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A long long time ago in a galaxy far far away, Star Wars happened! It was a war which involved a society that inhabited 100% of habitable worlds in an entire galaxy, whose only weapons were laser beams.

Assuming that the number of years ago that this happened is approximately equal to the number of lightyears away the galaxy is from earth, what is the probablility of me getting killed by a stray laser beam this year?

Estimation is a kind of math, I'll allow you to estimate galactic populations, percentage of population drafted, frequency of space battles, etc, etc. You may also need to research Cosmological facts such as the distance of galaxies, number of inhabitable planets, etc.

P.S. Please don't bother answering to say "well, it's close to zero". Everyone on this site is intelligent enough to realise that the probability is low. I'm looking for an order of magnitude, obviously.

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    Without any estimation, the probability is $0$. You are simply too far away :-) – 2017-01-27
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    Stack Exchange is a formal resource. Try asking a more casual audience like reddit.com/r/theydidthemath – 2017-01-27
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    @Ant You're saying that other galaxies are beyond the range of light? So how can we see them? – 2017-01-27
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    Nope :) but look at the stars that are a galaxy away. You can barely see them. And some of them are huge; the biggest known is 5 billion times bigger than the sun; if placed at the center of the solar system, it would cross Jupiter's orbit. Now imagine having a small gun firing stuff in random directions. What is the probability that they'll reach earth? Essentially zero – 2017-01-27
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    @Ant. I think what you mean is that the probability is less than negligible. But it's not even infinitesimal. It would be a rational number. It's mathematically incorrect to say that its a zero probability. Think of this as a theoretical math problem, not an engineering problem. – 2017-01-27
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    Yes, my point was that given the fact that the probability is essentially zero and the huge error bands on any assumption you can m take, 0 is one of the best estimate you can get. That is, it's not a particularly interesting question, because you have too much uncertainty and the probability at play are too small. Btw infinitesimal doesn't mean anything when talking about numbers; there are no infinitesimal numbers, only very small. Plus, how did you prove that the probability is rational? From a *probabilistic* point of view, the probability of being a rational number is 0 (exactly zero!) :D – 2017-01-27
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    @Ant - Assuming that you can draw a line from A to B, we know that the probability is not 0. Your point seems to be that the margin for error far exceeds the difference between 0 and the actual answer, making it incalculable. I disagree. Uncertainties such as physical obstructions, gravitational fields, number of lasers actually fired, etc would be scaled by the order of magnitude created by the underlying geometric component of the problem. You can see that someone has already supplied the geometry needed to account for trajectory, so we already have a very rough order of magnitude. – 2017-01-29

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The fraction of the shooting directions that will hit you is like $A/\pi d^2$, where $A$ is the area of your projection to the ground and $d$ is the distance to that galaxy. Assuming $n$ deadly shootings per year, the requested probability is about $nA/\pi d^2$.

Numerical example:

$$n=31400 \text{ (hundred a day, holidays excluded)},A=0.1 m^2,d=10^{18}\text { (106 light-years)},\\ p\approx 10^{-33}.$$

Update:

From new demographic information given by the OP, it appears that $n$ is exactly $10^{37}$ a year.

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    If you were born on a February 29th which was at the same time a Friday 13th, the probability is lower. – 2017-01-27
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    Think about how many times somebody fired a gun during WW2. Now think about what the population would be in an entire galaxy. Do you think that there might be more than 100 lasers fired per day? – 2017-01-27