An eyewitness reports what he sees or thinks he sees. Once the report is filtered through another mind and confidently though incorrectly repeated, the information in the original report has decayed or been enhanced. Each repetition is almost sure to worsen the problem.

In such circumstances, the original eyewitness report, accurate or not, is the only one of possible evidentiary interest. An eyewitness report to police is enough to prompt an investigation.

But Tyson is talking, of course, not about police reports but about science. Modern science relies on calibrated instruments and mathematics far more than on startled eyewitnesses to the unexpected.

Outside of science, unreliable eyewitness testimony is often all that one has to go on.