People used to say that's an impossible problem. Then people got to thinking about the fact that there are going to be constraints coming from some rather mundane facts -- that in principle will make the problem of deducing the phase like the solution of a solvable puzzle.

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If I set up waves with known amplitudes and synthesize them, I'll find that for essentially all random combinations of phases, the thing I get is an object not confined. It takes a very clever combination of the phases of all those waves to add up to something in only one region; and cancel out everywhere else.

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