Over the past 40 years astronomers have realised that everything we can see – all the stars, planets and galaxies – make up less than 5% of the entire universe. What is the rest? The short answer is, we have no idea.
What we do know is there are two gaping holes in our understanding of our universe. As a placeholder, physicists call them dark matter and dark energy.
In a nutshell, dark matter is the invisible stuff which we can only detect from the way its immense gravity moves stars and galaxies.
Dark energy, on the other hand, is the mysterious something causing the universe to expand with ever increasing speed.
We don’t know if dark matter and dark energy are related – in fact they’re probably two completely different phenomena, both called “dark” just because we can’t see them.
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