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The Golden Age of Cosmology

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  • The Golden Age of Cosmology

    THE FABRIC of the COSMOS, Brian Greene, 2004
    ```(annotated and with added bold highlights by Epsilon=One)
    Chapter 11 - Quanta in the Sky with Diamonds
    The Golden Age of Cosmology
    Dramatic evidence supporting these ideas comes from meticulous satellite-based observations of the microwave background radiation's temperature. I have emphasized a number of times that the temperature of the radiation in one part of the sky agrees with that in another to high accuracy. But what I have yet to mention is that by the fourth digit after the decimal place, the temperatures in different locations do differ. Precision measurements, first accomplished in 1992 by COBE (the Cosmic Background Explorer satellite) and more recently by WMAP (the Wilkinson Microwave Anisotropy Probe), have determined that while the temperature might be 2.7249 Kelvin in one spot in space, it might be 2.7250 Kelvin in another, and 2.7251 Kelvin in still another.

    Figure 11.1 (a) Inflationary cosmology's prediction for temperature variaČtions of the microwave background radiation from one point to another on the sky. (b) Comparison of those predictions with satellite-based observations.

    The wonderful thing is that these extraordinarily small temperature variations follow a pattern on the sky that can be explained by attributing them to the same mechanism that has been suggested for seeding galaxy formation: quantum fluctuations stretched out by inflation. The rough idea is that when tiny quantum jitters are smeared across space, they make it slightly hotter in one region and slightly cooler in another (photons received from a slightly denser region expend more energy overcoming the slightly stronger gravitational field, and hence their energy and temperature are slightly lower than those of photons received from a less denseáregion). Physicists have carried out precise calculations based on this proposal, and generated predictions for how the microwave radiation's temperature should vary from place to place across the sky, as illustrated in Figure 11.1a. (The details are not essential, but the horizontal axis is related to the angular separation of two points on the sky, and the vertical axis is related to their temperature difference.) In Figure 11.1b, these predictions are compared with satellite observations, represented by little diamonds, and as you can see there is extraordinary agreement.

    I hope you're blown away by this concordance of theory and observation, because if not it means I've failed to convey the full wonder of the result. So, just in case, let me reemphasize what's going on here: satellite-borne telescopes have recently measured the temperature of microwave photons that have been traveling toward us, unimpeded, for nearly 14 billion years. They've found that photons arriving from different directions in space have nearly identical temperatures, differing by no more than a few ten-thousandths of a degree. Moreover, the observations have shown that these tiny temperature differences fill out a particular pattern on the sky, demonstrated by the orderly progression of diamonds in Figure 11.1b. And marvel of marvels, calculations done today, using the inflationary framework, are able to explain the pattern of these minuscule temperature variations — variations set down nearly 14 billion years ago — and, to top it off, the key to this explanation involves jitters arising from quantum uncertainty. Wow.

    This success has convinced many physicists of the inflationary theory's validity. What is of equal importance, these and other precision astronomical measurements, which have only recently become possible, have allowed cosmology to mature from a field based on speculation and conjecture to one firmly grounded in observation — a coming of age that has inspired many in the field to call our era the golden age of cosmology.
    Last edited by Reviewer; 10-07-2012, 02:40 AM.
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