Is there any particle in physics that has a constant weight regardless of the environment it is in, with respect to gravity? something like light, roughly 300000000m/s always, but in terms of weight instead of speed. Everything that I have seen at this point is always relative to something its next to or something to that effect. I'm looking for something that is always the same weight with respect to gravity. I was thinking a light photon would be , from what I've seen this varies.