The Fate of the Universe

1. The Fate of the Universe AST 112

2. First, what is Earth’s fate?

3. Fate of the Earth • Earth will become geologically dead in a few hundred million years • Will lose greenhouse gases, freeze • The Milky Way will collide with Andromeda in a few billion years • Depending on what side we’re on, we could survive • The Sun will die in 5 billion years

4. The Fate of the Universe Hot or cold?

5. Hot? • If the Universe has enough mass, everything would collapse back onto itself (“Big Crunch”) • Density and temperature would become infinite • Could start another Big Bang (maybe we’re on the 231st one?)

6. The Cosmological Constant • In a universe filled with large objects that interact gravitationally: • Everything should at least slow down, or maybe eventually collapse • Einstein assumed a static universe • Unchanging; always has existed, always will exist • He added a “fudge factor” to his equations! • Produces a small repulsive force

7. The Cosmological Constant Gmu – Lgmu = 8pTmu Cosmological Constant(Fudge factor!)

8. The Cosmological Constant • Repulsive force is so small that it wouldn’t affect gravitationally bound systems • Over large distances, it can “accumulate” and push unbound objects away

9. The Cosmological Constant • When Hubble discovered the expanding Universe, Einstein abolished the cosmological constant • But even if the Universe is expanding, it should be slowing down – according to basic physics.

10. Expansion of the Universe • Gravity weakens as it gets farther away, so the expansion may never stop • High density: can slow the expansion and reverse • Low density: expansion will slow but never stop • “Critical density”: expansion stops but does not reverse

11. The Fate of the Universe • We can see how the expansion rate has changed over time! • Hubble Constant gives measure of expansion • Measure Hubble Constant farther and farther back

12. Hubble’s Law and Type 1a Supernovae • Type 1a supernovae are reliable distance indicators • Receding velocities show that Hubble’s Law “weakens” at earlier times

13. Hubble’s Law and Type 1a Supernovae • Hubble’s Law results from expanding space • If space is expanding more, Hubble’s Law is “stronger” • If Hubble’s Law went from “weaker” to “stronger”, is space expanding at a greater or lesser rate than before?

14. Expansion of the Universe • Measuring the Hubble Constant over time shows that… The expansion of the Universe has sped up as time has progressed!

15. The Energy of Nothing • We refer to the cause of accelerating expansion as dark energy. • Dark energy could be the energy associated with nothing. • Get rid of matter, light, etc. from a region of space • The space by itself has energy

16. Dark Energy • Quantum Field Theory: • Empty space is a bunch of “virtual particles” appearing and disappearing • Cannot see them but can see their effects • Excellent agreement between theory and experiment

17. Einstein’s “Greatest Blunder” – maybe not? • Now that we see the expansion accelerating, the Cosmological Constant may have been correct after all. • Instead of holding the Universe together, the Cosmological Constant may be pushing it apart!

18. Expansion of the Universe

19. Expansion of the Universe

20. The Fate of the Universe Hot or cold?

21. Critical Density • Even ignoring dark energy: • Stars contribute 0.5% of critical density • Dark matter contributes 10x to 50x as much • Taking 50x, we’re at 25% critical density

22. Add in dark energy…We’re in for a cold, lonely end.

23. If the expansion keeps speeding up: • We will not be able to see the CMB anymore • No evidence for Big Bang • We will not be able to see galaxies anymore • Future civilizations will take their own galaxy to be the entire Universe • Expansion of space will disassemble galaxies, solar systems, and eventually atoms • This is called “The Big Rip”

24. If the expansion continues but no big rip: • Consider the star-gas-star cycle: • What gets turned into what? • What gets used up? • Can it continue forever?

25. The Fate of the Universe • With each generation of stars, mass gets “locked up” in: • Planets • Brown dwarfs • White dwarfs • Neutron stars • Black holes

26. The Fate of the Universe • About 1 trillion years from now, longest-lived stars will burn out • Galaxies will fade into darkness

27. The Fate of the Universe • The only action that can take place: two objects (e.g. brown dwarfs) collide • A star system experiences a collision every 1 quadrillion years • But over time, this will disrupt galaxies • Some objects fall into central black hole • Some get flung into inter-galactic space

28. The Fate of the Universe • So the Universe will consist of: • Black holes with 1 trillion solar masses • Scattered planets, brown dwarfs, stellar corpses • “If Earth somehow survives, it will be a frozen chunk of rock in the darkness of the expanding universe, billions of LY away from any other solid object.”

29. The Fate of the Universe • Protons eventually fall apart (1033 years) • After 1040 years, atomic matter will become radiation and subatomic particles

30. The Fate of the Universe • Stephen Hawking: Black holes slowly turn into radiation (they “evaporate”) • Largest ones will be gone after 10100 years • At that point, the universe consists of non-interacting radiation and subatomic particles • Separated by unimaginable and increasing distances

31. The Fate of the Universe Nothing new will ever happen. Pastwill be indistinguishable from the future.This is the end of time.

32. The Fate of the Universe Perhaps a Universe that ends upas essentially nothing could have begunfrom nothing?