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

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

Searching for dark matter Oh dear, no dark matter (yet) solar atmospheric NO! Lee, S. + 2016 Bartels, R. + 2016 NO! NO!

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

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

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

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

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 + 2017: ~ 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

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

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

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?

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

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?

Is this achievable? We need to try! CMB: suborbital +space N~106 fnl~10 Optical/IR galaxy surveys N~108 fnl~1 far side of Moon…N~1010 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 + 2015