These last two are theoretical because they have yet to be directly measured — but even without a full understanding of these mysterious puzzle pieces, scientists can conclude that the composition of the universe can be broken down as follows: ComponentValue Dark energy68% Dark matter27% Free hydrogen and helium4% Stars0.5% Neutrinos0.3% Heavy elements0.03% Let’s look at each element in more detail.
Dark Energy
Dark energy is the theoretical substance that counteracts gravity and causes the universe to expand rapidly. It is the largest part of the makeup of the universe, permeating every corner of the universe and dictating how it behaves and how it will ultimately end.
Dark matter
Dark matter, on the other hand, has a constraining force that works closely alongside gravity. It is a kind of “cosmic cement” that is responsible for holding the universe together. Although it eludes direct measurement and remains a mystery, scientists believe it is the second largest component of the universe.
Free Hydrogen and Sun
Free hydrogen and helium are elements that float freely in space. Despite being the lightest and most abundant elements in the universe, they make up about 4% of its total composition.
Stars, neutrinos and heavy elements
All other hydrogen and helium particles that are not free floating in space exist in stars. Stars are one of the most abundant things we can see when we look up in the night sky, but they make up less than one percent—about 0.5%—of the universe. Neutrinos are subatomic particles that are similar to electrons, but are almost weightless and carry no electrical charge. Although they explode from every nuclear reaction, they account for about 0.3% of the universe. Heavy elements are all elements other than hydrogen and helium. The elements are formed in a process called nuclear fusion, which takes place inside stars throughout their lives and during their explosive deaths. Almost everything we see in our material universe is made up of these heavy elements, yet they make up the smallest part of the universe: a mere 0.03%.
How Do We Measure the Universe?
In 2009, the European Space Agency (ESA) launched a space observatory called Planck to study the properties of the universe as a whole. Its main task was to measure the brightness of the explosive Big Bang that started the universe 13.8 billion years ago. This afterglow is a special type of radiation called cosmic microwave background radiation (CMBR). Temperature can tell scientists a lot about what’s in space. When probing the “microwave sky,” researchers look for variations (called anisotropy) in the temperature of the CMBR. Instruments like Planck are helping to reveal the extent of the CMBR’s temperature anomalies and tell us about the various components that make up the universe. You can see below how the clarity of the CMBR changes over time with multiple space missions and more sophisticated instruments.
What else is out there?
Scientists are still working to understand the properties that make up dark energy and dark matter. NASA is currently planning a 2027 launch of the Nancy Grace Roman Space Telescope, an infrared telescope that will hopefully help us measure the effects of dark energy and dark matter for the first time. As for what exists beyond the universe? Scientists aren’t sure. There are hypotheses that there may be a larger “super universe” that contains us, or that we may be part of an “island” universe that is separate from other island multiverses. Unfortunately we are not able to measure anything that far yet. Unraveling the mysteries of the deep universe, at least for now, remains a local endeavor.
