Asklemmy

That the many worlds interpretation is sort of correct, but incomplete. Hear me out.

Many worlds isn't as mind bogglingly ridiculous if the worlds are constantly merging back into each other. Like the universe where a photon bounced left and the universe where it bounced right are functionally identical, then they ARE just the same universe. As long as which way the photon bounced didn't make a meaningful difference, those two realities aren't suddenly new separate lines, they're like a rubber band that stretched in two directions, then bounced back together.

But let's say you measure the photon and keep records of it. Now there's two versions of you right? One measuring the photon going left, one measuring it going right. You're in separate universes that shall never meet right?

No... you've stretched the rubber band a little further. Over a timescale that's totally meaningless compared to the age of the universe, you will die, your records will decay and once the information is effectively scrambled into chaos... the two realities can just snap back together. Two universe... but now one again.

Now for some really mind bendy stuff... this stretching isn't just localized in time it's also localized in space. Meaning... if you measure your photon and split into two versions of yourself, but I'm on the other side of the world (or even just down the street from you) and I have no idea that there's two versions of you, stretched across this temporary universe split... Well, there's still only one version of me. Up until I encounter one or the other version of you. And if I never do... or if we just cross paths in the local grocery store and your photon experiment doesn't come up at all... there's still just one version of me.

And that one version of me can EASILY encounter both versions of you simultaneously without me ever knowing or it making a meaningful difference in my life. So your split reality is localized... possibly even microscopically in your body (like... most of your neurons in your brain didn't really change at all because of your experiment, only a few of them have to fire differently, the rest don't have to split... also, wtf) and in the parts of your lab equipment that kept records of the photon measurement.

Now, even whackier... the remerging isn't perfect, just perfect enough that the universe doesn't fall apart. Like... you know how sometimes you're SURE that the neighbor had a red car, but then you look outside and it's green and your spouse tells you it's always been green? Stuff that fuels r/glitchinthematrix.

"OK thebardingreen," you say, "sure, but wouldn't that mean our records would detect the imperfections all the time and we'd have clear evidence when we go an check the database that it's impossible to keep consistent records because of this spliting and remerging?"

"NO!" I say, "because of entropy."

See, if the universe is going to try to flow along the arrow of time to it's lowest energy state... and as we all know, something stretched (like a rubber band, but ANYTHING really) is in a high energy state. If we found lots of evidence this was going on, well that would keep the universe stretched out more, over longer periods of time. The universe can't have that, so when you start checking records, things tend to snap to their lowest energy state (possibly even to the point that you realize the neighbor's car WAS always green, and you just had a dream last night that it was red. But something's bothering you about that... doesn't seem quite right. You post on the internet and tell a eerie story about your strange experience and then go on with your life. The feeling fades. Becomes a funny party story.

Decades later, your grand kids remember a story you used to tell... and they retell it, but they don't quite remember what color you said the car was. There's no need for them to split into multiple versions (one who says red and one who says green), they just both say "the car was blue, then it turned out to be yellow." The universe is FULLY collapsed.

(Also, we KNOW that keeping perfect records / taking perfect measurements is actually incredibly hard and we tend to throw out anomalous results as garbage data, especially if we can't reproduce them, this could be going all the time and we would just consider it statistically insignificant bad data, within our expected margin of error, easily explainable as a common, everyday screw up)

So yes, that means there could be a small infinity of parallel universes where evolution / history went differently. A universe where sapient rat people are squeeking over their version of the internet about weird science facts. Sure.... but so what? The sun is going to expand into a red giant and consume the Earth and erase most of that information and then the local planetary stretch collapses back into it's lowest energy state... one where there might have been rat people, or hairless ape people, but either way, they're gone.

Ready for MORE whackyness?? THIS is the Great Filter. Sort of.

Intelligent civilizations spreading across the stars will create a HIGH energy state, as all those potential diversions splinter in more and more ways across greater distances. SO the universe will tend to favor outcomes where chaotic, clever and unpredictable life forms DON'T spread out of their own solar system, or travel across vast distances, because THAT would be a high energy stretch state. Although even just spreading across a galaxy is still only a LOCAL stretch as far as the universe is concerned. Heck, beings 100 light years away who never build a huge solar system sized radio telescope to pick up our faint emissions don't need to cause weird reality splits. They could exist in a weird little myriad of their own stretched realities and NEVER interact with ours in a meaningful way. And if one day one of their radio astronomers detects a strange radio signal from our star that NEVER repeats and is NEVER explained... well it really doesn't matter to them at all if we sent that signal or the rats did or the sun just hiccuped in way their physical models can't explain. Our whole solar system becomes a Schrodinger's cat box in which both us AND the rat people sent that signal existing in a superpositioned state until someone measures it... which they probably won't and probably CAN'T so the universe maintains it's low energy state.

So if you're ever like "If I go back in time and kill my grandfather, does that mean I never existed", what if you just created a weird stretch reality that will paradoxically persist for a while and then all collapse back together as soon as the universe can get away with it?

In this thought experiment, it's possible that a small infinity of time travelers showed up to Stephen Hawking's time travel party. BUT, that would cause a high energy stretch over a weird knot in time... so the universe will TOTALLY favor outcomes in which no one showed up, so in the vast majority of universes, NO time travelers show up to hang out with Stephen Hawking, BECAUSE that's less stretching for the universe to do before it snaps back to a low energy state.

So, the many worlds interpretation doesn't mean that infinities of universes are being created constantly, it means there's JUST one universe, but multiple pocket realities can exist in it, localized in both space and time, and these pocket realities are constantly snapping back and merging with each other, sometimes inconsistently. Which is EXACTLY what we'd expect from an energetic system progressing through time, experiencing entropy.