20 January 2015


In general relativity, bodies always follow straight lines in four-dimensional space-time, but they nevertheless appear to us to move along curved paths in our three-dimensional space. This is rather like watching an aeroplane flying over hilly ground. Although it follows a straight line in three-dimensional space, its shadow follows a curved path on the two-dimensional ground.
— from A Brief History of Time by Stephen Hawking (1988)

Image: The Chocolate Hills, Bohol by P99

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