The Universe: What We Know and What we Don t Fundamental Physics - - PowerPoint PPT Presentation

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The Universe: What We Know and What we Don t Fundamental Physics - - PowerPoint PPT Presentation

Aug 22, 2022 178 likes •579 views

The Universe: What We Know and What we Don t Fundamental Physics Cosmology Elementary Particle Physics 1 Cosmology Study of the universe at the largest scale How big is the universe? Where did the universe come from?

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Fundamental Physics

The Universe: What We Know and What we Don’ t

  • Cosmology
  • Elementary Particle Physics
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Cosmology

Study of the universe at the largest scale

  • How big is the universe?
  • What is the fate of the universe?
  • What is dark matter?
  • What is dark energy?
  • Are there other universes? How many?
  • Where did the universe come from?
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Elementary Particle Physics

Study of the small scale structure of the universe

  • What are the basic building blocks?
  • How do they interact with one another?
  • Is there a smallest amount of space and time?
  • Is there a theory of everything?
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Particle-Wave Duality

E ∝ 1 λ

Energy inversely proportional to wavelength λ lower energy higher energy

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Study of small distances requires high energy probes

Large Hadron Collider Distance scale

10−19 m

Energy scale

103 GeV

Temperature

1016 K

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Big Bang

14 billion years ago the universe was much denser and hotter than today Has been expanding and cooling ever since To know the state of the universe at earlier and earlier times, need to know physics at higher and higher energy scales (smaller and smaller distances)

1016 K 10−12 s

after Big Bang

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  • Physics down to a distance scale of
  • Physics down to a time of

after the Big Bang

What we Know

10−12 s

10−19 m

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How big is the universe?

We don’ t know

  • At least about 100 times larger

than the visible universe

  • Could be infinite
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Steady State Universe

Pre 20th century

  • Stars fixed points in space
  • Universe unchanging
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General Relativity

Eistein 1915

  • Gravity due to

curvature of space-time

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Friedman Equation

Alexander Friedman 1922 Applied general relativity to the whole universe What is energy density due to ?

E = mc2

about one hydrogen atom per cubic meter

1 GeV / m3

energy density

⇣v r ⌘2 ∼

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⇣v a ⌘2 = 8πG 3 ρm − Λ

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Cosmological Constant

Prevents the universe from expanding (or contracting)

fudge factor matter energy density

⇣v r ⌘2

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Hubble Expansion

The universe is expanding Hubble 1927

distance v e l

  • c

i t y

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An Expanding Universe

  • riginal

expanded by 5% each dot represents a galaxy in the Universe

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An Expanding Universe

“velocity” is proportional to distance: Hubble’s Law!

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An Expanding Universe

everyone sees the same relationship: Hubble’s Law is universal!

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Cosmic Microwave Background Radiation

Penzias and Wilson 1965 Remnant radiation (photons) left over from 380,000 years after the Big Bang Cooled from 3000 K to 2.7 K Why?

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Something Wrong

H2

0 =

⇣v a ⌘2 = 8πG 3 ρm

⇣v r ⌘2

Ωm = 0.05

H2

0 / H2 0 = 8πG

3 ρm / H2

0 = Ωm

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Curvature

positive curvature negative curvature zero curvature (flat)

ΩK = − Kc2 R2 / H2

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Cosmology in 1970

1 = Ωm + ΩK

0.05 0.95

  • Expansion dominated by negative curvature
  • Relatively small R

This is wrong

Dark Matter Dark Energy

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Dark Matter

About 80% of the matter in the universe is dark

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Evidence for Dark Matter (1)

Rotational curve of galaxy

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Evidence for Dark Matter (2)

Gravitational lensing

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Evidence for Dark Matter (3)

Bullet Cluster

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different pasts and futures depend on gravity and the contents of the Universe

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Evolution of the Universe

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Dark Energy

Riess, Perlmutter, Schmidt 1998

Type Ia supernova

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Accelerated Expansion of Universe

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different pasts and futures depend on gravity and the contents of the Universe cosmic acceleration! different pasts and futures depend on gravity and the contents of the Universe DENSITY ≠ DESTINY

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Evolution of the Universe

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Cosmology in 2017

0.05

  • Dark Energy largest contribution to expansion
  • Universe is nearly or completely flat

0.25

0.7

≈ 0

How big is the universe?

1 = Ωm + Ωdm + ΩΛ + ΩK

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Vacuum Energy

  • Dark energy is the energy of vacuum
  • It has a fixed energy density that

doesn’ t change as the universe expands

ΩΛ

is constant

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20 Billion Years from Now

≈ 0 ≈ 0 0.01 0.99

Expansion completely dominated by Dark Energy

1 = Ωm + Ωdm + ΩΛ + ΩK

Ωm = 8πG 3 ρm ∼ 1 a3 Ωdm = 8πG 3 ρdm ∼ 1 a3 constant

ΩΛ = 8πG 3 ρΛ

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Exponential Expansion

Far in the future

⇣v r ⌘ = √ Λ v = dr dt = √ Λ r

r ∼ e

√ Λ t

Ωdm = Ωm = 0 ΩΛ = 1

⇣v r ⌘2 = 8πG 3 ρΛ = Λ

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The Future of the Universe

why now? why so small? a cosmological constant leads to exponential growth more precise measurements here are still needed to help answer these questions!

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How Far Back Can We See?

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Hubble Deep Field

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Evolution of the Universe

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Abundance of Light Nuclei

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To Learn More

Nima Arkani-Hamed Lenny Susskind Cornell Messenger Lectures