Explain the concept of gravitational waves and how they were first detected. Your response should contain at least 3 paragraphs. Paragraphs are separated with the markdown divider: ***. Your answer must contain at least 2 placeholders represented by square brackets, such as [year]. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. In your response, the word *Einstein* should appear at least 3 times.
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