Geir
Emperor Mongoose
Okay, for most readers this will be either Duh! or Huh? but for that tiny sliver of people in between, this is an answer to a question nobody asked:
Somewhere in the World Builders Handbook I wrote up a suggestion about using a body's mass instead of diameter to determine '100D' for things like stars, because both smaller red dwarf stars and the assorted menagerie of dead star types: white dwarfs, neutron stars and, of course, black holes, they have stellar-ish masses but much, in some cases very, very much, smaller diameters. This goes for a variety of brown dwarfs and such as well. But that's not exactly correct, now that I think about it more.
If the j-drive 100D and m-drive D1000 limits (for, let's be frank, totally fictional drives that can behave in totally fictional ways) are based on the strength gravity, like the local 'curvature' of space or some such, then diameter is actually less wrong than mass. Gravity for a body is related to diameter x density, but mass is related to the cube of diameter. So for instance, if you double the density of an object without changing its size, then gravity is also doubled, but its mass is increased by a factor of 2 cubed, or 8. So using mass as the 'D' limiter would kick the mass-derived D-limit out by four times too much for the fictional curvature involved - because, like, space is all 3-dimensional and such.
(Side note: a black hole has a singularity with all of the mass in it, so it's infinite density in an infinity small volume: this does not cancel gravity out or make it infinite across all of space and time. It just means you should probably use the event horizon as the diameter and avoid the migraine of dealing with infinities.)
When Traveller came out, at least until Book 6: Scouts came out in 1983, all you had to go on for a world was diameter, so 100D had to be diameter and not mass-based (or density based).
Technically (if that's a thing for something made up), you could now (since 1983) add in density (and for instance the 'D100' limit for Mars would be about 71 Mars diameters based on density, but not the 10 Earth diameters {about 20 Mars diameters} that it would be if based on mass), but that's a lot of work for not a lot of gain. It's a game, not a simulation.
So even though it's not exactly correct (assuming the functionality of these fictional space drives is actually based on 'curved space'), it sure is easier to treat every normal planet and star as 100D, and only deal with dead stars - white dwarfs, neutron stars, and black holes - as exceptions, and then use 100 Sol diameters (about 139 million kilometers) x mass in terms of Sol for these really dense things.
Anyway. Just wanted to get that off my chest. It ends up being pretty much what I had said in the first place, but the reasoning behind it has changed. Maybe I'm just dense.
Somewhere in the World Builders Handbook I wrote up a suggestion about using a body's mass instead of diameter to determine '100D' for things like stars, because both smaller red dwarf stars and the assorted menagerie of dead star types: white dwarfs, neutron stars and, of course, black holes, they have stellar-ish masses but much, in some cases very, very much, smaller diameters. This goes for a variety of brown dwarfs and such as well. But that's not exactly correct, now that I think about it more.
If the j-drive 100D and m-drive D1000 limits (for, let's be frank, totally fictional drives that can behave in totally fictional ways) are based on the strength gravity, like the local 'curvature' of space or some such, then diameter is actually less wrong than mass. Gravity for a body is related to diameter x density, but mass is related to the cube of diameter. So for instance, if you double the density of an object without changing its size, then gravity is also doubled, but its mass is increased by a factor of 2 cubed, or 8. So using mass as the 'D' limiter would kick the mass-derived D-limit out by four times too much for the fictional curvature involved - because, like, space is all 3-dimensional and such.
(Side note: a black hole has a singularity with all of the mass in it, so it's infinite density in an infinity small volume: this does not cancel gravity out or make it infinite across all of space and time. It just means you should probably use the event horizon as the diameter and avoid the migraine of dealing with infinities.)
When Traveller came out, at least until Book 6: Scouts came out in 1983, all you had to go on for a world was diameter, so 100D had to be diameter and not mass-based (or density based).
Technically (if that's a thing for something made up), you could now (since 1983) add in density (and for instance the 'D100' limit for Mars would be about 71 Mars diameters based on density, but not the 10 Earth diameters {about 20 Mars diameters} that it would be if based on mass), but that's a lot of work for not a lot of gain. It's a game, not a simulation.
So even though it's not exactly correct (assuming the functionality of these fictional space drives is actually based on 'curved space'), it sure is easier to treat every normal planet and star as 100D, and only deal with dead stars - white dwarfs, neutron stars, and black holes - as exceptions, and then use 100 Sol diameters (about 139 million kilometers) x mass in terms of Sol for these really dense things.
Anyway. Just wanted to get that off my chest. It ends up being pretty much what I had said in the first place, but the reasoning behind it has changed. Maybe I'm just dense.
