It might not be obvious to those of us only grappling with more mundane concerns, but for cosmologists bent on unlocking the universe’s deepest secrets, there’s no shortage of problems keeping them up at night. “Dark matter” is the shorthand explanation for stars and galaxies moving much more quickly than the gravity of their luminous matter should allow. Let’s not forget “dark energy,” too—the preferred solution to the mystery of the universe expanding faster than anyone expected and doing so at an accelerated rate. Meanwhile a hypothesized “evolving” form of dark energy might resolve something called the Hubble tension—the term used for a major disagreement among researchers about the present-day cosmic expansion rate.
Cosmologists have been losing sleep over such quandaries for generations, wondering what missing ingredients they need to add to their models to fix what seem to be glaring gaps in their understanding. But what if the answer to some—maybe even all—of these problems isn’t a radical new theory but rather an old one, devised almost a century ago by none other than Albert Einstein himself? It’s called teleparallel gravity, and according to a loose collection of theorists who study it, this theory deserves a closer look by the wider scientific community.
Dark matter, dark energy, the Hubble tension: underpinning these theories is Einstein’s general theory of relativity, which treats space and time as a unified “spacetime” and considers gravity as spacetime’s curvature. Perhaps, then, the answer is to modify, change or update relativity itself to gain a new understanding of gravity rather than hypothesizing mysterious dark substances and forces. But across the decades, theorists pursuing this general approach have delivered mixed results at best.
The best example may be Modified Newtonian Dynamics (MOND), an effort to banish dark matter that, according to some research, still has to allow for the existence of some dark matter. A more recent addition, dubbed “timescape” cosmology, seeks to account for dark energy by asserting that gigantic, matter-sparse “voids” in the cosmos are much larger than most other measurements say they can be. None of these possible solutions come without their own problems.
So if these new ideas aren’t working out, why not return to the old master? In 1928, about a decade after completing his greatest scientific achievement, general relativity, Einstein began work on an alternative form of this cherished idea. His dream was to find a single set of equations that could describe both gravity and electromagnetism. His idol James Clerk Maxwell achieved such a feat in the early 1860s, using a single set of equations to describe electricity, magnetism and radiation, and Einstein hoped to follow in Maxwell’s footsteps.






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