<**NOTE:
This is from the July 2002 edition of Discover. The hard copy is at the newsstands, but the soft copy is still on June 2002 (the link here is to a generic “index” page, which may later be updated to July 2002). That means this was all retyped by me -- so be nice. I tried to get it right.
;^)
SKY LIGHTS
Much Ado About Nothing
By Bob Berman
Time to let go of matter -- emptiness is what rules the universe
POETS WOULD HAVE YOU BELIEVE that the night sky is full of stars, but anyone lounging outside on a July evening knows the truth. Under open, clear skies a person can see perhaps 2,000 points of light, along with a few nebulae and the feeble glow of the Milky Way. The vast, vast majority of what is out there is nothing at all.
To get a sense of how empty the universe is, look at the bright star Vega, which hovers overhead at 11 p.m. in the middle of this month. Vega is so distant that its light takes 25 years to reach Earth. But if you extended a one-inch-wide tube all the way from Earth to Vega and scooped up every bit of matter within, the contents would weigh just one-millionth of an ounce, roughly equal to a grain of sand.
Even the dense regions of interstellar space are fantastically empty. Near Cygnus, the cross-shaped constellation shining high to the east a couple hours after sunset, the Milky Way appears to split in two, leaving a dark gap that spreads toward the south. The void is known as the Great Rift. Australia’s aborigines pictured it as the hindquarters and tail of a dark constellation, the Emu. Today we know the Great Rift is caused by thick clouds of hydrogen filled with carbon dust and other light-absorbent particles. Such dark nebulae have a density of 2,000 hydrogen atoms per cubic inch -- high for interstellar space, but a hard vacuum by terrestrial standards.
This dark cloud, called Barnard 68, looks like an empty hole. Actually it is full of matter compared with the space around it.
[More].
Image Credit: Astronomy Picture of the Day Archive.
Under the relentless attraction of gravity, however, these wisps of material can pull together into thicker, denser concentrations. Telescopic surveys reveal many small, intensely black patches silhouetted against more distant stars. These dusty clouds will keep contracting, eventually developing into future generations of stars and planets. The concentration of matter by gravity is why Earth and everything around you is so dense compared with outer space. Each of your fingertips, for instance, contains a trillion trillion atoms.
Surprisingly, there is still plenty of nothing in those fingertips. At least 99.995 percent of the mass of each atom resides in the tiny nucleus composed of protons and neutrons. I a typical atom were the size of a football field, the nucleus would be a grain of salt at midfield. A cloud of electrons marks the atom’s outer bounds; the rest is void. The only reason you cannot reach right through a wall is because negatively charged electrons in your hand repel like-charged electrons in the wall. Although you may feel solid, you are mostly emptiness. The same goes for Earth and even the sun.
But give gravity a chance and it will get rid of a lot of vacant space. This month offers a prime opportunity to witness that power. In late July, Saturn will appear to float in front of the Crab Nebula, a cloud of glowing gas in the constellation Taurus. At the center of the nebula sits a dim speck called the Crab pulsar, the densest object visible through a home telescope. The Crab was once a brilliant star that exhausted its fuel and exploded. The outer parts blew off to become the nebula. Bereft of any energy source to keep it puffed out, the star’s core collapsed. Gravity took over, squeezing all the space out of the atoms and leaving behind a neutron star -- essentially an atomic nucleus ten miles wide.
If the entire universe could be similarly compacted, it would fit into a ball smaller than Mars’s orbit. The only thing saving us from such a world-ending crunch is the sheer immensity of space. So ultimately, we owe our lives to -- nothing...
Dan
Much Ado About Nothing . . .