The First Elements
The first three elements are hydrogen, helium, and lithium, in order of increasing weight and complexity. Their nuclei have one, two, and three protons, respectively. Their international chemical symbols are H, He, and Li.
There are three types of hydrogen, called (ordinary) hydrogen, deuterium, and tritium, in order of increasing mass and decreasing abundance. The nucleus of ordinary hydrogen consists of a single proton. Deuterium has a neutron as well as a proton. Tritium has two neutrons with its proton.
There are three types of hydrogen, called (ordinary) hydrogen, deuterium, and tritium, in order of increasing mass and decreasing abundance. The nucleus of ordinary hydrogen consists of a single proton. Deuterium has a neutron as well as a proton. Tritium has two neutrons with its proton.
The excess of neutrons makes tritium unstable. One of the neutrons is likely to turn into a proton and emit an electron and a neutrino. This turns tritium into the lightweight stable isotope of helium called “helium-three.” Ordinary helium, usually written as He without a superscript, has two neutrons. Lithium-six has 3 neutrons but the much more abundant lithium-seven has 4 neutrons.
These elements formed when the original protons and neutrons collided and stuck together under the intense heat and pressure of early morning on the first day, the first few minutes of the universe. Some of the protons and neutrons made combinations of two, three, four, six, or seven nucleons, while other protons remained free. No free neutrons remained long after the first 15 minutes, because the weak force broke them up into protons, electrons, and neutrinos.
It was unlikely even under those early conditions for three particles to collide simultaneously. The first compound nucleus was deuterium, formed when a neutron hit a proton and the two nucleons stuck together. Almost all the deuterium that exists formed in the first four minutes of the universe, when there were still free neutrons available. Tritium and helium-three had to wait until after the first one or two minutes when there were enough deuterium nuclei to make collisions frequent between deuterium and either a proton or a neutron. Helium-three is stable but turns into helium-four when it collides with a neutron. Lithium-six usually comes from a collision between helium-four and deuterium. A collision between helium-three and tritium would also make lithium-six but the two parts would have to come together before the weak force turned the tritium into helium-three. If a helium-four nucleus hit one of the available tritium nuclei first that would make lithium-seven.
In this way protons and neutrons formed the nuclei of the three elements of lowest weight: hydrogen, helium, and lithium. The formation of lightweight nuclei was almost complete in the first four minutes after creation.
The above scenario agrees in detail with the relative abundances of the low-weight elements. Many physicists have sought alternative scenarios but none so far agrees so well. Therefore we think that the above scenario is close to what really happened.
These elements formed when the original protons and neutrons collided and stuck together under the intense heat and pressure of early morning on the first day, the first few minutes of the universe. Some of the protons and neutrons made combinations of two, three, four, six, or seven nucleons, while other protons remained free. No free neutrons remained long after the first 15 minutes, because the weak force broke them up into protons, electrons, and neutrinos.
It was unlikely even under those early conditions for three particles to collide simultaneously. The first compound nucleus was deuterium, formed when a neutron hit a proton and the two nucleons stuck together. Almost all the deuterium that exists formed in the first four minutes of the universe, when there were still free neutrons available. Tritium and helium-three had to wait until after the first one or two minutes when there were enough deuterium nuclei to make collisions frequent between deuterium and either a proton or a neutron. Helium-three is stable but turns into helium-four when it collides with a neutron. Lithium-six usually comes from a collision between helium-four and deuterium. A collision between helium-three and tritium would also make lithium-six but the two parts would have to come together before the weak force turned the tritium into helium-three. If a helium-four nucleus hit one of the available tritium nuclei first that would make lithium-seven.
In this way protons and neutrons formed the nuclei of the three elements of lowest weight: hydrogen, helium, and lithium. The formation of lightweight nuclei was almost complete in the first four minutes after creation.
The above scenario agrees in detail with the relative abundances of the low-weight elements. Many physicists have sought alternative scenarios but none so far agrees so well. Therefore we think that the above scenario is close to what really happened.
