## 1489: "Fundamental Forces"

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Dr What
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### 1489: "Fundamental Forces"

title=""Of these four forces, there's one we don't really understand." "Is it the weak force or the strong--" "It's gravity.""

I would use "interactions". Just because it sounds cool.

Jiffy
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### Re: 1489: "Fundamental Forces"

I literally just refreshed and found this.

rhomboidal
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### Re: 1489: "Fundamental Forces"

I translate "mumble" as "midichlorians."

rmsgrey
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### Re: 1489: "Fundamental Forces"

Yeah, the weak force is magic - and totally not a force - it transmutes fundamental particles and ignores symmetry...

The strong force does at least attract things to each other...

xokocodo
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### Re: 1489: "Fundamental Forces"

While I'd like to think I know a good amount of physics, the last two panels pretty much summarize my understanding of the Strong and Weak forces.

Rombobjörn
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### Re: 1489: "Fundamental Forces"

Also, one of these forces is extremely weak compared to the others, and it's not the weak force. It's gravity, the one that overwhelms all the others in black holes.

Ronfar
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### Re: 1489: "Fundamental Forces"

Of course, gravity doesn't actually follow an inverse square law, it follows general relativity, which can be approximated very well by an inverse square law...
- Doug

Envelope Generator
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### Re: 1489: "Fundamental Forces"

"Fundamental interactions, also known as fundamental forces or interactive forces, are the interactions in physical systems that appear not to be reducible to more basic interactions."[1] (italics mine)

Then this graph here:
http://en.wikipedia.org/wiki/Theory_of_ ... f_theories

If magnetism by itself is not a fundamental force because it's been reduced to electromagnetism, why is electromagnetism considered a fundamental force despite its having been reduced into the electroweak interaction which itself has been further reduced?
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niauropsaka
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### Re: 1489: "Fundamental Forces"

Who else said, "Exactly!" when they reached the mouseover text?

dtilque
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### Re: 1489: "Fundamental Forces"

Hey, we know lots more about gravity than we do about quiintessence...

Rombobjörn wrote:Also, one of these forces is extremely weak compared to the others, and it's not the weak force. It's gravity, the one that overwhelms all the others in black holes.

Is it weaker than quintessence?
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The Moomin
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### Re: 1489: "Fundamental Forces"

dtilque wrote:Hey, we know lots more about gravity than we do about quiintessence...

Rombobjörn wrote:Also, one of these forces is extremely weak compared to the others, and it's not the weak force. It's gravity, the one that overwhelms all the others in black holes.

Is it weaker than quintessence?

When I see quintessence, I always think of the dream sea from Clive Barker's books of the art.

In this sense, it makes as much sense as the other forces do to me.
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### Re: 1489: "Fundamental Forces"

xokocodo wrote:While I'd like to think I know a good amount of physics, the last two panels pretty much summarize my understanding of the Strong and Weak forces.

This.

Actually I came here hoping someone would be explaining them a little bit more....
There's no such thing as a funny sig.

Dr What
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### Re: 1489: "Fundamental Forces"

Envelope Generator wrote:If magnetism by itself is not a fundamental force because it's been reduced to electromagnetism, why is electromagnetism considered a fundamental force despite its having been reduced into the electroweak interaction which itself has been further reduced?

I think that's because EM and weak can only be unified at a very high energy scale - "on the order of 100 GeV". But E and M can be unified at energy scale of our everyday life.
I guess as the universe expands, someday EM interaction will also split into different interactions. Maybe it will happen on another interaction first... Or maybe it's already at the bottom, there will be no more splittings. Anyway...

Pfhorrest
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### Re: 1489: "Fundamental Forces"

Best XKCD in a while. I consider myself fairly knowledgeable about physics, for someone without a degree in it at least, and... what the hell does the weak force do? The friggin' Higgs mechanism makes more sense. (Does that count as a fifth fundamental interaction, if it actually exists as it now seems more likely to?) Actually, I guess the Higgs mechanism, if I understand it right, is kind of similar to the weak interaction in that it's somehow turning the kinds of particles that would be there in the absence of a Higgs field into the kinds of particles we see in reality by them interacting with it, and that part is equally mysterious to me as the weak force, but... ok, with Higgs at least, I get that there's some kind of field, that's just everywhere, and particles are interacting with it somehow, and being changed by it, and that interaction forces them to drop below c and gain mass; but with the weak interaction... a neutron is just sitting there and suddenly decides to become a proton, electron, and electron antineutrino, because, uh, weak interaction did it. What exactly was interacting with what, where? How is that an interaction?
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da Doctah
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### Re: 1489: "Fundamental Forces"

Gravity for the common man: "What goes up must come down".
Electromagnetism for the common man: "What switches on must switch off".
Strong force for the common man: "What have you been eating, onions?"
Weak force for the common man: "What are these Lego pieces doing all over the floor?"

Envelope Generator
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### Re: 1489: "Fundamental Forces"

Dr What wrote:I guess as the universe expands, someday EM interaction will also split into different interactions. Maybe it will happen on another interaction first...

That's an interesting thought! Wouldn't such a split be observable by some sort of low-energy experimentation? (I am quite clueless about physics.)
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Positron
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### Re: 1489: "Fundamental Forces"

As someone who stopped physics at end of high school, I'd like to join the chorus of enthusiastic head bobbing about particularly the explanation of the weak nuclear force.

Dr What wrote:
Envelope Generator wrote:If magnetism by itself is not a fundamental force because it's been reduced to electromagnetism, why is electromagnetism considered a fundamental force despite its having been reduced into the electroweak interaction which itself has been further reduced?

I think that's because EM and weak can only be unified at a very high energy scale - "on the order of 100 GeV". But E and M can be unified at energy scale of our everyday life.
I guess as the universe expands, someday EM interaction will also split into different interactions. Maybe it will happen on another interaction first... Or maybe it's already at the bottom, there will be no more splittings. Anyway...

What exactly constitutes "splitting", anyway? Why are electrical and magnetic forces considered aspects of electromagnetism, but electromagnetism and weak force aren't aspects of electroweak in the same way? And what changed since the time that they were unified?

Also, if gravity and electromagnetism both follow inverse square laws, how does gravity "catch up" at larger scales?

orthogon
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### Re: 1489: "Fundamental Forces"

Because bulk objects are electrically neutral, so over large distances there is no significant electrostatic force. Gravity on the other hand is always attractive, because (i think) we currently believe that all mass is positive. So big things are highly attractive. (Like your mom)
xtifr wrote:... and orthogon merely sounds undecided.

juanro
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### Re: 1489: "Fundamental Forces"

I think we should call "physics" to the knowledge up to about 1870.
Those theories and discoveries since then should be given another name and put in another compartment (of my mind, at least).
Then, "Yeah, I know physics pretty well, yes. And it works and it explains pretty much all that happens in real life, yes."

Juanro

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### Re: 1489: "Fundamental Forces"

juanro wrote:Those theories and discoveries since then should be given another name

I suggest calling them "sorcery"

Kit.
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### Re: 1489: "Fundamental Forces"

juanro wrote:I think we should call "physics" to the knowledge up to about 1870.

That would be very clumsy, because it would include Maxwell's equations, but not Lorenz transformations.

squareroot
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### Re: 1489: "Fundamental Forces"

As someone who doesn't actually know much physics, but is trying --

Electromagnetism is special as "one" force because it doesn't require energy to convert from one to the other. The equivalence between the two is just dependent on frame of reference -- https://en.wikipedia.org/wiki/Moving_ma ... or_problem is a good introduction to the kinds of problems that people had, and https://en.wikipedia.org/wiki/Relativis ... omagnetism is the solution (and more examples of problems it also resolves!). There is no natural energy scale necessary to observe the interchange, only changes of frame of references, which can be accomplished by an arbitrarily light particle with arbitrarily small energy.

Other force-splitting, like the electroweak, occurs because at when you get a particle to a very very high energy you can start to interchange between weak and electromagnetic particles. Like, you know how a photon can split into an electron and positron, and then back again -- but a certain minimum amount of energy needs to be in the photon for this to happen, because it has to make up all the mass of the positron and electron (which are, yes, both positive. Antimatter still has positive mass.) Thus, that kind of interaction has a characteristic energy scale. Similarly, there is a natural energy scale for EM-weak interchanges.

If you can imagine all of the world's photons being super-high energy, and tons of them everywhere (imagine a sun of pure gamma rays!), then they would be switching between photon and electron-positron very rapidly all the time. You wouldn't really talk about one or the other, just the constant mix. And in fact talking about one or the other would be wrong because they would be in a constant quantum superposition anyway. In this sense, you would have a "unified" photon/electron-positron "force". (If electrons and positrons were force particles. In a sense they're just weird bits of electromagnetism. With a weak interaction component. Yeah... anyway...)

The weak force has a similar characteristic energy scale required for Things to Happen, and if you get way above that scale, like 10x higher, then those things are constantly happening all the time, and it's a persistent soup of some things that are electromagnetic and some things that are weak. And since the universe used to be much hotter (energy is conserved (mostly ... see: redshit) but space got bigger; less energy per space now), that kind of thing just was happening all the time because all the particles in the universe had a higher average energy, and so the force acted like one.

As for how/what the weak force does/is/verbs ... hellihavenoclue
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drachefly
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### Re: 1489: "Fundamental Forces"

The weak interaction describes how and when the fairly-rigidly-defined type boundaries that underlie the structure of matter leak.

Aiwendil
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### Re: 1489: "Fundamental Forces"

I think part of the trouble that a layperson runs into in understanding the strong and weak interactions is that they are thinking in terms of classical 'forces'. But fundamentally, what's going on are 'interactions' rather than (what we'd normally call) 'forces'.

EM isn't fundamentally an inverse square law. Fundamentally, it's a set of rules for how photons couple to other particles. The nature of those rules, plus the masslessness of the photon, plus geometry, means that if you step back from the individual interactions and look at their net effect on a charged particle, what you see is an inverse square law.

Similarly, the weak interaction is fundamentally a set of rules for how the W and Z bosons couple to other particles (which is different from how a photon does). One of the interesting things about the W boson is that is charged, and this ends up meaning that it can effectively change one kind of particle into another. But this isn't some kind of special power that's added into the weak interaction ad hoc; it's just a consequence of what the rules are for the weak coupling.

The strong interaction is a set of rules for how gluons couple to other particles. And the really interesting thing about gluons is that they can couple to themselves - something photons, Ws and Zs can't do. This leads to interesting things like quark confinement.

If you want to understand this better, read about Feynman diagrams. I think it's actually fairly easy for a layperson to understand what they represent. The different fundamental interactions are essentially rules for what kinds of vertices you're allowed to include in a Feynman diagram, as well as rules for how to assign probabilities to them.

Edit: A more pedagogical link for Feynman diagrams (haven't really read through it yet, but it looks rather friendly): Let's draw Feynman diagrams!

Klear
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### Re: 1489: "Fundamental Forces"

Rombobjörn wrote:Also, one of these forces is extremely weak compared to the others, and it's not the weak force. It's gravity, the one that overwhelms all the others in black holes.

I love how Alpine Kat described that: "You see, gravity is weaker than weak."

rmsgrey
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### Re: 1489: "Fundamental Forces"

A possible analogy for electro-weak unification is the relationship between diamond and graphite - two substances with very different physical properties, but if you get them both hot enough, they become indistinguishable blobs of atomic carbon - which, when it cools again, could become diamond, graphite, soot, or any of the exotic allotropes.

Coyoty
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### Re: 1489: "Fundamental Forces"

Outlined against a blue, gray October sky the Four Forcemen rode again...

mathmannix
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### Re: 1489: "Fundamental Forces"

Let's see... the four forces are Thrust, Summer, Famine, and Phlegm.

Spoiler:
Or how about Drag, Fall, Death, and Blood?
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brenok
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### Re: 1489: "Fundamental Forces"

mathmannix wrote:Let's see... the four forces are Thrust, Summer, Famine, and Phlegm.

Spoiler:
Or how about Drag, Fall, Death, and Blood?

Actually, they are North, Air, Ganymede and Telophase.

Mokurai
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### Re: 1489: "Fundamental Forces"

This appears to be almost, but not quite, entirely backwards.

General Relativity explains gravity as the geometry of spacetime, which, in Newton's phrase, "answers pretty nearly". Spacetime is in turn explained by the distribution of energy, including matter, electromagnetic radiation, dark energy, and possibly other poorly known or even unknown cosmological fields.

Everything else fails to be explained at all. The EM, weak, and strong forces in the Standard Model can be represented up to a point by the Wave Equation with various energy terms in the Hamiltonian, but even apart from the terms that are still missing and our inability to solve many fundamental cases, none of that can be taken as an explanation, as Niels Bohr pointed out.

"If you think that you understand Quantum Mechanics, that is evidence that you don't."

After all, the Wave Equation is part of a construct, QM, that says that its solutions, when multiplied by their complex conjugates, give the squares of the probabilities of all observables. Sure, it gives all sorts of right answers to the extent that we can compute them, but if that explains anything, I'm the second-order Maxwell demon from the Cyberiad, producing not only order but information out of nothing. James Peebles of Princeton pointed out in his QM textbook many years ago that the greatest difficulty for beginning students of physics is giving up on the idea of understanding QM and accepting that all we have is the ability to get right answers some of the time. He noted that as QM penetrates the culture, the time required for new students to get to this acceptance has been getting shorter.

One of the main points where the Wave Equation breaks down in the presence of GR is that the necessary partial derivatives are defined only in flat spacetime, which does not exist. You can have a Newtonian or Special Relativistic approximation, but in cosmological or very high gravity GR you would get intersecting spacelike slices of spacetime under any sort of variable acceleration such as a gravitational orbit. That would make hash of forward causality if it was physically real. Unlike GR, you can't connect locally flat tangential coordinate systems into usable spacelike surfaces in curved GR spacetime within QM into something that works.

Actually we don't understand any of the supposed forces in physics. Force is an unobservable construct derived from observable effects such as accelerations, creation and absorption of particles, and transformations of one kind of particle to another. Assuming, of course, that there is such a thing as a particle, when in fact all that we can observe of supposed particles is certain kinds of acceleration, emission, absorption, and transmutation interactions with other supposed particles.

So anyway, gravity produces accelerations of particles, changes in the passing of time, frame dragging and more.

The electromagnetic force produces accelerations between charged particles (electrical) and sideways (magnetic), plus (along with the Pauli exclusion principle) electron shell structure in atoms with emission and absorption of photons over a wide range of energies, and more. The constancy of the speed of electromagnetic waves gives us Special Relativity.

The strong force (also with the Pauli principle) produces shell structure in atomic nuclei, a multitude of hadrons and mesons, incomprehensible (so far) quark-gluon interactions and glueballs, some forms of radioactive decay and fusion, such as deuterium to helium, and more.

The weak force produces quark and lepton transmutations and neutrino oscillations. Transmutation includes beta and inverse beta decay with emission or absorption of electrons and positrons and high-energy photons and neutrinos and antineutrinos, other forms of radioactive decay and fusion, such as protons to deuterium, and more.

Then we have inflation, the cosmological constant, the Higgs mechanism, and more to come, with the possibilities for supersymmetry, string theory, loop quantum gravity and, as I say, more.

Watch this spacetime.

Delosian
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### Re: 1489: "Fundamental Forces"

Hi, love the cartoon, it made me laugh.

Quick question, shouldn't Coulomb's Inverse Square Law (the second part) be divided by r^2 rather than d^2 ?

ilduri
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### Re: 1489: "Fundamental Forces"

Sometimes I wonder whether our descendants will look back at our QM models the way we look at the ancients and their struggles to understand the motion of the planets.

Ptolemy's model got the right answer more often than Aristotle's. Copernicus' and then Kepler's were right more often still. But none offered even a hint of explanation.

Will QM have an Issac Newton?
Or is it doomed to be inscrutable forever?
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ucim
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### Re: 1489: "Fundamental Forces"

ilduri wrote:Will QM have an Issac Newton?
Or is it doomed to be inscrutable forever?
I don't know. But the universe has no obligation to be understandable to minds as small as humans'.

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Mokurai
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### Re: 1489: "Fundamental Forces"

juanro wrote:I think we should call "physics" to the knowledge up to about 1870.
Those theories and discoveries since then should be given another name and put in another compartment (of my mind, at least).

The usual cutoff between Classical and Modern Physics is Max Planck's 1900 discovery that quantized emission of light solves the problem of black-body radiation, including the Ultraviolet Catastrophe. Several other critical problems were discovered before that date, and resolved afterward by Albert Einstein. They are the photoelectric effect (quantized absorption of light), the constancy of the speed of light (Special Relativity), and the perihelion of Mercury (General Relativity).

schapel
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### Re: 1489: "Fundamental Forces"

...and Brownian motion, too. Einstein was one seriously smart dude. It's too bad he never could accept some of the more bizarre consequences of the fundamental principles he discovered.

I looked up just exactly how the weak force causes beta decay. Really, a down quark in a neutron decays into an up quark and a W boson. Then the W boson decays into an electron and an electron antineutrino. Because the W boson is the mediator of the weak force, you can kind of think of the weak force as being responsible for beta decay. I think really the appropriate terminology is that this decay is a weak interaction. There isn't really any force involved.

This brings me to one of my pet peeves. It seems that most people think that particle colliders smash particles together and what's in them comes out, like smashing two TVs together and watching all the parts fly out. No, no, no! The collision creates entirely new particles that never existed before. The Higgs boson wasn't in the protons they collided. The Higgs boson was created from the kinetic energy of the protons.

da Doctah
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### Re: 1489: "Fundamental Forces"

brenok wrote:
mathmannix wrote:Let's see... the four forces are Thrust, Summer, Famine, and Phlegm.

Spoiler:
Or how about Drag, Fall, Death, and Blood?

Actually, they are North, Air, Ganymede and Telophase.

Khaz
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### Re: 1489: "Fundamental Forces"

A possible analogy for electro-weak unification is the relationship between diamond and graphite - two substances with very different physical properties, but if you get them both hot enough, they become indistinguishable blobs of atomic carbon - which, when it cools again, could become diamond, graphite, soot, or any of the exotic allotropes.

I like this. Following that line of thought, does it make sense to suppose that all these subatomic particles are really just different states of the same fundamental thing? Perhaps this thing is simply the physical manifestation of energy itself. I dunno. I would love to know what matter actually is someday.

bondsbw
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### Re: 1489: "Fundamental Forces"

squareroot wrote:...
And since the universe used to be much hotter (energy is conserved (mostly ... see: redshit)
...

lol

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### Re: 1489: "Fundamental Forces"

Mokurai wrote:The constancy of the speed of electromagnetic waves gives us Special Relativity.

Either you meant this sentence in a very different sense than the others around it, or it's really not at all right. All of those other statements were physical consequences of the thing you were describing. This one was a historical consequence that led to a discovery, but EM definitely doesn't make c be what it is in the actual physics of the universe. EM waves move at c, but everything that isn't a massy particle does, so there's nothing special about that. EM is a thing which obeys c.

The rest of that, I take that you're arguing that we "don't understand" the other forces more than we "don't understand" gravity. The reason the reverse is normally the thing people say is because it's true at the quantum level, and maybe that's an arguable standard. But ... saying that one set of equations (curvature of spacetime) is more an "explanation" than another (wave equation), I don't think that's really meaningful. They each mathematically model the behavior of the thing they're designed to model. They're equally explainy.
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### Re: 1489: "Fundamental Forces"

mathmannix wrote:Let's see... the four forces are Thrust, Summer, Famine, and Phlegm.

And Venus de Milo in that one TV show that we don't talk about.