Cosmic Microwave Background Radiation |
made the startling discovery that an all pervasive background radiation fills the Universe. Since then several further missions, Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP) and Planck, have probed deeper into the properties and meaning of the CMB.
The CMB has properties:
The CMB is uniform and isotropic, i.e., it has very close to the same temperature all across the sky -- temperature differences of < 0.004 % on angular scales of 7 degrees excluding a well-known 0.12 % variation known as the dipole anisotropy found after subtracting the average temperature from the image and finer, lower amplitude temperature variations found after subtracting the average temperature and the dipole anisotropy from the image.
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Gamow's prediction was slightly off because, for among other reasons, the Hubble constant had not yet been pinned down.
In addition, Planck and WMAP found that the expansion rate of the Universe, as measured by the current value for the Hubble constant, is Ho = 67.4 km/sec per Mpc. Recall that the best measurement made by work following Hubble was Ho = 73 km/sec per Mpc.
The disagreement is real in that each observation is secure; the small difference in Ho does not appear to be attributable to experimental error. This disagreement is what is referred to as the Hubble Tension. To resolve the Hubble Tension might mean that there is a piece of physics missing from the current models or that a piece of the physics that goes into the current models needs modification. Either possibility is interesting. |