Dark energy revived Einstein’s discarded cosmological constant and reshaped the leading model of the universe.
In 1917, Albert Einstein had recently completed his general theory of relativity, the framework that transformed how physics understands gravity. He soon applied those equations to a much larger question: how the universe changes over time.
Gravity was the natural place to begin. The universe is electrically neutral on average, so electromagnetism cannot explain its behavior across the largest scales. Einstein also knew nothing about the strong and weak nuclear forces (to be fair, nobody did), but both act only across extremely short distances.
Cosmology therefore begins with gravity. Once physicists gather matter and energy into something they call “a universe,” they can use Einstein’s equations to ask how it should evolve. The answer surprised him. General relativity naturally described a dynamic cosmos that either expanded or contracted, while the dominant scientific view held that the universe was static and had remained unchanged throughout its history.
Einstein forces the universe to stand still
Rather than accept what his equations implied, Einstein adjusted them to match the observations and assumptions of his time. He introduced a “cosmological constant,” represented by the Greek letter Lambda, which general relativity already allowed. The constant acts as a gravitational influence built into spacetime itself, even in otherwise empty space. Depending on its value, it can produce attraction or repulsion. Einstein selected a value that counterbalanced the gravitational pull of matter, allowing his model universe to remain stable.
Just a few years later, Edwin Hubble would discover that the universe is expanding, and other theorists, like Russian cosmologist Alexander Friedmann, would take Einstein’s equations at their face value and provide the theoretical backing for the Big Bang theory. As for Einstein himself, he would later remark to friends that the addition of the cosmological constant was his “greatest blunder.”
The expected slowdown becomes acceleration
Fast forward to 1998. Two teams of astronomers set out to settle a decades-long debate about how much matter was in the universe. Some observations said there was barely any matter at all, and others said there was a lot. The universe was expanding, but the matter inside of it should be slowing down that expansion – by measuring the deceleration, they could get a grip on this amount of stuff and settle the debate.
Which they did… sort of. Instead of finding a deceleration, they measured an acceleration. There was still not very much matter in the universe, but even what IS there is not enough to decelerate the expansion.
As for that acceleration, the simplest way to explain is to, you guessed it, invoke the cosmological constant, a fundamental background anti-gravity effect that simply exists in the universe. Decades after Einstein scrubbed away his blunder, the constant came roaring back to life as the best explanation for the data.
Dark energy replaces the old model
By the 1980s and 1990s, cosmologists had built a detailed framework known, somewhat boldly, as the Standard Model of Cosmology (physicists have a penchant for calling cohesive, collaborative, consensus models “Standard”’). The discovery that the universe’s expansion is accelerating made that model obsolete.
Its replacement is our best current account of how the universe has evolved since the Big Bang: LCDM cosmology. Lambda represents the cosmological constant, commonly associated with dark energy. CDM stands for cold dark matter, which provides most of the mass in nearly every galaxy. Cold dark matter is a separate topic, so the focus here is Lambda.
A successful model may still fail
The LCDM is enormously successful. It’s a relatively simple model: just a few free parameters and a couple of assumptions working within a framework of general relativity. And with that model, we are able to explain SO MUCH about the universe: its expansion history, the appearance of background radiation, the BAO feature, the growth of galaxies and large structures, and on and on and on. It’s one of the most well-studied and well-tested theories in ALL of science.
And it’s almost certainly wrong.
Adapted from an article originally published in UniverseToday.
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6 Comments
Nice summary. Of course, by it very nature everything in Science is always wrong. That’s is what scientists constantly strive to prove. That’s what leads to new discoveries and modifications that provide the extraordinary benefit we have received from Science. Embrace it. Enjoy it. Revel in it.
I don’t believe even 1% of readers can make any sense of cosmological theories.
To calculate the expansion rate of universe,total time period one billion years after the big bang,can be divided in to multiple epochs as per the convenience of treatment.One step is to determine the direction of acceleration for each specified epoch;if,the amount of acceleration is variable in any epoch,must be cited.
1. The Flaw of “Fudge Constants”Einstein introduced $\Lambda$ as an ad-hoc scalar to force a specific outcome (a static universe), and modern physics reinstated it as an ad-hoc scalar to force acceleration. The new DESI data proves that sticking fixed scalar terms into field equations fails when high-precision multi-epoch measurements are made. 2. Dynamic Evolution over Static Assumptions Torsion Hill treats geometry as continuous and dynamic across scale. Where $\Lambda$CDM gets stuck trying to explain why a “constant” is changing, a geometric model interprets these shifts as natural structural relaxation as the overall density gradient shifts across cosmic epochs. 3. Geometry Eliminates Exotic Mechanics Standard cosmology is currently forced to invent new “rolling scalar fields” (like axion quintessence) to fix $\Lambda$. A torsion-based model accounts for cosmic acceleration and its relaxation through geometric stress and vorticity, keeping the physics tied to structural geometry rather than exotic fluid additions.
When Einstein showed that space and time were curved rather than a rigid stage, he opened the door to treating the cosmos as a dynamic, physical system. But the moment mainstream physics took those field equations, they immediately tried to force them back into static, flat geometric baselines to keep the math predictable. When mainstream physicists built their standard cosmological models, they chose the “straight ruler” because calculating straight lines across flat geometry requires far less computational load. But when the universe doesn’t move in straight lines, their flat equations break down. To fix the broken math, they start adding artificial “fudge factors” like $\Lambda$ (dark energy) or dark matter. Continuous curvature isn’t “unpredictable”—it’s just higher-order geometry. A French curve proves that you can have smooth, exact precision along a changing curve without needing to force everything onto a flat grid.
Well said. Gravity like space & Time is Also Curved. We live in a Fractal Universe. If they compute it in whole Numbers they will never reach the right answer. I believe that the Big Bang is a flaw of mathematics & only exists on paper. I have been preaching that to people for thirty years now. It was More likely a collision of two Black Holes. Which Have Both a calculable Size & Mass. Dark energy as they call it is simply Mass outside of our visual ability. My models predicted the Dark matter strings that are throughout the universe Year’s before they were discovered. The rate at which these strings are collapsing into round droplets should help predict the actual age of the structures. Though their motion through space may hold them as strings Longer. Depending on their motion. You can also sling the neutrons or dark energy out of matter just as it passes through Galaxies several times before settling down throughout the Galaxies it’s bound to. I even drew up plans for a matter compressor that would leave torus shaped reactors in the dust making a continuous fusion reaction in the center. But a man who was Caused to be ill throughout his school years could not possibly have educated himself on the subject when he recovered. I have watched as Science slowly catches up with my conclusions. I know I don’t know everything. I don’t want to even try to learn everything. But I have found there’s Nothing common about the Things I considered to be common sense. Like using microwaves to enhance Jet fuel as it Burns in the combustion chamber in Jet engines. I sketched that out in highschool. But my teacher said it would melt the blades. He was somewhat correct. But now we have Much higher temperature alloy’s that Could take it. The same engine could be used as a rocket Once it reaches flame out altitude. One engine two functions. No One listens. Now China has developed a poor version of it. Excuse my lack of technical terms. Breaking my ideas down into the simplest language has become habit despite whomever I’m addressing.