Puzzle 19: Relativity and Space-Time

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Across
  1. 5. – Infinite density point in a black hole.
  2. 7. – Length shrinks at high speed.
  3. 9. – Theory by Einstein explaining space and time.
  4. 10. – Three-dimensional extension.
  5. 12. – Region of intense gravity.
  6. 13. – The universe.
  7. 16. – Measurable aspect of space.
  8. 17. – Massive star system.
  9. 19. – Combined space and time continuum.
  10. 20. – Developed the theory of relativity.
  11. 21. – Orbits a star.
  12. 22. – Relativity including gravity.
  13. 24. – Principle of general relativity.
  14. 25. – Explanation of natural phenomena.
  15. 27. – Reference frame for motion.
Down
  1. 1. – Attraction due to mass.
  2. 2. – Amount of matter.
  3. 3. – Change in position.
  4. 4. – Resistance to motion change.
  5. 6. – Point of measurement.
  6. 8. – Warping of space-time.
  7. 10. – Relativity without gravity.
  8. 11. – Maximum speed in the universe.
  9. 14. – Path around a celestial body.
  10. 15. – Time moves slower at high speed.
  11. 18. – Continuous progression.
  12. 19. – Luminous celestial body.
  13. 23. – Occurrence in space-time.
  14. 24. – Ability to do work.
  15. 26. – Boundary beyond which we cannot see.