The starship Leonora Christine is supposed to carry its 50 colonists to a distant star. The journey should take 33 years, but due to Time Dilation at near-light speed, only 5 years will pass for the crew. Then things go to hell when the ship collides with a nebula (due to the mass of the ship and nebula at that speed, it's like hitting a solid object); the ship's decelerator system is damaged, so they can speed up (and steer) but can't slow down.note The ship will keep getting closer and closer to light-speed, reducing the passage of time onboard (their "Tau") to nearly zero. In the time it takes them to repair the damage and stop the ship, billions upon billions of years have passed and the universe is reaching the point of imploding (a "Big Crunch") and starting over with a new Big Bang.
Tau Zero provides examples of:
- Artificial Gravity: The crew experiences gravity due to acceleration, however they board the ship weightless and again when the ship ceases to accelerate while moving between galaxies.
- Casual Interstellar Travel: Leonora Christine is monstrously expensive, and will take over five years of proper time (over 30 years for the people back on Earth) to carry its 50 inhabitants to Beta Virginis.
- The Chess Master: Reymont is a mild one. A member of his secret security force theorizes that Reymont's overall plan is to eventually make everyone on the ship either an official or secret deputy, in order to make sure everyone follows the rules and has something to do. After the disaster, he explains his theory on what people see as a Reasonable Authority Figure and makes sure everyone plays their part - he'll bully people into following the rules, and the first officer will be there to listen to people complain about Reymont.
- Cool Starship: Practically the entire story takes place aboard Leonora Christine. And, let's face it, a starship that can circumvent the end of the universe has a lot going for it.
- Creator Provincialism: While Anderson is American, few of the characters are. Nationality doesn't come up much in the book, but it's established that Sweden is the dominant powernote .
- Design Student's Orgasm: The 1970 first edition paperback cover was a Kandinsky-inspired surrealist image of dots and circles, superimposed with mysterious faces and a partly-obscured topless woman. It is a legendary example of over-the-top 60s pulp SF cover art, one that has little or nothing to do with the text. The covers for later editions were considerably toned down.
- A Father to His Men: Subverted with the captain, who starts off easy going and friendly but becomes more withdrawn from the crew after the disaster.
- Faster-Than-Light Travel: The ship gets infinitely close to the speed of light, but never passes it.
- Generation Ship: Leonora Christine nearly becomes this, when the occupants realize they might be stuck in interstellar space forever without a means of slowing down.
- Inertial Dampening: At high relativistic velocities, some magical property of Anderson's universe allows for gravity nullification so that the starship can accelerate at 3g while only subjecting its passengers to 1g.
- Info Dump: Many chapters have sections where Anderson takes a break from the story to explain the theories and math behind what is going on with the plot.
- Jerk with a Heart of Gold: Reymont is very abrasive and is seen as a bully by most of the crew, but is genuinely interested in maintaining order and keeping the ship safe.
- Last of His Kind: By the end of the book the universe has died and been reborn, with the crew the only remnants of the old one.
- Latex Space Suit: While the crew doesn't wear any kind of space suit normally, when bracing for the impact of the nebula, they are all fitted with very bulky suits.
- Multinational Team: The crew is from all over the world.
- Nightmare Fuel: In-universe example. The rogue star systems in interclan space* are enough to make the crew black the windows right away.
- Ramscoop: Leonora Christine is one. It's how they get so close to the speed of light.
- Really Gets Around:
- A lot of the crew. Justified in that the situation doesn't really allow for long-term commitments. Many of the crew that fall into this category plan on settling down when they reach their destination.
- Not that monogamous procreation would be an option for several generations, with fifty individuals trying to form the genetic base for a species.
- Sci-Fi Writers Have No Sense of Scale: Anderson does understand just how big the universe is.
- Secret Police: Security officer Reymont has his known deputies, and a number of deputies that no one knows about (including other members of his covert security force). A mild case since there is no real crime aboard the ship, and the security force is just there to keep the peace when tensions get too high.
- Space Clouds: The nebulina they run into, which damages their decelerator, is more rarefied than a laboratory vacuum. It's only because they slam into it at 99.9-some-odd percent of the speed of light that it's dangerous.
- Space Friction: Which allows for infinite acceleration (but not infinite velocity).
- Space Is an Ocean: None of the sub-tropes come into play.
- Reasonable Authority Figure: Reymont explains how everyone views their immediate superior as an unreasonable authority figure, but their superior's superior as a Reasonable Authority Figure.
- Shown Their Work: See the Info Dump entry. Anderson even takes the reader through the mathematical formula for "tau". Unfortunately Anderson is also the only person on Earth who calls it tau - most others use the letter tau for proper time
, and would call Anderson's tau 1/γ. Nevertheless, it's a real relativistic quantity. - Take a Third Option: Right before breaking the news to the crew that they have no hope, someone comes up with a possible way of stopping the ship.
- Time Dilation: It keeps increasing, to the point where years are going by for every second the ship experiences.
- Wham Episode: Chapter 7 is when the disaster hits. Before that, we just got a lot of info on what the ship was doing, introducing the crew, and showing their daily lives.
