However, the exchange will likely result in the collapse of the Earth's Sun into a supernova, and possibly even turning a large part of the Milky Way into a quasar.

In Part III, the novel states that the Earth's population has been reduced to two billion people following a "Great Crisis".

It caused significant ecological damage, with all apes except for gibbons extinct outside of zoos, and technological progress being viewed with suspicion – for example, genetic engineering research is banned outright.

As this is investigated, Hallam gets the credit for suggesting that the matter has been exchanged by beings in a parallel universe; this leads to the development of a cheap, clean, and apparently endless source of energy: the "Pump", which transfers matter between our universe (where plutonium 186 decays into tungsten 186) and a parallel one governed by different physical laws (where tungsten 186 turns into plutonium 186), yielding a nuclear reaction in the process.

The development process grants Hallam high status in public opinion, winning him power, position, and a Nobel Prize.

Lamont enlists the help of Myron "Mike" Bronowski, an archeologist and linguist known for translating ancient writings in the Etruscan language, to prove his claim by communicating with the parallel world.

Rationals and Parentals can do this independently, but in the presence of an Emotional, the "melt" becomes total, which causes orgasm and also results in a period of unconsciousness and memory loss.

In the past, some triads have repeated the cycle of births (thus ensuring population growth), but the declining amount of solar radiation no longer allows that.

"Stone-rubbing" is a practice of partially melting with solid objects like rocks, possible for Emotionals, but the other genders are only capable of it in a very limited form.

The hard ones regulate much of soft one society, allocating one of each sex to a mating group called a "triad," and acting as mentors to the Rationals.

Driven by an innate desire to procreate, Tritt, the "Parental" of the triad, at first asks Odeen to persuade Dua to facilitate the production of their third child.

When this fails, Tritt steals an energy-battery from the Pump and rigs it to feed Dua, which stimulates the triad into a total melt, resulting in conception.

With the scientists' help, Denison gets access to the technology and proves that the strong force is indeed increasing, and will cause the Sun to explode.

Matter from the cosmeg starts with very weak nuclear force, and then spontaneously fuses as our universe's physical laws take over.

The exchange with the second parallel universe both produces more energy at little or no cost, and balances the changes from the Electron Pump, resulting in a return to equilibrium.

Denison catches her and forces her to admit her secret purpose: Neville thinks the momentum exchange can be used to move anything without using rockets, including the Moon itself; he wants to break away from Earth in the most complete way possible.

Denison is appalled, although he sees the potential of the technology to make travel within the Solar System easier, and to the stars possible.

[6] Asimov's short story "Gold", one of the last he wrote in his life, describes the efforts of fictional computer animators to create a "compu-drama" from the novel's second section.

Asimov took the names of the immature aliens—Odeen, Dua, and Tritt—from the words One, Two, and Three in the language of his native Russia, i.e. odin (один), dva (два) and tri (три).

Asimov reasoned that it must belong to another universe with other physical laws; specifically, different nuclear forces necessary to allow a Pu-186 nucleus to hold itself together.

He wrote down these ideas, intending to write a short story, but his editor, Larry Ashmead, asked him to expand it into a full novel.

In the story Lamont suggests that quasars are in fact parts of galaxies that have undergone sudden increase in the strength of the strong nuclear force, resulting in an explosion of fusion energy.

The character Bronowski is imagined to have solved the puzzle by considering the Basque language, which is also unique in Europe, as a relative of ancient Etruscan.

Bronowski decides to help Lamont when the president of the university refers to the language as "Itascan", confusing it with Lake Itasca.