Every second for the last four-and-a-half billion years, trillions of hydrogen atoms have been converted into helium in the Sun's core and released an immense amount of energy in the process. This is a process known as nuclear fusion, and figuring out how to harness this source of virtually limitless clean energy on Earth has been a holy grail of physics for the last 80 years.In the early days, most of the pioneering fusion research was done behind the closed doors of top secret government labs. At places like Sandia National Laboratory, physicists are still studying fusion energy using some of the most complex machines in the world in order to better understand the nuclear weapons fusion research helped create.In the last two decades, however, venture capital has been pouring into fusion energy research and a number of private companies are locked in a race to be the first to connect a fusion power plant to the energy grid.Motherboard visited Sandia National Laboratory and General Fusion, two of the preeminent fusion research facilities in the world, to find out if and when we will ever see fusion energy hit the world's power grids. At Sandia, many of the physicists still consider fusion research to be in its early stages, despite its 80 year history. General Fusion, however, is convinced it can get a power plant online within a couple of decades.Both private and publicly funded fusion are in a race against the clock to push the limits of fusion energy ever further before their funding dries up. Significant progress has been made in the last two decades, but will it be enough to ever create the hoped for 'star in a jar' here on Earth?