Question: I’m 15 years old. I want to know how do scientists measure the size of universe or observable universe. — Hassan
Answer: There are several techniques that astronomers use to measure distances in the Universe. Most of these distance measurement techniques build upon other distance measurement techniques, giving us a distance measurement “ladder”. There is a very nice short video explanation of how scientists measure the size of the Universe from the Royal Greenwich Observatory that really does a great job of explaining this distance ladder, and how astronomers measure the size of the Universe. If you want even more information on cosmic distances, check out Dave Goldberg’s “Ask a Physicist” column describing how we measure the size of the universe. I hope that this answers your question.