The Engines Stop
Time dilation, zero gravity, and first contact
Spoiler warning: this page discusses the novel's plot up to this chapter. It doesn't quote passages from the book.
The engines stop and Grace experiences weightlessness for the first time. He calculates the spin drive's enormous power, understands relativistic time dilation, and upon activating the petrovascope discovers something terrifying and wonderful: an alien ship 200 meters away.
Spin drive power: E=mc² in real time
Grace calculates: 6 g/s of astrophages × c² = 540 trillion watts. This power prevents using the petrovascope while engines are on.
The science behind it
Applying E = mc² directly: 0.006 kg/s × (3×10⁸ m/s)² = 5.4 × 10¹⁴ W = 540 terawatts. For context: all of humanity consumes about 18 terawatts. The ship produces 30 times more.
The petrovascope is tuned exactly to the Petrova wavelength (25.984 μm). But the engines ALSO emit that frequency in astronomical quantities. It's like trying to see stars at noon: the Sun eclipses them.
This "signal interference" problem is real in astronomy. Infrared telescopes can't observe near the Sun, and radio telescopes avoid terrestrial communication frequencies.
Key terms
Time dilation: 12 light-years in 3 years of coma
Tau Ceti is 12 light-years away, but Grace only experienced ~3 years of coma. Special relativity explains the difference.
The science behind it
When something travels near the speed of light, time passes more slowly for it. It's not an illusion: it's a real effect, experimentally verified with atomic clocks on airplanes and GPS satellites.
At 0.9c (90% of light speed), time dilates by a factor of ~2.3. A 12-light-year trip would feel like ~5 years. At even higher speeds, the effect is more pronounced.
The formula is: t' = t × √(1 - v²/c²). At 0.5c: factor 0.87. At 0.9c: factor 0.44. At 0.99c: factor 0.14. At 0.999c: factor 0.045.
Crucial implication: on Earth, ~13 years have passed since departure (12 light-years distance + travel time). Any information Grace sends will take another 12 years to arrive. Earth has been suffering for at least 25 years.
Key terms
Try it yourself
How to use the simulator
Special relativity says a clock moving very fast ticks more slowly than one at rest. The Lorentz factor, γ = 1/√(1 − v²/c²), tells you by how much. At everyday speeds γ is essentially 1, but it soars as you approach light speed. For several destinations, the table works out how long the trip takes on Earth and for the crew, assuming a constant cruising speed.
Controls
- Speed (% of light): move the slider to change the ship's speed and the Lorentz factor.
Things to try
- At 97% of c, γ ≈ 4.1: each year on board equals about four on Earth.
- Drop to 50%: γ is only 1.15. Dilation barely matters until you're well past half the speed of light.
- Go to 99% and check the Andromeda row: millions of years on Earth, but "only" a few hundred thousand on board.
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Open “Time dilation calculator” on its own page, with an explanation and a worked example →
Zero gravity: panic when engines stop
When engines stop, gravity (which was engine acceleration) vanishes instantly. Grace vomits and panics.
The science behind it
The engines created a force indistinguishable from gravity (Equivalence Principle). When they stop, that force vanishes suddenly. It's as if the floor disappeared beneath your feet.
The human brain has a vestibular system (in the inner ear) calibrated for Earth's gravity. Sudden loss of gravity confuses the brain: it doesn't know where "up" is. Result: nausea, disorientation, vomiting.
"Space sickness" affects about 60% of astronauts in their first days on the ISS. Over time, the brain adapts and learns to function without gravity.
Key terms
The petrovascope detects an alien ship
With engines off, Grace activates the petrovascope. He detects astrophages at Tau Ceti, then Petrova flashes that turn out to be the engines of a triangular ship 200 meters away.
The science behind it
The petrovascope uses an occulter: a metal plate blocking the star directly, just like NASA's solar coronagraphs that block the Sun's disk to see its corona.
The alien ship has a triangular shape with flat surfaces. Flat surfaces are the WORST geometry for containing internal pressure (spheres are optimal). That the ship uses flat panels implies an extraordinarily strong material.
The Petrova-frequency flashes are the ship's engines: proof that the alien ALSO uses astrophages as fuel. Two separate civilizations, the same solution.
Key terms
Worked example: fuel and thrust of the spin drive
At 6 grams per second, in a day (86,400 s) the ship turns about 518 kg of astrophage into light, and about 190 tonnes in a year. A photon rocket pushes with a force equal to its power divided by the speed of light: F = P / c = 5.4 × 10¹⁴ W / 3 × 10⁸ m/s ≈ 1.8 million newtons.
That's far less than a Saturn V at lift-off (about 35 million newtons), but the Saturn V burned over 2,000 tonnes of propellant in under three minutes. With 1.8 MN, the spin drive could accelerate a mass of about 180 tonnes at 1 g, and keep it up for years.