In my minds' eye, I often consider gravity and photons as
   opposites. I don't know when that happened - somewhere as a
   young teenager, reading science books. But as mathematically
   incorrect as it most likely is, it works for me. Now they got
   Dark matter/energy and that's fine too. But I still gotta go
   with gravity. I'd say neutrinos (I love neutrinos because of
   their barely-there-but-everywhere-ness) 'cause they're the
   avoidant personality type like me smile emoticon but I gotta run
   with a photon <--> gravity spectrum, at least for my mental
   imagery.