Is there a way to know what the state of the universe is today. All observations are constrained by the time it has taken the light to reach Earth so we are observing the universe as it was millions of years ago.
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Well, on an object by object basis, assuming nothing interesting has taken place, we do have a pretty good idea how some things evolved. So say we’re looking at a star 1 billion light years away. We have a pretty good idea how that star will evolve and therefore approximately what it SHOULD look like today. But the truth is these are guesses.
We have models of the evolution of the Universe. If the natural processes are ongoing, then we can predict what we’re not yet able to observe. If there is some evil alien species going and imploding stars far away, we’ve got no way to know that.
Short answer: no.
Longer answer: “what the universe looks like today” relies on your definition of “today.” To be more specific, it relies on what is happening simultaneously across the universe. The problem is that “simultaneous” depends on your perspective. Two things that appear simultaneous to one observer might happen at different moments to another. (Example below.)
In a sense, the speed of light is really the speed of causality. What “today” means depends on where you are and how you’re moving in the universe. So all we can really use is what it looks like from here and now as restricted by the speed of light/causality.
Example: the barn pole paradox. Suppose someone is running near the speed of light towards a barn. The barn has a door at each side. From the point of view of people standing by the barn, the pole just fits inside the barn. There’s a moment where they can close the front door before the rear one opens, and the pole fits entirely in the barn. But to the person carrying the pole, the barn has shrunk in length due to relativity. So the pole is longer than the barn. So how can both doors be closed at the same time? The answer is that the runner doesn’t see the front door closing and the rear door opening as being simultaneous. Instead, the rear door appears to open first, then the front door closes.
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