where she meets Deutsch

On the experience of time, Ismael and Deutsch say almost the same thing. Deutsch writes that we do not experience time flowing. We experience differences between our present perceptions and our present memories, and misread them as motion through time. Each snapshot of an observer is conscious, and each regards its own moment as now. That is Ismael's changing perspective, described from the outside.

Both also hold that the future is open relative to an observer, and that the past is fixed for each. And both reject the idea that our consciousness travels along the line of moments.

Where they part

Can a block universe have open futures? This is the key difference. Ismael argues that openness, agency and freedom are fully compatible with a single, deterministic block: the openness is real from inside, and the inside is where we live. Deutsch denies it. In spacetime physics, he says, the openness of the future is an illusion, and causation and free will can be no more than illusions as well. Only the multiverse, in which the alternatives really exist, makes them real.

Counterfactuals. Ismael treats claims about what would have happened as made true by the laws together with our choice of what to hold fixed. Deutsch thinks that in a single spacetime such claims are irreducibly ambiguous. He looks for their meaning in the variant universes that actually occur.

Where the work is done. For Ismael, the explanation is perspectival: it lies in the structure of embedded information. For Deutsch, it lies partly in physics: the multiverse is what supplies real variants, and real causes.

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Further reading

• Jenann Ismael, Time: A Very Short Introduction (Oxford, 2021).
• Jenann Ismael, How Physics Makes Us Free (Oxford, 2016).
• Jenann Ismael, The Situated Self (Oxford, 2007).
• Temporal Consciousness, Stanford Encyclopedia of Philosophy.