Insight | Is spacetime fundamental, or does it emerge from something deeper?
Donald Hoffman argues spacetime falls apart at the Planck scale, Annaka Harris explores emergent space-time, and Andrew Strominger and Sean Carroll explain how the holographic principle hints that space is not basic. The convergence from philosophy and physics suggests the stage of reality may itself be a derived thing.
Space and time are probably not the bottom layer of reality. Four people who start from very different places share that doubt. They agree far less about what lies underneath, and one of them rejects the step from saying spacetime is derived to calling it an illusion.
Donald Hoffman, a cognitive scientist, argues that our best physical theories name their own limit. To look at smaller regions you need more energy, energy is mass, and enough of it in a small space collapses into a black hole. So below a certain tiny scale, distance and duration cannot be measured at all. He counts that as a strength of the theories. He adds that physicists have found mathematical structures outside spacetime that predict how particles behave inside it. Then he goes much further than the physicists he cites. He argues that evolution shaped our senses for survival, not truth, so spacetime is like the display of a headset, and that consciousness is what lies beneath.
Andrew Strominger, a Harvard physicist, arrives through black holes. A black hole stores information in proportion to its surface area, not its volume. Generalized, that is the holographic principle: the information in a region can be stored on its boundary. For certain black holes he and a colleague found the plate that holds the information, with the space near the horizon as its projection. So space can emerge. Of time he says, "I think ultimately it has to be emergent." He is frank that nobody knows exactly what the principle is, and that it has not been made precise for a universe like ours.
Sean Carroll, a physicist at Johns Hopkins, explains the same principle with the brakes on. He calls it speculative and productive. It clashes with our best working theory, which treats every point in space separately. A test he tried against neutrino data came out neither for nor against. He says holography gives no specific reason to change one's view of time. And he objects to Hoffman's wording. A theory's successful predictions stay true whatever the deepest ingredients turn out to be. "To call it an illusion is just wrong, I think."
Annaka Harris, a writer on consciousness, reports that many physicists she has interviewed think space and time are emergent. She holds a middle view: our perceptions map onto a real structure that does not look like what we experience. She puts the odds that consciousness is fundamental at slightly better than even.
They agree the pressure comes from combining quantum theory with gravity. They disagree on what is underneath: consciousness for Hoffman, unfinished physics and mathematics for the two physicists. None of this changes everyday physics, and none of it has been tested.
What to do with it: keep three claims apart. That spacetime is not fundamental is held by many physicists. That it is an illusion is disputed. That consciousness is fundamental is a minority view. Ask what scale is being discussed, since spacetime remains the working framework at human scales. Remember the area fact, the cleanest reason for the doubt. Treat a theory's breakdowns as clues. Keep trusting what works.
