Why? Couldn’t it absorb almost all energy that “touches” it? Making it impossible for us to detect the tiny amount of heat generated? Genuine question.

Energy can't disappear or be consumed - if energy doesn't get released out then it gets absorbed i.e. accumulates; if it accumulates then the Dyson sphere heats up a lot, if it heats up then it glows with blackbody radiation.

Can we detect tiny amounts of blackbody radiation? Not that such a sphere would release tiny amounts, but I'm curious about this as well.

We can detect the CMB which, using the Stefan-Boltzmann law [s-b] and a CMB temperature of 2.725 K, is about 3.12e-6 Watts/square meter. But, the CMB is pervasive. The blackbody sphere you're asking about is very far away, and the amount of power you'd receive scales like the inverse square of the distance from the sphere to us here. So forget it, the CMB's blackbody energy flux on/near Earth is ENORMOUS compared to the star's.

[s-b] https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

No; not without heating up (since the inside of the sphere can't radiate it back to the star at the center). As the sphere heats up it radiates outwards in increasingly energetic spectra. Since entropy (in this case in the form of unusable heat) always goes up, the sphere couldn't stay dark forever.

What about radiating it in a specific direction (one that just happens to be away from us)?

Heat radiates in all directions by definition.

It is theoretically possible to direct it to some extent (at the cost of raising entropy elsewhere) but it would require massive effort for no good reason.

You could never direct 100% of it, since any matter not at absolute zero has to radiate longer wavelengths.

Once you do direct it, someone will still see you if they are in the path of the beam. It appears to be an exercise in futility.

> You could never direct 100% of it

No, but you could direct enough of it that anything left is too dim to see unless you've got really good eyes ("eyes" in this case being whatever sensors we're using to detect black-body radiation).

> someone will still see you if they are in the path of the beam.

Space is big. What's the chance that we'd actually cross paths with that beam?

On the other hand, space is big. That beam would probably hit something eventually, and I suspect in that case we might pick up a reflection.

> It appears to be an exercise in futility.

Assuming the point is actually to hide. Maybe instead it's an attempt to recapture some of that energy otherwise lost as heat?

Beam it at a black hole

Hopefully it's a special kind of black hole like the one mentioned in the article. Wait...

That was one of the alternatives that I was thinking as well :)

> Why?

Physics. Entropy.

If it absorbed energy that touched it, it would heat up. You could then use the difference between it and its cooler surroundings to run an engine. Waste heat from the engine could then be absorbed to keep the engine running. You'd have created a perpetual motion machine, which is considered impossible.

But how hot does it really need to get? A solar panel doesn't heat up to sun temperatures, and a heat pump operating between the sun and the vacuum of space could be really efficient. The heat could be rejected elsewhere, no?

The important thing about space is that's there's no elsewhere.

In a closed system of a star, the sphere, and the outer space eventually energy will flow from the star to the outer space region.

There's no perfect insulation. (See also Maxwell's demon.)

Of course detection is a different matter altogether. Hiding better and better is possible. But if you really want to hide a Dyson swarm is not the best way :)

Anyone who figures out how to cheat the 2nd Law of Thermodynamics probably has no interest talking to riffraff like us. Just be glad they haven't harvested us for something and move on with your life and civilization. And whatever you do, don't make [eye] contact.