Expert: Philip A. Stahl - 5/13/2009

Question
Hi Philip

I was browsing through the WMAP website and found this time line of our universe.
http://map.gsfc.nasa.gov/media/060915/index.html
As we know now that the existing universe came from a cosmic egg which exploded as a big bang and that the force namely, Strong and Weak nuclear force, Electromagnetism and Gravity were one at this point called as Superforce.
If we see the timeline image, during the dark ages there were no such things as atoms and I understand at this stage all we have is pure energy. So from this atoms have formed. Can you explain how an atom is born.
And I am curious about my next thought below.
Can we take a Uranium atom and strip it down to a Hydrogen atom by removing off the electrons and required number of protons, neutrons. Is this possible.
I am not very good at Physics but still want to understand if this is possible theoretically.

Thanks very much in advance !

//Mohan

Answer
Hello,

You are correct that the universe had to cool down, a lot actually, in order for atoms to be able to form. Essentially, all one had at the outset was a very hot pure photon gas. Some estimates of the "separation temperature" - that is marking the transition from the radiation-dominated era to the matter dominated one, are from 5 x 10^3 K  to about 3 x 10^4 K, which seems reasonable. (We know in the Sun's photosphere, for example, neutral hydrogen atoms are still able to form with these temps. at the low end)

Since you say you are "not very good at physics" I suggest that to learn much more about how atoms are formed ("born") you get hold of the excellent book: 'Atoms, Stars and Nebulae' by Lawrence Aller, which is excellent. You can read and absorb it at your own pace, and the diagrams (which alas, I cannot begin to reproduce here) will aid in your concrete understanding.

Re: Your question on the U-atom and stripping it down to get a hydrogen atom, yes...I suppose that theoretically one could, but I've no idea why one would want to. Certainly, the reaction rates, and especially any disintegrations of the nuclei would have to be strictly controlled, and also the process essentially enclosed and away from outside influences. (We would not wish incoming solar neutrinos or cosmic rays interfering when we just about reached the H1 stage!)

Hope this helps!