>>10955079i think cosmological models are by far the least-well understood things in theoretical physics that normies hear about.
cosmology is very VERY poorly understood compared to say, normal astrophysics or quantum mechanics or particle physics. for sure you can expect the models to be updated.
right now the lambdaCDM model is the *simplest* best fit model to observations -- we see accelerating expansion now and so we fit a model that gives accelerating expansion. there for sure could be models with expansion that accelerates now but turns around in a few billion years, but that's not motivated by evidence. however, nothing rules it out.
even in string theory, a positive cosmological constant (a _constant_ cosmological constant, to make things crystal clear) is incompatible with string theory. (look up the "swampland conjecture"). so the top string theorists are talking about "quintessence" which would mean what we speak of as "dark energy" is really a dynamical field, which means it might not be a "constant" but turn around sooner or later.
in other words, the heat death is very speculative and even string theorists are proposing models that have the possibility to lead to many other things.
