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Aeon is a registered charity committed to the spread of knowledge and a cosmopolitan worldview. Our mission is to create a sanctuary online for serious thinking.

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The ‘mountain or valley’ illusion

4 minutes

Why can concave surfaces look convex when viewed from overhead (and vice versa)?

Mountain or valley? Concave or convex? Why is it so difficult to tell the difference when you’re viewing a surface from directly overhead? This short animation from MinutePhysics details how this perceptual illusion is explained by our natural conditioning to the Earth’s most powerful light source – the Sun – which has trained us to perceive light as always being on top and shadows as always being on the bottom.

Video by MinutePhysics

Support Aeon

Ideas can change the world

Aeon is a registered charity committed to the spread of knowledge and a cosmopolitan worldview.

But we can’t do it without you.

Aeon is a registered charity committed to the spread of knowledge and a cosmopolitan worldview. Our mission is to create a sanctuary online for serious thinking.

No ads, no paywall, no clickbait – just thought-provoking ideas from the world’s leading thinkers, free to all. But we can’t do it without you.

Become a Friend for $5 a month or Make a one-off donation

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