All measurements confirm that the universe is flat (Euclidean).
To astronomers, flat means that the usual rules of geometry are observed – light not being bent by gravity travels in straight lines, not curves. But since Albert Einstein proposed that the Universe may be “curved”, the debate has been open.
Scientific opinion has moved towards a flat Universe and the latest data confirm this with greater certainty than ever before.
The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If the universe were open, the brightest microwave background fluctuations (or “spots”) would be about half a degree across. If the universe were flat, the spots would be about 1 degree across. While if the universe were closed, the brightest spots would be about 1.5 degrees across.
Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know that the universe is flat with only a 2% margin of error.
The results of the first flight of the MAXIMA balloon-borne study of the cosmic microwave background radiation, released May 9, 2000, agree with the results of the BOOMERANG Antarctic flight, announced April 26, in the all-important conclusion that the universe is flat.