The night sky was once shrouded in total mystery. The human eye could only understand so much of what it saw, and it wasn’t until the first telescope was invented in the 1600s that the heavens became just a little bit clearer. But we do still have so much left to learn…not least about how and where it all ends, or whether it ends at all? Does anything exist outside of the universe?

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Outside of the universe”,we first have to ask where it ends. But, the truth is that we can’t be certain on an answer to that question… because we can’t see that far. The Universe came into existence some 13.8 billion years ago, which sets a limit for the distance that light can travel. Because of universal expansion, the farthest we can see, what we call the cosmic horizon, is about 46 billion light-years away. That marks the edge of the observable universe, and no one is really confident on what exists beyond that. It’s genuinely impossible to say with any certainty. It’s unfortunate, then, that we’ll probably never see the universe as a whole, to get a better understanding. In fact, according to some theories, we might never see more of it than we do now (at least, not from our current position). Meanwhile, according to estimates on the size of the entire universe (the observed and unobserved parts of it), it could be as much as four hundred times larger than what we can currently see! The earliest photons visible to us today makeup what’s called the “Surface of Last Scattering”. So, we need to go beyond that, to navigate through all of the unknown-ness of space, to even imagine what lies outside of it all. 

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One idea for what exists beyond is that nothing changes; or even that everything we do know end lessly repeats itself into infinity. In this understanding the universe is flat, and it’s as though everything there ever will be is basically skating across a border lessplane. That means that there are infinitely more galaxies, stars, planets, and even life forms - but that they’re all bound within one,u thing - the total universe. This idea corresponds somewhat with the multiverse theory, except that the infinite variations still exist in one, all-encompassing structure instead of an infinite number of different ones. In this case, “outside of the universe”means “outside of our comprehension”, but still inside of an infinite place. That’s if an infinite place can ever really have an “inside” and “outside” which, when you think about it, it can’t. So, working from the hypothetical reality that our universe does “end” and there is an “outside” to speak of, what then? Well, all kinds of weird stuff! In 2008, a team of astronomers noticed something decidedly strange about certain galactic clusters. While most cosmological models predict that clusters should be distributed randomly across the universe and that they should travel in random directions, the team found that the ones they were monitoring all seemed to move in a “surprisingly coherent” way, appearing to converge on one location towards the constellations Centaurus and Vela. 

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The phenomenon was soon christened “DarkFlow”, and it was theorized in some corners that there could be extremely massive objects, bigger than anything we’ve ever seen, pulling on these clusters from outside of the observable universe. On the one hand, these unknown, cosmic megastructures could be massive accumulations of physical, recognisable matter, yes on an unimaginable scale but still operating from inside our same universe, only out of sight. On the other, the “dark flow” could be being caused by something else pulling, pinching and generally influencing our universe from a far. Say the effects of gravity extend not just all across the universe but also all beyond it, then our universe might hang in equilibrium with other, unknown, truly massive entities - similar to how a planet is positioned around a star. The Earth is held in place by the mass at the centre of the solar system, the sun; which is held in place by the supermassive blackhole mass at the galactic centre of the milky way… Zoom further out, and could the universe be physically guided by something else, something bigger, at the centre of something unimaginably huge? Theories abound from genuine scientific hypotheses to straight-up sci-fi fantasies. At the time, NASA considered the “dark flow”discovery as possible evidence of “sibling universes”. 

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Quite what those “siblings” could be like is anyone’s guess, but it does set up the general possibility of “other universes” the idea that ours isn’t the only one and is, in fact, subject to how the others behave. One theory for what existed before the big bang says that there was an empty vacuum full of energy and here’s where these “other universes” might’ve formed… Assuming that the “vacuum full of energy”is correct, and that the formation of our universe didn’t use up all of that energy, there’d have been plenty more to spread around - resulting in, well, who knows what? What we do know is that there are region son the map of the cosmic microwave background radiation in our own universe, showing the after glow of the big bang, that don’t look at all as they should do. Scientists have dubbed one region the “ColdSpot” and the other the “Axis of Evil”, and both defy explanation. In the case of the “Cold Spot”, especially,one fairly far-out (but not disprovable) theory says that these anomalies could be like a“bruise” on the universe - caused by a collision or interaction with another universe outside of it. On the other hand, these anomalies could again be being caused by an unknown something, but one that’s still happening and existing inside the universe - just not inside the observable universe. The “Cold Spot” doesn’t prove that “there’s something outside” rather, “that there’s something outside” is just one possible solution for the Cold Spot.