How the Universe Got Its Spots by Janna Levin;

Author:Janna Levin;
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2022-08-25T00:00:00+00:00

19 JANUARY 2000

Sometimes the beauty of San Francisco gives way to muck. I love Chinatown but it is engulfed by an urban grit. I wander through Chinatown when I go back to California, taking poorly chosen routes. The people spill on to the street, having run out of room on the sidewalk lined by vegetable stands. I take a lot of extremely amateur photos of curbs, manholes and graffiti, and survey them now. I have pictures of modified Chinese architecture miniaturized to fit on the San Francisco streets and fronted by distinctly American car metres, concrete roads and steaming manhole covers. It’s hard for me to place the significance of culture and humanity in a universe that barrels along without concern for our welfare. Our city monuments are poignant, but maybe I don’t know how to assess our significance. Why are we all struggling so desperately to survive? I don’t know how to place us in the greater scheme of things. As Oscar Wilde said, ‘We are all in the gutter, but some of us are looking at the stars.’

Sometimes I’m looking at the gutter and sometimes the stars. But when we (the collective we) do look at the sky, what we see is tremendous. The cosmic background radiation is one of those remarkable discoveries that will mark the century. The last century that is. In the early 1990s the COBE satellite (another acronym: COsmic Background Explorer) launched into orbit around the earth. For a few years the detectors on the satellite pointed out into the sky and measured the temperature of the cosmic background radiation in every direction. The early COBE data were first presented at an astronomy meeting to spontaneous applause. I have never before witnessed spontaneous applause at an astronomy meeting. The results were impressive. The cosmic background radiation does in fact fill the sky and on average appears to be completely thermal: that is, it can be completely characterized by the temperature alone. The cosmic background radiation looks exactly like a hot bath of light left over from the big bang. Only it’s not so hot any more, just a few degrees above absolute zero.

After the COBE satellite a generation of cosmologists became devoted to the cosmic background radiation. Superb experiments are built to perform measurements of all kinds. Some are flown on high-altitude balloons and others are based at the South Pole. We’re still waiting for the future and possibly final generation of cosmic background radiation satellites. One of these is an American project called MAP (Microwave Anisotropy Probe) and another is a European project called Planck Surveyor. The satellites aim to resolve fine images of the primordial light.

The cosmic background radiation is impressively smooth, having a virtually identical temperature in every direction. The nearly impeccable cosmic background radiation offers stunning confirmation that as far as we can see the cosmos is homogeneous and isotropic. If anything, it is hard to foresee how the universe could survive so very homogeneous and isotropic.

Friedmann made some sweeping simplifications when he assumed the entire universe was homogeneous and isotropic.

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