Astroparticle Physics

262 12 InflationFig. 12.4Measurements of the powerspectrum P(k)from several typesof observations. The curve showsthe prediction of a model with thespectral index n equal to unity. Theparameter h isassumedtobe0.72(from [42])12.10 Outlook on Inflation“The argument seemed sound enough,but when a theory collides with a fact,the result is tragedy.”Louis Nizertests of inflationdark energy nowSo far, inflation seems to have passed several important tests.Its most generic predictions, namely an energy density equalto the critical density, a uniform temperature for the observableuniverse, and a lack of relic particles created at any preinflationarytime, are well confirmed by observation. Fur-thermore, there are no serious alternative theories that comeclose to this level of success. But inflation is not a singletheory but rather a class of models that include a period ofaccelerating expansion. There are still many aspects of thesemodels that remain poorly constrained, such as the nature ofthe energy density driving inflation and the time when it existed.Concerning the nature of the energy density, it will beseen in Chap. 13 that around 70% of the current energy densityin the universe is in fact ‘dark energy’, i.e., somethingwith properties similar to vacuum energy. Data from type-Ia supernovae and also information from CMB experimentssuch as WMAP indicate that for the last several billion