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gulfcoastfella

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Please don't respond with relativistic tests, as relativity doesn't deal with 4 spatial dimensions; it deals with 3 spatial dimensions and 1 time dimension.

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- Thread starter gulfcoastfella
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- #1

gulfcoastfella

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Please don't respond with relativistic tests, as relativity doesn't deal with 4 spatial dimensions; it deals with 3 spatial dimensions and 1 time dimension.

- #2

Bandersnatch

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Find out a faraway object of well-measured distance, whose size you can calculate from some well-established principles. Then measure the angular size on the 'sky' and compare with the predicted size for flat euclidean space.

If the surface is positvely curved, the angles in the triangle with vertices ABC where A is the observer and B and C are the opposite edges of the observed object, will add up to more than 180 degrees and the object will look larger. If negatively curved, it'll look smaller, and if it'll look about right it will mean that the space is flat within the error bars set by the accuracy of your measuring instruments.

- #3

gulfcoastfella

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Thanks Bandersnatch! Has an experiment been conducted to uncover the answer to this question?

- #4

Bandersnatch

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They measure Baryon Acoustic Oscillations in the CMBR. These are regions of overdensities in the early universe that left a 'footprint' on the CMBR when the photons were released ('decoupling').

See here:

http://en.wikipedia.org/wiki/Baryon_acoustic_oscillations#Cosmic_sound

for a bit more thorough explanation.

Since the size the overdensities should have can be calculated, and the distance to the surface of last scattering (CMBR emission surface) is known, they can be compared with observations.

The steadily improving observations all appear to zero in on a flat universe. Practically every year the minimum curvature radius the universe would need to have to fit the data goes up as the error bars go down. The last estimate I remember seeing was at least 220 Gly.

The most recent PLANCK results have been just released (there's a featured thread on PF), so expect further refinement of the flatness estimates.

- #5

gulfcoastfella

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