Measurment that proves that the universe is flat

AI Thread Summary
The discussion centers on understanding how the curvature of the universe is determined using the angular size of temperature fluctuations in the cosmic microwave background radiation. It raises the question of whether light rays from these fluctuations must be parallel to prove a flat universe, noting that in a positively curved universe, rays converge, while they diverge in a negatively curved one. The consensus is that while no visible curvature alone proves the universe is flat, it does set an upper limit on curvature in specific directions. The conversation emphasizes that in physics, theories are not proven but rather supported by evidence, and understanding the underlying logic is crucial. Overall, the exploration of these concepts highlights the complexity of measuring cosmic curvature.
alkmini
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hello
I have a question:
i am trying to understand how we find out that the curvature of the universe is zero using the angular size of the hot spots of the d microwave background radiation.
http://scienceblogs.com/startswithab...tire-universe/
there is a picture in this blog showing the light rays from the opposite sides of the hot spots.
My question is: doesn't the proof that the curvature is zero require that the rays are parallel to each other? If they are parallel in a positively curved universe they converge. But in a flat one they should remain parallel and in a negatively curved they should diverge. Then, in the last two cases, how do they meet in the eye?
 
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Space news on Phys.org
The universe may be flat, but locally there will be gravitational effects which curve light rays.
 
thank you for your reply mathman
when we measure the apparent size of temperature fluctuations, in order to determine the curvature of the universe, is the measurement local or global ?
 
Your link is broken.

My question is: doesn't the proof that the curvature is zero require that the rays are parallel to each other?
You can use non-parallel rays and see how the angle between them evolves. In a flat universe, it does not change, in a universe with curvature it does.

No visible curvature is not a proof that the universe is flat - that is impossible. But it set an upper limit on the curvature (at least in that direction of space).
 
i don't understand why the angular size of temperature fluctuations should be 1 degree to prove that it is flat
 
alkmini said:
the foolowing are 2 other links that say the same thing .
http://www.einstein-online.info/spotlights/cosmic_sound/?searchterm=angular size



i don't understand why it is a proof and i don't understand why it is not a proof either


Proofs are for math, not physics. NOTHING in physics is considered proven because you can never show that there will not some day be an example of it being false. The best you can do is show that a theory fits the evidence extremely well and better than anything else.
 
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well, maby it is not a proof, but this in not what i am looking for. I am just trying to understand the thought, the logic, behind what may , or may not be a proof. the insight is interesting
 

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