Asked by: Adam Greene, Portsmouth
Diverse thinkers, from the ancient Greek philosophers through to contemporary quantum cosmology and eternal inflation theory, have called time an illusion. For them, the perception of time passing from present moment to present moment is an artefact of our psychology, so that anything real or true is real or true eternally and timelessly. The belief that reality lies in a timeless realm of truth, rather than in the flow of events our perceptions show us, might be supported by scientific argument but equally it reflects a metaphysical prejudice.
Contemporary attempts to extend quantum theory to the cosmological, to encompass the whole Universe and not just a sub-system of it, are often couched in equations which suggest time is emergent from a timeless reality. But these attempts suffer from problems, both technical and conceptual, that are even more challenging than the usual conundrums of quantum theory. Several advances in the study of quantum gravity have shown that our four-dimensional space-time is only recovered in a version of the theory in which time is real and not emergent. I would hold that, contrary to the ancient metaphysical tradition, time is not only real, it is likely that it is the only aspect of reality we experience directly that is fundamental and not emergent from anything else.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA