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I'm reading Stephen Hawking's newest book right now, its really quite interesting. Anyone who enjoyed A Brief History of Time should definitely give it a read. Some fucking mindblowing shit in here.
"Wheeler even considered a cosmic version of the [double slit] experiment, in which the particles involved are photons emitted by powerful quasars billions of light-years away. Such light could be split into two paths and refocused toward earth by the gravitational lensing of an intervening galaxy... if we could collect enough protons from this light, they ought to form an interference pattern. Yet if we place a device to measure which-path information shortly before detection, that pattern should disappear. The choice whether to take one or both paths in this case would have been made billions of years ago, before the earth was formed... and yet with our observation in the laboratory we will be affecting that choice."
