Adventures with the
One-Point Distribution
Peter Coles
Castiglioncello, Italy
1st
September 2015
Lecture 1
Probability
“The Essence of
Cosmology is Statistics”
George McVittie
September 1, 2015
SAY “PRECISION
COSMOLOGY”
ONE MORE TIME…
Precision Cosmology
“…as we know, there are known knowns;
there are things we know we know. We also
know there are known unknowns; that is to
say we know there are some things we do not
know. But there are also unknown unknowns
-- the ones we don't know we don't know.”
Questionable Aspects of the
Standard Cosmology
•General Relativity
•Cold Dark Matter
•Cosmological Constant
•Cosmological Principle
•Primordial Gaussian fluctuations
•Inflation
•Baryons
•Neutrinos
•Radiation…
Ingredients of the Standard
Cosmology
•General Relativity
•Cold Dark Matter
•Cosmological Constant
•Cosmological Principle
•Primordial Gaussian fluctuations
•Inflation
•Baryons
•Neutrinos
•Radiation…
September 1, 2015
Direct versus Inverse
Reasoning
Theory
(Ω, H0…)
Observations
Cosmology is an exercise in data compression
Cosmology is a massive
exercise in data
compression...
….but it is worth looking at
the information that has
been thrown away to check
that it makes sense!
“If tortured sufficiently, data
will confess to almost
anything”
Fred Menger
A)!|P(MM)|P(A ≠
Beware the Prosecutor’s
Fallacy!
Weirdness in Phases
ΔT (θ,φ )
T
=∑∑ al,m Ylm(θ,φ)
| | [ ]ml,ml,ml, ia=a φexp
For a homogeneous and isotropic Gaussian
random field (on the sphere) the phases are
independent and uniformly distributed. Non-
random phases therefore indicate weirdness..
Edgeworth Expansion
This is useful for many things, but does not guarantee
that the result is a proper probability distribution!
Extreme Value Statistics
(exact)
Given the distribution of X, what is the
distribution of Xmax?
[ ]
[ ] 1
21max
1max
)()()(
)(
)Pr(.....)Pr()Pr()Pr(
).....sup(:}{
−
=⇒
=
≤××≤×≤=≤
=
n
n
n
ni
zFznfzg
zF
zXzXzXzX
XXXX
Extreme Value Statistics
(asymptotic)
For any distribution of exponential type, in the sense that
Then there is a stable asymptotic distribution
0
)(
)(1
lim =




 −
∞→
xf
xF
dx
d
x



















 −
−−→
∞→∞→≤
n
n
a
bz
zG
xaszX
expexp)(
)Pr( max
PDF
Waizman, Ettori &
Moscardini, 2011
arXiv:1105.4099See
also: Colombi et al.
2011; Davis et al. 2011
etc
These use alternative
parametrisations
Conclusions
• The success of the standard cosmology is
very constraining…
• But while we may have less freedom than
we did 30 years ago, we do have one thing
that we didn’t have then: DATA!
• Might there be things lurking in data we
already have?

Adventures with the One-Point Distribution Function

  • 1.
    Adventures with the One-PointDistribution Peter Coles Castiglioncello, Italy 1st September 2015
  • 2.
  • 3.
    “The Essence of Cosmologyis Statistics” George McVittie
  • 12.
  • 13.
  • 14.
    Precision Cosmology “…as weknow, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know.”
  • 15.
    Questionable Aspects ofthe Standard Cosmology •General Relativity •Cold Dark Matter •Cosmological Constant •Cosmological Principle •Primordial Gaussian fluctuations •Inflation •Baryons •Neutrinos •Radiation…
  • 16.
    Ingredients of theStandard Cosmology •General Relativity •Cold Dark Matter •Cosmological Constant •Cosmological Principle •Primordial Gaussian fluctuations •Inflation •Baryons •Neutrinos •Radiation…
  • 21.
  • 22.
  • 23.
    Cosmology is anexercise in data compression Cosmology is a massive exercise in data compression... ….but it is worth looking at the information that has been thrown away to check that it makes sense!
  • 24.
    “If tortured sufficiently,data will confess to almost anything” Fred Menger
  • 25.
    A)!|P(MM)|P(A ≠ Beware theProsecutor’s Fallacy!
  • 28.
    Weirdness in Phases ΔT(θ,φ ) T =∑∑ al,m Ylm(θ,φ) | | [ ]ml,ml,ml, ia=a φexp For a homogeneous and isotropic Gaussian random field (on the sphere) the phases are independent and uniformly distributed. Non- random phases therefore indicate weirdness..
  • 37.
    Edgeworth Expansion This isuseful for many things, but does not guarantee that the result is a proper probability distribution!
  • 38.
    Extreme Value Statistics (exact) Giventhe distribution of X, what is the distribution of Xmax? [ ] [ ] 1 21max 1max )()()( )( )Pr(.....)Pr()Pr()Pr( ).....sup(:}{ − =⇒ = ≤××≤×≤=≤ = n n n ni zFznfzg zF zXzXzXzX XXXX
  • 39.
    Extreme Value Statistics (asymptotic) Forany distribution of exponential type, in the sense that Then there is a stable asymptotic distribution 0 )( )(1 lim =      − ∞→ xf xF dx d x                     − −−→ ∞→∞→≤ n n a bz zG xaszX expexp)( )Pr( max
  • 40.
  • 47.
    Waizman, Ettori & Moscardini,2011 arXiv:1105.4099See also: Colombi et al. 2011; Davis et al. 2011 etc These use alternative parametrisations
  • 48.
    Conclusions • The successof the standard cosmology is very constraining… • But while we may have less freedom than we did 30 years ago, we do have one thing that we didn’t have then: DATA! • Might there be things lurking in data we already have?