Phase Space by Stephen Baxter
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.
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 Reid's reality begins to crumble around him. Huddling with his family, awaiting the end - or an unknown new beginning - Reid 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? 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.