I got the answer, after all this so-called time. It iis "evanescent waves". I want to know if they PAY someone to coe up with these remarkable phrases.

"For every burst of sound, there must exist a sound that bursts in reverse, according to the theory of time reversal acoustics. From their discoveries of some surprising characteristics of mediums and frequencies, scientists have gained insight into acoustic time reversal, which could impact applications such as sending confidential messages in cryptography.

Time-reversed focusing is based on the fact that when a wave is played backwards in time, wavelengths will retrace their paths. Although theoretically the overlap should be exact, the actual time reversal mirrors (TRMs) that play back the waves can not "catch" every frequency of the original wave. Scientists know that some media allow acoustic time reversal to occur with higher resolution than other media, and recently physicists from the University of Paris have discovered how disordered and ordered media affect this resolution.

In a study published in Physical Review Letters, physicists A. Tourin, F. Van Der Biest and M. Fink have found that, while sound waves traveling through a disordered medium can focus with high precision, waves traveling through an ordered medium do not have the same ability to focus. The team was also surprised to discover that for a certain type of wave called evanescent waves, an ordered medium exhibits better time compression than a disordered medium. "

'Course waves don't play backwards in time -- if you play an LP backwards, you get to the beginning later than when you were at the end. So maybe they never tried the "Paul is Dead" number when they were kids. Or forgot, or something.

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