Now I could write a book about this and we could dive through some lovely QFT but how about I just answer it in a much simpler way.
Pull up the page on wikipedia about Entropy and you will get this entropy, is proportional to the natural logarithm of the number of microstates.
At the big bang everything is in very close proximity and "almost" homogenous, as such it has very few microstates. I once saw Brian Cox series do this really well for layman, with a bucket of sand and we say that has low entropy. Now tip it on the ground and spread it out there is your high entropy.
Every bucket of sand is just itching to get out
We can put approximate numbers on the microstate counts the current number for the earliest point we can go to in the big bang is 10E88 and today we are at about 10E104 (http://www.mso.anu.edu.au/~charley/papers/EganLineweaverApJOnline.pdf
). That is the revised up from the previous estimate of about 10E102.
Tell me if you are happy with that and we can then talk about QFT and your wavelength issue, which is going to be fun to try and make it understandable to you