What Is Beyond Edge Of The Universe?

[00:00:09]There is a point where everything comes to an end. Not the universe itself, just the part of it we can ever see.

[00:00:19]It's a bit absurd when you think about it. We talk about the universe constantly, yet we only know a tiny fraction of it.

[00:00:26]The rest presumably exists anyway, just without us.

[00:00:31]Imagine standing outside at night gazing up at the sky. Everything you see, every star, every galaxy, is part of that single limited region.

[00:00:42]Beyond that, probably more of the same, or maybe not.

[00:00:47]The universe doesn't end at that boundary. Only our view of it does. And that's exactly where it gets interesting, because the question shifts entirely. It's no longer how big is the universe, but rather how much of it can we ever actually know?

[00:01:05]Two completely different questions.

[00:01:08]The observable universe has a radius of about 46.5 billion light-years. That makes for a total diameter of around 93 billion light-years.

[00:01:20]Sounds strange at first, doesn't it?

[00:01:22]The universe is 13.8 billion years old.

[00:01:26]Surely light can only travel 13.8 billion light-years in that time.

[00:01:32]That is true, yet the radius is larger.

[00:01:35]The reason, space itself expands while the light is in transit. A galaxy whose light set out 13 billion years ago is no longer where that light originated today.

[00:01:46]It has moved further away.

[00:01:49]The space between us expanded while the light was still traveling.

[00:01:54]This leads to a strange effect. The farther away something is, the faster it recedes from us, driven purely by the expansion of space, not by movement in the classical sense. Eventually, this recession velocity exceeds the speed of light, and at that point, seeing any farther becomes simply impossible.

[00:02:22]There is a limit beyond which no telescope will ever see, no matter how well it is built.

[00:02:28]The cosmic microwave background.

[00:02:31]This radiation originates from a time about 380,000 years after the Big Bang, when the universe became transparent for the first time.

[00:02:42]Before that, the universe was a hot, dense fog of charged particles.

[00:02:47]Light could not move freely within it.

[00:02:50]It was constantly scattered, absorbed, and re-emitted, much like light in thick fog that simply cannot break through.

[00:02:59]Only when electrons and protons combine to form neutral atoms, could light suddenly travel unimpeded.

[00:03:07]This initial free-streaming radiation is precisely what we measure today as the cosmic microwave background.

[00:03:15]It is present everywhere in the sky, uniform, yet with tiny temperature fluctuations.

[00:03:22]And beyond that, there is nothing to see.

[00:03:26]Not because there is nothing there, but because no light existed prior to that moment that could reach us. It is not a physical wall then, but a temporal one.

[00:03:38]We assume that the universe does not simply end at the edge of the observable region.

[00:03:43]There is no reason why we, of all observers, should happen to be sitting right in the middle of everything.

[00:03:51]What this means is that there are regions whose light has never reached us.

[00:03:56]Not because they do not exist, but simply because not enough time has passed since the Big Bang for their light to arrive here.

[00:04:05]These regions are out there, we just cannot see them.

[00:04:09]Some models suggest that the entire universe is at least a hundred times larger than the observable part.

[00:04:16]Others speak of something far greater.

[00:04:19]To be honest, no one knows for sure.

[00:04:22]And then there is the possibility that the universe could actually be infinite.

[00:04:27]Infinite space, infinite [music] galaxies. No edge where it all comes to an end.

[00:04:35]It is difficult to imagine, [music] yet current measurements of the curvature of space do not rule it out.

[00:04:42]Beyond the observable universe, there is a second boundary.

[00:04:48]The cosmic event horizon.

[00:04:50]This is the boundary beyond which light emitted today will never reach us.

[00:04:56]>> [snorts] >> Not even in a trillion years.

[00:04:59]The reason lies in the accelerated expansion of the universe, driven by dark energy.

[00:05:05]Some galaxies visible in the sky right now are already receding from us so rapidly that the light they emit today will never reach us.

[00:05:14]>> [music] >> We can still see them, but only because their light was already on its way before the expansion pulled them beyond this horizon.

[00:05:26]Over time, more and more galaxies will vanish behind this horizon.

[00:05:31]For future civilizations billions of years from now, the sky will look significantly emptier than it does today.

[00:05:39]Entire galaxy clusters will simply disappear from observable reality.

[00:05:46]Here's a little thought experiment.

[00:05:49]You board a spaceship capable of traveling at the speed of light and simply keep going, flying beyond the edge of our observable universe.

[00:05:58]What would you see?

[00:05:59]Presumably, more of the same. More galaxies, more [music] planets. No end, no wall, no point where silence suddenly takes over.

[00:06:10]By and large, the physics out there should be the same as it is here.

[00:06:14]What might change are the details. The distribution of matter, the density of galaxy clusters.

[00:06:22]The point of this thought experiment is actually simple. Our observable universe isn't a special zone. It is simply the bubble we happen to be in.

[00:06:32]From any other point in the universe, it would look exactly the same.

[00:06:36]One's own little bubble surrounded by the invisible rest.

[00:06:45]The Big Bang is often misrepresented as an explosion originating from a single point in space.

[00:06:53]That is not the case.

[00:06:54]The Big Bang was not an explosion occurring within pre-existing space.

[00:06:59]Space itself expanded along with it.

[00:07:03]This means there is no location in the present-day universe that could be identified as the point of origin.

[00:07:11]At the moment of the Big Bang, every point in the universe was equidistant from everything else. In a sense, every point is the center.

[00:07:22]For many models, the rule is that the universe need not be situated inside anything.

[00:07:28]It does not have to be an object that could be viewed from the outside. It is comparable to the surface of a sphere, finite in area, yet without an edge.

[00:07:38]No single point on the surface is more special than any other.

[00:07:49]So, what would really be outside?

[00:07:52]One possibility, there is no outside at all. If the universe is infinite, the question of an edge or an exterior simply ceases to make sense.

[00:08:04]Another idea stems from the theory of eternal inflation.

[00:08:08]According to this theory, the extremely rapid expansion following the Big Bang did not end everywhere at the same time.

[00:08:16]In some regions, [music] it is theoretically still ongoing.

[00:08:20]These regions would form their own completely separate bubble universes, potentially with entirely different physical properties.

[00:08:29]This forms the basis of many multiverse hypotheses.

[00:08:32]>> [music] >> An infinite number of universes, each with its own initial conditions, physical constants, and history.

[00:08:41]Some of them might support life. Most, presumably, would not.

[00:08:47]The problem with all this is that there is currently no way to test [music] these ideas.

[00:08:52]Other universes lie beyond the reach of anything we could ever measure.

[00:08:57]No matter how you look at it, a number of things simply remain unknown.

[00:09:02]The actual size of the entire universe, unknown.

[00:09:06]Whether it is finite or infinite, we simply do not know.

[00:09:10]The curvature of space that we measure is so close to zero that both possibilities remain open.

[00:09:17]Large parts of the universe, perhaps even the vast majority, could remain forever unobservable.

[00:09:24]Not because of a lack of technology, but because of the structure of space itself.

[00:09:31]This is a significant realization for a field that strives to explain everything.

[00:09:36]Some questions are not merely difficult to answer. They lie fundamentally beyond the scope of what observation can ever achieve.

[00:09:44]This differs from we don't know yet. It is more a case of we will never be able to know, no matter how long we wait or how advanced our instruments become.

[00:10:00]The observable universe has a clear boundary, about 46.5 billion light years in every direction.

[00:10:08]The universe itself likely has none, or at least none we will ever know.

[00:10:14]What we call the universe is essentially just a part from which light has had enough time to reach us, a bubble, centered on us by chance, simply because we are standing here and looking out from this spot.

[00:10:29]Beyond that, there is presumably nothing alien, no wall, no end, no cosmic boundary in the classical sense.

[00:10:37]Likely just more of the same, more galaxies, more stars, more space, forever beyond our reach.

[00:10:45]The edge we see reveals less about the universe than it does about us, about the limits of what an observer at a specific place and time can ever possibly see.

[00:10:58]I hope you enjoyed the video and I'll see you next time.