Wednesday, September 24, 2008

"Also, who the shooting back will do?", part I

As a kid I got Dragon for the game-able stuff, not the fiction. But one of my favorite pieces of fiction published in Dragon was "The Gun That Shot Too Straight" by Ralph Roberts. The story appeared in issue #94, February 1985. To sum up briefly, the story hinges on a young genius named Henry inventing an energy pistol that fires tiny balls of energy that disrupt molecular bonds. Henry's uncle, a defense contractor, is very interested in the device until they catch on the news that the test firing brought down a plane on the other side of the world. It seems the ever-expanding fireball punched all the way through the Earth, wrecking an Aussie military jet. The illo that opens the story depicts the event quite nicely:


Near the end of the story the uncle asks "I was wondering, if the energy balls continue travelling, how big will they get and what will they hit?" The young inventor doesn't have an answer. The last line of the story is the title of today's post. Over the years I've often thought about running some numbers on this scenario and today I'm going to finally do it. Please point out any math errors you spot in the comments.

Let's start with the easy one: the velocity of the fireball. We'll assume a constant velocity because we have no evidence of acceleration once the disruption ball exits the pistol aperture. According to the story it took approximately ten hours (36,000 seconds) to punch through the Earth, which has a diameter of roughly 12,742 kilometers. That's about 350 meters/second. Or roughly 390 yards/second, or about 1,200 feet/second, or about .2 mile/second if metric isn't your bag. Or 790 miles per hour. Not anywhere close to lightspeed, but not too shabby in general. By way of comparison that's about 40% faster than the muzzle velocity of a bullet fired out of a M1911 pistol.

Now let's look at the rate of expansion of the disrupting sphere. Again we're working with estimates. All we really know from the story is that the emitting aperture on the pistol is "a barely discernible pinhole" from the point of view of the old uncle. Let's call that a 1 millimeter diameter for our purposes. The fireball that brought down Captain Smythe's plane was described as "the size of a large beachball". I'm going to make the calculations as easy as possible by calling that 1 meter in diameter. So that's a thousandfold increase over the ten hour timeframe. For simplicity's sake we'll assume a constant growth of 1 meter per ten hours, or about .03 mm/second.

Tomorrow comes the fun part. We'll aim the fireball at various celestial objects and determine how long it takes to reach the target and how big the fireball is at the moment of impact. As I type this I'm not sure exactly how these scenarios are going to turn out, but I suspect that the relatively slow velocity is going to result in some pretty dang big fireballs once this baby starts hitting things in outer space.

11 comments:

  1. Actually, my assumption was that it only grew when pushing past matter. I don't see any mechanism for expansion in a vacuum. Which is good because at some point it's volume will take up all space if it can expand between galaxies.

    Fang Langford
    Creator of the Scattershot Role-Playing Game

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  2. I don't know about any of that, but I really used to have the hots for that girl in the Dragon cover. Although I knew her from the 2nd edition Complete Ranger's Handbook.

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  3. I remember that story.

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  4. Anonymous1:04 PM

    Yeah, that buckskin clad beauty looks familiar to me as well. Can't place exactly what book it was in, but I know I've seen her in other D&D stuff before.

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  5. Anonymous3:11 PM

    That opossum has a sword!

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  6. Actually, my assumption was that it only grew when pushing past matter.

    Ah, I never considered that as a possibility. Your assumption would keep the fireball dreadfully small.

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  7. Anonymous5:28 PM

    Actually, at that low rate of speed I suspect that it will never even get to another star system for billions of years. As the rate of expansion is linear and even slower, it would take almost forever to even reach the size of something like the sun. It certainly would never fill the universe because its rate of expansion if far greater than that...

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  8. Anonymous8:24 AM

    The assumption too is that acceleration (delta velocity) is constant. There are not enough data points to show that is true.

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  9. Anonymous9:40 AM

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  10. To this day I've never read more than three paragraphs in a row of any of the fiction in Dragon.

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  11. I've actually only read one story, partially because I liked the premise (the protagonist was the kid who grew up to be the innkeeper, while his friend went off to be an adventurer-type), and partially because I realized I had instinctively avoided ever reading any fiction in Dragon, and I began to wonder why that was.

    I liked the story. But the instinct remained firmly in place. I don't understand - I like fantasy, I like reading, I like gaming...why don't I like reading fantasy fiction in a gaming magazine?

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