Equation 3 · Part 4 · Comparing the Main Approaches to Precision Cosmology
√
√
What this part means
Take a square root.
Its job in the formula
Take a square root.
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The passage around this formula
The second, quieter disagreement is the S8 tension. S8 is a combination of the amplitude of matter density fluctuations and the matter density parameter , defined as . Weak gravitational lensing surveys — which measure the distortion of background galaxy shapes by intervening matter, and therefore probe how clustered matter actually is in the late universe — have historically reported S8 values a few percent below what Planck’s early-universe fit predicts [ 7 ] . This tension has been smaller and less consistent across surveys than the Hubble tension; the 2025 KiDS Legacy reanalysis, notably, shifted upward into consistency with Planck, while DES’s Y6…
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A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.
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