Thanks for all of the informed responses guys. I think I am going to have to read the bitcoin research paper published by Satoshi to find the real answer. I am sure I will be back with more things to talk about.

A lot of responses about changes seem to use the logic of "the majority will do or will not do this because they are driven by motives x, y & z"

But there is a couple of issues with this argument.

1. Don't trust the majority, even if you think you understand their motivation. The majority can be wrong, and they can be manipulated. Take US politics for example: The majority vote for more and more deficit spending even though it is not good for the country in the long run. The majority have gotten the US into an unsurmountable amount of debt. Likewise, the majority of bitcoin users could be fooled into accepting a change that would hurt the currency in the long run. (Like eliminating the true scarcity by removing the 21 million cap)

2. Correct me if I am wrong, but it is not the majority of bitcoin users that need to except the changes. Rather, a majority of miners. If bitcoin grows to be a commonly used currency, the miners will make up a small fraction of the total users. So when we are talking about the majority, we really mean the majority of a small subset. The problem with this is that the miners may have a different perspective on certain proposed changes. For example, it is reasonable that many of the miners would support fixing the solution reward at some number of bitcoins instead of having it trail off to zero. This would be more profitable for the miners. Logically, the normal users would be against this, but reference point one above. The normal users could be convinced through misinformation that this is a good solution.  Those that stand to benefit could argue that the supply of bitcoins needs to increase to help the economy move along, or to make transactions easier, or any other lie they can come up with to convince the majority. This is not unprecedented in history.

Take for example the countless countries that have moved their currencies off the gold standard. In this example, the politicians are the miners and the citizens are the normal bitcoin users. A majority of the politicians get to determine the outcome. And moving off the gold standard is analogous to eliminating the 21 million cap. The politicians stand to benefit because they get to delay dealing with a problem. The politicians convince a large subset of the citizens that this is the right move to make so that the citizens don't start and uprising. See how this is the same?

Right now, yes, it would be extremely difficult to get everyone to change. But what about in the future when the situation is different. Could a majority of bitcoin users/miners be convinced to change the 21 million cap? If the leaders of the bitcoin community all supported a change as the best solution to a serious problem that was haunting the currency/economy, is it still impossible that a majority would adopt the change?

The past shows that leaders are often able to sway the opinions of a majority. And with respect to all currencies, the majority always rules.

I am not trying to disagree or get in an argument with anyone. I am just trying to figure this out. I really like the idea of bitcoins, but I am trying to figure out what their long time viability is.

Lets compare to gold, one of the longest standing most globally accepted currencies in the history of mankind. People say that gold has intrinsic value. I think there is only 2 things in combination that give gold this supposed "intrinsic value".

1. True Scarcity
2. A majority that believes it is valuable

Bitcoins could be like gold. If the 21 million can indeed not be changed, then bitcoins have true scarcity. For the second point, bitcoins are on their way to a majority believing that they are valuable.

But, if the 21 million can be changed, then bitcoins are no different from any other fiat currency. Fiat currencies do not have true scarcity. They have artificial scarcity. The controllers of the currency get to control the scarcity.

Anyways, that is where I am coming from and why I asked those questions. I would love to hear the thoughts of others that think about this kind of stuff.

As software that can be changed, someone controls bitcoin. I am interested to know who can change it.

In particular, I am interested in knowing if the 21 million can ever be changed? And if not, why?

I looked around Google for a while but didn't find anything that definitively answered those questions. I personally don't think the 21 million should ever be changed. And I would like the answer to be that it is impossible to change it, but I don't think that is the case.