system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why is the Kessler effect so dangerous? Won't the space junk eventually fall out of orbit or drift off into space?

I saw the opening of *Gravity* and it was pretty terrifying, but to quote Billy Bob Thornton in *Armageddon*, it's a big-ass sky.
gpt
Yes, the space junk will eventually deorbit. But "eventually" is a long time and, before it does, it will take out most of our satellites. 

It's so dangerous because it's an expontential growth problem...the likelyhood of a collision depends on how many bits of junk there already are, and each collision creates more junk. You can reach a tipping point where the frequency of collisions goes up very abruptly and the probability of any particular thing getting hit goes from effectively zero ("big-ass sky") to something meaningfully high. j

It's taken decades and tens to hundreds of billions of dollars (possibly trillions) to build our existing space infrastructure. A runaway Kessler effect could wipe all that out in months, far faster than we can replace it, and it would render low-earth orbit effectively unusable for years/decades. It would ruin our ability to do a lot of stuff that we currently take for granted without \*tons\* of effort and money.