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Interstellar travel now seems a lot more hazardous than it did before. To quote one of my TAs in college, "it's the stuff you can't see that gets you" ...
by itronitron 8y ago
Interstellar travel now seems a lot more hazardous than it did before. To quote one of my TAs in college, "it's the stuff you can't see that gets you" ...
- lev99 8y agoThe article states that planets may outnumber stars 100,000 to 1. The Milky Way has 4E^11 stars. It has an upper estimate of 4E^16 planets. It has a lowest estimate diameter of 100kly. It has an estimated thickness of 2kly. It's lower estimate volume is 63,000 kly^2. ----------------------------- If planets are uniformly disrupted (they surely aren't), there are ~17 planets in every cubic light year. Sure, that's a hazard.
- nabla9 8y ago> ~17 planets in every cubic light year. The change of hitting one while traveling one light year is in the order of 10e-16.
- mrarjen 8y agoExactly, and I saw that when the Andromeda Galaxy collides with ours, it's unlikely many planets/systems will be colliding with one another.
- boznz 8y agoNever really understood how galaxies can collide if space has been expanding since the big bang and everything is moving apart
- ben_w 8y agoIt goes both ways depending on distance. Expansion is exponential (ish), gravity is inverse-square [1]. Only the few that happened to be close enough that gravity is more significant than expansion can collide. [1] at least in Newtownian physics. The argument is geometry, so I suspect but am not qualified to say it isn’t exactly inverse square in GR.
- mickronome 8y agoSame reason I can collide with someone on the sidewalk while the universe is expanding at tremendous speed. Over short distances, the expansion can easily be overcome by others forces like gravity or my muscles excerting force through friction against the ground. However, given enough time, there will be less and less objects that are close enough to be able to collide at all. Lots of time though, and there are already now lots of things over galaxy could never ever collide with.
- Retric 8y agoOn very large scales gravity collected mater into what look like spider webs, with vast amounts of empty space and threads of interstellar gass which can form galaxies. Those galaxies form little clumps within those threads with gravity causing them to orbit each other. However, as it's a many body problem things are not stable over very long time frames and galaxies often hit each other. This does slow down over time as there are fewer remaining galaxies in a cluster.
- nabla9 8y agoMetric expansion of space has effect only on very large scale. Galaxy clusters have enough gravitational force to keep them together.
- varjag 8y agoAbout the same as getting shot while drowning in bathtub stricken by lightning?
- gnarbarian 8y agoThat's how my uncle died.
- lev99 8y agoA few things make me thing it's a much larger risk than 10e-16. 1. My numbers are on uniform distribution of planets. The milky way is not uniformly distributed, and I suspect this isn't either. I hypothesis most of the planets will be on the spokes, just like most of the stars are. In addition, while it is 2kly tall, there is not a uniform distribution across the height. 2. Interstellar travel doesn't involves traveling a minimum of 4 lys, and a maximum distance without being intergalactic would be about 100,000lys. 3. Your assuming instantaneous travel across the light year. In reality we would consume at least 1 year in travel time, and likely much more. 4. The amount of resources it takes to build an intersellar ship is very large. The cost of a collision is high. This doesn't change the risk of a collision, but it does change what we consider acceptable risk.
- zaarn 8y agoPeople tend to forget how big a cubic light year is. The earth itself is only 0.02 light seconds in diameter, yielding a cube of 8000 cubic lightmilliseconds. Compared to the 2.910^31 cubic light milliseconds in a cubic lightyear... It's a rounding error inside a rounding error. For light seconds, you're looking at 2.910^22 (if my math isn't wrong). That's the amount of cubes fitting between earth and moon to fill a cubic light years. Even superplanets with 15 times the size of the earth are simply dwarfed by the sheer volume of a cubic light year. The largest stars we found measure 73 light minutes, a cubic size of 389017 cubic light minutes. How much of them fit in a cubic light year? 346 billion.
- kamaal 8y agoIf something doesn't shine already. The only way to detect its existence is to send radio waves and see if something bounces off(Like Radar). I guess the point people are trying to make here. If you can't see light coming off an object, then while traveling at interstellar speeds means it will be harder to spot objects until they get too close.
- zaarn 8y agoNot all black objects reflect radar, black holes don't reflect at all. I think if you were to encounter a black hole, esp an inactive one, in interstellar space, you'd probably just get sucked in if you didn't notice the black disk...
- kamaal 8y agoI thought black holes typically have accretion disk.
- zaarn 8y agoOnly when active and sucking in matter. If a black hole has been travelling without eating for long enough the accretion disk can disappear. If a black hole is large enough it won't form an accretion disk either as it swallows stars whole.
- gnulinux 8y agoI did no math to confirm this but intuitively it seems incredibly unlikely to hit a rogue planet if you shoot something to a star randomly. How's it any different than shooting something inside Solar system and accidentally hitting an asteroid?
- TheOtherHobbes 8y agoCollisions are not the problem. Gravitational perturbation is the problem. If most planetary systems are anything like this one, planetary orbits are quasi-stable, and a visitor could easily destroy that stability. It would take a while for that to play out - anything from months for a very unlikely very near miss, to many millennia for a distant visit.
- akvadrako 8y agoThe top post was talking about interstellar travel, not living on a planet.
- nabla9 8y agoPlanets can be detected by their gravity field. Collision with planet sized object in space would be extremely rare. Even if you would travel blind it would be very unlikely that you would hit star or plant while traveling trough galaxy.
- everdev 8y agoWell, if there's not much around it, it might be hard to detect it's gravitational effects. I'd imagine you could detect it blocking a circular patch of sky more easily and from farther off than you could detect the gravitational pull on your spacecraft. Just don't steer twords the black disc and you'll be fine.
- zaarn 8y agoI think not steering towards the black disc is a good advice for space travel in general...
- captn3m0 8y agoBut you can use it for gravitational slingshots.
- ben_w 8y agoFour ships (or a ship and three probes) arranged in a tetrahedron, where the distance between each pair is precisely measured with a laser or similar. Changes to the edge lengths of the formation show a nearby gravity gradient. What’s one wavelength per minute if the formation is 1000km?
- dragonwriter 8y ago> Changes to the edge lengths of the formation show a nearby gravity gradient. Or changes in density or relative velocity of the interstellar medium, etc.; gravity isn't the only feature that can alter the formation.
- hamilyon2 8y agoActually, one could refuel reactive mass by mining those planet if delta v is favorable. Reactive mass deficit is one of biggest problems with interstellar travel. Suddenly, I think interstellar travel is a bit less impossible.
- simonh 8y agoThe trouble is you'd need to stop, mine the mass, then accelerate back up again. If you have the fuel to stop to refuel in the first place, you don't need to stop refuel, unless there's something else you need as well.
- lucb1e 8y agoI think that's what your parent meant with "if the delta v is favorable", like, if you move in the same direction and the speed difference isn't too absurd, it might be worth mining there.
- smichel17 8y agoNaive comment here, but wouldn't it be highly unlikely to encounter such a planet given your low relative velocity to it?
- brazzy 8y agoQuite the opposite, actually. At near lightspeed, a pea-sized rock will kill your spaceship just as dead as a planet. So you actually want your interstellar masses to be as concentrated as possible.
- sundvor 8y agoThat's assuming we haven't figured out effective shielding by the time we have those near light speed engines.
- brazzy 8y agoDoesn't really make any difference. There is some size of rock that's too big for your shielding, and you rather want that mass concentrated in a handful of planets than spread around.
- vorg 8y ago> At near lightspeed, a pea-sized rock will kill your spaceship Why travel in a spaceship? If there's 100,000 starless planets for every star in the galaxy, then travel between stars on one of them instead. Build the habitations 10 km below water to avoid radiation. Travel at 0.1% light speed instead and get to the nearest star in 5000 yrs. Enjoy the journey, and slip into an orbit around the target star. Speaking of pea-sized rocks, periodically fire one laden with electronics/optics/quantumics at the target star at near light speed and receive its transmissions for recon.
- antisthenes 8y agoPowered by what?
- nickwalton00 8y agoI mean that would only take the energy of 200 Quadrillion Hiroshima nuclear bombs. No biggy.
- vorg 8y ago
- nkrisc 8y agoIt appears we'll need a guild of navigators, of sorts, to guide interstellar craft.