From what i understand, one argument for a flat universe is the fact that the sum of the angles of a cosmic triangle is more or less equal to 180 degrees. What i don’t understand is how we calculate the angles. Most of what I’ve read online state that since we can measure the 3 sides of the cosmic triangle, we can use trigonometry to calculate the angles. But doesn’t the fact that we are using trigonometry to calculate the angles already presume the universe is flat rather than proofs it?
In: Planetary Science
You are completely correct that knowing three sides is not at all enough. You either need to know the curvature already to get the angles (pointless!) or get one of the angles in a different way. Luckily we can: we usually take Earth as one of the 3 vertices, which means we can just measure the angle we see between the other two.
And indeed, from the 3 side lengths, 3 angles and the curvature (or alternatively the area) any 4 determine the rest, but 3 are _not_ enough.
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