muzik wrote:Could a gun similar to this one exist in normal life?

Sure! By "like this", you just mean a reflectorless rotating oscillator (every part of the pattern is active, no catalysts, nothing left behind) that spits out a glider with each rotation? Is 90-degree rotation required, or could it be 180 degrees, or a simple mirror reflection with no glide offset?

All of these options

must exist in B3/S23, thanks to the horrible old Universal Constructor argument which doesn't help at all with finding actual examples.

So it's just a question of how big the smallest example of each type is. We're not likely to find definite answers about "smallest" questions any time soon, in the absence of someone doing an exhaustive search, let's say of all 8x8 patterns, with a huge distributed search project.

If such a search happens to find one of these objects. then we'll know it's the smallest one -- but that seems pretty unlikely. And even if the smallest such object is only slightly larger, let's say, 12x12, it's going to be out of our reach to find it, pretty much indefinitely. If you call an 8x8 search a "One-Chessboard Search", then a 12x12 search is a million million million million One-Chessboard sized searches.

(And One-Chessboard is bad enough. I think it would absorb the entire world's current computing capacity for a noticeable amount of time. We're at, what, 10^20 operations per second globally nowadays? And 8x8 would be 10^19 cases to test, and each test is a lot more than ten CPU operations, even with very aggressive optimization.)

A really big

Volatility-Equals-One Gun could be constructed nowadays, which would actually run (slowly) in Golly -- but it would look suspiciously like a universal-constructor loop making a copy of itself, emitting a glider, and self-destructing.