system
Given the following post, respond as if you're commenting on Reddit:
human
What triggered cosmic inflation?

As far as I know the cause of inflation is debated. Some say it is caused by a phase transition (which I didn't fully understand) which happened when the strong nuclear force separated from the electroweak force. But I also heard that that theory is old and more or less abandoned now. What is the current most accepted theory for what triggered inflation (explained in a non-techincal way)?
gpt
Inflation is driven by a scalar field called the inflaton. (A scalar field being a field that is just a number, at any point in space and instant in time). The inflaton lies initially in an excited state which gives a large constant energy density in space. This triggers a violent exponential expansion exactly like dark energy does now, but at a more dramatic scale.

As the Universe expands exponentially the total energy grows immensely, because the energy density remains constant while the volume grows.

When the inflaton switches back to its ground state, inflation ends and the energy it had is developed in the degrees of freedom we know and love, and we enter what is known as the early Universe  (radiation-dominated). The temperature is probably of order 10^(16) GeV (GUT scale), that's why one gets the prejudice inflation has something to do with grand unification (which is the unification of the three forces of the standard model).

That's the general features of inflation. The different models (i.e. chaotic inflation) propose different mechanisms or details through which the above passages happen.

Inflation is not per se concerned with the origin or nature of the inflaton. Where the inflaton comes from or what it is is a separate, but interesting question. There's many ideas about that too.