It is going to be removed from the bottle if and when SETI succeeds in its mission to detect radio signals transmitted by an extraterrestrial intelligence. Hence, if you were to keep a careful watch on the cork, and one day saw it popping from the bottle, you could infer that an extraterrestrial intelligence exists. The configuration of the cork is what experimentalists call a ‘proxy’: a physical variable which can be measured as a way of measuring another variable. (All scientific measurements involve chains of proxies.) Thus we can also regard the entire Arecibo observatory, including its
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