What is there beyond the end of universe?

Universe never ends. Some stars or planets may disappear and reappear with changes. As per total energy theory, Energy is constant. It can change from one form to other, but cannot be destroyed or created. Hence Universe is eternal. This is true as per religious faith also. We need not worry about even our earth or solar system disappearance, for next millions and millions of years. Be happy and kind to other living beings and grateful to our Earth. Most scientists believe that you can never go outside the universe. Some say if you go far enough in one direction you will end up back where you started. Kinda like flying around the world, or like the spaceship in the game asteroids.. out one side, back in the opposite side before you know it. No one is really sure.

You cease to exist. That is a paradox. Universe only exist because mass and the gel that keeps everything along. If you go outside the universe, you are moving mass there, so the universe will expand, it means, you will never be outside the bubble. By other side, if you are able to go outside the bubble without expanding it, your mass cease to exist, so you instantly disappear. As the universe did not have a beginning, it will not have an end. If for any weird thing happen and the universe ended then to answer the question, the answer would be nothing. Because if the universe ended there would be nothing there or anywhere, and you cannot get something from nothing. As some may want to believe.

There isn’t an outside. One way to understand it is to forget the universe as being made of matter and think of it what it really is, excitations in the quantum fields. Outside of the universe (if it is not infinite) there are no quantum fields to excite, therefore there is nothing. There is only distance because of the space between the excitations in the quantum fields, if there is no field there is no space. If there is no space there is nowhere to ‘go’. There is not an ‘outside the universe’ because all that exists is quantum fields. So back to the ‘matter’, if you are just an excitations in a quantum field, there you cannot leave that field because there is nothing to excite beyond it.

We actually don't know the exact answer for this question but we do have many possibilities and the big bounce or the big crunch is one of them. We know the Universe started from a big bang but we don't know what happened before the big bang. Big bang is the singularity at the beginning of the universe. When universe ends one day it might be a Big crunch that is the singularity at the end of the universe. Then again there may be another big bang and likewise there may be an infinite repetitions this is the Big bounce theory.

The universe is everything-there-is. So you can’t leave it. If you postulate another universe ‘kinda like ours but different’, you could never go there. If you could, it would be part of our universe because you stop existing. Your body decomposes. The people who loved you remember you for a while. Then, they, too, die, and people mostly forget about you. Your grandfather had two grandfathers. If you’re like most people, you will know very little, if anything at all, about those men. They are dead. The people who knew them are dead. That’s what will happen to you. That’s what will happen to me. Is it sad? Maybe. But I’ll be too dead to notice.

The universe doesn't have to be expanding into anything in order to expand. I know that sounds ridiculous, so let me give you a different example that is easier to understand. Imagine that you have a line that goes on forever. On that line, you have a mark every inch. There are an infinite number of inches. Now move each marker so they are separated by two inches. The whole pattern has expanded. It still goes to infinity, but the markers are further apart. The pattern has expanded, but the length is still infinite.

Now a new example. Suppose you have a long piece of rubber, going all the way to infinity. (That piece of rubber represents the universe.) The rubber has marks on it every inch. Now stretch the rubber, until the markers are two inches apart. It still goes to infinity -- but it has expanded. Physicists think of "space" not as emptiness, but similar to a piece of rubber. (But they don't call it rubber; they call it the "vacuum". "Particles", in physics, are just vibrations of the vacuum.) The vacuum can expand, just like the piece of rubber. But because it goes all the way to infinity, it doesn't need more space. A clever way to say it is that "there's lots of room at infinity". (That's clever, but it doesn't really explain anything.)

Of course now here is something new that might confuse you, or might help. In the standard physics theory, the galaxies are all getting farther apart; that is the expansion of the Universe. Yet in the way the theory describes it (I mean in General Relativity Theory) none of the galaxies are actually moving. All that is happening is that the amount of space (vacuum) in between them is increasing. No, you will not learn this in school, or even in college (unless you have an extraordinary professor).?

It is usually taught in graduate school, when you are earning a Ph.D. degree. At that point the language you will encounter is this: "In the Big Bang Theory, all galaxies have fixed coordinates. (That means they are not moving.) The 'expansion' is described by the 'metric tensor', which describes the distances between those fixed coordinates. In the Big Bang Theory, it is the metric tensor which is changing; that represents the expansion of the Universe, even though the galaxies aren't moving. The recent discovery of accelerated expansion means that the rate of expansion is increasing."

Maybe you've read about the curvature of space. Put a black hole between two unmoving objects, and the distance between them will suddenly increase -- even though they haven't moved. So "distance" is not as simple as people thought. It was Einstein who came up with the remarkable idea that "space" (that is, vacuum) is flexible; it can curve and stretch. I expect you will find this to be very confusing. That's not a bad sign; it is a good one. When you learn new things that are completely different than you ever imagined, then "confusion" is the first step. Cheers!