What actually universe is:
In general universe is that place in where we are living. But scientifically, the whole space, matters, cosmos is all together called Universe. After the big bang, the universe is expanding rapidly greater than the speed of light. That is why it is too hard to measure the size of the universe. However, till yet the diameter of the universe is said to be 10 billion light years.
Actually, there are two types of universes. One is Observable Universe and the other is the Whole Universe. Sometimes it may confuse everyone. Because, some people think that observable universe and the whole universe is the same. But actually, it is not true. Here are the definitions of the two types of universes-
This is that spherical region of the universe which has been observed from earth in the present time. According to modern scientists, the diameter of the observable universe is about 93,000,000,000 light years. Beyond that, scientists do not know what lies beyond this limit. But that does not mean that nothing exist beyond this. For example, if you are standing in a long tower, then you can only observe that portion which comes within its range. You can not see the whole earth. But that does not mean that the rest portion (excluding your position) does not exist. Same concept is here.
This is that region which consists the whole universe, including that portion which scientists could not detect yet. No one exactly knows what lies in here. Even, scientists are also unable to detect the edge of the universe. This is because, to detect the distance of the object we have to observe the light coming from it. As according to Hubble’s Law, the galaxies are expanding so fast (almost in the speed of light), that is why, the wavelength of light coming from it increases hence frequency decreases. These galaxies are too far away that, light enters in InfraRed (IR) region after reaching the earth. That is why it is hard to detect such types of galaxies. As, they could not be detected yet, so these galaxies are kept beyond the edge of the observable universe. But in 2018, James Webb Space Telescope will be launched through which scientists will be able to detect the infrared rays. Then we will know about different types of galaxies which lies beyond the observable universe.
What lies beyond the universe:
We have discussed, what lies beyond the observable universe. But here is an another question,”What lies beyond the whole universe?” If I say directly, then the answer is unknown. Because scientists could not be able to detect the edge of the universe. But the answer can be given in different ways.
According to some scientists the same thing my be repeating beyond the universe. We could not detect these things, but it does not mean that nothing exists beyond this universe. May be the same thing is repeating beyond this, that means the same galaxies, stars, planets, pulsars are repeating there. But if we agree with this concept, then a question should be raised,”Are these things expanding in space infinitely?” If this theory is true, then all these things should be repeating for infinite time. Simply, according to this theory the universe is infinite.
According to this theory, the whole universe is in a contained bubble. That is why when we reach the edge of the universe, we will be able to travel outside the bubble. Like this, there are infinite numbers of bubbles each contains one universe which is called The Multiverse. The physical properties of each universe is different than the others. If this theory is true then like our universe, all universes should be expanding in a rate. Then a question should be raised,” If all universes are expanding then is collision possible among different universes?” The answer is May be. Because, we all know that our universe was created by the big bang. What if, some billion years before, two or more universes collided among themselves and created the strongest bang of all time to create our universe. We call it big bang. An another interesting theory about multiverse theory is, there may be infinite copies of you, me and everyone else.
This theory is almost same with The Multiverse theory. Actually, multiverse is a part of parallel universe theory. According to this theory, each universe is nothing but a membrane. The membranes (universes) are aligned parallel to each other. That means, out side our universe there may be another universes which are parallel to each other and can be communicate with each other by some special techniques. This theory also has a parent theory which is related to String Theory. This theory is called M-theory. M-theory predicts some membranes in the cosmos which keep vibrating. Each membrane contains one universe. There are infinite numbers of membranes parallel to each other and when these membranes collide each other big bang occurs which create another universe. However, this is just a theory.
According to some scientists, there may be a black hole outside our universe. Because, our universe is expanding rapidly like, the matters are thrown to a certain point. According to them, there is a giant black hole outside the universe which is increasing rapidly by feeding the matters of our universe and that is why it is seemed that our universe is expanding. But some scientists even NASA did not accept this theory. Personally, I also do not accept this theory, because to happen such kind of things the expansion rate of the universe should be increased which has not been seen yet.
What is the center of the universe:
Actually, we are talking about observable universe, not the whole universe. Because, we still do not know the actual size of the whole universe, but we know about the observable universe which is like a spherical cylinder. To understand this answer let us take an example, if you are standing in a top building, then what will be the center of your observable range? Obviously you. Right? But that does not mean that you are in the exactly center of your city. Same concept is here. We can observe to a certain limit in the space. So, we can assume that we are in the center of the observable universe. If we take ourselves as a center of the observable universe, then we can detect objects to 46,500,000,000 light years in the both sides which is total 93,000,000,000 light years. Simply, for us we are the center of the observable universe whereas for someone else which are very far away from us, they are the center of the observable universe.
These are some of the facts about the universe. However, these theories do not solve all the questions like dark matter, dark energy and many more. Because, we can only observe 5% of our universe and the rest 95% is still a mystery for us. May be in near future, we will be able to solve such kind of things.