5 ms·

> jet speed is 99.99% the speed of light Does that mean a wave of particles is coming at us right behind the light flash?

Renevith 4y ago
That was my first thought too. But even at that speed, we have quite a bit of time. Since the particles are 0.01% slower than the light that just reached us, the particles would arrive in: 8,500,000,000 light years away * 0.01% speed of light = 850,000 years. Humanity will be unrecognizable by that point.
- grayfaced 4y ago
  Wouldn't the galatic rotation mean the earth will be somewhere far away when the jet travels that far?
  - suzzer99 4y ago
    Yes, that and both galaxies careening through space on different trajectories.
  - garblegarble 4y ago
    That got me wondering how far we'd move - if my maths is correct then in 850,000 years time our solar system will have travelled 652 light years around the galactic core (230 km/sec * 850,000 years)!
    - deleted 4y ago
      [deleted]
    - d0mine 4y ago
      How wide is the beam? (given how far it started) Light-years? Is it still dangerous at this point? (If its energy is spread over a giant area radius billions light-years)
  - mynegation 4y ago
    On the flip side that also means that we might flow into a burst travelling through space without any warning (?)
- 22SAS 4y ago
  If it is 8.5 billion light years away and was traveling at the speed of light (100% instead of 99.99%) wouldn't it take 8.5 billion light years? Wonder how you got to the 850K years figure.
  - Victerius 4y ago
    By his logic, an object moving at 0% of the speed of light would arrive instantly.
    - alanbernstein 4y ago
      An object moving 0% slower than the speed of light would arrive instantly after the light arrives, yes.
  - monocasa 4y ago
    They're saying the difference between the time the light gets here and the particles 'only' going 99.9% of C is 850K years back of the napkin.
  - umvi 4y ago
    > wouldn't it take 8.5 billion [years]? Yes, if you are assuming the jet was emitted right now. But the jet was emitted roughly 8.5 billion years ago. The light in front of the jet has already reached us. If the jet were also travelling at the speed of light we'd be dead right now. But luckily it's travelling slower than light so that's why we have 850k more years before the jet reaches us.
    - darawk 4y ago
      Would we actually? If so, doesn't this imply that the probability of earth just having been destroyed by one of these things was roughly a coin flip, and therefore gives us a (much higher) rough estimate of how likely such an event might be?
    - 22SAS 4y ago
      > If the jet were also travelling at the speed of light we'd be dead right now Does that mean, once the jet reaches us 850K years from now, we can say that will be a mass extinction event, or even the end of life on Earth? Compared to a billion years from now when the Sun's luminosity increases.
- swamp40 4y ago
  A couple more 9's changes that drastically though. Maybe someone just truncated at 2 decimal places?
- deleted 4y ago
  [deleted]
- JW_00000 4y ago
  When doing such a calculation, would you need to take into account the fact that space is expanding while the particles are traveling? (And will have expanded a bit more in the time it takes for the particles to reach us than in the time it took for the light to reach us.)
twawaaay 4y ago
Not necessarily. Particles will all be charged plasma and it is possible that those will be deflected by magnetic fields. But I am not astrophysicist so you would want to check on it. Also, in contrast with the flash where all light has the same speed, the particles will have different speed so it will all be smeared in time (read -- much smaller in amplitude and hard to detect) and arriving much later than the flash. Then from the point of view of observer on Earth surface, charged particles will not be coming exactly from the source but at a bit of an angle (due to magnetic fields present). Again, I have no knowledge about the magnitude of the effect and I also suspect that the people who know this shit have some way to account for it...
cthalupa 4y ago
No. The light from these jets travels many many magnitudes farther than the actual material. You wouldn't want to be within a few million light years of it but these particles have mass and will be slowed by all of the matter they interact with in space. The vacuum of space still has roughly an atom per cubic centimeter, which really adds up over the distances we're talking about here. Edit: Left out a fairly important word. few million light years*

Renevith 4y ago

That was my first thought too. But even at that speed, we have quite a bit of time. Since the particles are 0.01% slower than the light that just reached us, the particles would arrive in: 8,500,000,000 light years away * 0.01% speed of light = 850,000 years. Humanity will be unrecognizable by that point.

grayfaced 4y ago
Wouldn't the galatic rotation mean the earth will be somewhere far away when the jet travels that far?
- suzzer99 4y ago
  Yes, that and both galaxies careening through space on different trajectories.
- garblegarble 4y ago
  That got me wondering how far we'd move - if my maths is correct then in 850,000 years time our solar system will have travelled 652 light years around the galactic core (230 km/sec * 850,000 years)!
  - deleted 4y ago
    [deleted]
  - d0mine 4y ago
    How wide is the beam? (given how far it started) Light-years? Is it still dangerous at this point? (If its energy is spread over a giant area radius billions light-years)
- mynegation 4y ago
  On the flip side that also means that we might flow into a burst travelling through space without any warning (?)
22SAS 4y ago
If it is 8.5 billion light years away and was traveling at the speed of light (100% instead of 99.99%) wouldn't it take 8.5 billion light years? Wonder how you got to the 850K years figure.
- Victerius 4y ago
  By his logic, an object moving at 0% of the speed of light would arrive instantly.
  - alanbernstein 4y ago
    An object moving 0% slower than the speed of light would arrive instantly after the light arrives, yes.
- monocasa 4y ago
  They're saying the difference between the time the light gets here and the particles 'only' going 99.9% of C is 850K years back of the napkin.
- umvi 4y ago
  > wouldn't it take 8.5 billion [years]? Yes, if you are assuming the jet was emitted right now. But the jet was emitted roughly 8.5 billion years ago. The light in front of the jet has already reached us. If the jet were also travelling at the speed of light we'd be dead right now. But luckily it's travelling slower than light so that's why we have 850k more years before the jet reaches us.
  - darawk 4y ago
    Would we actually? If so, doesn't this imply that the probability of earth just having been destroyed by one of these things was roughly a coin flip, and therefore gives us a (much higher) rough estimate of how likely such an event might be?
  - 22SAS 4y ago
    > If the jet were also travelling at the speed of light we'd be dead right now Does that mean, once the jet reaches us 850K years from now, we can say that will be a mass extinction event, or even the end of life on Earth? Compared to a billion years from now when the Sun's luminosity increases.
swamp40 4y ago
A couple more 9's changes that drastically though. Maybe someone just truncated at 2 decimal places?
deleted 4y ago
[deleted]
JW_00000 4y ago
When doing such a calculation, would you need to take into account the fact that space is expanding while the particles are traveling? (And will have expanded a bit more in the time it takes for the particles to reach us than in the time it took for the light to reach us.)

twawaaay 4y ago

Not necessarily. Particles will all be charged plasma and it is possible that those will be deflected by magnetic fields. But I am not astrophysicist so you would want to check on it. Also, in contrast with the flash where all light has the same speed, the particles will have different speed so it will all be smeared in time (read -- much smaller in amplitude and hard to detect) and arriving much later than the flash. Then from the point of view of observer on Earth surface, charged particles will not be coming exactly from the source but at a bit of an angle (due to magnetic fields present). Again, I have no knowledge about the magnitude of the effect and I also suspect that the people who know this shit have some way to account for it...

cthalupa 4y ago

No. The light from these jets travels many many magnitudes farther than the actual material. You wouldn't want to be within a few million light years of it but these particles have mass and will be slowed by all of the matter they interact with in space. The vacuum of space still has roughly an atom per cubic centimeter, which really adds up over the distances we're talking about here. Edit: Left out a fairly important word. few million light years*