Key Terms
Cosmology
The study of the character and evolution of the universe.
Light year
Distance light travels in one year. Used to measure galactic and intergalactic distances.
Example
Galaxy 100 Mly away moves away at ~2,000 km/s. Example: Galaxy moving at 100,000 km/s is at ~5,000 Mly (5 Gly).
Big Bang
The gigantic explosion that created the universe ~13-15 billion years ago.
Evidence
Viking probes landing on Mars produced no annihilation explosion; relative absence of 0.511-MeV gamma rays (produced by
Explanation
Particle physics is almost, but not perfectly, symmetric in matter and antimatter. The decay of certain neutral K-mesons
General Relativity
Einstein's theory describing all relative motion, including accelerated motion and the effects of gravity. Encompasses s
Quantum Gravity
The theory that deals with particle exchange of gravitons as the mechanism for the gravitational force; applicable where
Thought Experiment
Mental analysis of clearly defined situations used to develop physical ideas. Einstein relied on these heavily.
Consequence
If acceleration bends light, gravity must also bend light.
Experimental verification
During the 1919 solar eclipse, starlight passing near the Sun was deflected; the measured shift agreed precisely with Ei
Microlensing
Star brightening caused by gravitational lensing from a small body passing in front of it.
Black holes
Objects whose escape velocity exceeds c; nothing, not even light, can escape.
Event horizon
The boundary around a black hole from which nothing can escape; located at the Schwarzschild radius.
Formation
Black holes can form from supernova collapse of a massive star, producing an object ~10 km across with mass greater than