There are many forms of energy in the universe, from mechanical energy and nuclear energy to potential energy and kinetic energy.
But recently, a mysterious force has been discovered lurking in the depths of space. We can’t see it, but we know it’s there. And it’s brought a friend.
Dark energy, and its counterpart, dark matter, are making cosmologists rethink everything we thought we understood about the universe.
Join us as we shed some light on how our studies of the observable skies have brought more questions than answers about dark energy and dark matter.
Defining Dark Energy: What Does Dark Energy Do?
Firstly, we must forget “dark” as a color or a word describing something that is opaque. Why? Because we cannot see dark energy nor dark matter. We’re not talking about the color black that we imagine when we picture the empty voids of space.
But before we go any further, let’s start at the beginning of the history of the universe. The Big Bang Theory explains how the dense early universe expanded rapidly, creating matter. As the universe cooled, it became less dense, with stars and galaxies spreading far and wide.
Between these planets and galaxies exists empty space, which is a vacuum. These spaces were assumed to be empty, but now we know they are home to a form of energy. Ours is not a static universe, and as the expansion of the universe continues, there is more space — and vacuum — created.
Dark energy can be thought of as vacuum energy, the energy that a vacuum contains. If there is more space, there is more vacuum in space, and therefore more dark energy. The more dark energy in existence, the more influence it can have.
The stumbling block is that we cannot see dark energy. Physicists now understand that, in theory, dark energy is a repulsive form of energy. No, we don’t mean repulsive in the sense of causing disgust or distaste. Rather, the nature of dark energy is that it exerts negative pressure on objects, working in opposition to the attractive forces of gravity.
What Does Dark Energy Mean for the Universe?
Previous astrophysics theory focused on how gravity and the mass of objects affected the expansion of the universe.
Early universe theories posited that matter and antimatter should exist in equal quantities. Yet, there is a lot more matter than antimatter in the universe. Does that missing antimatter happen to be our new friend, dark energy?
The discovery of dark energy has profound implications for cosmologists. Dark energy could be a cosmological constant, something that always happens. That would mean dark energy is created proportionally to the amount of new space brought into existence as the universe expands.
Some cosmologists speculate that dark energy is a brand-new energy field or even a liquid that fills space, which they’ve dubbed quintessence. This is all theoretical pondering.
Two more apocalyptic scenarios have developed around dark energy too. The first will lead to the Big Rip. The ever-accelerating expansion of the universe caused by the creation of dark energy leads to the destruction of the universe. Eventually, the sheer quantity of dark energy causes planets and galaxies to shred and be ruptured by holes.
The second equally foreboding possibility is the Big Crunch, where the universe stops accelerating outwards and starts to retract and compress. This could happen if dark energy changes property or gravity “wins out” in its battle with the repulsive properties of dark energy.
What Does Dark Energy Look Like?
As we’ve mentioned, we cannot see dark energy, but we know it’s there because we can detect it. The Big Bang produced matter and radiation, and it is radiation that helps us understand that dark energy exists.
Cosmologists scan the Milky Way and beyond, studying radiation left over from the Big Bang, known as Cosmic Microwave Background, or CMB. This CMB has a uniform temperature, so cosmologists look for temperature changes and fluctuations called Baryon acoustic oscillations to help unravel the universe’s mysteries.
Those temperature changes show that the universe is made up of three things:
- Normal matter, also known as baryonic matter. Planets, black holes, supernovae, and all objects with mass contain protons, neutrons, and electrons, making them baryonic matter.
- Dark matter
- Dark energy
How Much Dark Energy Is There in the Universe?
There have been several studies of the celestial sky in an attempt to measure its total mass.
In 2013, the European Space Agency (ESA) published its dark energy survey based on readings from its high-precision Planck probe. Planck found the universe composed of 5% normal matter, 27% dark matter, and 68% dark energy.
More recently (June 2021), The National Science Foundation’s Dark Energy Survey completed the most precise picture of one-eighth of the night sky. They found it to be 5% matter, 25% dark matter, and 70% dark energy.
NASA’s Fermi Large Area Telescope (LAT) scans the Milky Way and beyond, looking for gamma-rays that may give us clues about dark energy and dark matter. Gamma-rays are an energy-intense radiation form, emitting radiation from large-scale structures like black holes, supernovas, and more.
Can Dark Energy Be Harnessed?
We know of the existence of dark energy but have yet to define, see, or understand dark energy fully. Therefore, harnessing dark energy is currently in the theoretical stage.
Can Dark Energy Be Destroyed?
Dark energy may destroy itself and decay. It may convert into baryonic matter or even birth a brand-new particle. Because we don’t understand how it is made, we also do not know how to destroy it.
What’s the Difference Between Dark Energy and Dark Matter?
Dark energy is a force of energy that is driving the universe apart. Its cosmic acceleration works counter to the force of gravity. Dark matter, which has mass, helps glue and bind galaxies and the universe together, thanks to its gravitational influence.
Who Discovered Dark Energy?
There were several essential stages to the discovery of dark energy. First, we must travel to 17th century England, where Sir Isaac Newton’s law of gravity proved there is a gravitational force between all objects of mass.
Fast-forward to the early 20th century when Albert Einstein took Newton’s law further with his theory of general relativity. Einstein believed mass could pull, bend and warp space, whether on Earth or a cosmic scale. Einstein’s theory meant gravity would eventually bring deceleration to the expansion of the universe.
How Did Edwin Hubble Help Discover Dark Energy?
In 1929, American cosmologist and astronomer Edwin Hubble deduced that we are living in an expanding universe.
Hubble observed many clusters of galaxies, all of which were moving away from Earth and our solar system. What he noted was that distant galaxies were traveling faster away from Earth than galaxies closer to Earth. He saw the expanding universe and devised a calculation to prove his observations.
How could Hubble be so sure? Well, light travels as waves. We know space is expanding and getting bigger. For light to cross over this expanding space, it has to stretch. When wavelengths stretch, they get longer, and longer wavelengths look redder to the human eye. This phenomenon is called redshift. The redder the light from a galaxy, the further the light has traveled.
The next step to discovering dark energy involves us taking a slight detour to find dark matter.
How Was Dark Matter Discovered?
In the 1930s, Swiss-American astronomer Fritz Zwicky saw evidence of dark matter. Zwicky was observing the Coma Cluster and the galaxies’ movements within. He had calculated their expected speed beforehand, based on their visible matter. But Zwicky was wrong, and his calculations were out. Was it a blunder? Perhaps not, and more people continued his work.
The idea of undiscovered particles was popular in particle physics’ circles in the 1960s. Could they be part of the calculation problems Zwicky faced?
In the 1970s, American astronomer Vera Rubin saw something similar to Zwicky in galaxy clusters, but with an extra touch. Her observations demonstrated that outer regions of spiral galaxies were rotating faster than expected.
Both Zwicky and Rubin knew something was adding to the gravity and speed of galaxies.
Next to pick up the baton, in 1974, was American physicist James Peebles. He didn’t just look at visible matter for weighing the mass of galaxies. Peebles incorporated galaxies’ movements into his workings and found them to be much heavier than expected.
What was this missing mass? The missing matter was given the title of dark matter.
New calculations were devised to take this dark matter into account. Factoring in dark matter now meant estimates of mass balanced when applied to weighing everything from the mass of galaxies to large-scale structures like clusters of galaxies.
Is Dark Energy the Opposite of Gravitational Forces?
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By the 1990s, more and more people were becoming aware of something unseen happening in the universe.
In 1998, NASA’s Hubble Space Telescope based at the Space Telescope Science Institute (STSCI) was trained onto very distant supernovae; a supernova is an exploding star.
Type Ia Supernovae are very bright, making them ideal for studies. What the Hubble telescope demonstrated rocked all previous ideas about the early universe. The Big Bang hadn’t led to accelerated expansion. The universe had a slower rate of expansion in its infancy and much slower than the expansion rate seen today.
Experts were shocked and started questioning Einstein’s theory, gravity, and matter, to no avail.
Who Discovered Dark Energy and Dark Matter?
The 2011 Nobel Prize in Physics recognized a watershed for dark energy.
Three astrophysicists — Saul Perlmutter, Brian Schmidt, and Adam Riess — were celebrated “for the discovery of the accelerating expansion of the universe through observations of distant supernovae.”
Their initial aim had been to demonstrate how gravity was causing the gradual slowing of the expansion of the universe. American Perlmutter started the Supernova Cosmology Project in 1988 to that effect. In 1994, The High-z Supernova Search Team led by Schmidt and vital cog Riess joined Perlmutter.
They discovered dark energy was the universe’s dominant component, a repulsive force that was accelerating the expansion of the universe. The theory was tight, but still, no one had been able to explain what dark energy or dark matter was.
What Is Dark Matter?
Dark matter is outside the Standard Model of Particle Physics. Dark matter particles are unknown non-baryonic matter.
The standard model describes the universe’s building blocks of all known matter, ordinary matter, which includes old friends like photons and electrons. The model also consists of the now-famous Higgs boson, discovered in 2012 by scientists using the Large Hadron Collider (LHC) for the European Council for Nuclear Research (CERN).
Dark matter is invisible but has mass that has gravitational effects. What we don’t know is why it has mass. Dark matter doesn’t absorb light or stop light from passing through it. It doesn’t interact with anything we know. But we know it interacts with gravity because it distorts light, so there is proof of the existence of dark matter.
There is no fixed definition of dark matter. Some of the dark matter candidates include:
- Weakly interacting massive particles: Also called WIMPS, these hypothetical particles interact weakly with other particles and do not emit or absorb light. When WIMPS collide, they annihilate and produce gamma-rays.
- Axions: These are another type of hypothetical subatomic particle that could be dark matter.
- Neutrinos: Neutrinos are known but mysterious particles, with ideas ranging from dark matter being a standard neutrino, a massive neutrino, or even a sterile neutrino.
- Neutralinos: Similar-sounding to neutrinos, neutralinos are theoretical, undetected large but light particles.
Is Dark Matter a Powerful Force in the Universe?
The term “dark matter” seems to suggest something dark or black — it’s perhaps how many of us visualize space. Although we can’t see dark matter, it has a profound effect on the universe, some of which we can detect.
Cosmologists look at stars, galaxies, and supernovae many light-years away from Earth. The light that shines from these objects and travels to Earth is distorted by dark matter in a process called gravitational lensing.
Einstein’s theory of relativity also included space-time, a single continuum that linked space, gravity, and time together. Space has three dimensions — up and down, left and right, back and forth — and when connected to time, creates the fourth dimension.
Einstein realized that objects with mass, like planets, distort space-time, slowing and speeding time. The stronger the gravitational pull, the slower time proceeds.
Think about the GPS satellites that orbit the Earth. They travel at around 14,000 kilometers (8,700 miles) per hour. They carry clocks to remain in sync with time on Earth. However, the satellite’s clocks are traveling a lot faster than clocks on Earth. They go out of sync by 38 microseconds per day. The satellites are reset daily, so they don’t give inaccurate readings.
Dark Matter and Dark Energy Remain a Mystery
Space, time, and the universe’s energy density are puzzles that continue to stretch our scientific boundaries.
The human imagination loves to speculate about space through science fiction, imagining ourselves living in distant galaxies, time-traveling through wormholes, and perhaps even meeting a possible God. The possibilities of dark energy and dark matter are endless.
Understanding dark energy and dark matter may bring us closer to some or none of those things. Invisible but known, these mysterious forces may cause a paradigm shift in our perception of our place in space. Only time will tell.
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