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What is the edge of the universe?



Giz Asks In this series of Gizmodo, we ask questions about everything from space to ass and get answers from different experts.

It is a routine emotion in 201

9 for an urgent desire, four or five times a day, to be released not just in space, but by as much as the edge of the universe as far as possible to obtain from the dream the bad weather fever, dropped trains and potentially cancerous thighs that represent life on Earth. But what would be waiting for you at the cosmological border? Is it a limit, or what are we doing here more like some unimaginably large ceiling? Is there even a boundary / ceiling there at all? For this week, Giz Asks talked to a number of physics-oriented physicists to find out.

Sean Carroll

Professor of Physics, Caltech, whose research focuses on quantum mechanics, gravity, cosmology, statistical mechanics, and the fundamentals of physics, among other things

There is no end to the universe as far as we know. There is an end to the observed universe – we can only see that far out there. This is because light travels at a limited speed (one light year per year), so when we look at distant things, we also look back in time. Eventually, we see what happens almost 14 billion years ago, the residual emanation of the Big Bang. This is the cosmic microwave background that surrounds us on all sides. But this is not actually a physical "end" in any useful sense.

As we can only see so far, we are not sure what things are outside our observed universe. The universe we see is quite even on large rocks, and maybe it's going literally forever. Alternatively, the universe can be embraced as (a three-dimensional version of a) sphere or fertilizer. If this is true, the universe will be limited in the overall size, but there will still be no edge, just as a round has no beginning or end.

It is also possible that the universe does not have the same past what we can see, and the conditions are wildly different from place to place. This opportunity is the cosmological multiverse. We do not know whether there is a multiverse in this sense, but since we can not actually see one way or another, it is wise to keep an open mind. "Because we can see only so far, I'm not sure what things are outside our observed universe. The universe we see is pretty much the same on big rocks and maybe it's going literally forever. "

Jo Dunkley

Professor, physics and astrophysical sciences, Princeton University, whose studies are in cosmology and study the origin and evolution of the universe

More than the same!

Well, so we do not really think there's an end to the universe. We think it either goes indefinitely in all directions, or maybe it's closed so it's not infinitely large, but there are no edges yet. The surface of the donut is such: no end. It is possible that the whole universe is the same (but in three dimensions – the surface of the donut is just two-dimensional). This means that you can go anywhere in space on the rocket ship and if you have traveled long enough, you will return to where you started. There are no edges.

But there is something we call the observed universe, which is part of the space we can see. The end of this is the place beyond which light has not had time to reach us from the beginning of the universe. It's just the edge of what we can see, and beyond it's probably more of the same things we can see around us: super-groups of galaxies, every huge galaxy containing billions of stars and planets. or it continues indefinitely in all directions, or maybe wrapped on itself so that it is not infinitely large, but there are no edges yet. The surface of the donut is such: no end. It is possible that the whole universe is the same (but in three dimensions – the surface of the donut is just two-dimensional).

Jesse Shelton

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

This depends on what you mean by the edge of the universe. Because the speed of light is extreme, looking further and far in space, we look further back in time – even when we look at the next galaxy, Andromeda, we do not see what is happening now, and what was happening now. two and a half million years ago when Andromeda stars emit the light that our telescopes only detect. The oldest light that we can see comes from the farthest side, so in one sense the edge of the universe is what we can see in the oldest light that reaches us. In our universe, this is the cosmic microwave background – a weak, long-lasting reflection of the Big Bang, noting that the universe is cooled sufficiently to form the atoms. This is called the surface of the last distraction as it marks the place where the photons stop ping-pong between the electrons in hot ionized plasma and begin to flow through a transparent space all the way through billions of light-years to us on Earth. So it can be said that the edge of the universe is the surface of the last distraction.

What is now at the end of the universe? Well, we do not know – we can not, we have to wait for the light to radiate here now to reach here many, billions of years in the future, and since the universe is expanding faster and faster, I probably will not succeed to do it here, but we can assume. On the largest rocks, our universe seems almost the same in every direction. So if you were on the brink of our observed universe today, you will see a universe that looked more or less the same as ours – galaxies, large and small in all directions. Thus, a very good assumption of what is on the brink of the universe is now simply the universe: more galaxies, more planets, perhaps even more living beings who ask the same question. The universe is what we can see in the most ancient light that reaches us. "

Michael Truskell

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

Although the Universe is probably endless, it actually has more than one practical edge.

We believe the universe is actually endless – it has no end. If the universe is "flat" (as a sheet of paper), because we feel it is better than percent accuracy, or "open" (like a saddle), then it really is infinite. If it is "closed," which is like basketball, then it is not endless. However, if you go far enough in one direction, you will eventually return back where you started – just think about moving around the ball. As once a hobbit named Bilbo said, "The road goes on and goes out of the door where it started" (again and again …). The universe still has a "edge" for us, although … two really. This is due to part of the general theory of relativity, which states that all things (including light) in the universe have a speed limit of about 670 million miles an hour, and this speed limit is the same everywhere. Our measurements also tell us that the universe is expanding in all directions and not just expanding, but expanding faster and faster with time. This means that when we observe an object very far from us, the light from this object takes some time to reach us (the distance divided by the speed of light). The tricky thing is that as the space expands as light travels to us, the distance that light has to travel also increases with time on our way to us.

So the first thing you could ask is what is the farthest distance we can observe from an object if it radiates at the very beginning of the universe (which is about 13.7 billion years old). It turned out to be about 47 billion light-years (the light year is about 63,241 times the distance between the Earth and the Sun) and is called the "horizon." You can also ask the question a little differently. If we send a message at the speed of light, what is the farthest distance that any other planet could ever get? This is all the more interesting because the speed of expanding the universe becomes faster in the future (rather than slowing down in the past). It turns out that even if the message has traveled forever, it will only be able to reach someone who is 16 billion light-years from now. This is called the "space horizon of events". The farthest planet we can observe is only about 25,000 light-years, so we can still say hello to all we know they can exist in the universe so far. The farthest distance our current telescopes may have identified from a galaxy is only about 13.3 billion light-years, so we can not see what's on any of these "edges" right now. So no one knows what's on the brink! "

" If you go far enough in one direction, you will eventually return to where you left. "

Abigail Vireg

assistant at the Cavill Institute of Cosmology. Physics at the University of Chicago

Using telescopes on Earth, we look at the light coming from remote places in the universe. The further the source of light, the longer it takes this light to get here. So when you look at distant places, watch what these places were when the light you saw was created and not what those places are today. You can keep looking farther and farther, answering farther and farther into time until you hit a spot corresponding to a few hundred thousand years after the Big Bang. Before that, the universe was so hot and dense (before there were stars and galaxies!) That every light in the universe just rocked and we can not see it with our telescopes today. This place is the end of the "observed universe," sometimes called a horizon, because we can not see beyond it. Over time, this horizon changes. If you could watch from another planet somewhere else in the universe, you will probably see something very similar to what we see here on Earth: your own horizon, limited by the time elapsed from the Big Bang, the speed of light, and how the universe expanded

What place today, which corresponds to the Earth's horizon, looks today? We can not know, because we can only see this place, just as it was after the Big Bang, not as it is today. However, all measurements show that the entire universe we can see, including the edge of the observed universe, looks like our local universe today: with stars, galaxies and galaxy clusters and lots of empty space.

We also think the universe is much larger than the universe we can see on Earth today, and there is no "end" to the universe itself.

"All measurements show that the whole universe we can see, including the edge of the observed universe, looks like our local universe today: with stars, galaxies and clusters of galaxies and lots of empty space."

Arthur B , Professor of Physics, University of Pittsburgh, whose research focuses on cosmology and related theoretical physics

the age we have now estimated to be 13.7 billion years, because we also know that light This means that the light beam, which begins at a very early point in time, has gone a certain distance today (called "horizontal distance" or "Hubble distance"), since nothing spreads faster than the speed of light, Hubble's distance is the farthest distance we can observe in principle (unless we find a way around the theory of relativity!). almost Hubble's distance: cosmic microwave background radiation. We know there is no "end" of the universe to the distance from the microwave background, which is almost the entire distance of Hubble from us. So we usually make the assumption that the universe is much larger than our own volume of Hubble, and any real end that may exist is far farther than we can observe. This may not be true: maybe the universe has a rib just off Hubble from us and beyond are sea monsters. But since the whole universe we can observe seems relatively similar and equal, it would be an extremely strange state of affairs.

So I'm afraid we will never have a good answer to the question: The universe may have no end, and if it has an edge, that edge is far enough that the edge light has not yet had enough time to reach us in the entire history of the universe. We have to agree with the understanding of the part of the universe we can actually observe.

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