"The phase space of a system is the set of all conceivable states of that system," says the first page. As with "Manifold" these stories explore possible (and significantly linked) states of Earth and the universe, alternate timelines offering different solutions to Baxter's favourite cosmological question--the Fermi Paradox.

It's a simple idea. According to our best scientific theories there's nothing special about Earth or the Solar System. Intelligent life has evolved here--ourselves. It's likely to evolve elsewhere. The skies should be full of other intelligences. Where are they?

Perhaps our theories are wrong and we're in a galactic quarantine. Perhaps what we see through our telescopes is a clever fake--but supposing we overload the capabilities of the fakers? Maybe intelligence always destroys itself before crossing interstellar space, or something kindly takes emerging life away to a safer place. Perhaps there's teeming intelligence out there, but we're not listening on the right wavelength. Perhaps they're hiding...?

Another Baxter theme revisited again in this mind-stretching collection is the high-tech romance of the space programme and walking on the Moon. Alternate histories of space exploration are deftly conjured up, some of them wonderfully paranoid. Yet another theme is deep time--the unthinkable gulf from Big Bang to the final extinction of the universe and possibilities of life at both extremes.

Baxter at his best has a bleakly lyrical view of the remote future, reminiscent of Arthur C Clarke. There are homages to other classics, including Asimov's "Nightfall" and even Dante's Divine Comedy whose final vision of paradise takes on a highly unexpected SF meaning. --David Langford

Synopsis
Tied in to Baxter's masterful Manifold trilogy, these thematically linked stories are drawn from the vast graph of possibilities across which the lives of hero Reid Malenfant have been scattered. It is the year 2025. Reid Malenfant is the commander of a NASA earth-orbiting science platform. The platform is intended to probe the planets of the nearest star system by bouncing laser pulses off them. But no echoes are returned...and Malenfant's reality begins to crumble around him. Huddling with his family, awaiting the end -- or an unknown new beginning -- Malenfant tells stories of other possibilities, other realities. The linked stories encompass the myriad possibilities that might govern our relationship with the universe: are we truly alone, or will we eventually meet other lifeforms? Perhaps intelligent species decide to turn their back on the stars, or maybe expansionist species are destined to fail. The final possibility -- that the Universe as we know it is in fact an elaborate illusion designed to protect us from the fearful reality -- is brilliantly explored in the tour de force novella that ends the volume.