Looking back to dark cloudless summer nights in the Sierra Mountains long ago, I lay atop a sleeping blanket looking up at a sky full of stars with an occasional meteor streaking across the sky. The image of those times comes with a sense of wonder inspired by the stars. Then, and now, I felt both a connection and immense curiosity about what I was seeing, and knowing there was so much more to it all. Follow along where my curiosity has led me over the years.
(BTW the picture is from that wonderful site APOD and it is of ARP's colliding galaxies.)
That curiosity has a long history for humans. Through history we have given various names to those who watch the stars ranging from shaman, astrologer, astronomer, and more recently cosmologists. Cosmology, the 5-dollar word for the study of the beginnings of the universe. How did it all begin? Leaving religion aside for the moment, there is a fair amount of inspiration and wonder in the cosmologist’s story to retell on its own.
Within the confines of science the most recent answers (theories) have changed even in our lifetimes with the most current called the Accelerated Big Bang.
First of all, the Big Bang theory of the beginnings of the universe describes only the aftermath of the event. It doesn’t say why it banged, or what existed before it banged. Such are the self-imposed limitations of a science that looks to match its theories to observations and proofs. Nonetheless, the idea of a singularity that was smaller than the smallest part of an atom banging to become the known universe is fascinating.
In that theory there was no time, nor space, no gravity, nor stars or any other material known to us in existence. The theory begins with the singularity, extremely small, containing within it all of the energy that would create the universe and everything in it. In science-speak, energy implies mass, heat and pressure. In the singularity this energy existed in a state that had its own rules of behavior. When it exploded, or banged, it’s expansion created the space, matter and other properties that govern our universe. The term ‘Accelerated Big Bang’ refers to the aspect of the theory that for some period this expansion was faster than light itself. 13 to 15 billion years ago are the current estimated time since the big bang. The residual evidence of the bang is called the cosmic radiation background that was only confirmed in the last 40 years.
The material to form stars was born out of the Big Bang. Primarily hydrogen and helium, these were the earliest of the atomically structured materials that seeded the universe. Aligned theories such as nucleo-synthesis have described how the very stuff of our world, including that which makes up our very bodies, were formed inside the life and death cycle of stars. Many have said it, we are truly stardust. For myself, that is a rather inspirational finding. Another amusing idea taken from creation of elements in the stars is that a large component of white-dwarf stars is diamond! Imagine a diamond larger than the earth! However there is more to the story.
Present day cosmologists predict the following future for our universe. Their most recent findings (theories) describe the universe as continuing to expand. The distant galaxies are continuing to accelerate away from each other. Of course there are nearer by galaxies to our Milky Way that are estimated to be crashing in to us at some point, but that’s not the big picture for the Big Bang theorists.
There are now theoretical postulations of Dark Matter, which have gravity: and more mysterious Dark Energy, that is viewed as the cause of the universe's expansion. The sky-scape of a future universe (assuming there was an earth, and human eyes to see it) would be a completely dark sky. All of the nearby stars would have died out, and the distant galaxies would have accelerated away. Space would have the remnants of dead stars, left over planets and asteroids, but all of it dark. That’s a rather gloomy proposition, isn’t it?
More importantly, in my opinion, is that current cosmologists estimate that matter in the universe comprises a small percentage of everything. A much larger percentage is taken up by Dark Matter, and even larger percentage of Dark Energy! Those are aspects of the universe we can't even see! Shows us the current outer limits of scientific theory! Spurs one's curiosity does it not?