Is there a boundary in the universe?

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Is there a boundary in the universe?

2019-03-01 15:47:38 17 ℃

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Levitan Press: Let's not talk about the universe, let's talk about the near-Earth. We all know now that the earth is round, not flat as people thought thousands of years ago. But even after Columbus discovered the New World and Magellan walked around the earth, many people still believe that the earth is flat. The International Horizon Society still exists today, with about 500 members.

And we are still facing similar divergences on the subject shown in the title: what shape is the universe (circular or circular)? Is there a boundary (imagine the Earth's "finite and unbounded")? It's really too difficult...

Wen/Daniel Kolitz





This article is based on the Creation Common common Agreement (BY-NC). Fuel Rat was published by Fuel Rat in LeviatThe results of this study are as follows:1. No longer able to satisfy people's fantasies, the human mood for exploring the boundaries of the universe is becoming an urgent expectation, and those daily trifles, such as bad weather, crowded subway, or worry about their thighs will be cancerous, boring life on earth is giving birth to a hot-blooded space dream.

But at the edge of the universe, what is waiting for you? When we talk about this cosmic boundary, is it a boundary line or a large unthinkable ceiling? Or does it really exist, whether on the edge or on the ceiling? In this week's "Giz Questions and Answers" column, we have several cosmologists looking for answers.

Sean Carroll

Professor of Physics, California Institute of Technology. His research fields include quantum mechanics, gravity, cosmology, statistical mechanics and basic physics. As far as we know, there is no boundary in the universe. The universe has an observable boundary - that is to say, there is a limit to how far we can see. This is because light has a limited propagation speed (1 light year per year), so when we look at distant objects, we are also looking back at ancient time and space. The so-called limit is that we can almost see what happened nearly 14 billion years ago, that is, the radiation remnants of the Big Bang. This is the Cosmic Microwave Background that surrounds us from all sides. However, this is not what we usually call a "visible boundary".

Source: Futura-Sciences

Because our observable range is limited, we are still unable to determine what the universe looks like outside the Observable Universe. Within our visibility, the state of space is very balanced, and it will probably remain so for almost eternal time. The universe looks like either a three-dimensional sphere or a three-dimensional bread ring. If this is true, the total volume of the universe is finite, but it still does not have a boundary, is like a ring without a starting point or an ending point.

However, beyond our visible range, the universe may not be balanced, and its states may vary greatly from place to place. This possibility is Multiverse in cosmology. We are not sure whether the multiverse exists or not, but it is because we can't observe it with the naked eye in any case. It is reasonable to keep an open mind on this concept.

"Because our observable range is limited,

so we can not determine the appearance of things outside our observable universe. The state of our visible universe is very balanced,

, and

maybe in almost eternal time,

it will continue to be like this.


Map Source:

Jo Dunkleyp>

Professor of Physics and Astrophysics, Princeton University. Her research fields include the origin and evolution of the universe.

is a cliche and has to be talked about!

Well, we don't think there is a specific boundary in the universe. We believe that the universe either extends infinitely in all directions or is self-enclosed, but there is still no boundary. Like the surface of a doughnut: it has no edges. The universe may look like it, but the universe is three-dimensional, and the surface of the doughnut is two-dimensional. The so-called no boundary means that you can launch a rocket in any direction of the universe, and if you travel long enough in the universe, you will eventually return to the starting point.

Another concept of boundary is observable universe, which refers to the space we can see with the naked eye. Beyond this observable boundary, the light generated since the Big Bang has not even reached our location. And that boundary is the limit of the range that we can see. The universe beyond the boundary, perhaps as we can see around it, is a supercluster of galaxies, and each galaxy contains billions of stars and planets.

"We believe that the universe either extends infinitely in all directions,

or it is self-enclosed, but there is still no boundary.

is like the surface of a doughnut: it has no edges. The universe may look like it, but the universe is three-dimensional,

and the surface of the doughnut is two-dimensional.

Jessie Shelton

Assistant Professor of Physics and Astronomy at the University of Illinois at Urbana-Champaign. Her research includes Astrophysics and cosmology. The content of the topic

depends on what your definition of the "cosmic boundary" is. Because the speed of light is limited, when we look farther into the universe, we are looking deeper into time - even when we look at the next Galaxy Andromeda, what we see is not what it looks like at this moment, but what we saw 2.5 million years ago, when the light emitted by stars in Andromeda was not seen by our telescopes until today. We can see the ancient light from the farthest distance, so in a sense, the so-called boundary of the universe is what we see when the oldest light reaches us. This is the Cosmic Microwave Background that exists in cosmic space, a faint afterglow left by the Big Bang, which indicates that the universe has cooled enough since then to form atoms. The limit we reach with the naked eye, also known as the Surface of Last Scattering, marks the moment when photons first flow out of the voids between particles. From that moment on, photons are no longer high-temperature plasma in ionized state, but can only bounce between electrons like table tennis balls. After that moment, the photons traveled billions of light years and finally reached Earth. So you can say that the boundary of the universe is the critical final scattering surface.

Andromeda galaxy is a spiral galaxy, about 2.5 million light-years away from Earth, the nearest Galaxy except Magellan Cloud (companion galaxy of the Milky Way where Earth is located). Source: Wikipedia

So at this moment, what are the boundaries of the universe? We don't know --- we don't know, we have to wait for those places to shine, and then after billions of years we finally get to where we are. Because the universe is expanding faster and faster, those lights may not be able to reach here at all --- but we can at least guess about that.

If we look at it at the most magnificent scale, we can see almost the same picture in any direction of the universe. So if you look at the boundary of the observable universe of Earth's people and look across the boundary, what you see is probably another Universe similar to the one we already know, filled with galaxies of all sizes and sizes in every direction. Therefore, the best guess about what's on the edge of the universe is simple. There are just more universes, more galaxies, more planets, and perhaps more organisms confusing the same question.

"In a sense,

the so-called boundary of the universe,

is what we see in our eyes when the oldest light reaches us,


Michael Troxel

Assistant Professor, Department of Physics, Duke University. His research scope includes observational cosmology and theoretical cosmology.

Although the universe is likely to be infinite in size, it may have more than one "boundary".

We believe that the universe is infinite-that is, it does not have any edges. If the universe is "flat" (paper-like) or "open-curved" (saddle-like) - as we measure with high percentage accuracy, it is infinite. If the universe is "closed", then it is not infinite.

But no matter how it looks, if you go far enough along one direction of the universe, you will eventually return to the starting point --- in this regard, you can imagine moving on the surface of a sphere. As Bilbo Baggins of the Hobbit sings in his two lyrics, "The Road goes ever on and on/down from the door where it began." It not only extends forever, but also goes round and round.

Map Source: Daily Express

Although the shape of the universe is infinite, it still has boundaries-and there are two boundaries. Because general relativity points out that all matter (including light) in the universe has an upper limit of speed -- about 670 million miles per hour -- and that matter at any point in the universe has the same ultimate speed. According to our observations, the universe is expanding in every direction, and as time goes on, its speed of expansion is increasing. The fact that

means that when we look at a very distant object, it takes a certain amount of time for light from that object to reach our position (that is, distance divided by the speed of light). The trouble, however, is that even as these rays travel, the universe is expanding, so they have to travel in order to reach us.