Star power

The Sun is a huge nuclearA nuclear weapon has a devastating potential to cause damage. A few countries around the world have them. reactor. Every second, 500 million tonnes of hydrogen fuse under extreme pressure and heat, releasing enormous amounts of energy.

For over 70 years, scientists have tried to copy this fusion reaction. An artificial "star in a jar" would offer limitless clean fuel and end our need for coal, oil and gas.

Last week, an "artificial sun" ran for a record-breaking 403 seconds. China's Experimental Advanced Superconducting Tokamak (EAST) uses powerful magnets to hold together superheated 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.. Hydrogen atomsThe smallest unit of any chemical element. fuse to form helium and energy.

Could this power our homes and cities? The potential is vast. A litre of seawater contains enough fusion material to produce the same energy as 300 litres of petrol. And without any of the polluting CO2Carbon dioxide. emissions.

Critics say fusion power is always just around the corner, but the technological challenges are too great. Starting a fusion reaction is very difficult. It needs temperatures ten times hotter than the Sun and powerful lasers and magnets to contain it. All of this is very expensive.¹

Physicist Daniel Jassby says it is not the "perfect" energy source, it has many drawbacks and is an enormous black hole for money and resources.²

Physicist Arthur Turrell disagrees. Building these "star machines" is humanity's greatest challenge. A global effort "could provide millions, perhaps billions, of years of clean energy". Limitless power everywhere would change the world, ending energy poverty and wars over fuel.

Many are betting big on a fusion future. The  International Thermonuclear Experimental Reactor (ITER) in France is a joint project of 35 nations. It will use the most powerful magnet ever built.

The word nuclear conjures up images of ChernobylThe disaster, in 1986, involved a meltdown at a nuclear plant in Ukraine. and radioactive waste. But fusion is much safer. Splitting atoms in nuclear fission sets off dangerous chain reactions. "In fusion," says expert Chris Warrick, "we have the opposite problem". Fission is difficult to stop, fusion is hard to start.

But if we can keep it running, Turrell says fusion rockets will be our "best hope" for space travel. Humanity's future may depend on building stars on Earth.

Yes: Fusion is the longest of long shots - the hardest thing we have ever done. It may take decades to perfect, but this ambition and foresight will give future generations the gift of limitless energy.

No: Fusion is science fantasy. Physicists and governments are wasting time and money on a pet project while the world burns. We already have the technology of the future in wind and solar power.

Or... No single technology will decide our future. Optimists always believe new technology will change everything and fix all our problems. In reality, we will need a variety of inventions working together.