I don’t exactly remember now, but the ring-building aliens ran out of space on their local planets, one way or another.
It would make sense. In the 70’s in particular people though fusion reactors were right around the corner, and were worried about the waste heat from those.
Isn’t this a major plot point in Larry Niven’s Ringworld in 1970?
it involves the Pierson’s Puppeteers
It is yes!
I don’t exactly remember now, but the ring-building aliens ran out of space on their local planets, one way or another.
It would make sense. In the 70’s in particular people though fusion reactors were right around the corner, and were worried about the waste heat from those.