is there a border we will never cross? are there places we will never reach,no matter how hard we try? turns out there are. even with science fiction technology,we are trapped in our pocket of the universe. how can that be?and, how far can we go?
local travel , we live in a quiet arm of the milky way;a spiral galaxy of average size, – about 100,000 light years across – consisting of billions of stars, gas clouds,dark matter, black holes, neutron stars, and planets, with a supermassiveblack hole in the galactic centre.
>from afar, our galaxy seems dense, butin reality, it consists, mostly, of empty space. with our current technology, sending a humanto the closest star, would take thousands of years. so, our galaxy is pretty big. the milky way is not alone, though. along with the andromeda galaxy,and more than fifty dwarf galaxies, it's a part of "the local group"; a region of space about ten million light yearsin diameter. it is one of the hundreds of galaxy groups inthe "laniakea supercluster", which, itself is only one of millionsof superclusters,
that make up the observable universe. now, let's assume, for a moment, thatwe have a glorious future; humanity becomes a type three civilisation, does not get wiped out by aliens, and develops interstellar travel based onour current understanding of physics. in this best case scenario,how far could we possibly go? well; the local group. it's the biggest structure that humanitywill ever be a part of. while it's certainly huge, the local groupaccounts for only 0.00000000001 % of
the observable universe. let this number sink in for a moment. we are limited to a hundred billionth ofa percent of the observable universe. the simple fact that there is actuallya limit for us, and that there is so much universe that we will neverbe able to touch, is kind of frightening. why can't we go further? well, it all has to do withthe nature of nothing. nothing, or empty space, isn't emptybut has energy intrinsic to itself; so-called "quantum fluctuations".
on the smaller scale, there isconstant action, particles and antiparticles appearing and annihilating themselves. you can imagine this quantum vacuum asa bubbling part: with denser, and less dense regions. now, let's go back 13.8 billion yearswhen the fabric of space consisted of nothing at all. right after the big bang, in an event knownas cosmic inflation, the observable universe expanded from the size of a marble to trillions of kilometres, in fractions of a second. this sudden stretching of the universe wasso fast and extreme,
that all those quantum fluctuations werestretched as well, and subatomic distances becamegalactic distances, with dense and less dense regions. after inflation, gravity began to pulleverything back together. at the largest scale, the expansion wastoo quick and powerful to overcome but in smaller scales,gravity emerged victorious. so, over time, the denser regions,or pockets, of the universe, grew into groups of galaxies, like the onewe live in today. only stuff inside our pocket – the local group –is bound to us gravitationally.
but wait, what is the problem then? why can't we travel from our pocket,to the next one? here, dark energy makes everything complicated. about six billion years ago, dark energy took over. it's basically an invisible force or effect,that causes, and speeds up the expansion of the universe. we don't know why, or what dark energy is,but we can observe its effect clearly. in the early universe, there were larger, cold spots around the local group, that grew into clusters with thousandsof galaxies.
we are surrounded by a lot of stuff,but none of those structures and galaxies outside of the local group are gravitationallybound to us. so the more the universe expands,the larger the distance between us and other gravitational pockets becomes. over time, dark energy will push the restof the universe away from us, causing all the other clusters, galaxies, andgroups to eventually become unreachable. the next galaxy group is already millionsof light years away, but all of them are moving away from us,at speeds we can't, ever, hope to match. we could leave the local group, and thenfly through intergalactic space,
into the darkness, but we would neverarrive anywhere. while we will become more and more stranded,the local group will become more tightly bound, and merge together to form one giant elliptical galaxy,with the unoriginal name "milkdromeda" in a few billion years. but it becomes even more depressing: at some point, the galaxies outsidethe local group, will be so far away, that they will be too faint to detect, and the fewphotons that do make it to us, will be shifted to such long wavelengths,that they will be undetectable. once this happens, no information outsideof the local group will be able to reach us.
the universe will recede from view. it will appear to be dark and emptyin all directions, forever. a being born in the far future inmilkdromeda, will think there is nothing but its owngalaxy in the entire universe. when they look far into empty space, theywill only see more emptiness and darkness; they won't be able to see thecosmic background radiation, and they won't be able to learn aboutthe big bang. they will have no way of knowingwhat we know today; the nature of the expanding universe,where it began, and how it will end.
they will think the universe is static and eternal. milkdromeda will be an island in the darkness,slowly getting darker and darker. but still, with its trillions of stars,the local group is certainly large enough for humanity. after all, we still haven't figured outhow to leave our solar system, and we have billions of yearsto explore our galaxy. we have the incredible luck to exist atthe perfect moment in time to see, not only our future but also ourmost distant past. as isolated and remote as the local group is,we can perceive the entire universe,
grand and spectacular as it is right now. this video was sponsored by squarespace.com/nutshell do you feel isolated in a humongous universe? why not set up a website or blog and share your thoughts with other humanoids around you? squarespace lets you do thatwith easy-to-understand tools very quickly and without any knowledge of web design. you can also use the code "nutshell" to save10 % and support kurzgesagt in making more videoes about our placein the universe.
thanks so much for the help with the videoto ethan siegel. follow his astronomy blog here. you can support us directly at patreonor get kurzgesagt merch here. it really helps. it is awesome that you watched this far,so we have made a playlist for you about more universe stuff. subtitles made by sebastian winkelmann subtitles by the amara.org community
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