The Large Hadron Collider is big, eight and a half kilometers across. It’s expensive, with a cost to construct and operate in the billions. And with an energy of 6.5 TeV per proton, it’s the most powerful collider in the world, accelerating protons to 0.99999999 of the speed of light.
The LHC is reasonable. After all, it was funded, and built. What does an unreasonable physics proposal look like?
It’s probably unfair to call the Superconducting Super Collider unreasonable, after all, it did almost get built. It would have been a 28 kilometer-wide circle in the Texas desert, accelerating protons to an energy of 20 TeV, three times the energy of the LHC. When it was cancelled in 1993, it was projected to cost twelve billion dollars, and two billion had already been spent digging the tunnel. The US hasn’t invested in a similarly sized project since.
A better example of an unreasonable proposal might be the Collider-in-the-Sea. (If that link is paywalled, this paper covers most of the same information.)
If you run out of room on land, why not build your collider underwater?
Ok, there are pretty obvious reasons why not. Surprisingly, the people proposing the Collider-in-the-Sea do a decent job of answering them. They plan to put it far enough out that it won’t disrupt shipping, and deep enough down that it won’t interfere with fish. Apparently at those depths even a hurricane barely ripples the water, and they argue that the technology exists to keep a floating ring stable under those conditions. All in all, they’re imagining a collider 600 kilometers in diameter, accelerating protons to 250 TeV, all for a cost they claim would be roughly comparable to the (substantially smaller) new colliders that China and Europe are considering.
I’m sure that there are reasons I’ve overlooked why this sort of project is impossible. (I mean, just look at the map!) Still, it’s impressive that they can marshal this much of an argument.
Besides, there are even more impossible projects, like this one, by Sugawara, Hagura, and Sanami. Their proposal for a 1000 TeV neutrino beam isn’t intended for research: rather, the idea is a beam powerful enough to send neutrinos through the Earth to destroy nuclear bombs. Such a beam could cause the bombs to detonate prematurely, “fizzling” with about 3% the explosion they would have normally.
In this case, Sugawara and co. admit that their proposal is pure fantasy. With current technology they would need a ring larger than the Collider-in-the-Sea, and the project would cost hundreds of billions of dollars. It’s not even clear who would want to build such a machine, or who could get away with building it: the authors imagine a science fiction-esque world government to foot the bill.
There’s a spectrum of papers that scientists write, from whimsical speculation to serious work. The press doesn’t always make the difference clear, so it’s a useful skill to see the clues in the writing that show where a given proposal lands. In the case of the Sugawara and co. proposal, the paper is littered with caveats, explicitly making it clear that it’s just a rough estimate. Even the first line, dedicating the paper to another professor, should get you to look twice: while this sometimes happens on serious papers, often it means the paper was written as a fun gift for the professor in question. The Collider-in-the-Sea doesn’t have these kinds of warning signs, and it’s clear its authors take it a bit more seriously. Nonetheless, comparing the level of detail to other accelerator proposals, even those from the same people, should suggest that the Collider-in-the-Sea isn’t entirely on the same level. As wacky as it is to imagine, we probably won’t get a collider that takes up most of the Gulf of Mexico, or a massive neutrino beam capable of blowing up nukes around the world.
If you are interested in this kind of speculations, I have a post on my blog discussing an even crazier idea – a collider orbiting around the sun!
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Off topic: Curious how big a deal this paper is and it seems to be in the general vicinity of your specialty. https://arxiv.org/abs/1802.02657
Hmm. It’s a bit off my specialty, really: I’m not usually working in non-renormalizable theories besides gravity, so four-fermion operators don’t show up, and this is mostly true of other amplitudes people. This guy visited NBI briefly (mentioned in his acknowledgements) but I don’t think his talk covered any of this, so I’m not sure he thinks this is amplitudes-adjacent either.
Anyway, on a skim through the paper I’m mostly surprised that four-fermion vertices are so complicated one has to resort to this kind of thing. I don’t know how bad the previous methods were, so I don’t know how big of an improvement this is. As an amplitudes person I of course can’t help but wonder if these things would look simpler in an on-shell formalism, but that may just be amplitudes-chauvinism talking.
I’m sure this may ruffle some feathers, but the international linear collider, in my view, is unreasonable (cost $6 – $10 billiion), just purely in terms of opportunity cost (think of how many theoreticians could be paid with that much money…). There seems to be be diminishing returns with these projects, both in terms of developing accelerator science and advancing particle physics. Just how certain are we that we may actually see a superpartner at such a project? (as far as I have seen, we’re not certain at all, whereas with the Higgs people had some good reasons to think they could spot it. ).
The argument behind most of the upcoming big collider projects isn’t about seeing a superpartner per se. For most, that sort of thing is a welcome bonus: obviously, if there’s any significant physics in the 100 TeV range, we’d want to be able to see it, but there’s no guarantee that there is. The actual proposals tend to focus on more certain stuff: measuring various parameters of the Higgs more precisely and ruling out alternate models that way, that sort of thing. When I see Nima talk about the Future Circular Collider, that’s usually what he focuses on. One thing that makes me more skeptical of the Collider-in-the-Sea getting going is that I don’t see them making that kind of case. Instead they put more emphasis on the argument that because we don’t know what we’ll find it makes sense to go to as high energy as we can afford (for a given investment). This is a perfectly sensible scientific point, but it has the downside of reminding funding agencies that it’s entirely possible that we won’t see anything at all.
As for more generally weighing different things they could be funding…I suspect it doesn’t trade off quite way. Regardless, I’m glad I’m not one of the people in charge of making that kind of decision at this point.
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