According to the Standard Model, the elementary building blocks of nature are not particles but quantum fields, a fact that is crucial for understanding the early Universe.
With the discovery of the Higgs boson in 2012, particle physicists have now found all the elementary particles predicted by the Standard Model, effectively confirming the theory. However, with open questions still remaining about the quantum field aspects of the theory, this particular story, and its implications on our understanding of the earliest moment of the Universe, remains incomplete.
In this lecture, I explain what we mean by quantum fields and why they are so successful in describing the laws of nature. I will discuss ongoing problems and mysterious phenomena which cannot be understood purely in terms of elementary particles, concentrating on questions that are relevant for both particle physics and cosmology. These include magnetic monopoles, which are the focus of the new MoEDAL experiment at CERN, and the interplay between the Higgs field and cosmological inflation, which can be probed with future gravitational wave detectors and other cosmological observations.