The promise of tomorrow is a long-time coming. In 1943, a Western Airlines advertisement declared: “TOMORROW, you can live a new life of unhurried speed, where family helicopters, super airliners and many amazing new machines will provide ample leisure.”

More than 70 years later, that future still seems far away. Flying cars and intelligent robotic assistants – all things “The Jetsons” experienced before the Internet – are still the stuff of science fiction.

Big ideas like these are commonly referred to as “moonshots” for their long time horizons and the massive amount of resources they require to get off the ground. The numbers are staggering – Alphabet, the holdings company created last year to oversee Google and all its associated ventures, spent more than $3.5 billion on longshot bets in 2015 alone, according to the company’s financial reports. And its projects such as Calico’s effort to slow aging and Project Loon’s mission to beam Internet to remote regions via balloons are a long way away from commercialization.

The future relies on wild ideas, but somebody has to cut the check to get things rolling. With so much money required for an uncertain return that could take decades to materialize, who’s keeping us moving forward?

Josh Lerner, professor at the Harvard Business School, said that venture capital has been at the start of many recent large-scale innovations.

“When you look at many of the industries that have emerged as important economic drivers, venture capital has played an important role,” Mr. Lerner says.

However, when it comes to paying for long-term projects, institutional investing has limits. Venture capital firms are beholden to investors, which shapes the type of bets they make. Typically operating in a 10-year timeframe, they are more likely to look for companies that they can make money in the foreseeable future than those working on a “moonshot idea.”

“Our financial market’s just not ready to do that type of thing,” says Matthew Rhodes-Kropf, associate professor at the Harvard Business School. “It is very difficult to find capital for something that might work many, many years from now.”

Because of this, Mr. Rhodes-Kropf says, the best way to fund a moonshot is with the support of giant corporations – or at least the billionaires running those giant corporations. While Alphabet as a company has spent years developing driverless cars, business leaders have invested personal fortunes in large-scale change.

Mark Zuckerberg and his wife, Priscilla Chan, have pledged to sell 99 percent of their Facebook shares (currently worth more than $40 billion) to advance causes such as curing diseases and improving education through the Chan Zuckerberg Initiative. And Bill and Melinda Gates have pledged to give away the majority of their fortune, which sits at $85.7 billion, according to Wealth-X.

But while these wealthy benefactors can make a huge impact in the areas they choose to support, Lerner says that relying on their good will may not be a sustainable business model.

Historically, funding the research that eventually leads to commercialized ventures has fallen to the government, especially in the realm of defense and energy spending. Technologies such as cochlear implants, solar power cells, and satellites have come about from various levels of government involvement, and government entities support forward-looking research.

The federal government’s Small Business Innovation Research program, which provides funding to research-intensive companies, has helped create at least 180 technologies that were licensed to outside companies, according to a 2014 economic impact study from the US Air Force. In addition, the Pentagon’s Department Advanced Research Projects Agency (DARPA), known for laying the groundwork for the Internet, finances new technologies related to national security with an annual budget of $2.9 billion.

“DARPA explicitly reaches for transformational change instead of incremental advances,” said a 2015 report from the agency.

There have also been nonprofit efforts to prompt large leaps forward, an approach that works particularly well in software. Linux, the software that undergirds many computing systems and smartphones around the world, operates on the principle of open collaboration, the idea that anyone can contribute to and improve the project’s code. The open nature of the software has helped it spread  – it can now be found running Internet servers, supercomputers, and financial trading systems.

Linux’s development is supported by the nonprofit Linux Foundation, a model that Jim Zemlin, the foundation’s executive director, says is necessary to provide a neutral and interoperable development process. However, Mr. Zemlin also acknowledges that the finances of running a nonprofit are challenging, since the foundation relies on donations to keep operating.

“Just like any other nonprofit, we are constantly under stress,” he says.

For those who prefer to work on innovative ideas in the for-profit market, it seems the best way to attract funding is figuring out how to turn a profit while spending money on research. Josh Cohen, managing partner at venture capital firm City Light Capital, says that he invests in companies with a social mission, but only if that mission intersects with profitability. “The way they accomplish the impact is the same way that they make money,” Mr. Cohen says.

Other companies have been able to achieve success following this same model. Elon Musk’s SpaceX, which is working toward a manned spaceflight to Mars, announced last September that it had more than $7 billion in contracts. And 2U, a company that aims to improve access to higher education online, went public in 2014 and has been able to grow revenue from $28.4 million in Q3 2014 to $37.1 million in Q3 2015.

Jim Shelton, president of 2U, sees the for-profit model as a vital component of change, especially in education, since it provides a sustainable source of revenue to support the social mission.

“This is an area where being able to invest in creating scale creates benefits for everyone,” Mr. Shelton says. “And that means you need to be able to raise value and you need to be able to retain really top talent.”

In the end, it may not be the multi-billion-dollar ventures or large-scale research projects that build the future. These efforts contribute to significant leaps, but they’re also difficult to measure and control once they’ve been started. If a project has been going for decades, there will be a lot of inertia behind keeping it going, even if it won’t pay off.

“The problem is that those companies are for the most part wasting money,” says Rhodes-Kropf of Harvard. “It is quite possible that some 30-year project is a great idea. It’s going to be pretty hard to get the incentives right for figuring that out.”

Rhodes-Kropf adds that smaller projects are becoming more powerful as technology has driven startup costs down. Taken together, smaller ventures can figure out what works and what doesn’t in a field much faster than one research project could, speeding up the pace of innovation. This acceleration seems to be bearing out in the market – the number of utility patent applications filed per year has increased by more than 100,000 since 2009 to reach nearly 580,000 in 2014.

And if that trend continues, it could be many smaller companies that finally bring us the amazing new machines and ample leisure time that we’ve been promised for so long.

“Even in things like alternative energies or nuclear power, there are startups being formed that are making these things faster,” Rhodes-Kropf says. “In some ways, we’ve never been in a better place.”