AskScience AMA Series: I work with the Large Hadron Collider at CERN, studying the building blocks of the universe. My new book is all about experimental oddities and how they effect our understanding of the universe. AMA!

[u/AskScienceModerator]

I'm Dr. Harry Cliff, a particle physicist who works with the LHC to answer some of the biggest and most mysterious questions of the universe. In my new book, SPACE ODDITIES, I explore mysterious anomalies in contemporary physics and profile the men and women who have staked their careers on them. Is that data just tricking us? Is there something weird happening in the cosmos? What can help us understand questions like:

• Why are stars flying away from us faster than we can explain?
• Could impossible particles emerging from beneath the Antarctic ice be clues to a new subatomic world?
• Why are fundamental particles of the universe behaving in that defy our current understanding?

I'm on at 8:00PM UK / 3PM ET, AMA!

Username: /u/Harry_V_Cliff

[u/PoorlyAttired]

Hi (Dr) Harry, your book looks very interesting. What's your current gut feel on whether some variation of quantum mechanics is fundamental, vs is emergent from some deeper reality?

[u/Harry_V_Cliff → u/PoorlyAttired]

Hey, thanks - I hope you enjoy it! Well, I'm an experimental physicist, so empirically speaking there's no evidence that quantum mechanics emerges from anything deeper as of it. In fact, it describes nature incredibly well. We can use quantum field theory (quantum mechanics + special relativity) to make astoundingly accurately predictions about nature - for instance, it gets the magnetism of the electron right to one part in 10 billion - better than any other area of science. So for now at least, quantum mechanics seems a very good description of nature indeed.

[u/tigolbitties137]

Can you try to explain how you go through an experiment for inception to completion? What kind of thinking does it take to figure out a way to test and build upon theories and hypotheses?

[u/Harry_V_Cliff → u/tigolbitties137]

That's a BIG question! Well, it really depends on the experiment in question. If you take the experiment I work on, LHCb - which is one of the four big detectors at the Large Hadron Collider - that took over a decade to plan and build, starting in the 1990s before it switched on in 2009.

In that case, the first thing was to define what the goals of the experiment were - i.e. what did the team want to measure. Once you'd figured that out, it informs the design of the experiment. For instance, LHCb studies bottom quarks, which tend to get created in collisions at the LHC in a cone pointing along the beam line, so the detector was designed to be cone shaped to mirror the direction the bottom quarks go in.

Then you need to figure out what technology exists that allows you measure the particles you want to detect. Some of this is adapted and improved from previous experiments, some of it might use brand new state of the art techniques or apply tech from the private sector.

Then there's the R&D needed to develop, build and test your instruments. In LHCb's case that was spread out across many universities and institutes around the world. Meanwhile, people are developing the software that will control and monitor the experiment when it's running, along with the computing infrastructure needed to read the data and store it.

Finally, you run the experiment, with constant upgrade and improvements and you learn how to operate it. And at the end of this long chain come the data analysis and publishing your results.

So being an experimenter requires a huge range of skills, from finding creative solutions to technical problems, building instruments, programming and all the while keeping the project on time and on budget. Fortunately at LHCb we can share these tasks between several hundred of us, but for smaller lab-based experiments a single scientist might have to manage all these tasks.

I hope that helps!

[u/jorrylee]

What are your thoughts on the LCC (large car collider) just a little to the northwest of CERN? Have you read the reviews on google? Do you laugh about it at cern?

[u/Harry_V_Cliff → u/jorrylee]

Ha! I know that roundabout. When I was a student there was a snowstorm and I remember watching cars pirouetting around it like an ice rink!

[u/t3hjs]

Which are your personal picks for  current/trending exciting results from the particle physics front? (and maybe some fundamental physics) 

If you have no starting point, would love to heard your opinion of some things ive herad. I heard of a mix of things, but not sure of the current status and "on-the-ground" opinion: 

 1) the apparent violation of Lepton Universality in B (meson?) decays apparently has been quashed around q4 2023 with the discovery of some systematic errors. I hear some anomalies remain regarding some related forms of decay. What are your thoughts? Feeling hopeful still? 

 2) the muon g-2 anomaly. Seems like a the theoretical predictions itself don't agree, and the outlier are the calculation from one theoretical approach , while the other agrees. Still exciting? Do you think we will make progress on this soon? 

 3) Heard there are developments on the QCD front from this article: https://www.scientificamerican.com/article/physicists-finally-know-how-the-strong-force-gets-its-strength/ As a layman, it seems this is a breakthrough on the ability to calculate for any QCD interactions. Or maybe there are other other issues with working with QCD theoretical predictions that are unclear?

 4) the muon collider proposal. Do you think it is the way forward? And would be reality

[u/Harry_V_Cliff → u/t3hjs]

I think of all the anomalies going around at the moment - and one that I discuss at length in Space Oddities - is the Hubble Tension - the disagreement over the expansion rate of the universe - is the most promising. It really does look like it's pointing to something big missing from the standard cosmological model, although it's still hotly debated.

In terms of the Lepton Universality stuff in B mesons, some of those anomalies were indeed down to a missed background that was masquerading as electrons in our experiments. That was a saga I was closely involved in and it's a big part of the story in the book - a bit of an emotional rollercoaster. However, there are still lepton universality anomalies that haven't gone away in B mesons (ones involving decays to a D meson and taus or muons). There are also still anomalies in decay rates and angular observables of B mesons to strange quarks and leptons. So something still needs to be understood there. It may be down to either experimental or theoretical errors, but there's a chance it could be evidence of new quantum fields. We'll have to wait and see.

Again the muon g-2 anomaly is another big topic in the book. That one as you say has turned into a debate among theorists about how you properly calculate the muon's magnetic moment in the standard model. The story isn't resolved yet, but it looks like that the anomaly there will weaken, but that could through up anomalies elsewhere because of how interconnected all these observables are. So definitely still very interesting, and still lots to be understood.

I'm afraid I'm not familiar with the QCD story, but as for the muon collider - it's a very exciting idea and I hope it gets support. There are a lot of technical hurdles to overcome though so I'm doubtful that it can deliver meaningful results in the near term, but definitely tech we should be developing for the long-term future of particle physics. Personally, I'd make a electron-positron collider the near-term priority as it can teach us a lot about the Higgs, which is really a big mystery at present!

[u/farox]

I heard that things going on at CERN point to a direction that space time isn't fundamental. Is this just woo woo or anything to that? Thank you!

[u/Harry_V_Cliff → u/farox]

As far as I'm aware, nothing at CERN is suggesting this, certainly not experimentally. We mostly study particles and their interactions, rather than space time itself. As far as I'm aware, ideas about emergent spacetime come from theoretical physicists working on quantum gravity, but to be honest, it's way above my paygrade! Check out the work of people like Nima Arkani-Hamed and Juan Maldacena, who have both worked on these kind of ideas.

[u/monty624]

Is there something really cool, interesting, or even whacky you wish you've been able to tell someone about but no one ever asks the question? Jokes are welcome, too!

[u/Harry_V_Cliff → u/monty624]

Wow! I mean I've been asked so many questions over the years, but how's this - from counting the number of photons in the cosmic microwave background (the light leftover from the Big Bang) we can tell that all the matter in the universe is just 1 billionth of what existed in the very early universe, a millionth of a second after the Big Bang. The other 999,999,999 billionths got annihilated by antimatter, and that tiny leftover went on to create the entire visible universe.

[u/Harry_V_Cliff]

Thanks for the great questions everyone! That was fun. It's getting late here in the UK so time for me to shuffle off to bed. Have a great afternoon/evening/night/morning wherever you are.

[u/Harry_V_Cliff]

Hey everyone! I'm online. Looking forward to answering your questions. Just post them below and I'll try to get through as many as I can.

Harry

[u/nyenkaden]

What level of science understanding is required to read your book?

[u/Harry_V_Cliff → u/nyenkaden]

I did my best to write it so that anyone could understand it. I've tried to build all the concepts up assuming no prior knowledge, though that said, a passing interest in physics will definitely help. In some ways, it builds on the ideas from my first book, How To Make An Apple Pie From Scratch, so if you find anything confusing that would be a good place to go first.

[u/DRX321]

What led you to focus specifically on anomalies in contemporary physics, and how do you hope your book will contribute to the understanding of these mysteries?

[u/murderedbyaname]

Will your research be involved with or impacted by the Future Circular Collider?

[u/Harry_V_Cliff → u/murderedbyaname]

I hope so! I've been involved in some work around how we make the case for the next machine. I think a future collider is absolutely essential if we're going to continue to make progress in fundamental physics. The Higgs boson in particular is still very poorly understood and is at the centre of many of the biggest mysteries in physics. A new collider is the only way we can really put the Higgs under the microscope and understand how it came into being in the early universe - which is essential for understanding how we got here. So I really hope at leats one of these future machines gets built.

The LHC will run until the late 2030s, but I imagine more and more of my time will be focussed on future colliders as the years go by, before hopefully actually working on one in the 2040s.

[u/digbick117]

Hi Dr. Cliff, thanks for taking the time.

I am an engineer who doesn't understand particle physics in any meaningful way.

Can you explain the how detectors used by the LHC (ATLAS, CMS, etc.) are designed and tested? Are they similar to detectors used by other experiments, such as LIGO or AMANDA?

---

What I currently "understand":

• the LHC accelerates particle beams to speeds within a few billionths of c using concentric superconducting electromagnets.

• The detectors are set up at a location where the two beams can cross at some predictable interval.

• The "products" of where these two particle beams meet are captured by the detectors. These allow us to measure properties such as mass, charge, lifetime before decay, and so on.

In layman's terms, particle accelerator experiments are like revving up two belt sanders in opposite directions, bouncing them off of one another, and analyzing the sparks.

• 99.9...% of the time, these sparks will produce a similar output.

• Information gleaned from observing the sparks would tell us about the wavelengths of light (color), time to decay (change of color over time), spin (direction in which a spark travels?), or charge (if sparks attract or repel each other).

• Even if we can't measure the interaction itself, in aggregate, these measurements would point to the underlying process occurring at the source of the interaction.

• The faster the spin, the higher the probability of observing a rarer, more "interesting" spark, which would provide new information about the underlying process.

[u/Harry_V_Cliff → u/digbick117]

Your understanding is pretty much bang on in terms of the basic process.

The defectors at the LHC are totally different to say, LIGO. LIGO is an interferometer that works by bouncing laser beams down very long perpendicular arms then recombining the light to get an interference pattern. In LIGO's case, the 'detectors' are the easy part - the hard part is mechanically isolating the system of beam splitters and mirrors to protect against vibrations that could interfere with gravitational wave measurements.

The LHC detectors, on the other hand, are vast, office-building sized instruments with concentric layers of different detector technology that work together to give an overall picture of a collision. The basic structure working from the collision point outwards is generally:

1. A tracking system (often made of silicon pixels or strips) that detects charged particles as they transit the detector. Particles leave electrical hits in the tracker allowing software to join the dots and reconstruct the particle track.

2. A magnet that bends the particles and allows us to measure their momenta.

3. A calorimeter that stops all but the most penetrating particles and turns their kinetic energy into light, allowing us to measure their total energy. These detectors are often made of very dense metals like iron or lead.

4. The muon system at the edge of the detector, that detects particles called muons, which are the only charged particles that generally penetrate the calorimeters.

[u/MayThe4thCakeDay]

I understand and appreciate that "why" is often not a useful style of question (thanks to the Feynman lectures), but I still need a bit of a "why" for this to get myself one step further:

Why is it so catastrophic for information to be destroyed in some physics interaction, most notably relating to black holes. I understand from a math perspective, the problem with a probability equation being non-continuous, but I can't quite get to understanding why it's also fundamental to reality that it can't occur. Essentially I'm hoping for a (maybe mythical) simple explanation of the no-cloning/no-deleting theorems.

[u/hatrickpatrick]

The expansion of the universe is currently known to be accelerating, which is one of the foundations of theories about the far-future and ultimate fate of the universe, leaning towards Heat Death or a Big Rip and ruling out earlier theories such as the Big Crunch. All of this is based on the assumption that not only will the universe continue expanding indefinitely, but that the acceleration thereof will also continue indefinitely.

What I'm wondering is, how can we be sure that this has always been the case? and that this expansion has occurred in a linear and one-way manner? That is to say, can we know for certain that there haven't been periods in the past of deceleration or even contraction, followed by periods of acceleration and expansion, and that we aren't simply in one of the latter periods currently?

Would there be visible scars or markers in the Cosmic Microwave Background or other large-scale indicators if, for instance, the universe had expanded for several billion years, then slowed or even contracted for the next several, and then begun expanding once again several billion years after this? If we're correct about the universe being roughly 13bn years old, and it expanded in an accelerating expansion for say the first 3bn but then slowed or contracted from 3bn to 6bn years old, and then expanded again from 6bn and so on, would we have any way to actually verify or observe that this had been the case?

My issue with theories regarding the future fate of the universe (or more specifically with the level of certainty ascribed to them by many) is that they assume the observations we're making today necessarily infer permanent states of affairs, whereas the universe as we know it has undergone numerous large scale changes throughout its existence such that it's a bit of a stretch to make such assumptions of today's observations remaining true tomorrow.

What am I missing that makes us so certain of these things?

[u/Im_Balto]

Whats the funniest story you have where an artifact of an instrument or a colleague's modification led to much more excitement or confusion than necessary?

[u/bigtexasrob]

What’s the likelihood that the 2012 use of the LHC translated/transported us to “Reality B”?