THE STATE OF THE COSMOS OR BETTER, THE STATE OF COSMOLOGY — SOME THOUGHTS

Abstract

Two standard models have now emerged: the standard model of particle physics and the standard model of cosmology. (Unfortunately, both terms, “standard” and “model”, are rather misleading, the results of history.) Some students recently asked if they are of the same status. They are not, as surely everyone here knows, particularly the observational cosmologists in the audience. In spite of the fabulous success of the standard model of cosmology, there is a sense of unease. After all, dark energy was largely unexpected and has proved to be an embarrassment for particle theory. Let us recall a fundamental principle of cosmology, namely the Gamow principle: “If you understand physics at the energy scale E, then you could describe the universe at temperature E”. There is also a corollary: “If you don’t, then you could only speculate”. Thus for example, we certainly have a detailed understanding of the physics at the energy scale of the order of the decoupling temperature and so we could claim to understand the universe at decoupling. While the Gamow principle is obviously true, many particle theorists apparently need to be reminded of it from time to time. One nagging problem in cosmology is due to those colorless individuals with no character and personality who could blend in anywhere, namely the annoying yet well-beloved scalar fields. We could use these “fields without qualities” to do practically anything we want. They fit in anywhere. They could drive inflation. They could account for dark energy, and perhaps even dark matter. They have become the workhorses of theoretical cosmology. Perhaps we should feel a bit uneasy?