(When I launched the Advent Calendar of Science Stories series back in December, I had a few things in mind, but wasn't sure I'd get through 24 days. In the end, I had more than enough material, and in fact didn't end up using a few of my original ideas. So I'll do a few additional posts, on an occasional basis, to use up a bit more of the leftover bits from Eureka: Discovering Your Inner Scientist...)
One of the tricky things about writing this book was that I didn't just need stories from the history of science, but stories that fit a particular pattern. The point of the book, after all, is to illustrate the universal process of science, so I needed stories where that process was clear and reasonably comprehensible. Which takes out a big class of anecdotes about interesting personalities that boil down to stuff like "the key to this discovery is that Emmy Noether was super smart and good at math." Which, you know, kind of undercuts the whole point of the book.
It also knocks out a somewhat smaller class of wonderful stories that can't be used because they're not really science. These are stories of "discoveries" that didn't pan out for one reason or another. Many of these are incidents of fraud or self-deception, but there are some fascinating stories out there about things that have never been replicated.
Probably the most famous of these is the "Wow!" signal, which is (in)famous in SETI circles. This is a famous not-quite-result from a passive radio astronomy survey using the "Big Ear" telescope, which basically just recorded radio waves from whatever section of sky happened to be right overhead at the moment. For the most part, this was just faint static, but one August day in 1977 they picked up an extremely intense signal at a frequency very close to that of an important transition in atomic hydrogen. This was sufficiently intense that one of the scientists circled it on the printout and wrote "Wow!" in the margin.
And nobody has ever seen it again.
This is not for lack of trying-- there have been dozens of follow-up attempts looking for a bright radio source in that part of the sky at that particular frequency, but nothing has ever shown up. So nobody has any clue what happened back in 1977, and we'll probably never know.
The other classic example of this actually made it into Physical Review Letters. This is the so-called Valentine's Day Monopole, and again, has never been repeated.
The story here dates all the way back to the early days of electricity and magnetism, when it was noted that while you can separate positive and negative electric charges, you can never separate the north and south poles of a magnet. If you try, say by cutting a bar magnet in half, you just end up with two separate magnets each with its own north and south poles. The absence of "magnetic monopoles" (that is, a north by itself or a south by itself) is written into Maxwell's equations of electromagnetism.
Of course, this is an odd sort of asymmetry, and one of the many cool theoretical discoveries made by Paul Dirac is a connection between magnetic monopoles and electric charge. He was able to show that if magnetic monopoles exist somewhere out in the universe, that would explain why it is that every charge we see is a simple multiple of the charge of the electron. You don't need a lot of these monopoles, either, so it would be perfectly reasonable for nobody to have seen one well into the twentieth century.
This seemed like a tempting target for an experimental search, so a physicist at Stanford named Blas Cabrera set out to detect a monopole, using a big loop of superconducting wire. Well, eight loops, really. The idea being that, as we've known since the time of Michael Faraday, a change in the magnetic field passing through a loop of wire will induce current to flow in that loop-- unless you're in a place where all of your electricity comes from solar photovoltaics, this is how the electricity to power the computer you're reading this post with is generated. Cabrera's superconducting loop functioned as an extremely sensitive detector for such induced currents.
If you take a bar magnet and drop it through a loop, you see a characteristic signal that changes sign-- there's a spike of current flowing in one direction, then that drops away, and there's current flowing in the opposite direction. A monopole, though, would make a "one-way" current, which would be clearly distinguishable from anything else. The multiple loops also provided some discrimination, as induced fluctuations from a magnetic monopole passing through would be magnified by a factor of eight, while most local sources of variation would be much smaller.
Cabrera set this up, and within the first six months of operation, on the evening of Feb. 14, 1982, got a signal of exactly the type he expected for a monopole-- one direction, right magnitude, everything. The data graph is reproduced as the "featured image" up top, taken from this blog post. Cabrera did all the sanity checks you would do, wrote up his result, and published it.
And it never happened again. This led to some gentle mockery-- Steven Weinberg a year later sent a note reading "Roses are red, violets are blue, it's time for monopole, number TWO," but neither Cabrera's experiment nor any of the several follow-up experiments ever detected another candidate monopole. At around the same time, Alan Guth invented the theory of inflationary cosmology as a solution to, among other things, the problem of monopoles. The idea being that the Big Bang created the bunch of magnetic monopoles needed for Dirac's charge quantization argument towork, but then the universe rapidly inflated by some outrageously huge factor, so the chances of there being a monopole in our observable universe are exceedingly small. At this point, people have pretty much stopped looking for magnetic monopoles of the particle physics variety, though people have done some exceptionally cool experiments making analogues in other systems).
Science, pretty much by definition, deals in repeatable phenomena-- you need to be able to test and verify your model, and that requires stuff to happen the same way on several different occasions. Singular events are spectacularly ill-suited to science, which is part of the reason why cosmology is such an endless source of messy arguments. One-of-a-kind events like the "Wow!" signal and the Valentine's Day Monopole are never going to be properly understood, unless they somehow happen again. It's sort of romantic to imagine that they were, in fact, grand discoveries-- the the single monopole in our Hubble volume just happened to pass through Palo Alto in 1982, on its way to parts unknowable-- but we'll never know that for sure.
Which is why these stories aren't in Eureka. Happily, though, I have this blog to celebrate the singular events that can't really be science, but make for such fun speculation...
- Log in to post comments
A current of electrons produce a magnetic field. So it seems that a current of monopoles would create an electric field. But it seems like it would be a strange kind of electric field as there would be no excess of electrons in the field. But wouldn't the electric field attract electrons in a way so as to counter the electric field?
Sorry, just trying to wrap my mind around this thing.
It is not a difficult exercise to design a device that uses a supply of charges and monpoles to endlessly break the conservation of angular momentum.
Given the existence of the 1-form 4-potential A (this existence being required because the 4-potential of a charge is necessarily a conserved source of gravity), then the Bianchi identities from geometry mandate the non existence of monopoles.
I tell my students that the zero in Maxwell's equations is experimental, not theoretical. (Ditto for the force law.) There is a source term for B, it just happens to always be zero, as far as we can tell, except for perhaps that one time.
Cabrera's monopole is absolutely one of my favorite stories, partly because you only need ONE to make Dirac's result work and it could have been just spectacular luck that he saw the only one of a few in the entire universe. The other part is that it is my understanding that the strip recorder paper underwent some careful forensic analysis to see if it had been a prank. (The signal was recorded on a weekend when the lab was empty.) No indication of a manual adjustment could be seen.
Also, it was easy to believe such a discovery was possible in 1982. Charmed quarks (with fractional charge) had been discovered to be a real thing just a half dozen years earlier.
ppnl, wrap your mind around this:
The E-field from a moving magnetic monopole would indeed form closed loops (because divE = 0 with no electric charges around) just as happens with a dB/dt Faraday's Law source for E. That page has a nice picture comparing the two phenomena as well as the equations used.