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We must never conceal from ourselves that our concepts are creations of the human mind which we impose on the facts of nature, that they are derived from incomplete knowledge and therefore will never “exactly” fit the facts, and will require constant revision as knowledge increases.
-- A.G. Tansley (1871-1955)


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The Big Bang

 

We are the first generation of human beings to glimpse the full sweep of cosmic history. The portals of our Universe's early origins have been opened by a vast new arsenal of sophisticated telescopes and intergalactic probes, revealing an incredible wealth of detail on the structure and movement of the cosmic world. By gaining an understanding of the cosmic forces that govern the Universe, we can better appreciate the place our own planet occupies in the cosmic web.

 

 

Somewhere in a galaxy far, far away...no, check that, no galaxies yet...somewhere in a voidless nothing (there we go), some 13.7 billion years ago (give or take 1.37 billion) a burst of unfathomable energy (all that exists or ever existed) sparked from a singular somethingness (called, cleverly enough, a singularity), an event described as the biggest of all bangs (also known as the Big Bang) gave rise to our Universe and soon afterwards, everything in it as we know it.

How do we know that?

Because science rests on the idea that observations can be explained rationally, we look for bodies of evidence that support or reject our ideas of the way things work. When new evidence appears that is out of line with our ideas, we revise our ideas. This idea, called parsimony, leads us hopefully to one idea, called a theory, which cannot be rejected by observations or experiments no matter how hard we try (like the theory of gravity, for example, which, yes, is just a theory, because that’s as far as any scientist is willing to go, in keeping with our philosophy that anything may be possible, given new observations and data).

The inflationary model of Big Bang—one of many hypotheses to explain the origin of the Universe but the one that is currently purported to be the model best supported by available data—postulates that all matter and energy in the Universe were present in a small volume (perhaps as small as our current solar system), very dense and very hot. (If you want real numbers here you’ll have to explore more fully the different scenarios for this beginning—positively curved, negatively curved or flat—which influence the volume, density and heat predictions). At the “instant” of the “big bang”, the Universe expanded rapidly and simultaneously. If we use the positively curved model, we can think of the Universe as looking like a balloon which is suddenly filled with air. If you had marked dots on the balloon before you inflated it, you would note that all the dots moved away from each other at the same rate. (Try it!) Note that the Universe (and your balloon) did not explode and it did not come from any single point. Everything expanded at the same time in all directions. In the inflationary model, the Universe (and your balloon) expanded more rapidly in the beginning (inflation) and then settled down into a steady rate of expansion.

Okay, this is heady stuff and I love it. I would love to spend time telling you about it too, but then this book would be about 10,000 pages and you’d have to get a bigger backpack. Fortunately, much smarter people than me have prepared Cosmology 101, a clear and accurate description of current models for the formation of our Universe. Please visit them here: http://map.gsfc.nasa.gov/m_uni.html.

These smart folks manage the Wilkinson Microwave Anisotropy Probe (WMAP), a space-based satellite-mounted sensor system for studying small-scale temperature fluctuations across the Universe. In February 2003, they released a fine-scale “map” of their initial results (see Figure above).

Depicted in this photo are very small-scale variations in microwave radiation (yes, very similar to the radiation that heats your pizza) distributed across the Universe (shown as an oval to make it friendly to our eyes, like a map of the Earth, which, you know, is not flat and oval-shaped, but is a sphere aha! like the Universe). This microwave radiation (also known as Cosmic Background Radiation), discovered by two Bell telephone workers (Penzias and Wilson) provides the strongest evidence of the birth of our Universe from an “explosion”. It’s ubiquitous (distributed across the entire Universe everywhere we look), it’s at a temperature consistent with mathematical calculations and it’s supported by independent observations of galaxies, stars, elements and other features of our Universe.

 

These new results from WMAP rejected some ideas that some scientists held about the way the Universe looked and worked. No, those scientists weren’t fired; they took their lab notebooks, added the WMAP data to them and started to work revising their ideas and coming up with new ones supported by the evidence.

Based on these new results, scientists now believe (with a fair amount of certainty) that:

  • the Universe is about 13.7 ± 1% billion years old
  • the first stars lit up about 200 million years after the Big Bang (a lot earlier than scientists originally thought and putting the nail in the coffin on the idea that neutrinos played a role in the evolution of the early Universe...aren’t you glad we settled that?
  • the Universe is composed of 4% atoms, 23% cold dark matter and 73% dark energy, the latter of which was thought to exert a negative pressure on the expansion of the Universe but which now may just be a constant (you know, scientists just aren’t sure about this one)
  • the Universe is expanding at the rate of 71 ± 5% kilometers per second per megaparsec (a megaparsec is one million parsecs, a unit of intergalactic distance equivalent to about 3.26 light years and likely the distance of some extreme sport in the future)
  • the Universe inflated at its birth, which means that it expanded very rapidly first, then settled down to a more constant rate of expansion (known as the Hubble constant)
  • the Universe is flat and will expand forever, although not knowing much about dark energy, this conclusion could change as we learn more about its characteristics

Cool, huh?

Wanna explore more?

See From Proplyds to Solar Systems

Also Origin Myths and Science


   
   
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