Hacker News Reader

Waste heat must be radiated away, though thermodynamics would be quite content if that radiation is anisotropic.

For example, consider a perfectly insulating black box with small hole. Observers on the opposite side from the hole will not observe any radiation from the interior of the box.

I don't think there's any physical limit on collimating the outgoing radiation to hide from everyone outside a narrow beam. It's "just an engineering problem".

View on HN

Actually, I believe the law of Etendue[1] covers that. Basically, any focusing of the area of light must be balanced by a widening of the angle of that light.

1: https://en.wikipedia.org/wiki/Etendue

In terms of hiding an emitter, the relevant quantity is the beam solid angle in the far field. This is wavelength dependent which implies temperature dependence if we're talking thermal radiation.

The lower the temperature, the longer the wavelength and the wider the beam (given fixed emitter geometry). So there's a tradeoff between hiding your Dyson sphere vs extracting the most energy from the source.

Reply on news.ycombinator.com