Ask Ethan: Why Was The Universe Dark For So Long?
“One thing I wonder though is why did the dark ages last hundreds of millions of years? I would have expected an order of magnitude smaller, or more.”
There’s a troubling puzzle when it comes to the Universe: the so-called ‘dark ages’ don’t come to an end until 550 million years after the Big Bang. But this is a big problem when you consider that we’ve already imaged a galaxy from when the Universe was only 400 million years old, and that we fully anticipate the first stars to form when the Universe is only 50-100 million years old. So what’s with all the darkness, then? And how do we expect the James Webb Space Telescope to see back to the very first galaxies? The answer lies in two parts. First, even though you have stars, the Universe is still filled with neutral atoms, which block visible and ultraviolet light. We need to ionize those atoms in order to have a transparent Universe, and that takes lots of time. But the second key is that the Universe, even with neutral atoms, is quite transparent to other wavelengths of light, like infrared light. And that’s where an observatory like James Webb is going to be looking!
The Universe was dark for so long because it doesn’t just need light, it needs for all the light-blocking material to disappear. But we’re going to overcome that obstacle in less than two years anyway, and that’s something we should all be excited about!