Download 1. What is meant by spacetime?

1. What is meant by spacetime? Whats a spacetime diagram? Whats a worldline? Whats an event?
1a. Spacetime is the combination of space and time: it is the same for all observers though space is different
for different observers and time is different for different observers. An event is an occurrence in spacetime.
A worldine is a path in spacetime connecting a series of events.
2. Draw a spacetime diagram showing you working on this worksheet for 10 minutes in Piez 329, SUNY
Oswego.
2a. This will be just a straight line on a spacetime diagram.
3. What is the equivalence principle?
3a. The effects of gravity can be mimicked by accelerating appropriately.
4. What are the characteristics of a flat, open and closed geometry for spacetime?
4a. Flat: Angles in a triangle add up to 180 degrees. Parallel lines remain parallel. The circumference of
a circle of radius r is 2πr. Open: Angles in a triangle add up to less than 180 degrees. Parallel lines
diverge. The circumference of a circle of radius r is less than 2πr. Closed: Angles in a trainagle add up
to more than 180 degrees. Parallel lines converge. The circumference of a circle of radius r is greater
than 2πr.
5. Does spacetime vary for different observers?
5a. No.
6. What is the equivalence principle?
6a. The effects of gravity can be mimicked by accelerating appropriately.
7. Spacetime is a) another name for gravity b) a curved rubber sheet c) the combination of time and the
three dimensions of space.
7a. c).
8. According to the the theory of general relativity, the Earth goes around the Sun because a) the force of
gravity makes it do so b) the Earth does this because of the curvature of spacetime caused by the Sun
c) In its own reference frame, Earth can consider itself to be stationary.
8a. b)
9. What causes spactime to curve?
9a. Mass.
10. What determines the paths of freely moving objects?
10a Spacetime.
11. In a spacetime diagram, my worldline is a vertical line. Am I moving?
11a. No.
12. In spacetime diagram, my worldline is a horizontal line. Is this sensible?
12a. No, because it means you are at many different places at once.
13. What is the precesion of the perihelion of Mercury?
13a. The movement in space of the point of closest approach of Mercury to the Sun.
14. What is gravitational lensing?
14a. The bending of light by the curvature of spacetime.
15. Which makes a bigger dent in spacetime: the Sun or the Earth?
15a. The Sun because of its greater mass.
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