If there is one word associated with scientific curiosity, it鈥檚 鈥渨hy鈥�. Why is the universe expanding? Why are cases of cancer rising in young people? Why is the sky blue?
In contrast, it is rare for us to give so much attention to questions that begin with 鈥渨hen鈥�. Indeed, it is often written almost in passing that the universe began 13.8 billion years ago, that our planet is 4.5 billion years old or that Homo sapiens evolved 300,000 years ago. Yet these confident statements conceal plenty of scientific intrigue, mystery and uncertainty. All of which might make one wonder, well, why? Why don鈥檛 we focus on 鈥渨hen鈥� a little more?
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Asking when forces us to sharpen our thinking, to carefully define our terms and think through what beginnings really look like. It is in this spirit that we tackle seven of the most crucial 鈥渨hen鈥� questions in a special package beginning here 鈥淲hen did time begin? Hint: It wasn鈥檛 at the big bang 鈥�. Each piece shows that 鈥渨hen?鈥� can be one of the most interesting questions it is possible to ask.
Asking when has already taught us so much about the grand sweep of cosmic history
To take one example, we have recently begun to find that the first galaxies appeared far earlier than we thought possible. The 鈥渨hen鈥� here dramatically changes our understanding not only of the early universe, but also of how the chemical elements that went on to create life as we know it could have come about. Without 鈥渨hen鈥�, there is no 鈥渉ow鈥�, and certainly no 鈥渨hy鈥�.
Science is increasingly well-equipped to investigate when things happened. We can deduce dates in the distant past using evidence from radioactive isotopes or by extrapolating from known points in history. Our special feature serves as a reminder of how much asking when has already taught us about the grand sweep of cosmic and terrestrial history, from the switching on of the first stars to the first life on this planet.
Asking why is also an important part of scientific curiosity, of course, and something we do often, but let鈥檚 not give it all the glory. It鈥檚 time 鈥渨hen鈥� got some of the limelight too, because if not now鈥�
This article is part of a special series exploring seven of the biggest chronological conundrums of all time.
When did time begin? Hint: It wasn鈥檛 at the big bang
When did the first galaxies form? Far earlier than we thought possible
When did life begin on Earth? New evidence reveals a shocking story
Why it鈥檚 so hard to tell when Homo sapiens became a distinct species
We are finally getting to grips with how plate tectonics started
We鈥檙e uncovering a radically different view of civilisation鈥檚 origins
Why geologists can鈥檛 agree on when the Anthropocene Epoch began
