The Planck era refers to the A) time at which the expanding universe became transparent to radiation. B) time of extremely rapid inflation that started 10^-35s after the universe began. C) first 10^-43s of time, when all four fundamental forces are believed to have been united. D) present age of the universe as given by the Hubble law.

Question

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The Planck era refers to the earliest period in the history of the universe, the first 10^-43 seconds after the Big Bang, when it is believed that all four fundamental forces (gravity, electromagnetism, strong nuclear force, and weak nuclear force) were unified into one force.

The Planck Era Refers to the