Light & BB?

[kristina3313]

It looks like one of the evolution threads managed to veer of the course into the realm of physics yet again.
The statement was made that at the the time of Big Bang there was no light and the universe existed in a cosmic darkness till about 100 million years after the Big Bang. I have recently read a book where it states that at the time of Big Bang universe was filled with light. But there was another statement made, that "only after the stars formed and began to burn their hydrogen through fussion reactions did the universe light up. Before that all we can see is the CMB."
I am looking for some clarification regarding this subject and I have two questions: was there light at the time of Big Bang... and how long did it last before universe entered "cosmic dark ages"?

 

[MeteorWayne]

There was light at the time of the big bang, but the light was blocked by an opaque medium of electrons and protons. After about 300,000 years, the first atoms were able to form, and the light was free to travel throughout the Universe.

 

[DrRocket]

It looks like one of the evolution threads managed to veer of the course into the realm of physics yet again.
The statement was made that at the the time of Big Bang there was no light and the universe existed in a cosmic darkness till about 100 million years after the Big Bang. I have recently read a book where it states that at the time of Big Bang universe was filled with light. But there was another statement made, that "only after the stars formed and began to burn their hydrogen through fussion reactions did the universe light up. Before that all we can see is the CMB."
I am looking for some clarification regarding this subject and I have two questions: was there light at the time of Big Bang... and how long did it last before universe entered "cosmic dark ages"?

MeteorWayjne has it about right. There were a lot of photons, but the universe was pretty opaque. Depending on how early you are talking about, the elementary particles that we have today may not yet have formed.

For a nice treatment of this question you might want to read Steven Weinberg's book The First Three Minutes. It is quite good. It does pay to remember that it was written before the current data suggesting that the expansion of the universe is accelerating was found.

 

[kristina3313]

"At the end of the first three minutes the contents of the universe were mostly in the form of light, neutrinos, and antineutrinos. There was still a small amount of nuclear material, now consisting of about 73 percent hydrogen and 27 percent helium, and an equally small number of electrons left over from the era of electron-positron annihilation. .....universal background radiation left over from the time universe was opaque."
This is pretty much all that I was able to find in the book "The First Three Minutes" by Steven Weinberg regarding my question about light and the BB, I couldn't find exactly when the universe was opaque, but I am currently only on chapter 5. I've also tried to search the web and I'm still not really sure about it. Is it then right from the initial state (the Big Bang) the universe was optically opaque? Or did it happen after 1st second or so?
I looked at different websites and this is what I got so far:
At the instant of the Big Bang the universe was infinite and very hot, space-time was expanding very violently creating high energy fundamental particles. Within the first second quarks and leptons and their antiparticles anti-quarks and positrons exist and are colliding and annihilating each other and releasing energy in the form of photons. Protons, atomic nuclei of Helium, Deuterium, little amount of Lithium were formed sometimes within first 3 seconds (or 100 seconds?). And then for the next 300,000 years the protons and atomic nuclei travel trough opaque sea of electrons and neutrinos.
The opaque medium is made up of free electrons and electrons absorb and emit photons. Free electrons can release light when they attach themselves to nucleus of an atom. This is a bit confusing as well, electrons are responsible for photon creation and for their captivity in the opaque medium?, and then photons are responsible for knocking
electrons out of atomic nuclei?

<emphasis is mine>

 

[SpeedFreek]

Maybe this link will help...

Timeline of the Big Bang