Science Floats

What a satellite can do, balloons can do cheaper.

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A balloon of 40 million cubic feet has 172 gores and takes about three weeks to assemble. Raven's workers unroll sheets of polyethylene film, which comes folded lengthwise in rolls of 54 inches wide, down the length of a table. They then run a sealing machine down the edges where two gores join; the machine uses heat to fuse the film and form gas-tight seams. The panels are cut along a curve, marked on the work tables with tape. As workers join the gores, they install load-bearing tapes that run the length of the balloon. The balloon stays folded during construction and prior to launch. It expands to full size only at altitude.

Ravens build about 20 balloons a year. Most of their instrument packages tip the scales at a ton and more.


The Big Push

Minute variations in the temperature of the very early cosmos, mapped by Boomerang in 1999, support a theory known as inflation. Inflation theorists assert that in the course of the Big Bang, there was an inconceivably rapid expansion, during which the universe grew from a size a trillion times smaller than a proton to that of a grapefruit in less than 10-32 second.

Astrophysicists find this scenario compelling, for it predicts a universe with features that match observations: among them, uniformity over the universe's vast expanse. In an article about the Boomerang project, investigator Andrew Lange explains: "[T]he microwave background can be the same temperature everywhere because, before the universe inflated, all its parts were in very close contact and would naturally equilibrate to the same temperature."

But even in this uniformity—the temperature of the microwave background over the entire universe is 2.73 degrees Kelvin (about absolute zero)—there is variation on a very small scale. In one patch of sky, the temperature of the microwave background may be 2.7283. Inflation theorists believe that these "hot" and "cold" patches are traces of quantum fluctuations in the pre-inflationary universe and, as such, are also proof of instantaneous expansion.

The laws of quantum mechanics recognize that a small amount of energy is always present, even in empty space. Quantum fluctuations are jiggles in this background energy. (Evidence for the energy's existence was found in laboratory experiments in which closely spaced metal plates were found to be pushed together by quantum force.)

The process by which quantum fluctuations wink in and out of existence occurs at the speed of light and over a distance of 10-33 centimeters, known as the Planck length, for the German physicist who identified it. Had the universe expanded at the speed envisioned in the standard Big Bang theory, the expansion would have been far too slow for any trace of the quantum fluctuations to exist today. But according to the inflation theory, space itself expanded at a rate enormously faster than the speed of light. Inflation acted like stop-action photography, freezing the fluctuations in mid-jiggle, and at the same time, blowing them up from the "Planck length" to a macroscopic scale. At their post-inflationary size the fluctuations were no longer quantum—they now behaved according to the rules of classical physics. They took on the character of seismic waves within a universe filled with plasma, or ionized gas.

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