The Fermi Paradox refers to the contradiction between the high probability of extraterrestrial life and the apparent lack of evidence that such life exists. We've now identified a handful of potentially habitable 'Earth- like' planets, but we're still yet to see any signs of intelligent life from 'out there. So why the radio silence?
Black holes are regions of space in which the force of gravity is so powerful that everything around is drawn in. Not even light can escape. Once anything crosses event horizon, it becomes invisible from us. But we don't know what happens when objects pass through the centre
We all know that the universe is expanding, but it's expanding more and more quickly than it should be, and scientists think that dark energy is the culprit. But where's dark energy coming from? Some believe that it's produced from collisions between quantum particles, but no-one knows for sure.
We have plenty of evidence that dark matter exists, but as for what it is, that remains a mystery. Some think dark matter is composed of an undiscovered particle or particles, others believe it's an undiscovered property of gravity. Whatever the truth; dark matter is a real puzzle