Atoms are the fundamental building blocks of all ordinary matter, defined by a dense nucleus of protons and neutrons surrounded by electrons. The identity of an element is determined solely by the number of protons in its nucleus. Atoms can be created, but only through intense nuclear processes, not standard chemical reactions. Chemical reactions only rearrange electrons, leaving the nucleus unchanged. Creating a new atom requires altering the number of protons within the core, a process known as nucleosynthesis.
The First Atoms: Birth After the Big Bang
The first atoms were forged during Big Bang Nucleosynthesis (BBN). Immediately following the Big Bang, the universe was too hot and dense for stable nuclei, existing as a turbulent plasma of fundamental particles. Only after the universe expanded and cooled significantly, reaching approximately one billion Kelvin, could protons and neutrons combine. This window for creation was brief, lasting only from about three to twenty minutes after the Big Bang began.
During this short period, the lightest nuclei were rapidly synthesized through fusion reactions. Protons and neutrons combined to form deuterium, which then quickly fused further. The primary products of BBN were the lightest elements: hydrogen (about 75% of the universe’s mass) and helium (roughly 25%). Trace amounts of lithium were also created, but the rapid drop in temperature and density halted the process before any heavier elements could be formed.
Forging Common Elements Inside Stars
Elements heavier than hydrogen and helium formed hundreds of millions of years later when the first stars appeared. Stars function as fusion reactors, where gravitational pressure and internal temperatures overcome the repulsive force between positively charged nuclei. Stellar nucleosynthesis begins with the fusion of hydrogen into helium, powering the star for most of its life. Once a star exhausts its core hydrogen fuel, it contracts and heats up, igniting the next stage of creation.
In this phase, three helium nuclei fuse together in the triple-alpha process, creating a carbon nucleus. Following this, a sequence of further helium capture reactions, known as the alpha process, builds up the next series of elements. These reactions progressively create common elements like oxygen, neon, magnesium, and silicon. Stellar fusion continues this chain of element building until it reaches iron (element number 26).
Iron represents a limit for stellar energy production because its nucleus has the highest binding energy per particle. Fusing elements lighter than iron releases energy, sustaining the star. However, fusing iron or heavier elements consumes energy instead of releasing it. At this point, the star can no longer generate the outward pressure needed to counteract gravity, leading to a catastrophic collapse.
Synthesis of Heavy Elements in Cosmic Explosions
Elements heavier than iron, such as gold, platinum, and uranium, require energy far exceeding what a stable star can provide. These elements are synthesized in the universe’s most violent events: core-collapse supernovae and the merger of two neutron stars. When a massive star collapses, the resulting supernova explosion generates a flood of free neutrons. This environment facilitates the rapid neutron capture process, or r-process.
In the r-process, atomic nuclei rapidly absorb a large number of neutrons in seconds, quickly increasing their mass. This capture happens faster than the nuclei can undergo radioactive decay, driving the reaction path far from stability. The resulting unstable, neutron-rich nuclei then decay toward a stable state, forming the heaviest naturally occurring elements, including those heavier than bismuth. Evidence from a neutron star merger in 2017 confirmed these events are a major source for the universe’s heaviest elements.
Creating Synthetic Elements on Earth
Humans have successfully duplicated atom creation by synthesizing elements that do not exist naturally or exist only briefly. These artificially produced atoms are primarily transuranic elements, those with an atomic number greater than 92 (uranium). Creating these new elements involves using particle accelerators to force nuclei together at high speeds. Scientists fire a beam of one type of nucleus at a target made of another element.
The particles must be accelerated to overcome the electrostatic repulsion between the positively charged nuclei, allowing them to briefly combine and form a nucleus with a higher atomic number. The first synthetic element, neptunium, was created by bombarding uranium with neutrons in a nuclear reactor. For heavier elements (atomic numbers 96 and above), particle accelerators are necessary for fusion. These synthetic elements are highly unstable, often existing for mere fractions of a second before decaying.