Science is not a collection of eternal truths carved into stone—it is a story of curiosity, skepticism, and courage. Theories are born, celebrated, and then relentlessly tested until they either shatter or emerge stronger than before. This process of testing and attempting to disprove ideas is what makes science extraordinary. It thrives not on certainty, but on doubt.
Nowhere is this tension more profound than in cosmology, the study of the universe on its grandest scales. When scientists peer into the vast stretches between galaxies, they find compelling evidence that something invisible—dark matter and dark energy—dominates the cosmos. But closer to home, within our solar system, these mysterious forces seem to vanish without a trace. This puzzling contradiction is what physicists call the Great Disconnect, and it may be one of the biggest mysteries of modern science.
The Invisible Hand of the Universe
For decades, astronomers have observed galaxies rotating faster than they should if only visible matter were at play. Entire clusters of galaxies bend light more strongly than their visible mass can explain. And the universe itself is not merely expanding, but accelerating in its expansion. The evidence is overwhelming that something unseen is influencing cosmic behavior.
We gave these mysteries names—dark matter to account for hidden mass, and dark energy to explain the accelerated expansion. Together, they make up about 95% of the universe. That means everything we see—planets, stars, nebulae, galaxies—is only a small fraction of reality.
But here’s the paradox: in our own solar system, where we can measure the pull of gravity with exquisite precision, there is no hint of dark matter or dark energy at all. The orbits of planets align perfectly with Einstein’s general relativity. Space probes sent past Saturn and Pluto behave exactly as expected. Radio signals curving around the sun match predictions flawlessly. On local scales, Einstein’s theory reigns supreme, and the invisible forces shaping the cosmos appear to be missing.
The Great Disconnect
This discrepancy is not just inconvenient—it challenges the very foundation of physics. Why does gravity need help from dark matter and dark energy in the vastness between galaxies, but not in the solar system? Is there a hidden property of the universe that changes depending on scale?
Dr. Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory, is among those wrestling with this puzzle. In a recent paper, he points to the need for more selective and targeted experiments within our solar system to look for faint signs of whatever new physics might be hiding there. But first, he argues, theorists must provide falsifiable predictions—clear ideas that can be proven wrong. Without that, new experiments risk being blind hunts in the dark.
Screening: A Universe That Hides Its Secrets
One leading explanation for the Great Disconnect is the idea of screening mechanisms. In this view, the mysterious “fifth force” of physics—beyond gravity, electromagnetism, and the strong and weak nuclear forces—may change its behavior depending on its environment.
The Chameleon Model
The chameleon model proposes that this fifth force adapts to its surroundings. In the emptiness of intergalactic space, where matter is sparse, the force is strong, creating the effects we attribute to dark energy. But in dense regions, like our solar system, the force becomes extremely weak, almost undetectable. It hides itself, like a chameleon blending into its environment.
According to this idea, the Sun itself might still carry traces of the fifth force, detectable only in a thin shell around its surface. But finding it would require instruments of extraordinary sensitivity—far beyond what we currently have.
The Vainshtein Mechanism
The alternative is the Vainshtein model. Here, the fifth force doesn’t change its nature—it’s simply suppressed by the powerful gravitational field of massive objects. Around the Sun, the region where this suppression holds sway extends roughly 400 light-years—large enough to encompass not only our solar system but countless nearby stars. Only far beyond the edges of the Milky Way would this hidden force emerge again in full strength.
Both models explain why we see dark energy effects at cosmic scales but not locally. Both remain unproven. And both offer tantalizing clues that physics may be hiding something more profound than we yet understand.
The Hunt for Clues
Cosmological surveys like the European Space Agency’s Euclid mission and the Dark Energy Spectroscopic Instrument (DESI) are gathering data on millions of galaxies, mapping how cosmic structures form and evolve. Within their immense datasets may lie subtle hints of whether a fifth force exists and how it behaves.
But there’s a catch: these missions look far into space, not within our solar system. To test screening mechanisms here, we would need entirely new kinds of missions—probes designed to measure faint deviations from general relativity in environments where screening might just slip up.
Dr. Turyshev’s call is clear: until theorists provide precise, testable predictions, launching new solar system missions to search for dark matter or dark energy effects is premature. But once such predictions exist, the race to design instruments sensitive enough to probe the Great Disconnect will begin.
Building the Future of Discovery
What might those missions look like? Some scientists imagine ultra-precise spacecraft sent to regions of low density in our solar system, such as the outer reaches beyond Pluto. Others propose using laser interferometers to measure minute changes in space-time curvature near massive objects like the Sun. These missions would push technology to its limits, requiring advancements in navigation, stability, and sensitivity.
It may take decades to develop the tools needed to make progress. But even incremental steps—developing better detectors, refining theoretical models, expanding our cosmological surveys—bring us closer to resolving one of the deepest mysteries of existence.
Why This Matters
The search for dark matter and dark energy is not just an abstract puzzle. It touches the very foundation of our reality. If a hidden fifth force is shaping the universe, then our current theories of physics—our best attempt to describe reality—are incomplete.
The history of science is filled with such turning points. Newton gave way to Einstein, who revealed that space and time themselves are malleable. Now, dark matter and dark energy may force another revolution, one that redefines our understanding of gravity and the cosmos.
For humanity, this is more than a scientific quest. It is a story of identity. To know the universe is to know ourselves, for we are made of its dust and bound by its laws. Every discovery about the cosmos is, in a profound sense, a discovery about what it means to be human.
Conclusion: The Road Ahead
The Great Disconnect remains unsolved, a riddle written across the heavens. In the silence between galaxies, the universe whispers of forces we cannot yet grasp. Within the solar system, the whispers vanish, leaving only the elegance of Einstein’s equations.
Somewhere between these scales lies the truth. Perhaps it is a hidden fifth force, screened from our sight. Perhaps it is an entirely new way of thinking about gravity. Perhaps it is something no one has yet imagined.
The only certainty is that the search will continue. With each new theory, each test, each failed attempt and each glimmer of evidence, humanity edges closer to understanding the cosmos that cradles us. Science is not about final answers—it is about the courage to ask the hardest questions.
And this question—what is the true nature of dark matter and dark energy—may be the hardest, and most transformative, of all.
More information: Slava G. Turyshev, Solar System Experiments in the Search for Dark Energy and Dark Matter, arXiv (2025). DOI: 10.48550/arxiv.2509.05910
