The book examines some of the universe's greatest mysteries, and promotes the view that science is very important in helping to solve problems on planet Earth.

[8] The book was incomplete at the time of the author's passing in March 2018, but was completed with "his academic colleagues, his family and the Stephen Hawking Estate".

[5] The book discusses many of today's challenges, including the biggest threat to the planet (an "asteroid collision", like the one that wiped out the dinosaurs 66 million years ago ... "we have no defense" against that),[4][6] climate change ("a rise in ocean temperature would melt the ice caps and cause the release of large amounts of carbon dioxide ... [making] our climate like that of Venus with a temperature of 250 °C (482 °F)"), the threat of nuclear war ("at some point in the next 1,000 years, nuclear war or environmental calamity will 'cripple Earth'"), nuclear power ("that would give us clean energy with no pollution or global warming"), the development of artificial intelligence (AI) ("in the future AI could develop a will of its own, a will that is in conflict with ours") and humans ("a genetically-modified race of superhumans, say with greater memory and disease resistance, would imperil the others").

After discussing the inhomogeneities in the cosmic background radiation, detailed by the WMAP satellite, the book concludes "So look carefully at the map of the microwave sky.

"[11] Further, Hawking believed the universe could reach an end point, either through an eventual cosmic "crunch or an expansion" ... "In the interim ... We are all time travelers, journeying together into the future.

Focusing his attention in the book on three related questions – the future of our planet, colonization of other planets, and the rise of artificial intelligence – he charts his strategy to save us from ourselves ... Only science, Hawking argues, can save us from our mistakes ... Hawking believes that humanity's evolutionary mission is to spread through the galaxy as a sort of cosmic gardener, sowing life along the way.

He believes ... that we will develop a positive relation with intelligent machines and that, together, we will redesign the current fate of the world and of our species.

"[15] According to award-winning science editor Tim Radford, writing for The Guardian, Hawking's book is "effortlessly instructive, absorbing, up to the minute and – where it matters – witty."

The universe is the ultimate free lunch"; "our worst mistake ever" [if we are dismissive about artificial intelligence]; "Our future is a race between the growing power of our technology and the wisdom with which we use it.

Radford writes, "People who argue for good education for all, a decently funded NHS (National Health Service) and serious investment in research will rediscover him as a friend.

"[8] Reviewer Abigail Higgins, writing for Vox, notes that author Hawking, in the book, is "funny and optimistic, even as he warns us that artificial intelligence is likely to outsmart us, that the wealthy are bound to develop into a superhuman species, and that the planet is hurtling toward total inhabitability ... [the] book is ultimately a verdict on humanity's future.

"[9] According to John Horgan, science journalist writing for The Wall Street Journal, Hawking, in his book, prefers string theory as a way of explaining the "theory of everything" (which Hawking predicts to be solved by "the end of this century") and, based on quantum mechanics, considers empty space as filled with virtual particles, "popping into and out of existence", suggesting our entire universe began as one of those particles, and additionally, that our cosmos is "just a minuscule bubble in an infinite ocean, or 'multiverse'".

[19] Reviewer Zayan Guedim, commenting on EdgyLabs, writes, "The book is not a culmination of all of the great scientist's works, and it doesn't provide any particularly new discoveries.