[TangoTrotFox]

How do you propose to measure the ROI of the completely unknown? This is not just related to your comment here, but it's a very general and important part of science. In the early part of the 20th century it was felt that physics was basically 'solved' and the only changes would come in refining values to another decimal point. Of course that was before the discovery of quantum mechanics or the explosion in particle physics. Have we started reach a valley at which point there's nothing but ever more diminishing returns ahead in the future? Or are we just about over the precipice onto a new explosion of revolutionary knowledge? I don't see how you can propose to meaningfully answer this one way or the other.

I'd also prioritize manned exploration above particle physics, but I think they should continue and grow in tandem as I see no way of knowing exactly what the future of these endeavors holds, other than that there is a reasonable argument to be made that either could produce discoveries of tremendous value.

[sovande]

Using probability is a good start I think. As I understand it, CERN should be able to find new particles below about 2–3 TeV in energy. It hasn't and physicists say it’s a reasonable assumption that there might not be anything new to find until energy scales of 100,000,000 TeV or more. You'll need to build and accelerator around the Sun to reach those energy levels. With that in mind, does it make sense to build something slightly larger than LHC? At billions of dollars?

[yoklov]

> physicists say it’s a reasonable assumption that there might not be anything new to find until energy scales of 100,000,000 TeV or more

This is an extremely pessimistic view. Yes, we're almost certainly going to find something there, but that doesn't mean there's nothing before then. I'd bet a reasonably large sum of money that there's something before around 10TeV.

Also, this collider isn't looking for new particles so much as trying to improve our understanding of ones we know about already.