To answer the question, the divergent streams seem to be caused by the penile opening not fully opening. The “floppy” bits in the middle stay togetherish, and create two separate openings, sort of like putting your thumb over the end of a hose.
The obvious follow on question is, of course, why does that start happening? Are you having prostate troubles? Your urine pressure dropped? Or is it something to do with elasticity of the penile skin?
Now I am in my late 40’s I wish for the halcyon days of my early 40’s, where I still had enough pressure for bifucated urinary flow.
I’m back to one stream, with an associated (significant) dribble of droplets falling straight down, usually splashing off the rim of the toilet and splattering my lower calves and/or shoes.
I thought this was going to be a tribute to RP’s wonderfully informative aviation posts. Never expected to learn instead about bifurcated pee – but as a 45-year-old man, I guess it’s good to know about.
Thanks Irishman. This was of course a complete hypothetical and had nothing to do with any personal experiences I’ve had. I do however have a friend who tells me he, for a long time, had an easily aimed single stream of urine except for occasions following sex when there might be some residue interrupting the flow. When he got to his late 30s though things changed and he now finds that more often than not there is more than one stream and often they diverge at an angle that makes getting both streams into the bowl difficult. Even when both streams can be manoeuvred into the bowl the “surprise stream”* (the one typically at right angles to the aiming direction) normally has a chance to send a few drops on to the seat or the floor. Sometimes a bit of manipulation of the nozzle can fix the problem but there are also times where, with a sigh, he must resort to sitting down in an unmanly fashion that generally causes his partner to laugh at him (though this is preferable to having her hit him which is what happens when he attempts to persevere with his unsuccessful attempt to get it all in the bowl.)
The only time he finds the double stream effect useful is when he is required to give a urine sample. He can then aim one stream at the bowl while he sends the other into the sample bottle. There is sometimes a moment of minor panic however, when the sample bottle becomes full and with one hand aiming and the other holding a soon to be overflowing bottle, he must either manoeuvre himself into a seated position (often not on the seat because, like a good boy, he’s lifted it up) or stop the flow mid stream–doable, but uncomfortable.
Not to be confused with the “stealth stream” that presents at right angles to the aiming direction at a low enough pressure that it is not noticed until well over halfway into the urination process, normally shortly after congratulating yourself for having an easily aimed single stream while simultaneously pondering the warm, wet sensation gradually becoming noticeable on one foot.