Measurment that proves that the universe is flat

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Discussion Overview

The discussion revolves around the methods used to determine the curvature of the universe, particularly focusing on the angular size of temperature fluctuations in the cosmic microwave background radiation. Participants explore the implications of these measurements for understanding whether the universe is flat, positively curved, or negatively curved.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether the proof of zero curvature requires light rays to be parallel, noting that in a positively curved universe, rays converge, while in a flat universe, they should remain parallel, and in a negatively curved universe, they diverge.
  • Another participant mentions that while the universe may be flat, local gravitational effects can curve light rays.
  • A participant seeks clarification on whether the measurement of apparent size of temperature fluctuations is local or global in nature.
  • One participant argues that the absence of visible curvature does not prove the universe is flat but sets an upper limit on curvature in a specific direction.
  • Several participants express confusion about why a specific angular size of temperature fluctuations is used as evidence for flatness, questioning both the proof and its limitations.
  • Another participant emphasizes that proofs are not applicable in physics in the same way as in mathematics, suggesting that theories can only be shown to fit evidence well rather than being proven definitively.
  • One participant expresses a desire to understand the underlying logic and thought process behind the arguments regarding curvature, rather than seeking definitive proof.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of proof in physics and the implications of angular size measurements for curvature. There is no consensus on whether these measurements definitively prove the universe's curvature or not, indicating ongoing debate and uncertainty.

Contextual Notes

Participants highlight the complexity of interpreting measurements of cosmic phenomena and the influence of local gravitational effects on light propagation. There are unresolved questions about the definitions and assumptions underlying the measurements discussed.

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?
 
Last edited by a moderator:
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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.
 
Last edited by a moderator:
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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