Gold has nothing to do with US Dollar value! Then that makes me think about Bitcoins' value.

“Why does this piece of paper have value?
One person said “gold,” which has nothing to do with it. There was a time when you could demand a fixed weight in gold in exchange for a dollar, but those days are gone. Another said, “You can buy things with it” — an answer that only begs the question why that it so. “Faith,” said yet a third. Not quite.
The answer is one that (some) economists have known about for a long time. I’ll tell you about it below along with three other counterintuitive and seemingly bizarre conclusions about the twisted world of modern money. I don’t think you would draw it up this way if you had the chance but it’s the way the system works.
Government debt… is a form of savings for the private sector.
Tax liabilities give otherwise worthless paper value. The U.S. dollar has value because the government levies $3 trillion in tax liabilities annually and accepts only U.S. dollars in payment — which only it issues. And there is the credible threat of penalties if you don’t settle up with dollars. In so doing, the government turns all of us into dollar chasers. It’s how a state, any state, can turn worthless pieces of paper into valued currency.
“The modern state can make anything it chooses generally acceptable as money,” economist Abba Lerner wrote in 1947. “If the state is willing to accept the proposed money in the payment of taxes and other obligations to itself, the trick is done.” Brilliantly devious, isn’t it?
A dollar is, essentially, a tax credit. Economists call this the tax-driven view of money, and it is at least as old as Adam Smith. It is also one of the core principles of Modern Monetary Theory, or MMT. (This is a macroeconomic school of thought that has taken the deep dive into the plumbing of how modern money works.)
The principles of MMT have a certain forceful logic. And they can lead to some shocking and uncomfortable conclusions…
One example is that government deficits increase financial savings. It sounds outrageous. How can government deficits increase savings? Well, how else is the nongovernment sector supposed to get dollars? The only way is for the government to spend more than it collects — thereby leaving money in the economy.
Or think of it this way, as economist Warren Mosler puts it: “When the government spends, only two things can happen to that money… the money can be used to pay taxes, or it isn’t used to pay taxes. In which case, somebody out there still has it.” So deficit spending equals financial savings at the macro level.
Government debt, then, is a form of savings for the private sector. Everywhere there is a Treasury security there is someone who owns it. For that holder, it is a part of his financial wealth, or savings.

But aren’t government deficits and debt too large? They can be too large, which then causes the dollar to lose value. However, in a fiat currency system, it is natural for the government to be in deficit, because the private sector usually wants to save something.
Then what give bitcoin value?

Although a simple question, "What gives Bitcoin value?", the answer is not as simple as the question. What gives Bitcoin it’s value, can best be answer by the formula
PB = (SW + TX) / BC
The value of a Bitcoin is derived from the total value of the Bitcoin used for storage of wealth (SW) plus the total amount of the Bitcoin required for concurrently transacting in it (TX). The sum of these two numbers divided by the amount of Bitcoins in circulation (BC) (currently 12.2 million, ultimately 21 million), will give you the price of Bitcoin (PB).
There are estimates of the total amount of gold in existence (mined) in the $10-13 Trillion range. If $1 Trillion (10%) of the amount of wealth that would have gone into gold, instead lands in Bitcoin, that would increase the price of Bitcoin to ($1Trillion + TX) / 12.2 million, or by $83,000 per Bitcoin. Remember, this leaves out the TX component, which will further increase the price of Bitcoin. Over time, funds will shift from other asset classes being used for wealth storage to Bitcoin.
There are many advantages to storing wealth in Bitcoin as opposed to specifically gold, for example, as you can divide Bitcoin into very tiny pieces (difficult with gold) and you can send Bitcoin to someone on the other side of the planet within minutes (impossible with physical gold). These use cases illustrate why Bitcoin is a good alternative for gold (and other assets) for storage of wealth.
From a transaction perspective, as more citizens, businesses, and governments transact in Bitcoin, the amount of ‘wealth’ that must be placed into Bitcoin must be large enough to allow these transactions to happen.
For example, if it becomes common place for real-estate purchase payments to be processed via Bitcoin, then the amount of value in Bitcoin required to allow this to happen will need to be as large as the current working set of real estate transactions in progress. This logic applies to online sales and brick and mortar sales. If, on a daily basis, $250 Billion is required to allow all Bitcoin transactions to occur, the Bitcoin price only in terms of TX requirements, is $20,500.
The price of Bitcoin (PB) = (SW + TX) / BC. SW and TX will both change as time passes. In geek terms, SW, TX, and BC are functions of time f(t). Therefore to more accurately predict the price of Bitcoin, you need to estimate these two components for a given time, and then divide by the number of Bitcoins in circulation. BC can easily be obtained from many websites and is updated live.
Bitcoin works well as a storage of value and for financial transactions, therefore it will often be used as a substitute for both currency as well as common wealth storage assets (e.g., gold). Bitcoins utility (global register – the block chain) is what makes this possible. The worth of Bitcoin comes into play because of this utility, wealth storage and transactions will happen ontop of this platform. And using the formula above, the price of Bitcoin (PB) can be computed by estimates of these two quantities.