\n The Carina Nebula viewed by the Hubble Space Telescope<\/p>\n NASA\/ESA\/M. Livio, The Hubble Heritage Team & Hubble 20th Anniversary Team (STScI)<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n Start off in any direction and fly through the universe. Out of our solar system, beyond the edge of the Milky Way, through the forest of galaxies that make up our Local Group into the wilderness of the distant cosmos, past black holes and galaxies and near-infinite worlds\u2026 or are they infinite?<\/p>\n Could you keep travelling forever or would you eventually reach an edge? Or perhaps end up right back where you began? This is the biggest problem in cosmology, especially if you take the word \u201cbiggest\u201d literally: what, exactly, is the size and shape of our universe? We\u2019ve got a few hints, but they don\u2019t point in any one particular direction, so it remains largely a mystery.<\/p>\n <\/p>\n When I talk about the universe with friends or colleagues, I often find myself reminding them that space is huge, perhaps even unending. It\u2019s a hard thing to get your head around, but cosmologists and great thinkers have been puzzling away at it for centuries. The best way to figure out its size is to start by sorting out what shape it is. And there are plenty of ideas for what form our universe might take.<\/p>\n The simplest shape for the universe would be essentially a flat sheet. Of course, it\u2019s far more complicated than that, but it\u2019s a useful metaphor (which you could say about most things in physics). I\u2019m going to hand-wave past some of the technical details, but suffice it to say that if the universe is flat, all the geometry you learned in school works: draw a triangle and its angles will add up to 180 degrees and all its lines will be straight. But if the cosmos is curved, things start to get funky. Your triangle wouldn\u2019t be a triangle as you know it, but the effects would be so small you wouldn\u2019t notice. The universe could be shaped like a saddle or even like a sphere, and either way geometry becomes non-Euclidean and therefore a bit strange.<\/p>\n The size and shape of the universe are governed by two quantities: gravity and dark energy. The gravity of everything in the universe pulls it in, and dark energy pushes it to expand. If these two are perfectly matched, the universe is flat. If dark energy is winning, it\u2019s Pringle-shaped. Either of these forms would allow the universe to be finite or infinite \u2013 there are models that work for each.<\/p>\n If gravity is winning, the universe is spherical and therefore finite \u2013 which is the simplest solution. However, as far as we can tell from various large-scale observations of the cosmos, it seems like the universe is probably flat. Then again, recent observations have shown that dark energy may be weakening over time, which really underlines how little we actually know for sure about the universe writ large. Dark matter is similarly mysterious, even as we build increasingly precise maps of it throughout the cosmos, and it is a crucial component in the gravity of the universe. So \u201cprobably flat\u201d should still be taken with a grain of salt.<\/p>\n At this point, I should tell you that I\u2019m not an entirely impartial narrator here. I, along with many physicists, do not like infinities. Sure, they\u2019re fun to think about, but plug one into the physical world and what does it even mean? Maybe it\u2019s just the limits of my human brain, but I have a hard time accepting that anything can be meaningfully infinite. Everything must have some limit, even if that limit is extremely big. Infinity strikes me as a bit of a cop-out. There\u2019s no way to measure it. If our equations aren\u2019t working right, we\u2019ll just assume it goes on forever? Give me a break.<\/p>\n I\u2019m not alone in that view, and given the general distaste for infinities, there are a lot of theories of what a finite universe might look like. Even if it\u2019s flat, there are plenty of options for how different parts of space-time might be connected to one another \u2013 like I said, the sheet\/sphere\/saddle distinction is a simplification. For one, there\u2019s the question of whether a finite universe has to have an edge. If the universe is finite and flat like a sheet of paper, it must have one \u2013 but then we must ask, what\u2019s beyond the edge? Maybe other universes, maybe nothing at all. It could be anything. But what happens right at the edge? Does existence just\u2026 stop? That\u2019s a bit unnerving and hard to imagine, and it\u2019s also hard to work into the equations that describe our universe.<\/p>\n \n Is one of these the shape of the universe?<\/p>\n Nataliia Pyzhova, MAXSHOT.PL, Sashkin\/Shutterstock<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n If space-time is curved, the options open up a little bit. A sphere doesn\u2019t have an edge, so if you travelled too far in one direction, you\u2019d just end up back where you started. Or it could be shaped like a doughnut or a Klein bottle or a weird wormhole-pocked sponge, or any number of other possibilities \u2013 some physicists have suggested it could be shaped like a peanut, a cone or an apple, the last of which is made possible only by adding more dimensions than we currently exist in. Like I said, it\u2019s complicated.<\/p>\n All those shapes that I just mentioned are finite. Add infinities into the mix and it all gets even wilder \u2013 one might even say unwieldy. You could travel forever and all you\u2019d find is endless space, an infinite variety of galaxies and stellar systems and worlds. There\u2019d be no worrying about edges or what\u2019s \u201coutside\u201d the universe because everything would be inside it.<\/p>\n In some sense, the prospect is exciting. You could find anything out there. There\u2019d definitely be other life forms \u2013 just by sheer probability \u2013 although that pretty much still holds for a universe that isn\u2019t infinite but just really, really big. Personally, though, I can\u2019t help but think that an infinite amount of universe is just too much. I love imagining what might be out there, but if the answer is \u201ceverything possible because the universe goes on forever and ever\u201d, there seems to be no point in imagining.<\/p>\n Those are personal feelings, though, and like everything in physics, in the end it\u2019ll come down to observations and maths. That\u2019s part of what I love about physics, its concreteness \u2013 and infinity just isn\u2019t concrete enough. If I choose a direction and fly off through the universe, eventually I want to reach something, whether it\u2019s an edge or just home again.<\/p>\n <\/p>\n Spend a weekend with some of the brightest minds in science, as you explore the mysteries of the universe in an exciting programme that includes an excursion to see the iconic Lovell Telescope.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<\/section>\n![\"\"](\"https:\/\/images.newscientist.com\/wp-content\/uploads\/2026\/02\/11171641\/SEI_284521528.jpg\")
<\/div>![\"Jodrell](\"https:\/\/images.newscientist.com\/wp-content\/uploads\/2025\/01\/15113200\/img_6300.jpeg\")
\n <\/picture>\nMysteries of the universe: Cheshire, England<\/h3>\n