The Big Bang Theory

2. The simplest and most abundant element in the universe.
4. The scientific study of celestial objects and the physical universe
5. The astronomer who discovered that the universe is expanding.
10. Partner of Arno Penzias in discovering the "echo" of the Big Bang.
13. The leftover thermal energy from the early universe that fills all space.
16. A massive system of stars, gas, and dust held together by gravity.
17. The second most abundant element in the universe, formed shortly after the Big Bang.
18. The physicist who developed the general theory of relativity.

1. Co-discoverer of the cosmic microwave background radiation using a radio telescope.
3. The simplest and most abundant element in the universe.
6. The full range of all types of radiation, from radio waves to gamma rays.
7. All existing matter, space, and time considered as a whole.
8. The portion of electromagnetic radiation that can be seen by the human eye.
9. The scientific model explaining the origin of the universe as a rapid expansion from a high-density state.
11. An instrument used to split light into its component colors for study.
12. According to Einstein, this is equivalent to mass multiplied by the square of the speed of light.
14. The displacement of spectral lines toward longer wavelengths in objects moving away from the observer.
15. The shortening of light wavelengths from an object moving toward the observer.