Chapter 8 - The Physics of the Very Large

Question 1

3-D space and 4-D spacetime

Answer 1

Time in 4D space can only move in one direction; an event can be specified by its 3D location in space plus position in time

Question 2

Perception and measurement of time

Answer 2

For societies closer to nature, time is circular and there is no history, only natural rhythms and cycles
Cyclic time different from circular, patterns recur but never repeated precisely, so time spirals
Whether perceived in straight line or spiraling cycles, still has definite direction

Question 3

Processes that create arrow of time

Answer 3

Second law of thermodynamics (chaos)
self-organization/evolution (complexity)
Electromagnetic radiation (light and radio waves - always spreads out as it travels
Big bang

Question 4

Relativity of space and time

Answer 4

Time varies between observers depending on where they are and how they’re moving
Time runs slower close to massive body
Speed of light is absolute, nothing can travel faster; we can’t access our past or future even though everything that happens is spread along time dimension of 4D spacetime
Only objects without mass, such as photons of light, can attain speed of light

Question 5

Spacetime

Answer 5

There is nothing but spacetime and motion within it; electromagnetism (has gravitational effects on particles) and gravity (has electromagnetic effects) are waves and energy (mass) is curvature; time itself is an illusion

Question 6

Matter

Answer 6

concentrated energy, experienced wherever spacetime is sharply curved
Doesn’t have precise location in space, nor is it a clear identity independent of all other objects - waves and curves of spacetime twist and overlap and interact with each other, forming interdependent whole; everything is present everywhere and everywhen

Question 7

Gravity

Answer 7

Gravitational pull of earth around sun is actually twist in spacetime following curved lines of space around twist, which is itself moving around a larger curve