The cosmological horizon — the edge of the observable Universe, which is expanding at an accelerating rate — is like a safe with a timer. Information about what crosses this boundary doesn’t vanish but returns, albeit with a delay. Physicists have figured out how long this pause lasts.
Scientists constructed a model of curved spacetime and traced the birth of a pair of quantum particles: one flies away, the other falls inward. By tracking entropy (a measure of disorder), they found that its minimum occurs after 1/8 of the horizon’s traversal time — that’s when hidden information begins to leak out, as if the safe’s door cracks open.
This process echoes the black hole paradox, first described by Stephen Hawking: it is believed that black holes also release information as they evaporate. The safe-like horizon isn’t silent: it has a temperature of about 10⁻³⁰ K, many orders of magnitude colder than any known object. Detecting this thermal “breath” is still impossible, but the calculation gives an exact time when the horizon reveals its secrets.
Our cosmological horizon is a sphere with a radius of about 46 billion light-years. Inside it lies all the matter we will ever be able to observe. Its thermal radiation is so weak that its temperature (around 10⁻³⁰ K) is trillions of times lower than that of the coldest corners of space.