It’s several hundred years in the future on earth. Humans have figured out how to become immortal by using a drug. It has been hundreds of years that anyone has died. Of course, as a result, procreation is strictly controlled.

To create new living space, humanity has outfitted an expedition to another star, Beta Hydrii, about 20 light years away, where a planet that seems very earth-like has been identified. A starship is designed that can accelerate to about one fiftieth the speed of light, a speed at which an object traverses the United States from Los Angeles to New York in one second. Even at that mind-boggling speed, the trip to Beta Hydrii takes 1,000 years.

How do you build a ship, an enclosed eco system, that lasts 1,000 years without some critical component failing? They end up with building five identical ships, basically large cylindrical objects with a diameter equal to the length of a football field or larger. Four of the ships are for habitats for about 200 people each, and the fifth as a tool ship with extra supplies, spare parts and anything else that might fail in the other four. If any of the ships fail, the population of that ship can be moved to another.

Each ship has the rough shape of a soda can and it rotates along the longitudinal axis to generate about one earth gravity in the outermost deck. Gravity decreases as you ascend toward the center. The five ships are arranged in a pentagonal pattern, with about a kilometer on edge. Now try to picture five giant rotating soda cans in a pentagonal pattern only a mile or so apart hurtling away from the sun at a speed that traverses the United States in a second, and doing that for 1,000 years. The ships are connected by shuttles that travel back and forth between them, allowing the occupants to move around.

The ships contain plants, livestock, including goats, chickens, ducks and fish, so in addition to vegetables, there is some animal diet.

The 800 people that embark on the 1,000 year journey certainly don’t think of ever coming back, no matter their immortality. But first, they are stuck in the cans for a long time.

To spend the time, they have a virtual reality machine with them. The machine allows them to immerse themselves in some other environment. Once inside, the occupant or player has no idea things are not real. The machine is connected directly to the brain and it creates an interactive “movie” involving all five senses, basically making the experience indistinguishable from reality.

The protagonist is the engineer in charge of the machine. He discovers some oddities that make him suspicious. Needless to say, some things start going wrong. Eventually it becomes clear that we, the reader, don’t really know what is real and actual, and what is virtual, and neither do the occupants. As  it turns out, the machine has put the majority of the humans to sleep using a drug that basically arrests all body functions. Time stands still while the bodies hang in weightlessness, sleeping the decades and centuries away, waiting for their eventual awakening.

And while most of the “old ones” are sleeping, some of the occupants are allowed to procreate. We get a glimpse of the journey about 100 years into the schedule. The grass and the trees are dead. The livestock gone. The ponds evaporated. There are generations of mothers walking around the ship with children in tow. Many of the newlings have never seen earth. Their entire existence has been inside the pentagon of ships in the interstellar void.

And the thing is all controlled by an apparently sentient virtual reality machine.

I enjoyed reading this book, as you may be able to tell. Haldeman tells a good story. The segments of the story when we observe travelers in the machine to the distant past, in the twentieth century (hence the title) were too long for my taste and I found myself skipping over some of the descriptions. I wanted to go on with the story. But I can handle that in a paperback just shy of 300 pages anytime.