Friday, March 17, 2006

The Big Bang and the Anthropic Principle

Dan alerted me to this fascinating story this afternoon:

New Images Support 'Big Bang' Theory

By Guy GugliottaWashington Post Staff WriterFriday, March 17, 2006;

Scientists said yesterday they have found the best evidence yet supporting the theory that about 13.7 billion years ago, the universe suddenly expanded from the size of a marble to the size of the cosmos in less than a trillionth of a second.

A team of researchers used data collected by a NASA satellite measuring microwave radiation to offer direct, experimental support for the theory of "inflation" put forth 25 years ago -- that the expansion of the universe, commonly known as the "big bang," began with a single burst of repulsive energy acting in a tiny fraction of time. The expansion continues today but at a much slower rate.

This new image of the universe indicates "warmer" (red) and "cooler" (blue) spots. The white bars show the "polarization" direction of the oldest light. ,,"We can measure the sky to tell what powered this expansion," said Goddard Space Flight Center astrophysicist Gary Hinshaw. "It's really amazing, actually. I was in graduate school when the theory was first proposed, and I've been working on it ever since. It's gratifying to see the idea hold up now.
Hinshaw is a member of a team monitoring data from NASA's Wilkinson Microwave Anisotropy Probe, a satellite launched in 2001. The findings were announced yesterday at a Princeton University news conference and will appear in the Astrophysical Journal.

The theory, developed by Alan H. Guth of the Massachusetts Institute of Technology, holds that during the universe's first moments, inflation produced a sudden burst of heat and light that left an afterglow about 400,000 years after the event. The first stars were formed about 400 million years after the big bang.

The original afterglow has been cooled by the universe's expansion until all that is left is a faint microwave "signature.""You're looking out to the edge of space and time," Hinshaw said in a telephone interview. "It's like trying to see a car's headlights through the fog."

It reminded me of an article in First Things by Stephen Barr, entitled "Anthropic Coincidences." Copyright (c) 2001 First Things 114 (June/July 2001): 17-23.

Barr writes,
"Hydrogen has been around since very soon after the Big Bang. But almost all of the other elements were forged later, either in the deep interiors of stars, or in the violent explosions called supernovas with which some stars end their lives. These supernova explosions are also important for life because they spew the elements made within stars out into space where they can form new stars, or planets, or people. Indeed, most of the elements in our bodies were made inside stars that exploded before the sun was born. We are quite literally made of stardust.

For our purposes, it is crucial to note that the elements are formed in a sequential manner by nuclear reactions in which the nuclei of smaller atoms fuse together to make the nuclei of larger atoms. These same “nuclear fusion” reactions also produce the energy radiated by stars (including, of course, the sun), energy that is essential to support life. The first step in the process of forging the elements is the fusing together of pairs of hydrogen nuclei to make something called “deuterium.” Deuterium is the first and vital link in the whole chain. If deuterium had been prevented from forming, none of the later steps could have taken place, and the universe would have contained no elements other than hydrogen. This would have been a disaster, for it is scarcely conceivable that a living thing could be made of hydrogen alone. Moreover, had the deuterium link been cut, the nuclear processes by which stars burn would have been prevented.

Everything thus depends on hydrogen being able to fuse to make deuterium. Here is where the first remarkable anthropic coincidence comes in. The force of nature that cements nuclei together is called the “strong nuclear force.” Had the strong nuclear force been weaker by even as little as 10 percent, it would not have been able to fuse two hydrogens together to make deuterium, and the prospects of life would have been dim indeed. But this is only the half of it. Had the strong nuclear force been only a few percent stronger than it is, an opposite disaster would have occurred. It would have been too easy for hydrogen nuclei to fuse together. The nuclear burning in stars would have gone much too fast. Stars would have burned themselves out in millions of years or less, rather than the several billion years that stars like the sun last. However, the history of life on earth suggests that billions of years are required for the evolution of complex life such as ourselves. The upshot of all these considerations is that the strong nuclear force has just the right strength: a little stronger or weaker and we would not have been here.
Once deuterium is made, deuterium nuclei can combine by fusion processes to make helium nuclei. These steps happen very readily. At this point, however, another critical juncture is reached: somehow, helium nuclei must fuse to make yet larger elements. But all the obvious ways this could happen are forbidden by the laws of physics. In particular, two helium nuclei cannot fuse together. This was quite a puzzle for nuclear theorists and astrophysicists. How did all the elements larger than helium come to be made?

The answer was found by Fred Hoyle, who suggested that nature in effect did a large double step to get past the missing rung in the ladder. When two helium nuclei collide in the interior of a star they cannot fuse permanently, but they do remain stuck together momentarily—for about a hundredth of a millionth of a billionth of a second. In that tiny sliver of time a third helium nucleus comes along and hits the other two in a three–way collision. Three heliums, as it happens, do have enough sticking power to fuse together permanently. When they do so they form a nucleus called “carbon–12.” This highly unusual triple collision process is called the “three–alpha process,” and it is the way that almost all of the carbon in the universe is made. Without it, the only elements around would be hydrogen and helium, leading to an almost certainly lifeless universe...."

Read the rest of this at

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