Dark energy
Dark energy is the most abundant component of the universe—and the most mysterious. It is estimated to account for approximately 68% of the total content of the cosmos, ahead of dark matter (27%) and ordinary matter (5%). Its primary role is believed to be driving theaccelerated expansion of the universe, as if space itself were being pushed by an invisible repulsive force.
Where did this idea come from?
In 1998, two teams of researchers were studying distant supernovae to measure the rate of the universe’s expansion. They expected to find that this expansion was slowing down, held back by the gravity of all the matter. An unexpected result: the universe is expanding faster and faster. To explain this acceleration, physicists introduced the concept of dark energy— an energy intrinsic to space itself.
What exactly is it?
We don’t know. Dark energy could be the cosmological constant introduced by Einstein—a form of quantum vacuum energy that exerts a negative pressure against gravity. It could also be a form of dynamic energy called quintessence, whose intensity would vary over time. None of these hypotheses has been confirmed.
What is certain is that it acts uniformly throughout the universe, unlike matter, which concentrates into structures. It does not form clumps, does not accumulate, and its effects are only felt on a very large scale.
Why is it fundamental?
Dark energy determines the fate of the universe. If it remains constant, the universe will continue to éexpand indefinitely, at an ever-increasing rate, until galaxies drift apart beyond any visible horizon. Some more extreme scenariosenvision a Big Rip: the expansion would become so violent that it would tear apart all matter, down to the atoms themselves.
A concrete example: Type Ia supernovae
Type Ia supernovae serve as standard candles in cosmology: they all have similar luminosities, which allows us to calculate their distances. By comparing their distance to their recession velocity, astronomers have determined that the expansion of the universe has been accelerating for about five billion years— a discovery that earned the 2011 Nobel Prize in Physics.
Did you know?
Dark energy was not given this name until 1998 by cosmologist Michael Turner. Before that, Einstein had already introduced a similar constant into his equations—which he later removed, considering it his greatest mistake. History proved him wrong.
Frequently Asked Questions
Are dark energy and dark matter related?
No. Despite their similar names, they are fundamentally different. Dark matter is a form of matter that exerts a gravitational pull. Dark energy is a form of energy that causes repulsive expansion. Both remain unexplained, but they are independent of one another.
Can dark energy be measured?
Not directly. It is measured indirectly through its effects on the expansion of the universe, particularly by observing distant supernovae, the cosmic microwave background, or the large-scale distribution of galaxies.
Will dark energy destroy the universe?
That depends on its nature. If it remains constant, the universe will expand indefinitely but without a sudden catastrophe. If it increases over time, it could tear all matter apart in a scenario called the Big Rip. These questions remain open.