The Ultimate Fate of the Universe

Cosmological Structure

-Infinite universe: no boundaries to spacetime; space goes on forever

-Flat infinite universe: 3-dimensional space goes on in all directions

-Hyperbolic universe: universe is a "saddle-shaped" hyperbolic paraboloid

-Finite universe: amount of space in universe is limited

-Disc universe: there exists a 3-dimensional edge to the universe

-Spherical universe: universe shaped like a "sphere"

-Torus universe: going in a straight line eventually leads to where you began

Importance of the Universe's Composition

-Dark energy density is constant throughout space and time

-Matter (visible + dark) and radiation (light + neutrinos) spread out over time

Densities of matter and dark energy in the universe over time

Theory of the "Big Crunch"

-Universe must be closed and/or finite

-Matter/radiation concentration greater than dark energy concentration

-Gravity overpowers the force of dark energy

-Universe's expansion reverses itself

-Galaxies merge with each other

-CMB radiation rapidly heats up

-Stars "cooked" from the inside

-Atoms and their nuclei break apart

-Black holes merge and swallow everything

-Universe collapses into a singularity

The "Big Bounce" Theory

-Universe is repeating and eternal (has existed forever)

-After Big Crunch, singularity will undergo a Big Bang again

Simplified diagram of the "eternal" cyclical universe model

False Vacuum Decay

-Subcategory of "Big Rip" scenario

-There is energy within spacetime; hence "false vacuum"

-A "true vacuum" has little to no energy within space

-It likely cannot sustain atoms/molecules

-Anything with energy is "unstable"

-A quantum process may occur, lowering the energy state in a "quanta" of space

-The process spreads out at the speed of light

-Whole universe collapses into true vacuum

-Part of the universe may survive if spacetime expansion speed is greater than the speed of light

A quantum tunneling process allows a quanta of space to reach a lower energy state.

What is the "Heat Death"?

-Generally accepted concensus on the end of the universe

-Universe cannot be "closed"

-Universe must be "infinite"

-Very far into the future

-Matter/radiation to dark energy ratio must not be too high/too low

Timeline of the far future according to the "Heat Death" theory

The "Big Freeze"

-Most accepted model of the "Heat Death"

-Local galaxies merge

-larger structures fall apart

-Stars burn out

-No new stars created due to lack of nebulae

-Galaxies/star systems collapse

-White dwarfs eventually fade

-Black holes dissipate

-Atoms/nuclei eventually decay

-Nothing left except for sparcely spread particles

-Universe "temperature" approaches absolute zero

-"Big Rip" may occur in the far future

Glossary of Terms

Topology: the "shape" of the universe in higher dimensions

Spacetime: "space" and "time" combined; the "fabric" of the universe

Dark energy: a force, presumably a property of space, that works against gravity

Density: the average concentration of matter/radiation/dark energy across the universe

Hyperbolic paraboloid: a 3- or higher-dimensional shape, roughly analagous to a saddle shape

3-torus: a 4-dimensional structure formed by connecting the opposite ends of a cube

Dark matter: matter that only inteacts through gravity and emits no light; thought to account for ~90% of matter in universe

Neutrino: a particle that, like light, is a form of radiation; unlike photons of light, it has mass

Omega-M: the density of matter throughout the universe

Omega-Lambda: the density of dark energy in spacetime

Big Crunch: a hypothetical event where the universe collapses into a singularity

Singularity: a structure of infinitesimal size and infinite density, such as a black hole

CMB radiation: Cosmic Microwave Background; radiation produced by the Big Bang

Big Bounce: a model of the universe where a Big Crunch is followed by another Big Bang

Big Rip: a hypothetical event where spacetime and its contents are ripped apart by dark energy

False Vacuum: the current state of a "vacuum"; its space still contains energy

True Vacuum: a hypothetical form of space that contains very little or no energy

Quantum tunneling: a spontaneous "teleportation" on the quantum scale to a different location/state of existence

False Vacuum Decay: an event where a true vacuum is produced via quantum tunneling, and spreads at the speed of light in all directions

Big Freeze: the generally accepted theory of how the universe will end; everything reaches equilbrium and energy transfer becomes impossible