adventures with the one-point distribution function
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Adventures with the One-Point Distribution
Peter Coles
Castiglioncello, Italy1st September 2015
Lecture 1Probability
“The Essence of Cosmology is Statistics”
George McVittie
1 May 2023
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…
1 May 2023
Direct versus Inverse Reasoning
Theory (, 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 PhasesΔT (θ,φ )T
=∑∑ a l,mY lm (θ,φ )
ml,ml,ml, ia=a exp
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)(
)(1lim
xfxF
dxd
x
n
n
abzzG
xaszX
expexp)(
)Pr( max
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?
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