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evanb

5,032 karma · joined February 8, 2012

I am a professor of physics at the University of the Virgin Islands [0].

I was previously a staff scientist at Forschungszentrum Jülich [1] and a postdoc at Lawrence Livermore National Lab [2] doing computational nuclear [3] and atomic physics on absolutely gargantuan computers.

[0] https://en.wikipedia.org/wiki/University_of_the_Virgin_Islands

[1] https://en.wikipedia.org/wiki/Forschungszentrum_J%C3%BClich

[2] https://en.wikipedia.org/wiki/Lawrence_Livermore_National_Laboratory

[3] https://en.wikipedia.org/wiki/Lattice_QCD

submissionscomments
evanb··on Show HN: What if the speed of light was 5 km/h?
You can adjust the speed of light and hold the fine structure constant (and all other dimensionless parameters) fixed by adjusting some of the other dimensionful parameters.
evanb··on Biggest dark matter detector spots a single weird particle
But you could collect this data point by chance in a bigger or smaller detector.

What I was addressing was whether this detector is big enough for a reliable discovery. In that case what you really want to constrain is the rate, such-and-such events per kilogram of xenon per year (the per-kilogram-of-xenon can be traded for a per-liter rate given the density of the xenon).

evanb··on Biggest dark matter detector spots a single weird particle
No one knows if it’s big enough—-that depends on the properties of dark matter and its interaction with xenon.
evanb··on Biggest dark matter detector spots a single weird particle
Whether or not they've "seen" 3x more events is a little bit of a tricky question, because while they may have captured 3x the data exposure (see sibling comments) experiments often operate blinded to the data. They can develop their analysis scripts, play out various different scenarios via Monte Carlo simulation, and get their whole pipeline working without the bias of actually seeing how each change in algorithm alters the outcome for the real data.

Then, at some point, they freeze their pipeline, "open the box", run the analysis on the real data, and report what they find. But they can only "open the box" once per exposure, after that you can worry that human bias can creep in.

evanb··on Biggest dark matter detector spots a single weird particle
Maybe there are even dark scientists trying to explain the missing 15% of the universe! One such scientist, easily pegged as a kook, suggests a model with SU(3) x SU(2) x U(1) gauge symmetry, with one sector spontaneously broken by a scalar field, and three flavors of fermions to allow for enough CP violation and masses spanning 10 or 11 orders of magnitude.
evanb··on Biggest dark matter detector spots a single weird particle
The total cost of this experiment may be a lot less than you expect. I'd encourage you to make a guess as to what you think it could cost the US taxpayer and then check what the Department of Energy contributed [1].

The LZ collaboration is going to run their machine until at least 2030. They have almost no hope of making a meaningfully larger detector, no will you hear them suggest one. Their detector is already designed at such a scale that it contains a substantial fraction of all the needed xenon isotope available on Earth.

[1] https://news.wisc.edu/dark-matter-detection-receives-10-ton-...

evanb··on Biggest dark matter detector spots a single weird particle
Yeah but no matter how hard I look I never seem to be able to read anyone else's email. Maybe OpenAI's upcoming models can help me find those references.
evanb··on Longest Straight Line Paths on Water or Land on the Earth (2018)
They aren't, as clicking through on a sibling's link demonstrates. Moreover, Senegal is nowhere near Cape Town.
evanb··on Black hole singularity is a surface not a point
Both / they're related. More mass gravitates more.

Suppose you had an infinite universe that was filled with a cool gas of low uniform density. Then the gravitational field at any particular point would be 0, by Gauss' law.

But, if you wait a brief moment the gas will not stay uniform, because each atom of the gas will have some velocity. You'll observe fluctuations: places with small over-density and small under-density (compared to the average). The places with over-density will gravitate more than the average and places with under-density will gravitate less, and gravity will cause the gas to clump.

Wait a few billion years and some places will have amalgamated whole galaxies' worth of matter around them and other places will be empty.

evanb··on Black hole singularity is a surface not a point
No, sorry, the singular surface in a Schwarzschild spacetime is not the event horizon. Nothing particularly interesting (from the GR point of view) happens at the event horizon.
evanb··on Black hole singularity is a surface not a point
Yes it is?
evanb··on Olo (Color)
This page, which predates the recent olo work, calls it psychedelic aquamarine. https://jila.colorado.edu/~ajsh/colour/primary.html
evanb··on The only road in London where you have to drive on the right
Also the whole of the Virgin Islands!
evanb··on ArXiv's Next Chapter
I’m RSS-subscribed to a few sections relevant to my research.
evanb··on Alan Greenspan has died
The gilded age’s wealthy were also the winners of winner-take-all technologies such as the railroad and oil.
evanb··on Introducing Boron Buckyballs: Theory that B80 cages can’t be made is disproved
Given the energy scales involved, it's more likely that the issue lies with the approximations DFT makes to quantum mechanics, rather than the approximations quantum mechanics makes to quantum field theory.
evanb··on Ask HN: What was your "oh shit" moment with GenAI?
I'm a professor of physics; my research area is computational quantum field theory. I was beginning a new approach for a certain kind of model. I know the model has not been simulated before (a collaborator has just constructed it for the first time using in-field knowledge developed in the last year).

I've been steadily more impressed, but the real startling moment was earlier this week, I could show that in a particular operation I had a bug (some identity wasn't satisfied) but I couldn't understand why. In one try Claude Code grokked my code, explained the problem to me (there were some dimension-dependent minus signs that needed to be computed), and fixed it.

evanb··on Apartment Birds Heard Recently
The description is at https://theodore.net/projects/AvianVisitors/
evanb··on Quarkdown – Markdown with Superpowers
By the Standard Model of Physics Software you can edit Quarkdown in Atom to get Quarkup and change your Neutron Mail to Proton Mail, but it only works if you type with your left hand and create an Electron app and an anti-Neutrinos AI blogpost.
evanb··on Introduction to spherical harmonics for graphics programmers
In case the author is reading this, if you're going to introduce the complex-valued harmonics you should be careful to put the complex conjugate in the inner product

    <f, g> = ∫ f(ω)^* g(ω) dω
which does match the corresponding linear-algebra inner product if the vectors are over the complex numbers

    p . q = Σ_i p^*_i q_i
which guarantees that p.p ≥ 0 even for complex p (and does not change the only-real case).
evanb··on Tofolli gates are all you need
Hmm. As a physicist my intuition is that information-preserving transformations are unitary (unitary transformations are 1-to-1). If a compression algorithm is going to yield a bit string (the zip file, for example) shorter than the original it can't be 1-to-1. So it must yield the zip file and some other stuff to make up for the space saved by the compression.
evanb··on Tofolli gates are all you need
You could package all your data into a zip using this language but you would also have a worthless stretch of memory seemingly filled with noise / things you’re not interested in.
evanb··on John Coltrane illustrates the mathematics of jazz
I don't remember much about music theory but I know enough about symmetry to know that there's a mistake in the diagram at 9 o'clock.
evanb··on Isseven
Bug report: I tried 6.999999̅ and got false. So there's some nonstandard model of the reals being leveraged here.
evanb··on Prompt Injecting Contributing.md
Of course that's true, but (in the context of the GP) code's bespoke artisanal nature is not the one most people value.
evanb··on Prompt Injecting Contributing.md
I have always anthropomorphized my computer as me to some extent. "I sent an email." "I browsed the web." Did I? Or did my computer do those things at my behest?
evanb··on Why Mathematica does not simplify sinh(arccosh(x))
As a term-rewriting system the rule x-x=0 presumably won’t be in Simplify, it’ll be inside - (or Plus, actually). Instead I’d expect there to be strategies. Pick a strategy using a heuristic, push evaluation as far as it’ll go, pick a strategy, etc. But a lot of the work will be normal evaluation, not Simplify-specific.
evanb··on Rethinking Syntax: Binding by Adjacency
Mathematica has Infix [0], which expresses the adjacency with a ~ (because Mathematica reserves pure blankspace for multiplication). But it works fine to do eg. `"hello"~StringJoin~" world"`; I was always surprised we could only have the predefined operators in many other languages and we couldn't define our own.

This seems like a great attempt. I would be worried about how much parsing and backtracking might be required to infer the infix precedence in a totally general system (like garden-path sentences[1]) or actually ambiguous parse trees (which is cured by adopting some rule like right precedence and parens, but what rule you pick makes some 'natural language' constructions work over others).

[0] https://reference.wolfram.com/language/ref/Infix.html

[1] https://en.wikipedia.org/wiki/Garden-path_sentence

evanb··on Woxi: Wolfram Mathematica Reimplementation in Rust
Mathematica has symbolic and infinite-precision addition, so you can't automatically take advantage of obvious compiled code.
evanb··on Woxi: Wolfram Mathematica Reimplementation in Rust
> The initial focus is to implement a subset of the Wolfram Language so that it can be used for CLI scripting and notebooks.

If you have Mathematica installed you can write CLI scripts and notebooks.

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