The deep mystery physicists call “the problem of time” | Jim Al-Khalili: Full Interview

Quick Overview

Physicist Jim Al-Khalili outlines four distinct problems of time: whether time flows, reconciling general relativity with quantum field theory, the nature of 'now', and the origin of time's directionality, concluding that while physical laws often suggest time is a static coordinate or an illusion, psychological experience and quantum entanglement strongly suggest time is real and possesses an inherent, irreversible directionality.

Key Points: Al-Khalili defines four problems of time: flow, reconciling relativity and quantum theory, what is special about 'now', and the origin of time's directionality. Physical time in equations treats time ('t') as a humble, timeless coordinate or parameter, contrasting sharply with 'manifest time' (psychological time) where humans strongly feel time is flowing. Einstein's relativity proves time is not absolute; special relativity shows time dilation due to speed (verified by muon lifetimes), and general relativity shows time slows down due to gravity (essential for GPS functionality). The Wheeler-DeWitt equation, an attempt to unify quantum mechanics and relativity, famously contains no time variable, supporting the notion that time might be an emergent property or an illusion at the most fundamental level. The directionality of time (the arrow of time) is absent in fundamental time-symmetric physics equations but is clearly present in thermodynamics (Second Law: entropy increases) and, fundamentally, in quantum entanglement and decoherence, which Al-Khalili argues is the truly irreversible process. Eternalism, the view derived from relativity that all points in time (past, present, future) are equally real in a block universe, conflicts with psychological notions of free will but aligns best with current quantum gravity theories like string theory and loop quantum gravity. The Big Bang, according to basic general relativity, marks the beginning of time, similar to reaching the South Pole where no further 'south' exists, though speculative multiverse theories suggest time may predate it.