What is the point of the Large Hadron Collider?

Every time fundamental research hits the headlines you can be sure that someone - maybe lots of people - will question whether it's worth it, the BBC reports.

And so it is with the restart of this mother of all physics experiments, ready after its two-year upgrade to explore uncharted corners of the sub-atomic realm.

This vast machine ranks as one of the world's biggest experiments, with incredibly sophisticated machinery filling a 27km circular tunnel, and the bill so far has come to a little under £4 billion.

Back in 2008, when the vast device was first brought to life, one senior British scientist grumbled to me that "the particle physicists seem to get all the money they want".

His view was that humanity faces a long list of severe and immediate threats which are more deserving of the kind of massive scientific investment devoted to the research at Cern.

Top of his list was clean energy. If we could start with a blank sheet of paper, he said, would we really choose to devote all those billions to particle physics?

I heard a similar complaint on the day that the Rosetta spacecraft achieved its historic rendezvous with a comet far beyond Mars.

As the mission controllers erupted around me, one of my tweets attracted a sternly-worded demand to know how anyone would benefit from this venture to a distant and icy rock.

"What good," I was asked, "might any knowledge that it might obtain do for mankind?"

One answer might be pragmatic: if a comet ever headed our way, it would be good to know what they are made of and how they might be deflected.

Another could be that it would surely satisfy our curiosity to know if comets were the source of our water or even of life itself.

But a response that feels more compelling is that previous generations have only been able to gaze at comets in awe or fear while ours might be the first to understand them.