HeliopauseIntergalactic
spaceInterstellar
spaceSunWWW.ASTRONOMY.COM 33In addition to those absorption lines, support for a thin inter-
stellar medium came from the cosmic rays that continuously hit
our planet. They presumably originate in distant violent events like
supernovae, as stars get shredded and their detritus f lung wildly
outward. What’s weird is that they’re composed of 99 percent pro-
tons and atomic nuclei. When there are just as many electrons as
protons in the universe, why are cosmic rays so proton-heavy?
Write that off as an unsolved mystery, even while cosmic rays
prove that particles do fill the void.
Some of these particles are barely there, streaming right
through most other matter with their immeasurably tiny masses.
Neutrinos fill the cosmos. So do photons of all kinds. And there’s
more to space than a mere recitation of its particle density. It’s also
permeated by “fields.” Magnetic and electric fields f low across the
whole of space. Gravity waves rock its very fabric. Thus, a lot is
present even if it all weighs little or nothing.The power of nothing
Most intriguing, perhaps, is space’s omnipresent “vacuum energy”
first postulated in the 1930s. Also called zero-point energy, it’s
the underlying matrix of the cosmos. While mysterious, there are
good reasons to believe it exists. For example, in 1948, the Dutch
physicist Hendrik Casimir showed that closely spaced metal plates
become powerfully pressed together, presumably by the waves of
vacuum energy outside them. (The tiny space between the plates
stif les the energy waves by leaving them insufficient “breathing
room” to push back against the force.)Most physicists accept that vacuum energy causes the Casimir
effect. Calculations of how much vacuum energy lurks every-
where vary greatly (in fact, the 100 orders of magnitude difference
between theoretical predictions and measured values is known as
the vacuum catastrophe), but it’s substantial. By the larger estimate,
if this energy could be extracted and utilized, each empty mayon-
naise jar of space contains enough power to boil off the Pacific
Ocean in one second. This underlying energy seems to be caused
by an endless whirl of particles and antiparticles springing brief ly
into existence in every tiny piece of space and then vanishing
again. It’s as if the entire cosmos, despite the appearance of empti-
ness, seethes with so much energy that it can barely contain itself.
This may be the so-called “dark energy” making the cosmos
expand. If this quality of space is the underlying cause of the Big
Bang, then the universe is still banging. All thanks to “empty” space.A matter of perspective
Weird, but we could live with it. Harder to grasp is an entirely dif-
ferent aspect of emptiness — one that has changed space from logi-
cal to enigmatic. Since the late 1990s, experiments have confirmed
the reality of an aspect of quantum theory known as entanglement.
Here, two bits of light or actual physical objects, even clumps of
material that were created together, f ly off and live separate lives,
but are always “aware” of the other’s status. If one is measured or
observed, its twin knows this is happening and instantaneously
assumes the guise of a particle or bit of light with complementary
properties. No matter how far these twins are separated, they behaveThe average density of space drops dramatically from the familiar region around our Sun, to interstel-
lar space, out to the lonely reaches of intergalactic space. ASTRONOMY: ROEN KELLYAlbert Michelson’s experiment with collaborator
Edward Morley disproved the existence of the
mysterious ether once and for all. COURTESY OF THE
SMITHSONIAN LIBRARIES, WASHINGTON, D.C.How empty is it?
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Star cluster Oort Cloud Solar system Earth’s orbit The Moon’s orbitESA/PLANCK COLLABORATION (1026 ); NASA/ESA/M. MONTES (IAC)/J. LOTZ, M. MOUNTAIN, A. KOEKEMOER, HFF TEAM (STSCI) (1023 ); NASA/ESA/HUBBLE HERITAGE TEAM (STSCI/AUR A) (1021 , 1018 );ASTRONOMY: ROEN KELLY (1016 , 1013 , 1011 , 108 )