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this post was submitted on 23 Nov 2023
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It wasn't a beam, it was a single particle slamming into the atmosphere. When it comes to particles like this, it's yes/no on whether they arrive. They don't lose energy as they travel.
As for the source, it would have been energetic to say the least. Less sterilising planets and more eating large stars like smarties.
Amusingly the actual energy was around 4 joules. An obscene energy for a particle, but tiny on human standards. (About 1 second of phone battery usage)
Yea, "beam" was a misnomer from my side. I basically meant "whatever part from that source hit us". It could just be an absolute singular event, accellerated by a cosmic cataclysm or doing a swing-by maneuver around an event horizon. I simply assumed an omnidirectional source.
They don't? As my physics teacher once said: "Gravity does not sleep." Any particle with mass interacts with the rest of the Universe (within limits, OK), so it can be assumed that it actually lost energy on the way. Which, in a way, makes it even more scary.
The "far away" thing was about particles spreading to the law of square, and how many of those particles near the source where they would be much more common could do to whatever had been there. Imagine something like Earth getting hit by, e.g. a bucket full of this "stuff".
4J is a lot for a single particle, where one usually thinks in multiples of 1.6x10⁻¹⁹J...
Agreed on all points.
The gravity drag would be tiny however. The gravitational gradient in deep space is tiny, it's being dragged forward almost as much as backwards. Further, (with a 2 mass approximation) it's reliant on both masses. The equivalent mass of a photon is via E = MC^2 . Therefore M=E/C^2 . Plug the numbers and this Uber photon weighs 4.45x10^-17 kg. Stupidly huge for a subatomic particle, stupidly tiny for a relativistic mass.
Depending how far it's travelled, it likely has more loss from the universe expanding. Unfortunately, I can't remember the equations for that however.
The main point is that, beyond these effects, there is no slowdown. It either flies at full speed, or hits something and creates a cascade of far slower (boring) particles.
Thanks! I learned a lot in this discussion!