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Equation 11 · Part 4 · Decoherence: The Quiet Selection That Makes the World Look Solid

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t∼1/(Λ Δx2)t \sim 1/(\Lambda\, \Delta x^2)
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What this part means

Capital delta attached to a quantity marks a difference between two values of that quantity; the article’s sign convention determines the order.

Its job in the formula

Capital delta attached to a quantity marks a difference between two values of that quantity; the article’s sign convention determines the order.

The passage around this formula

Reading a decoherence time off this table only requires the exponent above: a superposition separated by Δ\Delta x decays with a characteristic time t ∼\sim 1/(Λ\Lambda\, Δ\Delta x2x^2) . Take the largest grain delocalized over roughly its own diameter, Δ\Delta x ≈\approx 10^{-3} centimetres, and the numbers in the first column turn into times measured in seconds only in the single, almost pathologically clean case of the cosmic background radiation acting alone — about one second. Every other row is not a slower version of the same story; it is a different order of magnitude of story entirely. Ordinary air brings that same superposition down to roughly 10^{-30} seconds, and a superposition…

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Learn the underlying idea

Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.

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Sources cited in the surrounding passage

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