superposeur

The scar tissue model sounds convincing and there’s something to it. But when I reflect on my very long term relationships, it doesn’t seem to get at the core of why we’ve stayed together. Instead, for these relationships there is a deeper alignment of interests / alignment of values / alignment of outlooks (whatever you want to call it) that allows us to get past the annoying stuff. Put differently, a model that resonates more with my experience is that there are two baskets of conflicts: core stuff and peripheral stuff. As long as the peripheral conflicts don’t get too egregious, they don’t actually matter if the core stuff is still working.

I’m old enough to remember the advent of YouTube and remember thinking that it would obviously be one of zillions of video-streaming sites. Nope. Still I am mystified by the dynamic whereby there is just one website people go to to watch videos and just one Twitter and just one Facebook. Somehow, having all the choice in the world funnels into its opposite.

yes pun intended

What is it about theoretical physics that makes people on the internet (with zero understanding of the context) feel entitled to snarkily attack results such as this?

The research in the article is about as innocuous as it gets — uncovering another possible way to get a handle on the math of quantum field theories. It’s not like millions of dollars went into the research (just the modest salaries of the four theorists). No major applications as yet — the Quanta title “…shaking up physics” is certainly not true. But it’s another stone in the edifice of science.

And my god when you see the esoterica in some (most?) other academic fields, the unrelenting complaints about the solipsism of physics seem totally misdirected. When an upper bound on some complicated measure on the distribution of prime numbers is lowered, no chorus of jackals assembles on the internet to mock the proof for its lack of real world relevance. The other day I spoke with a classics professor whose primary research was on a possible alternative interpretation of one line in a Latin poem. I found it interesting and worthwhile, but wow another level of remove from the so-called real world of engineering application and commerce.

Also, to be clear, whether or not mathematical physics work winds up elucidating experiments, it is still correct and “useful” math. It’s not for nothing that the math community gave Edward Witten a Fields medal.

No, the language of “perfect sphere” versus “bumpy sphere” used by the article is just an analogy with a classical object that would interact with an external electric field in a similar way. Even when it is in a single position eigenstate, an electron has another degree of freedom, its spin orientation, that has nothing to do with its position. This is “like” a spinning pool ball in the sense that it possesses angular momentum in a certain direction and reacts to torques like a spinning thing, but beyond this the analogy breaks down. For one thing, its spin can never be increased nor slowed; for another it has this intrinsic spin even when its position is localized to a dot.

Similarly, a non vanishing Electric Dipole Moment would be some preferred direction to its electric interactions in relation to its spin. Its electric field would be slightly oblong even when position is localized to a dot.

So to clarify, there are multiple senses of “electron cloud” at play — the superpositions of positions is what is usually meant by the term, as in electron cloud around nucleus of atom. The article’s use of the term is a tad sloppy since it invites confusion with this — it means something that generates an oblong electric field and reacts to an external electric field through a term in the energy of the form p.E (with p the EDM and E the external electric field).

Yes an electron is a “quantized vibration” of a quantum field (the electron field). The vibration is quantized in the sense that you can only turn on the amplitude of vibration in discrete clicks, not in a continuous way. Two clicks would be two electrons.

Such a quantized vibration has all the properties of a particle: it has a certain mass, it has a certain momentum, it has a certain angular momentum, and when you look at it in another frame of reference, all these quantities transform just as would a particle’s. And, when you “perform a position measurement” it shows up as a single dot. If you don’t do a position measurement it spends most of its time quantum superposition of states of definite position; hence the “cloud” aspect.

Because she doesn’t present a consistent model or indeed any model at all.

Hard to say, but other videos I've seen are in areas where things are genuinely murkier; for instance, the status of fine-tuning arguments and the interpretation of quantum mechanics. Not so for this video, which is settled territory (and presents no extraordinary counter evidence). Generally, I do enjoy her off-kilter takes.

The form of argument "maybe X invalidates theory Y, so we shouldn't trust prediction of Y" isn't terribly useful since it could be applied to any prediction of science; "Maybe quantum gravity so let's not worry about conservation of energy." "Maybe comoving frame, so maybe we can build antigravity devices", etc. Of course, it could be true. Most anything could be true. It's just not a useful basis for adjusting one's priors.

Yes, at the fringes of known physics, as you say. My point is that this question is not at the fringes known physics. Earth and Alpha Centauri are not near the singularity of a black hole and special relativity is perfectly adequate to predict that events now on Earth will take some time to influence events on Alpha Centauri.

No OP is correct, her use of the term CTC is not what is usually meant. The curve she draws is not timelike along the faster than light segments in the sense of having tangent 4-vector with timelike norm with respect to the underlying metric. She would not disagree I think.

This is easily Sabine Hoffstader’s fringiest video. Please don’t get the wrong idea that this is a point of controversy within physics! As a physicist I’d estimate 99.9% of her colleagues would disagree and I would too. She has no real argument, just vaguely gestures at “maybe the comoving frame makes relativity invalid” and then vaguely gestures at “quantum gravity spoiling everything we know so far about physics”.

As to the second point, quantum gravity is a thing but almost certainly will not upend the special relativistic account of the large scale causal ordering of events. This is for the same reason that it almost certainly won’t change the calculation of the amount of time it takes an apple to drop from a tree —- within the domain of validity of the old theory, its predictions will agree.

I’m not an expert in this but know the relevant physics well. Here are my thoughts on this good question.

Answer 1: Gravity is just like electrodynamics in this respect: as you say, the force vector is determined by the position of the other mass at the so-called retarded time not the current time. Specifically toward the position the other mass would occupy right now, had it kept moving at constant velocity using the velocity its velocity at the retarded time.

Hence, all deviations of the force vector from current position are due to the acceleration of the gravitating mass. The significance of the deviation is roughly estimated by the dimensionless ratio : a*x / v^2, where v is speed, a is acceleration, x is distance from gravitating mass. Accelerations are very very tiny in galactic contexts, so numerator is smaller than denominator.

Answer 2: A galaxy is like a fluid with approximately steady flow; hence, even if a given gravitating mass has moved since the retarded time, some other mass has taken its place.

I haven’t put numbers on these though.

I actually dig this film, it didn’t bore me until the very final stretch. (Much like a Philip Glass work.)

Reflecting on the complementary strengths of Wolfram and GPT reminds me of Daniel Kahneman’s distinction between “system 1” and “system 2” in the human brain. One system is a kind of freely-associating autopilot (like gpt) and the other kicks in when some deliberate logical manipulation of facts needs doing (like wolfram). (Or at least this was my layman’s impression from reading Thinking Fast and Slow.)

Have others thought of this and, if so, is the comparison apt? Is it possible the human brain is simply an LLM melded to a symbol-based system in dialogue with each other?

I was there too and, at first, was wondering if the music thing was just a warm up to the main talk. But soon enough I settled into the flow of it.

His slides were incredibly minimal throughout and then, at the end, he played a video of maple leaf rag pouring forth from his player piano midi setup and it was like choirs of angels singing.

How many boring ass talks have I sat through that I’ll never remember — but I suspect I’ll remember his talk for a long long time.

Note: this was at a linux conference.

Definitely one of the cat-and-mouse games between Kublai Khan and Marco Polo is him trying to pin down just what is real in the stories. He wants to totally possess his lands not just through conquest but also through knowledge and understanding of them. Some of the tales may be baloney but not all. After all, even if Marco Polo is just associatively spinning tales GPT style, his “training data” inputs had to come from somewhere. Going meta, we the readers holding this absurd book are in the position of k.k. and Calvino the writer is m.p.

Ever since I first read it in college, I've cited Invisible Cities as my favorite fiction book. As highly rated as it is, I still think its philosophical depth is underrated.

In particular, I think it holds wisdom for how to live in this age. Everyone says, to the point of cliche, that institutions and information can't be trusted; all is uncertain; all is illusion; distrust sources. But this is no answer, in itself, for how to live. Instead, I often think of the last paragraph of Invisible Cities:

"The inferno of the living is not something that will be; if there is one, it is what is already here, the inferno where we live every day, that we form by being together. There are two ways to escape suffering it. The first is easy for many: accept the inferno and become such a part of it that you can no longer see it. The second is risky and demands constant vigilance and apprehension: seek and learn to recognize who and what, in the midst of inferno, are not inferno, then make them endure, give them space.”

There’s an aspect of path integrals that’s always bugged me. They rely on an underlying classical field configuration space to integrate over. But, this seems problematic to me, since properly the objects of classical physics should emerge as limits of quantum physics. Shouldn’t we be able to start with “pure” quantum mechanics (a state space, a Hamiltonian operator), with no mention even of “paths” and get out classical physics? I.e. it seems backward to speak of a particle trying out different paths since a “path” is a classical notion; it’s as though quantum mechanics is merely a superstructure on top of an underlying classical layer rather than the other way around. Know what I mean?

Short answer: only things like light waves moving at the universal speed c have the same speed in all frames, not objects like balls moving at slower speeds.

Longer answer. The principle of relativity doesn’t claim that particular objects have the same speed in different frames, it claims that the fundamental laws of nature take the same form in different frames.

In the 1860s Maxwell wrote down a set of four equations governing ripples in the electromagnetic field (=light waves). They naively seem to only be exactly true in one frame of reference since they predict the light waves move at one particular speed c. Einstein made the leap to suppose that the Maxwell equations continue to take the same form in all frames of reference, so that each observer sees the ripples moving at the same speed c.

This doesn’t apply to balls because the fundamental laws make no such prediction for the speed of a particular ball. (Obviously! You can hold the ball, or throw it.) Hence the ball being different speeds in different frames is just something about a particular ball — it doesn’t contain a grander implication about the laws of nature.

I have trouble reconciling the insanely impressive pre-mid-80s Wolfram with the post-80s Wolfram. All his productions before a certain time are touched with brilliance and a preternatural orderliness of mind (including Mathematica, which was a groundbreaking and beautiful piece of software). Then he started making pictures of cellular automata.

And allowing non-flat space time refines but doesn’t alter the picture.

For instance, it’s a common misconception that wormholes circumvent the relativistic prohibition against ftl travel. Actually, if a wormhole could facilitate travel between two events faster than a light ray moving between the same two events on the outside of the wormhole, then all the same causality troubles would ensue. This just highlights that that the particular mode of transport between events is not important to the argument. (Whether it be warp drive or secret tunnel.)

Most physics revolutions refine rather than replace their predecessors. So, for instance, gr gives similar predictions to to Newtonian gravity in an appropriate limit.

It is possible that relativity will be refined by further developments (quantum gravity?), but it is reasonable to expect that the refined understanding will reduce to relativity in an appropriate limit, one core feature of which is the causal structure of events in space time.

Hoping that exotic physics will allow ftl travel is like hoping that an exotic theory of gravity will give a radically different prediction for the time it takes an apple to drop from tree to ground. True that “never” is a strong word but this is just about as never as any fact we know.

I use this strong word as a corrective to the impression you get reading discussion threads, where you may suppose ftl is next up on musk’s bucket list, or just limited by sluggish tech development.

Yes it’s really interesting how the quantum information folks have managed to recast known features of classical physics (second law of thermodynamics, no closed timelike curves) as “implausible computational tasks”.

Most sci fi just pretends relativity doesn’t exist.

Yes, the point is that any way to send a signal between space like separated events A and B (in sr or gr) would also allow a return signal to be sent back from B to event C in the past of A. So any means of ftl signaling (wormhole, warp drive or whatever) is tantamount to building a time m achine. No amount of techno optimism or can-do cleverness will ever be sufficient to surmount this obstacle in real life.

Incidentally the Gödel metric runs into causality violation in a different way: closed timelike curves. No need for ftl , it’s even less realistic as Einstein is quoted pointing out in the article.

Yes, which is why sci fi scenarios in which ships whiz between star systems will never, ever, ever happen.

Yes these are huge numbers, but quantities associated with physical space (# of objects) are nothing compared with quantities in combinatorial spaces (# of possible 256 bit passwords or # of possible games of chess).

It seems plausible that getting the sustained chain reaction of life going in a soup of organic molecules and not immediately interrupting it may be at least as unlikely as randomly guessing a 256 bit password, in which case it will certainly never have happened a second time in the volume of space time we call the “observable universe”.

Indeed it doesn’t even need to be that small — even a 10^-28 chance makes it unlikely to have arisen anywhere else in the observable universe.

I’ve been aware of this fact as Feynman points it out in the course of the lectures, but find it totally nuts — there is some sense of scale I’m missing.

Matter consists of discrete chunks, atoms, but these chunks are so infinitesimal and numerous that there is no question of seeing them and any effect involving a handful of them is far, far below the human scale.

Light also comes in chunks, and the number of these chunks should be comparable to number of atoms since, e.g every single atomic transition generates a photon. Actually they should be far more numerous as they are massless and easily created, destroyed.

Yet, somehow, they are not far below the human scale of detection — as few as 5 (!) results in a perceivable flash.

What am I missing here? (Obviously this boils down to a numeric estimation and the numbers are what they are — my question is why do the numbers wind up even remotely in the human ballpark.)