4 ms·

>When you look at all the stars in the vicinity of the sun, they move relative to the sun, the sun moves relative to them, but only one in five hundred stars in

>When you look at all the stars in the vicinity of the sun, they move relative to the sun, the sun moves relative to them, but only one in five hundred stars in that frame is moving as slow as ‘Oumuamua. You would expect that most rocks would move roughly at the speed of the star they came from. If this object came from another star, that star would have to be very special. If we're to assume that this is something that was expelled from a remote solar system, wouldn't you then also assume that there had to be some explosion or collision to get this thing on its current course? And wouldn't that account for a speed that doesn't match nearby objects?

dbingham 8y ago
But not for the odd shape, or for the apparent change in acceleration with out any off-gassing.
joe_the_user 8y ago
As your quote indicates, it's not just not going at the speed of any nearby star, it's going at the particular speed of the galaxy (or galaxy's average rotation). If an object were expelled randomly by a nearby star, it's speed would be: star's speed + random extra boost. The chances this would exactly the galactic speed seems small.
- Symmetry 8y ago
  But given a long enough time and an object with a low enough ballistic coefficient I'd expect it to come to rest with respect to the interstellar medium, maybe. I don't know if that works out quantitatively in this case.
- jerf 8y ago
  Kinda a weird speed for an alien artifact too, though. One would expect for it to be launched. Humans may in some sense have a small time horizton, but you have to have an absurdly long time horizon to fling probes out into the universe at the local average speed and expect them to encounter anything, since by definition of "local average speed" that's literally the speed least likely to encounter anything. In some sense, that's actually literally the least likely velocity I'd expect to be an alien result. (And it's also conceivable that humans have bizarrely long time horizons, if the future of all intelligence is moving into a machine intelligence on a computational substrate as fast as possible. If intelligences subjectively experience hundreds or thousands or millions of times faster, it's like dropping the speed of light by the same factor, and it still takes all the same amount of energy to launch probes. I'm not saying this is inevitably true, but I do think there's an excessively strong bias to assume that humans are as bad as possible in every possible way.)
  - nerfhammer 8y ago
    It's exactly what you would want to do if you didn't want someone who found it to be able to tell where it came from
    - jerf 8y ago
      For that, you just need the velocity vector not to be in the very narrow class of vectors that point back at you. There's no need to put it in "galactic neutral", especially given that, as I said, that's literally the worst possible speed to get anywhere. That's just one possible choice from the almost-every-possible-vector selection set that will work to disguise your origin. Of course, we also have the question of why you would care to disguise your origin for a "space probe" traveling at such a slow speed. (Pretty much every conceivable mechanism that could have something traveling at any appreciable speed and that slowed it down anytime in the recent past would be very easily detectable. Of course you can invoke inconceivable mechanisms, but as I often say, you have to understand you have left rationality and logic behind when you do that; if we're going to say this object has a magic drive that decelerates without any detectable emissions, we might as well ask why it's not just using an FTL drive, or why any alien civilization is bothering to "probe" us when they've long since landed at Area 51 and have long since been running our civilization anyhow as our secret leaders.)
      - ncmncm 8y ago
        Whipping it around a nearby unoccupied star would be an easy way to obscure its origins. Just their bad luck that Sol turned out to be occupied, by a primitive civilization that might be able to act on knowledge of its origin vector in a few centuries or millennia. It looks slow to us, but it might be that whatever method it uses to skip big distances doesn't steer, so the only way to get pointed somewhere else is a close approach. And, of course, the method doesn't work in a gravity well, so it has to coast until it's a few hundred AU out. Will enough records be preserved through the coming dark ages (after the ecosystem collapses) for the raccoons or macaques or whatever inherits the earth to act on them?
        8y ago
- SiempreViernes 8y ago
  Well, it also is very likely to go at a speed that makes it easy to spot (easy for its class), because otherwise we would have seen the easier ones first (except if this one is a super fluke and we’ll never see its like again)

dbingham 8y ago

But not for the odd shape, or for the apparent change in acceleration with out any off-gassing.

joe_the_user 8y ago

As your quote indicates, it's not just not going at the speed of any nearby star, it's going at the particular speed of the galaxy (or galaxy's average rotation). If an object were expelled randomly by a nearby star, it's speed would be: star's speed + random extra boost. The chances this would exactly the galactic speed seems small.

Symmetry 8y ago
But given a long enough time and an object with a low enough ballistic coefficient I'd expect it to come to rest with respect to the interstellar medium, maybe. I don't know if that works out quantitatively in this case.
jerf 8y ago
Kinda a weird speed for an alien artifact too, though. One would expect for it to be launched. Humans may in some sense have a small time horizton, but you have to have an absurdly long time horizon to fling probes out into the universe at the local average speed and expect them to encounter anything, since by definition of "local average speed" that's literally the speed least likely to encounter anything. In some sense, that's actually literally the least likely velocity I'd expect to be an alien result. (And it's also conceivable that humans have bizarrely long time horizons, if the future of all intelligence is moving into a machine intelligence on a computational substrate as fast as possible. If intelligences subjectively experience hundreds or thousands or millions of times faster, it's like dropping the speed of light by the same factor, and it still takes all the same amount of energy to launch probes. I'm not saying this is inevitably true, but I do think there's an excessively strong bias to assume that humans are as bad as possible in every possible way.)
- nerfhammer 8y ago
  It's exactly what you would want to do if you didn't want someone who found it to be able to tell where it came from
  - jerf 8y ago
    For that, you just need the velocity vector not to be in the very narrow class of vectors that point back at you. There's no need to put it in "galactic neutral", especially given that, as I said, that's literally the worst possible speed to get anywhere. That's just one possible choice from the almost-every-possible-vector selection set that will work to disguise your origin. Of course, we also have the question of why you would care to disguise your origin for a "space probe" traveling at such a slow speed. (Pretty much every conceivable mechanism that could have something traveling at any appreciable speed and that slowed it down anytime in the recent past would be very easily detectable. Of course you can invoke inconceivable mechanisms, but as I often say, you have to understand you have left rationality and logic behind when you do that; if we're going to say this object has a magic drive that decelerates without any detectable emissions, we might as well ask why it's not just using an FTL drive, or why any alien civilization is bothering to "probe" us when they've long since landed at Area 51 and have long since been running our civilization anyhow as our secret leaders.)
    - ncmncm 8y ago
      Whipping it around a nearby unoccupied star would be an easy way to obscure its origins. Just their bad luck that Sol turned out to be occupied, by a primitive civilization that might be able to act on knowledge of its origin vector in a few centuries or millennia. It looks slow to us, but it might be that whatever method it uses to skip big distances doesn't steer, so the only way to get pointed somewhere else is a close approach. And, of course, the method doesn't work in a gravity well, so it has to coast until it's a few hundred AU out. Will enough records be preserved through the coming dark ages (after the ecosystem collapses) for the raccoons or macaques or whatever inherits the earth to act on them?
      - 8y ago
SiempreViernes 8y ago
Well, it also is very likely to go at a speed that makes it easy to spot (easy for its class), because otherwise we would have seen the easier ones first (except if this one is a super fluke and we’ll never see its like again)