cosmology - How necessary is inflation given the laws of physics?

How deeply is cosmic inflation required for the laws of physics? Is inflation required for a universe remotely like ours, or is it simply a contingent on the starting conditions of the universe?

For example, is time as we experience it a byproduct of inflation, something that could not exist without it?

The (limited) research I've done seems to suggest that inflation is deeply embedded in the laws of physics, but I don't really understand that. If it is so, how can our part of the universe not expand (within a galaxy), yet the laws of physics still apply here?

Answer

Time has nothing to do with inflation. Clocks would tick even if the universe had not inflated.

Inflation is not “deeply embedded” in the laws of physics. You can have the Standard Model and a Big Bang based on General Relativity without having inflation.

Inflation is an ad hoc add-on to cosmological models to explain certain features of our universe — such as its homogeneity, isotropy, flatness, lack of magnetic monopoles, etc. — that would be hard to understand without it. Most inflationary models uses a so-far-unobserved scalar “inflaton” field to cause a brief period of inflationary expansion. We know that scalar fields exist (the Higgs field is scalar) and they can have the negative pressure that is required for inflation. Thus many physicists see inflation as fitting comfortably and plausibly into existing ideas about particle physics and cosmology, but inflation is not required by them.

Addendum for @safesphere: A scalar Higgs field is a critical part of the Standard Model of particle physics. With this field, the model is in impressive agreement with all observations of electromagnetic, weak, and strong interactions between various particles at, say, the Large Hadron Collider. Without it, the model utterly fails. For mainstream physicists, this evidence more than suffices to consider the Higgs field to “exist”. Whenever a physicist says “X exists”, she means “A model with X in it works really well to explain what we observe”.