The Battle Against the Underdetermination of Dark Energy
Cosmological data has opened up new vistas on fundamental physics yet it is limited in its scope. While it has given us tantalizing hints at how the Universe might be expanding, it is unclear whether it can ever be used to find the microphysical structure of whatever is driving this expansion. I will discuss the evidence for what is, by far, the most thoroughly explored proposal – dynamical dark energy driven by a scalar field – pointing out what we can and cannot say about its fundamental nature. I will argue that it is unlikely (but not impossible) that it is normal quintessence, that there is strong evidence that there is some type of non-minimal coupling but which brings with it a host of undesirable consequences. I will try to look at the various loopholes and present what I think is the current status of cosmology as a probe of fundamental physics.