“DISJOINT · 2010. 11. 5. · Microsoft PowerPoint - Ppt0000003.ppt [Read-Only] Author: george...
Transcript of “DISJOINT · 2010. 11. 5. · Microsoft PowerPoint - Ppt0000003.ppt [Read-Only] Author: george...
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radiation epoch
matter epoch
dark energy epoch
Big Bang/Inflationary Picture
big bang
inflationary epoch
“DISJOINT”
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Great explanatory power:
horizon – flatness – monopoles – entropy
Great predictive power:
Ωtotal = 1nearly scale-invariant perturbationsslightly red tiltadiabaticgaussiangravitational wavesconsistency relations
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Inflation: How does it work?
V
φ
1)(
)(2
21
2
21
−≈+−
=φφφφ
V
Vw
&
&
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
Analyzing inflation in a simple, model-independent way
“survival of the smallest”
How inflation flattens and smoothes the universe
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
Analyzing inflation in a simple, model-independent way
“survival of the smallest”
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
Analyzing inflation in a model-independent way
“survival of the smallest”
HtetaG
a
aH ~)(inflaton
2
2
3
8⇒
== ρπ&
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How inflation creates a nearly scale-invariant spectrum of density perturbations:
Minkowski fluctuations scale invariant cosmic perturbations
begin with fluctuations in the scalar fieldon length scales small compared to H-1
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(Planck units: 8πG=1)
)1(23 w+≡ε
1with~ /1 <εεta
M = mass scale for inflation (ρ ~ V(φ) ~ M4)
= equation of state (w = p/ρ)
N = number of e-folds of inflation remaining
Analyzing inflation in a model-independent way
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Scalar field fluctuationsbecome fluctuations in time when inflation ends
which become temperature fluctuations
whose amplitude is determined by M and ε
t
t
t
tt
T
T δδδ~
/1
/~
2/1
2/3
tHδ~
φδφ&
H~ρ+p
H 2
~
εδ 2
~M
T
T
φ&
2
~H
ρρ+p
~
gaussianadiabatic
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( ) 1~ −−=
== ee
a
a
t
t
H
H N
endend
end ε
ε
taaHandta εε /1/~ /1 =≡ &Recall:
What do we know about ε ?
And inflation ends after N e-folds. That means:
Nor 1~ε 22
2
8~~~ MNMM
T
T
εδ
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ερ
εδ
~~2M
T
T 2/)1(~
−snk
kd
dns
ln
/ln2~1
ερ−
Nd
d εε ln2~ +−
ερ 2/1~ a
from before:
N/1~ε
spectral tilt ns ?
N
3~ −
N
I eaHk −~~
95.0~sn Also predicts the “run”
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AG2 ~ H2 ~ ρ ~ M4
What does inflation predict aboutGravitational wave (tensor) fluctuations
Many authors have claimed: because the amplitude depends on M4
it can vary by many orders of magnitude…
so no clear target for experiment
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εδ 2
5 ~10~M
T
T −!!10~ 4/12/5 ε−⇒ M
Flaw: The mean square scalar fluctuation amplitudeis ALSO proportional to M4
So we know the scale of inflation:
For ε ~ 1/N, M ~ 10-3
(and making it smaller requires extraordinary fine-tuning)
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scalar
tensorr ≡
ε/#
4
4
M
M=
N
1616 == ε
%27~16
16N
r == ε
Flaw: The mean square scalar fluctuation amplitudeis ALSO proportional to M4
ε#=
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Great explanatory power:
horizon – flatness – monopoles – entropy
Great predictive power:
Ωtotal = 1nearly scale-invariant perturbationsslightly red tilt (ns ~ 0.95)
adiabaticgaussiangravitational waves (r ~ 27%)consistency relations
-
???
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1) Fine-tuning problem?
2) So many models, many with differing predictions!
Two views of inflation:
a) a theory how the universe was made featureless (smooth, flat,) -- namely, by a period of smoothly varying accelerated expansion (with smoothly varying w and H)
b) Anything goes: any kind of accelerated expansion produced by a scalar field and a potential
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“the classic perspective”
dominantly a classical process…
an ordering process…
in which quantum physics plays a small but important perturbative role
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“the (true) quantum perspective”
Inflation is dominantly a quantum process…
in which (classical) inflation amplifiesrare quantum fluctuations…
resulting in a peculiar kind of disorder
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Lecture 2
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The “classic” picture we present to the public…
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… but the truth is:
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Linde, Linde, Mezhlumian, PRD 50, 2456 (1994)
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• Unpredictability Problem
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Maybe string theory will save the day?
Energy Landscape – vacua w/different properties
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The Anthropic Principle?
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• Maybe we can find a measure that explains why our universe is more probable?
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• Source of the Problem: Inflation is too powerful for our own goodInflation is too powerful for our own good
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• Source of the Problem: HHsmoothing smoothing > H> Hnormal normal >> H>> Htodaytoday
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• But what if HHsmoothing smoothing << H<< Hnormalnormal ??
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How do we go from small H to large H ?
ερπ 2)(4 HpGH −=+−=&
Hsmooth small and contracting!
but then how do we smooth ?!
Of course, then big bang not the beginning!
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
Recall how inflation worked:
Expanding universe: “survival of the smallest”
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
“survival of the largest”
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
“survival of the largest”
)1(3
0
38
++a
G φρ
πw
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
“survival of the largest”
)1(3
0
38
++a
G φρ
πw w >> 1
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
)1(3
0
38
++a
G φρ
πw w >> 1
A NEW NON-INFLATIONARY SMOOTHING MECHANISM: no acceleration; not after the big bang; not superluminal; not nearly de Sitter; …
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
)1(3
0
38
++a
G φρ
πw w >> 1
and no chaotic mixmaster behavior …
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
)1(3
0
38
++a
G φρ
πw w >> 1
and Hsmooth << Hnormal …
What if the universe is contracting?
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( )inflaton3
8382
26
2
4
0
3
0
... ρπσρρπ G
a
k
aaa
G rmH +−+++=
)1(3
0
38
++a
G φρ
πw w >> 1
and makes scale-invariant fluctuations!!
What if the universe is contracting?
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Nearly scale-invariant density perturbations?the reverse of inflation
H-1 ~ t and a(t) ~ t1/ε with ε >> 1 and t 0-
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εε11
)(~~)( 1−Htta
)1(23 w+≡ε
expanding contracting
:1≈sn
scale-invariant fluctuations?
approach: quantum fluct. exit horizon & re-enter later
ε << 1 ε >> 1 (or w >> 1)
ε < 1 ε > 1
Nd
dns
εε
ln21 −−=−
dN
dns
εε
ln21 +−=−
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εε11
)(~~)( 1−Htta
)1(23 w+≡ε
expandingε < 1
contractingε > 1
:1≈sn ε << 1
Nd
dns
εε
ln21 −−=−
dN
dns
εε
ln21 +−=−
“dual”ε 1/ ε
ε >> 1 (or w >> 1)
scale-invariant fluctuations?
approach: quantum fluct. exit horizon & re-enter later
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Ekpyrotic contraction
ek-pyr-o-sis: (Gr.) conflagration
Heraclitus
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How to get w >> 1 ?
“branes”
1)(
)(2
21
2
21
+>>+−
=φφφφ
V
Vw
&
&
V
φ
Y = distance = e cφ
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“bang”
radiation
matter
dark energy
“ekpyroticcontraction”
“crunch”
The Cyclic Model of the Universe
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radiation epoch
matter epoch
dark energy epoch
Big Bang/Inflationary Picture
big bang
inflationary epoch
“DISJOINT”
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t
Richard Tolman
size ofthe universe
What about the Tolman Entropy Problem?
Or violating the laws of thermodynamics?
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How can we distinguish whichmodel is right?
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• Hsmoothing is exponentially different
• w is orders of magnitude different
Curiously, precision tests can distinguish the two key qualitative differences
between inflation and ekpyrotic/cyclic models
gravitational waves
local non-gaussianity
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“non-gaussianity generated when modesare outside the horizon (“local” NG)
ζ ~ (δρ/ρ)2 = ζ L + fNL ζL23
5
MaldacenaKomatsu & Spergel
ε~NLf
9110 −>>+ observed
NLf (WMAP5 team)
27147 +>>+ observed
NLf (Yadav & Wandelt)
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What is at stakeWhat is at stakeWhat is at stakeWhat is at stake
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our vision is limited:our vision is limited:our vision is limited:our vision is limited:
the future is bleakthe future is bleakthe future is bleakthe future is bleak
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what we see is atypicalwhat we see is atypicalwhat we see is atypicalwhat we see is atypical
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Landscape of Possibilities ?Landscape of Possibilities ?Landscape of Possibilities ?Landscape of Possibilities ?
. . . or the End of Science ?. . . or the End of Science ?. . . or the End of Science ?. . . or the End of Science ?
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our vision extends beyond the big bang:our vision extends beyond the big bang:our vision extends beyond the big bang:our vision extends beyond the big bang:
the future is hopefulthe future is hopefulthe future is hopefulthe future is hopeful what we see is typicalwhat we see is typicalwhat we see is typicalwhat we see is typical
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Appendix IThe discussion of the cyclic modelwas only the tip of the iceberg:
Some interesting topics we did not discuss:
Getting through the bounce(non-singular vs. singular bounces)
How cycling might address the cosmological constant problem
The axion problem and how cycling might address itConversion of scalar fluctuations to temperature
fluctuations from 4d and 5d point of view(entropic mechanism)
Generation of scalar-induced gravitational waves
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Appendix IISome References
More efficient than going to the arXiv:Check my website
www.physics.princeton.edu/~steinhto find to a collection of articlesranging from popular to advanced:
I might recommend: “The Cyclic Model Simplified”
See also recent review article by Jean-Luc Lehner(bit more technical, but more up-to-date:
a lot of progress has been made in just the last year)
For popular discussion of both inflation & cyclic:Endless Universe by Neil Turok and myself
(almost all the ideas but no equations)
An interesting variant by Khoury, Ovrut & Buchbinder isCalled the “new ekpyrotic model”
(look on the arxiv)