The Universe: What We Know and What we...
Transcript of The Universe: What We Know and What we...
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Fundamental Physics
The Universe: What We Know and What we Don’t
•Cosmology•Elementary Particle Physics
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CosmologyStudy 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 PhysicsStudy 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
�Energy inversely proportional to wavelength
�
lower energy
higher energy
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Study of small distances requires high energy probes
Large Hadron Collider
Distance scale10�19 m
Energy scale103 GeV
Temperature1016 K
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Big Bang14 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 UniversePre 20th century
• Stars fixed points in space• Universe unchanging
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General RelativityEistein 1915
• Gravity due to curvature of space-time
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Friedman EquationAlexander 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⇣vr
⌘2⇠
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⇣va
⌘2=
8⇡G
3⇢m � ⇤
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Cosmological Constant
Prevents the universe from expanding (or contracting)
fudge factor
matter energy density
⇣vr
⌘2
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Hubble Expansion
The universe is expanding
Hubble 1927
distance
velo
city
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An Expanding Universe
original 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!
An Expanding Universe
original expanded by 5%
each dot represents a galaxy in the Universe
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An Expanding Universe
everyone sees the same relationship: Hubble’s Law is universal!
An Expanding Universe
original expanded by 5%
each dot represents a galaxy in the Universe
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Cosmic Microwave Background RadiationPenzias 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
H20 =
⇣va
⌘2=
8⇡G
3⇢m
⇣vr
⌘2
⌦m = 0.05
H20 / H2
0 =8⇡G
3⇢m / H2
0 = ⌦m
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Curvature2/16/16, 9:24 AMEnd_of_universe.jpg 557×501 pixels
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positive curvature
negative curvature
zero curvature (flat)
⌦K = � Kc2
R2/ H2
0
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Cosmology in 1970
1 = ⌦m + ⌦K
0.05 0.95
• Expansion dominated by negative curvature• Relatively small R
This is wrong Dark MatterDark Energy
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Dark MatterAbout 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
lensing_jpg_83751.jpg (JPEG Image, 370 × 199 pixels) http://www.naturalhistorymag.com/sites/default/files/media/2009/07/lensing_jpg_83751.jpg
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Evidence for Dark Matter (3)Bullet Cluster1e0657_scale.jpg (JPEG Image, 3000 × 2168 pixels) - Scaled (31%) https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_scale.jpg
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History and Future of the Expansion
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 EnergyRiess, Perlmutter, Schmidt 1998
Type Ia supernova
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Accelerated Expansion of UniverseHistory and Future of the Expansion
High-Z SN Search Team Supernova Cosmology ProjectRiess et al. (1998) Perlmutter et al. (1999)
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History and Future of the Expansion
different pasts and futures depend on gravity and the contents of the Universe
History and Future of the Expansion
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 = ⌦m + ⌦dm + ⌦⇤ + ⌦K
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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
⌦⇤ is constant
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20 Billion Years from Now
⇡ 0⇡ 0 0.01 0.99
Expansion completely dominated by Dark Energy
1 = ⌦m + ⌦dm + ⌦⇤ + ⌦K
⌦m =8⇡G
3⇢m ⇠ 1
a3⌦dm =
8⇡G
3⇢dm ⇠ 1
a3
constant⌦⇤ =8⇡G
3⇢⇤
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Exponential Expansion
Far in the future
⇣vr
⌘=
p⇤ v =
dr
dt=
p⇤ r
r ⇠ ep⇤ t
⌦dm = ⌦m = 0 ⌦⇤ = 1
⇣vr
⌘2=
8⇡G
3⇢⇤ = ⇤
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The Future of the UniverseA Bleak Future? Maybe, Maybe Not
why now?why so small?
a cosmological constantleads to exponential growth
but dynamic dark energy means many outcomes are possible, including a Big Crunch (recollapse) or a Big Rip (in finite time)
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 Nuclei2/29/16, 12:38 PM101087b.png 600×818 pixels
Page 1 of 1http://map.gsfc.nasa.gov/media/101087/101087b.png
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What Happened Before Recombination
10-12 s limit of our knowledge of physics1016 K
10-6 s protons and neutrons form1012 K
1 s matter anti-matter annihilate1010 K
10 s photon dominance (e+e- annihilation)1010 K
3 min nucleosynthesis109 K
4 x 105 y atoms form (CMB from this era)3000 K
What happened before 10-12 s?
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Problems with Simple Big Bang Theory
1) Where are magnetic monopoles?
2) Why is the universe so flat?
3) Why are distant parts of the universe in thermal equilibrium? The horizon problem?
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CMB
WMAP_2010.png (PNG Image, 4096 × 2048 pixels) - Scaled (26%) https://upload.wikimedia.org/wikipedia/commons/2/2d/WMAP_2010.png
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2.7 K microwave photons streaming to us from there recombination era 380,000 years after the Big Bang
non-uniformities 1 part in 105
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Inflation• Around 10-32 s universe increased
in size by more than 1026
• Doubling time 10-34 s
What was driving the exponential expansion?
not exactly zero
Current doubling time 1010 years
Cosmological constantVacuum energy
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Planck ScalePlanck’s constant (quantum mechanics):
Speed of light (special relativity):
Universal gravitation constant:
~cG
mPl =
r~cG
= 0.02 mg
EPl = mPlc2 =
r~c5G
= 1019 GeV
lPl =~
mplc=
r~cG
= 10�35 m
tPl =lPl
c=
rG~c5
= 10�43 s
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Cosmological Constant Problem
Natural value for : ⇤Planck energy in Planck cube
1019 GeV
(10�35 m)3= 10124 GeV/m3
Measured value for : ⇤ 1 GeV/m3
Off by 124 orders of magnitude!!!
Biggest mistake in all of physics!
science
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Limit of Cosmological ConstantSteven Weiberg 1987
• Calculated the upper limit of cosmological constant that would allow for us to be here.
• Larger values would cause the universe to expand to quickly for galaxies, stars, planets, life to evolve.
Calculated value in excellent agreement with the value measured in 1998
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Anthropic Principle
• The universe is the way it is because we are here
• Gives the appearance that the laws of physics are fine tuned for our existence.
• We live in a Goldilocks universe. One of a huge number of universes in which we couldn’t exist
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Multiverse
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Multiverse
Vacuum energy different in different universes
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Outstanding Problems
• Why is the vacuum energy so small?
• What is the physics at 10-35 m?
• What is the quantum gravity?
• Is there any new physics between 10-19 m and 10-35 m?
• Why are the parameters of the universe so finely tuned?
• Why is there an excess of matter over antimatter?
• Are space and time fundamental?
![Page 49: The Universe: What We Know and What we Don’tsquirrelmail.physics.rutgers.edu/quarknet/lunchtime_talks/SteveSchnetzerTalk.pdfSteven Weiberg 1987 • Calculated the upper limit of](https://reader036.fdocuments.net/reader036/viewer/2022071517/613ae827f8f21c0c8268b442/html5/thumbnails/49.jpg)
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Nima Arkani-Hamed
Lenny Susskind
Cornell Messenger Lectures