Read an extract from Chanda Prescod-Weinstein’s The Edge of Space-Time

it is not incorrect to go back and get what you forgot We are called to go back and get the history of space-time. And who am I to argue with the ancestors? Science in this society is often done for the wrong rea­sons, I find myself telling them.

And they remind me that because it’s my job to study the origin and evolution of the universe and every­thing inside it, I know there is a location in space-time where the uni­verse became transparent to light: the first place where light could fly free. The ancestors insist: This is a story that I have learned so I could tell it to others. To do cosmology—to study the beginning and evolu­tion of space, time, and matter—is to be a griot, a keeper of stories and history.

To do cosmology is to go back and get the beginning, to map out the future. So: Quite nearly at the beginning, the universe said let there be light. And particles of light—photons—all of them traveling at the speed of light, the fastest in the universe, couldn’t get very far.

They were stuck in a plasma stew where they constantly bumped into par­ticles, especially electrons, which swallowed their energy and spat it out in the form of new photons and other particles. Humanity has only been aware of this cosmic light for eighty-two years. It has been there almost since the beginning of everything and has been traveling for nearly 14 billion years.

It was there when the universe was cool enough for atoms to form. It was with the sun when it was just a cloud of gas, and it was there when the sun’s hydrogen ignited with fusion, turning the sun into a star. It was there when the leftovers from the gas cloud condensed into planet Earth.

And it was there when carbon-based life forms evolved into apes. This light is a cosmic edge: We cannot look past it because at any time earlier than that, the photons were trapped, unable to get out. And this edge is a reminder that physics is a way of gaining deep insight into the universe, one we can add to the variety of overlapping forms of knowing that we have long used.