10 Biggest Unexplained Mysteries Of The Universe

1. Dark Energy/The Universe Horizon

If you've heard the phrase Dark Matter, then you may have heard of Dark Energy. Though still technically a theory and not solid fact, it is widely understood that dark matter is what makes up 85% of the universe. The black bit, the bit you assumed was just empty, is actually a something, it's just a something that we can't see. It explains how galaxies can hold their structure as well as a nod towards why the universe is expanding, which is where Dark Energy comes in.

Dark energy is essentially the energy that is pushing everything outwards, and is the explanation as to why the speed with which the universe is expanding is actually accelerating, instead of slowing down or remaining constant as would be expected.

Again, this is still a theory, so we could discover that it's something else entirely but the current thinking behind dark energy suggest that at the edge of the universe, the expansion is starting to accelerate beyond the speed of light, which up til now was thought to be the speed limit of the universe.

If this is the case, then what if there is more beyond the 'edges' that has been expanding faster than the light within it can reach us, meaning we'll never see it? These are the sorts of things that keep scientists up at night. There could be a universe we'll never see.