...In just the last decade or so, astronomers working in a remarkable specialty have determined — with high accuracy — such things as the date of the Big Bang, the amount and makeup of all the matter and energy in the universe, the large-scale shape of space, and how cosmic structure (galaxy clusters, galaxies, stars) grew and evolved from the very beginning to now, and why.
Along the way, researchers have confirmed some key predictions of the "inflationary universe" theory of how the Big Bang itself erupted from a much larger, underlying pre-existence, which could be producing inconceivable numbers of other, separate big-bang universes all the time.
This has become possible not by conventional astronomy, but by analyzing the cosmic microwave background radiation that covers the entire sky. This weak radio glow is literally the white light emitted by the still-white-hot universe as it stood just 380,000 years after the Big Bang. The light has been redshifted down into the microwave part of the spectrum (by a factor of 1,091) by the expansion of space since that time.
Dozens of experiments have mapped tiny, telltale irregularities in the microwave background, working at various scales and pointing at various parts of the sky. But the most important instrument now doing this work is the orbiting Wilkinson Microwave Anisotropy Probe (WMAP). It is mapping the background radiation's temperature and polarization across the entire celestial sphere, and at a wide variety of angular scales: from large (many degrees wide, constellation-size) to nearly as small as the resolution of the human eye.
As time goes on, WMAP has continued to sharpen its picture...
• The universe is 13.73 ± 0.12 billion years old. That's an uncertainty of only 0.9% now (at the 68-percent confidence level). Astronomy books in your public library probably say the universe is "between 10 and 20" billion years old.
• The Hubble constant, the rate of the universe's expansion today, is 70.1 ± 1.3 kilometers per second per megaparsec. Books in your library probably say it's "between 50 and 100." These refinements affect everything else. For instance:
• The sum total of everything in the universe consists of the following: matter made of atoms ("baryonic matter") 4.6% ± 0.15%, nonbaryonic dark matter 23% ± 1%, dark energy 72% ± 1.5%. We know almost nothing about what the dark matter and dark energy are, but we do know quite well now how much of each is out there.
• All this matter and energy adds up, within just 1% uncertainty, to exactly enough to make space "flat," as inflationary-universe theories predict. That is, empty space on the largest cosmic scales is just like the ordinary space right around you: having no overall curvature or weird geometry. This also implies that space extends infinitely far beyond our visible horizon, equally in all directions, as best we can tell...
• The behavior of the mysterious dark energy is becoming clearer. Its "equation of state," a parameter known as w, equals –1 to a precision of 6%. That's the best determination of it yet. This implies that dark energy is not something that spreads out as space expands, the way particles in space would, but is something inherent to spacetime itself — so that one cubic centimeter of space always contains the same amount of it no matter how greatly space has expanded. This matches Albert Einstein's idea of a "cosmological constant" from the 1920s (referred to by the Greek letter Λ) and argues against the dark energy being a sort of physical substance that has been proposed, dubbed "quintessence." ...
• WMAP also finds concrete evidence for a "cosmic neutrino background" filling space. The neutrinos (weak, extremely low-mass particles) came from nuclear reactions in the dense matter that filled the universe in the Big Bang's first few minutes. By the time of the visible microwave background, 380,000 years later, neutrinos still amounted to 10% of all matter and energy in the universe, compared to their vanishingly small proportion today.
In addition, the three types of neutrinos that exist have masses that can add up to no more that 0.61 electron volt, agreeing with laboratory experiments.
• The cosmic "dark ages" — the era between when the Big Bang cooled and the first stars formed (an era when the universe became so cold that molecular-hydrogen snowflakes may have formed) — began ending around cosmic age 400 million years (redshift 11). This change is known as the "reionization era." The date fits in with evidence that's been coming from more normal astronomical methods. (Reionization apparently was, however, a drawn-out affair, happening by fits and starts in different places.)
Everything in the universe, now and long ago. The top chart shows the constituents today. The bottom one shows the composition just 380,000 years after the Big Bang, when the microwave background radiation broke free.
The relative composition changed greatly as the universe expanded. Dark matter and baryonic matter ("atoms") just thinned out as the universe expanded, like ordinary gases. But photons and neutrinos also lose energy in expanding space, so their energy density decreased faster than the matter. They're an insignificant portion now. Meanwhile, the proportion of dark energy increased with the increasing volume of space.
NASA / WMAP Science Team
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From www.princeton.edu:
The results also are providing the best data yet for examining the astonishing burst of growth in the first trillionth of a second of the universe, when ripples in space itself may have been created.
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