---
title: "What happens if — physics"
description: "10 what-if questions in the physics category, each labelled by how confident the answer actually is."
url: https://atoneplace.net/what-happens-if/physics/
site: "At One Place"
---

# Physics

10 questions in the physics category.

| Question | Answer | Confidence |
| --- | --- | --- |
| 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. | Established science |
| What would happen if gravity disappeared? | The Earth itself would come apart — gravity is the only thing holding a planet together. | Speculative |
| 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. | Reasoned extrapolation |
| 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. | Reasoned extrapolation |
| 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. | Reasoned extrapolation |
| 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. | Established science |
| 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. | Reasoned extrapolation |
| What would happen if you were shrunk to the size of an ant? | The square-cube law would break you: you would freeze, suffocate, and be unable to drink from a surface of water. | Reasoned extrapolation |
| 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. | Speculative |
| 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. | Reasoned extrapolation |

- [What would happen if an asteroid hit the Earth?](https://atoneplace.net/what-happens-if/asteroid-hit/) — 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?](https://atoneplace.net/what-happens-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?](https://atoneplace.net/what-happens-if/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?](https://atoneplace.net/what-happens-if/fall-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?](https://atoneplace.net/what-happens-if/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?](https://atoneplace.net/what-happens-if/travelled-at-light-speed/) — You cannot — accelerating any mass to light speed requires infinite energy. Approaching it, time dilates dramatically.
- [What would happen if gravity doubled?](https://atoneplace.net/what-happens-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 you were shrunk to the size of an ant?](https://atoneplace.net/what-happens-if/shrunk-to-ant-size/) — The square-cube law would break you: you would freeze, suffocate, and be unable to drink from a surface of water.
- [What would happen if the speed of light were slower?](https://atoneplace.net/what-happens-if/speed-of-light-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?](https://atoneplace.net/what-happens-if/gamma-ray-burst/) — 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.