1. Cosmology from the Moon?
Joseph Silk
IAP/JHU/Oxford
June 22, 2017

2. Inflation? best theory so far! needs confirmation
We have made remarkable progress
in cosmology in past 100 yrs.
its now a precision science
But the big questions are unanswered
What is the matter?
Dark matter no success yet
Dark energy no prediction of deviations from L
Where do we come from?
Inflation? best theory so far! needs confirmation

3. Searching for dark matter
Oh dear, no dark matter (yet)
solar
atmospheric
NO!
Lee, S
Bartels, R
NO!
NO!

4. DARK MATTER CRISIS What if we don’t find dark matter
in the next decade(s)?
So far, modifying gravity
is ugly and doesn’t work!
Look elsewhere…….which
leads to increasingly exotic
options for dark matter, eg
primordial black holes
cross-section
particle mass

5. Where next in cosmology?
Dark matter? No detection in prospect
Dark energy? no prediction for w ≠ -1
2001
Particle Data Group 2014 Review of Particle Physics WL
2017
2017 Wm

6. THE FUTURE FOR DARK ENERGY
E-ELT
LSST
LiteBIRD
PIXIE
EUCLID
DES
JWST
KECK ARRAY

7. Where next in cosmology
Dark matter? No detection in prospect
Dark energy? no prediction for w ≠ -1
Probing inflation via CMB polarization? no lower bound! E
To B or not to B B

8. Where next in cosmology?
Dark matter? No detection in prospect
Dark energy? no prediction for w ≠ -1
Probing inflation via CMB polarization? no lower bound!
Primordial non-gaussianity: predicted by all inflation models
dT/T (1+ fNL dT/T)
fnl ~ ns-1 ~ 0.03 with Planck ns=0.96 is generic
Maldacena 2003; Cabass : ~ 0.1 (ns-1)
fnl < 10 (current limit from Planc k)
What we need: ~0.1 (optimistic); best 0.01 (vanilla inflation)
Can we improve on Planck by 1000? Very difficult!
test inflation at small scales. Bonus: probe PBH ns

9. Power spectrum: CMB vs 21cm
Sweet spot at z ~ 50 or 30 MHz
first clouds
21cm
galaxies
LSS
clusters
CMB
Kleban+ 2007
Loeb & Zaldarriaga 2003

10. Power spectrum: CMB vs 21cm
Cosmic microwave background: l ~ 103 for N ~ 106
galaxy surveys: LSST to have 1010 photometric redshifts.
N ~ 108
first clouds
21cm
21 cm in dark ages: tomography at l ~ 105: N ~ 1010 x 102
N~1012
To acquire needed N1/2 precision requires
many more modes ie few arc-sec resolution
galaxies
LSS
clusters
CMB
21 cm at z=50 means
100 km baseline + millions of 10m dipole antennae

11. 21 cm astronomy in dark ages
achieve 1000 times better precision than CMB
and 100 times better than any galaxy survey
array size l l/2p or D ~100 km for l ~ 105 at l~ 10m
need ~107 dipoles to reach ~10mK
Radio: SKA-Low2: ~106 antennae in 2025 at 30 MHz
need a quieter environment
with no ionosphere, no mobile phones… the moon?

12. Most radio-quiet environment in inner solar system
30-50 MHz is a very difficult frequency range to map from the Earth
Need to go to far side of MOON for low radio interference
Most radio-quiet environment
in inner solar system

13. Computing power
CHIME: 1015 multiplies/sec for 1024 antennae at 400 MHz (Canada)
SKA-low 105 antennae in 2025 (Australia)
LUNAR RADIO ARRAY: 1020 multiplies/sec for 106 antennae at 30 MHz
computing power achievable in 15 years from now?

14. Is this achievable? We need to try!
CMB: suborbital +space N~ fnl~10
Optical/IR galaxy surveys N~ fnl~1
far side of Moon…N~ fnl~0.1 by 2035
goal: N~1012 to probe non-gaussianity fnl~0.01
+ tomography helps! (by 100)
to seek novel signatures in the sky
the only way to falsify inflation
Is this achievable? We need to try!
Meerburg