Why does the invisible ninety-five percent of the universe remain completely unaccounted for by our best physical theories?

During a wide-ranging conversation on The Diary Of A CEO, astrophysicist Neil deGrasse Tyson highlighted a humbling reality about our current understanding of the cosmos. He explained that while humans have spent centuries cataloging stars and planets, these objects represent only a tiny fraction of what actually exists. According to Tyson, approximately 95 percent of the universe is composed of 'dark' components—dark matter and dark energy—that do not interact with light. Everything we have ever seen, touched, or measured in the history of science accounts for a measly 5 percent of reality. The guest emphasized that we are essentially guests in a universe driven by forces we cannot yet identify.

This discrepancy isn't just a minor accounting error in physics; it is a total crisis of identity for the natural sciences. For decades, astronomers assumed that gravity from visible matter would eventually slow the expansion of the universe down, like a ball thrown upward that eventually falls back to Earth. The 1998 discovery that the universe is actually accelerating outward shattered that analogy and forced the introduction of dark energy as a placeholder for our ignorance. If we cannot explain what 95 percent of the universe is made of, it suggests our fundamental laws of physics might be incomplete or entirely wrong at large scales. Caring about this means acknowledging that we are living in a 'Hubble bubble' of ignorance, trying to decipher a script where nineteen out of every twenty words are redacted.

The evidence for this invisible majority is anchored in the behavior of Type 1a supernovae, which serve as 'standard candles' for measuring cosmic distances. In 1998, two independent teams led by Saul Perlmutter, Brian Schmidt, and Adam Riess observed that these distant stellar explosions were much dimmer than expected, meaning they were farther away than gravity should allow. Their work, which earned the 2011 Nobel Prize in Physics, confirmed that a repulsive force is pushing space apart at an increasing rate. NASA’s WMAP and Planck satellite missions later analyzed the cosmic microwave background—the 'afterglow' of the Big Bang—to refine the numbers. These measurements consistently show that dark energy provides roughly 68 percent of the universe's energy density, while dark matter provides about 27 percent.

The most counterintuitive twist is that dark energy was once considered Albert Einstein’s greatest embarrassment before it became his greatest vindication. In 1917, Einstein added a 'cosmological constant' to his equations to keep the universe static, only to delete it when Edwin Hubble proved the universe was expanding. He reportedly called it his 'biggest blunder,' a sentiment documented by physicist George Gamow. However, modern cosmologists have been forced to resurrect that very constant to explain why the expansion is speeding up today. It turns out that the 'empty' vacuum of space may possess its own inherent energy, meaning that the more the universe expands, it creates more space, which in turn provides more dark energy to fuel further expansion.

There is a solid scientific consensus that the universe began roughly 13.8 billion years ago from an infinitesimal point and has been expanding ever since. Researchers agree that for the first nine billion years, gravity successfully slowed that expansion, allowing for the formation of the complex galaxy clusters we see today. Astronomers also reach a consensus on the math: we know exactly how much dark energy is needed to match our observations of the sky. Institutional bodies like NASA and the European Space Agency concord that without these dark components, the universe’s geometry would not be 'flat' as current measurements of the cosmic microwave background suggest. The existence of these forces is no longer debated, even if their specific identity remains a total mystery.

The primary battlefield in modern cosmology is the 'Cosmological Constant Problem,' where quantum field theory and general relativity clash. Quantum physicists like those at the University of Chicago have calculated the energy of the vacuum, but their result is 120 orders of magnitude larger than what astronomers actually observe. This discrepancy, often called the worst prediction in the history of physics, leads some researchers to propose 'quintessence,' a dynamic field that changes over time, rather than a constant. Meanwhile, skeptics like David Wiltshire suggest that dark energy might be an illusion caused by the way we average out the density of empty space versus galaxy-filled regions. The debate remains active between those looking for a new particle and those who believe Einstein’s theory of gravity needs a fundamental rewrite.

It is vital to clarify that the terms 'dark matter' and 'dark energy' are not descriptions of what these things are, but rather admissions of what we don't know. They are not necessarily related to each other simply because they share a name; dark matter acts like extra gravity that clumps things together, while dark energy acts like a cosmic pressure that pushes them apart. We should also avoid the trap of thinking that because 95 percent is missing, our local physics is invalid. The laws that fly planes and power smartphones remain perfectly functional within our 5 percent slice of reality. Predicting the 'Big Rip' or 'Big Crunch' is also premature, as a 2024 study from the Dark Energy Spectroscopic Instrument (DESI) suggests dark energy might actually be evolving or weakening over time.