No.
No, no, no.
I was tempted to blame the science journalists for the incredibly wrong articles about this, but in fact it seems entirely the fault of the scientists involved.
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POSTED BY Matt Strassler
ON June 11, 2022
Here’s a tip. If you read an argument either for or against a successor to the Large Hadron Collider (LHC) in which the words “string theory” or “string theorists” form a central part of the argument, then you can conclude that the author (a) doesn’t understand the science of particle physics, and (b) has an absurd caricature in mind concerning the community of high energy physicists. String theory and string theorists have nothing to do with whether such a collider should or should not be built.
Such an article has appeared on Big Think. It’s written by a certain Thomas Hartsfield. My impression, from his writing and from what I can find online, is that most of what he knows about particle physics comes from reading people like Ethan Siegel and Sabine Hossenfelder. I think Dr. Hartsfield would have done better to leave the argument to them.
An Army Made of Straw
Dr. Hartsfield’s article sets up one straw person after another.
- The “100 billion” cost is just the first. (No one is going to propose, much less build, a machine that costs 100 billion in today’s dollars.)
- It refers to “string theorists” as though they form the core of high-energy theoretical physics; you’d think that everyone who does theoretical particle physics is a slavish, mindless believer in the string theory god and its demigod assistant, supersymmetry. (Many theoretical particle physicists don’t work on either one, and very few ever do string theory. Among those who do some supersymmetry research, it’s often just one in a wide variety of topics that they study. Supersymmetry zealots do exist, but they aren’t as central to the field as some would like you to believe.)
- It makes loud but tired claims, such as “A giant particle collider cannot truly test supersymmetry, which can evolve to fit nearly anything.” (Is this supposed to be shocking? It’s obvious to any expert. The same is true of dark matter, the origin of neutrino masses, and a whole host of other topics. Its not unusual for an idea to come with a parameter which can be made extremely small. Such an idea can be discovered, or made obsolete by other discoveries, but excluding it may take centuries. In fact this is pretty typical; so deal with it!)
- “$100 billion could fund (quite literally) 100,000 smaller physics experiments.” (Aside from the fact that this plays sleight-of-hand, mixing future dollars with present dollars, the argument is crude. When the Superconducting Supercollider was cancelled, did the money that was saved flow into thousands of physics experiments, or other scientific experiments? No. Congress sent it all over the place.)
- And then it concludes with my favorite, a true laugher: “The only good argument for the [machine] might be employment for smart people. And for string theorists.” (Honestly, employment for string theorists!?! What bu… rubbish. It might have been a good idea to do some research into how funding actually works in the field, before saying something so patently silly.)
Meanwhile, the article never once mentions the particle physics experimentalists and accelerator physicists. Remember them? The ones who actually build and run these machines, and actually discover things? The ones without whom the whole enterprise is all just math?
Although they mostly don’t appear in the article, there are strong arguments both for and against building such a machine; see below. Keep in mind, though, that any decision is still years off, and we may have quite a different perspective by the time we get to that point, depending on whether discoveries are made at the LHC or at other experimental facilities. No one actually needs to be making this decision at the moment, so I’m not sure why Dr. Hartsfield feels it’s so crucial to take an indefensible position now.
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POSTED BY Matt Strassler
ON June 9, 2022
Why have I been debunking Professor Muller’s claim that “the Sun orbits the Earth just as much as the Earth orbits the Sun”? Understanding why he’s wrong makes it easier to appreciate some central but subtle concepts in general relativity, Einstein’s conception of gravity.
What I want to do today is look at the notion of tides. Tides take on more importance in general relativity than in Newton’s theory of gravity. They can tell you which objects are gravitationally dominant in a coordinate-independent way.
A few posts ago, some of the commenters attempting to refute Professor Muller focused on showing the Sun is gravitationally dominant over the Earth. They were on a correct path! But nobody quite completed the argument, so I’ll do it here.
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POSTED BY Matt Strassler
ON June 7, 2022
Advanced particle physics today:
Another page completed on the explanation of the “triplet model,” (a classic and simple variation on the Standard Model of particle physics, in which the W boson mass can be raised slightly relative to Standard Model predictions without affecting other current experiments.) The math required is still pre-university level, though complex numbers are now becoming important.
The first, second and third webpages in this series provided a self-contained introduction that concluded with a full cartoon of the triplet model. On our way to the full SU(2)xU(1) Standard Model, the fourth webpage gave a preliminary explanation of what SU(2) and U(1) are.
Today, the fifth page explains how a U(1)xU(1) Standard Model-like theory would work… and why the photon comes out massless in such a theory. Comments welcome!
POSTED BY Matt Strassler
ON June 6, 2022
Particle physics news today...
I’ve been spending my mornings this week at the 11th Long-Lived Particle Workshop, a Zoom-based gathering of experts on the subject. A “long-lived particle” (LLP), in this context, is either
- a detectable particle that might exist forever, or
- a particle that, after traveling a macroscopic, measurable distance — something between 0.1 millimeters and 100 meters — decays to detectable particles
Many Standard Model particles are in these classes (e.g. electrons and protons in the first category, charged pions and bottom quarks in the second).
But the focus of the workshop, naturally, is on looking for new ones… especially ones that can be created at current and future particle accelerators like the Large Hadron Collider (LHC).
Back in the late 1990s, when many theorists were thinking about these issues carefully, the designs of the LHC’s detectors — specifically ATLAS, CMS and LHCb — were already mostly set. These detectors can certainly observe LLPs, but many design choices in both hardware and software initially made searching for signs of LLPs very challenging. In particular, the trigger systems and the techniques used to interpret and store the data were significant obstructions, and those of us interested in the subject had to constantly deal with awkward work-arounds. (Here’s an example of one of the challenges... an older article, so it leaves out many recent developments, but the ideas are still relevant.)
Additionally, this type of physics was widely seen as exotic and unmotivated at the beginning of the LHC run, so only a small handful of specialists focused on these phenomena in the first few years (2010-2014ish). As a result, searches for LLPs were woefully limited at first, and the possibility of missing a new phenomenon remained high.
More recently, though, this has changed. Perhaps this is because of an increased appreciation that LLPs are a common prediction in theories of dark matter (as well as other contexts). The number of new searches, new techniques, and entirely new proposed experiments has ballooned, as has the number of people participating. Many of the LLP-related problems with the LHC detectors have been solved or mitigated. This makes this year’s workshop, in my opinion, the most exciting one so far. All sorts of possibilities that aficionados could only dream of fifteen years ago are becoming a reality. I’ll try to find time to explore just a few of them in future posts.
But before we get to that, there’s an interesting excess in one of the latest measurements… more on that next time.
POSTED BY Matt Strassler
ON June 2, 2022
Could you, merely by changing coordinates, argue that the Sun gravitationally orbits the Earth? And could Einstein’s theory of gravity, which works equally well in all coordinate systems, allow you to do that?
Despite some claims to the contrary — that all Copernicus really did was choose better coordinates than the ancient Greek astronomers — the answer is: No Way.
How badly does the Sun’s path, nearly circular in Earth-centered (geocentric) coordinates, violate the Earth’s version of Kepler’s law? (Kepler’s third law is the relation T=R3/2 between the period T of a gravitational orbit and the distance R, which is half the long axis of the ellipse that the orbit forms.) Since the Moon takes about a month to orbit the Earth, and the Sun is about 400 = 202 times further from Earth than the Moon, the period of the Sun would be 4003/2 = 8000 times longer than the Moon’s, i.e. about 600 years, not 1 year.
But is this statement coordinate-independent? Can it serve to prove, even in Einstein’s theory, that the Earth orbits the Sun and the Sun does not orbit the Earth? Yes, it is, and yes, it does. That’s what I claimed last time, and will argue more carefully today.
Of course the question of “Does X orbit Y?” is already complicated in Newtonian gravity. There are many situations in which the question could be ambiguous (as when X and Y have almost equal mass), or when they form part of a cluster of large mass made from many objects of small mass (as with stars within a galaxy.) But this kind of ambiguity is not what’s in question here. Professor Muller of the University of California Berkeley claimed that what is uncomplicated in Newtonian gravity is ambiguous in Einsteinian gravity. And we’ll see now that this is false.
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POSTED BY Matt Strassler
ON June 1, 2022
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