Basically, the Universe began, according to scientists, as a single infinitely compact fireball, which over a lot of time grew to form planets and stars. We know this as the Universe. The Universe is constantly expanding. It's kind of like a fruitcake, where the whole cake constantly expands while the fruit inside just grows farther apart.
Space pretty much is an endless void. Literally. It's just a black void that goes on forever. But that doesn't mean it's empty. As you know, there are trillions upon trillions of stars and galaxies that are constantly growing and expanding in an attemp to completely fill space. In space there is no air or gravity, or anything at all for that matter, except for that which is the planets and stars. All of it, however, started out in the form of a small, ultimately hot fireball, according to scientists.
The Big Bang Theory is the start of existence. By the sound of the name Big Bang, you'd probably think something along the lines of a large explosion. Well, actually, it was just a fiery ball that expanded. That was all. The ball expanded slowly, and was made up of millions of little tiny particles. At the time there was no light in the galaxy because it was all trapped in the ball by the particles, and space was completely opaque.
After about three hundred thousand years, the Universe cooled to about the temperature equal to our sun, and the millions of tiny particles joined to form atoms. With all the particles now spread out, light was free and quickly began filling the Universe. The afterglow formed a bright halo which filtered through space and time. Also, when all of this happened, it released a cosmic wave which pulses through the galaxy even today, and evidence of this pulse can be found in our own homes. The static on an untuned TV. is actually the cosmic wave.
Also, scientists have discovered something called inflation. This is the action of the Universe growing, where galaxies are formed from other galaxies in a never ending evolution. So, basically, new galaxies just grow off older ones, and that chain never ends.
All of these galaxies are made up of matter, which are tiny particles that take up space. Then, there is antimatter. Basically, it's the opposite of matter. When matter and antimatter meet, they completely obliterate each other. When the Universe was created, matter and antimatter were created in equal amounts. These two things should have wiped each other out, but for some reason they didn't. So, in theory, we shouldn't even exist. Something happened that made matter either overrule antimatter, or matter just got really for apart from antimatter. No one knows for sure, and scientists are still stumped. They do think, however, that should we come into contact with antimatter we will be destroyed.
So, whatever happened with antimatter and matter happened, and when they seperated, they started forming galaxies, planets, and stars. Currently, we live in a galaxy of matter. But, how was our galaxy made? Well, what happened was this.
A drifting gas cloud shrinks, and begins spinning around until it forms a disc. Then it splits apart into two clouds. One of them heats up and begins to form a sun, while the other forms an orbit disc. Tiny particles are attracted by this, and as they gather 'round, they smash together, and they too begin spinning. They continue spinning and smashing for about 100 million years before they eventually form nine happy planets peacefully floating around the sun.
But this process wouldn't really work to form gas giants like Saturn and Jupiter, so how were they made? Well, the process began the same for them, too. When the particles had smashed and spun until they formed the planets' cores, vapor that had evaporated from planets that were close to the sun were pushed outward towards cooler planets, and began to cling to the planet cores that had formed. These vapors built up until forming Jupiter and Saturn as we know them today.
Well, that is how our galaxy was created. But at the time only one planet had just the right stuff to support a lage population of life. That planet was and is Earth.
Life started out at the bottom of the ocean, drawing it's energy from the heat exerted from the fiery planet core. Slowly, it got bigger and braver, and traveled closer to the srface. Still, it did not draw energy from the sun. Eventually, the small amount of life moved to the surface of the ocean where it began to live from the sun, and then it crawled out onto land and over a period of millions of years life grew and grew to what we know today.
There is no doubt, however, that there is probabely even a lot more life on other planets posibly from other galaxies. However, in our galaxy the next closest planet to forming life like Earth would be Mars.
Scientists have discovered that there used to be lare amounts of water flowing freely across the surface of the red planet, and it is currently stored in the planet's polar ice caps. In fact, scientists have actually found life on Mars. It is actually a nearly microscopic organism that can also be found in Timpanogos cave. It is quite possible that there may have been even more life on Mars at one time, and there still may be life in Mars' future.
Either way, the galaxy still holds many surprises, and in a Universe like this anything can happen...