"For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring."
― Carl Sagan
This is amazing. This is a recent photograph of Spiral Galaxy NGC 2903 taken by Hubble's Advanced Camera for Surveys and Wide Field Camera 3. The galaxy was discovered by British astronomer William Herschel in 1784, but he did not know what it was. To him, it was merely a small blob in the sky. Without sufficient optics or astrophotography gear, he thought it a nebula within our galaxy. But even he didn't know about galaxies in his time. Sadly, over 200 years later, many people today do not even know what a galaxy is, even though we reside in one ― one of about 200 billion. However, that number is sure to increase as we improve telescopic imagery technology down the road of discovery.
Like our Milky Way galaxy, a typical galaxy has around 100 to 500 billion individual stars (suns), and we know today from recent extra-solar planet science that most stars have planets orbiting them. This would mean there are literally trillions of other worlds in our Universe, most of which are likely devoid of life as barren rocks or gaseous uninhabitable giants like Jupiter. At least, in the way we understand life from a sample size of one (Earth) and the other planets in our solar system.
Either way you look at life in the Universe, there are profound philosophical implications to contemplate. If in the vastness of the Cosmos it's just Earth, that would be utterly astounding. On the other hand, if the Universe is teaming with life throughout, that would mean that the ingredients of the singularity that wrought existence included ubiquity for living organisms. My thought on this is that life is probably exceedingly rare, but we're likely not the only planet in the Universe with living creatures ― the probability it's only us given the number of potential worlds is simply highly improbable.
Did you know that there was huge span of time on Earth when life only existed as single-celled forms ... for roughly two billion years, around half the age of our planet. If any intelligent alien beings had visited our planet back then, they may have merely remarked nothing more to see here and left. That's the tricky thing about potential life in the Universe ― it may be difficult to detect without sufficient evolution to render profound biodiversity like what we have. Wow, are we ever lucky ― we have birds, tiger beetles, sharks, meerkats, oaks, turtles, frogs, snails, and so on.
When you look at the stars at night from sufficiently dark location, you can see a spiral arm of the Milky Way spanning across the sky. All the individual stars you see are in just our galaxy, save for other galaxies, most of which cannot be seen with the naked eye. Between galaxies there is only intergalactic space and dim matter. Galaxies are kind of clumped together in clusters and superclusters.
The above map, first published by National Geographic over two decades ago, is one of the best illustrations I've come across that shows the scale of the known Universe. It shows our solar system (lower-right) to our local group of galaxies, and then to our supercluster of galaxies ― the largest structures we know of in the Universe. Even so, galaxies are typically millions of light-years apart form one another. In fact, NGC 2903 is 30 million light-years from the Milky Way. That's 5.88 trillion times 30 million miles. And here you thought it was a long way to the cabin!
So, what does it all mean? Why does any of this exist? In the sense of the anthropic principle, you need intelligent lifeforms to exist to even contemplate such questions. Some people will claim that they know why there is existence and things that exist, but as the late Carl Sagan said: "The Cosmos is all that is or was or ever will be. Our feeblest contemplations of the Cosmos stir us ― there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, of falling from a height. We know we are approaching the greatest of mysteries."
The truth is ... nobody knows. And that's what makes it so damn interesting. The frustrating thing is those who come across possessing the greatest degree of existential certainty also appear to be the same people who know the least about Cosmology. We see that pattern a lot today, don't we.
NGC-2903 Hubble Space Telescope/NASA 2021