Nostr notes by David Quintero

The book of course deals with CCC (Conformal Cyclic Cosmology), ...

2026-10-25T14:01:38Z

In reply to nevent1q…mqf0
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The book of course deals with CCC (Conformal Cyclic Cosmology), developed by Penrose. The key idea is that a universe heavily expanded under dark energy turns out to be so homogeneous as the very first moments after the hot and dense Bing Bang. This equivalence is named conformal, meaning that the shapes are preserved. I can more or less see the idea but I don't understand how the universe would go from the mathematical duality to the physical realisation.

Anyway, the idea needs 2 things that Afshordi says the community is finding difficult to accept. First, in the hyper faraway future all the matter should have been converted into radiation. This is problematic because some particles are considered forever stable, like the electron. But perhaps the last word on particle physics hasn't been uttered.

But the second necessity is even worse. CCC needs to break the unitarity of quantum mechanics, so the information is lost from one cycle to the other. I wonder if all cyclical cosmologies need this. This means that General Relativity > Quantum Mechanics. This is a minority position, although it's not that Penrose is alone either.

I'm reading "Battle of the Big Bang", by Afshordi and ...

2026-10-25T00:36:24Z

I'm reading "Battle of the Big Bang", by Afshordi and Halper. It's about before the Big Bang, and I can tell you there're *many* theories proposed.

Nowadays, many cosmologists think the universe has existed forever, whether through eternal inflation, cyclic cosmologies with a bounce or other variant. (Fred Hoyle must be turning in his grave).

Indeed, an important part of the book is about inflation. The best definition of the current status of inflation is given by the applied cosmologist (and a world expert on the CMB) Douglas Scott: "something like inflation is something like proven".😅

no, not really. They explain the experiment and the result. I ...

2026-10-18T22:22:13Z

In reply to nevent1q…2pvq
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no, not really. They explain the experiment and the result. I think they do it well. They don't speculate with the possible nature of the particle. (I have heard speculations about a possible "Higgsino", but not from this video).

About the recent recoil of a xenon atom that could, could be a ...

2026-10-18T21:26:03Z

About the recent recoil of a xenon atom that could, could be a signal of dark matter.

https://youtube.com/watch?v=N86IOd6nYvo&is=OEegx4qssLqhGgU9

wishing you the best, and thanks for the explanation.

2026-10-12T15:18:31Z

In reply to nevent1q…p6v6
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wishing you the best, and thanks for the explanation.

I remember Wang's Carpets, and also Diaspora, as some of my ...

2026-10-08T11:12:10Z

In reply to nevent1q…86rj
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I remember Wang's Carpets, and also Diaspora, as some of my favourites short sf stories ever, although I don't remember that detail exactly!😅 I should reread them.

just by chance I found this. So, now there're doubts that ...

2026-10-07T11:11:49Z

In reply to nevent1q…nzzw
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just by chance I found this. So, now there're doubts that neutrinos can be used for communication in the way previously proposed: https://news.mit.edu/2026/new-research-shows-neutrino-laser-impossible-0902

It has been suggested that advanced civilisations could use ...

2026-10-06T11:08:45Z

In reply to nevent1q…y6ex
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It has been suggested that advanced civilisations could use neutrinos for communication, but I wonder how these civilisations could eschew the faint interaction of neutrinos with matter to send messages with enough complexity.

This year's Nobel Prize in Physics has been somewhat ...

2026-10-06T11:03:29Z

This year's Nobel Prize in Physics has been somewhat unexpected. As far as I remember, Francis Halzen wasn't among the favourites. Of course, I'm not saying he doesn't deserve it, just that it's a kind of surprise.

the fact that after n=8 everything breaks up reminds me a bit of ...

2026-09-19T10:27:24Z

In reply to nevent1q…3fvr
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the fact that after n=8 everything breaks up reminds me a bit of the Hurwitz's theorem for normed division algebras, that with n=8 you get the octonions and that's the last one. But probably not related at all.

thank you very much! Minor comment: it's "laurisilva" ...

2026-09-14T10:17:14Z

In reply to nevent1q…evau
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thank you very much! Minor comment: it's "laurisilva" instead of "laurasilva".

curiously, the Savage Islands don't appear explicitly ...

2026-09-13T13:28:58Z

In reply to nevent1q…rq28
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curiously, the Savage Islands don't appear explicitly mentioned in the Macaronesia article in English, although they appear draw in purple over the Canary Islands. In the article in Spanish they are mentioned. 🤔

😅😅 yeah, not a lot of people know about Macaronesia. ...

2026-09-13T12:44:07Z

In reply to nevent1q…nsch
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😅😅 yeah, not a lot of people know about Macaronesia. It's a set of archipelagos that include the Canary Islands, Cape Verde, Madeira, Savage Islands and Azores. I don't know about the relation of the name Laurasia and laurisilva, but it seems a reasonable hypothesis!

I love them, too. Ferns are part of the laurel forests ...

2026-09-13T10:49:51Z

In reply to nevent1q…68da
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I love them, too. Ferns are part of the laurel forests (laurisilva), typical from the Macaronesia region, and they were present in the Gondwana supercontinent.

thanks for sharing. These two guys really deserve recognition. ...

2026-09-10T12:31:51Z

In reply to nevent1q…glqa
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thanks for sharing. These two guys really deserve recognition. They also show that there's much more in Spain than football. Science is not very popular here, nor well paid. These guys are worth a lot.

but is time fundamental or emergent?

2026-09-03T18:03:46Z

In reply to nevent1q…5ppd
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but is time fundamental or emergent?

there's a hard ethical question here: is it morally ...

2026-08-26T11:50:12Z

In reply to nevent1q…xvhr
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there's a hard ethical question here: is it morally justified/ethic for a young mathematician to use AI if it's going to be great for his/her career, but if at the same time is supporting these companies and damaging the environment?

(It can be applied to other people, too, not only mathematicians).

Marco Gualtieri (npub1juz…njnt)

interested in your opinion once you finish it.

2026-08-23T15:27:35Z

In reply to nevent1q…k530
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interested in your opinion once you finish it.

thank you very much 👍👍

2026-08-16T16:05:03Z

In reply to nevent1q…s0t0
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thank you very much 👍👍

could you please further explain or point out to a resource about ...

2026-08-16T15:17:57Z

In reply to nevent1q…973f
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could you please further explain or point out to a resource about the "true by chance" and its relation to Gregory Chaitin?

interesting! It certainly makes sense. It makes me wonder about ...

2026-08-13T23:11:05Z

In reply to nevent1q…hrp9
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interesting! It certainly makes sense. It makes me wonder about an "easy" example: proposing marriage.

The accept or decline decision would be determined by *many* factors. How can someone be sure that the emergent behaviour of all that factors leads always to accept (or to decline)? Perhaps those cases exist, and there would be no branching, if I'm right. But those cases seem very unusual.

The physicist and writer Clifford Pickover said once that you ...

2026-08-13T22:31:56Z

The physicist and writer Clifford Pickover said once that you should never suffer for love because, if the many worlds interpretation of QM is correct, there's a branch of the multiverse where you're with that person. This consolation is for you...

I loved his "White Noise". Do you recommend this one?

2026-07-30T09:50:57Z

In reply to nevent1q…hhft
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I loved his "White Noise". Do you recommend this one?

200 $ per month?! Perhaps that could be possible for some ...

2026-07-24T14:15:05Z

In reply to nevent1q…338u
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200 $ per month?! Perhaps that could be possible for some graduate students in the US, Germany, UK and a few other countries, but it would rule out most students from South and Central America, Southern and Eastern Europe, not to mention Africa or many other parts of the world.

wishing that you can recover asap.

2026-07-23T09:12:45Z

In reply to nevent1q…zhtx
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wishing that you can recover asap.

oh, sorry for that. I hope you can recover soon. Hugs🫂.

2026-07-14T10:32:10Z

In reply to nevent1q…3lw9
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oh, sorry for that. I hope you can recover soon. Hugs🫂.

thanks for your answer! You certainly belong to category of ...

2026-07-11T12:07:28Z

In reply to nevent1q…aelu
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thanks for your answer! You certainly belong to category of people I have admiration for. I also listen to the radio when doing house chores, spoken programs. Indeed, I think that I listen to more podcasts than music, which I guess it's the opposite to most of the people.

Do you know what I would truly like in biographies of the people ...

2026-07-11T10:07:04Z

Do you know what I would truly like in biographies of the people I admire (mostly scientists and writers)? How they managed their house chores. Because, seriously, between working and managing the house a *huge* percentage of my waking time is gone.

TIL: there's a whale "speaking" in the 52 hertz ...

2026-06-03T23:06:25Z

TIL: there's a whale "speaking" in the 52 hertz frequency, where no other whale speaks or can hear. It has been called the "world's loneliest whale". It's argued that it can be a malformed animal or a hybrid, but it has been recorded since the late 1980s and it has been detected along many different places of the Pacific ocean, a sign of a healthy specimen.

In 2010 another simultaneous recording of the 52 hertz song was detected elsewhere, suggesting that even the loneliest whale of the world could have a potential soulmate.

52-hertz whale - Wikipedia
https://en.wikipedia.org/wiki/52-hertz_whale

ah, thanks! I think that to get your full explanation I should ...

2026-05-30T23:41:03Z

In reply to nevent1q…m6nn
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ah, thanks! I think that to get your full explanation I should arrive to the lesson on the density matrix, not there yet. Curiously, I studied QM until QFT, but the density matrix was out of the curriculum.

Something I learnt recently in the online course on quantum ...

2026-05-30T22:33:43Z

Something I learnt recently in the online course on quantum foundations I'm following is that, in the double slit experiment, you can put in one slit a vertical polarizer, in the other an horizontal. You'll get two bands, as expected, since you're measuring.

But you can introduce, after the two slits with polarizers, diagonal polarizers, and you'll get the interference pattern! With the diagonal polarizers you don't know where the photons come from, you lose information, you have "undone" your measurement, so to say.

Curiously, you can explain everything with classical physics: a vertical and horizontal rays of light can't interfere, so two bands on the screen. And the diagonal polarizer allows interference again.

it represents me.

2026-05-25T10:06:53Z

In reply to nevent1q…nmxw
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it represents me.

I'm following an online course where they are going to ...

2026-05-23T23:59:08Z

In reply to nevent1q…5htn
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I'm following an online course where they are going to explain all that, but probably not at the same level as the book.

The MWI has grown in recent years among mostly theoretical physicists, as some surveys have shown. I wonder if Peres would have been more appreciative had he lived longer.

I heard today that Asher Peres, in his famous book on QM, was not ...

2026-05-23T23:19:26Z

I heard today that Asher Peres, in his famous book on QM, was not very appreciative of the many worlds interpretation of QM...

TIL: there's a museum of broken relationships in Zagreb, ...

2026-05-18T07:39:49Z

TIL: there's a museum of broken relationships in Zagreb, Croatia. The two creators had a 4 years love relationship that ended, and decided to store their personal and common objects in a museum. The collection grew fast with donations from many people and their failed relationships.

(Via: Hannah Grace (npub1cu7…4j9j)).

Museum of Broken Relationships - Wikipedia
https://en.wikipedia.org/wiki/Museum_of_Broken_Relationships

The recent list of the 100 best novels of all time by The ...

2026-05-17T14:58:41Z

The recent list of the 100 best novels of all time by The Guardian is so, so, so Anglo-Saxon centered that it can be basically read as a parody.

no worries!

2026-05-14T22:41:39Z

In reply to nevent1q…k02m
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no worries!

ah, ok! I haven't arrived to the part of the supervillain ...

2026-05-14T22:36:28Z

In reply to nevent1q…yf5y
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ah, ok! I haven't arrived to the part of the supervillain yet; now I'm very intrigued.

Murdoch Mysteries is a Canadian TV series set in the last years ...

2026-05-14T22:28:29Z

Murdoch Mysteries is a Canadian TV series set in the last years of the XIXth century. It has a detective that is very interested in science and uses science to solve crimes. The characters are lovable, and it's all surrounded by a steampunk atmosphere. The series is based on a saga of books, has anyone read them?

I'm surprised by this and by the rest of classifications ...

2026-05-10T11:26:07Z

In reply to nevent1q…zt9k
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I'm surprised by this and by the rest of classifications cited in the thread. My library follows the author's name classification, which I think it's an international standard. The bookstores, however, follow a classification by topics.

TIL: the number of atoms outside galaxies is roughly the same of ...

2026-05-08T22:53:01Z

TIL: the number of atoms outside galaxies is roughly the same of atoms inside galaxies. This is because of the long filaments or tendrils that emanate from galaxies and connect with another galaxies.

These filaments are supposed to be like the tracers of dark matter, where the gas (normal atoms) coalesce.

(From Daniel and Kelly's Extraordinary Universe podcast, episode: "Do we live in a super bubble?")

I may cite two: - that the wave particle duality and the ...

2026-05-07T15:32:30Z

In reply to nevent1q…9uxu
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I may cite two:

- that the wave particle duality and the complementary principle are old fashioned ways of talking, that in modern quantum mechanics is preferred to talk about superposition and collapse of the wave function.

- the concept of eusociality, a high level form of sociality, where individuals take care of the offspring of others... Edward O. Wilson says that we humans have a weak form of eusociality (Wikipedia).

"The Royale" is the Star Trek TNG episode where Picard is ...

2026-04-23T22:10:31Z

"The Royale" is the Star Trek TNG episode where Picard is (how not) trying to solve Fermat's Last Theorem. Because in that world, supposedly, the theorem was in the XXIII th century still unsolved.

And there's a book by Arthur C. Clarke where Fermat's original proof is found and it turns to be much more elegant and simpler than Wiles' proof. Even Clarke shows his dislike for the complexity of the proof.

yet using time as imaginary was a key ingredient for the no ...

2026-04-08T07:57:57Z

In reply to nevent1q…eudk
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yet using time as imaginary was a key ingredient for the no boundaries proposal by Hawking and Hartle about the origin of the universe. You know, ideas obey Nietzsche's eternal return.

When my mother was grading exams, she saw the same grammatical ...

2026-02-12T12:27:57Z

When my mother was grading exams, she saw the same grammatical error over and over again, so that at some moment she had to go to the dictionary to check the word because she began to doubt.

That happens to me with LLMs. I'm skeptical, but I receive so much hype, that I began to question myself.

Greg Chaitin on famous physicist John Wheeler asking Gödel about ...

2026-01-27T22:33:58Z

Greg Chaitin on famous physicist John Wheeler asking Gödel about uncertainty: 'Well, one day I was at the Institute for Advanced Study, and I went to Gödel's office, and there was Gödel. I said "Professor Gödel, what connection do you see between your incompleteness theorem and Heisenberg's uncertainty principle?" And Gödel got angry and threw me out of his office!'

Whiteson and Warner tell this in their book. Others say that Gödel just changed the topic of the conversation (which it seems more plausible to me). Anyway, W & W explain that in physics you look for the axioms instead of building from them, which "sidesteps incompleteness". You are constantly adding extra axioms whenever you need them, which is something that is not seen as elegant, mathematically speaking.

that painting definitely has something.

2025-12-31T00:04:15Z

In reply to nevent1q…ln7j
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that painting definitely has something.

Sometimes you don't like a book that is considered a classic ...

2025-12-27T00:04:40Z

Sometimes you don't like a book that is considered a classic or that most people consider good. It may happen. It has even happened to scholars. You approached the book in a neutral way and you didn't like it.

But sometimes you actually *want* to like a book, but you can't! It happened to me with Kim Stanley Robinson Mars trilogy. I really wanted to like it, but I couldn't: overwritten, excessive. I read Red Mars, was able to finish Green Mars skipping many parts and didn't have energy to grab Blue Mars. (I emjoyed a lot KSR Aurora, though).

Has this happened to you and with what book?

Alain Aspect tells that Feynman considered the EPR paradox in his ...

2025-12-18T22:29:50Z

Alain Aspect tells that Feynman considered the EPR paradox in his famous "Lectures on Physics". Feynman said that the EPR could be explained as the case of the interference of just one particle was explained. But not.

Decades later, Feynman changed his mind, as he stated in a famous article, pioneer in quantum information. And when Aspect gave a conference about EPR in Caltech in 1984, an old Feynman attended to the conference.

Rainer Maria Rilke, the great German poet, said that the purpose ...

2025-12-16T12:12:37Z

Rainer Maria Rilke, the great German poet, said that the purpose of life was being defeated by greater and greater things.

But I have been defeated just trying to hide the warning messages in a jupyter notebook...

Regarding "QFT for the Gifted Amateur" explains a little ...

2025-12-10T15:45:53Z

In reply to nevent1q…fwzq
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Regarding "QFT for the Gifted Amateur" explains a little bit its motivation, but I don't remember it exactly. A bit I didn't like is that when explaining the SM, they expressed the non-abelian field strength with a cross product,

\[G_{\mu\nu}=\partial_{\mu}W_{\nu} - \partial_{\nu}W_{\mu} +g(W_{\mu}\times W_{\nu}\]

I know it's a minor detail, but somehow I found it annoying. I would have left the cross product restricted to classical physics, chained there for all the eternity.

Although I took QFT courses, most of it is forgotten, so some ...

2025-12-10T11:12:12Z

Although I took QFT courses, most of it is forgotten, so some years ago I bought "Quantum Field Theory for the Gifted Amateur" (which I'm probably not).

I should revisit it, but I remember it as a good introduction, with more solid state applications than it is usual.

About extensions beyond the SM there's almost nothing. It's a pity but I guess that they don't fit in an introductory text.

regarding the mysteries by Jessica Fletcher, an uncle of mine ...

2025-12-09T20:47:46Z

In reply to nevent1q…ccae
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regarding the mysteries by Jessica Fletcher, an uncle of mine said that the coincidences of her presence and the murders were so striking that the only explanation was the she was committing the crimes.

I learnt some new stuff in Daniel and Kelly's Extraordinary ...

2025-11-27T00:03:35Z

I learnt some new stuff in Daniel and Kelly's Extraordinary Universe episode "Relativistic beaming". For instance, it's a mystery how super massive black holes in the center of galaxies form (it doesn't seem that they're the result of collapsing stars). And it's a mystery how they accumulated such mass so early in the universe.

Last thing happening in Spain now, with the crazy prices of ...

2025-11-22T14:17:05Z

Last thing happening in Spain now, with the crazy prices of houses and flats: ask for loan in a bank, then in another bank, then another... buy as many flats as possible and rent them, mostly to foreigners, with a higher purchasing power.

The "human factor", as Graham Greene put it, plus capitalism is an incredibly dangerous combination.

I bought a copy of "Explorations in Mathematical ...

2025-11-17T23:02:20Z

I bought a copy of "Explorations in Mathematical Physics", by Don Koks. It includes a wide variety of topics: random walks, discrete Fourier transform, geometric algebra, tensors (how not!), a bit of cosmology...

Of course, it's not a treatise on any of these topics, and I think I know some of them. But the mixed approach called my attention, it's good to revisit material and many stuff are certainly new for me. So I hope buying it was a correct decision.

In his episode on October 2nd, the podcast "Daniel and ...

2025-11-16T11:36:19Z

In his episode on October 2nd, the podcast "Daniel and Kelly's Extraordinary Universe" interviews Phil Metzger, who mentioned something curious, he thinks there will never be an upper limit of the demand of intelligence, so AI servers would eventually need to go to the space, and hopefully as soon as possible, for the good of the planet.

He also mentioned that the concept of Von Neumann probe (self-replicant probes) would be more like an ecosphere of robots with different activities each one, that just one probe doing everything seems too much.

"These and other threats, including tariffs, sanctions and ...

2025-11-07T10:52:22Z

"These and other threats, including tariffs, sanctions and the revocation of diplomats’ U.S. visas, effectively killed the deal, according to the nine American, European and developing-nation diplomats directly involved in the negotiations. They spoke on the condition of anonymity out of fear of retribution from the Trump administration."

Trump Officials Accused of Bullying Tactics to Kill a Climate Measure - The New York Times
https://www.nytimes.com/2025/11/06/climate/trump-climate-international-bullying.html

"Dostoevsky gives me more than any scientist, more than ...

2025-10-30T23:39:46Z

"Dostoevsky gives me more than any scientist, more than Gauss!"

Einstein, as told by his friend Alexander Moszkowski.

I managed to watch 30 minutes of a YouTube video. I mean 30 ...

2025-10-22T20:41:48Z

I managed to watch 30 minutes of a YouTube video. I mean 30 minutes entangled with 30 interruptions for commercials.

When my mother was correcting exams and she saw the same mistake ...

2025-10-17T22:40:50Z

When my mother was correcting exams and she saw the same mistake over and over again, sometimes she had to go to the dictionary because she began to doubt herself.

I went to a dancing lesson. It finished at 22.00. I'm among the youngest. Once it finished, colleagues at least 15 years older than me went to a pub to listen to music. I didn't want to go. This has happened to me so many times that, as in the example before, sometimes I wonder if everything's ok with me.

TIL: with an estimated lifetime of 1000 years, acid-free paper ...

2025-09-20T16:39:19Z

TIL: with an estimated lifetime of 1000 years, acid-free paper (pH neutral) is almost surely more reliable than any digital storage device we currently have.

"A Geometrical Introduction to Tensor Calculus," by ...

2025-08-27T22:04:10Z

"A Geometrical Introduction to Tensor Calculus," by Jeroen Tromp, teaches you differential geometry with a focus on continuum mechanics and materials, not relativity (although examples for relativity are given). This has been surprising for me in many ways.

For instance, in continuum mechanics, you may need to account for deformations. For instance, dislocations and disclinations are 2-forms (vector valued form and tensor valued form). They are the equivalent of torsion and curvature in relativity, respectively. They obey Bianchi identities, too.

In General Relativity, you can have torsion, then you have the Einstein-Cartan gravitation. But it seems that the universe doesn't need torsion. We're lucky because the field equations with torsion are (even more) horrible to solve!

But in materials science (continuum mechanics), you can have these deformations. So, you need more sophisticated differential geometry than for gravitation. But although you could need all that sophistication to _describe_ your continuum media, I'm not sure if people are actually using it. (I mean, if it's practical).

"Life need not be easy, provided only that it is not ...

2025-07-29T22:40:42Z

"Life need not be easy, provided only that it is not empty." Lise Meitner.

TIL: perhaps you have heard that black holes are something ...

2025-07-06T19:51:58Z

TIL: perhaps you have heard that black holes are something detected (Cygnus X-1) and well established, while white holes are a mathematical solution, but probably they don't exist.

But the theoretical physicist Carlo Rovelli thinks the opposite! He suggests that there're essentially no black holes in the universe, only stars collapsing more and more slowly due to time dilation. His proposal is that the singularity never forms because of the effects of quantum gravity and that these effects somehow spit out all the matter, creating a white hole.

I guess the community is very sceptical of all this, and rightly so. I wonder how Rovelli explains the detection of gravitational waves via black holes merging. (I'm not discussing his height as a physicist, though. I'm sure he has developed an explanation).

I'm in the middle of this video, and I'm astonished by ...

2025-06-30T22:32:28Z

I'm in the middle of this video, and I'm astonished by the clarity of the explanations. It's about parallel transport, both from the perspective of Relativity and gauges theories.

Javier García is a physics professor with online courses on mechanics, QFT, General Relativity and more. Yes, it's in Spanish, but it's so good that I think his presentation can be followed and I dare to recommend it.

Transporte paralelo y DERIVADA COVARIANTE: la piedra angular de las teor...
https://youtube.com/watch?v=fqj9pjhZ7CU&si=ndA6cXP-StpNddMD

I guess this comes from the expression for the Schwarzschild ...

2025-06-10T23:16:46Z

In reply to nevent1q…ny4z
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I guess this comes from the expression for the Schwarzschild radius: more mass means bigger radius. What I'm not sure of is if the mass of the black hole takes into account only the interior of the event horizon or exterior parts as well.

TIL: the claim that says that you'll never see a probe you ...

2025-06-10T14:33:37Z

TIL: the claim that says that you'll never see a probe you sent towards a black hole crossing the event horizon is correct, but it assumes that the probe is the last object entering into the black hole. If more objects go into the black hole, the event horizon expands and "absorbs" the probe, hiding it from you, forever.

(Learnt in the podcast Daniel and Kelly's Extraordinary Universe"). #physics

More in this vein: he also answers the question of why in the ...

2025-06-01T12:28:58Z

In reply to nevent1q…4v9g
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More in this vein: he also answers the question of why in the double slit experiment, the electron doesn't get entangled with the slits. The reason is that you can assume that the slits are big and solid, and there's no entanglement because there's barely any interaction. (Actually, there's a little bit of entanglement, but you can safely ignore it).

Indeed, Carroll mentions the book "Quantum Paradoxes" by Aharonov and Rohrlich, where the double slit is set over wheels, so the electron passing through the slits can transmit momentum. Then, the degree of entanglement depends on the lightness of the structure with the two slits.

I would certainly love to see that calculation, but the book has an incredibly funny price, and it is only reasonable to buy it second hand.

I liked it a lot, Bryan.

2025-05-30T12:14:31Z

In reply to nevent1q…mhgt
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I liked it a lot, Bryan.

Something cool I learnt in the video of the chapter 8, ...

2025-05-29T17:18:46Z

Something cool I learnt in the video of the chapter 8, Entanglement, Q&A, by Sean M. Carroll: not every interaction creates an entanglement. You need each part of the superposition to act differently in the interaction.

For instance, an electron in a superposition of spin up and down states falling in a gravitational field doesn't get entangled with the environment (the field) because both spins act equally under the gravitational field; whereas if instead of a gravitational field you have a magnetic field then spin down and up interact differently, so there you have entanglement with the field.

I guess I should have known this, but in my defense I should say that my QM classes were solving the Schrödinger equation under different circumstances and diagonalising hamiltonians, and almost nothing regarding more conceptual ideas...🤷‍♂️

Geographiclib solves both geodesic problems: the direct problem ...

2025-05-10T16:32:49Z

Geographiclib solves both geodesic problems: the direct problem (given initial problem and a distance, find a point), and the inverse problem (given initial and final point, find the distance). It also gives angles with respect to meridians.

They claim to have an ellipsoid model of the Earth with a maximum error of the order of nanometers (!!). The Vincenty approximation for the Earth is at around 0.1 mm of maximum error. One of the authors they cite is Bessel, the mathematician of the XIX century.

Geodesics on an ellipsoid — geographiclib 2.0 documentation
https://geographiclib.sourceforge.io/html/python/geodesics.html

Interesting bit about Sean Carroll's April AMA. He says he ...

2025-05-05T12:01:19Z

Interesting bit about Sean Carroll's April AMA. He says he assumes that brute facts exist (although he says other people think differently). But that for him it's clear.

He mentions the work of the philosopher David Lewis, who wrote about the plurality of the worlds: there're many possible worlds (for instance a world with a different charge for the electron, or different initial conditions...) but we happen to live in this one. That's a brute fact. We can't explain why we live in this particular world.

Anthropic considerations allow you to leave out worlds where it would be impossible for us to exist, but you still have a plethora of possible worlds. Even if you have a principle that selects the world (the best or the simplest world), Carroll says, that principle would be a brute fact, because it could have been another one.

Some people have even claimed that the universe is the greatest brute fact ever.

Interesting comment on Sean Carroll's last AMA: he says that ...

2025-04-27T11:26:28Z

Interesting comment on Sean Carroll's last AMA: he says that Steven Weinberg's book "Gravitation and Cosmology" was a way to teach General Relativity in a very anti-geometric way.

Carroll says that Weinberg wasn't interested in curvature or the geometry of spacetime. Weinberg saw things like, we have a field (the metric), and it has this dynamic, it obeys these differential equations and we solve them. That how we think about the spacetime, the curvature or the geometry wasn't relevant at all. That the only relevant stuff were dots in photographic plates. A very particle physicist point of view, Carroll says.

Carroll says that, while being humble and acknowledging that Weinberg was a much more important physicist than him, he thinks Weinberg was wrong. Carroll thinks that the metaphors and terms we use to understand science are essential to improve and go beyond of our present knowledge, and that they offer understanding.

perhaps Élie Cartan? Although the idea could be in the air ...

2025-04-14T14:40:05Z

In reply to nevent1q…ce8a
_________________________

perhaps Élie Cartan? Although the idea could be in the air before.

Since loneliness is high in our societies, I guess someone should ...

2025-02-26T21:38:13Z

Since loneliness is high in our societies, I guess someone should have thought that LLMs can keep to those alone some company.

A colleague, but above all a friend has created his own YouTube ...

2025-01-29T22:53:05Z

A colleague, but above all a friend has created his own YouTube channel to teach Special Relativity with a different point of view.

Another way to introduce Einstein's Special Relativity based on Minkowsk...
https://youtube.com/watch?v=QHAt8vrQ5LE&si=35zxr7oGFLqnRMJ2

For instance, here he comments that electricity was thought to be ...

2025-01-27T17:02:47Z

In reply to nevent1q…ztfj
_________________________

For instance, here he comments that electricity was thought to be a fluid time ago. And more recently, some people tried to connect the continuum equations of materials with Maxwell's equations.

If you understand Spanish, I recommend this channel, where the ...

2025-01-27T17:00:15Z

If you understand Spanish, I recommend this channel, where the author speaks about books on mathematics and physics.

El átomo vorticoso, el rayo globular, los campos de Beltrami y la topolo...
https://youtube.com/watch?v=p91i4ICyPcQ&si=N3SlD2K1mQeQDQ6o

I'm reading "The Best of All Possible Worlds," a kind ...

2025-01-17T16:42:35Z

I'm reading "The Best of All Possible Worlds," a kind of biography of Leibniz. The author, Michael Kempe, is a world expert on the work and life of Leibniz.

At some moment in 1696, after his 50th birthday, it seemed that Leibniz, always very active and hard worker, was tired, felt uneasy, distracted, and had some apathy. He didn't feel well. He thought that beginning a diary could help him.

In the diary it can be appreciated that Leibniz decided to redouble his efforts, doing even more stuff than before ("actionism", in the words of Kempe); and that, combined with the self-reflection that the diary offered, helped him to surpass that moment he was experiencing.

ah, that perspective I didn't know, perhaps it's one of ...

2025-01-05T20:22:54Z

In reply to nevent1q…6rmt
_________________________

ah, that perspective I didn't know, perhaps it's one of the ideas that appear in the debate after Norton's paper. I found interesting what Nick has moved to Mathstodon (npub1hnp…26ht) said that after the physics of the XXth century, what happens in a set of zero measure is not so disturbing (although yes, it's a quite interesting result).

Philosopher of #physics John Norton found a solution to Newtonian ...

2025-01-05T11:54:48Z

Philosopher of #physics John Norton found a solution to Newtonian physics that seems to show that indeterminism is indeed at the heart of the previously thought deterministic Newton laws.

This video does a *great* job explaining it. Except for a few math details regarding the exact building of the dome, everything's in the video!

As you can guess, there has been a lot of heated debate around this problem, but in my humble opinion, what Norton has found seems entirely valid. #philosophy

https://youtube.com/watch?v=EjZB81jCGj4&si=rss7mvG2BU3d4HRq

I'm far from being an expert, but I think that part of the ...

2024-12-23T13:11:00Z

In reply to nevent1q…2l0c
_________________________

I'm far from being an expert, but I think that part of the problem with Copenhagen is that even the supporters had different views. Bohr, Pauli and Heisenberg didn't say exactly the same.

Physicists like Sean Carroll say that the Copenhagen interpretation is not very well established, but Carroll is a strong MWI supporter, one has to say.

Kurt Gödel found a solution to Einstein's equations that ...

2024-12-22T14:33:02Z

Kurt Gödel found a solution to Einstein's equations that depicted a rotating universe, where all the space-time rotates. This universe would have closed timeline curves, that is, time travel would be possible.

Gödel presented this result in a conference. John Wheeler was there and wrote that in such a universe you could live your life over and over again. In his book on Gödel, Palle Yourgrau says that Wheeler misunderstood Gödel (!).

What Gödel was trying to show was that if time travel is possible, then time, as a subjective experience, can't exist, it's just an illusion. It's not that you repeat your life. Yourgrau says that such closed timelike curves are like circles: points in a circle aren't moving around forever. They just stay there.

Gödel was a platonic mathematician, so if in one possible universe the subjective passing of time is an illusion, then the concept itself is not reliable, not something that universally exists, just an artifact, an illusion just convenient for our universe.

Yourgrau says that these results by Gödel regarding the illusory nature of time haven't been widely accepted.

(More details in "A World Without Time", by Palle Yourgrau). #physics #philosophy

Is "perhaps" more American English and "maybe" ...

2024-12-18T17:02:07Z

Is "perhaps" more American English and "maybe" more British?

I'm reading these days "Reflections on Kurt Gödel", ...

2024-12-16T17:33:27Z

I'm reading these days "Reflections on Kurt Gödel", by Hao Wang. One of the things that surprised me considerably is that it seems Gödel was as much a philosopher as a mathematician. Perhaps even more a philosopher than a mathematician! At least if you count the time dedicated to each activity. He felt close to Leibniz. #philosophy

is this a generic declaration (very reasonable, by the way), or ...

2024-12-01T22:31:47Z

In reply to nevent1q…gqjq
_________________________

is this a generic declaration (very reasonable, by the way), or has the context been lost?

have you ever read Chandrasekhar? Wald seems much more succinct: ...

2024-11-24T00:36:22Z

In reply to nevent1q…hjxl
_________________________

have you ever read Chandrasekhar? Wald seems much more succinct: few calculations in detail for a dense material. Chandrasekhar looks like exactly the opposite: lots of calculations in detail. (Well, and Chandrasekhar deals only with the subtopic of black holes).

a little bit off topic: I've always found that textbooks on ...

2024-11-23T13:08:09Z

In reply to nevent1q…zlfs
_________________________

a little bit off topic: I've always found that textbooks on GR arrive to black holes after such a long way behind that they're like exhausted, and deal with the topic lightly. Perhaps this is not the case with an specific book, like the one by Chandrasekhar.

David Lewis was a philosopher proponent of Humeanism. He was ...

2024-11-22T18:18:42Z

David Lewis was a philosopher proponent of Humeanism. He was famous for his support of the plurality of possible worlds, which have resonated with those who sympathize with the many worlds interpretation of quantum mechanics. He said once: "anything can coexist with anything else, at least provided they occupy distinct spatiotemporal positions. Likewise, anything can fail to coexist with anything else". That's his so called _principle of recombination_.

From his entry in Wikipedia: "Combined with the assumption that reality consists on the most fundamental level of nothing but a spatio-temporal distribution of local natural properties, this thesis is known as 'Humean supervenience'. It states that laws of nature and causal relations merely supervene on this distribution of local natural properties".

Curiously, for some people, this last definition (Humean supervenience)
seems to be in conflict with quantum entanglement (QE)! Thay argue that
QE precisely says that laws of nature don't just supervene (are a consequence) from the distribution of local natural properties in spacetime, because QE seems to "break" the notion of locality. For others, Humean supervenience can still be saved. There's debate around.
#philosophy #physics

I would have taken one, too!

2024-11-22T18:12:54Z

In reply to nevent1q…kevh
_________________________

I would have taken one, too!

In his October AMA, Sean Carroll explained (at around the ...

2024-11-21T17:54:06Z

In his October AMA, Sean Carroll explained (at around the beginning of
the third hour) why he supports Humeanism as a philosophy of science. Summing up a lot, he says it's what gives more from less.

Humeanism is big, it deals with many issues, and I wonder if Hume
himself would have subscribed everything. Perhaps the two main points are the "bundle theory of the self", i.e., that there's no such thing as
a self contained in the brain, but a continuous flux of states and
conceptions. I think this idea detaches you from taking yourself too
seriously, and it could bring some peace of mind to people who tends to
worry or be nervous a lot.

Regarding the philosophy of science, Humeanism rejects the independent
reality of the laws of nature. This collides with Platonism, a way of
thinking that many mathematicians (perhaps most of them?) support. A
humeanist would say that the laws of nature explain the regularities
observed, but, following Hume, you can never be absolutely, 100 % sure
that tomorrow the Sun will rise. I don't know what to think here. My
sympathies lie toward Platonism, but I can't say Humeanism is not
reasonable. #philosophy #physics

"The condition of being good is that it should always be ...

2024-10-27T11:00:13Z

"The condition of being good is that it should always be possible for you to be morally destroyed by something you couldn’t prevent. To be a good human being is to have a kind of openness to the world, an ability to trust uncertain things beyond your own control, that can lead you to be shattered in very extreme circumstances for which you were not to blame."

Martha Nussbaum #philosophy

I have a doubt (actually, I have many doubts, but let's go ...

2024-10-23T22:54:29Z

I have a doubt (actually, I have many doubts, but let's go step by step beginning with a #physics doubt):

Every equation written with classical vector calculus can be translated into tensorial form (and many times, it's desirable). But can every equation of physics written with vectors (or tensors) be also expressed with differential forms?

I always see differential forms in the context of electromagnetism, classical mechanics, and (rarely) thermodynamics. But differential forms are essentially absent in areas like fluid dynamics (how many times have you seen the Navier-Stokes equations written with differential forms?), optics, and other areas of physics.

Nostr event nevent1qqstut5qhtegflhl8l6l4g9s857znm0y26pj5amhstd7m25g4vatrngzyqpyh8e8jmjmwvm77djet7xhp8lnpx4andkfcjmclljttuussh6cc6hau88

2024-10-20T14:50:41Z

#silentsunday

Due to analysing the movement in a rotating frame, the famous ...

2024-09-28T17:38:02Z

Due to analysing the movement in a rotating frame, the famous Coriolis term appears: $\boldsymbol{a}_C=-2\boldsymbol{\omega}\times\boldsymbol{v}$, with $\boldsymbol{v}$ your velocity in the rotating frame and $\boldsymbol{\omega}$ the angular rotation velocity of the Earth (or another rotating system).

One of the consequences of this term is that, depending on your velocity, a vertical acceleration with respect to the surface of the Earth can appear. It's called the Eötvös effect. If you're moving eastwards, the Eötvös effect pulls you upwards, and if you're moving westwards, the effect pulls you downwards.

It's a certainly small effect for typical velocities in comparison with gravity, but it's there. #physics

I discovered that this existed recently, so I'm incredibly ...

2024-09-26T19:47:17Z

I discovered that this existed recently, so I'm incredibly late, but I want to participate anyway. 10 authors you’ve read at least 5 books by

- Agatha Christie.
- Isaac Asimov.
- Arthur C. Clarke.
- Arthur Conan Doyle.
- Greg Egan.
- Stephen Baxter.
- Stanislaw Lem.
- Walter Jon Williams.
- David Foster Wallace.
- Cormac McCarthy.

#10authors5bookseach

I had to look up for the term quantale, I thought you were being ...

2024-09-13T21:56:06Z

In reply to nevent1q…z680
_________________________

I had to look up for the term quantale, I thought you were being critic of some interpretation or similar of quantum mechanics (I thought in terms of quantum + tale).

The book looks really cool, BTW.

After spending some time familiarising myself with pywavelets, I ...

2024-09-12T22:24:43Z

After spending some time familiarising myself with pywavelets, I have found that an R library (WaveletComp) is probably more convenient. It has confidence intervals (pywavelets not at the moment of writing), and the cone of influence seems to be automatic.

pywavelets is a generic tool for wavelets, while WaveComp is more focused on statistics for time series. I tend to go directly to Python, and I think I need to change my default when thinking in software to do somewhat advanced statistics.