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I've sometimes heard of galaxies that are millions or billions of light years away but if we could instantly travel 786 trillion light years in any direction, what are we likely to find? And what if we continued on for another 786 trillion light years?

PS: I'm not a physicist.

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I really find this question confusing because it doesn't explain why you picked that number. If it's arbitrary, you should say so. –  ThePopMachine Jan 5 at 17:27

5 Answers 5

We would likely find galaxies. The universe, as far as we can observe, is very uniform on the large scale. Depending on the geometry of the universe, may be the place we left for travalling. For a fixed cosmic time the spacetime seems to be curved in a way that the universe looks finite when travelling along a straight (geodesic) line, although without boundary.

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I'm afraid the only correct answer to this question is that nobody knows.

Cosmology is based on a number of simplifying assumptions (sometimes called principles) - the most basic of which is that the universe is "isotropic and homogeneous on large scales". Isotropic means that is (or looks) the same in any direction; homogeneous means that what we see does not depend on our position in the universe.

This "cosmological principle" is reasonably well tested and would certainly make sense if the universe were very much bigger than we are capable of seeing. The most distant thing we can "see" in our universe is the cosmic microwave background (CMB), the light of which has been travelling for about 13.6 billion years. However, if we were to think about a parcel of gas that emitted the CMB and where it is now, we could calcuate that it is about 46 billion light years away due to the expansion of space in the universe. Thus the "edge of the observable universe" is about 46 billion light years.

What we can say, is that on these scales the Universe is very isotropic, and homogeneous, because the CMB is very smooth and looks the same in all directions to a very good approximation (but see below). This suggests that if you were to travel 46 billion light years in any direction, that you would probably have a very similar view to what we have now (that is, if you were able to miraculously travel instantaneously; if you travelled more slowly then of course the universe would continue to get older).

You are talking about travelling more than a factor 10000 further. On these scales we do not know anything outside of speculation. The inflationary model for the big bang might suggest that our observable universe is just a tiny part of a much greater entity and that within this very much larger entity everything will be homogeneous and isotropic at a given cosmic time. However, the recent very precise Planck measurements of the CMB, suggest there may be small, but real, anisotropies on scales as big as the observable universe, which would then suggest that any extrapolation by a factor of 10000 might be wishful thinking.

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You think it's possible that there are big bangs happening somewhere in space every second, thus creating an infinite amount of universes as we know ours (the one that's 13 billion years old)? –  frenchie Dec 29 '14 at 12:12

There is one principle that says "The universe is isotropic". It means it looks the same (on large scales) from any point you look from.

This means, in turn, that if you travel 786 trillion light years instantaneously in some direction, you'll find a very differnt sky but with exactly the same general structure: stars, galaxies, clusters of galaxies, and attractors.

Altough you can NOT travel so far so fast, you can make this mind experiment:

Send a spaceship so far at (almost) speed of light with a photo camera, take a 360º photo, come back, arrive 1572 triilion years afterwards. While awaiting for the spaceship return, wait 786 trillion light years, take a 360º photo, wait the othe 768 trillion years.

Compare the two photos. They were taken at the same "Cosmic time", one of them 768 trillion years ago, here, and the other one maybe two or three years of spaceship time ago, 768 trillion light years afar.

The photos will look the the same on the rough scale.

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1 light year is equal to 5,878,499,810,000 miles, so 786,000,000,000,000 light years would be 4,620,500,850,000,000,000,000,000,000 miles. If every star in the Milky Way is a speck of dust, our galaxy would be the size of America. Furthermore, there are around 200 billion galaxies in the Universe. That being said, since it would take many stars to reach the distance of a light year, but there would be more than 4,620,500,850,000,000,000,000,000,000 specks of dust to make up a whole continent, we would be somewhere around the border of the galaxy. However, leaving our solar system would never happen as we would have no connection with Earth because of leaving the orbit of the entire solar system and we would have no way of getting back.

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The figures may be accurate, but this doesn't address what we would find if we went 786 trillion light-years away. –  HDE 226868 Dec 29 '14 at 1:13

Well, considering that the Big Bang is less than 14 billion years ago, and the observable universe can't expand faster than the speed of light, nobody knows what's farther than 14 billion light years away, or if there is a "786 trillion light years" away. We certainly have no information from such a place, and as far as we know, there is no place farther than 14 billion light years away.

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this is not true, the universe itself seemingly CAN expand faster than light (nothing can travel through space fasther than light, but space can do what the hell it wants, according to wiki for example the radius of the ovservable universe is about 47 billion lightyears. –  DrCopyPaste Feb 10 '14 at 11:03
So, have we any way of knowing what's a trillion light years away? Can we know if there is a trillion miles away? At least can we know that now? –  Marc Feb 10 '14 at 18:38
from what I've heard: no, we cannot. We cannot see past the CMB (radiation from supposedly ~350,000yrs after the big bang), because it is opaque –  DrCopyPaste Feb 12 '14 at 14:54
One trillion miles away is actually about 1/6 of a light-year, so we can definitely see that far. One trillion light years, on the other hand, . . . –  HDE 226868 Aug 5 '14 at 20:19
I meant trillion light years, not miles, as I said in the original answer. –  Marc Aug 5 '14 at 23:45

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