3 ms·

> All that momentum is focused in a single direction, straight down Well, no. Straight down is possible, but not necessary or even necessarily likely. I thin

by JackFr 4y ago

> All that momentum is focused in a single direction, straight down Well, no. Straight down is possible, but not necessary or even necessarily likely. I think there's relatively little empirical evidence with respect to relativistic collisions at macroscopic scales, but isn't there a simpler conservation of energy argument to be made? Absent fancy orbital mechanics maneuvers, isn't the upper bound of the 'planet killing' energy of impact the total energy imparted by the accelerating lasers? Or am I missing something (could be physics was 30+ years ago.)

SideburnsOfDoom 4y ago
> isn't the upper bound of the energy The energy of a 10g object at 0.2c is not just bounded, it is calculatable, and not really that large. The earth has had worse encounters, multiple times, in the last century. The above wildly overstates even a "best case straight down direct hit" scenario. https://news.ycombinator.com/item?id=33177030 https://news.ycombinator.com/item?id=33177030
- fallingfrog 4y ago
  Sure, but the energy of a bomb explodes outwards in all directions, such that at a distance of R the amount of energy per square meter decreases according to 1/R^2. while this projectile's energy is concentrated in a tiny area and all in the same direction, so it won't dissapate the same way. A cherry bomb and a bullet with the same amount of total kinetic energy are going to act in very different ways. And this thing is going at .2c. The time it would take to go from very top of the atmosphere to ground is 1.6 milliseconds (on Earth, assuming 60 miles thick atmosphere). That's not a meteor. And certainly not a bomb. That's a railgun. I did misspeak I said "straight down", that's not necessarily true. Could be along a diagonal at any angle.
  - SideburnsOfDoom 4y ago
    > Sure, but the energy of a bomb explodes outwards in all directions. while this projectile's energy is concentrated in a tiny area and all in the same direction ... That's not a meteor. With respect, I think that _is exactly_ how a meteor works. So the extreme velocity times smaller mass gives us a middling kinetic energy. The difference, the extreme velocity, means that the energy is burned up as the object disintegrates into atoms over milliseconds not seconds as a regular meteor with the same energy would. Atoms and small fragments won't sustain their velocity. There's a fast bright flash of superheated air, a clap of thunder as the trail collapses, done.
    - fallingfrog 4y ago
      Yes, you know I did some more research, and it's too late to change what I wrote earlier- but you're probably right, or at least I'm not sure anymore. I still think my version would be more fun! But, I'm the kind of person who is willing to reevaluate in the face of evidence and I think I was probably not correct. Respect to you as well!

by JackFr 4y ago

SideburnsOfDoom 4y ago

> isn't the upper bound of the energy The energy of a 10g object at 0.2c is not just bounded, it is calculatable, and not really that large. The earth has had worse encounters, multiple times, in the last century. The above wildly overstates even a "best case straight down direct hit" scenario. https://news.ycombinator.com/item?id=33177030 https://news.ycombinator.com/item?id=33177030

fallingfrog 4y ago
Sure, but the energy of a bomb explodes outwards in all directions, such that at a distance of R the amount of energy per square meter decreases according to 1/R^2. while this projectile's energy is concentrated in a tiny area and all in the same direction, so it won't dissapate the same way. A cherry bomb and a bullet with the same amount of total kinetic energy are going to act in very different ways. And this thing is going at .2c. The time it would take to go from very top of the atmosphere to ground is 1.6 milliseconds (on Earth, assuming 60 miles thick atmosphere). That's not a meteor. And certainly not a bomb. That's a railgun. I did misspeak I said "straight down", that's not necessarily true. Could be along a diagonal at any angle.
- SideburnsOfDoom 4y ago
  > Sure, but the energy of a bomb explodes outwards in all directions. while this projectile's energy is concentrated in a tiny area and all in the same direction ... That's not a meteor. With respect, I think that _is exactly_ how a meteor works. So the extreme velocity times smaller mass gives us a middling kinetic energy. The difference, the extreme velocity, means that the energy is burned up as the object disintegrates into atoms over milliseconds not seconds as a regular meteor with the same energy would. Atoms and small fragments won't sustain their velocity. There's a fast bright flash of superheated air, a clap of thunder as the trail collapses, done.
  - fallingfrog 4y ago
    Yes, you know I did some more research, and it's too late to change what I wrote earlier- but you're probably right, or at least I'm not sure anymore. I still think my version would be more fun! But, I'm the kind of person who is willing to reevaluate in the face of evidence and I think I was probably not correct. Respect to you as well!