“It is always wise to look ahead, but difficult to look further than you can see.” –Winston Churchill
We’ve come a long way in this Universe. Over the past 13.7 billion years, we’ve formed the light elements out of a sea of protons and neutrons, cooled and expanded to form neutral atoms for the first time, gravitationally collapsed hydrogen and helium gas clouds to form the first stars, borne witness to generations of stellar deaths and rebirths, lived through the formation of hundreds of billions of galaxies and the clustering together of thousands or more galaxies into clusters, filaments, and superclusters.
At the end of all this, at the present time, we find ourselves tucked away in a large but unremarkable spiral galaxy, the second largest one in our local group, more than 50 million light years from the nearest large cluster, in a Universe filled with over 100 billion large galaxies, ranging from just a few million to many tens of billions of light years away.
But although 13.7 billion years is a long time, it’s just the early stages of a Universe that’s going to be around for a very long time indeed. Thanks to our understanding of physics, astronomy, and the Universe as a whole, I’d like to leap 100 billion years into the future, when the Universe is many times its current age.
The Sun will be long dead, having burned out the very last of its nuclear fuel some 93 billion years earlier, having blown off its outer (mostly hydrogen) layers in a short-lived planetary nebula, while the inner (carbon, oxygen and heavier) layers contract down to form a white dwarf. Although eventually this white dwarf will lose its heat and cool off, becoming a black dwarf, that will not have happened after only 100 billion years. Our Earth, unfortunately, will be just a barren, lifeless rock, if it survives our Sun’s death at all.
Our galaxy will also look very different. Rather than the great spiral structure it currently exhibits, with its disk and its spiral arms, its big sister Andromeda, and the many dwarf satellite galaxies populating our local group, the irresistible gravitational force will eventually bring us all together.
The first few billion years of the merger will cause intense star formation initially, turning both galaxies blue with hot, young stars. But those stars don’t live very long. After multiple new generation of stars are born, go supernova, die, and trigger the formation of still newer stars, we will be mostly out of unburned hydrogen gas.
But even this is not terribly different from the sky we have today. Sure, the stellar population will be skewed to be lower in mass, the galaxy dominating the night sky will be more massive and shaped differently, and the vast majority of light we receive will be red and infrared light, rather than the ultraviolet-visible-infrared mix we see today. Stellar corpses — white dwarfs, black holes and neutron stars — will be far more abundant than they are today, but all of these things still exist today.
The big difference, however, will come when we look out beyond our galaxy.
Instead of clusters and superclusters of galaxies, there will be… nothing. Dark energy will take care of that, driving all the other galaxies in the Universe, everything that isn’t bound to our local group, our beyond our visible horizon. If we were born on a habitable planet 100 billion years from now, we’d conclude we were the only galaxy in the Universe.
Even the leftover glow from the Big Bang would be undetectable!
100 billion years would shift the cosmic microwave background far into radio wavelengths, and dilute the density of photons so severely that it would take a radio telescope the size of Earth in order to observe it!
How fortunate we are to exist when the Universe is still young: when new, blue stars are abundant, when the sky is full of galaxies and clusters, when dark energy has only begun to take over the Universe, and when the leftover glow from the Big Bang is still hanging around in the microwave.
Only by chance did we arise here and now; a hundred billion years from now, many of our bodies atoms will be a part of different stars and solar systems, joined together with atoms that aren’t even a part of our galaxy today.
Our Sun will be long gone, having died like the nebula above more than 90 billion years in the past, but the matter and energy from our Solar System continues throughout the Universe.
And that’s the future of each and every one of us, so don’t miss out on today!