Scientists are currently grappling with some of the biggest unsolved questions out there.

Here are 7 that they are working on the answers to right now:

1. Dark Matter

The distribution of dark matter throughout the Universe as suggested by a numerical simulation. A new study suggest that the effects of dark matter could actually be the result of an discovered form of gravity. Herschel/ESA

Planets, stars, galaxies and everything we can see make up less than 5 percent of the total universe. Scientists think 26.8 percent is a substance they call "dark matter."

This matter doesn't interact with light or visible matter, but everything moves to its gravitational tune.

According to the European Space Agency (ESA), "although thought to be invisible, neither emitting nor absorbing light, dark matter can be detected through its gravitational influence on the movements and appearance of other objects in the Universe, such as stars or galaxies."

And based on this indirect evidence, "astronomers believe that dark matter is the dominant type of matter in the Universe – yet it remains obscure," says ESA.

2. Dark Energy

So, what about the other 68 percent of the universe? Cosmologists think it's "dark energy."

If dark matter seems to join galaxies together, dark energy wants to push everything apart. However, no one is quite sure what dark matter or energy are comprised of.

According to the American Space Agency, "we know how much dark energy there is because we know how it affects the universe's expansion. Other than that, it is a complete mystery. But it is an important mystery."

3. Quantum Entanglement

Quantum entanglement (the idea that pairs of particles separated even across great distances are inextricably linked) is key to developing tomorrow's secure communications channels.

Albert Einstein once called quantum entanglement, "spooky action at distance."

It is the phenomenon by which two particles in totally different parts of the universe can be linked to one another, reproducing the behaviour of their partner.

For particles to be connected across such distances, they must be sending signals that move faster than the speed of light—something the known rules of physics judges impossible.

Objects are only supposed to be affected by their surroundings, so the notion of a particle being affected by something on the other side of the universe is baffling.

4. What's Inside Black Holes?

Researchers may have explained where massive black holes over 40 times the size of the sun come from.

Black holes are regions of space in which the force of gravity is so powerful that everything near it is drawn in—not even light can escape its pull.

Scientists predict there are millions of black holes in our galaxy, but no one knows what is inside it. At its center, many suspect a singularity—a region of zero size and infinite density.

Understanding what is inside, could help explain quantum gravity. While physicists can predict the influence of gravity on sizeable objects, when it comes to minute particles (quanta), it's a mystery.

5. What Caused the Big Bang?

The Big Bang is the most widely accepted theory for the origin of the universe.

From an almost infinitely dense state, a huge expansion expanded space like a balloon.

"Time, space and matter all began with the Big Bang," the European Space Agency explains. "In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy. And it kept on growing at a fantastic rate. It is still expanding today."

Using the Hubble Space Telescope, scientists have been effectively able to look back in time to shortly before the event, about 13.8 billion years ago, because light from the earlier universe taking so long to reach Earth.

So what caused this Big Bang? Nobody knows.

6. Space Roar

In 2006 when scientists began to look for distant signals in the universe using an instrument fixed to a huge balloon that was sent to space, they detected a mysterious roar.

The instrument built by NASA was the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE) and it was able to pick up radio waves from distant stars and a signal that was louder than expected by cosmologists.

The powerful signal caused great puzzlement and scientists still don't know where the roar is coming from.

7. Cosmic Rays

Cosmic rays are high energy atom particles that rain down on the Earth from outer space at the speed of light. Cosmic rays are thought to be harmless as Earth's atmosphere protects us from them but they have been blamed for electronics problems in satellites and other machinery.

These high energy particles can disrupt electronic data, leading to system crashes and scientists are trying to find a solution.

Discovered in 1912, cosmic rays remain a mystery and we still don't know their origin.

Newsweek