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A comment on A new Einstein cross is discovered. Parent comment

Re:A new Einstein cross is discovered by earenndil on Monday March 25, 2019 @02:43PM (#19485432)
I'm no expert (so correct me if I'm wrong), but from what I'm read, flat, concave, and convex universes are all possibilities and they would all look flat to us because our measurements take place on such a small scale.
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Re:A new Einstein cross is discovered by sandworm101 on Monday March 25, 2019 @03:15PM (#19485786)
Our measurements occur across billions of light-years. By comparing redshift agaist the standard candles we measure relative speeds of vastly distant objects. And given the speed of light, we are also measuring what those speeds were billions of years ago. It is a very big ruler.
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Re:A new Einstein cross is discovered by roywiggins on Monday March 25, 2019 @04:11PM (#19486322)
We've measured the flatness of the universe on the scale of the cosmic microwave background, which is essentially as big a ruler as could possibly exist.

https://map.gsfc.nasa.gov/mission/sgoals_parameters_geom.htm...

https://wmap.gsfc.nasa.gov/universe/uni_shape.html

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