What Is Space?
One of the ones that gets me and may be central to <i>space</i> is the central idea in the Young&#x27;s double slit experiment, the Michelson-Morley interferometer, the Fabry-Perot interferometer, etc.  Indeed, the night I was studying for my final in optics and radiography, I thought of this stuff and never really studied for the exam!<p>So, just shine a light through a beam splitter.  So, ballpark half of the light continues on essentially straight and the other half is deflected 90 degrees.<p>Such a beam splitter is in the M-M experiment.  For the double slit, it divides the beam.  For a Fabry-Perot, it ends up making many such splits.<p>Okay, as we heard from Feynman, we could send just one photon through any of those devices and still get the same interference effects.  Feynman also explained that we&#x27;d get the same result sending one electron at a time instead of a photon.<p>So, here, to heck with recombining the beams and getting it to interfere with itself.<p>Instead, consider just the beam splitter.  So, the photon (or electron, neutron, whatever) is a wave function, and after the beam splitter that wave function is in two parts traveling apart, in the case of the photon, if we add a mirror to have the two halves going in opposite directions, at the speed of light.<p>But such splits of the wave function happen at every window pane, no doubt in every water droplet, etc., that is happen all the time.<p>And such a wave function doesn&#x27;t split just once but commonly many times.  So, the one, poor photon as one simple wave function is soon in dozens of pieces all moving away from each other usually never to come together again.  After a billion years, the pieces are still moving away from each other.<p>Then, presto, bingo, one part of that wave function enters our telescope and hits our detector.  Then all the dozens of pieces of that wave function, scattered across a billion light years, have to disappear, instantly, since with two telescopes we can never get two detections from the one photon.<p>Well, that&#x27;s tough to believe.<p>So, maybe the universe is filled with tiny pieces of wave functions condemned to go on forever.  Maybe that&#x27;s the dark matter?