3 ms·

Regarding those two points: A very good laser has a beam divergence of tenths of milliradians, or 0.01 degrees. At the radius of planet 9, this is a very large

Regarding those two points: A very good laser has a beam divergence of tenths of milliradians, or 0.01 degrees. At the radius of planet 9, this is a very large beam, and we'd have a hard time putting out enough power to compete with the sun. Furthermore, the sky has an area of 40,000 square degrees. Our little laser beam projects a circle with an area of 0.0000785 square degrees. You'd need to aim at 500 million spots to see the whole sky.

avar 8y ago
> You'd need to aim at 500 million spots to see the whole sky. That's smaller than I expected. To convert that into human scale sqrt(500 million) = 22360, in millimeters that's around 22 meters (72 ft). So if we had a square wall 22 meters by 22 meters we could paint a grid of 1 mm by 1 mm squares on it and end up with around 500 million squares. Then we'd need to stand there in front of the wall with a laser pointer and shine the laser at each individual square and check the light bouncing back at us.
- hughes 8y ago
  Don't forget - due to the speed of light it takes 5-10 hours to get feedback on if the square illuminated, but maybe more because you don't know exactly how long you'll need to wait. And there's uncertainty in whether your measurement is accurate. And there's a background of other illuminated squares that can interfere with your readings. And you're spinning while this is going on. And the target square is continually moving. You might have just missed it.
burtonator2011 8y ago
this has an easy solution. 1. Build a Dyson sphere around the sun. 2. Capture all the mass in the solar system to build a giant freaking laser. 3. Use the energy to from the Dyson sphere to power the laser. 4. Melt your entire civilization.
- nerfhammer 8y ago
  If it's a super-earth it probably has an iron core. We should be able to use magnets to crash it into the sun. The impact event will be hard to miss. We'll know where it is for sure then. This is a lot less work than building a Dyson sphere.
celrod 8y ago
Relevant xkcd: https://what-if.xkcd.com/13/ https://what-if.xkcd.com/13/

avar 8y ago

> You'd need to aim at 500 million spots to see the whole sky. That's smaller than I expected. To convert that into human scale sqrt(500 million) = 22360, in millimeters that's around 22 meters (72 ft). So if we had a square wall 22 meters by 22 meters we could paint a grid of 1 mm by 1 mm squares on it and end up with around 500 million squares. Then we'd need to stand there in front of the wall with a laser pointer and shine the laser at each individual square and check the light bouncing back at us.

hughes 8y ago
Don't forget - due to the speed of light it takes 5-10 hours to get feedback on if the square illuminated, but maybe more because you don't know exactly how long you'll need to wait. And there's uncertainty in whether your measurement is accurate. And there's a background of other illuminated squares that can interfere with your readings. And you're spinning while this is going on. And the target square is continually moving. You might have just missed it.

burtonator2011 8y ago

this has an easy solution. 1. Build a Dyson sphere around the sun. 2. Capture all the mass in the solar system to build a giant freaking laser. 3. Use the energy to from the Dyson sphere to power the laser. 4. Melt your entire civilization.

nerfhammer 8y ago
If it's a super-earth it probably has an iron core. We should be able to use magnets to crash it into the sun. The impact event will be hard to miss. We'll know where it is for sure then. This is a lot less work than building a Dyson sphere.

celrod 8y ago

Relevant xkcd: https://what-if.xkcd.com/13/ https://what-if.xkcd.com/13/