There is an ongoing debate on whether the money of billionaires like Elon Musk is actually "real".
One way of addressing the question would be to ask what does "real" mean.... ;-) I will forgo that extreme, and just focus on what money is. While I won't try and define what "real" means, much of the rest of this Short Thought is going to be defining terms around money, wealth and assets.
There are many different ways to define what money is, if with money you mean the stuff in your wallet, or even the stuff in your bank account. (Which is NOT the same thing.)
But people also use the word money to describe many different other things as well. A person with a nice house is described as having lots of money, the same way that a billionaire has a lot of money.
Physical money (wallet money) is an asset, and EVERY asset has a valuation that fluctuates, something that the gold standard people conveniently ignore. (Silver and gold are actually extremely bad candidates to serve as wallet money.)
Let's start by defining money, and its various forms: In general, economists define money as any item or medium of exchange that is accepted by people for the payment of goods and services, as well as the repayment of loans. (For more https://www.investopedia.com/insights/what-is-money/)
As Investopedia explains, there are categories of money, and they range, in essence, in how quickly one can make use of the money.
The first is called M1, and it is made up out of all physical money, money in current (checking) accounts and travellers checks. Strangely, the second is called M2, and its definition expands to include savings accounts, time related deposits and non-institutional money market funds. M3 is the broadest category, and also includes institutional money market accounts, short term-repurpase agreements and some other larger liquid assets.
All of these categories maintain their value well, but they do fluctuate. Internal to a country, the fluctuation in value is measured in the rate of inflation. (And in very simplistic terms, interest rates are an attempt to compensate for inflation - which leads to the insight that countries where interest rates are below the rate of inflation over the long term. WILL develop structural problems, among others leading to rising inequality and entrenching the poor in poverty.)
Elon Musk has relatively little money as defined above, but does have an obscene amount of assets, in the form of shares in companies. He has massive stakes in Tesla, Twitter and the unlisted SpaceX. As opposed to money, shares fluctuate more, and sometimes wildly.
Now we need to move to the next discussion - what determines valuation? And the short answer is that (monetary) value is whatever somebody is willing to pay. There are many, many ways, tools and methodologies that can be used in calculating a value, but in the end - if nobody wants to pay what the tools say, it simply is not worth that.
In the case of listed shares we have the stock exchange as a mechanism to bring buyers and sellers together, and where they place bids for the price they are willing to sell or buy at. But the exchange is only the mechanism - the price the people feed into the mechanism comes from their mind. Where they make completely rational calculations about market situations, future expectations for the company and the economy, future interest rates, inflation rates, expectations of war, peace, famine and abundance.
Until they don't, if they ever did..
One of the biggest mistakes economist academicians used to make, was the assumption that economic decisions are made (economically) rationally. And they are not, hell no, they are not. It is hard for even the most seasoned professional investors.
In reality, valuations of assets, and including shares, is made as part of a complex adaptive system. Complex Adaptive Systems are large systems, that are able to react to changes in the environment. (Economies, ecosystems, etc). And they all share a number of features: for example, they go through cycles of boom and bust. They evolve through points of punctuated equilibrium, where they will be in equilibrium for a while, until they suddenly adjust to a new point of equilibrium. However, these fluctuations take place around a point where the price is reasonable, rational, traders always say prices regress to the mean.
These non-rational valuation decisions are made about individual companies, as well as about the economy as a whole. So yes, Musk does something silly at Twitter, people are not only going to react, they are going to overreact. If Musk's actions create a negative feedback spiral at Twitter that turns into an avalanche, Twitter could well completely implode, and all that "value" will evaporate. (I do think that other shareholders might bring him to ground before that happens. Billionaires don't like people losing their money, even if the person doing the losing is Elon Musk.)
But back to the larger economy: The larger economy is simply the sum total of tens of thousands of these companies, fluctuating in value all the time. And periods of growth are ALWAYS followed by busts. At roughly 10-15 year cycles: We are on the cusp of a (major?) correction at the moment. In 2008/9 we had the Great Recession, in 2000 we had the Y2K dot.com bust, etc. etc, etc.
The good news though is that the recovery from busts has happened everytime in the history of the world, it will do so again after the coming bust. The big thing is not to be caught invested in a company that does not survive, which is why Warren Buffet always recommends to invest in the broader market.
On a world wide scale, it's just another winter tale....