How far can you go in Chicken Invaders? You'd think that you could play it potentially forever, right? Let's check this.
Beginning
The first chapters are easy to go through, but the further you go, the harder the game gets. Everything falls faster, the chickens drop eggs a lot more often, and everything requires more hits to be killed.
Problem #1
After some time, your shots won't be enough, and you'll have to start using Missiles, unless you want to shoot for 5 minutes to get a single chicken down. This will get worse over time.
Problem #2
Everything gets quicker and quicker. The asteroids, the eggs, the chickens... Soon enough, some waves will be impossible to survive through.
Problem #3
There will be more and more chickens in the Protect Earth and the Be Quick or Be Dead waves...
After some time, so many of them will spawn that the game will crash, and this happens on wave 100000004. Before that you'll have to put up with huge slowdowns when there are more chickens onscreen, which will make it tedious to get through.
Problem #4
Although this won't be as much problematic (the crashes on those 3 waves should worry you more), things will get so fast that they won't be able to hit you. They will just teleport. That will make it easier for you to kill chickens as they won't be such a threat, but there's still the boss to worry about, which is a massive damage sponge compared to the ordinary chickens you fight.
Problem #5
If you somehow manage to go through all of the crashes all the way through two billion waves, the number will finally overflow after Wave 2147483647, at which point chickens require whopping 4 billion ion blaster shots to be defeated! (or about 100 million rockets, but who would have that many?). You must be quite strong and determined at this point, after somehow being able to skip through 300 million of those waves described in Problem #3 that could crash the game at any moment. Now as the Wave number overflows into a negative number, the game enters a weird state, where the loop changes and you get a Chicken Invasion wave, and then nine waves of nothing, then another Chicken Invasion wave, then another nine waves of nothing, etc. You'd think this would be easy, but it isn't. That's because chickens in this minus wave state will get a huge jump in health, even though they technically have minus health. This is because the game only checks for when the chicken should die when it's health is 0. So, as the chickens have -200 million health, you will have to underflow the amount to 2 billion and then you'll be able to get it to zero. That's four billion shots for each chicken! And as you approach wave 1, more and more shots will be required to kill them. Good luck! After you get to wave 1, the game loops starts to behave normally.
Verdict
The game indeed can be played forever, but only if you have infinite patience for having to shoot chickens billions of times before they die, the crashes at the Be Quick or Be Dead and Protect Earth waves, and if you have god-like skills to somehow survive with only 3 lives after this. But since there's no way you're going to skip the impossible waves unless you use cheats (and those are going to make up ~3/20th of every loop), you will likely meet your demise as late as on Wave 100000004.