Sometimes seeing is disbelieving.

At the recent European Science Open Forum conference in Barcelona, for example, I was strolling through exhibits aimed at — please don't gag — science outreach. The underlying theme of all these displays seemed to me to be: since their schooling actually teaches many ordinary people to be discomforted by — if not to actually fear and loath — science, let's see if we can't do something in these venues to get people to hate science a little bit less.

In this regard I was struck by two exhibits. One was for ITER, a multinational effort centred in Cadarache, France, trying to create a fusion energy power reactor. As background, fusion is the physical principle by which the sun produces heat and sunlight as it fuses together hydrogen atoms, not to mention being the chemical reaction that unleashes the H-bomb's lethal and terrifying force.

ITER (pronounced Eater and originally an acronym for International Thermonuclear Experimental Reactor, although that has been dropped) — in which the European Union, India, Japan, China, Russia, South Korea, and the U.S.A. are participants - is going to cost five billion euros and take 10 years to simply build. It will take another five billion euros to operate for 20 years. If it works as planned, it should be able to sustain a fusion reaction for a bit more than 15 minutes.

No electricity will be generated, just proof of a concept that you can get significantly more energy out than you put in. Even this is important, because previous fusion reactors have only been able to get about as much energy out as it took to fuse the atoms together, and then only for about a second. To get actual power you would have to build a bigger reactor, generating four times as much power, for - well, billions and billions of euros more.

ITER itself is being constructed in the face of extreme doubters. In 2003, Canada looked at the cost and the potential benefits and backed out of participating in the project. More pointedly, Nobel laureate in physics Pierre-Gilles de Gennes is once supposed to have said about the problem of fusion power in general, "We say that we will put the sun into a box. The idea is pretty. The problem is, we don't know how to make the box."

Sébastien Balibar, a professor of physics who is director of research for France's national scientific research centre, last year wrote a blistering critique that both doubted the project could be done at all and pointed out that, while in the process of fusing the hydrogen atoms together, the reactor might also produce masses of exploding helium bubbles. He also warned, "the danger is that ITER will squeeze out funding for other vital research." (For a positive view on things see David Ward's presentation.)

The European Science Open Forum exhibit didn't go into a whole rebuttal of critics, but rather tried to explain to people how the reactor would work, why it was a good thing (no radioactive waste left after the reaction, for one, and no greenhouse gases are produced) and why it was hard to do. Containing the heat long enough to produce a controlled reaction — not the uncontrolled bang of an H-bomb or the sun — and generating electricity from it has proven to be harder and more complicated than anyone thought.

Indeed, the complications are such that a session at the European science forum about fusion had the purposely provocative title "Fusion, will it always be 40 years away?"

Right across from ITER was an exhibit in which a group of paleo-archeologists had set up a display to show the technology of the past in operation. So you had a guy sitting cross-legged, banging away at a rock to make a hand ax. Chip, chip, and chip. You had someone else weaving plants together to make a mat. Weave, weave, and weave. Someone else was taking clay and making a pot. There was no placard asking: Hand axe making, will it always be 40 years away? There were no critics of the effort calling it a huge waste of national resources.

So what does the juxtaposition of the two very different demonstrations of technology tell us about disbelief?

To begin with, the ITER project and all hugely expensive big science efforts — think the International Space Station, think Large Hadron Collider, which recently has received a tonne of press — aren't like making hand axes. I looked at the man diligently chipping away and realized that the price of his failure wasn't very high. So what if it turned out the rock type you made axes from wasn't strong enough to chop wood? You simply went back and made axes from something else until you got an ax that worked.

And you, in this case, would simply be some intrepid carver and not some large part of the Paleolithic science world.

On the other hand, if ITER fails, it is massively unlikely there is going to be another effort to correct its errors. Research on its level is simply too big and expensive and time-consuming. But what if it succeeds — but only kinda? What if its results show that you can produce energy, but that it is 10 time times more expensive than energy from other sources? What if figuring out how to make that equation more favorable will require at least three iterations of ITER?

Who's going to back that kind of research effort?

What you put in place with these vastly expensive research efforts is a "can't afford to fail" paradigm. Unlike trying to find the best plant material to weave into a mat, ITER, the Large Hadron Collider, etc., must succeed on first go-round. With ITER, there is no second kind of rock to be chipped away, no other plants to be woven, no different type of clay to be baked into a plate.

And that's what I so disbelieve about it. It's not really experimental science; it's risky, we-can't-fail, all-or-nothing science and I would respond to that paradigm with the wisdom of stone axe makers.

Sometimes your research should be based not on how glorious success might be, but on how little you will have lost if you screw up.