'Fudge factors' in physics?

October 11, 2018 by Tracey Bryant, University of Delaware
UD doctoral student Muhammed Shahbaz (left) and his adviser, Prof. Krzysztof Szalewicz, have shown that the “fudge factors” commonly used with a theory for predicting how atoms will interact are actually based on a faulty assumption. Credit: University of Delaware

Science is poised to take a "quantum leap" as more mysteries of how atoms behave and interact with each other are unlocked.

The field of quantum , with its complex mathematical equations for predicting the interactions and energy levels of atoms and electrons, already has made possible many technologies we rely on every day—from computers and smartphones, to lasers and . And experts say revolutionary advancements are destined to come.

But to take a giant leap, you have to be physically fit, and researchers at the University of Delaware have found an area of quantum physics that could use some more calisthenics, you might say. The research, performed by doctoral student Muhammed Shahbaz with his adviser, Prof. Krzysztof Szalewicz in the UD Department of Physics and Astronomy, was published recently in Physical Review Letters, the journal of the American Physical Society.

Just like people, atoms can be attracted to each other, or, well, be repulsed. Take argon—the third most abundant gas in Earth's atmosphere. This non-reactive gas has a variety of uses, from protecting historical documents to preventing the tungsten filament from corroding in fluorescent lights. When two argon atoms are far away from one another, they will be attracted to each other until they get down to about 3.5 angstroms and then they will repel each other. It's as though once they've gotten a really good look at each other, they're ready to move on.

But that's not what physicists found about two decades ago when they tested the density-functional theory (DFT), which is now widely used to model and predict the electronic structure of atoms. Most versions of DFT were either predicting no attraction or only a very weak one. Where did the failure lie? The attraction between argon atoms originates from "dispersion interactions" between electrons, as the motions of the electrons of one atom influence the motions of the electrons of its partner. DFT can't accurately account for these correlated motions at long range.

And that's a problem, especially in a field like materials science, where physicists may design and predict the properties of a new material—from its strength to its magnetism to its ability to conduct heat—without ever going into a lab to do an experiment.

So physicists began developing "fudge factors" in the early 2000s to account for this dispersion energy. Some of these methods turned out to give reasonably good results and became an extremely popular tool in computational physics, chemistry and . The scientific papers proposing such methods have been cited tens of thousands of times.

What Shahbaz and Szalewicz have shown, after more than a year of intense analyses, is that all of these fudged methods are actually based on a faulty assumption. DFT can describe how the motion of one electron both affects, and gets affected by, the motion of another electron when the distance between them is on the order of one angstrom. At separations above one angstrom to about seven angstroms, the correction methods assume that DFT recovers a fraction of these effects. Shahbaz and Szalewicz have found that this quantity does not have the characteristic properties of dispersion energy and actually originates from errors in the theory that are unrelated to dispersion. Thus, the researchers say, the correction methods may get good results, but for the wrong reasons.

"We are telling the physics community that you have to go further, toward a universal method of prediction that works for the right reasons," Shahbaz says. "We are not here to criticize, but to help improve," he humbly adds.

Currently, Szalewicz and Shahbaz are on a team of theorists and experimentalists from universities across the United States who are using to predict the structures and energies of crystals, the stuff of which snowflakes, ice, most rocks and minerals, some plastics, pharmaceuticals, energetic material and other products are made. Their complex calculations predict, for example, how much energy can be packed into a given volume of rocket fuel.

Shahbaz, who is the first author on the journal article, says he never would have guessed as a child in his small village in Pakistan that he would someday become a physics professor. He grew up helping his father, who is a farmer, grow reed, rice, chilis, tomatoes, eggplants, radishes and okra. Now he is the first in his family to be awarded a college diploma—not to mention academia's highest degree, which is now in plain sight.

When he was applying to graduate school, he received offers from universities in the U.S. and Canada, but says he ultimately decided on UD because of the University's reputation and the flexibility to work on a master's degree first. He says that helped him decide what he really wanted to focus his research on.

When he completes his doctorate in the next few months, he already has a job lined up, as an assistant professor of physics at the University of the Punjab in Lahore, where he is destined to hook students on how light and gravity work, just as he was enthralled as a youngster.

So why does he like physics so much? "Physics tells you about the laws of nature," Shahbaz says. "It also demands reasoning. You don't have to memorize anything—just absorb life."

Explore further: Energy in action: For two molecules on blind date, new method predicts potential for attraction or repulsion

More information: Muhammad Shahbaz et al. Do Semilocal Density-Functional Approximations Recover Dispersion Energies at Small Intermonomer Separations?, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.121.113402

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Scroofinator
1.7 / 5 (12) Oct 11, 2018
is that all of these fudged methods are actually based on a faulty assumption


Much of physics is based on faulty assumptions.

How is space-time conceptually different from a frictionless aether again?
jonesdave
3.5 / 5 (19) Oct 11, 2018
is that all of these fudged methods are actually based on a faulty assumption


Much of physics is based on faulty assumptions.

How is space-time conceptually different from a frictionless aether again?


Because GR is tested, and works. Aether theories are pure woo, and shown to be wrong. That simple, really.
Scroofinator
1.7 / 5 (11) Oct 11, 2018
And works in most cases... Ftfy

If aether is pure woo why was Einstein an aetherist?
http://www-histor...her.html
Eikka
4.4 / 5 (11) Oct 11, 2018
If aether is pure woo why was Einstein an aetherist?


Einstein's "aether" was in name only. It was stripped of all the qualities previously ascribed to it. Einstein's whole point was that space IS the aether, whereas previously people thought space is just empty and without any properties, and is filled with a medium called the aether.

But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.


Most modern "aetherists" confuse these definitions, and don't really know what they're arguing about. They're just repeating words that sound good and plausible in their heads, picking a phrase from here and another there.
Scroofinator
1.5 / 5 (8) Oct 11, 2018
Right that's why I said "frictionless" aether. It was assumed previously to have drag, which the Michelson-Morely experiment proved it didn't. To quote Einstein:
To deny the ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view.
Eikka
5 / 5 (11) Oct 11, 2018
Right that's why I said "frictionless" aether. It was assumed previously to have drag, which the Michelson-Morely experiment proved it didn't. To quote Einstein:
To deny the ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view.


Yet:

The ether of the general theory of relativity is a medium which is itself devoid of all mechanical and kinematical qualities, but helps to determine mechanical (and electromagnetic) events.


Einstein's aether is an elaboration on Lorenz's aether, which was already a complete departure from all the traditional aether theories. An aether in name only. This was an idea in transition, and the term "aether" was used as an anachronism - it no longer applied but they hadn't anything better to use instead.

It's like, there used to be people called "computers" in the past. Naming isn't explaining.
Eikka
4.7 / 5 (9) Oct 11, 2018
The thing about Einstein's "aether" vs. all the previous aethers is that it's Machian, in that all the previous aethers suppose the medium is actually physically THERE as some sort of a THING, in space or instead of space, whereas the Mach's principle roughly states that the local laws of the universe are determined by the distant (non local) environment, i.e. how space behaves here depends on where you are in relation to everything, and what that everything is.

And that no longer jives with any traditional understanding of aether. It doesn't fit with any sort of "frictionless fluid" oozing around in space, or any other ad-hoc patch put on the aether theory. That's why the name was dropped to avoid confusion.
Eikka
5 / 5 (8) Oct 11, 2018
It was assumed previously to have drag, which the Michelson-Morely experiment proved it didn't.


The drag hasn't got to do with friction in the medium, but the fact that you're moving relative to the medium which is carrying the waves that you're sending out. That is, there's a "fixed" (though it might be mobile) background of the aether, to which you can say you're moving relative to. It's like shouting into the wind - your voice is carried faster downwind than upwind.

Instead, Einstein's relativity says anyone at any (moving) frame of reference should measure the speed of light to be the same in every direction. In other words, they're not moving relative to any background, since space isn't a THING, nor is there any THING called aether IN space.
Eikka
5 / 5 (7) Oct 11, 2018
To make the aether theory compatible with Einstein, you'd have to imagine that each particle in space has its own private aether that travels along with it, or vice versa.

If we then suppose that each of these private aethers interact with others, you get a kind of fudged up version of Quantum Mechanics where the wavefunction of a particle is named its "aether".
Whydening Gyre
5 / 5 (5) Oct 11, 2018
The one major property of space is, well, 3 dimensional space.

Whatever is physically IN it are properties of other stuff...
Scroofinator
1.8 / 5 (6) Oct 11, 2018
To make the aether theory compatible with Einstein, you'd have to imagine that each particle in space has its own private aether


That's exactly how it works in my mind. Everything is fields, and the aether to me represents the field lines created by each individual mass, from atoms to planets. The aether doesn't move, but it does distort like GR says and masses travel along the lines. As far as I can tell, there's two basic distortions of the field, curling in (magnetism) and diverging out (electricity), and in the case of a black hole both.

Each aether field is unique, but they all interact. The hydrogen bond is one of the strongest we know of so it makes sense that its field would be stronger than the rest (DM), while helium is happy on its own (DE). Each field has it's specific frequency, hydrogen's is the Lyman-alpha frequency and the Earth's is the Schumann resonance.

Field strengths are defined by magnetic moments, but my maths sucks so no proof yet.

rrwillsj
3.8 / 5 (5) Oct 11, 2018
I have two rules of thumb about the variety of claims for the actual existence of aether. Which is a good constraint with me only having two thumbs!

First Rule: Explode a nuclear bomb over a city? Utter devastation!. That is a real event made possible by the SR & GR Sciences involved in creating that explosive device.

Explode am Aether bomb over a city? And not a damn thing happens? Cause there is not a shred of empirical evidence for it.

Second Rule: Following the guidelines st for filing a patent with the US Patent Office. A claim for patenting aether would require the presentation of an actual, working, physical device clearly operational upon claimed aether principles that can be tested by multiple third-parties to prove that it is a functioning innovation.

A, what? Two centuries of vaporware bombast and no results?

"Jam Yesterday..."
"Jam Tomorrow..."
"But Never, Jam Today!"
Scroofinator
1.8 / 5 (5) Oct 12, 2018
Aether bomb


An EMP is a pretty potent weapon. Its a disturbance of the field after all.
Ojorf
4.6 / 5 (9) Oct 12, 2018
Why do you call it 'aether' then if you actually mean the fields in quantum field theory?
Or don't you mean those fields? Have you sucked a new field out of your thumb?
Scroofinator
1.3 / 5 (4) Oct 12, 2018
I consider quantum fields at scales smaller than an atom, where as aether signifies the fields created by atoms and larger.
Ojorf
4.4 / 5 (7) Oct 12, 2018
That makes no sense, quantum fields are at scales much smaller than an atom.
What fields are you talking about?
Scroofinator
1 / 5 (4) Oct 12, 2018
Right, QFT comprises of fields at the particle level, not atomic level. AFAIK there's not a hydrogen field in QFT, but I admit I'm not super well versed in it.
rrwillsj
3.7 / 5 (6) Oct 12, 2018
D, what scrotum is talking about is deliberately to avoid facing up to the issues I raised. My challenge to the aether-suckers too put up or shut up!

To show us a working device based on aether blather.

Betcha the aether-dolts will either claim to have one but only available to view on a utube video.

Or, they'll get back to us with a miracle-machine just as soon as they receive their back-order of the unobtanium needed to power it. Whenever it can be delivered from the order they placed out of the Montgomery Wards catalogue.
Ojorf
4.2 / 5 (10) Oct 12, 2018
... I admit I'm not super well versed in it.


Quite an understatement.

Scroofinator
1 / 5 (5) Oct 12, 2018
To show us a working device based on aether blather

Have you not been paying attention? The aether is a concept, not a thing. Do we have a device based on the Higgs field?

Quite an understatement

What you want me to lie like the rest of the chaches on this site? I'll ask you, is there a specific field for each element in QFT?
Ojorf
4.5 / 5 (8) Oct 12, 2018
There are 12 fundamental fields each for bosons and fermions, so 24 in all according to the standard model.
Scroofinator
2 / 5 (4) Oct 12, 2018
All of those are generated at the sub-atomic level. The only thing we can classically test is at the atomic level and above, and we don't have well defined fields for much of it. Energy in my mind only forces the field into different configurations. Masses flow along established lines, there's no real attraction or repulsion.

I estimate there's 137 different fields at the classic level including: elements and they're naturally found clouds, different types of planets, stars, galaxies, and black holes.

The average strength of each field is extremely close, but hydrogen is relatively more energetic than all other elements so it distorts the field slightly more:
https://en.wikipe...c_masses
This theory potentially explains DM, especially considering the recent Lyman-alpha findings by MUSE, extra dense giant molecular clouds, and the anomalous increase of the AU just by considering the idea that all matter doesn't create equal fields.
Da Schneib
4.2 / 5 (5) Oct 12, 2018
ASSuming the fields that are expressed in open space are limited to gravity and EM is teh stoopit.
Scroofinator
1.8 / 5 (5) Oct 12, 2018
It even potentially explains the argon gas enigma in this article. At distances further than 3.5 angstroms the argon field is stronger than the electron field so there's an "attraction", but within that electron field is stronger. Like charges repel so away they go.

Helium, another noble gas, is the second most abundant element in the universe, and also repels. This could explain DE when considering energetic outbursts such as supernovae and quasars/polar jets. Free helium gas is constantly being accelerated away.
Da Schneib
4.3 / 5 (6) Oct 12, 2018
It's called Van der Waals effect.

On Earth.
Scroofinator
1.8 / 5 (5) Oct 12, 2018
Oh the same earth where we create fudge factors to account for an observation that we can't explain? A lot of good that thinking does here. Did your snide ass not even read the article?

Shahbaz and Szalewicz have found that this quantity does not have the characteristic properties of dispersion energy and actually originates from errors in the theory that are unrelated to dispersion. Thus, the researchers say, the correction methods may get good results, but for the wrong reasons.


So while yes, VDW forces explain the repulsion, we don't have an explanation for the attraction.

I wonder how often we may get good results for wrong reasons?
Da Schneib
4.1 / 5 (8) Oct 12, 2018
If you're just going to lie about it, there's no point in arguing. There never is a point to arguing with a liar. I assume you're lying and just not stupid.

Van der Waals forces are both attractive and repulsive, depending on distance. This has been known for decades.
Scroofinator
1.7 / 5 (6) Oct 12, 2018
Uh what? The point of this article is that we made assumptions based on VDW principles that have been proven wrong at distances greater than 1-7 angstroms. What am I misunderstanding here?
Da Schneib
4.4 / 5 (7) Oct 12, 2018
Maybe if you did a little more research or read the article a little more carefully you'd come across DFT, density functional theory. Which is what's really being challenged.
Scroofinator
1.7 / 5 (6) Oct 12, 2018
Of which the VDW is a part of, especially when dispersion effects are specifically mentioned as being in error.

Look if you want to accept false assumptions and fudge factors as good enough, that's fine keep at it. I don't accept it, so unless you are either trying to help or trying to prove me wrong with evidence, you might as well not comment because I'm done entertaining your basic mind.
Da Schneib
4.5 / 5 (8) Oct 12, 2018
No, Van der Waals forces are a feature of reality.

DFT is the only theory we have of how they work. What's being proposed is that some simplifications in DFT don't accurately represent Van der Waals forces and that we have the numerical processing power to stop using those simplifications.
rrwillsj
4.2 / 5 (5) Oct 13, 2018
Oh scroofed, you and your cult of fraudulence have had two centuries to produce any physical, repeatable empirical evidence.

Total Fail.

The Higgs particle has only been confirmed a few years ago. I'd bet that we will see technology from it a lot sooner than you can show a working devise based on aether lack-of-principals.

Heck, it took only a few decades to achieve tech based on SR, GR and QM theories.

You may as well be preaching spiritualism and mesmerism as aetherism!
torbjorn_b_g_larsson
4.8 / 5 (6) Oct 13, 2018
This is ridiculous, on both sides - the critical paper and the cranks that takes one small model problem to imply that physics does not work which we know it mostly does. The paper is arguing about how many angels can fit a needle point, since they analyse a 5 % component of the modeled energy. So maybe it will lead to a better understanding of the modeling and/or the modeled system, maybe not.

"The aether is a concept, not a thing. Do we have a device based on the Higgs field?"

If it is not an existing thing, we have nothing pertaining to reality to discuss. A device using Higgs fields (there are 4 of them - now mostly accepted - but only 1 free particle - also accepted; you may want to read up) are stuff like the universe (they give many particles mass) or even the LHC in some specific experiments.
torbjorn_b_g_larsson
4.8 / 5 (6) Oct 13, 2018
"the argon field".

Here is another thing you may want to read up on. There is no such field, as already explained to you the fields are related to elementary particles.

You seem to say that the quantum field vacuum of dark energy - which we do not understand well for similar reasons as the Van der Wall forces, it is complicated yet can sum to a weak result - is your "aether". That was precisely what Einstein made an advance on, his "ether" was space which may be filled with such fields but differ in predictions. Fields are special relativistic and "flat space", space is general relativistic and potentially curved*. Say, linearized field theory cannot predict the relativistic effects used in GPS systems.

[*Except when used in cosmology, which shows space is large scale flat and linear fields is a pretty darn good approximation outside of black holes and GPS systems. But that is another story.]

Simple as that.
Anonym625467
2.2 / 5 (6) Oct 13, 2018
Article author Tracey Bryant writes the following about argon: "This non-reactive gas has a variety of uses, from protecting historical documents to preventing the tungsten filament from corroding in fluorescent lights."

Fluorescent lights don't use tungsten filaments or argon gas. How are we supposed to take a story like this seriously if it contains such a basic error?
Eikka
4.4 / 5 (5) Oct 14, 2018
Each field has it's specific frequency, hydrogen's is the Lyman-alpha frequency and the Earth's is the Schumann resonance.


That's still complete woo, and not even wrong because it's based on a fundamental misunderstanding of what either of those things mean/are.

Like I said, many people who discuss the aether are simply pulling words and phrases and combining them in a way that sounds plausible to them. That sort of "science by semantic association" is actually a feature of schitzophrenia and bipolar disorders.

https://en.wikipe...disorder

zz5555
5 / 5 (5) Oct 14, 2018
Article author Tracey Bryant writes the following about argon: "This non-reactive gas has a variety of uses, from protecting historical documents to preventing the tungsten filament from corroding in fluorescent lights."

Fluorescent lights don't use tungsten filaments or argon gas. How are we supposed to take a story like this seriously if it contains such a basic error?

From https://www.pacif...-gas.asp :
Argon gas is used in fluorescent and incandescent light bulbs to stop the oxygen in the light bulbs from corroding the hot tungsten filament.

Wikipedia says the same thing, but not as succinctly.

How are we supposed to take anything you say seriously if your comment contains such a basic error? ;)
Nik_2213
3 / 5 (2) Oct 14, 2018
Fluorescent 'strip' lights have a heated starter filament, which erodes to leave the infamous darkening near tube ends, and high-frequency CFLs certainly have electrodes which run hot...
Steelwolf
3 / 5 (2) Oct 14, 2018
Not only do they use Argon in fluorescent lights to protect the Tungsten electrodes at the ends, but it is there to displace the oxygen that would react with the mercury vapor also present in fluorescent lights to produce mercury fulminate and detonate the tube.

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