WE’RE all familiar with black holes, those exotic beasts that we believe populate the universe, lurking in the hot cores of galaxies and sucking in everything that gets too close.
Black holes emerge from Einstein’s theory of general relativity; they are the graves of stars, places where space-time becomes curved beyond recognition. But an even stranger distortion of space-time might be lurking in Einstein’s equations: the anti-black hole, aka the white hole.
What exactly are white holes? For starters, they live on the other side of black holes, sporting large signs that read “No Entry”. Just as nothing can escape a black hole, nothing can enter a white one. Black holes swallow matter; white holes spit it out.
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If a black hole is rotating, then it can open up into a kind of tunnel. The tunnel that connects a black hole to its white hole is known as a wormhole. If you stumbled into one of these, you’d probably shoot back out of the white hole on the other side. That way you could end up in some other corner of our universe, or in the future, or in another universe altogether.
But do white holes really exist? No one has ever seen one, although astronomers once thought quasars – the brightest objects in the universe, which shine at the centres of some galaxies – might be white holes. Now they believe that quasars are the glow of hot matter and radiation swirling around super-massive black holes.
White holes are black holes running backwards in time. This means they violate one of the pillars of classical physics: the second law of thermodynamics, which states that order can turn into disorder, but never the other way round. If a piano falls into a black hole and gets crushed, that’s fine. If a white hole spits out a piano from nowhere, something has gone wrong. But that’s just in classical physics. In the quantum world, things are never so black and white.
It is just possible that our whole universe might be one giant white hole. How so? Well, if the singularity at the centre of a black hole lies in the future, representing a final state, the singularity of a white hole lies in the past, as a beginning, as in the big bang. So, if our universe is a white hole, the big question is: is there a black hole universe on the other side of the big bang? And if there is, how will we ever know?
