A Force-to-Force Meeting

The Crazy Theory contest is still going strong in the back room at Al’s coffee shop. I gather from the score board scribbles that Jim’s Mars idea (one mark-up says “2 possible 2 B crazy!“) is way behind Amanda’s “green blood” theory.  There’s some milling about, then a guy next to me says, “I got this, hold my coffee,” and steps up to the mic.  Big fellow, don’t recognize him but some of the Physics students do — “Hey, it’s Cap’n Mike at the mic.  Whatcha got for us this time?”

“I got the absence of a theory, how’s that?  It’s about the Four Forces.”

Someone in the crowd yells out, “Charm, Persuasiveness, Chaos and Bloody-mindedness.”

“Nah, Jennie, that’s Terry Pratchett’s Theory of Historical Narrative.  We’re doing Physics here.  The right answer is Weak and Strong Nuclear Forces, Electromagnetism, and Gravity, with me?  Question is, how do they compare?”

Another voice from the crowd. “Depends on distance!”

“Well yeah, but let’s look at cases.  Weak Nuclear Force first.  It works on the quarks that form massive particles like protons.  It’s a really short-range force because it depends on force-carrier particles that have very short lifetimes.  If a Weak Force carrier leaves its home particle even at the speed of light which they’re way too heavy to do, it can only fly a small fraction of a proton radius before it expires without affecting anything.  So, ineffective anywhere outside a massive particle.”

It’s a raucous crowd.  “How about the Strong Force, Mike?”

.  <chorus of “HOO-wah!”>

“Semper fi that.  OK, the carriers of the Strong Force —”

.  <“Naa-VY!  Naaa-VY!”>

.  <“Hush up, guys, let him finish.”>

“Thanks, Amanda.  The Strong Force carriers have no mass so they fly at lightspeed, but the force itself is short range, falls off rapidly beyond the nuclear radius.  It keeps each trio of quarks inside their own proton or neutron.  And it’s powerful enough to corral positively-charged particles within the nucleus.  That means it’s way stronger inside the nucleus than the Electromagnetic force that pushes positive charges away from each other.”

“How about outside the nucleus?”

“Out there it’s much weaker than Electromagnetism’s photons that go flying about —”

.  <“Air Force!”>

.  <“You guys!”>

“As I was saying…  OK, the Electromagnetic Force is like the nuclear forces because it’s carried by particles and quantum mechanics applies.  But it’s different from the nuclear forces because of its inverse-square distance dependence.  Its range is infinite if you’re willing to wait a while to sense it because light has finite speed.  The really different force is the fourth one, Gravity —”

.  <“Yo Army!  Ground-pounders rock!”>

“I was expecting that.  In some ways Gravity’s like Electromagnetism.  It travels at the same speed and has the same inverse-square distance law.  But at any given distance, Gravity’s a factor of 1038 punier and we’ve never been able to detect a force-carrier for it.  Worse, a century of math work hasn’t been able to forge an acceptable connection between the really good Relativity theory we have for Gravity and the really good Standard Model we have for the other three forces.  So here’s my Crazy Theory Number One — maybe there is no connection.”

.  <sudden dead silence>

“All the theory work I’ve seen — string theory, whatever — assumes that Gravity is somehow subject to quantum-based laws of some sort and our challenge is to tie Gravity’s quanta to the rules that govern the Standard Model.  That’s the way we’d like the Universe to work, but is there any firm evidence that Gravity actually is quantized?”

.  <more silence>

“Right.  So now for my Even Crazier Theories.  Maybe there’s a Fifth Force, also non-quantized, even weaker than Gravity, and not bound by the speed of light.  Something like that could explain entanglement and solve Einstein’s Bubble problem.”

.  <even more silence>

“OK, I’ll get crazier.  Many of us have had what I’ll call spooky experiences that known Physics can’t explain.  Maybe stupid-good gambling luck or ‘just knowing’ when someone died, stuff like that.  Maybe we’re using the Fifth Force in action.”

.  <complete pandemonium>
four forces plus 1

~ Rich Olcott


Note to my readers with connections to the US National Guard, Coast Guard, Merchant Marine and/or Public Health Service — Yeah, I know, but one can only stretch a metaphor so far.

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Gargh, His Heirs, and the AAAD Problem

Gargh the thinkerGargh, proto-humanity’s foremost physicist 2.5 million years ago, opened a practical investigation into how motion works.  “I throw rock, hit food beast, beast fall down yes.  Beast stay down no.  Need better rock.”  For the next couple million years, we put quite a lot of effort into making better rocks and better ways to throw them.  Less effort went into understanding throwing.

There seemed to be two kinds of motion.  The easier kind to understand was direct contact — “I push rock, rock move yes.  Rock stop move when rock hit thing that move no.”  The harder kind was when there wasn’t direct contact — “I throw rock up, rock hit thing no but come back down.  Why that?

Gargh was the first but hardly the last physicist to puzzle over the Action-At-A-Distance problem (a.k.a. “AAAD”).  Intuition tells us that between pusher and pushee there must be a concrete linkage to convey the push-force.  To some extent, the history of physics can be read as a succession of solutions to the question, “What linkage induces this apparent case of AAAD?”

Most of humanity was perfectly content with AAAD in the form of magic of various sorts.  To make something happen you had to wish really hard and/or depend on the good will of some (generally capricious) elemental being.

aristotle 1Aristotle wasn’t satisfied with anything so unsystematic.  He was just full of theories, many of which got in each other’s way.  One theory was that things want to go where they’re comfortable  because of what they’re made of — stones, for instance, are made of earth so naturally they try to get back home and that’s why we see them fall downwards (no concrete linkage, so it’s still AAAD).

Unfortunately, that theory didn’t account for why a thrown rock doesn’t just fall straight down but instead goes mostly in the direction it’s thrown.  Aristotle (or one of his followers) tied that back to one of his other theories, “Nature hates a vacuum.”  As the rock flies along, it pushes the air aside (direct contact) and leaves a vacuum behind it. More air rushes in to fill the vacuum and pushes the rock ahead (more direct contact).

We got a better (though still AAAD) explanation in the 17th Century when physicists invented the notions of gravity and inertia.Newton 204

Newton made a ground-breaking claim in his Principia.  He proposed that the Solar System is held together by a mysterious AAAD force he called gravity.  When critics asked how gravity worked he shrugged, “I do not form hypotheses” (though he did form hypotheses for light and other phenomena).

Inertia is also AAAD.  Those 17th Century savants showed that inertial forces push mass towards the Equator of a rotating object.  An object that’s completely independent of the rest of the Universe has no way to “know” that it’s rotating so it ought to be a perfect sphere.  In fact, the Sun and each of its planets are wider at the equator than you’d expect from their polar diameters.  That non-sphere-ness says they must have some AAAD interaction with the rest of the Universe.  A similar argument applies to linear motion; the general case is called Mach’s Principle.
JCMaxwell

The ancients knew of the mysterious AAAD agents electricity and its fraternal twin, magnetism.  However, in the 19th Century James Clerk Maxwell devised a work-around.  Just as Newton “invented” gravity, Maxwell “invented” the electromagnetic field.  This invisible field isn’t a material object.  However, waves in the field transmit electromagnetic forces everywhere in the Universe.  Not AAAD, sort of.

It wasn’t long before someone said, “Hey, we can calculate gravity that way, too.”  That’s why we now speak of a planet’s gravitational field and gravitational waves.

But the fields still felt like AAAD because they’re not concrete.  Some modern physicists stand that objection on its head.  Concrete objects, they say, are made of atoms which themselves are nothing more than persistent fluctuations in the electromagnetic and gravitational fields.  By that logic, the fields are what’s fundamental — all motion is by direct contact.einstein-tongue edged

Einstein moved resolutely in both directions.  He negated gravity’s AAAD-ness by identifying mass-contorted space as the missing linkage.  On the other hand, he “invented” quantum entanglement, the ultimate spooky AAAD.

 ~~ Rich Olcott

Particles and Poetry

“Hoy, Johnny, wotcher got inna box?”
“Hit’s a particle, Jessie.”
“Ooo, lovely for you.  Umm… wot’s a particle then?”
“Me Pap says hit’s sommat you calc’late about wiffout knowin’ wot ’tis.”


Pap’s right.  Newton was a particle guy all the way (he was a strong supporter of the idea that light is composed of particles).  One of his most important insights was that he could simplify gravitational calculations if he replaced an object with an equally massive “particle” located at the object’s center of mass.  Could be a planet, or a moon, or that apple — he could treat each of them as a “particle.”  That worked fine for his purposes, because the distances between his object centers were vastly larger than the object sizes.

Fleas
“Great fleas have little fleas upon their backs to bite ’em / And little fleas have lesser fleas and so on infinitum.” ~~ Augustus De Morgan

It took Roche to work out what happens when the distances get small.  Gravitational forces break the original “particles” into littler particles.  And when two of the little ones approach closely enough they break up, and then those break up…  You get the idea.  Take the process far enough and you get Saturn’s Rings, for instance.

But the analysis can keep going.  Consider one “particle” in Saturn’s A-ring.  It’s probably about 3″ across, made of ice, and contains something like 1024 particles that happen to be molecules of H2O.  Each molecule contains 3 nuclei (2 protons and one oxygen nucleus) and 10 electrons, all 13 of which merit “particle” status if you’re calculating molecules.  They’re all held together by a blizzard of photons carrying the electromagnetic forces between them.  The oxygen nucleus contains 16 nuclear particles, each of which contains 3 quarks.  The quark structures would fly apart except for a host of gluons that pass back and forth transmitting the nuclear strong force.  Hooboy, do we got particles.

“Particle” is a slippery word.  For Newton’s purposes, if an object is small relative to its distance from other objects, that was all he needed to know to treat it as a particle.

One dictionary specifies “a small localized object which has identifiable physical or chemical properties such as volume or mass.”  However, there are theoretical grounds to believe that the classic “particle of light,” the photon, has neither mass nor volume.  Physicists have had long arguments trying to devise a good working definition.  Nobelist (1999) Gerard ‘t Hooft ended one such discussion by saying, “A particle is fundamental when it’s useful to think of it as fundamental.”

It may seem a little strange for a physicist to argue for imprecision.  In fact, ‘t Hooft was arguing for a broad, even poetic but still precise understanding of the word.

Poets use metaphor to help us understand the world.  Part of their art is to pack as much meaning as they can into the minimum number of words.  In the same way, scientists use mathematics to pack observed relationships into a simile called an equation  — a brief bit of math may connect and illuminate many disparate phenomena.

Think of physics as metaphor, with numbers.

Newton’s Law of Gravity works for for galaxies roving through a cluster and for basketball-sized satellites orbiting Earth and for stars circling a black hole (if they don’t get too close).  Maxwell’s Equations, just 30 symbols including parentheses and equal signs, give the speed of light and describe the operation of electric motors.  The particle physicists’ Standard Model makes predictions that match experimental results to more than a dozen decimal places.

Good equations are so successful that Nobelist (1963) Eugene Wigner wrote an influential paper entitled The Unreasonable Effectiveness of Mathematics in the Natural Sciences.

We sometimes get into trouble by confusing metaphor with reality.  Poetic metaphors can be carried too far — Hamlet’s lungs were not in fact filling with water from his “sea of troubles.”

Mathematical models can also be carried too far.  Popular (and practitioner) discussion of quantum mechanics is rife with over-extended metaphors.  QM calculations yield only statistical results — an average position, say, plus or minus so much.  It’s an average, but of what?  The “many worlds” hypothesis is an unnecessarily long jump.  There are simpler, less extravagant ways to account for statistical uncertainty. les Etats Unis

~~ Rich Olcott