Based on my very limited knowledge, there is no way to calculate these equations exactly for the entire universe, the way they are currently formulated. Perhap

Based on my very limited knowledge, there is no way to calculate these equations exactly for the entire universe, the way they are currently formulated. Perhaps more importantly, we don't even have complete information, but only measurements that are necessarily 'averages'. We don't even have a formulation of this model that allows us to understand the 'error' in these measurements, where here error is about making future predictions based off those measurements. To use a perhaps tenuous analogy, say we have a model that describes exactly how air molecules interact with each other. We take measurements of parcels of the atmosphere and are able to describe what the molecules within are doing - pressure, temperature, humidity, etc. If we want to describe what happens to the entire atmosphere, however, we need a different model that describes how the parcels of air interact - cold fronts, wind patterns, rainfall etc. We have continuity between these two models, because as far as we can tell the way these parcels of air interact is consistent with the way individual molecules interact, but the actual models are very different to each other. With general relativity we have a model that works incredibly well for understanding how a small number of things interact with each other, and we assume that it describes the interactions of every object in the universe. We currently use the exact same model to talk about parcels of objects (eg galaxies) in just the same way as we talk about individual objects (atoms? stars?), and we don't know if that is reasonable or not. It's obviously reasonable at a small scale, as when we model things like our solar system we are accurate to an extremely high level of precision but it's not obvious that this continues to hold as we scale up. When trying to work out a weather forecast we don't simulate every single molecule, but instead large parcels of air (at a surprisingly fine level of detail, it must be said, but still relatively huge). It's not even reasonable for us to measure every single molecule, even if we had the computing power to simulate it. Even so, it is far more tractable to simulate every molecule of air in our atmosphere than to simulate GR for every body in the universe, or even every galaxy! We need a model for the interaction of large collections of objects in the universe, and at the moment the best we have is GR. What we don't have is a way of measuring how accurate that is, or even a way of formulating the model that would be consistent when applied to the kinds of collections of objects we're capable of measuring. It's possible that dark energy and dark matter are real things we can't (currently) directly observe, or they could be artefacts that arise when you try and apply GR to 'averages' of large collections of objects, but right now we don't have a way to quantify how accurate those models are in order to rule out the possibility one way or the other.