Curiosidades cuánticas

Este artículo aún no está traducido al idioma seleccionado. Se muestra en un idioma disponible.

Can mirrors make a black hole immortal?

Reflecting a black hole's radiation back toward it could extend its lifetime. But even a tiny leak through the mirror can change the question of eternal survival.

Imagine surrounding a black hole with mirrors. Hawking's quantum calculation predicts that a black hole emits radiation; unless that energy loss is replenished, its mass decreases. Could mirrors prevent this loss by sending the radiation back?

The first step can work: a black hole can reabsorb returning radiation. If enough energy comes back, its net mass loss decreases. Under suitable conditions, returning its own radiation could therefore extend its lifetime.

In an ideal cavity that traps all relevant radiation, equilibrium between the black hole and the radiation can exist for suitable cavity sizes and total energies. The black hole still emits radiation, but on average absorbs just as much energy. Energy exchange continues at equilibrium.

Entropy does not automatically rule this out. A black hole has an entropy related to the area of its event horizon. When the total entropy is considered, some conditions favor a black hole coexisting with radiation. Increasing entropy does not necessarily require the black hole to disappear.

But now comes the crucial question: could the radiation also pass through the mirror? Experiments have shown that photons can tunnel through finite dielectric mirror structures and emerge on the other side.

This is where the difference between extremely small and exactly zero becomes significant. A leak that seems negligible during a short experiment can change the energy balance over a sufficiently long time. If net leakage continues without replacement energy arriving from outside, the total energy inside decreases. The black hole cannot reabsorb energy that escapes and never returns.

Mirrors therefore offer a way to potentially extend a black hole's lifetime. The same thought experiment also reveals a limit: keeping energy inside for an extremely long time does not establish that it will remain there forever.