But what are gravitational waves, and why couldn’t anyone measure them until now? The answers involve the nature of gravity.
So what is gravity? Isaac Newton says, “Gravity is a force of attraction between any two objects.”
This sounds mysterious. Why would two objects attract each other? Albert Einstein says, “Because they warp the fabric of space, so that moving objects curve toward each other.”
Back when Einstein proposed this, scientists wanted to see evidence before they believed it. But the evidence quickly started to mount, and today this theory has passed every test we’ve managed to give it. However, as of September 2015, there was still one thing the theory predicted which we had never seen—and that was gravitational waves.This is Einstein’s theory of general relativity—and it says that all things (including you and me) “curve” or “warp” the space around them. If you roll a ball across a curved surface, the ball won’t go straight (try playing soccer in a skatepark). And for the same reason, something flying past the Earth through space won’t go straight either—because Earth curves the space around it. So according to Einstein, gravity isn’t some mysterious force that reaches out across space and grabs stuff—instead, it’s just what happens when things move through curved space.
So why weren’t they detected until a few years ago? After all, you don’t really need two stars orbiting each other—technically if you and your sister run circles around each other, you’ll make your own (very small) gravitational waves. But the problem is that space is very “stiff.” A stiff trampoline won’t bend as much as a loose trampoline—and space is incredibly stiff. It’s so stiff that we can only measure these waves when two super-dense objects spiral into each other.Go back to the idea of soccer in a skatepark—but now change it to soccer on a huge trampoline (because the soccer players bend the trampoline at the same time the trampoline affects them). Better yet, imagine a very strong trampoline as big as a city block—and now put two four-wheelers on top of it, and have them drive circles around each other. What will happen? As they move, they will send out waves across the trampoline—and anyone sitting on the trampoline will bounce up and down when the waves get to them. And according to Einstein’s theory, that’s what happens in space when two stars orbit each other—each of them curves the space around it, and their orbiting motion sends waves of curvature out across space. These waves of curvature are what we call gravitational waves—and it was these waves that scientists first detected in 2015.
And the densest objects we know of are black holes. Black holes are places in space where the gravity is so strong that not even light can make headway. And it was the merger of two black holes that created the gravitational waves—ripples in the fabric of the universe—that we finally measured a few years ago.
It’s hard to grasp just how much energy these merging black holes released. The Death Star (in Star Wars) was puny by comparison—these black holes released much more than enough energy to vaporize a planet. In fact, they released more than enough energy to vaporize all the planets in dozens of galaxies the size of our own. In fact, for a tiny fraction of a second, the merging black holes were putting out more power than all of the stars in all of the galaxies in all of the universe. And all of this energy went into the gravitational waves. But because space is so stiff, by the time the waves got to earth their size was less than one one-hundredth the width of a proton. It was an incredible feat of engineering to detect them at all.
When they analyzed the waves, scientists deduced that the merger took place over 1 billion light years away, and the merging black holes were about 30 times as massive as the sun. This was (and is) puzzling. We know how to make smaller black holes (a few times the mass of the sun)—it happens when the biggest stars run out of fuel and collapse. And we know there are supermassive black holes (millions of times the mass of the sun) at the centers of galaxies. But no one expected to find black holes thirty or so times the mass of the sun—and right now scientists aren’t sure how they would form. It shows that there still are lots of things to discover about the universe (maybe some of you can help discover the answers)—and that’s part of what makes science so exciting.
But before we end, let’s go back to the questions from before. We asked Newton what gravity was—and he told us it was a force of attraction between two objects. We asked Einstein why two objects attract each other—and he told us it’s because they warp the space around them. But we could keep on asking the questions—“Why do objects warp the space around them?” No one really knows the answer to this question, although one day a theory of quantum gravity might help us figure it out. And when that day comes, we can ask why that theory works—and the answer would involve a yet deeper theory, which would raise even more questions.
But at the end of the day, these answers—even though they’re very helpful for understanding the universe—they tell us how things work but not why those things are there working in the first place. Why is there any force at all, or any matter or energy for those forces to affect? And gravity is nothing special in this regard—we could ask the same questions about the electromagnetic force, or the nuclear forces. Physics can tell us how things work—but to know why things happen at all takes us beyond physics.
And the Bible gives us the ultimate answer. Why does matter exist? Why does every atom, and every planet, and every black hole hold together—and why do they interact the way they do? It’s because Jesus Christ, the Almighty Creator and Sustainer of the Universe, chooses daily to make it happen:
He is the image of the invisible God, the Firstborn over all creation. For by him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things were created by him and for him. He is before all things, and in him all things hold together (Colossians 1:15–17).
The Son is the radiance of God’s glory and the exact representation of his being, sustaining all things by his powerful word (Hebrews 1:3).
Gravity is one of the ways God the Son sustains all things and holds them together. When we see the power of black holes—or anything else in the Universe—we are seeing the work of the very power of God.
 Technically, it curves both space and time—and it’s the time curvature that produces most of the force. But time curvature is harder to think about than space curvature—so we’ll just stick to talking about space.
 The technical name for the detection was GW150914: the GW stands for “gravitational wave,” and the numbers give the date it was detected—2015 September 14.
 That’s what the word metaphysics means.