Electromagnetism

You've felt this shape before — you just called it gravity.

Gravity is also, it's worth saying, pathetically weak. You overpower the entire Earth's pull every time you lift a coffee mug off the table. The force actually winning that tug-of-war — holding the mug together, holding you together — is electromagnetism.

It plays by gravity's rule with one new twist. Gravity only ever pulls. Charge does both:

• Like charges — two pluses, or two minuses — shove apart.
• Opposite charges pull together.

How does one charge reach across empty space to push another? Michael Faraday's answer was the field: every charge fills the space around it with a kind of invisible tension, and any other charge that wanders in feels it. Faraday was a bookbinder's apprentice with almost no mathematics — where everyone else saw spooky action across a gap, he saw lines of force, physical and real, threading through space. Decades later James Clerk Maxwell took those pictures and turned them into equations, and out of the equations fell something nobody expected: light itself is a ripple traveling through this very field.

The red (positive) and blue (negative) charges on the right do exactly what Faraday imagined — the little needles trace the field, and they redraw themselves the instant anything moves.