What is there at the edge of the universe?

Professor of Physics and Astrophysical Sciences at Princeton University, whose research focuses on cosmology and studies the origins and evolution of the universe

More of the same!

So, we do not think there is a benefit to the universe. We think that this continues to be infinitely far in all directions, or perhaps it is wrapped up on itself so that it is not infinitely large, but still has no edge. The surface of a donut is like that: it has no edge. It is possible that the whole universe is like that too (but in three dimensions – the surface of a donut is only two dimensions). This means that you can leave in any direction in the space on board a rocket, and if you traveled long enough, you would return to your starting point. No edges.

But there is also one thing we call the observable universe, which is the part of the space that we can actually see. The edge of this place is the place beyond which the light has not had time to reach us since the beginning of the universe. This is only the edge of what we can see, and beyond that, it's probably the same thing we can see around us: super-clusters of galaxies, each huge galaxy containing billions of stars and planets.

"We think it's going on either way far in all directions, or maybe it's wrapped up by itself, so that it's not infinitely big, but that it's not Still has no edge The surface of a donut is like this: it has no edge.It is possible that the whole universe is like that too (but in three dimensions – the surface of a donut is only two dimensions). "

Assistant Professor, Physics and Astronomy, University of Illinois, Urbana-Champaign, whose research focuses on astrophysics and cosmology

It depends on what you mean by the edge of the universe. Because the speed of light is over, as we look further and further into space, we look more and more far back in time – even when we look at the galaxy next door, Andromeda, we do not see what is happening now, but what was happening Two and a half million years ago, Andromeda stars emitted light that our telescopes only detect now. The oldest light we can see comes from the farthest, so in a sense, the edge of the universe is what we can see in the oldest light that comes to us. In our universe, it is the cosmic microwave background – a faint persistent glow of the Big Bang, which marks the cooling of the universe that left enough atoms to allow the formation of atoms. This is what is called the last scattering surface because it marks the place where the photons stopped playing between electrons in an ionized and hot plasma and began to spread in the ## EQU1 ## 39, transparent space, up to billions of light years away on Earth. So we could say that the edge of the universe is the surface of the last scattering.

What is at the edge of the universe right now? Well, we do not know – we can not, we should wait for the light to be emitted here now to get here many billions of years in the future, and since the universe is growing more and faster, probably will not be able to do it here at all – but we can guess. On larger scales, our universe is pretty much the same in all directions. So, if you were at the edge of our observable universe today, you would see a universe that looked more or less like ours – galaxies, large and small, in all directions. Therefore, a very good idea of ​​what is at the edge of the universe is simply another universe: more galaxies, more planets, maybe even more living beings asking the same question.

"… in a sense, the edge of the universe is all we can see in the oldest light that comes to us."

Assistant Professor of Physics, Duke University, whose research focuses on theoretical and observational cosmology

Although the universe is probably infinitely large, there is actually more than one practical "advantage".

We think that the Universe is in fact infinite – it has no advantage. If the Universe is 'flat' (like a piece of paper), as we have tested it, it is greater than a percentage of precision or 'open' (like a saddle), it is really infinite. If it's "closed", which is a bit like a basketball, then it's not infinite. However, if you go far enough in one direction, you will eventually come back to where you started. Just think about moving along the surface of the balloon. As a hobbit named Bilbo once said, "The road always goes through the door where it started" (again and again …).

The universe always has a "benefit" for us, however, two. This is due to some of the general relativity that says that all things (including light) in the universe have a speed limit – about 670 million miles per hour – and that the speed limit is the even everywhere. Our measurements also tell us that the Universe is expanding in all directions, not just expanding, but expanding rapidly. This means that when we observe an object very far from us, the light of this object takes a long time to reach us (the distance divided by the speed of light). The problem is that because space is growing and light is coming in, the distance it has to travel also increases over time.

So the first thing you can ask is what is the farthest distance at which we could see the light of an object if it was emitted at the very beginning of the Universe (which is about 13.7 billion years). It is about 47 billion light-years away (a light-year is about 63,241 times the distance between the Earth and the Sun) and is called the "common horizon". You can also ask the question slightly differently. If we send a message at the speed of light, what is the farthest distance a person from another planet can ever receive? This is all the more interesting as the rate of expansion of the Universe accelerates in the future (instead of slowing down in the past).

It turns out that even if the message traveled forever, it could never reach anyone who was 16 billion light years away from us now. This is what is called "the horizon of cosmic events". The farthest planet we could observe is only about 25,000 light-years away, so we could always say hello to all those who, to our knowledge, could exist in the universe so far . The farthest distance that our current telescopes have been able to identify a galaxy is only about 13.3 billion light-years away, however, so we can not see what is in one or the other other of these "edges" for the moment. So nobody knows what's on each side!

"If you go far enough in one direction, you will eventually find your starting point."

Assistant professor at the Kavil Institute of Cosmological Physics at the University of Chicago

With the help of telescopes on Earth, we observe light from distant regions of the universe. The farther away the light source is, the longer it takes for the light to reach us. So when you look at distant places, you look at what they were when the light you saw was created – not what they look like today. You can keep looking farther and farther, which is a step back in time, until you reach a place corresponding to a few hundred thousand years after the Big Bang. Before that, the universe was so hot and dense (long before there were stars and galaxies!) That all light in the universe was only vibrating, and we can not see it with our telescopes today. hui. This place is at the limit of "the observable universe", sometimes called horizon, because we can not see beyond. Over time, this horizon changes. If you could look from another planet somewhere else in the universe, you would probably see something very similar to what we see here from Earth: your own horizon, limited by the time elapsed since the Big Bang, the speed of light, and how the universe has expanded.

What does the place that corresponds to the horizon of the Earth look like today? We can not know because we can only see this place right after the Big Bang, not as it is today. However, all measurements indicate that all the universe we can see, including the edge of the observable universe, resembles approximately that of our local universe today: stars, galaxies and clusters of galaxies and a lot of empty space.

We also think that the universe is much larger than the part of the universe that we can see here from Earth today, and that there is no "Edge" to the universe itself. It's just space-time, expanding.

"All measurements indicate that all the universe we can see, including the edge of the observable universe, resembles approximately that of our local universe today: with stars , galaxies and clusters of galaxies and a lot of empty space.

Professor of Physics at the University of Pittsburgh, whose research focuses on the cosmology and related issues of theoretical physics

One of the most fundamental properties of the universe is its age which, according to various measures, was 13.7 billion years old. Because we also know that light travels at a constant speed, it means that a light ray that started very early has traveled a particular distance until today (called the "distance of the horizon "or" Hubble distance "). Since nothing propagates faster than the speed of light, Hubble's distance is the greatest distance we can ever observe in principle (unless we discover a way around the theory of relativity!).

We have a source of light that reaches us from almost the distance of Hubble: cosmic microwave background radiation. We know there is no "boundary" between the universe and the origin of the microwave background, which is almost the entire distance from Hubble. We therefore generally assume that the universe is much larger than our own observable volume of Hubble, and that any real edge that might exist is much farther away than we can ever observe. That might not be right: the universe may have a benefit just beyond the distance of Hubble, and beyond, sea monsters. But since all the universe we can observe is relatively similar and uniform, this state of affairs would be extremely strange.

So I'm afraid we never have a good answer to the question: the universe may not have any edge at all, and if it has an edge, that edge is far enough away that the Light from the edge has not yet had enough time to meet us throughout the history of the universe. We must be content to understand the part of the universe that we can actually observe.