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Why is Maxwell's theory so hard to understand? (2007) [pdf]

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161–170 of 250 posts

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#161
post #94

Earlier quoted context omitted.

You don't have to imagine an ordered grid. If grid unit is small enough (say plank length 1,6 10^-35) and the grid is chaotic, for the distances of ~ 10^-16 that we can measure, everything will look the same in all directions. This happens the same way in which steel demonstrates isotropic behavior although its microscopic structure is anisotropic. So there is no easy way to prove or disprove continuity of space.

A chaotic grid would be macroscopically observable because random + random != 2 random, it's equal to 'bell curve'. Everything would be smeared as a function of distance, which we don't see. This characteristic is observable for metals as well. Steel becomes less flexible as it's worked because it's grains become smaller and more chaotic - A microscopic property with a macroscopic effect.

In physics you never have measurements differentiating between distance 2 and say 2+10^-20, and that gives enough space to hide any 'bell curve' you want.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#162
post #138

Earlier quoted context omitted.

That's the "trivial sense" I'm talking about. If we restrict "cognition" to the stuff we know is discrete then trivially it's discrete. But cognition is a hell of a lot more than that.

I don't see how what we know is discrete. A word doesn't even have a discrete meaning, except locally in relation to other words. Saying A = B + C looks discrete, just by hiding any potential non-discreteness inside B and C.

I entirely agree. I wasn't making a statement that "what we know is discrete". I was referring to a particular subset of cognition as "what [i.e. the things that] we know are discrete".

There are aspects of cognition that are discrete: a language contains a finite set of phonemes and words, a human mind is capable of (painfully slowly) carrying out purely symbolic algorithms like those a computer performs, etc. My point was that these things are a small subset of cognition, and most of cognition we have no particular reason to think depends on discreteness, which I think is the same point you're making.

Personally I strongly suspect that the "discrete" aspects of cognition are things that have evolved on top of / within a system that is fundamentally continuous (analogue) in nature.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#163
post #125

Earlier quoted context omitted.

A discreet unit of measure exists in dynamics & its relationship to position space is informed by Heisenberg’s theorem. (My actual point is that Reality is neither continuous nor discreet - it is an infinitesimal point and it is our mind — that likes to name and number things and relies on duality to make ‘distinctions’ — that creates the universe, the subjective reality that we perceive as inhabiting.)

What is an infinitesimal point?

The tao that can be told is not the eternal Tao The name that can be named is not the eternal Name.

The unnamable is the eternally real. Naming is the origin of all particular things.Free from desire, you realize the mystery. Caught in desire, you see only the manifestations.

Yet mystery and manifestations arise from the same source. This source is called darkness.

Darkness within darkness. The gateway to all understanding.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#164
post #114

Maxwell didn't have the nice differential geometric notations that we use today, which allow us to write his equations in a very concise and easy to understand form. His original paper is way more convoluted, so at the time it must have been really difficult to understand for everyone except the subject matter experts. And he was of course building on the work of Faraday, Ampere and others. But like with other theori…

True, but he did use quaternions (by 1873), which allow the field properties to be written as a single equation. It's kind of sad that more physicists don't use or teach quaternions, while math and CS have fully adopted them. I really liked Kathy Joseph's historical reviews of vector physics and the people who developed it, which explain some of the reason's for how it's taught. Most texts don't even develop electrod…

Unfortunately he didn't use quaternions in his initial formulation (that was all split into xyz coordinates) and in his later revision he took apart the quaternions into scalar and vectors parts. It could have been so much prettier....but luckily we have geometric algebra for that today.

On the other hand he did derive the electric and magnetic fields from a scalar and potential field. In that sense Heaviside made a step backwards.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#165
post #61

Earlier quoted context omitted.

> continuity of spacetime is a convenient approximation I disagree, and there's no evidence for this. This is computer science leaking out; physics has no formulation of spacetime in discrete terms, and indeed, all of physics presumes continuity. In QM, the space of wavefns is infinite-dim continuous, and if wasnt, QM wouldnt be linear. Cognition is discrete, but the world is continuous.

If it really was continuous so that physical quantities were real numbers as defined in mathematics, then it is in contradiction to maximal information density. Because almost all real numbers contain infinite amount of information. Full argument is elaborated here "Indeterminism in Physics, Classical Chaos and Bohmian Mechanics. Are Real Numbers Really Real? by Nicolas Gisin": https://arxiv.org/abs/1803.06824

I am very sympathetic to Gisin and his cause, but he does not propose any sensible resolution. By the way, not a fault, and no blame for him. Pointing out logical deficiencies always comes before a satisfying solution, and he is to be praised for his insight.

There are many interesting ways to probe this problem.... here's one:

Say I tell you to imagine a circle, an ideal Platonic circle in a Cartesian coordinate system (real coordinates, first uneasiness). Let's ignore translation, so it is centered at (0,0). I tell you the radius. Can you imagine the circle with Plato? Model the circle? Reproduce the circle? Do you need pi? Does the circle include or encode pi? But pi is has infinite information.

Perhaps all you need is the square root function? But that's also an infinite Taylor series expansion. You can plot and recreate the circle to any precision if you have a square root function. The series will only need to run to the required precision. The circle will always be granular, depending on the number of terms you use in pi, or the square root function. Yeah, right, obvious, so why is that a problem?

What if I tell you the circle is the physical manifestation of equipotentials of a stationary charge (say, nucleus), or mass (say Earth), with inverse square law - so basically a geometric fall-off with range determined by spatial (circular, spherical) considerations. What is the force at some distant point? Do you need pi? Do you need square root function? Or reciprocals? How does the other charge or mass feel the 56,323rd decimal place of the force due to the potential?

Maybe it doesn't, because by the time it has felt the second decimal place, time has moved on, the charges/masses have moved on, and the nuance of what would've/should've been felt in a never changing universe are never experienced. There is a modified differential equation that relates various time derivatives to precision of experienced forces (this almost sounds like relativity :)

The discrete explanation with photons goes like this: the force is produced by radiating photons. They automatically encode the geometric expansion as inverse square law, because of their pathways, no need for pi, or sqrt functions. But that is statistical, the accuracy is only as good as the number of photons that can arrive from the source. The circular/spherical nature of the force only emerges over time, as photons arrive and act. The accuracy of smooth circularity and inverse square only establishes itself over time...

Elapsed time affects experienced precision - hmmm, interesting.

How would you quantify such a thing, where time changes the precision of what you feel? Well, the other obvious example is the Heisenberg Uncertainty Principle. This is just a simple and obvious example of Fourier Analysis for any theory based on a linear wave equation. It almost doesn't need stating, and if it must have a name, it is certainly Fourier, not Heisenberg. Anyway, any math/physics/engineering student knows Fourier to their core, and it gives a nice solution to the information problem: coordinates may be real-valued degrees of freedom, but there is no way to mathematically or physically resolve all coordinates and their derivatives to infinite precision. It's just not possible, even if the underlying equations/reality maintain the fiction of real-valuedness.

Fourier combines time, waves, amplitude, velocity (momentum, etc.) with a specific expression for possible information. A picture is worth a thousand words at this point, just look at a wave-packet, it's obvious. Fourier is a masterwork, and vastly underappreciated as a fundamental limit on knowledge, in a real world sitting on smooth continuous waves.

So Fourier sets limits on knowledge, even in the wavy world of the smooth continuum. Of course, I do not believe in the smooth continuum anyway, but Fourier is my wingman to fight the real-infinitists on their own smooth turf.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#166
post #135

Earlier quoted context omitted.

No, position and time are typically continuous variables in quantum mechanics. You can have formulations in which they are discrete but they are not required and are relatively exotic. QM certainly doesn't say they must be discrete.

I feel that a lot of people here are confusing the math and "reality". You're definitely correct about the math, i.e. the systems that we humans have invented to model reality. But I guess most of us don't really care about what mathematical model scientists like to use (especially not whether they're "exotic" or not), but rather what reality could be like. And the quantum properties of QM do seem to suggest that the…

I responded to a couple of people who claimed with great certainty that QM meant spacetime had to be discrete, when it says nothing of the sort. I haven't claimed we have proof that it is continuous and I doubt we ever will as that seems akin to proving a negative existential.

Your penultimate paragraph suggests some confusion about ideas like Planck scale and quantisation.

Firstly, there is nothing special about the Planck length itself. It's just a unit of length. Around that sort of scale, though, our current theories of physics happen to break down because both quantum and gravitational effects become significant. That doesn't imply spacetime is discrete (or preclude it being discrete) at that scale. It's just a realm that our current theories don't work in.

Secondly, while describing aspects of nature that are quantised was a large part of why quantum mechanics was developed (and the source of its name), it in no sense says anything like "there's some sort of fundamental discreteness in reality". Quantum mechanics deals with both discrete and continuous observables in a single framework: functional analysis, essentially. The set of possible values for an observable is modelled as the spectrum of an operator, which can be either continuous or discrete. Which sort of observable is appropriate for a given physical theory is a choice made in constructing that theory. For things like charge and spin we use discrete (quantised) values because we have evidence that those things are quantised. For things like position we use continuous values and have no evidence that using discrete observables would better match nature.

Space could in reality be either discrete or continuous, or not even exist in any form we'd recognise as "space" on those scales. Quantum mechanics doesn't give us any hints one way or another.

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#167
post #100

Earlier quoted context omitted.

All the people who use thinks like the word "information" in this context are confusing thermodynamic, logical, probabilistic, (+ many others) and equivocating. "Information" is not a physical quantity, and there cant be a "volume" of it. Nor does this have anything to do with real numbers. It is impossible for there to be any system extended in space and time to "zoom infinitely" into a continuous range and hence re…

Some people would disagree with dismissing information as non physical. For instance: https://scottaaronson.blog/?p=3327 The argument there would be that stuffing an extra bit of information in an information saturated volume would make it collapse into a black hole.

Yes, the thermodynamic properties of information are well established.

Various Hawking-Bekenstein results about black holes relate to information density, especially, shockingly, that information is proportional to surface area, not volume. This makes perfect sense because a black hole has all its incoming matter and energy sprawled, flattened and red-shifted on its horizon (to a distant observer). It can never export its internal state to the outside world, so you might never expect a volume's-worth of states to be exposed.

The idea was generalized by 't Hooft to the Holographic Principle, for 2D screens encoding the state of 3D volumes on the other side.

However, the full AdS/CFT Correspondence only applies to a certain type of AdS space, not our actual dS space. At the moment, it seems half of theoretical physics doctoral students are trying to extend AdS/CFT to dS space (obviously - strings :) and half of observational astrophysics doctoral students are desperately hoping to show we live in AdS space - LOL

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#168
Prior to computer-generated 3D animation, I can imagine it was very difficult to float and spin vector-arrows in mid-air with enough accuracy to show what goes on without having to resort to reams of explanatory paragraphs.

Eugene Khutoryansky is something of a lesser-known 3b1b that's more focused on physics than math. I found his animations very helpful for building intuition around Maxwell's equations:

https://www.youtube.com/watch?v=9Tm2c6NJH4Y

Re: Why is Maxwell's theory so hard to understand? (2007) [pdf]

#170

Earlier quoted context omitted.

As someone who was once a, "I've watched a lot of YouTube videos about physics", person, i think it's very interesting how confident people are in their understanding of what is essentially the edge of physics, something only seen in a masters or doctorate degree. Specifically the whole spacetime and qm thing. There's so many videos on it that you begin to feel like you really understand it after half a dozen or so r…

My favorite phenomenon of which you speak are the guys who haven’t thought about math since 11th grade or physics ever aside from seeing some Joe Rogan clips with Eric Weinstein but will pound their keyboards with fury that “STRING THEORY IS A BIG LIE!!!”

Well, unfortunately some otherwise great physics educators intentionally stoke that fire, portraying the current particle physics agenda as if its some conspiracy to waste funding rather than the consensus of thousands of the best minds in physics. Selling people a superficial sense of contrarian insight ends up being a very successful marketing tactic.
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