What does it mean when we say that space-time is expanding?

When it comes to something as complex as space-time, intuition comes in different ways, depending on the level of science you have access to, writes Chanda Prescod-Weinstein

Physics | Columnist 6 July 2022

2F8Y7GF Spacetime Scifi Digital Arts concept, Twist clock time distortion warp on space bended curved as hole represent Space and Times of Einstein Theory

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THE origin story we tell about the universe goes roughly like this: there may have been a big bang (we aren’t sure), then space-time expanded extremely rapidly (we think) and has continued to expand ever since, even picking up the pace in relatively recent times (we are fairly certain). It is a nice story, and one I largely believe is true. But what does it mean when we say that space-time expanded?

In presentations to broad audiences, I explain by asking people to imagine an unfilled balloon with special dots on it. Imagine that as the balloon fills with …

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