How bizarre is our universe?

• The Past

• The Future

• Black Hole Evaporation

• Dark Energy

• What Caused the Big Bang?

• The Multiverse

Four separate forces today(t=13.75 billion years after Big Bang)

• Particle with mass? Affected by gravity.

• Particle with ‘colour charge’? Affected by strong force.

• Particle with ‘flavour charge’? Affected by weak force.

• Particle with electric charge? Affected by electromagnetic force.

• (The above is a simplification, but useful.)

Four known forces in universe:

Strong Force Electromagnetism

Weak Force

Gravity

Recall that forces unify at high temperatures

Separation of GUT force intostrong force + electroweak force releases energy

Only one force (we think)at t<10-43 seconds after Big Bang

• Particle with mass, colour, flavour or electric charge? Affected by quantum gravity force.

GUT Eralasts from Planck time (~10-43 sec) to end of GUT force (~10-38 sec). At that point, inflation occurs as the strong forces separates from gravity & releases energy (first kinetic, then thermal)

Two separate forcesat t<10-38 seconds after Big Bang

• Particle with mass? Affected by gravity.

• Particle with colour, flavour or electric charge? Affected by GUT force.

Three separate forcesat t<10-30 seconds after Big Bang

• Particle with mass? Affected by gravity.

• Particle with ‘colour charge’? Affected by strong force.

• Particle with flavour or electric charge? Affected by electroweak force.

Four separate forces today(t=13.75 billion years after Big Bang)

• Particle with mass? Affected by gravity.

• Particle with ‘colour charge’? Affected by strong force.

• Particle with ‘flavour charge’? Affected by weak force.

• Particle with electric charge? Affected by electromagnetic force.

The fate of Earth, and our universe

• 1 billion years: runaway greenhouse effect on Earth, making Earth as hot as Venus, unless something is done (for example: orbiting sunshades; changing Earth’s orbit)

• Not to be confused with ongoing greenhouse effect, which could be disastrous to many species of life on Earth, but not to Earth itself.

The fate of Earth, and our universe

• 1 billion years: runaway greenhouse effect on Earth, making Earth as hot as Venus

• 6 billion years: Sun becomes a red giant, Earth a lava planet (unless something is done)

• 8 billion years: Sun becomes a slowly cooling white dwarf, Earth a slowly cooling rock

• ~10+ billion years: Milky Way likely merges with Andromeda & other galaxies, forming a giant elliptical galaxy (call it FMW - former Milky Way; Earth’s night sky will no longer have a Milky Way)

The fate of the former Milky Way (FMW)

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• 10 trillion years: conventional star formation stops

• 100 trillion years: lowest-mass stars stop burning hydrogen (only white dwarfs & brown dwarfs left)

• 1 quadrillion (1015) years: ‘star-star’ collisions & close encounters have disrupted all solar systems

• 1020 years: ‘star-star’ collisions have ejected all ‘stars’ from galaxies or sent them into central BHs

• 1025 years: any remaining binary ‘star’ or planetary systems have merged via gravitational radiation

The fate of our universe

• 1040 years (?): protons and bound neutrons decay (?) as a probable consequence of there being more protons and neutrons than anti-protons and anti-neutrons in the universe in the first place. If such decay happens, universe left with only: photons, (anti)electrons, neutrinos, dark matter?, black holes.

• 1070 years: stellar-mass black holes start evaporating

Hawking radiation & black hole evaporation

• If nothing escapes a black hole, how can it evaporate?

• Remember quantum fluctuations: particle-antiparticle pairs can appear and disappear, as long as they last for a short enough time

Quantum fluctuations

• On the smallest possible scales, the universe doesn’t play by “normal” rules.

• Particle/antiparticle pairs can appear & disappear, if they last for a short enough time

• electron-positron pairs can last for 10-22 seconds

• proton-antiproton pairs have higher mass-energy and can last for only 10-25 seconds (at most)

• So on extremely short timescales and extremely small spatial scales, the amount of energy in existence at one time in one spot fluctuates

Hawking radiation & black hole evaporation

• If nothing escapes a black hole, how can it evaporate?

• Quantum fluctuations are stronger when gravity is stronger, and the smallest black holes have the strongest gravity at their event horizons

• So what happens if a particle and antiparticle both appear near the event horizon of a black hole, but one falls in and one flies away?

Timeincreasesupwards

Hawking radiation & black hole evaporation

• If nothing escapes a black hole, how can it evaporate?

• Quantum fluctuations are stronger when gravity is stronger, and the smallest black holes have the strongest gravity at their event horizons

• So what happens if a particle and antiparticle both appear near the event horizon of a black hole, but one falls in and one flies away?

• Then from our point of view, the black hole has emitted a particle (or antiparticle) and has lost mass!

• So black holes should eventually evaporate (Hawking radiation not observed, but accepted).

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW (former Milky Way) beyond detection

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

• Big Rip: happens if dark energy is a ‘phantom’ energy which grows stronger with time and rips apart planets, molecules, nuclei, nucleons.

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

• Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.

• ‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

• Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.

• ‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time

• Decaying dark energy: acceleration stops, reverses?

Dark energy and the fate of our universe

• 100 billion years: acceleration of universe redshifts all light from beyond the FMW beyond detection

• Beyond that, we don’t know enough about dark energy to know what it might do. Some ideas:

• Big Rip: ‘phantom’ energy grows stronger with time and rips apart planets, molecules, nuclei, nucleons.

• ‘Standard’ dark energy yields accelerating universe but no big rip: vacuum energy is constant with time

• Decaying dark energy: acceleration stops, reverses?

• Won’t know fate of universe for sure until we understand dark energy. (If then!)

The (probable) fate of our universe

• 1040 years (?): protons and bound neutrons decay (?) as a probable consequence of there being more protons and neutrons than anti-protons and anti-neutrons in the universe in the first place. If such decay happens, universe left with only: photons, (anti)electrons, neutrinos, dark matter?, black holes.

• 1070 years: stellar-mass black holes start evaporating

• 10100 years: even the most supermassive black holes have evaporated (by Hawking radiation) at this point

• Universe is cold, dark, nearly empty.

So much for the end of the universe:the universe seems to go from

Big Bang to Big Whimper.

But what about the beginning?What caused the Big Bang?

What caused the Big Bang?

• Currently (always?), science runs out of answers to “why?” questions at this point.

• But cosmologists have lots of ideas!

What caused the Big Bang?

• Currently (always?), science runs out of answers to “why?” questions at this point.

• But cosmologists have lots of ideas!

• Conservation of energy: The universe’s positive kinetic & mass-energy plus its negative potential energy (gravitational, electroweak, and strong-force) can sum to zero.

What caused the Big Bang?• Currently (always?), science runs out of answers to “why?”

questions at this point.

• But cosmologists have lots of ideas!

• Conservation of energy: The universe’s positive kinetic & mass-energy plus its negative gravitational, electroweak, and strong-force potential energy can sum to zero.

• Superstrings: in this currently popular theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)

• Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny rolled up or 'compactified' space dimensions)

A two-dimensional cylinder looks like a1-dimensional line if the width of the

cylinder is much smaller than its length

With 6 or 7 dimensions, you get weirder geometric shapes, but the idea is the same:

A point in spacetime would not be t,x,y,zbut t,x,y,z,a,b,c,d,e,f & maybe g

What caused the Big Bang?

• Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)

• Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)

What caused the Big Bang?

• Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)

• Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)

• M-theory (M for membrane, a 2-D string) predicts 11 dimensions, with the 11th reached only by gravity

What caused the Big Bang?

• Superstring theory might unify gravity and quantum mechanics. In this theory, all particles are actually vibrating 1-dimensional strings of the minimum possible size: the Planck length (10-33 cm)

• Superstring theory predicts there are 10 dimensions, not four (1 time, 3 space, and 6 very tiny ‘compactified’ space dimensions)

• M-theory (M for membrane, a 2-D string) predicts 11 dimensions, with the 11th reached only by gravity

• Big Bang caused by (mem)branes colliding in that 11th dimension? Cyclic Big Bangs?

What caused the Big Bang?

• Did the Big Bang occur as a quantum fluctuation in another universe?

Quantum energy fluctuations = quantum mass fluctuations

= quantum spacetime fluctuations

What caused the Big Bang?

• Did the Big Bang occur as a quantum fluctuation in another universe?

• …or did the universe create itself? (Quantum fluctuations at the Planck length might be able to create a wormhole through which energy travels back in time 10-43 seconds to create the spacetime!)

Wormhole in spacetime

What caused the Big Bang?

• We don’t know! (Yet…)

Just how bizarre is our universe?

• The Multiverse: if our universe is finite, there might be other universes beyond it (separated by regions of eternal inflation)

Duplicate universes?

• If our universe (or the multiverse) is infinite, then any part of it must eventually repeat itself.

• The consequences may argue against universe/multiverse being infinite!

• No communication between island universes, however.

Just how bizarre is our universe?• Regardless of

whether our universe is finite or infinite, quantum mechanics might allow parallel universes to exist.

• Such universe might overlap with ours yet be impossible for us to perceive!

Is any of this testable?

Is any of this testable? Yes!

• (Though not all of it, and not easily)

• Analogs to Hawking radiation exist (e.g., high acceleration substitutes for strong gravity)

• Patterns in CMBR constrain amount of inflation, cyclical Big Bang theories, bubble universes, etc.

• Quantum gravity theory would aid in understanding both general relativity (wormholes) and quantum mechanics (parallel universes) better

• Measuring history of universe’s expansion will tell us more about dark energy (e.g., Big Rip or not)

Just how bizarre is our universe?

• The Multiverse: regions of eternal inflation separating island universes where inflation stopped?

Just how bizarre is our universe?

• The Multiverse: regions of eternal inflation separating island universes where inflation stopped?

• Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop?

Just how bizarre is our universe?

• The Multiverse: regions of eternal inflation separating island universes where inflation stopped?

• Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop? Because by definition, life will develop only in universes that allow life to develop (e.g., that don’t have too much dark energy or dark matter).

Just how bizarre is our universe?

• The Multiverse: if our universe is finite, there might be other universes beyond it (eternal inflation)

• Weak Anthropic Principle: why are the physical constants of our universe just right to allow stars and planets to form and thus give life a chance to develop? Because by definition, life will develop only in universes that allow life to develop (e.g., that don’t have too much dark energy or dark matter).

• Only universes that can support life will have life in them wondering why the universe supports life!