Point two beams derived from the same source at each other, change the phase of one and see if they cancel. If they do cancel then they are waves in a medium displacing the medium as they travel. If they do not cancel then they are particle beams.
Water is H2O particles. Plenty of waves.
Space is a light medium, the double slit experiment was misinterpreted. Slow electrons was "made to interfere" in a double slit setup. Space itself squeeze through the double slit and forms the channels patterns. Only low momentum particles are channeled and spread as interference patterns on screen. Fast electrons break through everywhere and do not form interference patterns. Slow electrons stay within the space channels, at least for short distances to the screen and so form up interference patterns.
Gravity has an reverse effect on photons; pushes them away. On earth, photons tend to float up.
