SPIDER: Imaging the birth of the universe from 38,000 meters above Antartica

On March 17th 2014, Harvard University and the BICEP2 experiment issued a press release titled "First Direct Evidence of Cosmic Inflation", claiming the first detection of primordial gravitational waves. If correct, this detection would both prove the inflationary cosmological paradigm, and provide the first ever image of gravitational waves. It was an obvious Nobel prize candidate. However, other researchers quickly demonstrated that the BICEP2 signal was polluted by local radiation from our own Galaxy. A combined Planck+BICEP2 analysis the following year showed that at least a dominant part of the signal was due to vibrating dust grains in the Milky Way. The search therefore continues. Among the most promising experiments is SPIDER, BICEP2's sister project. Both SPIDER and BICEP2 aim to detect the imprint of inflationary gravitational waves on the cosmic microwave background radiation. SPIDER employs the same type of detectors as BICEP2, but instead of measuring from the ground, mount them on a stratospheric balloon to reduce atmospheric loading and thereby instrumental noise. The first flight was successfully concluded in January 2015, with a second scheduled for December 2019. However, already the current observations will provide maps with the same sensitivity per area as BICEP2, but covering 7% of the sky rather than just 1%. SPIDER therefore has great potential to either detect or significantly constrain primordial gravitational waves. Researchers at the University of Oslo plays an important role in the SPIDER collaboration through our focus on global analysis of complementary CMB experiments. The combination of different data sets is essential to distinguish between cosmological valuable signals and contamination from our galaxy, the Milky Way. During the last year, UiO researchers have developed an innovative algorithm for joint analysis of data from the ESA-funded Planck satellite and from SPIDER. The first results from this work are expected toward the end of 2020.

SPIDER er et Princeton-ledet eksperiment som leter etter signaturen av gravitasjonsbølger som ble skapt rett etter Big Bang. Disse målingene utføres med ultra-sensitive bolometere. Denne sensitiviteten er nødvendig for å måle det svake signalet, men den gjør også at dataene er svært utsatt for forurensning fra ikke-kosmologiske kilder. Hoveddelen av arbeidet som har funnet sted siden observasjonene ble tatt i 2015 har dreid seg om å forstå disse usikkerhetene, og utvikle stadig bedre algoritmer for å ekstrahere det kosmologiske signalet fra rå-dataene. Resultatene som vil publiseres mot slutten av 2020 vil sette en øvre grense på gravitasjonsbølger fra Big Bang som vil være blant de sterkeste i verden. Dette arbeidet har også bygget opp essensiell erfaring med bolometere i Norge. Dette har bidratt til at UiO nå er i ferd med å ta en sentral rolle i analysen av både ESAs Planck og JAXAs LiteBIRD.

On March 17th 2014, Harvard University and the BICEP2 experiment issued a press release titled "First Direct Evidence of Cosmic Inflation", claiming the first detection of primordial gravitational waves. If correct, this detection would both prove the inflationary cosmological paradigm, and provide the first ever image of gravitational waves. It was an obvious Nobel prize candidate. Prof. Clem Pryke noted in the press release that "This has been like looking for a needle in a haystack, but instead we found a crowbar." However, other researchers quickly demonstrated that the signal did indeed look more like iron than gold. A combined Planck+BICEP2 analysis this year showed that at least a dominant part of the signal was due to vibrating dust grains in the Milky Way. The search therefore continues. Among the most promising experiments is SPIDER, BICEP2's sister project. SPIDER employs the same type of detectors as BICEP2, but mount them on a stratospheric balloon to reduce atmospheric loading and thereby instrumental noise. The first flight was successfully concluded in January 2015, with a second tentatively scheduled for 2017. However, already the current observations will provide maps with the same sensitivity per area as BICEP2, but covering 7% of the sky rather than just 1%. The projected 3-sigma constraint on the tensor-to-scalar ratio is 0.03 before foreground marginalization, dramatically improving on the BICEP2 results. However, due to severe delays, SPIDER is in critical need for additional analysis manpower and expertise. Oslo has therefore very recently been invited to join the experiment by Prof. Bill Jones (PI), to focus on low-level processing, component separation and parameter estimation. This is a truly unique window of opportunity for Norway to participate in a world-leading - and possibly Nobel-prize winning - CMB B-mode experiment in the coming years. Securing funding for this effort is the primary goal of the current application.