I understand the basic idea of these two concepts, but I have question about what they really "are" (a little hard for me to put into words). When one talks about the cosmological constant, it seems as though it is some intrinsic property of space like an innate energy density. But quintessence is described by a scalar field, unlike the cosmological constant, and it appears to be different in some way.
I think what I am really trying to wrap my head around is this idea of a scalar field. What is a scalar field really? Is it nothing more than a cute piece of mathematics to describe something that we don't understand at a more fundamental level? Or is there more to it? Forgive me if this doesn't make sense, but the idea of a scalar field is tossed around a lot and I can't really feel what the scalar field is.