Can we bottle a star? Almost all the energy we use on Earth comes from the sun, an immense fireball at the centre of our solar system.

It is a giant thermonuclear fusionAn atom's nucleus contains a large amount of energy. This can be released either by fission (splitting the atom) or fusion (joining lighter nuclei together to form heavier nuclei). reactor, smashing hydrogen atoms together under intense heat and high pressure. These reactions will keep the sun burning bright for another seven billion years.

For the last six decades, scientists have dreamed of building their own star on Earth. A clean and cheap source of power.

However, creating star-like conditions is not easy. Physicist Arthur Turrell says it is "the greatest technical challenge humanity has ever taken on". 

The sun's core is over 15 million degrees Celsius, hydrogen atoms break apart to form plasmaa gas charged with electricity, found in stars such as the Sun. Physicists regard it as a state of matter, along with gas, liquid and solid.. Weighing 333,000 times more than Earth, the sun's gravitational pull fuses particles together into helium and energyWhen two atoms fuse, they lose some of their mass as energy. Einstein's famous equation E = mc2 shows that a small mass contains a huge amount of energy..

Scientists use laser beams, x-rays, microwaves and powerful magnets to replicate this extreme environment. But there is a problem: all these approaches use more energy than they create.

Now, scientists believe they are on the brink of "ignition" - the point where fusion will start fueling itself.

In August, a US lab fired 192 lasersThe combined energy of the lasers at the National Ignition Facility makes them the most powerful laser in the world. at a hydrogen pellet, turning it into a blob of superhot plasma, the width of a human hair. For the first time, it generated more energy than it absorbed.

Physicist Jeremy Chittenden says it is like striking a match. Once you light the flame, fusion becomes a "self-sustaining process - for as long as we can hold the burning plasma together."

Which is only a tenth of a billionth of a second. In May, another machine in China kept a reaction going for a record-breaking 101 seconds. But "we're still doing science," says expert Steven Krivit, "we're not doing technology". Fusion needs to last for more than a few seconds in a laboratory before it can save the world.

Industry leader Andrew Holland is hopeful. "Fusion is coming," he says, "faster than you expect". He counts at least 35 companies globally, aiming to have working reactors by 2025. And hook up power plants to the grid by the 2030s.

The potential is enormous.

Fusion will get most of its hydrogen fuel from waterFusion uses two types of hydrogen. Deuterium is found naturally in water. Tritium must be artificially created in a nuclear reactor.. And a small amount goes a very long way. Scientists estimate one glass of fusion energy could replace a million gallons of oil to power a home for 800 years.

It is also green. Fusion does not release greenhouse gasses or leave behind radioactive wasteNuclear fission uses uranium which stays radioactive. Fusion can only take place in the unique conditions of the reactor.. As fuel for carbon captureTechnology which captures carbon dioxide from the air and transports it to storage sites underwater, preventing it from warming the atmosphere. , it might even help reverse climate change.

Some are unconvinced. "Bottling up the power of the sun will always be 20 years away", says science writer Charles Seife. In 1951, Argentina declared it would offer fusion like bottled milk. In 1989, US chemists claimed to have created fusion energy at room temperature. Bottled star-fuel and cold fusionThe results turned the science world upside down, but other scientists could not replicate the experiment. turned out to be too good to be true.

But as the world aims for net-zeroCountries have committed to not putting more CO2 into the atmosphere than they are removing through carbon capture. This is also known as carbon neutral. by 2050, physicist Nicholas Hawker says we need to develop fusion technology "at maximum speed".

Some say no, the Earth already has a functioning fusion reactor. It's called the sun. We should improve and build more solar panels to soak up its rays, rather than waste money on unproven technology. It's too expensive and complex to ever be an affordable source of energy.

Others say yes, a revolution is taking place. Like space flight and computers, fusion began as a long-term research project funded by governments. Now, dozens of companies are taking over in a race to be the first to build a working reactor. Competition and investment will make fusion a success.