Some physicists doubt on inflation evidence

Circa una settimana fa, la notizia della presunta scoperta delle “tracce” impresse nella radiazione cosmica di fondo dovute al passaggio delle onde gravitazionali primordiali ha preso d’impatto come una tempesta improvvisa il mondo dei media (post). Non solo, ma si vocifera già la nomination per il Premio Nobel al gruppo di ricercatori di Harvard che non solo avrebbero trovato la “prima evidenza diretta” del processo dell’inflazione cosmica ma anche degli indizi a supporto dell’esistenza di altri universi. Nonostante ciò, alcuni fisici stanno suggerendo di “rimettere nel frigo lo champagne”, almeno per ora.

Theoretical physicists and cosmologists James Dent, Lawrence Krauss, and Harsh Mathur have submitted a brief paper (arXiv:1403.5166 [astro-ph.CO]) stating that, while groundbreaking, the BICEP2 Collaboration findings have yet to rule out all possible non-inflation sources of the observed B-mode polarization patterns and the “surprisingly large value of r, the ratio of power in tensor modes to scalar density perturbations.”

“However, while there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves, it is important to demonstrate that other possible sources cannot account for the current BICEP2 data before definitely claiming inflation has been proved”, as stated by the authors in the paper

Inflation may very well be the cause, and Dent and company state right off the bat that “there is little doubt that inflation at the Grand Unified Scale is the best motivated source of such primordial waves“, but there’s also a possibility, however remote, that some other, later cosmic event is responsible for at least some if not all of the BICEP2 measurements. (Hence the name of the paper: “Killing the Straw Man: Does BICEP Prove Inflation?”). Not intending to entirely rain out the celebration, Dent, Krauss, and Mathur do laud the BICEP2 findings as invaluable to physics, stating that they “will be very important for constraining physics beyond the standard model, whether or not inflation is responsible for the entire BICEP2 signal, even though existing data from cosmology is strongly suggestive that it does“.

The Physics arXiv Blog: Cosmologists Say Last Week’s Announcement About Gravitational Waves and Inflation May Be Wrong
arXiv: Killing the Straw Man: Does BICEP Prove Inflation?