Many events that have occurred in the universe and we know a great deal about them. Still, it’s worth thinking about the timelines involved. When we look back into time and space, the farther we are able to go the longer it takes the light from these deeper regions to get to us. Indeed, we are looking back in time. We are able to see the the primordial universe nearly 14 billion light years away as a very weak background of reasonably uniform microwave radiation coming at us from every direction. As time began during the “Big Bang” with the creation of matter and energy, hydrogen and helium were the dominant elements.
At an early stage, the expanding universe is thought to have undergone an inflation, perhaps using this period to create the discrete structure of space, thus giving us matter, energy, time and space (or what Einstein referred to as space-time). This early inflation perhaps lasted 300,000 years, and we may be looking at the microwave background of the early universe after that brief period. Remember that we think the universe is about 13.6 billion years old. That’s 13,600,000,000 years ago. Thus 300,000 years is like a brief moment–hardly any time passed at all.
After that we see early ancient stars and galaxies. Many of these early stars that are large in mass have by now blown up and become neutron stars or black holes. Stars and galaxies that are closer are younger and represent structures created in the first several billion years of the universe. As we come forward we see structures 5-10 billion years back in time and then the nearer objects are less than 5 billion years back in time. The closer the observation the more time objects have had to form later in the time available in the universe, mature and come to the end of a natural evolution. Large mass stars have had time to form, burn out and form neutron stars or black holes. The latter have had the chance to absorb other stars and smaller black holes and develop into supermassive black holes that are observed often in the center of spiral galaxies. These supermassive black holes may guide the evolution of the larger spiral galaxies. We don’t know all the answers. But it is clear that some nearby galaxies have had the time to form, mature and even collide with other galaxies. Any large massive and highly luminous stars are by definition young stars as such stars die off in tens to hundreds of millions of years.
Our own sun was formed only about 5 billion years ago, or about 9 billion years after the big bang. The Earth and the other planets of the solar system were created about the same time, and after cooling and condensation of the water to form the oceans, primitive life appeared in the seas about one billion years after the Earth cooled and the oceans appeared. About two billion years later more complex photosynthetic organisms appeared and the oxygenation of the atmosphere began. As the oxygen in the atmosphere gradually builds, more complex life appeared and finally humans appeared, but only in the last 2-3 million years. This process could have occurred many times in the history of the universe on planets formed around millions if not trillions of similar stars in the universe formed since time began. We don’t know the answer to the question or even the probability of appearance of planets or of life on those planets which appeared orbiting around stars of a size to last 10-15 billion years or more.