3 ms·

Indeed ultra high energy photons "decay" by interacting with the CMB.

• ben_w 5y ago
  Using the word “decay” to include that feels like it can’t be right. But I’m not a proper physicist, just an amateur.
  • cozzyd 5y ago
    Yeah, you're right, it's not the right word at all!
    • ben_w 5y ago
      Good to know — I was worried I might have stuck my foot in my mouth when I looked at your profile and saw your profession.