Critical density

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Critical density is the value at which the Universe is at balance, and expansion is stopped. This value is estimated as (1-3) * 10^-26 kg/m^3.

This is related to the cosmic density parameter in many ways; this term describes the ratio of the actual density value of the Universe to the critical density value. If the ratio is one, then the Universe is at balance, and the Universe is flat. If the ratio is greater than one, then the actual density of the Universe is greater than the critical density, and thus the Universe will eventually become closed. If the ratio is less than one, then the actual density is less than the critical density, and the Universe is open.