What is a White hole?
A white hole is a bizarre cosmic object which is intensely bright, and from which matter gushes rather than disappears. In other words, it’s the exact opposite of a black hole. But unlike black holes, there’s no consensus about whether white holes exist, or how they’d be formed.
They are predicted by Einstein’s theory of gravity, and are most often mentioned in the context of ‘wormholes’, in which a black hole acts as the entry point to a tunnel through space and time, ending in a white hole somewhere else in the Universe. But this is deeply controversial, because Einstein’s theory predicts the existence of a so-called singularity at the centre of black holes – a state of infinite gravity which would prevent anything from passing through to the white hole on the other side.
However, some theorists think that a combination of Einstein’s theory and quantum theory points to a new way of thinking about white holes. Instead of being the ‘exit’ from a wormhole, they may be a slow-motion replay of the formation of the original black hole.
What is Dark Energy and Dark Matter?
More is unknown than is known. 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. It turns out that roughly 68% of the universe is dark energy. One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. The first property that Einstein discovered is that it is possible for more space to come into existence. As a result, this form of energy would cause the universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there.
We are much more certain what dark matter is not than we are what it is. First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the universe to make up the 27% required by the observations. Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them. Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see.