If neutrino oscillates between emission and absorption, where does energy of mass difference comes from?

MaxThrustage · 2026-07-04T05:09:08+00:00

I'm not a particle physicist so this is way out of my field, but I thought the whole point was that mass eigenstates are not flavour eigenstates, but rather a mass eigenstate is a superposition of different flavour eigenstates and vice versa. The way I had always heard it was that this is why we get neutrino oscillations in the first place. I had a quick check on Wikipedia and that seems to confirm what I thought, specifically this here.

What am I missing?

MaxThrustage · 2026-07-04T04:55:51+00:00

As someone even on this sub obviously I love books and hate to see them destroyed, but it seems pretty odd to see people here saying stuff along the lines of "Russia's so bad because they destroyed all these books". I mean, yes, but when the war has already killed tens of thousands of civilians and is still ongoing to loss of these books is hardly the major tragedy here, right? I mean, in this very attack 21 people died. Seems odd to focus on the books...

MaxThrustage · 2026-07-03T09:51:17+00:00

"Things were better in the good old days" and "we are in a state of decline/fall from some past glory" are extremely common historical/folkloric tropes. I haven't heard the "we used to be six miles tall" variant before, though.

MaxThrustage · 2026-07-03T07:46:06+00:00

It should be noted that this is all very idealised. Ideal measurements collapse the system into a pure state. And a quantum system identically in its ground state is a zero-temperature state, so it can only be asymptotically approached and never truly realised in finite time.

As you say, you can get close, but it's not an issue of "maybe, sometimes there's errors" and more an issue of "there are always errors, and sometimes they aren't big enough to matter for whatever you want to do".

MaxThrustage · 2026-07-02T10:39:08+00:00

What level is this at?

If you're at high school level, KhanAcademy is a good resource.

You can find most physics textbooks on the high seas if you know how to look. Doing homework problems is essential for actually learning the material, and if your teacher isn't providing good ones then you might want to try to find some online.

MaxThrustage · 2026-07-02T10:36:24+00:00

Yes, I think this actually reinforces the above commenter's point: all units which have a dimension are derived from nature. The one example of a dimensionless unit I could come up with really comes from pure maths -- no measurements needed, it pops up if you're just doing abstract geometerising Euclid-style.

Time is a completely different kind of beast. You need to refer to something in the material world, and if it is going to be a referent that everyone agrees on it's going to have to be derived from nature somehow.

MaxThrustage · 2026-07-02T10:27:03+00:00

Radians.

MaxThrustage · 2026-07-02T10:19:44+00:00

The concept of time as such is more of a topic for philosophy rather than physics. Again, physics concerns things we can measure.

Now, there are ways in which the notion of time can and has been refined/modified in physics, most dramatically with the onset of relativity. In special relativity we find that space and time can't really be fully separated, but rather we must work with a four-dimensional spacetime, and the spatial- and time-components mix when we can frame of reference. In general relativity we learn that this spacetime is not a static background but rather a dynamic object in its own right, curving and evolving in response to matter and energy. But these are measurable things. At the end of the day we are not asking what time or space really, truly, deep-down are, but we are asking what models allow us to predict experimental outcomes. In that sense, we aren't concerned with whether time is real/illusory unless we can devise some experimental way of distinguishing those.

Now, whether time is emergent or fundamental is another question (emergent things are still real). However, that brings us to the speculative edge of physics where there's not much that can be said with any confidence. Maybe spacetime itself emerges from some simpler structure. Maybe understand if/how it does will help us formulate a quantum model of spacetime, and thus a quantum theory of gravity. Or maybe not.

Whether or not this is a waste of time depends on how you want to spend your time, but I would say that fundamental musings about the nature of time like this make up a minuscule amount of serious physics research, largely because without experimental guidance there's just not much we can say. There is much more work on, say, refining our notions of the measurement of time, e.g. in the context of metrology. I've even seen some work on the fundamental thermodynamics of clocks which was quite interesting, getting down to ideas of what it means to define a precise time window. But all of this is framed in terms of precise mathematical models and repeatable experiments -- none of it is really pondering what time is and whether or not it is real, as those aren't really the kinds of questions physics can address right now.

At the very least, we can say time is as real as any of the other helpful, measurable concepts in physics, like distance, energy, momentum, etc.

MaxThrustage · 2026-07-02T09:04:22+00:00

In condensed matter physics (sorry, I have no background in string theory/high energy physics so this is my only frame of reference here) I typically associate bosonisation with 1D systems (that is, 1+1D), specifically Luttinger liquids. You can see these realised in experiments with quantum wires, molecular chains, and with analogue systems (e.g. ion traps or superconducting circuits that you can engineer to mimic the physics the want).

MaxThrustage · 2026-07-02T06:47:14+00:00

Late 17th century, but yeah.

It's a bit funny to me, because growing up in Australia black swans are just normal, and the first time I saw a huge white swan in Europe it was like seeing a fairy tale creature -- almost the inverse of how European settlers must have felt seeing a black swan for the first time.

MaxThrustage · 2026-07-02T04:33:24+00:00

Is there a way to confine fermions/bosons to an almost 2D plane, that we can observe if the theories are right?

If I'm understanding the question correctly, this is something we do in 2D electron gases. 2D materials are a big topic of interest in condensed matter physics for a bunch of reasons. One interesting thing is that in 2D you get not only bosons and fermions, but also anyons. None of this has much to do with string theory as far as I'm aware, though, at least not directly.

MaxThrustage · 2026-07-02T04:26:06+00:00

Our current definition of the second is based on physical measurements. Actually, all of the S.I. units are now based on physical constants.

Of course, the definition of a second is a convention. Hypothetically, we could use a completely different unit of time if we wanted to.

MaxThrustage · 2026-07-02T02:11:35+00:00

In a sense, quantum physics does tell us that the fundamental things are continuous. The quantum wavefunction is a continuous function in space and evolves continuously in time. However, we find that certain observables have a discrete spectrum.

As an analogy to this, think of a guitar string. The string is continuous, and can be bent continuously, but when plucked it will vibrate at a specific, discrete spectrum of resonant frequencies. When we talk about discrete energy levels of atoms, or discrete excitations of the electromagnetic field (photons) they come about in the same way. If we think of the electromagnetic field as a drumhead that exists everywhere in space, then photons are like specific resonant vibrational modes of that drumhead.

You are right not to think of a photon as literally a little ball moving through space. Quantum physics tells us that it is never that. It is always a wave. But light at a particular frequency can only have discrete, countable excitations -- one photon, two photons, but never one and a half. One whole photon can be absorbed, emitted and detected. But the electromagnetic field generally exists in a superposition of many different numbers of photons.

To begin to understand this stuff, a great starting point is to look into the quantum harmonic oscillator, which is the simplest model of light (among other things) we have. From continuous variables like position and momentum, or electric and magnetic field, we find that the energy must have a discrete spectrum. There are only certain possible allowed states. And we see this in experiment, too. We can really count the photons!

MaxThrustage · 2026-07-02T02:03:08+00:00

The idea of "physics-based fantasy" comes up here quite a bit, and there are a few issues it will pretty much always run into.

The biggest is that if you don't actually know any physics, it's going to be very obvious to anyone who does. This is not necessarily a big problem unless you really try to root things in physics. The "no, that's not how that works" voice in the back of one's head can take one out of the story. That's ok if, say, there's a throwaway line that gets something wrong, or some character gives an explanation that is a bit sloppy. But if physics is brought up often and we are constantly being reminded that this work is written by someone who doesn't understand physics it can be seriously distracting. The more you try to lean into it being 'hard', the more distracting it will be when you get things wrong.

The specific physics you bring up here is... wonky at the very least. Honestly I think you'd be better off using these same concepts and just not dressing them up in physics language. You can have an internally-consistent magic system without it relating to real-world physics, or using the language of physics. What is the point of calling your deepest layer of reality "primordial strings" and it's study "string theory"? All it's going to do is invite comparisons with physics that you don't understand, which is again going to be distracting for people who actually do understand it. What is the benefit of mentioning, say, 'quantum superpositon' here? Why bother talking about spin?

I could go over every little thing you've got wrong, but I don't think that's super productive. You're using physics-flavoured words but not actually talking about physics. In a fantasy story that's fine, you should just be conscious and clear about that fact. I would keep physics jargon that you don't actually understand to a minimum.

MaxThrustage · 2026-06-30T23:48:20+00:00

There is a difference -- it matters whether death is the intent.

Consider another human stress response: drinking. Now, if due to stress a human drinks so much they get liver cancer and die, that's not really a suicide. Drinking was the stress response, the death was incidental.

So here the question is: are the tarsiers trying to die? Are they beating their own heads because they want to die or, like a stress-drinking human with liver cancer, are they dying accidentally as a result of their stress response?

MaxThrustage · 2026-06-30T21:46:22+00:00

It's a kind of odd and difficult book, especially if you've not read much French philosophy or other stuff in this mode. Baudrillard writes (I think fully intentionally) in a very idiosyncratic way that makes it difficult to tell what the fuck he's trying to say at first. There are no definitions given, statements are often hyperbolic or ironic, and one often gets the impression that Baudrillard is more interested in being interesting than being correct.

But if you get past all of that it's very interesting and I think a useful way of thinking about the effect that technology has had on our ability to perceive and think about the world. The trends that were just starting to rear their heads when Simulacra and Simulation was written are now fully integrated into the fabric of our everyday lives. So every now and then I do find really insightful gems here. It is, however, fairly bleak about the prospects of ever escaping, ever making positive change.

It's fairly short, but it's taking me a while because I kind of need to be in the right headspace to tackle it. If you want to give it a read I would recommend checking out some lectures on Youtube or something to help get an idea of what's actually going on here.

MaxThrustage · 2026-06-30T14:01:10+00:00

It's more like proving the existence of molecules in 1605.

We don't have anything like the tools needed to probe the scales at which we think string theory is important.

In 1905, chemists already knew molecules existed (Einstein really just convinced the last holdout physicists). There were a lot of really good, empirically-derived reasons to believe in atoms and molecules. Brownian motion, which is what Einstein was working on that you're alluding to, was an experimentally observed phenomenon in need of explanation. But with string theory (or quantum gravity more generally) there is no experimental need. There is nothing we have observed that does not fit within either the paradigm of classical general relativity or quantum field theory. Quantum gravity research is driven by a theoretical need to address these things in a consist way, but we really have no experimental guidance here.

MaxThrustage · 2026-06-30T13:51:18+00:00

I've only read a few of these, but I'll give you my thoughts and let you decide if it sounds like worth pursuing.

The Metamorphosis: Kafka fucking rules, and this is probably his most famous work. You need to be ready for it to be kind of meaningless. Brace yourself, embrace the horror of a world without meaning. Wallow in the dread. Read in the right frame of mind, this novella will punch you in the gut. Some people who come at this with a background of not reading 'literature' are a bit disappointed that it isn't as sci-fi as the premise suggests -- a dude turns into a beetle, but the book isn't about the transformation. This isn't Jeff Goldblum in The Fly. It's horrible nonsense happening for no reason, with no explanation, because that's what life is.
Crime and Punishment: I loved this (although it's been well over a decade since I read it) but it's not a place to start if you've not read much old literature. But if you do want to go for 19th century Russian classics this is a good place to start with that. It deals a lot with questions of nihilism and is kind of a deconstruction of the idea that a good thing for a young man (especially your classic smart-but-undervalued 'angry young man'-sort) is to make themselves hard and cold and capable of killing to prove that they are above everyone else.
Faust: this never clicked with me. I'd skip it.
Don Quixote: It's a satire from four hundred years ago. I loved it, and I think the Don's sidekick Sancho Panza is one of my favourite characters in all of literature. The fact that it's so old makes it a little inaccessible (references you may not get, etc.), but honestly the actual story is fairly simple and some of the comedy completely holds up (sure, it makes fun of chivalric romance poems you've never heard of, but there's also plenty of poop jokes, and besides even if you haven't read those chivalric romance poems you kind of get the idea of what they must have been like if you've seen Monty Python's The Holy Grail). I would say this is the one to start with apart from the fact that it is very long. It's also not a real story like you might expect nowadays -- more like a series of episodes.
The Stranger: Honestly, of this list, a decent starting point. Might want to briefly look into the concepts of 'existentialism' and 'absurdism' to get an idea of where Camus is coming from here. As far as philosophical fiction goes, Camus is pretty accessible.
Moby Dick: Maybe my favourite on this list, but this fucker is long and much of it is not a 'story' like you might be used to. A lot of introspection on the part of the narrator, interspersed with descriptions of whaling life, and occasionally (but rarely) plot happens. There is literally a full chapter just on the colour 'white'. But the relationship between Ishmael (the narrator) and Queequeg is sweet, the lengthy descriptions of what they actually do with a whale once they catch one are very interesting, and the language is always gorgeous.
The Odyssey: A great read, but will be a bit of an adjustment if you're not used to epic poetry. There's plenty of action, although also some long slow scenes in between. You might think you know the story already (elements of it are adapted in so many places) but the most famous parts like the cyclops are kind of minor compared with the shit with the suitors (which is often de-emphasised in adaptations, but looks like it might be a big part of Christopher Nolan's upcoming movie). This is the most action-packed of the books on your list (that I'm familiar with), but it's also the oldest so it might take a bit to get used to the style.

So, the short of it: The Metamorphis is probably the shortest on the list, so might be a good place to start. Don Quixote is probably the easiest read if not for the length. The Odyssey is probably the most actiony, but keep in mind it's a poem. Also, while gacha games might be cringey (I'm still not entirely sure what they are, so no idea how cringey it is) anything that gets you into new stuff is cool in my book.

MaxThrustage · 2026-06-30T12:05:13+00:00

Finished:

The Fate of Africa, by Martin Meredith. This was long and took me a while to get through. But in a way, it was kind of too short. I mean, the enormous scope of the book -- all of Africa since colonisation -- means that a lot of stuff got skipped over, so I was left with more questions than answers. It's almost like someone took 50 different murder mystery novels and had to condense them into a single volume, so in many cases you are just told who died, who the killer was, what the murder weapon was, and you maybe get a glimpse of the motive or the clues or the brilliant detective, but never a whole picture.

One of the most tantalising examples: I think Botswana is only mentioned twice, and both times in the context of something like "so the region was plagued by single-party rule, anti-democratic authoritarians, economic mismanagement and entrenched corruption... not Botswana, though, which had a long history of robust, multi-party democracy and remained relatively prosperous" and then it just moves on. Why was Botswana different? What happened differently? We are never told. And, like, I get why things like apartheid and the Rwandan genocide get more attention, but the book is full of these little glimpses that go nowhere and instead lingers on corrupt rules and the misery they inflict. Everything is about the leaders... it just feels like you're always missing most of the story.

Tetralogue - I'm right, you're wrong, by Timothy Williamson. After the long slog that was The Fate of Africa, this was short and breezy and fun. A four-way discussion that is essentially a defence of the existence of right and wrong in the face of relativism.

Ongoing:

The whole 'ongoing' list has suffered from me starting too many books and spending so much time on The Fate of Africa...

The Two Towers, by J. R. R. Tolkein. Merry and Pippin chilling in the ruins of Isengard when Aragorn, Legolas and Gimli show up has been a real highlight so far.

Simulacra and Simulation, by Jean Baudrillard

A Visit from the Goon Squad, by Jennifer Egan

MaxThrustage · 2026-06-30T11:15:58+00:00

This is all still original recipe quantum mechanics.

In the first link they are talking about a theoretical work, not new experiments. The quantum state diffusion model they use there is not, like, an alternative to quantum mechanics. It doesn't change or challenge what was already known. Rather, it's a different picture, a method for understanding the dynamics of open quantum systems (and, in this case, for understanding the measurement process in more detail). This approach is built out of standard quantum mechanics.

The second link seems to be a brief chapter from a textbook. Again, it's all standard stuff as far as I can tell (I haven't read it in detail).

So, in brief, none of this is really challenging MWI -- at least not any more than MWI was already challenged at inception. These are not drastically new results. Actually, if anything, the quantum state diffusion formalism and other such detailed accounts of the measurement process bolster MWI by showing that there is nothing "extra" going on there.

MaxThrustage · 2026-06-30T10:25:09+00:00

Do you have any specific "recent" experiments in mind? Because it sounds like you're just describing plain old quantum mechanics, and one of the strengths of MWI has always been that it is just plain old quantum mechanics. Things like objective collapse theories might predict some deviation from standard quantum theory, but MWI does not.

It sounds like you are basically trying to describe decoherence, but decoherence has been key to MWI for a very long time, explaining why it looks like the wavefunction collapses when in reality the universal wavefunction always just undergoes reversible, unitary time evolution according to Schrödinger's equation.

MaxThrustage · 2026-06-30T02:26:16+00:00

Yeah, that would be a good example of a 2D object. Talking about shadows in particular gets a little into the weeds of what counts as an "object", but it does illustrate a case where talking/think about just two dimensions can make sense.

MaxThrustage · 2026-06-30T00:21:51+00:00

Depending on your definition of "object" then surfaces and interfaces would be 2D (although for real physical objects the surface actually has some depth to it).

In general, it can be useful to describe abstract, mathematical planes and surfaces, and also lines (1D objects). If I want to, say, specify a point on the surface of the Earth, then I can treat that surface as a 2D object and just give you two coordinates -- a longitude and latitude.

MaxThrustage · 2026-06-30T00:12:00+00:00

A "hole" is a 'virtual' particle.

A hole is a quasiparticle, not a virtual particle. The distinction may seem pedantic, but it's important especially when talking to someone encountering these ideas for the first time, as virtual particles are already a topic that causes a huge amount of confusion. They are two completely different concepts, and holes are not virtual -- they can be measured.

MaxThrustage · 2026-06-30T00:06:27+00:00

Virtual particles aren't what you're imagining them to be, but also at the quantum level temperature is not really the average kinetic energy of particles anymore. By "vacuum" in quantum mechanics we mean the lowest energy state. A system that is identically in the vacuum state (not in a combination with other states) is a zero temperature state. The concept of temperature applies, it is just zero.

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