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CERN's Future Circular Collider (FCC) Conceptual Design Report [pdf] (researchgate.net)
57 points by movaxdx 8 days ago | hide | past | web | favorite | 36 comments

would love to read comments on Sabine Hossenfelder book "Lost in Math" related to this


She basically makes the claim we have no good scientific reason to build this at the moment

Me too, though I think her concern is more the huge amount of money being spent on a project with nebulous aims, and what she perceives as an unhealthy tribalism or peer pressure that discourages hard questions.

I don't think many would object to research that probes rather than has a specific end goal like discovering a predicted particle; it's the billions diverted from other potential smaller projects to one that might not reveal anything new - beyond a torchlight sweeping through and revealing just an extension to our current darkness - that is more questionable.

A Problem with accelerator physics particularly is that there is a large scientific industry around the actual experiments that depend on these experiments continuing. The engineers just get told what to build and they get going, without having a deep understanding why this particular experiment is really necessary. I worked in accelerator physics for 5 years and on all the conferences, meetings etc. I had yet to meet anyone who understands, why we are doing this (with an understanding that goes deeper than Wikipedia).

Well, accelerator physicists work with particle physicists who do understand these things. More often than not particle physicists don't understand how the accelerator works. Particle physics is complicated, and so is the LHC. I am not sure it's right to expect people to be experts on both, it's surely better for people to specialise.

Regarding Hossenfelder: I think she is an iconoclast and arch contrarian.

"arch contrarian"

Could make a good title for one of her German synthpop music videos, which I kindof dig.

The omega tau podcast had an interesting episode on this.


There is also an interesting episode on mega projects in general.


yes, the few omega tau podcasts I have listened to, have been excellent. Alas, many of them are not in English.

Well, why not? As many point out it has interesting engineering challenges, and gives particle physicists something to do.. However, maybe there is nothing to do after all. One wonders if this is a last hail mary for those clinging to super symmetric particle theories or maybe for multiple higgs ideas. Or just for a job. There doesnt seem any sound reason to me to think the particle desert isnt real and wont stretch all the way to GUT energy. Though i suppose 13.4 - 100 may yield extra discoveries of some nature. I used to read this blog http://resonaances.blogspot.com, though im not a particle physicist, it was interesting. The posts dried up and it was hard not to detect pessimism after a null result via supersymmetry. Indeed i seem to remember hearing no one would want to go into particles as a career now and many will pivot into condensed matter physics etc. So what are they gonna do for 25 years? I guess the youngsters 25 years hence will have to dust off the particle books. Meta materials, gravity waves and plasma physics are so much more intetesting now.. I seem to remember reading about plasma wave accelerators the size of a table top many years ago with giant theoretical energies. Interesting to note the ssc had 40 Tev energy which would have fairly concretely answered the ss question without the need of another machine

> So what are they gonna do for 25 years?

Run 2 of the LHC ended in 2018. Currently the experimentalists are busy analyzing that data, and the theoreticians are busy improving the theoretical prediction precision to the level of the experiment. If we had no new data, it would take a decade for this work to be finished.

Run 3 of the LHC is scheduled for 2021-2023. After that the High Luminosity LHC upgrade will take place, with data taking currently scheduled for 2026-2038 [1].

Overall, just with the LHC-related projects in the foreseeable future we are looking at decades worth of measurement and research. There's no reason to worry about the lack of work to do :)

[1] https://project-hl-lhc-industry.web.cern.ch/content/project-...

Contrary to popular belief, there’s lots of work going on in experimental particle physics, and there’s a lot planned. Physics didn’t stopp in 2012 with Higgs discovery, it is not likely to stop in the near future either.

High energy experimental physics died in the 1973. It's long since been time to pull the plug on this zombie. It was obviously true in the 90s when I was picking a specialization. It's even more true today.

I’ve spent 18 years in the field. But what would I know...

Compare the last 18 years with, say, the period from 1955 to 1973. There are still people who write poems in Latin as well. They don't cost much, nor do they channel large populations of intelligent people away from real problems.

You imply there were no benefits from lhc? It’s not incredibly expensive per scientist (there are single hospitals with larger budgets than a lhc experiment), and it had a massive impact - for instance you know about it. Basic research is important, if you don’t agree, try educating yourself - i won’t do it for you.

>You imply there were no benefits from lhc?

I have overtly stated as much, in as public a way as I had access to at the time. I don't care if it's "not incredibly expensive per scientist" -it is a wasted effort, and an awful lot of what gets published (with 1000 "authors") as being bullshit. I've also seen the lifestyle and read the "results" of both experimental high energy and the theorists: it's basically a cargo cult at this point, imitating the glory days in the 50s and 60s.

Let me ask you a question: what lack of result would convince you that high energy as practiced today is a waste of time? I look at stuff like this and see sheer decadence:


The "muh basic research" argument doesn't work forever. "Which basic research" is a question we should be asking, and building yet another giant accelerator and detector set up is not necessarily the answer, just because that's been useful in the (now distant) past. Phil Anderson is probably right.

Some interesting numbers:

- From the abstract:

> Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV.

- From the paper:

> The overall project duration of FCC-hh as a “stand-alone” project is 23 years, composed of two major parts: the preparation phase spanning 8 years and the construction phase spanning 15 years.

- From Wikipedia [1]:

> First collisions were achieved in 2010 at an energy of 3.5 teraelectronvolts (TeV) per beam, about four times the previous world record. After upgrades it reached 6.5 TeV per beam (13 TeV total collision energy, the present world record).

[1] https://en.wikipedia.org/wiki/Large_Hadron_Collider

Annoying that this apparently isn't on the arXiv. Here's an alternative direct link.


This is super fun! It’s huge but just skipping through to check out diagrams and read bits and pieces is great.

The LHC, has 13 TeV total collision energy, this intends to go to 100TeV in about 20 years. Is that sufficient to find new science? Should they be aiming for a much higher energy? Less than 10 times increase doesn't seem much, for a multi billion dollar project.

It isn’t a simple matter of making a number bigger. The size and cost goes up exponentially. There are potential new particles that can be teased out of 100 TeV. Some important particles aren’t expected to be seen in colliders smaller than a thousand light years.

Worth noting that the increase from the Tevatron (2TeV) to LHC (14TeV) was the same as this proposed step from the LHC to the FCC.

A dozen (!) pages listing the contributors, then an abstract which ends with the paragraph quoted below which essentially says it's more powerful and wth vague aims.

I hope the intended audience aren't political and financial decision makers who are otherwise laymen on the subject.

Presumably this is aimed at fellow scientists? What's the goal of the document? What is the specific Higgs-equivalent target of the proposed collider? I didn't read further tbh, I wasn't encouraged by the first few pages, but then I'm not a physicist so perhaps that isn't intended.

From the abstract:

the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre- of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

Sorry, but I am afraid you are ill informed on the ammount of complexity that this document cover.

Please note that never ever in the history of mankind a project so ambitious has even be thought. Already the amount of complexity in LHC is considered far greater than the complexity of the Apollo mission. FCC is a different order of magnitude than LHC already.

Then if you just skim the report you will notice how wide are the topic covered.

Leaving aside the physics, the document talk about the magnets, how to detect quenches, how to discharge magnets that hold 37MJ of energy, how to monitor the beam of particle, how to dump the beam, how to inject the beam into FCC, how to accelerate the beam,how to keep 100km of magnets at 1.9k when particles at 100TeV are running inside and doing it not for a bit, but continuosly for months and months.

And then other points more pragmatic, where to get the electric energy to run the whole machine?

And this just skimming the document and looking at pictures.

Honestly, how many would you expect to write such a document?

I think you've completely missed my point and have not answered a single of my questions.

In particular, I'd like you to not "leave aside the physics" - my understanding is that's quite important here - and specify what part of theory this will confirm or reveal.

I may well be "ill-informed", I'm happy for you to clear that up with an example along Higgs-discovery lines - the abstract and first dozen pages were unable to.

You reference the Apollo mission as a relatively minor affair in comparison, so that could serve as an example.

What is the "putting a human being on the moon" thing we are doing here? The abstract as it stands is more like "we're gonna shoot some multi billion dollar rockets into space and see what happens".

I wonder whether it is worth spending as much as this would cost, but I don’t expect that to be answered in a “Conceptual Design Report. Design time is not where you justify why you’re building what you’re building; you only describe how you’re planning to do it.

Presumably (I haven’t looked hard for them) there are earlier report(s) that argue why we would want to look at 100 TeV.

Edit: https://fcc-cdr.web.cern.ch/ has some more high-level info, such as ‘FCC Physics Opportunities’ (https://fcc-cdr.web.cern.ch/#FCCPO), which refers the “European Strategy for Particle Physics” (https://europeanstrategyupdate.web.cern.ch/) which, presumably answers the ‘why’

That's a fair answer thank you (and why I asked about the intended audience and purpose of the document); however as they put the blue sky goals in the abstract, I would have expected something more specific as well.

Wrt your first observation, yes it's particularly the amount that it costs that I think makes this clarity in communication especially important.

Sorry, I was trying to explain why there are so many contributors on this document.

I am not so much into the details but I can try to explain a little bit more.

First of all is important to understand the time scope of the project. The whole FCC is suppose to run until the end of the 21st century and one way or another will shape the general knowledge of us as human.

Then, it is a CERN project, so it's CERN that decided whenever this get build or not. CERN has it's own budget and decide what to do with it.

Of course, the project is so big, that is expected some level of (at least general) agreement between the member state of CERN.

Given the context, the document aim to create a general understanding of what will be FCC, what will be its cost, what the benefits and what the challenges.

Nothing is yet, set on stones, but it is a first high level sketch of the project.

In my understanding the target of the document are the people that decide what to do with the CERN budget, which are generally ex-physisct, with a deep understanding of the matter, but that now are into management.

They will need to manage the balance between costs, opportunities and expected reward of the project. They will need to decide if it is actually worth to build it or not.

Unfortunately I cannot speak about physics, I am an engineer who happens to work at CERN.

However the general model at CERN is been to build a "small" accelerator to discover new things and a new bigger one to measure this new thing. LHC is the small one that discovered Highs. More precise measurements will required something bigger.

Given this context, my understanding is that particle physics is a little in a tough spot. Everything seems to work kind of alright, but there are few points not well understood or predicted. It is not like we have no idea of what is happening, but we are not even super super sure of everything.

Interesting to know that there is another project "competitor" of FCC, CLIC which is a linear accelerator and in my understanding should explore a different space of the problem.

Given all this, sorry that I cannot comment on the physics, but if there is enough interest in the community we can try to get in touch with somebody more informed than me on both the physics and the technology side.

If you guys have more questions please ask, and I will try to do my best...

Thank you.

Wrt your physics "tough spot" observation, yes that's my understanding as well.

I think the concern is just that this is hugely expensive and there appears to be no guarantee or even confidence that it will get us out of that difficulty.

But... Why?

Why not?

CERN culture dictates that everyone involved with the team should be listed as contributors. This is due to the fact that experimental result papers, written up by small teams who analyze data, are only made possible by the work of many other scientists who do not themselves produce papers. The contributor list probably includes everyone that would normally be listed as part of any paper published by the group.

Thanks - I understand the idea, but I think it would be better suited to an appendix.

Followed by the table of contents and the actual CDR. You can't skip the details then ask "Where're the details?"

I didn't ask for the details. There were too many details before a point revealed itself.

I asked for the specific overarching, clearly specified. targeted discovery goal of the whole thing.

Feel free to answer that - it appears to be missing from the abstract.

Why would I continue beyond the abstract if it is not clear what the specific goal of the project is and I've already gone through a dozen pages to get there?

That's not really the point of a CDR, it's saying "if we were to build a 100TeV machine, this is, broadly speaking, how we would do it". Particle physicists may (or may not) determine it worthwhile, that's another question altogether.

Thank you. That makes sense (and why I asked about the intended audience and purpose of the document); however as they put the blue sky goals in the abstract, I would have expected something more specific as well.

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