INSUBCONTINENT EXCLUSIVE:
Second, there was a time, within the first few hundred million years after the Big Bang, before stars and galaxies had even formed
sources to generate light for us to look at.But there was neutral hydrogen
Most of the Universe is made of hydrogen, making it the most common element in the cosmos
Today, almost all of that hydrogen is ionized, existing in a super-heated plasma state
But before the first stars and galaxies appeared, the cosmic reserves of hydrogen were cool and neutral.Neutral hydrogen is made of a single
proton and a single electron
In its lowest-energy state, the proton and electron will have spins oriented in opposite directions
But sometimes, through pure random quantum chance, the electron will spontaneously flip around
Very quickly, the hydrogen notices and gets the electron to flip back to where it belongs
This process releases a small amount of energy in the form of a photon with a wavelength of 21 centimeters.This quantum transition is
exceedingly rare, but with enough neutral hydrogen, you can build a substantial signal
Indeed, observations of 21-cm radiation have been used extensively in astronomy, especially to build maps of cold gas reservoirs within the
But that radiation was emitted in the distant past, well over 13 billion years ago
As it has traveled through the cosmic distances, all those billions of light-years on its way to our eager telescopes, it has experienced
the redshift effects of our expanding Universe.
