Why Earth Is at the Centre of the Universe – What’s Beyond the Edge¿

If you look at the official numbers given by science, it appears that Earth is located in a very suspicious place, right at the center of the universe. We are told that the universe we see extends about 46.5 billion light years in every direction. This immediately creates a fascinating logical puzzle. How can we appear to be at the center of the universe? Why does the universe seem to have an edge at 46.5 billion light years? And what lies beyond this edge? And if the universe itself is expanding, it naturally leads to another question. What exactly is it expanding into? And what would we see if we could travel all the way to its boundary? In this video, we will build a simple geometric picture of the cosmos to resolve this paradox of the edge of the universe in a logical and intuitive way, without relying on complicated mathematics. Hi friends, welcome to a new episode of Science Simplified for All. If we want to talk about where the edge of the universe is and what happens beyond it, the first thing we need to understand is what we actually mean by the word edge. Because the location of an edge depends entirely on how we define it. When the definition changes, the edge also changes. To understand this idea, let us start with a simple example. Imagine standing on a seashore and looking out toward the ocean. Far away, you see a line where the sea appears to meet the sky. This is called the horizon. But in reality, the sea and the sky are not meeting there. What you are seeing is a visual limit created by the curvature of the earth. Objects beyond this line are hidden from view because of the curvature of the earth, which creates the illusion of an edge. Now imagine that you are standing in the middle of the ocean. In that case, you would see this horizon all around you, forming a circle, with you standing exactly at its center. Here is the key point. If you are not in a position to use modern technologies like satellites or radio communication, the part of the world you can directly see and understand is limited to what lies within this horizon. You receive no direct information from beyond it. In that sense, your knowledge about your surroundings ends at the horizon. But this does not mean the earth ends there. It only means that from where you are standing, there is no direct way to know what lies further. And remember, the earth itself has no edge. It is a sphere. Yet, for every observer standing on it, there is still a clear limit to what can be seen. That limit is the horizon. Now comes the most interesting part. If you sail toward the horizon, you never actually reach it. As you move forward, the horizon also moves along with you. Imagine that you are initially standing at a point called A on the earth, and another point called B lies exactly at the edge of your horizon. You start traveling from A toward B. When you finally reach B and turn around, you will find that A is now lying at the edge of your horizon. This happens because the horizon is not something fixed on the earth. It does not belong to the earth. It belongs to the observer. It always moves along with you, and you are always at its center. Keep this idea in mind because this behavior of the horizon is the key to understanding what we really mean by the edge of the universe. Now let us apply the same logic to space. Almost everything we know about the universe comes to us through light. We learn about stars and galaxies only through the light that reaches us from them. The key limitation here is that the speed of light is not infinite. It has a fixed speed limit of about 300,000 kilometers per second. Because of this limit, light from distant objects takes time to reach us. This leads to an important consequence. We never see distant objects as they are right now. We only see them as they were in the past. Take the sun as an example. Light from the sun takes about 8 minutes to reach the earth. So when we look at the sun, we are actually seeing light that left it 8 minutes ago. The sun as it exists at this exact moment will be visible to us only after another 8 minutes. This also means that if something were to happen to the sun right now, we would not become aware of it immediately. Any change would be visible to us only after those 8 minutes have passed. Now let us bring back our geometric picture. Imagine drawing a circle around the earth with the earth-sun distance as its radius. Light from every point on this boundary takes 8 minutes to reach us. What we see from all those locations is how they were 8 minutes ago. Strictly speaking, this is not a circle but a sphere surrounding the earth. But for ease of visualization, we can think of it as a circle for now. The nearest star beyond the sun is Proxima Centauri, about 4 light years away. Light from that star takes 4 years to reach us. So what we see today is how that star was 4 years ago. As we extend this boundary farther outward, we are not just looking deeper into space, we are also looking further back in time. Take the Andromeda galaxy, our nearest galactic neighbor. It lies about 2.5 million light years away. If we draw our boundary at this distance, light from objects lying on that boundary has taken 2.5 million years to reach us. So, when we observe Andromeda, we are seeing it as it existed 2.5 million years ago. If we want to know how Andromeda looks right now, there is no immediate way to find out. We would have to wait another 2.5 million years for that information to reach us. Now let us push this boundary much farther outward, to a distance from which light has taken about 10 billion years to reach us. Everything we see from this boundary today is how stars and galaxies looked 10 billion years ago. If we extend this boundary even further, to around 13 or 13.5 billion years of lookback time, we begin to see the universe in its very early stages. At this distance, we see the first galaxies just beginning to form. It is important not to misunderstand this. This does not mean that new galaxies are forming there right now. Just like the regions around us today, those distant regions are also filled with mature galaxies at present. We simply cannot see them as they are today. We only see their ancient past. Finally, if we extend this boundary to a circle from which light took 13.8 billion years to reach us, we should be seeing what happened there 13.8 billion years ago. But 13.8 billion years ago is the time when the Big Bang happened. So theoretically, if we look that far, we are supposed to see the Big Bang itself. But what we actually observe is the cosmic microwave background radiation. This is the leftover radiation from the early universe, the faint afterglow of the hot, dense state that followed the Big Bang. It is the oldest light we can ever observe. Two points need special attention here. First, just because we see the Big Bang when we look at the farthest observable circle around us, it does not mean that the Big Bang is happening there now. Those regions are also filled with mature galaxies today, just like our own neighborhood. What we are actually seeing is light from the Big Bang that occurred 13.8 billion years ago, finally reaching us now. Second, just because we see the Big Bang only when we look at this farthest boundary, it does not mean that the Big Bang happened only there. The Big Bang happened everywhere in the universe, not at one particular location. The Big Bang also occurred at the place where we are standing now, as well as in all the earlier circles we discussed that are closer to us, such as the 2.5 million year circle and the 10 billion year circle. In fact, the Big Bang happened everywhere in the universe at the same time. But since those regions are much nearer, the light from the Big Bang that occurred there has already passed us long ago. That is why we do not see the Big Bang happening in those nearby regions today. Instead, what we see from those closer regions is what happened after the Big Bang, such as the formation of new galaxies. That is because light from those later events is what is reaching us now. Now, the next point is very important to pay attention to. This circle, corresponding to a look-back time of 13.8 billion years, represents the farthest part of the universe that we can possibly observe from the Earth. Light from these regions has taken the entire age of the universe to reach us. A natural question now arises. What about regions beyond this boundary? Light from regions beyond this circle has not yet reached us. The reason is simple. The universe itself is only 13.8 billion years old, and there simply has not been enough time for light from beyond this boundary to arrive here. Because of this, we have not yet been able to see or directly understand anything that lies beyond this circle. When we discussed the example of the horizon on Earth earlier, we pointed out that if we do not use any modern technology, the horizon represents the maximum distance from which we can see and know things directly from the Earth. Everything within it forms our observable world. In the same way, we know that light is the fastest thing that can travel through the universe. So, if even light from regions beyond this circle has not yet reached us, it means that we currently have no direct information about anything beyond it. This boundary is what we call the particle horizon. Everything that lies within the particle horizon is called the observable universe or the visible universe. And when we usually talk about the size of the universe, we are actually referring to the size of the observable universe. The particle horizon marks the outer limit of the observable universe. It is what we usually refer to as the edge, the boundary, or the limit of the universe, at least from our point of view. In scientific and astronomical discussions, when we talk about the universe, in most cases, we are actually talking only about the observable universe. Since we have no information about what lies beyond it, we generally do not talk about those regions. So, when we say that the universe was compressed into a very small region at the time of the Big Bang, what we are really referring to is the matter, energy, and space contained within the observable universe being concentrated into a very small region. We are not talking about the entire universe as a whole. Now, if we ask what lies beyond this boundary of the observable universe, the honest answer is that we cannot say anything with clear evidence. At best, we can only assume that regions beyond this boundary are similar to Let us imagine a thought experiment. Suppose at this very moment, we could instantly travel to any location on this circle, in any direction. If we then look beyond that boundary, we would most likely find stars and galaxies similar to those in regions closer to us. And if we turn around and look back toward the place we started from, toward where the earth is right now, we would not see the earth there. Instead, we would see the Big Bang taking place in that direction. This means that the region we call the observable universe always moves along with us. We are always located at its center. Earlier, when we discussed the example of the horizon, I mentioned that as we move along the surface of the earth, the horizon also moves along with us. In the same way, when we arrive at this new location, this circle becomes our observable universe. The earth will now lie at the edge of this observable universe. But when we look from here toward the place where the earth is currently located, we will not see the earth there. The reason is that light from the time of the Big Bang emitted from the location where the earth now stands is what is reaching us at this moment. So, when we look in that direction from here, what we will actually see is the Big Bang taking place. Now comes the next question. How large is the universe beyond this observable universe? Does it have an edge or a boundary? The honest answer is that we do not know for sure. Based on the calculations we can make using the methods currently available to us, the universe beyond the observable universe appears to be infinite or at least far larger than what we can currently observe. However, we cannot say how accurate this conclusion really is with our present understanding. The next question is this. Did the Big Bang happen only to the observable universe or did it happen to the entire universe? The most likely answer is that the Big Bang happened to the entire universe. We have already said that all the regions within our observable universe were compressed into a very small, hot and dense state at the time of the Big Bang. In the same way, it is reasonable to assume that matter, energy and space lying outside our observable universe were also in a similarly compressed, hot and dense state at that time, surrounding us in all directions. However, we cannot state this with certainty. The reason is simple. There is no practical or experimental way for us to directly know or verify what lay beyond the observable universe at the time of the Big Bang. Through this video, I hope you got a fairly good idea of what we mean by the observable universe, why we are always at its center and what may possibly lie beyond its edge. Before we end, let us pause and note two intriguing questions that naturally arise from everything we have discussed. First, we said that the age of the universe is about 13.8 billion years. So, at first glance, it feels logical to expect the distance to the particle horizon to be about 13.8 billion light years because that is the time light has taken to reach us from there. But in reality, the distance to the particle horizon is about 46.5 billion light years. In other words, the observable universe has a diameter of nearly 93 billion light years. How can a universe that is only 13.8 billion years old be this large? Second, the boundary of this observable universe is continuously increasing with time. At present, we can see only up to this circle. We cannot see regions beyond it because light from those regions has not yet reached us. But as time passes, light from slightly more distant regions will begin to reach us. Then, light from even farther regions will arrive. As days, months, and years go by, light from more and more distant parts of the universe reaches us. As a result, the size of our observable universe keeps increasing with time. This naturally raises an interesting question. If we wait long enough, an infinite amount of time, will the entire universe eventually become observable? There is another unavoidable limitation that prevents this from happening. Beyond a certain distance, light from some regions of the universe will never be able to reach us, no matter how long we wait. But why is that? These two questions are closely connected, and answering them requires us to understand some deeper aspects of how space itself behaves. We will explore both of these ideas in detail in another video. 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