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. It acts on any particle with mass, and its range is infinite—give it up for gravity! In the other corner, our contender can push matter away with spectacular strength. When the going gets tough, this fighter just gets tougher. That’s right, it’s pressure! Over the next several hundred thousand years, these two contenders will be wrestling for the fate of the universe. The ripple effects of this historic match will shape the structure of the universe as we know it today.
But what are these powers fighting over? We’ll find out when the Big Bang hits right… now! Let’s zoom in for the play-by-play. This epic event has brought three components into our infant universe. Dark matter, which only interacts with gravity. Baryonic matter, which makes up all matter you’ve ever seen, is affected by both gravity and pressure. And radiation is composed of innumerable particles of light, also known as 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. Dark matter begins to collect at the center of these increasingly dense regions, forming the foundations of future galaxies. Meanwhile, pressure begins gathering its strength. 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, specifically radiation pressure, battling to push things apart.
With each of gravity’s vicious tugs squeezing photons and matter together, pressure exerts a forceful shove back. As the two giants struggle, they heave this fluid back and forth—creating massive waves called baryonic acoustic oscillations. 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.
We can still see these ripples in the background radiation of the universe, a permanent reminder of this epic brawl. But after being locked in a stalemate for roughly 370,000 years, the tide of our battle finally begins to turn. After all this time, 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. Known as the “era of recombination,” this stops electrons from recklessly pinging around. This allows light to stream freely for the first time, illuminating the universe. These photons now only exert a tiny force on the neutral atoms they interact with, gradually reducing the power of pressure. And with that, it’s time to crown our champion! The undefeated force, the most pervasive power in the universe: it’s gravity!
And yet, this rivalry isn’t over. 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 while their greatest fight might have ended, these two warriors are still to be locked in combat—even as a new challenger approaches.
Using the information from the article, create a detailed timeline of the events that occurred from the moment of the Big Bang to the era of recombination. Include key events such as the formation of dark matter, baryonic matter, and radiation, as well as the development of baryonic acoustic oscillations. Use drawings, labels, and descriptions to make your timeline visually engaging.
Split into two groups: one representing gravity and the other representing pressure. Each group will prepare arguments on why their force is more crucial in shaping the universe. Use examples from the article to support your points. After preparation, hold a debate where each side presents their case and responds to the other group’s arguments.
Using a large piece of paper or a digital drawing tool, create a visual model of baryonic acoustic oscillations. Illustrate how gravity and pressure interact to create these waves. Show the peaks and troughs and explain how these oscillations influence the distribution of galaxies and empty space in the universe.
Use an online simulation tool to explore the effects of gravity and pressure in the early universe. Adjust parameters such as the strength of gravity and pressure to see how they affect the formation of structures in the universe. Record your observations and discuss how these forces balance each other out over time.
Write a short story or comic strip that imagines the ongoing battle between gravity and pressure within a star. Describe how these forces interact to keep the star stable and what might happen if one force were to suddenly become stronger than the other. Use scientific concepts from the article to make your story both creative and informative.
gravity – the force that attracts objects towards each other, especially the force that makes things fall towards the Earth – The apple fell from the tree due to the force of gravity.
pressure – the force exerted by a substance per unit area – The tire pressure must be checked regularly to ensure safe driving.
dark matter – a type of matter that does not emit, absorb, or reflect light, and is thought to make up a large percentage of the total matter in the universe – Scientists are still studying dark matter to understand its properties and interactions.
baryonic matter – ordinary matter composed of protons, neutrons, and electrons – Stars, planets, and all visible matter in the universe are made up of baryonic matter.
radiation – the emission of energy as electromagnetic waves or as moving subatomic particles – The doctor advised wearing sunscreen to protect the skin from harmful UV radiation.
photons – particles of light that carry energy – Photons from the Sun travel through space and provide light and warmth to the Earth.
equilibrium – a state of balance or stability – The market reached an equilibrium where supply and demand were equal.
density – the degree of compactness of a substance, measured by the mass per unit volume – Ice floats in water due to its lower density compared to liquid water.
baryonic acoustic oscillations – regular variations in the distribution of baryonic matter in the universe, caused by acoustic waves in the early universe – The study of baryonic acoustic oscillations provides important insights into the large-scale structure of the universe.
background radiation – the low-level radiation that is present everywhere in the environment, often originating from natural sources – Geiger counters can detect background radiation, which is constantly present but usually at harmless levels.
