From lesson 1, any measurement of the speed of light will yield about 1 foot per nanosecond. Based on the Nostromo-Sulaco example from lesson 2, the spacecrafts' crews will conclude the following:
According to Nostromo's crew, the distance traveled by their own light beam during a mirror-to-mirror "roundtrip" is shorter than the corresponding roundtrip distance traveled by the moving Sulaco's beam. Sulaco's (moving) light clock takes longer to generate one "tick" than Nostromo's (stationary) light clock. The moving clock ticks more slowly than their own clock.
According to Sulaco's crew, the distance traveled by their own light beam during a mirror-to-mirror "roundtrip" is shorter than the corresponding roundtrip distance traveled by the moving Nostromo's beam. Nostromo's (moving) light clock takes longer to generate one "tick" than Sulaco's (stationary) light clock. The moving clock ticks more slowly than their own clock.
Nostromo's cook has programmed the ship's clock to initiate the autobreakfast galley sequence each time a number of ticks corresponding to 24 hours has passed since the previous breakfast. Crew members are very fond of waffles, and will become so upset if their waffles are late that they will explode the ship in protest. Fortunately, the clock is very accurate (breakfast always arrives just as hungry, sleepy crew members arrive at the galley), so the mutiny-free ship continues its journey undisturbed.
Sulaco's cook has programmed the ship's clock to initiate the autobreakfast galley sequence each time a number of ticks corresponding to 24 hours has passed since the previous breakfast. Crew members are very fond of pancakes, and will become so upset if their pancakes are late that they will detonate the ship in protest. Fortunately, the clock is very accurate (breakfast always arrives just as hungry, sleepy crew members arrive at the galley), so the mutiny-free ship continues its journey undisturbed.
Nostromo's crew observes Sulaco's crew as the ships pass each other. Not realizing that the constancy of the speed of light has unusual consequences, Nostromo crew members observe that pancakes on Sulaco are slow to arrive. They are puzzled to see Sulaco (and its sluggish crew) intact, many breakfasts into the long voyage.
Sulaco's crew observes Nostromo's crew as the ships pass each other. Not realizing that the constancy of the speed of light has unusual consequences, Sulaco crew members observe that waffles on Nostromo are slow to arrive. They are puzzled to see Nostromo (and its sluggish crew) intact, many breakfasts into the long voyage.
There is nothing special about either ship which could ever allow us to identify one of them as the ship that's "really" at rest. (They're deep in space, coasting in freefall.) Crew members will see nothing unusual happening on their own ship: breakfasts arrive on time, and so forth.