Our universe is a whirlwind of motion. Earth orbits the sun, the sun circles the galaxy, and even galaxies themselves are constantly on the move. But why is everything in space in motion? The answer lies in the very origins of the universe and the fundamental forces that govern it.
Scientists believe the universe began with the Big Bang, a cataclysmic event where an infinitely dense point rapidly expanded, ultimately leading to the formation of all the matter we see today. This initial expansion, driven by the Big Bang’s immense energy, imprinted motion into the fabric of the universe. “From the very beginning, the universe has been expanding outwards,” explains Edward Gomez, an astrophysicist and education director at Las Cumbres Observatory. “It’s the imprint of the beginning.” Carol Christian, an astrophysicist and outreach project scientist for the Hubble Space Telescope, adds, “The beginning was movement, and so movement has been built into the universe from the very beginning.”
While the expansion of the universe is responsible for the movement of objects on the largest scales, it’s not the only force driving motion. On smaller scales, rotation is the dominant factor. “There isn’t anything that doesn’t rotate,” Christian says. This rotation is a result of angular momentum, a fundamental property of objects in motion. When two objects in space approach each other, their mutual gravity pulls them together. If they don’t collide, they often end up orbiting each other. This phenomenon influences everything, from tiny mineral grains to colossal galaxies.
The formation of our solar system is a prime example of how angular momentum shapes the universe. “The solar system was made like a pizza is made,” Gomez explains. “When you throw the dough, it spins and flattens into a disc. That’s fundamentally how our solar system formed; angular momentum stretches things out into a disc.” This is why planets orbit the sun; the solar system began as a swirling cloud of gas and dust that eventually coalesced into a star and planets, and angular momentum ensured it never stopped spinning.
Interestingly, the spinning motion of galaxies is more complex than what we see in the solar system. Galaxies spin as if they were solid discs, even though they are composed of individual stars. “The stars further out should be going slower than the ones in the center, but that’s not what we observe,” Gomez explains. “This led to the discovery of dark matter, an invisible substance that interacts with regular matter through gravity, contributing to the galaxy’s spinning motion.”
Dark matter, although invisible to telescopes, has mass and interacts gravitationally, experiencing angular momentum. Its presence adds another layer to the complex tapestry of motion in the universe.
Ultimately, motion is an integral part of the universe, a testament to its dynamic nature. “It shows that the universe is alive – not in the sense of being conscious, but in the sense that things are happening: chemical reactions, physical reactions, and that requires energy,” Gomez says. “And the most basic form of energy is motion.”
