3 ms·

If this were a scifi horror story, it would be that there was a high energy event so far away and so long ago that the protracted duration is due to red-shift.

If this were a scifi horror story, it would be that there was a high energy event so far away and so long ago that the protracted duration is due to red-shift. Those X-rays were actually unimaginably higher energy particles and the duration of the event was also brief but has gotten smeared over time by inflation.

btilly 7mo ago
That's actually not possible due to something called the GZK cutoff. Which is a weird phenomena that causes apparently empty space to turn somewhat cloudy for sufficiently high energy photons. Here is how it works. If an electron and a positron meet, they turn into two very high energy photons. Because physics is time reversible, if two high energy photons meet, they have a chance to turn into an electron-positron pair. If an extremely high energy photon meets a low energy one, there is a moving reference frame in which they have the same energy, and are both high energy. Therefore they have a chance to turn into an electron-positron pair whose center of mass is in that reference frame. The result is that if a photon is above something like 10^15 eV in energy, it can annihilate itself against any photon in the cosmic microwave background radiation (CMBR). There are lots of photons in the CMBR. Those collisions are sufficiently likely that such photons essentially cannot travel intergalactic distances. If you go back to the early universe, the CMBR was much denser than it is today. Making the distance that such photons could reasonably travel even shorter then than it is today. That said, no good storyteller should let inconvenient physical fact keep them from writing a good story.
- saltcured 7mo ago
  Does that interaction cascade such that space is effectively even more opaque as the flux increases? Or could we inlist an even more unimaginable flux of high energy photons to clear the path and allow the observed x-rays to come out the other end of the very long path..?
  - btilly 7mo ago
    My understanding is that it doesn't. Though if the energy gets high enough, you can start to get other particles out. As for protecting one photon with a sheathe of other photons, the energy density required for that tube is absolutely insane. We're talking photons spaced the width of a proton apart, with very high energy. Even assuming that it could be assembled, the gravity from the leading edge of the tube is going to do "interesting things" to the rest of the tube. Maybe even black hole levels of interesting...

btilly 7mo ago

That's actually not possible due to something called the GZK cutoff. Which is a weird phenomena that causes apparently empty space to turn somewhat cloudy for sufficiently high energy photons. Here is how it works. If an electron and a positron meet, they turn into two very high energy photons. Because physics is time reversible, if two high energy photons meet, they have a chance to turn into an electron-positron pair. If an extremely high energy photon meets a low energy one, there is a moving reference frame in which they have the same energy, and are both high energy. Therefore they have a chance to turn into an electron-positron pair whose center of mass is in that reference frame. The result is that if a photon is above something like 10^15 eV in energy, it can annihilate itself against any photon in the cosmic microwave background radiation (CMBR). There are lots of photons in the CMBR. Those collisions are sufficiently likely that such photons essentially cannot travel intergalactic distances. If you go back to the early universe, the CMBR was much denser than it is today. Making the distance that such photons could reasonably travel even shorter then than it is today. That said, no good storyteller should let inconvenient physical fact keep them from writing a good story.

saltcured 7mo ago
Does that interaction cascade such that space is effectively even more opaque as the flux increases? Or could we inlist an even more unimaginable flux of high energy photons to clear the path and allow the observed x-rays to come out the other end of the very long path..?
- btilly 7mo ago
  My understanding is that it doesn't. Though if the energy gets high enough, you can start to get other particles out. As for protecting one photon with a sheathe of other photons, the energy density required for that tube is absolutely insane. We're talking photons spaced the width of a proton apart, with very high energy. Even assuming that it could be assembled, the gravity from the leading edge of the tube is going to do "interesting things" to the rest of the tube. Maybe even black hole levels of interesting...