Have you ever pondered on the great vastness of our universe and on all of its colossal—near frightening—constituents and thought: Wow, our existence is so miniscule in comparison to all that is out there.
And yet, we’re made of the same stuff that’s up there, in the blazing ball of plasma that is the Sun and in the boundless collection of particles from which star systems form. We are made of star-stuff, as Carl Sagan says.
But, how? How do we even begin to process the fact that we exist so intimately related to the matter that lies billions of light years away?
We can begin with the observation that our universe is expanding. What does that mean exactly? I mean, the notion of this expansion implies that we’re expanding into something right? Well, not really…this expansion is known as an intrinsic expansion, with that quality meaning that the universe is expanding with respect to itself only. That is, there isn’t necessarily anything that exists outside of it that it expands into. This may be a little difficult to process, so let’s think of a simple analogy…
Imagine a balloon that has not yet been inflated, then imagine that we take a marker and we mark a handful of points along the balloon that are reasonably spaced apart. With one big puff into it, you may notice that the distance between two points on the balloon has increased. If that growth isn’t yet noticeable, give the balloon a couple more puffs until you really see it, and you’ll find that as you continue to inflate this balloon, the space between the points continues to grow as the rubber continues to stretch. This is exactly how you can imagine the intrinsic growth of our universe, with the points representing galaxies and the balloon's surface representing the space that continues to grow between them.
So if our universe is continually expanding outwards, that must mean that at some point, stuff that’s moving away from us used to be much closer to us. And if we continue to go backwards in time (sort of like putting a video in reverse) then we can imagine everything getting closer and closer as we approach the beginning. Therefore, that must mean everything had once upon a time been as closely mashed together as possible, perhaps at a single point.
This leads us to the idea of the Big Bang, which is what is thought of as essentially the beginning of everything—a single point in space and time from which everything afterwards had grown from. We and the Sun and the Andromeda galaxy and everything that exists within and outside of the bounds of the observable universe had originated from the same single point.
Moreover, while the universe continues to grow in the sense that galaxies continue to move away from each other, if we zoom in a little bit into these galaxies, we can see growth in a different sense. We observe the formation of new stars from clouds of gas and dust—from which new elements are generated through a burning process in their hot, dense cores. And at the end of their lives, these stars blow off their layers into space, leaving behind the materials that will eventually be clumped together to form new stars, planets, and even us—we are star-stuff.
Sources
Bennett, Jeffrey O., Megan O. Donahue, Nicholas Schneider, and Mark Voit. The Essential Cosmic Perspective. 8th ed. Upper Saddle River, NJ: Pearson, 2017.
Carroll, Bradley W., and Dale A. Ostlie. An Introduction to Modern Astrophysics. Cambridge University Press, 2017.
