Seventy percent of our universe is made up of something so weird and so strange it continues to baffle the world's brightest minds. We are absolutely still lacking great ideas. It is crying out for some new breakthrough, new thinking. It's the greatest remaining mystery in our universe. Dark energy is basically our name for that thing that we don't understand. It's not the color of dark, it's just an expression of our ignorance as to what is this stuff. A genius? Yeah, it is quite possible. I'm kind of hoping it's me.
Why do we think dark energy exists?
Ever since the Big Bang, our universe has been expanding with space itself stretching, moving galaxies further apart. Now, physicists used to think that the energy that was made in the Big Bang to power that expansion would eventually start to run out and the expansion would start to slow down. Then, a Nobel Prize-winning discovery turned all of that on its head. Saul Perlmutter and his team measured the way the universe was expanding by comparing the brightness of supernovae. This is when a star runs out of fuel at the end of its life, they brighten as a fireworks and fade away, and they reach the same brightness. And you can then use that as an indicator of how far away it is, by just looking to see how bright it appears to you. Just like when you watch a car recede in the distance, you can tell how far away it is by how faintly the tail lights look. If you can use the brightness of the supernova to tell you how far away it is, that's really telling you how long ago the explosion occurred, because you know how long it takes for light to travel that great distance. And what they discovered definitely shook the physics world. Suddenly, they were saying that we were living in a universe that was accelerating. I remember it just being just incredible. I mean, all the astronomers walking around scratching their heads, saying this can't be right, surely it can't be right.
Now exciting as this finding was, like many things in science, it raised a lot more questions than answers. Once you know that the universe is actually speeding up, then you're faced with the question of, well, what could make it speed up? This mysterious thing that was causing this newly spotted phenomenon that no one could explain was immediately called dark energy. Now, it's great to have a name for this, but it doesn't exactly explain what is driving this accelerated expansion.
What is dark energy?
Just like with dark matter, which makes up 25% of the universe and is also currently unexplained, this weird type of energy seems to defy our laws of physics and has properties that our current models just cannot explain. So, you can think of it as you get more space, you actually get more dark energy, which is like getting something for nothing, which is clearly ridiculous. The way we think about it is that it's either some new stuff in the universe, some particle, or even just a new field that you put into the universe to explain the properties of the universe.
So, what is it that's changing evolves? Well, scientists differ in their thoughts of what it could be, from a liquid or a brand new particle like dark matter, or even an unknown force. Now, scientists at Berkeley in California are looking for something that they call chameleon particles. This is a whole new type of particle that's thought to create a force which, when it interacts with other particles, changes those particles' mass. By putting atoms in a vacuum, they're hoping to expose these chameleons. The experiment works by first collecting a cloud of cesium atoms on top of the spheres, and the atoms are free to fall, subject only to the Earth's gravity and the potential chameleon force. We will either discover the particle or rule it out once and for all. So far, they haven't found any evidence for the particles and their elusive force, but it is an idea that continues to be explored.
How can we figure out what dark energy is?
Now, the obvious place to start is by looking at how the universe formed and has evolved. With incredibly powerful telescopes, one of the things that I do is try to simulate the entire universe and tie what we think about the physics of the evolving universe to what we actually see with surveys like DESI (Dark Energy Spectroscopic Instrument). DESI is one of these incredibly powerful telescopes observing the distant universe. Now, the further away galaxies are, the younger they appear to us. That's because light takes time to travel to us. It can take even a billion years to reach us here on Earth. Thanks to this, we can look at the average distance between galaxies at different cosmic times and look how it's changed
Neutron stars are incredibly dense, with a matchbox full of neutron star material weighing approximately three billion tons. The density of neutron stars is still a mystery, but it is believed to be related to their magnetic fields. When neutron stars merge, they can create black holes or give birth to magnetars.
Magnetars are one of the rarest stars in existence and have incredibly strong magnetic fields. They exist in binary systems with another star, feeding off its lower density companion and emitting bursts of x-ray pulses.
Studying parallel universes was once considered bonkers, but now it is a dominant scientific paradigm. Quantum mechanics suggests the existence of multiple universes, and the mathematical inevitability of different arrangements of matter supports this idea. The theory of inflation also proposes the existence of pocket universes with their own laws of physics.
While scientists cannot directly prove the existence of other universes, they are getting closer to understanding the possibility.
