Big Bang

The big bang theory of the universe starts with a single point which rapidly expanded and slowly evolved into the cosmos we see today.

This animation opens on a bright explosion which fills the screen with white, which then fades back to a point at the center of the screen. As the point fades, galaxies rush from the center of the image off the screen, as though passing by the viewer.

Some 13.8 billion years ago, the universe was a dense, tremendously hot (too hot for the existence of atoms), extremely tiny point that rapidly surged outward in all directions. For a fraction of a second, the universe expanded faster than the speed of light. We do not know what triggered that initial, rapid expansion, but this period, called cosmic inflation, explains much of what we see in the universe today.

About one second after the big bang, the rapid expansion slowed. The universe was an extremely hot, uniform, cosmic soup of subatomic particles and light. As the universe continued to expand, its temperature and density decreased. A few minutes after the big bang, the universe had cooled enough for subatomic particles to form atomic nuclei. Protons and neutrons formed the nuclei of hydrogen and helium, the basic building blocks of stars, but it would be some 380,000 years before the universe cooled enough for these nuclei to capture electrons, forming the atoms we are familiar with today. As they became part of atoms, the captured electrons slowed down, releasing some of their energy that we detect as cosmic microwave background radiation today.

The anisotropies of the Cosmic microwave background (CMB) as observed by Planck Satellite. Credits: ESA and the Planck Collaboration
This detailed map reveals the cosmic microwave background (CMB) radiation. The orange or blue splotches in the map are the seeds from which matter grew, forming stars, then galaxies, and then clusters of galaxies.
ESA and the Planck Collaboration
A very bright-white point on the left side of the image. A rounded cone extends to the right. It initially rapidly enlarges then gradually enlarges as you move toward the right. An image of the cosmic microwave background fills the bottom of the cone, then darkness, then a plane of bluish-white light that over an extended period of time clump together to form the galaxies we know today.
This illustration represents the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe.
NASA, Illustrator: Britt Griswold (Maslow Media Group)

Continued cooling allowed atoms to clump up and form molecules. Eventually greater and greater clumps of matter formed the stars, planets, and galaxies so familiar to us today. The universe was no longer a smooth, uniform expanse of hot energy and light, but a lumpy expanse ruled by gravity. These gravitational lumps eventually formed a cosmic web of filaments and vast sheets of matter that shape the underlying structure of the universe we see today.

Hubble observations have given us a better understanding of the age of the universe with a much higher precision. Using gravitational lenses, Hubble observations have peered back in cosmic time to image some of the earliest galaxies. Hubble has even mapped sections of the cosmic web, and in a Nobel Prize winning discovery, it uncovered the acceleration of our expanding universe along with ground-based observatories. These discoveries have rewritten textbooks and changed our fundamental model of the universe.

Helium nuclei were created in the Big Bang and contain two protons and two neutrons each. Helium is the second most abundant element, comprising roughly one quarter of the mass of the universe. This animation zooms into a standard helium atom, showing its protons (green), neutrons (white), and electrons (blue).
NASA; Animator: Dana Berry (Skyworks Digital)
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