how bizarre is our universe? the past the future black hole evaporation dark energy what caused the...
TRANSCRIPT
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How bizarre is our universe?
• The Past
• The Future
• Black Hole Evaporation
• Dark Energy
• What Caused the Big Bang?
• The Multiverse
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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.)
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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
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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.
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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)
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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.
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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.
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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.
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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.
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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)
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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
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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
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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
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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
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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?
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Timeincreasesupwards
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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).
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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
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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:
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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.
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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
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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?
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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!)
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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.
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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?
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What caused the Big Bang?
• Currently (always?), science runs out of answers to “why?” questions at this point.
• But cosmologists have lots of ideas!
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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.
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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)
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A two-dimensional cylinder looks like a1-dimensional line if the width of the
cylinder is much smaller than its length
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With 6 or 7 dimensions, you get weirder geometric shapes, but the idea is the same:
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A point in spacetime would not be t,x,y,zbut t,x,y,z,a,b,c,d,e,f & maybe g
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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)
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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
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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?
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What caused the Big Bang?
• Did the Big Bang occur as a quantum fluctuation in another universe?
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Quantum energy fluctuations = quantum mass fluctuations
= quantum spacetime fluctuations
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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!)
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Wormhole in spacetime
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What caused the Big Bang?
• We don’t know! (Yet…)
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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)
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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.
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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!
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Is any of this testable?
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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)
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Just how bizarre is our universe?
• The Multiverse: regions of eternal inflation separating island universes where inflation stopped?
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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?
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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).
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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!