the big bang theory...

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Across
  1. 2. the lightest, simplest, and most abundant element in the universe
  2. 4. the scientific study of celestial bodies—such as stars, planets, comets, and galaxies—and phenomena outside Earth's atmosphere, including their motion, composition, and evolution
  3. 5. a pioneering American astronomer
  4. 10. provided definitive evidence for the Big Bang theory in 1964 by discovering the Cosmic Microwave Background (CMB)
  5. 13. faint, nearly uniform, residual radiation left over from the Big Bang
  6. 16. a massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas, dust, and dark matter
  7. 17. a colorless, odorless, tasteless, and non-toxic noble gas
  8. 18. German-born theoretical physicist recognized as one of the most influential scientists in history
Down
  1. 1. German-American astrophysicist and radio astronomer
  2. 3. prominent British astrophysicist and mathematician
  3. 6. the complete, ordered range of all types of electromagnetic radiation
  4. 7. the total sum of all matter, energy, space, and time in existence, encompassing all galaxies, stars, and planets
  5. 8. the narrow portion of the electromagnetic spectrum detectable by the human eye, with wavelengths ranging from approximately 400 to 780 nanometers (nm)
  6. 9. the prevailing scientific model explaining that the universe expanded from an extremely hot, dense state roughly 13.8 billion years ago
  7. 11. an instrument that separates incoming radiation (such as light or sound)
  8. 12. the capacity to do work, produce heat, or cause physical change in a system
  9. 14. the stretching of light waves toward longer, redder wavelengths as an object moves away from an observer
  10. 15. a decrease in the wavelength (and increase in frequency) of electromagnetic radiation, such as light