Monday, June 25, 2012

Let there be light! - CMBR

In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.

And God said, “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning —the first day.
Genesis 1:1-4

There are many very interesting things in this beginning of the ancient story of Creation. Just think the first word in the first verse - Beginning.

Of course, the language is ancient and the geocentric scenery strange and we may wonder how the days and nights of creation are separated long before Sun is created on the fourth day.

But note the delay - God creates heavens and earth and then there is a period of mysterious time when the Spirit of God "hovers" over the waters of deep (Tehom).

And then there is light!

Cosmologists and astrophysicists are telling today that after the initial Big Bang there was a period when the newly born Universe was opaque. Protons and electrons where flying after the plasma stage preventing photons from moving freely.

After some 379.000 years things changed, hydrogen was being formed and photons were free to fly - let there be light!

Modern theory suggests that origins of space and time, matter, and energy come from a time when the Universe was extremely hot and dense. About 13.7 billion years ago, the Universe exploded, forming space itself, which would later be populated with the galaxies we see today.

Very soon after the Big Bang, matter in the Universe was so hot that it formed a plasma, a state in which atoms are separated into nuclei and free electrons, similar to the Sun’s interior. These free electrons prohibit the free flow of light in the Universe. The Universe was opaque to light in these early times. Later, as the Universe expanded and cooled, the electrons combined with the nuclei and formed hydrogen atoms. With few free electrons, light was now free to travel the Universe. This transition took place about 379,000 years after the Big Bang, ushering in a new era in the Universe.

The Universe was then transparent to light as photons, which traveled freely across the Universe, encountering few collisions that would absorb or scatter the light. If we could have seen it, the Universe would have been about 3,000 Kelvin and would have glowed orange in visible light.

In fact, the peak intensity of the Universe at that time was around 1 micron (in the infrared). Since that time, the Universe has expanded 1,000-fold and the light waves have expanded along with space. The light, then, appears redshifted as space itself expands.

Today, the peak intensity of the Universe is 1,000 times lower than it was then, so the wavelength is 1,000 times greater and is close to 1 millimeter (1 micron 1,000 = 1 mm). This peak intensity corresponds to a gas temperature 1,000 times less, or 3 Kelvin (3,000 K 1,000 = 3 K). Light at 1mm is in the microwave portion of the EM spectrum, and this is where we see the remnant light from the Big Bang, called the Cosmic Microwave Background radiation, or CMBR.

The CMBR pervades the Universe. It is an imprint of the time of recombination in the Universe, when protons and electrons combined to form hydrogen, when light began to travel in space unimpeded.

When we look at that light, we are looking back in time to that event, 379,000 years after the Big Bang. Before that time, the Universe was opaque, like looking through a fog, so we will never see the Big Bang event itself. The CMBR, then, defines that part of the Universe that we can see, what we call our Observable Universe. While the CMBR is everywhere in the Universe, we can also think of it as our outer limit, that which we cannot see beyond.
Brian Abbott Digital Universe Atlas Guide 2012

Let us here it one more time
Astronomers believe that the Universe was born from the Big Bang, when space expanded from an extremely hot and dense condition. You might imagine that this event was spectacular in its energy and luminosity output. If we think quasars are bright, the creation of the Universe must have been incredible. Given that, wouldn’t you expect to see something from this energetic event?

In fact, astronomers do see the light from just after the Big Bang. At that time, the Universe was very hot, so hot that atoms could not form. Instead, there were free electrons and protons and neutrons that made up the primordial Universe. Light could not travel very far before it collided with a free electron. Thus we say the Universe was opaque, as radiation and matter were constantly interacting. As the Universe expanded, the temperature of the plasma dropped and, after 379,000 years, the Universe was cool enough to allow electrons and protons to combine, forming hydrogen atoms. Once this occurred,the light from the Big Bang was free to traverse the Universe, since the free electrons were captured by atomic nuclei.
Brian Abbott Digital Universe Atlas Guide 2012 p.169

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