From the vantage point of Earth, astrophysicists have estimated that our observable universe has a diameter of approximately 93 billion light years. A light year is approximately 5.9 trillion miles, so multiply those miles times 93 billion, and you have an approximation of the observable cosmos: 549 x 1021 miles—and that’s just the observable region!
Our minds cannot begin to wrap around that kind of magnitude. Contrast the unimaginable vastness of space with our home planet, which isn’t quite 8,000 miles in diameter and circles a star that is only one of 100 billion others in our Milky Way galaxy—a galaxy which is only one of 100 billion others in the known universe!
By comparison, a human being is a minuscule fraction of a speck on a teensy-tiny bit of rock floating around in an average solar system situated in an unremarkable suburb of a galaxy that is itself dwarfed by the homogeneous enormity of space. Thus the reality is, the entire human race makes far less material impact on the cosmos than flicking a single grain of table salt into the ocean—virtually nil.
Some materialists have argued that these facts strongly suggest that the Christian doctrine of man is false and materialism is true. In other words, rather than being the crown of creation—the central reason for the existence of the universe—mankind is merely one insignificant, accidental by-product of physics and chemistry. Moreover, human existence is only a blip on the cosmic timescale, a brief spark that, in a future epoch, no one will be around to remember.
The problem with this argument is, it totally begs the question in favor of materialism. In other words, it uses materialism as its starting assumption when attempting to argue for materialism. Yes, if materialism is true, if the physical stuff of nature is all there is, then it is reasonable to use material size and longevity as a rubric for comparing things. If we eliminate the fallacy by excluding the starting assumption, the argument is still fatally flawed. As we have already seen, humanity is microscopic (huge understatement) relative to the universe. BUT, we can’t make a philosophical leap from this fact to the conclusion that mankind is not of the utmost cosmic significance. Here’s why.
If humans have immortal, immaterial souls made in the image of God, then we are different kinds of things than inanimate matter and lower creatures. If we are more than physical bodies, we cannot be valued according to our relative size. In order to argue that the Christian conception of human beings is false, a case needs to be made against the existence of the soul. Talking about how small we are physically is completely irrelevant; it says nothing about Christian doctrine whatsoever.
I highly recommend Dr. J.P. Moreland’s excellent short book entitled, The Soul. It does an outstanding job of boiling down dense metaphysical arguments for the soul to a more accessible length and level!
It certainly boggles the human mind to even try to conceive of the sheer enormity of our universe and how comparatively small we are. Nevertheless, Christianity teaches that mankind is cosmically significant by virtue of the kind of thing he is, a creature made in the image of God, possessed of an immortal soul, with life purposes that transcend the material and temporal. As the psalmist remarked, “When I look at your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is man that you are mindful of him, and the son of man that you care for him? Yet you have made him a little lower than the heavenly beings and crowned him with glory and honor.”
 Psalm 8:3-5, ESV.