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The 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 e
by lev99 8y ago
The 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.
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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.