Posted on October 10, 2004

Soapbox Seminar #12

Black Monopoles!?!

The Missing Piece. You’ll maybe recall that, back when we were talking about why Alan Guth invented inflation, I made mention of something called the “monopole problem.” And I promised to explain it later, when the time came. Well, the time’s come.

Almost. Before I can tell you what the monopole problem is, I’ve first got to tell you what a monopole is.

And that’s simple enough: A monopole’s the missing piece. Missing from our picture of electromagnetism, that is.

’Course, for the longest time nobody knew it was missing. The first hint we got was in 1855, when James Clerk Maxwell showed that, down deep, electricity and magnetism were really just two sides of this one thing: the electromagnetic force.

But it took pretty nearly another forty years before physicist Pierre Curie, Marie’s husband, pointed out that Maxwell’s equations were kind of lopsided in the way they treated electricity vs. magnetism. That, whereas electrical charges actually existed according to Maxwell, magnetic charges didn’t. Instead, magnetism was supposed to be produced by the movement of electrical charge.

In other words, you could have an electrical charge all by itself — a positive charge, say, without a negative — but there just wasn’t any such thing as an isolated magnetic charge.

That matches the observational evidence, all right: Every magnet in our patch of the universe comes with two charges as standard equipment, two inseparable opposite poles. North and South, we call them, after the big ones near either end of the earth’s axis.

And it’s not like you could make two single poles by cutting a normal magnet in half; all that gives you is two smaller, weaker, but equally normal magnets — two smaller, weaker versions of the same dipolar arrangement.

That’s too bad, because if magnetic charges don’t exist, it sort of spoils the symmetry of Maxwell’s equations. And, to physicists, things like symmetry, elegance, simplicity — beauty, in general — matter a whole bunch. It’s not a proof, mind you, but when a theory’s got those qualities — well, it’s a sign we’re on the right track.

But let’s say it were possible to have a single magnetic pole — a magnetic monopole — all by its lonesome, with only one kind of charge, be it north or south. That would be the finishing touch, you see, balancing Maxwell’s equations and establishing a perfect equality between magnetism and electricity at long last.

And that’s not all. As Paul Dirac went and showed back in the early 1930s, the existence of even a single magnetic monopole anywhere in the universe would be enough to prove one of quantum mechanics’ bedrock assumptions: namely, that electrical charge can’t take on just any value, but can only occur in multiples of chunks called quanta.

So, there’s more than a little riding on finding one of these critters. Meaning there’s been some pretty serious hunting for them going on down through the years — all of which has so far come up empty.[1] What keeps us at it, though, is what some of our theories of the early universe are telling us: that not only do magnetic monopoles exist, but that by rights there ought to be a whole slew of them out there.

Gaining Weight. Telling you about this next part’s going to take some GUTs.

That’s GUTs as in Grand Unified Theories. An ugly-sounding name for a beautiful idea. Because GUTs are what we call our modern-day stab at making Einstein’s old dream of a unified field theory come true.

We’ve met GUTs before, only not by name. They’re the theory, or theories, behind that picture of the Big Bang my author friend Bill DeSmedt gave us a while back. You remember — the one where the primordial superforce breaks down into electromagnetism and the strong and weak forces? Well, it’s Grand Unified Theories that try to guess what the universe might have been like before the breakdown, and what might have done the breaking.

It’s the actual symmetry-breaking mechanism we care about here. And that turns out to be the same thing as gave the elementary particles their mass.

Nowadays, mass seems like such a basic thing that it’s hard to conceive of a time when there wasn’t any. Still, that’s what the GUTs are telling us: That subatomic particles didn’t start out having mass; it’s something they sort of picked up along the way, by interacting with a very special field called the Higgs field.

One way to think about the Higgs field is to start with that old line about “whoever discovered water, it wasn’t a fish.” Because the Higgs is like that: a field that fills all of space so completely we’ve got no way of noticing it, any more than a fish notices water.

Higgs is like water in another way, too: Just like some things’ll float in water while others sink, so the effect of a Higgs field varies depending on what’s immersed in it. Put plain, the stronger a thing interacts with (”couples to” in physics-speak) the Higgs, the more mass it’s going to have.

(So, the good news is: maybe you’re not really overweight, after all — maybe you’re just very strongly coupled to the Higgs field!)

How does all this fit in with GUT symmetry breaking? Well, turns out that the photon — the particle that acts as the carrier (the “exchange particle”) of the electromagnetic force — doesn’t interact with Higgs fields at all, making it massless (which it has to be, or it couldn’t travel at the speed of light). On the other hand, the W and Z bosons that carry the weak force couple strongly to the Higgs field; so much so that they were the heaviest particles yet at the time of their discovery back in the early 1980s.

Now, then, according to the Grand Unified Theories, both of those forces —and the strong nuclear force that holds protons and neutrons together besides — were united in a single superforce at the moment of creation. But once the universe had cooled enough for all these Higgs fields to deploy (and the simplest GUT calls for at least 24 of them), the exchange particles for the different forces acquired very different masses. As a result, the forces themselves began behaving very differently.

So it’s adios, symmetry ...

... and hello, monopoles!

Because the thing of it is, when these Higgs fields did their symmetry-breaking, it supposably happened too fast for them to work uniformly everywhere throughout the universe — even as small as the universe was back then. Instead, they went and got themselves all tangled up. And anywhere two or more tangles met, they tied the fabric of space into knots.

Knots we call magnetic monopoles.

Very big knots: most GUTs predict that the monopoles produced by these topological defects would have been quadrillions of times more massive than a proton.

And lots of them: So many that the mutual gravitational attraction of such heavy particles would’ve recollapsed the universe after only thirty thousand years: would’ve turned the Big Bang into a “Big Crunch” before it’d had a chance to really get going.

Well, Bishop Usher might’ve gone along with that — he being the 17th century Irish cleric who calculated that the Biblical Creation took place on October 23rd of the year 4004 BCE. Cosmologists, on the other hand, weren’t anywhere near as happy about that result. We dubbed it the “monopole problem.”

That’s where the inflationary scenarios come in. They assume that the universe underwent an enormous expansion as part and parcel of this symmetry-breaking episode. So, right there, that gives the Higgs fields a much smaller pre-inflationary playing field out the outset. Small enough, maybe, for them to iron out most of their little tangles before they could grow into great, big monopoles.

Then, too, inflation could have taken however many monopoles were produced and scattered them all to hell and gone. Picture the early universe being as big as your backyard, and full to the fence-line of monopoles. Now along comes inflation, and — bang! — your yard expands to the size of the solar system! All of a sudden, those monopoles are going to be pretty few and far between.

So, if some flavor of the inflationary scenario (and these days there’s more of them than you can shake a stick at!) really happened, then chances are monopoles are rarer than hen’s teeth in our little corner of the universe.

Lifetime Warranty. On the other hand, any monopoles we’ve still got, we’ll keep. Because they just don’t go away by themselves. They can’t.

I’ll admit, thirteen billion years seems like a long time to hold a charge. An electrical charge, for instance, could never go that distance. That’s because an electrically-charged object would sooner or later attract something carrying the opposite charge, and when they slammed into each other the two charges would cancel out.

That’s just not going to happen with a magnetic monopole, though. All the other magnetic fields it runs up against are going to have both poles, north and south. So, however much charge one pole takes away, the other’ll give back. A monopole can bump into all the garden-variety bar magnets it wants, and never lower its field strength by a picogauss.

The only way to put a dent in that magnetic field would be if it ran into another oppositely-charged monopole. And, if Guth and friends are right, there just aren’t that many around: The same inflationary mechanism that brought them into being in the first place also went and slung them far and wide, all across the universe.

Even so, there could still be a few left in our neck of the cosmos. But so what?

Well, if you’ve been following right along, you maybe already guessed what.

That’s right: What if one of those few remaining magnetic monopoles was also a primordial black hole?

A “black monopole,” in other words.

What’re the Odds of That? Better than you might think, actually.

For starters, there’s nothing in our current understanding of black holes to rule out the possibility of one’s being magnetic. Even John Wheeler’s old “no hair” theory counted charge among the (very few) physical properties a black hole could exhibit. No real reason that the charge couldn’t be magnetic, rather than electrical.

At the same time, if a black hole was magnetic, it’d just naturally have to be a monopole. The poles of a normal magnet have to be kept separated a skootch, or they’ll cancel each other out. But a black hole singularity’s a dimensionless point — no room in there to squeeze in a dipole.

And there’s an extra-good reason why a primordial black hole — one of the real little guys — might be a monopole. It comes down again to that Hawking radiation we talked about last time.

What we said then was that the more massive a particle is, the less likely it gets that a black hole’ll emit it. Long wavelength photons, what with their low energy and zero rest-mass, are dead easy; even the super-stellar-sized black holes can crank them out. But you’ve got to get down into the billion-ton primordial range or so (atom-sized or less) before you’d start seeing the heavier stuff — such as electrons, positrons, maybe even protons and neutrons — come streaming off the event horizon.

As for “magnetons,” individual magnetic monopole particles, well, you can forget about them. Like I just finished saying, they tip the scales at quadrillions of times the weight of a proton — a couple grams or so. (Think of it: a subatomic particle so heavy you could heft it in your hand and feel the weight!) The odds on a pair of those critters popping out of the vacuum, much less on just the right vectors that one falls into the hole and the other gets away clean — well, we’re not just talking a cold day in hell here, we’re talking a whole ice age!

But, unless it can emit magnetons, there’s just no way a magnetically-charged black hole — a black monopole — can shed its charge. There aren’t any other charge-neutralizing mechanisms in the cards, you see. Swallowing ordinary two-pole magnets won’t do the trick. And, thanks to inflation, there’s next to no chance of it encountering another, oppositely-charged monopole nowadays.

What all that means is that, if a black hole should happen to have a magnetic charge, then it’s going to hang onto it. It can’t just evaporate away, not ever.[2] No, unlike “normal” primordial black holes, black monopoles are here to stay.

Assuming they exist at all, that is. And, far as that goes, the jury’s still out. Though there are some inklings. Back in 2001, Tom Banks and Willy Fischler concocted a new “holographic cosmology” that might have yielded “a relic density of highly charged extremal black monopoles” as part and parcel of the Big Bang.[3] This year, Dejan Stojkovic and Katherine Freese went them one better, proposing primordial black monopoles as a solution to the monopole problem itself!

Anyway, granting for the sake of argument that black monopoles do exist, what makes us think that Vurdalak, our Tunguska PBH, might’ve been one of them?

Storms and Jiggles. There are, as it turns out, a couple pretty good pieces of evidence suggesting that — whatever it was that fell in the Tunguska hinterlands that summer day in 1908 — it was putting out one hell of a magnetic field. I’m talking about the geomagnetic storm that raged for four or five hours on the morning of the Event, and the compass deviations that were recorded over the three nights preceding it.

That geomagnetic storm had been tracked at the time by instruments at the Irkutsk Observatory, but it took another half-century before somebody tied it in with Tunguska. It wasn’t till 1958 that Tunguska researchers G.F. Plekhanov and our old friend Nikolai Vladimirovich Vasil’ev began canvassing a number of local observatories, looking for records dating back to 1908. Here’s what happened next[4]:

In February 1960 the above investigators received a reply from the Irkutsk Observatory geophysicist Kim G. Ivanov informing them that he had discovered two unusual magnetograms dated 30 June 1908. Both almost certainly had recorded the Tunguska disturbance. Ivanov himself did not offer his own interpretation of the physical nature of this unusual, unexpected effect. The analysis by geophysicist Alexander F. Kovalevsky and other researchers from Siberia’s university city of Tomsk led scholars there to conclude that the magnetic effects of the Tunguska explosion had nothing in common with disturbances usually caused by typical meteors’ bodies. The closest analogy of the recorded magnetic effects, strange for meteoritics, turned out to be regional geomagnetic storms.

Well, okay, you say — but couldn’t a meteorite be magnetic?

Sure thing. Only then you’ve pretty much got to be talking about a ferrous meteorite, basically just a big hunk of iron. And that lands you right back smack dab in the middle of the no-crater, no-fragments problem. Because it’s hard to see how that much iron could vaporize completely, with not a wisp left behind. So hard, in fact, that most of the meteorite-impact theories have taken to using a stony meteorite — a “carbonaceous chondrite” is a particular favorite — that could totally self-destruct.

Only stone’s not magnetic.

Now, that’s not to say a meteorite couldn’t have generated an electromagnetic plasma as it interacted with the atmosphere on its way down. A stretch, maybe, but not beyond the realm of possibility.

But there’s no atmosphere to interact with in hard vacuum. So, what do you make of the claims by Professor L. Weber of Kiel University — namely, that he tracked a powerful magnetic source over the three evenings prior to the Event, at a time when the Tunguska impactor would have been far out in space?

In the course of the last 14 days, the photographically recorded curves of magnetic declination showed no disturbance of the sort that usually accompanies the Northern Lights. But it should be noted that several times, and indeed all the time over several hours, there were observed small, regular, uninterrupted vibrations [of the magnetic-declination curves] of about a 2’ amplitude and a 3m [=minute?] period, which could not be traced back to known causes (e.g., streetcar vibration). These as-yet unexplained disturbances took place:

   * June 27-28 — 6:00 pm to 1:30 am

   * June 28-29 — the same

   * June 29-30 — 8:30 pm to 1:30 am[5]

It begins to look, in other words, like the “Tunguska Cosmic Body” might’ve been carrying a powerful magnetic charge of its own around. That doesn’t sound much like a stony asteroid, much less an icy cometary nucleus — now does it?

Sounds, in fact, like it might have been our old friend, Vurdalak.

And next time, for one last time, we’ll try to see how.

[Notes and Further Reading]

[1] An experiment conducted by Stanford physicist Blas Cabrera seems to have recorded a single “monopole event” on Valentine’s Day 1982. The result has never been reproduced. Still, it’s never been explained away, either.[Return to text]

[2] Mass and charge and spin are conserved quantities. No way you can just sweep them under the rug. If you don’t pass them on to some other poor sucker, you’ve still got them.

Now, electric charge turns out to be pretty easy for a hole to pass on. Suppose it has a slight positive e-charge; just one excess proton. If it had to wait around till a proton-antiproton pair shows up before it could ditch the charge, it could be looking at a long wait — those particles are heavy and hard to make. But it doesn’t. Even a much lighter, much more likely electron-positron pair will fill the bill. If one of those materializes nearby, the positron’ll be repelled and the electron attracted (it’s no longer 50-50 which particle drops into oblivion, you see). That single positron can carry off the whole positive charge of our extra proton, even though it’s carrying off just a fraction of the proton’s mass-energy. The hole’ll lose its electrical charge long before its mass is gone.

That trick doesn’t work for monopoles, because a magnetic monopole is already the lightest magnetically-charged particle there is. So, till a pair of magnetons pops out of the vacuum (there’s that cold-millennium-in-hell scenario again), the hole is pretty much going to be stuck with its m-charge.

It’s stuck with the mass of the particles too. Leastways, the alternative doesn’t make much sense. Suppose it could lose the mass (as radiation) but keep the magnetic charge. Eventually, all the mass is gone, the hole evaporates into nothingness — and you’ve still got magnetic lines of force pointing to where the hole was. Now, they just stop. That’s as crazy an idea as a one-ended string. So, the mass-equivalent of the “embedded” monopoles has got to stay behind too, even if the protons and whatever else fell in have trickled away as gamma rays. [Return to text]

[3] Interestingly enough, Tom and Willy proposed this while they were both at U. Texas, Austin — Al Jackson and Mike Ryan’s old stomping ground. There must be something in the Texas air that makes people dream up these far-out theories. Anyway, no sooner was Tom safely cross the border back in Santa Cruz CA than he and Willy retracted that particular prediction, in the 2003 version of their holographic cosmology.[Return to text]

[4] From Victor Zhuravlev, “Geomagnetic Effects as one Aspect of the Tunguska Event,” Paper delivered at the International Workshop Tunguska -’96 Bologna, Italy, at: http://omzg.sscc.ru/tunguska/en/articlese/zhur_us.html. [Return to text]

[5] Kiel is six time zones to the west of the Tunguska epicenter, so Weber’s saying that the effect cut off just about the time of the Event itself: June 30, 7:14 a.m. local time.[Return to text]

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T. Banks and W. Fischler, “An Holographic Cosmology,” arxiv:hep-th/0111142v1, 15 November 2001.

T. Banks and W. Fischler, “Holographic Cosmology 3.0,” arxiv:hep-th/0310288v1, 31 October 2003.

Sir Michael Berry, “Paul Dirac: the purest soul in physics,” PhysicsWeb, February 1998.

Raphael Bousso and Stephen W. Hawking, “Pair Creation and Evolution of Black Holes in Inflation,” arxiv.org: gr-qc/9608008v1, 2 August 1996.

Alan H. Guth, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins, Reading MA: Perseus Books, 1997.

John David Jackson, Classical Electrodynamics, New York NY: Wiley, 1999.

Leon Lederman with Dick Teresi, The God Particle: If the Universe is the Answer, What is the Question? , New York NY: Houghton Mifflin, 1993.

Dejan Stojkovic and Katherine Freese, “A black hole solution to the cosmological monopole problem,” arxiv:hep-ph/0403248v2, 2 April 2004.

L. Weber, 11 July 1908 communication to the editor, cited in “On the lightshow in the night sky at the beginning of July,” Astronomische Nachrichten [Astronomical News], Vol. 178, No. 4262, pp. 239-40.

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