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Gauss's Principle of Least Constraint (2017) (nakkiran.org)
90 points by vectorrain on Jan 8, 2019 | hide | past | favorite | 12 comments



This reminds me of the rule in particle physics: Anything not forbidden is mandatory.

i.e. There are no events (interactions) that could happen, but just don't.

https://en.wikipedia.org/wiki/Totalitarian_principle


Very cool, I wonder if this applies to interactions that "can't" happen in our current universe? I have read in the early big bang, forces "combined" together, like the electric and nuclear weak force. Could a electron interact with a neutrino for example?


> Could a electron interact with a neutrino for example

Could, and it does happen. Observed about sixteen years after the first direct observation of a neutrino interaction:

https://www.worldscientific.com/doi/abs/10.1142/S02177323930... (PDF directly at https://cds.cern.ch/record/248487/files/ppe-93-065.pdf )

More modernly and generally, neutrino-lepton scatterings are part of the weak interactions in the Standard Model: https://www2.ph.ed.ac.uk/~playfer/PPlect11.pdf

(and of course there is an even weaker gravitational interaction between leptons and neutrinos that we cannot demonstrate directly with current technology)


Landau had a similar formulation but about symmetries - what isn’t forbidden is permitted.


Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth. - Arthur Conan Doyle


That is such a useless quote.

I throw a ball to my friend. The ball doesn't turn in to chocolate and fly away etc.

What happened to the ball? Caught or not?

To take the quote literally, neither. The rarest bird on earth capable of catching the ball swoops down and lifts it away while I win the lottery and so on.


Disclaimer: I am absolutely not a physicist, and so the following might be quite incorrect.

It seems that your interpretation of the rule is actually an assertion of the many world's interpretation of quantum mechanics. If you don't mention that caveat then you're actually asserting determinism in this particular universe.


No, GP means (in the second line) that because nature (and particle colliders) perform so many "experiments", even very rare outcomes will be spotted eventually.

It's a statistical statement about many particles (or field-values in a sufficiently large spacetime(-region)-filling set of quantum fields), not an interpretational statement about a single particle.


Then I don't understand this, from the article that was cited:

In the many-worlds interpretation of quantum mechanics, the principle has a more literal meaning: that every possibility at every interaction which is not forbidden by such a conservation law will actually happen (in some branch of the wavefunction).


The key there is "at every interaction".

Consider lots and lots of interactions.

In what I was explaining, you have highly probable outcomes being observed a lot, and very low probability outcomes being observed rarely.

In what you are reading on wikipedia, you have at each and every one of those lots and lots of interactions a "splitting" into a different world per possible outcome. That's MWI's core content, and it seems to help some people develop intuitions about outcomes of experiments where small numbers of interactions (perhaps even just one, especially where it involves entanglement) determine much larger systems.


By looking at the references, the author may not be aware of the use of Gauss' principle in molecular dynamics, see e.g. Ch. 3.1 in Evans, Morriss: Statistical mechanics of nonequilibrium liquids. (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.296...)


their double pendulum applet has a bug that occasionally causes it to gain energy.




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