The massive problem of trying to fully explain what mass actually is

A simulation of gravity showing curved space-time. The ball represents the sun and is resting on a sheet of plastic that stretches under its weight. The curved sheet of plastic demonstrates the way a gravity curves space.


LAST month, I wrote about the challenge of explaining space-time. To give people a feeling for what I mean when I say that space-time is curved, sometimes I talk about a rubber sheet with a ball sitting on it. I point out that the ball causes the sheet to curve and the curvature of the sheet literally shapes where the ball will roll. I say we can think of this as an analogy for our local star – the sun – curving space-time around it. How is the sun able to do this? Because it has mass.

Increasingly, I think it …

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