by: kleinbl00

comment by
dirkson
badged comment

It would blind you instantly, kill you, and probably end all life on the planet, so maybe what it looks like is less important than ya' might think.

So earth receives about 1386 watts per square meter under the sun at full brightness. Let's assume, (Although it's a bad assumption) that exactly half the earth gets that at full blast each day. The math of that is: 1,368 * (SurfaceAreaOfEarth/2) = 0.1346796 terawatts

Cool. So each day earth receives nearly 1/5th of a terawatt from the sun.

In order to be able to see the output of our 68-million-terawatt rocket, we have to assume it's not 100% efficient - If it were, no photons from it would end up striking the object we're trying to move. (AKA "The Earth") Assuming less than 100% efficiency is usually good practice anyway. So let's assume an efficiency of 99.9%. That seems pretty good, right?

So 1/10th of 1% of the output of the rocket is going to strike the earth. I wonder how its brightness would compare to that of the noonday sun? Let's assume it strikes half the planet evenly again, just to make out math easier. 68,000,000 / (SurfaceAreaOfEarth/2) = 690,705,942 watts. Per square meter. 500,000 times the brightness of the sun.

Ok, so maybe that's not all bad. I mean, sure, it's going to blind us all instantly. But it's not like it's going to cook us alive, right? Right? Well, let's assume, for the sake of ballpark estimation, that is has the same spectral characteristics as sunlight. That means about 50% of its output is going to be in the infrared.

Due to my day job, I happen to have the energy required to heat a meter cube of water right here. Assuming the average water temperature was 18C (~64F) a cubic meter of water would boil away in less than a second. You are much warmer than that, and much smaller than that - You wouldn't last nearly as long.

Ok, so maybe 99.9% efficiency is too low. Maybe we need to design our rocket a little better. How does 99.999999% efficient sound? That's one photon in each million striking earth! Well, let's do the math: (68000000 / (AreaOfEarth/2)) * 0.00000001 = 6907 watts per square meter. Hey, that's only five time the brightness of the midday sun! We're blind, but not instantly dead!

I mean, it's still going to kill us all eventually. It's still dumping enough spare energy to boil about a cubic meter of water every day. I doubt it'd actually boil off much water - Most of the extra heat is going to get spread around the volume of the planet more rapidly than it comes in. But with global climate change, we're worried about a few degrees on average over a century or so... This change would produce far, far worse effects over a far shorter time frame.

It's really more of a doomsday device than a way to save the earth.

Cheers!

EDIT: I completely failed at math here, but corrected myself in the comments. Turns out the rumors of earth's demise were greatly exaggerated!