The cosmos comprises many universes of different ages and sizes, which we can also call a multiverse. Of course, this is not a stable, stationary state; each universe is moving and changing shape. The galaxies, solar systems, nebulae, black holes, and so on within them are constantly changing.

Infinite and eternal multiverse

Although our technical knowledge is insufficient to detect the radiation outside our universe, we can think about what is there.

After all, it is clear that the universe, as a space, ends up nowhere. It goes on and on and on. We can perform a mind play, taking a star in the sky as our target and draw a line between ourselves and it—a straight line in three-dimensional space. We can continue that line from that star straight through our galaxy and through subsequent galaxies until we come to the outer limits of our universe. We continue from there, probably in relatively sparse matter and for a long time, until at some point that line meets another universe, goes through that too, and continues in rather empty matter and again for a long time, until it meets another universe again. Forever.

We can also argue that our known universe was not created out of nothing. Of course not. There has been matter and energy before it, a universe that predates us. Was it created by the destruction/shrinking of the previous universe or by adjacent universes merging into one?

It's interesting to think about what kinds of species might have evolved in universes that have evolved and destroyed long before our universe was even born. The cosmos, comprising all the universes, is eternal and infinite. This immense size is one of the reasons why we have not yet encountered species far more advanced than us. Another reason is that we would not even notice the visit of such species because they could do it completely unnoticed.

Sometimes, you come across an idea that plays with the concept of infinity by saying that there are infinite numbers of the same universes, including ours. In that case, each of us would also live in some other parallel universe. 

I don't agree with this concept. I see that each universe is unique. Even though space and the amount of mass are infinite, this does not lead to the repetition of similar universes because the number of different development paths is also infinite. Even though the multiverse is infinite, it is not infinite to the power of infinity.