[Banthum]

In about a billion years the sun will exhaust enough nuclear fuel to cool and expand, boiling the oceans, blowing off our atmosphere, and turning Earth back into a sterile rock.

It's predicted by astronomers and physicists who study stellar evolution.

[antisthenes]

No, that doesn't happen until 5 billion years into the future.

The Sun will gradually keep getting hotter and slightly more luminous up to that point.

Earth will be a desert long before the Sun exhausts nuclear fuel to start expanding and becoming a red giant.