What would happen if you were shrunk to the size of an ant?

Scaling a body down keeps its shape and destroys its physics, because area falls with the square of length while volume falls with the cube. Surface area per unit mass therefore rises enormously, and a shrunken human would lose body heat far faster than metabolism could replace it — small mammals solve this with heart rates in the hundreds and near-continuous eating, which a scaled-down human physiology could not match. Breathing would also fail: human lungs rely on bulk airflow and a circulatory system sized for it, while insects use passive diffusion through tracheae precisely because at that scale diffusion works and pumps are unnecessary. Surface tension would dominate over weight, so water would behave like a rubber sheet and a droplet clinging to you would be genuinely difficult to escape. On the encouraging side, falls would be harmless, because terminal velocity drops with size, and relative strength would rise since muscle force scales with cross-sectional area.

How confident this is

This is a reasoned extrapolation rather than an observation. The mechanism is understood, but the scale of the consequences depends on assumptions that could reasonably be argued differently.

Physics

• What would happen if an asteroid hit the Earth? It depends enormously on size — most burn up, a 20-metre one broke windows across a city, and a 10-kilometre one ended the dinosaurs.
• What would happen if gravity disappeared? The Earth itself would come apart — gravity is the only thing holding a planet together.
• What would happen if the Sun became a black hole? Earth's orbit would not change at all — the mass would be the same. It would simply go dark and cold.
• What would happen if you fell into a black hole? Into a small one, tidal forces would stretch you apart before you arrived; into a supermassive one, you would cross the horizon without noticing.
• What would happen if you fell into a hole through the Earth? You would oscillate from one side to the other and back, with a one-way trip of about 38 minutes.
• What would happen if you travelled at the speed of light? You cannot — accelerating any mass to light speed requires infinite energy. Approaching it, time dilates dramatically.
• What would happen if gravity doubled? You would weigh twice as much, most tall structures would need rebuilding, and no bird larger than a sparrow could fly.
• What would happen if the speed of light were slower? Chemistry, nuclear fusion and the mass-energy relationship would all change — stars would not work as they do.
• What would happen if a gamma-ray burst hit the Earth? A nearby one aimed at us would strip a large fraction of the ozone layer within seconds, with the damage arriving as ultraviolet over the following years.