Plasma Tv Sale

There's a lot of it out there but, thankfully, not too much of it down here.

Only rarely does the medical doctor's vocabulary overlap with that of the astrophysicist. The human skull has two "orbits," the round cavities where your two eyeballs go; your "solar" plexus sits in the middle of your chest; and your eyes, of course, have "lenses"--though our bodies contain no quasars and no galaxies. For orbits and lenses, the medical and astrophysical usages resemble each other greatly; on the other hand, the term "plasma" is common to both disciplines, yet the two meanings have nothing whatever to do with each other. A transfusion of blood plasma can save your life, but a brief encounter with a glowing blob of million-degree plasma would leave a puff of smoke where you had just been standing.

Astrophysical plasmas are remarkable for their ubiquity, yet they're hardly ever discussed in introductory textbooks or in the press. Writers of science books often call plasmas the fourth state of matter because of a panoply of properties that sets them apart from the familiar solids, liquids, and gases. A plasma has freely moving particles, just as a gas does, but a plasma can conduct electricity as well as interact strongly with magnetic fields passing near it or through it. Atoms within a plasma have had some or all of their electrons stripped from them by one mechanism or another. And the combination of high temperature and low density in a plasma only occasionally allows electrons to recombine with their host atoms. Taken as a whole, the plasma remains electrically neutral, because the total number of electrons (which are negatively charged) equals the total number of protons (which are positively charged). But a plasma can seethe with electric currents and magnetic fields, so in many ways, it behaves nothing like the ideal gas we all learned about in high-school chemistry class.

The effects that electric and magnetic fields have on matter almost always dwarf the effects of gravity. The electrical attraction between a proton and an electron is forty powers of ten stronger than their gravitational attraction. So strong are electromagnetic forces that a child's magnet easily lifts a paper clip off a tabletop, despite Earth's formidable gravitational tug. Want a more interesting example? If you managed to extricate all the electrons from a cubic millimeter of atoms in the nose of a space shuttle and if you attached those electrons to the base of the launch pad, then the attractive force would inhibit the launch. All engines would fire, but the shuttle wouldn't budge. And if the Apollo astronauts had brought back to Earth all the electrons from a 100-inch cube of lunar dust (leaving behind the atoms from which they came), the force of attraction would exceed the gravitational attraction between Earth and the Moon.

Earth's most conspicuous plasmas are lightning, the trail of a shooting star, and the ordinary electric shock you get after shuffling around on your living-room carpet in your wool socks and then touching a doorknob. Electrical discharges are jagged columns of electrons that abruptly move through the air when too many collect in one place. Lightning, for instance, happens to strike Earth's surface thousands of times per hour. The centimeter-wide air column through which a bolt of lightning travels is turned into glowing plasma in a fraction of a second, having been raised to a temperature ten times that of the Sun's surface by these flowing electrons.

Every shooting star is a tiny particle of interplanetary debris moving so fast that it burns up in the air and descends to Earth as harmless cosmic dust. Almost the same thing happens to a spacecraft that reenters our atmosphere. Since its occupants don't want to land at the near-Earth orbital speed of 18,000 miles per hour (about five miles per second), the craft must slow down and its kinetic energy must go somewhere. Shock waves along the leading edge heat the craft during reentry. The heat is rapidly whisked away by protective shields. This is why the astronauts, unlike shooting stars, do not descend to Earth as dust. For several minutes during a descent, the heat is so intense that every molecule surrounding the space capsule becomes ionized, cloaking the astronauts in a temporary plasma barrier that none of our communication signals can penetrate. This is the infamous blackout period, when the craft is aglow and Mission Control knows nothing of the astronauts' well-being. The craft continues to slow down as it plows through the atmosphere. Along the way, the temperature drops, the air gets denser, and the plasma state can no longer be sustained. The electrons go back home to their atoms, and communication is quickly restored.

While relatively rare on Earth, plasmas comprise more than 99.99 percent of all the visible matter in the cosmos. This tally includes every glowing star and "gas" cloud. Nearly all the Hubble Space Telescope's beautiful photographs of nebulae in our galaxy depict colorful gas clouds in the form of plasma. The shape and density of some of these clouds are strongly influenced by the presence of magnetic fields from nearby sources such as pulsars. The plasma can lock a magnetic field into place and torque or otherwise shape the field to its whims.

This marriage of plasma and magnetic field is a major feature of the Sun's eleven-year cycle of activity. The plasma near the Sun's equator rotates slightly faster than the plasma near its poles. This differential is bad news for the Sun's complexion. With the Sun's magnetic field "frozen" into its plasma, the field gets stretched and twisted. Sunspots, flares, prominences, and other solar blemishes come and go as the gnarly magnetic field punches through the Sun's surface, carrying solar plasma along with it.

Because of all this hubbub, the Sun flings charged particles into space, up to a million tons of them per second--including electrons, protons, and bare helium nuclei. The resultant particle stream, sometimes a gale and sometimes a zephyr, is more commonly known as the solar wind. This most famous of plasmas ensures that comet tails point away from the Sun, no matter whether the comet is coming or going. By colliding with molecules in Earth's atmosphere near our magnetic poles, the solar wind is also the direct cause of the aurora borealis and aurora australis (the northern and southern lights), not only on Earth but on all planets with atmospheres and strong magnetic fields.

Depending on a plasma's temperature and its mix of atoms, some free electrons will recombine with needy atoms and cascade down the myriad energy levels within. En route, the electrons emit light in prescribed wavelengths. The auroras owe their beautiful colors to these electron hi-jinks, as do neon tubes, fluorescent lights, and those glowing plasma spheres offered for sale next to the lava lamps in tacky gift shops.

These days, satellite observatories give us an unprecedented capacity to monitor the Sun and report on the solar wind as though it was part of the day's weather forecast. My first-ever televised interview for the evening news was triggered by the report of a plasma pie hurled by the Sun, at 300 miles per second, directly at Earth. Everybody (or at least the reporters) was scared that bad things would happen to civilization when it hit. Severe plasma ejections can fry the circuits on satellites and knock out transformers at power stations. But this one was mild and innocent. I told the viewers not to worry--that Earth's magnetic field protects us--and I invited them to use the occasion to go north and enjoy the aurora that the solar wind would cause.

The Sun's rarefied corona, visible during total solar eclipses as a glowing halo around the silhouetted Moon, forms a five-million-degree plasma that is the outermost part of the solar atmosphere. With temperatures that high, the corona is the principal source of the Sun's X rays. Without the benefit of an eclipse to block the Sun's bright surface, the corona easily gets lost in the glare.

There's an entire layer of Earth's atmosphere where electrons have been kicked out of their host atoms by ultraviolet light from the Sun, creating a plasma blanket called the ionosphere. This layer reflects certain frequencies of radio waves, including those of the AM dial (which can reach hundreds of miles) and of shortwave (which can reach thousands of miles beyond the horizon). FM signals and those of broadcast television, however, pass right through the ionosphere, traveling out to space at the speed of light. Any eavesdropping alien civilization will know all about our TV programs (probably a bad thing), will hear all our FM music (probably a good thing), and will know nothing of the politics of AM talk-show hosts like Rush Limbaugh (probably a safe thing).

Most plasmas are not friendly to organic matter. The person with the most hazardous job on the Star Trek television series is the one who must investigate the glowing blobs of plasma on the uncharted planets they visit. (My memory tells me that this person always wore a red shirt.) Every time this crew member meets a plasma blob, he gets vaporized. Born in the twenty-third century, these space-faring, star-trekking people would, you'd think, have long ago learned to treat plasma with respect (or not to wear red). We in the twenty-first century know enough to treat plasma with respect, and we haven't been anywhere.

In the center of our thermonuclear fusion reactors, where plasmas are monitored at a safe distance, we attempt to slam together hydrogen nuclei at high speeds and turn them into heavier helium nuclei. By doing so, we liberate energy that could supply society's need for electricity. Problem is, we haven't yet succeeded in getting more energy out than we put in. To achieve such high collision speeds, a blob of hydrogen atoms must be raised to tens of millions of degrees--at least as hot as the center of the Sun, where thermonuclear fusion is a routine thing. No hope for attached electrons here. At these temperatures they've all been stripped from their hydrogen atoms and roam free. How might you hold a glowing blob of hydrogen plasma at millions of degrees? In what container would you place it? Even microwave-safe Tupperware will not do.

What you need is a bottle that will not melt, vaporize, or decompose. To design it, we'd use the relationship between plasma and magnetic fields to our advantage, creating a container whose walls are intense magnetic fields that the plasma cannot cross. One of the pesky problems with the confinement of plasma is that if you squeeze it in one place, it tends to pop out someplace else. It's like trying to squeeze a balloon to make it smaller. The economic return from a successful fusion reactor will rest in part on the design of this magnetic "bottle" and on our understanding of how the plasma interacts with it.

Among the most exotic forms of matter ever concocted is the quark-gluon plasma, newly created by physicists at the Brookhaven National Laboratory, a particle-accelerator facility on New York's Long Island. Rather than being filled with atoms stripped of their electrons, a quark-gluon plasma comprises a mixture of some of the most basic constituents of matter: fractionally charged quarks along with the gluons that normally hold them together to form protons and neutrons. This unusual form of plasma greatly resembles the state of our trillion-degree cosmos a few microseconds after the big bang--about the time the observable universe was not much larger than our solar system. Indeed, in one form or another, every cubic inch of the universe was in a plasma state until a half-million years had elapsed.

A half-million years into its history, the universe had cooled down to a few thousand degrees. Before then, all light was getting scattered to and fro by the free electrons in the plasma--a phenomenon that greatly resembles what happens to light as it passes through frosted glass or through the Sun's interior. Light can travel through neither without scattering, and this renders both of them translucent instead of transparent. As the universe cooled to below a few thousand degrees, each electron in the cosmos combined with an atomic nucleus, creating complete atoms of hydrogen and helium and trace amounts of lithium.

As soon as every electron had found a home, the pervasive plasma state no longer existed. And that's the way it would stay for hundreds of millions of years, at least until quasars were born, with their central black holes that dine on swirling gases. Just before the gas falls in, it releases ionizing ultraviolet light that travels across the universe, kicking electrons back out of their atoms with abandon. Until the emergence of quasars, the universe enjoyed the only interval of time (before or since) when plasma was nowhere to be found. We call this era the dark ages and look upon it as a time when gravity was silently and invisibly assembling matter into the plasma balls that became the first generation of stars.

Neil de Grasse Tyson, an astrophysicist, is the Frederick P. Rose Director of New York City's Hayden Planetarium. He is (along with Steven Soter) coeditor of, as well as a contributor to, Cosmic Horizons: Astronomy at the Cutting Edge, a collection of essays written by astrophysicists working on the frontiers of cosmological research.

COPYRIGHT 2001 American Museum of Natural History
COPYRIGHT 2001 Gale Group

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