Basic physics dictates that the first method is impossible without the use of heavy pharmaceutical aids, which is not encouraged.

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In the wacky world of quantum physics, however, it is not always impossible to work out what a particle once was but no longer is.

ECONOMIST: The arrow of time

This older technology is limited by the laws of optical physics that result in form factors that are large, heavy, and practically impossible to make into fashion eyewear.

ENGADGET: Vuzix designs Smart Glasses to look like sunshades, tout connected transparent display