evanb

19 ms·

241.
by evanb 4y ago
TORQUE EQUALS R CROSS F!
242.
by evanb 4y ago
The number of SM parameters is not a lot, given the reach of the model, which is literally every physical phenomenon ever observed on Earth with enough detail, but gravity. Thousands of independent experiments, and observational data on a
243.
by evanb 4y ago
"Highly parameterized" meaning O(20) free parameters. It matches thousands upon thousands of detailed precision data points.
244.
by evanb 4y ago
It predicts much more than what has been put in. The SM has 22 free parameters. I agree that if it predicted exactly 22 data points it'd be a pointless encoding of what was put in. But it predicts thousands and thousands of data poi
245.
by evanb 4y ago
"That predicts nothing" is very far from the truth! It predicts almost everything we have ever observed experimentally!
246.
by evanb 4y ago
In Michener's Chesapeake a great deal is repeatedly made of the supply of two things: nails and coins.
247.
by evanb 4y ago
“Emit” usually means as radiation. The photons that take every path are not on-shell. When your refrigerator is open the light you see contains an amplitude of the photon going around Uranus.
248.
by evanb 4y ago
OK, I think I appreciate the issue: “multiverse” is overloaded. When people talk about the many worlds of quantum mechanics, or alternate histories, they’re talking about the terms in the path integral sum. But multiverse can also mean, se
249.
by evanb 4y ago
Agree with your first paragraph and the first half of your second paragraph. But if you listen to Feynman talk about the path integral, he emphasizes that all the paths are real, are in fact critical to describing experimental results, a
250.
by evanb 4y ago
Well, it depends on what you mean by "two systems". If they are described by one Hamiltonian the result is one path integral. In a relativistic quantum field theory, for example, one may describe systems of any number of particl
251.
by evanb 4y ago
> The path integral really shouldn't be taken too literally. It's not reality, it's just an equation. While it's always important to point out that the current paradigm might be overthrown tomorrow, it is ALSO import
252.
by evanb 4y ago
Well it depends on what you mean by "quite a bit of work"! Wick rotate, focus on a finite volume of spacetime, and discretize the spacetime. That's all. The first step changes a difficult-to-sample distribution exp( i S )
253.
by evanb 4y ago
One absolutely astounding aspect of the path integral is that it ascribes amplitudes to trajectories that don't obey the (classical) equations of motion. If you like: the classical paths are at turning points of the action (loss funct
254.
by evanb 4y ago
If we falsified quantum mechanics we might expect some formalisms (Hamiltonian, Lagrangian, path integral, whatever) to continue to work while others don't. So it's perfectly possible to falsify the idea that path integrals do no
255.
by evanb 4y ago
If you have a quantum-mechanical system that you describe by specifying a Hamiltonian, I can always write down an exactly equivalent path integral. A failure of equivalence between these two descriptions would be extremely exciting, as it&
256.
by evanb 4y ago
The path integral is used for computational approaches all the time.
257.
by evanb 4y ago
"Monte Carlo approaches" like lattice QCD do use the path integral directly!
258.
by evanb 4y ago
> The only official flag for Northern Ireland is the Union Flag, the flag of the United Kingdom; there is no official local flag that represents only Northern Ireland. The flying of various flags in Northern Ireland is a significant sec
259.
by evanb 4y ago
Time translation symmetry yields energy conservation; time reversal is a discrete symmetry and does not.
260.
by evanb 4y ago
In fact this can also be understood "just" as a simple change of variables in either Newton's law (as you have shown) or Einsteins' field equations, to dimensionless quantities!
261.
by evanb 4y ago
This article commits the most annoying [to me] error in financial reporting: it compares a debt [rupees] with GDP [rupees per year], comparing two quantities with different units. Compare Adani's debts to all the wealth in India, for
262.
by evanb 4y ago
"Critical" has a precise meaning in these kinds of systems; it essentially means when correlation lengths diverge (or, with a finite brain, become the size of the whole). In physical systems this happens at 2nd order phase transi
263.
by evanb 4y ago
What is it per mile? Wouldn't surprise me at all if autonomous vehicles made up less than 1/37th of all driven miles (or driven hours). So, even if there is a double standard, the number you quote doesn't make it obvious.
264.
by evanb 4y ago
I was a postdoc at Lawrence Livermore National Lab (LLNL) from 2013-2016, working on computational particle physics (lattice QCD). Pay was extremely high (for a postdoc) but not high by comparison to other bay-area employers. What you get
265.
by evanb 4y ago
My collaborators and I settled on Blaze for the linear algebra backend of a small physics library. We ultimately regretted it as there was no support or roadmap to GPU support.
266.
by evanb 4y ago
I tend to play with the River and Inns and Cathedrals. We also play with a house rule that you have a hand of 3 tiles to alleviate some of the draw-dependence of whether a strategy is successful or not.
267.
by evanb 4y ago
I've never met at adjunct administrator, and that tells me all I need to know.
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by evanb 4y ago
The linked tweet points to October 2020. That's before the election and long before Biden was installed; the requests were not from the government.
269.
by evanb 4y ago
My mom has told me that the rat problem in NYC used to be a lot less. The rat population exploded when buildings were no longer allowed to incinerate their garbage for air-quality considerations.
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by evanb 4y ago
crickgit, mosgito, gnit, ...

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