Every time they would attempt to do so, a photon would blast the individual protons and neutrons apart, preventing them from building up to heavier elements. We can go all the way back to an epoch where the Universe was so hot that even atomic nuclei couldn’t bind together. If an early form of dark energy exists, the early expansion history, and hence the scale at which we see acoustic peaks, will fundamentally change. Once the Universe cools enough, and is devoid of such high-energy photons (right), they cannot interact with the neutral atoms, and instead simply free-stream, since they have the wrong wavelength to excite these atoms to a higher energy level. Īt early times (left), photons scatter off of electrons and are high-enough in energy to knock any atoms back into an ionized state.

An electron annihilating with a positron, for instance, produces two photons of precisely 511,000 electron-Volts of energy apiece: the energy equivalent of the mass of the particles that annihilated, via Einstein’s E = mc². When a particle of matter collides with its antimatter counterpart, it typically results in the production of two photons (in the center-of-momentum frame of reference of the collision) with equal energies and opposite momenta. Whenever matter and antimatter meet in the Universe, they annihilate, and matter-antimatter annihilation produces a very specific signal. The first step in solving any problem is making sure it’s actually the problem you think it is. Aguilar (main) NASA/GSFC/Fermi (inset)) What is the Universe made of? These “bubbles” arise from the energy produced by electron-positron annihilation: an example of matter and antimatter interacting and being converted into pure energy via E = mc^2. In the small, inset image, actual Fermi data shows the gamma-ray emissions resulting from this process. In the main image, our galaxy’s antimatter jets are illustrated, blowing ‘Fermi bubbles’ in the halo of gas surrounding our galaxy. Although we haven’t uncovered the solution to this puzzle, there’s an awful lot we do know about it. This is one of the great unsolved problems of existence: the baryogenesis puzzle, or why there’s a matter-antimatter asymmetry. Somehow, the Universe is in a matter-dominated cosmic imbalance. This is a big deal, because as far as we can tell, the only way to create or destroy matter is to create or destroy, along with it, an equal amount of antimatter. Yet, everywhere we look, we see the same thing: the material that makes up every planet, star, galaxy, and cloud of gas or dust is composed of matter. On smaller scales, meanwhile, we have unveiled the building blocks of the Universe, discovering molecules, atoms, and the subatomic particles that fundamentally compose our reality.

On cosmic scales, we’ve discovered that the Universe is filled with planets, stars, galaxies, and more, extending to the limits set only by the speed of light and the Big Bang. Hundreds of thousands of years later, we began to unravel many of the mysteries of the Universe. After more than 13 billion years of cosmic evolution, on a planet orbiting a rather unremarkable star in a common, run-of-the-mill galaxy, human beings came into existence for the first time.

Antimatter universe