So, the next time you’re outside, take a moment to thank gravity and pressure for their never-ending cosmic battle.
Welcome One and All!
It’s time to grab your seat for the biggest battle in the soon-to-be-formed universe. That’s right - the Big Bang is about to go down! In one corner is the force that brings all matter together - gravity - whose range is infinite. In the other corner, pressure is the contender that can push matter away with spectacular strength. Over the next several hundred thousand years, these two contenders will be wrestling for the fate of the universe, with ripple effects that will shape the structure of the universe as we know it today.
Three Components
The Big Bang has brought three components into our infant universe - dark matter, baryonic matter, and radiation composed of innumerable particles of light (photons). In the moments just after the Big Bang, all three components are in equilibrium, meaning no one location is denser than another. But as the universe starts expanding, differences in density start to emerge. Gravity immediately gets to work pulling matter together, while pressure begins gathering its strength.
The Struggle
In this hot, high-energy environment, protons and electrons can’t come together to form atoms, so these loose particles zip around freely interacting with ambient photons. The result is almost a fluid of baryonic matter and radiation. But the closer these baryonic particles get, the hotter the fluid becomes, pushing photons to ping around with incredible force. This is the power of pressure battling to push things apart, with each of gravity’s vicious tugs squeezing photons and matter together. With each tug, pressure exerts a forceful shove back. And as the two giants struggle, they heave this fluid back and forth, creating massive waves called baryonic acoustic oscillations.
The Aftermath
Moving at almost two thirds the speed of light, these BAOs ripple across space, impacting the universe on the biggest scale imaginable. These rolling waves determine the distribution of matter throughout space, meaning that today - almost 14 billion years after this fight began - we’re more likely to find galaxies at their peaks and empty space in their troughs. After being locked in a stalemate for roughly 370,000 years, the tide of our battle finally begins to turn. The heat from the Big Bang has dissipated significantly, cooling the universe down to a temperature at which loose electrons start to pair up with protons. This stops electrons from recklessly pinging around, allowing light to stream freely for the first time.
The Winner
It’s time to crown our champion - the undefeated force, the most pervasive power in the universe - gravity! This rivalry isn’t over though, as a similar battle continues between these two sworn enemies today, within every single star. As gravity pulls a star’s gas inward, pressure increases and pushes the matter back outward. This push and pull keeps the Sun, and all other stars, stable for billions of years. In fact, this clash of the titans is the same reason Earth’s atmosphere doesn’t collapse to the ground. So, the next time you’re outside, take a moment to thank gravity and pressure for their never-ending cosmic battle. Though their greatest battle may have concluded, these two warriors remain locked in combat, even with a new opponent on the horizon.