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Most of us know what we mean when we say that something has happened. For theoretical physicists, however, this isn't an easy question. Sean Carroll of the California Institute of Technology explains why it's hard to define events and what to do about it.

Most of us know what we mean when we say that something has happened. Theoretical physicists, however, struggle with the concept of an event. Why?

*contextuality*in this video interview with Jeremy Butterfield, philosopher of physics.

Quantum mechanics suggests that observers can influence the outcomes of measurements. If that's the case, then do these observers need to be conscious? Does consciousness play a special role in physics at all?

Modern theories suggest that the Universe really is unimaginably large — perhaps it's infinite, but even if it's not, it's so large it may as well be. But does this sheer scale affect how we reason about cosmology? In this video interview, we talk to David Wallace to find out more.

Quantum mechanics seems to suggest that passive observation is impossible: the very act of looking at something can change what's being looked at. In this video interview, we talk to David Wallace and Adrian Kent to find out more.

*Women of Mathematics*photo exhibition.

Holly Krieger works in dynamical systems theory, in particular on chaotic systems. Some of her greatest mathematical moments have come from teaching students.

Julia Gog is a mathematical biologist, helping to understand how infectious diseases spread. One of her favourite eureka moments came while she was playing a computer game.

Nilanjana Datta works in quantum information theory. She loves how mathematics can describe nature simply and elegantly.