Dark Energy. The name sounds like something out of science fiction, and so does the description: A mysterious force that's pulling the universe apart. It was discovered in 1998 by two separate teams of astronomers who were competing to solve a simpler problem. They wanted to know the rate at which gravity is slowing down the universe's expansion.
But what they found surprised everyone. The universe's expansion is not slowing down. It's speeding up. Which means that something is pushing against gravity to pull the universe apart. Sound complicated? It is! We had so many questions about so many things. Dark energy, why are you so darn mysterious? We couldn't fit them all in the show. So here are our frequently asked questions about dark energy. Explore more information about the answers in the links!
Wait, the universe is expanding? How did we know that in the first place?
For a long time, people assumed that the universe was static, or not changing. But in the 1920s, the brilliant astronomer Edwin Hubble discovered that the universe is expanding, by measuring the distances between galaxies. Hubble was able to show that more distant galaxies were moving away from us faster than nearby galaxies. This discovery began the modern age of cosmology, or the study of the origin, evolution, and fate of the universe.
Here's Bill Nye, the Science Guy, explaining the expanding universe.
If the universe is expanding, what is it expanding into?
This is a really, really interesting question. When Jeff brought this up in our interview, he said, "That's not a defined question, and I try not to think too hard about it." I wondered what that meant, it's not a defined question?
Here's the short answer, from Ask an Astronomer:
...Because we are, by definition, stuck within the space that makes up our universe and have no way to observe anything outside of it, this ceases to be a question that can be answered scientifically. So the answer in that case is that we really don't know what, if anything, the universe is expanding into.
For the long answer, listen to this episode of Astronomy Cast: What is the universe expanding into? where two astronomers dive in deep to the question. (There's also a transcript.)
Or check out this video that claims to "break your brain." Watch out!
How close are astronomers to understanding what dark energy is?
Not very close. Fifteen years after the discovery of dark energy and with no shortage of astronomers interested in finding the answer, progress is slow, says Jeff. I mean, dark energy is a lot more complicated than a Rubix Cube. There are plenty of spectacular efforts to unwrap the mystery. Here's a two fascinating articles about astronomers' hopes for discovery:
Astronomers travel to the end of the Earth to do research at the South Pole Telescope
A new experiment at McDonald Observatory in Far West Texas
What is dark matter, and how is related to dark energy?
As Jeff says on the podcast, "[Dark matter is] totally different from dark energy, except it's also dark and we don't know what it is." NASA has a great explainer of dark energy and dark matter, right here.
Do you have your own questions about dark energy? Post them below in the comments, and we'll see if we can answer them!