The Universe is everything that there is, this includes space, planets, galaxies, stars and every other object in outside the Earth's atmosphere that we know and don't know about. The difference between space and the universe is that space is the gaps between objects in the universe and not any physical objects such as an asteroid. The universe is everything as mentioned at the start of the sentence. The size of the universe is unimaginably large, it stretches further than we could ever imagine and we would never be able to travel to the outskirts of the known universe. If the Universe is expand out then there is probably a location where when you look out in one direction there are no stars.
The Universe is widely recognised to be about 13.7/8 billion years old, having been created when the universe came into existence in the Big Bang. Some places say 13.7, others will say 13.8 billion years ago. Our Earth is just one of many planets orbiting a star called the Sun which in turn orbits a supermassive black hole in the centre of our galaxy known as the the milky way.
Currently the furthest galaxy that we can see from the Earth is called UDFj-39546284, it can be found in the constellation of Fornax in the southern hemisphere. You won't be able to see it in the night sky, it was spotted by National Aeronautics and Space Administration (N.A.S.A.) using the Hubble space telescope. The galaxy is currently 13.2 billion light years away from the Earth. The galaxy of blue stars formed a mere 400 million years after the Big Bang.1 There could be a galaxy that is further away but its light has not reached us or we've not discovered it. If a galaxy was further than 13.8 billion light years away, we would have to rethink the age of the Universe. There have reports that Methuselah Star is older than the Universe itself.
Since the moment it was born, the universe has been expanding from the singularity from which he was born. It is believed that the universe was tinier than a garden pea with all the universe's matter inside and that it started to expand over time. The term Big Bang was given to the theory of its birth by opponents of the theory but was then taken up by the supporters who liked the term. The universe is still expanding in all directions. Galaxies are moving closer to one another, the Andromeda Galaxy is a galaxy that is moving towards us. Some galaxies are moving away from us at a speed faster than the speed of light, some galaxies are so far away that their light is so faint we can't measure. 3 . One of the causes of why the universe is expanding is believed to be dark energy and matter, something scientists don't yet understand.
There is a theory known as the multiverse and parallel universes / worlds theory which says our Universe is just one of many universes that live in the Multiverse. These universes could be similar but for subtle changes, a change in decision, a change in the fundamentals of science, one that could allow faster than light travel.
The Universe is just like everything else, it has a beginning, a middle and an end. It theorized that the Universe will one day end like most things and there are a number of competing end of the universe theories. Don't have nightmares, these events causing the end of the universe will not happen for an unimaginable period of time. In Wonders of the Universe television programme starring Professor Brian Cox of Manchester University, Brian said that there is not enough particles in the Universe to represent a year until the end of the Universe. We are currently in the Stelliferous Era of the life of the universe. It is also detailed in the book the Five Ages of the Universe2 There are five eras of the Universe, they are :-
|Primordial Era||This is the earliest of the five eras when the Universe was very young and had not yet formed into molecules that we know of today.|
|Stelliferous Era||This is the era in which the Universe is currently in, it is the age of Stars. By the end of this era, the stars will all have burnt themselves out and all that remains are Black Holes, neutron stars and brown and white stars. This era is a very long time. During this time stars will be born, die and born again.|
|Degenerate Era||All that exists now will be neutron stars, black holes and brown and white dwarfs, the stars will have burnt themselves out and no longer be being created. At this point, protons, the smallest particles of matter will start to break down and decay.|
|Black Hole Era||By this time, black holes will be the sole survivors but over time these will start to break up and die. All that will be left are the protons and particles that haven't decayed yet|
|Dark Era||Its just particles and protons and light protons that inhabit the universe, it will be as it was near enough a second before the Big Bang happened.|
It does assume those that the universe will end in the Big Freeze when the Universe just slowly dies over time. Like stars that are reborn from the ashes of old stars, a new Universe could be born from the old.