# Why is the transition into N proportional to N+1?

I am having trouble understanding the origin of the bosonic stimulated emission. How can I qualitatively understand why bosons Boson's attract each other into similar quantum states.

The furtherst I was able to get was to simulate the feedback process, in my mind, but I don't have the foggiest of ideas why this rule must be the case. I haven't taken any classes on quantum or statistical mechanics.

Explicitly, if N bosons occupy a given state, the transition rates into that state are proportional to (N + 1).

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The quote isn't right. The rate of the emission from (not into) the state with $N$ quanta is proportional to $N+1$. This may be divided to $N$, the stimulated emission, and $1$, the spontaneous one. It's $N+1$ because that's the number of quanta in the final state and by time reversal symmetry, the opposite process with the "same" probability starts with $N+1$ quanta and its rate is obviously proportional to $N+1$ because it's purely stimulated absorption. – Luboš Motl Dec 12 '12 at 9:32
@LubošMotl Thanks for the comment, the quote is actually from a paper, I wonder if you could expand your comment into answer so that I can give you the award... – Mikhail Dec 15 '12 at 6:50