Overall, the independence of the terms of the Drake equation is likely fairly strong. However, there are relevant size scales to consider.

• Over multiple gigaparsec scales there can not be any correlations, not even artificially induced ones, because of limitations due to the expansion of the universe (unless there are super-early or FTL civilizations).
• Over 100s of megaparsec scales the universe is fairly uniform, so any natural influences will be randomized beyond this scale.
• Colonization waves in Brin’s model could have scales on the galactic cluster scale, but this is somewhat parameter dependent.
• The nearest civilization can be expected around , where is the galactic volume. If we are considering parameters such that the number of civilizations per galaxy are low V needs to be increased and the density will go down significantly (by a factor of 100), leading to a modest jump in expected distance.
• Panspermias, if they exist, will have an upper extent limited by escape from galaxies – they will tend to have galactic scales or smaller. The same is true for galactic habitable zones if they exist. Percolation colonization models are limited to galaxies (or even dense parts of galaxies) and would hence have scales in the kiloparsec range.
• “Scars” due to gamma ray bursts and other energetic events are below kiloparsecs.
• The lower limit of panspermias are due to being smaller than the panspermia, presumably at least in the parsec range. This is also the scale of close clusters of stars in percolation models.
• Time-wise, the temporal correlation length is likely on the gigayear timescale, dominated by stellar processes or advanced civilization survival. The exception may be colonization waves modifying conditions radically.

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