A realistic cosmological model based on observations and some theory developed over the last 90 years

This article is the written version of the closing talk presented at the conference `A Century of Cosmology' held at San Servolo, Italy, in August 2007. I focus on the prospects of constraining fundamental physics from cosmological observations, using the search for gravitational waves from inflation and constraints on the equation of state of dark energy as topical examples. I argue that it is important to strike a balance between the importance of a scientific discovery against the likelihood of making the discovery in the first place. Astronomers should be wary of embarking on large observational projects with narrow and speculative scientific goals. We should maintain a diverse range of research programmes as we move into a second century of cosmology. If we do so, discoveries that will reshape fundamental physics will surely come.