Nuclear matter, the stuff that neutron stars are made of, is essentially a mass of neutrons packed together. It weighs millions of tons per cubic millimetre; even a microscopic quantity would be hard to keep at the Earth's surface. Last week Daedalus argued that neutron-rich material would be stable, as neutron stars are. He is now working out how to hold it against gravity.

He planned to make it by persuading the electrons of an atom to dive into the nucleus. If not all of them did this, the result would still be normal atoms, with electrons orbiting the space outside each nucleus. Each atom would be superheavy, its dense nucleus stabilized by a vast excess of neutrons. The resulting solid would be a hundred times as dense as water, and very strong. The jewel in the crown of such materials, and the strongest of them all, would be superheavy diamond.

Daedalus recalls the Eiffel Tower, which has a sharply diverging base that supports its top load. He is designing a tiny 'Eiffel Pyramid', topped with a microscopic sliver of pure nuclear matter. The wider layers beneath are dense, strong, intermediate matter; under these are wider layers of less dense matter; the broad base of the Pyramid is less dense still, the strongest normal matter. The Eiffel Pyramid could test Daedalus's bold prediction that nuclear matter should absorb neutrinos.

Normal matter is mainly empty space, so neutrinos go straight through it; indeed, billions of neutrinos a second penetrate all normal matter in every direction. Even the Sun, from which neutrinos escape so easily, has such a low density that it would float in strong potassium carbonate solution. But nuclear matter is over 1015 times denser. It should absorb the neutrino background. Indeed, black holes and neutron stars could be the only neutrino sinks known.

Daedalus would love to exploit our own neutrino background in this way. He will be alert for warming at the top of his Eiffel Pyramid of nuclear matter — a sign that neutrinos are being absorbed. How splendid it would be to capture neutrinos, the ultimate waste product of the Universe, and use their energy for our own needs. The neutrino flux would be useful even as background heating; if it generates temperatures above 100 °C it could be used to raise steam and power. Compared with the vast sums expended on the magnetic fusion reactor ITER, and the ever-receding dream of fusion power, the idea of exploiting free solar or cosmic neutrinos looks quite attractive.