ELI5: Explain Like I'm 5

Scale factor (cosmology)

Scale factor is a number used in cosmology (the study of the universe) to measure how big the universe is at different times. Think of it like a scale on a map: if you multiply your scale factor by the size of the universe, you can see how big it is at that time. For example, if the scale factor is 4, then the size of the universe would be four times larger than it was before!
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