By Andy Tomaswick, Universe Today October 29, 2025
Collected at: https://scitechdaily.com/what-if-einstein-was-only-half-right-nasas-new-test-for-dark-energy/
New strategies may soon allow scientists to test dark energy theories within our own solar system, linking cosmic-scale physics to local observation.
Science advances through a cycle of proposing theories and rigorously testing them in search of contradictions. This process is especially challenging when dealing with vast, cosmological theories that are difficult to disprove. One of the most enduring examples involves dark energy and dark matter—forces that clearly distort space on cosmic scales but appear absent within our own solar system.
Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory, has published a new paper suggesting that this apparent contradiction might be addressed by refining how scientists search for evidence of dark energy and dark matter locally, using more selective testing methods.
The “Great Disconnect” between cosmology and local physics
Turyshev’s research seeks to resolve what he calls the “Great Disconnect” between the physics observed across the universe and that within our solar system. In regions with little or no matter (and therefore minimal gravitational influence), the effects of dark energy or modified gravity—forces that deviate from Einstein’s General Relativity—appear most prominent. But in dense regions where gravity is strong, such as the solar system, these effects seem to vanish entirely, at least within the sensitivity limits of current technology.
Within our solar system, everything appears to operate as general relativity predicts. Planetary orbits remain precise, the curvature of spacetime around the Sun aligns perfectly with radio measurements from spacecraft, and every probe we’ve launched behaves exactly as expected under standard gravitational theory. So far, there’s no observable sign that any other forces are at work.
But at larger scales, like that between galaxies, the evidence is hard to miss. The universe itself seems to be expanding, and while there’s some debate about how quickly it is, we currently don’t have any other way to describe it other than to say that something is messing with our understanding of either relativity or gravity itself.
The screening effect and fifth-force theories
Physicists think that might have something to do with a “screening” process, where whatever is causing this discrepancy changes its physical properties when is areas of increasing density. There are two main categories of “screening” models. One is known as a “chameleon” model, where a theoretical fifth force of nature (other than gravity, electromagnetism, and the two nuclear forces) changes its effect whether or not there are large amounts of other matter around.
In large, low-density areas, it’s very strong and causes the effect that we attribute currently to dark energy. But in highly dense areas, it is extraordinarily weak, to the point where it’s essentially undetectable to modern instruments, though it is still there. In highly dense environments, like the Sun, it might only be noticeable in a “thin shell” around the object, but at least in theory it would still be detectable there.
An alternative model for this discrepancy is the Vainshtein screening model. In this case, instead of the force itself changing its properties, it is essentially paralyzed by the gravity surrounding massive objects, making it look weak but not really changing its own physical properties. In this model, there is an idea called a Vainshtein Radius, where the fifth force returns back to normal outside the influence of a massive object. However, for our Sun, its Vainshtein radius is estimated to be 400 light-years, an area which includes many, many other stars, so in effect the fifth force would be suppressed entirely until you reach some distance past the edge of the galaxy.
How cosmological missions may hold the clues
Each of these models would have “hints” in the data sets collected by large cosmological missions like Euclid and The Dark Energy Spectroscopic Instrument (DESI). However, since they are only looking at faraway space and large numbers of galaxies, they wouldn’t be able to prove how the fifth force would change when only interacting with objects in the solar system. That would require a specific mission in the solar system, and more importantly, a falsifiable theory that makes a prediction about what that mission should see.
According to Dr. Turyshev, without the theoretical backing of a falsifiable theory, there’s no point in continuing to conduct experiments in our own solar system – we’ve already proved that our best efforts aren’t able to detect anything out of the realm of general relativity. But if theoreticians can extrapolate testable hypotheses from the data collected by the big cosmological surveys that can be tested in the solar system, then we should design a mission to do so.
Admittedly, it might be a while before we can develop instruments sensitive enough to disprove the theory. So, if we aren’t able to yet, then we should focus on missions to incrementally develop those instruments. But if there is a testable hypothesis based on “hints” from cosmological surveys that can be falsified by an experiment we can actually build, then we should do it – and potentially fundamentally change our understanding of how the universe works.
Reference: “Solar System Experiments in the Search for Dark Energy and Dark Matter” by Slava G. Turyshev, 15 September 2025, arXiv.
DOI:10.48550/arXiv.2509.05910
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