Surprising Boomerang

The BOOMERANG (Balloon Observations Of Millimetric Extragalactic Radiation And Geophysics) mission flew for 10 days in late 1998 and early 1999. The balloon-borne craft flew around Antartica, collecting high-resolution data at microwave frequencies sensitive to the part of the spectrum where the universe emits photons that are a remnant echo of the Big Bang. The results were nothing short of breathtaking. While the craft mapped only a small part of the sky, it did cover that small portion with much higher resolution than was available to the COBE mission. As a result, BOOMERANG detected the scale of the fluctuations in the cosmic microwave background. In a flat universe (one that has critical density) the scale of these fluctuations is expected to be about 1 degree. Fluctuations smaller or larger than this mean that the universe has a curvature.

Well, which is it?

The scale size of the detected fluctuations is about 1 degree. Now, a flat universe requires that the universe be at critical density, and we have seen that, even including dark matter, we are far from closing the universe with matter. All told, luminous and dark matter only account for about 30 percent of the required critical density. The remaining 70 percent may be contained in the energy of the vacuum. And if this other 70 percent is there, it might also explain our accelerating universe!

We defined neutrinos in Chapter 18, "Stellar Careers," as subatomic particles without electric charge and with virtually no mass. As a result, these are sort of stealth particles, hard little neutral ones to detect. On June 5, 1998, U.S. and Japanese researchers in Takayama, Japan, announ-ced that, using an enormous detection device, they found evidence of mass in the neutrino. The device, called the Super-Kamiokande, is a tank filled with 12.5 million gallons of pure water and buried deep in an old zinc mine.

Because neutrinos lack an electric charge and rarely interact with other atoms, passing unnoticed through virtually any kind or thickness of matter, they have proven especially elusive. They are the greased pigs of the subatomic world, so plentiful that 100 billion of them (that's as many stars as there are in the Galaxy) pass through your body every second. The Super-Kamiokande contains so much water, however, that occasionally a neutrino collides with another particle and produces an instantaneous flash of light, which is recorded by a vast array of light-amplifying detectors.

Just how much mass does a neutrino have? This is not yet known, but it does not appear that neutrinos can contribute enough mass to the universe to affect critical density.

To predict whether the universe will expand infinitely, it is necessary to calculate critical density and to see whether the density of our universe is above or below this critical figure. By measuring the average mass of galaxies within a known volume of space, astronomers derive a density of luminous matter well short of critical density, about 10-28kg/m3. That figure is about 1 percent of what is required. After factoring in

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