Science Talk

The Complete Idiot's Guide to String Theory

George Musser talks about his new book, The Complete Idiot's Guide to String Theory. Plus, we'll test your knowledge of some recent science in the news


George Musser talks about his new book, The Complete Idiot's Guide to String Theory. Plus, we'll test your knowledge of some recent science in the news. 

Podcast Transcription

Welcome to Science Talk, the weekly podcast of Scientific American for the seven days starting July 16th, 2008, I'm Steve Mirsky. This week on the podcast: something for the complete idiots out there, me included. We'll talk with Scientific American editor, George Musser, who is not a complete idiot; plus we'll test your knowledge about some recent science in the news.

George Musser is our resident astronomy and physics editor. He is the author of the brand new book, The Complete Idiot's Guide To String Theory. To become something less than a complete idiot, I spoke to George in the library at Scientific American.

Steve: What is string theory? I mean everybody has heard of string theory; I think it has been on the cover of Time magazine, probably on Newsweek, certainly on our covers and everybody talks about it as some kind of new-fangled big deal in physics, which it is. What is it?

Musser: It's a good question because the theory itself is being developed by scientists. It's not a fully formed theory, so what I'll tell you, the summary version I will give you, is the current level of understanding; but what's so wonderful about string theory is that it seems to open up new levels even below that.

Steve: One of the things in your book that I've not seen before was that string theory really goes back about 80 years.

Musser: Yep.

Steve: The first formulation was back in the '20s.

Musser: Yeah, even most string theorists don't realize that. This is something that Steve Weinberg, the Nobel laureate physicist actually pointed out in a talk that I kind of plucked and put in the book—that the concept of string theory goes way back.

Steve: As most physicists think it started in the '70s.

Musser: Yeah, it started in late '60s, but it was one of those things that was invented and then forgotten and then re ... invented actually isn't even the word, it was more of discovered; it was stumbled upon as a potential theory not even of everything as it is now portrayed, but as a theory of nuclear forces. It didn't work out for that. It was re-branded as a theory of everything; everything meaning everything—electricity, magnetism, matter, space, gravity and you name it, it's supposed to be in the string theory at some level. So the basic idea is that when you zoom in on matter, you zoom in, you see molecules and you zoom in on the molecules, you see atoms and you keep on zooming, you see the particles in the atoms ...

Steve: Protons, neutrons, electrons ....

Musser: Precisely, and then you zoom in on for instance, a proton, it turns as you zoom in and you see quarks and then you keep on zooming and those quarks according to string theory are actually tiny, tiny, tiny little strings that are vibrating and moving around. The beauty of the theory is that one type of thing—namely a string—can vibrate in different ways and give you different types of particles. It can give you an up-quark, down-quark, and electron, photon, the whole zoo of particles that have been discovered.

Steve: What does that give you other than a felicitous kind of aesthetic feeling about the universe, that it's all connected together in some kind of unified whole?

Musser: Well, of course I wouldn't put that down on a felicitous aesthetic view of the universe; I think that's important.

Steve: No, absolutely not!

Musser: No, I am being precocious a little bit, but [a] lot of the big brick theories in physics over the past hundreds of years have come from unification, have come from trying to bring together that which had seemed so impossible to bring together. It seemed desperate. Electricity and magnetism were unified in the theory of electromagnetism. One thing actually we take for granted today—which is that the stars and planets follow the same laws that we observe on the Earth—was really unification that Newton did. Prior to that people had separated those two grounds and Newton unified them into a single theory of motion and of universal gravitation; and in turn, when you boil everything down and unify, then you can build up again, and you can see how many new phenomena you would have no idea even existed. So Newton opened our eyes to all that motion of the universe and the ways that planet systems can form in galaxies and beyond galaxies.

Steve: And one of the great things about the book is that it goes off on a lot of digressions as you just did, because you really do need a background in the entire history of physics, to a certain degree, to understand string theory, even at a relatively rudimentary level. But what is it now that string theory is trying to accomplish that has remained unaccomplished?

Musser: So, I bring up those other examples as it is just historical, like scene setting to this, but string theory has similar consequences in terms of bringing things together and then opening our eyes to new things. So the mere act of bringing together gravity and quantum mechanics, that was Einstein's dream. That was a major accomplishment, because the theory of gravitation, which is Einstein's theory, and quantum theory seems to sync completely incompatible. They are used today in conjunction; they will be applied, like, the first one then the other, but they are not actually used together in any deep sense; so that already is a conceptual breakthrough. Those two theories approached the world in such a different way that to unify them gives you something you didn't have before. And then there is a whole stream of possible phenomena; none has really been proved or observed, but [they] are predicted by the theory. For instance, other dimensions of space and time; other universes that could be out there; different particles in our own universe that we are oblivious to right now, but which might be discovered, at for instance, the Large Hadron Collider when it starts up later this year.

Steve: You talk in the book about what it would feel like if asense being in one of these other dimensions actually try [tried] to touch you.

Musser: Yep.

Steve: And you allege that you would have some sort of sensation, but you wouldn't really know what it was.

Musser: Yeah, that's an amazing thing about extra dimensions—asthey feel so magical; the kinds of things that would to us appear like hocus pocus would be possible in extra dimensions.
And that also feeds into some of the physics as well, but your example of, if you had a multidimensional being or force, does not have to be artificial intelligence, tap you on the shoulder, you would look around you and you wouldn't see it by definition, because it wouldn't exist in the dimensions that you have access to, that you can observe. So, it would feel to you as some ineffable force acting on you, you couldn't localize it, but it would still be there. And that actually comes up in theories of cosmology, for example. If, For instance, the forces that may have caused the universe to expand very early in the history of our universe—they seemed to require a force that lacks direction; it has no directionality to it. It's called a scalar field in the jargon and that's precisely the kind of thing you might get from an extra dimension. You would get a directionless type of force acting on you. Such type of things string theory might give you. I should point out that there are other explanations for scalar fields as well, but string theory does seem to give those naturally to you.

Steve: Well, so let's review: just basically string theory says that there are many dimensions that we're not aware of in our three-dimensional world of perception and that all the fundamental particles are actually tiny little strings that are vibrating in different ways from each other.

Musser: Precisely. I would actually phrase it a little differently than that. I would take the second idea as the primary one and the dimensions are actually derived from that. It isn't as though someone is sitting around one day at the bar and saying, "Hey, wouldn't [it] be great to have 10 extra dimensions of space?" These actually just fall out of that theory naturally. If you didn't have them, the strings could not vibrate in a consistent way. You might, for instance, have reversals of cause and effect, where the string would react to you before you touched it. That might occur if the string didn't have these extra dimensions, to play in, to act, to vibrate in and to move in.

Steve: Early in the history, the modern history of string theory formulations, there were some physicists who really didn't like string theory, because it wasn't testable enough to be other than—in their opinion—kind of, philosophical musings; and they thought it wasn't even really science. And how has the field progressed since then?

Musser: Well, it's kind of, it has been a to and fro, kind of, ping-pong effect. A lot of the criticism for string theory is there even today comes down to that same question of, is it testable? And that's actually a criticism, as I try to discuss in the book, not specific to string theory. It's also true of the various alternatives to string theory; and when I think that, I think I tried to do it in the book that other books haven't done so much, is to really address those theories as well. Although the book is entitled Idiot's Guide to String Theory it's also an idiot's guide to look on gravity, the cause of dynamical triangulations to the other types.

Steve: Supersymmetry.

Musser: Right ... exactly.

Steve: Little idiot's guide.

Musser: Little idiot, or many idiot's guides within the book. So the problem is that gravity is very weak as we experience it, so that implies, just as a matter of course, it's an empirical fact that the unification of gravity with other quantum forces must occur at very, very, very short distances. This isn't a failing of string theory; this isn't failing of loop quantum gravity or anything else. It's a fact to[of] the world. So quantum gravity, of which string theory is an example, is distant from experiment, and we have to live with that fact. So, a lot of the criticism of string theory isn't specific to string theory, it's bemoaning this fact of nature that quantum gravity is such a distant phenomenon. So I think it is important to separate those questions; that there are criticisms of string theory per se, but this most common lack of experimental tests isn't about string theory per se, it's again a broader criticism.

Steve: Most people might be surprised that gravity is so weak, because it's the one we really experience and if you fall down a flight of stairs—which I have done—gravity doesn't seem so weak.

Musser: Yep, exactly. It is ironic, and I actually do have a short discussion in the book about how—did I put it? If gravity is still weak, why does it hurt so much when I fall? And the reason is it is fairly straightforward; gravity is a cumulative force. For instance electrical and magnetic forces have offsetting contributions; you might have a positive and negative charge or a north pole and south pole and those things tend to cancel out. And anytime you have a whole bunch of electrons together, they tend naturally to draw in positive charges to neutralize them. So electromagnetism is self negating in that way whereas gravity is not. Gravity only adds and it only adds up; there is only essentially positive gravitational charge. So in case of the earth, [it] has so many protons, neutrons, electrons and other particles in the earth and they all add up producing what we experience as a fairly large gravitational force. I should point out that large though it is, we are still able to resist it. We can still maintain our integrity. We can avoid falling down stairs. We can lift things up off a table and when we lift a book off the table, we are opposing the entire might of the earth to do so. So the essential electromagnetic forces that let us lift the book are opposing the entire earth's gravitational force. So it's, I think, it's 1039 or it is some other ungodly large number times more powerful than gravity, electromagnetism; and the strong force of the atomic nucleus is even stronger than electromagnetism. So this is just something we have to live with. And that implies, in turn, that whatever unifies gravity with other types of particles and other types of forces occurs at very, very short distances those are the kind of flip side of that.

Steve: These are distances that are not only too small to see, they are too small to even perceive with an electron microscope.

Musser: Oh, yeah, .yeah! This is just a way off.

Steve: They are orders and orders of magnitude smaller than the smallest thing you can visualize with our best microscopic technology.

Musser: Right and even our best microscope or, in a sense, microscope, is the Large Hadron Collider—the one being built or one about to start up, really, now in Switzerland—and it can penetrate to, I think it is 10-19 to -20 meters; in effect it's a microscope down to those distances; and the plank scale, the scale at which strings seem to operate these other types of entities is another 1015 times smaller; it is 10-35 meters. I should point out, just as a caveat, that strings might be a bit bigger than that strictly speaking, but usually people thought by 10-34 and 10-35 meter in size. So it's not something we're ever going to see it directly. In the case of atoms, we can see them now using various kinds of microscopes, but a string will never be directly visible to us. So you have to come out to it indirectly. So I think the way I describe it in the book is you tell physicists, "Hey, you're never going to be able to observe strings, sorry," and what's their first reaction? "Aaakkkhhe ... I've got to find a way to observe strings." They take it as a challenge. So I actually have a list of 10 possible ways not to observe strings, not even to prove that they exist, but to test the idea. And I think that's the way science usually works. You don't ever disprove something strictly or prove something strictly; it's always, sort of like, I think you've tilted it for or against; it's a balancing act. So slowly, over time, you tend to bring more and more evidence for something until we reach a point where, "Wow, it must be true" or conversely we pile up so much negative evidence we say, "No, can't really be true."

Steve: I was thinking if it's a long legal case with an accretion of evidence so that you finally come to a conclusion beyond the reasonable doubt about something.

Musser: Right, exactly, exactly.

Steve: What is the Large Hadron Collider actually going to enable us to start to see in concrete terms? What kind of evidence is it going to supply that we haven't had before that could play into our acceptance of string theory or any of the competing unification ideas?

Musser: Yeah, the Large Hadron Collider will really be the most closely watched instrument in physical science, at least over the next few years. It is actually the most expensive scientific instrument of any sort ever built. It involved, a tour de force of engineering and of organization and computing and all the rest. So I am really excited about it. It is not specific to string theory, of course. It's meant generally to prove beyond the current standard model of particle physics, and I want to emphasize that, because the standard model of particle physics is pretty much at the end of its rope when it comes to the energies probed by the Hadron Collider. Something has to happen at the Hadron Collider. There has to be some new physical process of some sort or other that current theories can handle. There [are]is just too many loose threads in the standard model and they all seem to kind of begin to matter. They began to affect observational predictions at the energies probed by the Hadron Collider. So number one, whatever comes out of the Hadron Collider will be a guide to [the] unification of physics, be it string theory, be it one of these other theories I have mentioned. Now there are specific types of phenomena that string theory would prove or would predict that the Hadron Collider might see. Now it's, again—as I've emphasized earlier—it's not a question of strictly proving or strictly disproving string theory; that's beyond even the Hadron Collider's ability. It's more of a hint level. and one is called super symmetry; and this is the idea that the two main types of particles in nature which are basically particles in matter and particles of force. So, particle matter might be an electron, a particle force might be a photon, a particle of light. Those are the two kinds of families of particles, the two types of particles, and super symmetry says they are actually united. There is actually, in essence, one type of particle that has these different manifestations, be it a matter or be it a force. So the electron is related—like a family relationship—to the photon, which is related to other types of particles as well; and that is the prediction of string theory [that] seems to be required—though not strictly required—but seems to be required by the behaviors of the strings and probably would be observable at the Hadron Collider. And you would see it because you would see a whole new gaggle of particles just start to pop out of thin air when they start to collide these particles at the Collider. So you are going to smash the protons together. They spew out countless other types of particles that we know of and hopefully that we don't know of. That's the whole purpose: is to find something that we don't know, some of which may be the super symmetric particles. Bottom line: the discovery or non-discovery of super symmetry, the Hadron Collider will be a huge clue. It's just going to be the elephant in a room holding the dagger clue.

Steve: The elephant in the room holding the dagger ...

Musser: Okay ...

Steve: So the elephant did it ...

Musser: The elephant did it, exactly, so it makes metaphor or whatever.

Steve: So, the results that we see from the Hadron Collider should start coming in pretty soon actually.

Musser: Let's see they are supposed to start up July, so this month or maybe August.

Steve: By the time papers come out with new particles, if there are any discovered—I mean, they're going to come out pretty quick.

Musser: Probably, but no, they have to take it slowly. Their actual first goal at the Collider is to rediscover the standard model.

Steve: Right.

Musser: So they are going to just recreate all the models they know, then remeasure them and ...

Steve: That will make sure that the Collider itself is working properly.

Musser: And also to really add another decimal place beside the measurements, so they can then look for deviations at a finer level than they were before. Now there are all sorts of exotic predictions that people have made about the Hadron Collider; about looking for black holes that it might produce for example; that if they did see, it would just already just be it like, start handing out Nobel prizes to the string theorists. Now most people think that's pretty unlikely, even if string theory is true that those black holes could be found, but the possibility is there and if they see a black hole already they just start ticking off names on who they are going to send to Stockholm, because it is going to be a huge, major discovery; not to mention they will be humanity's look into extra dimensions because of black holes—should they be creatable at the Hadron Collider—will be an indication that space has extra dimensions.

Steve: We're talking about teeny, tiny black holes, because I know that there are people out there who are afraid to press the start button on the Hadron Collider because they think it could destroy the world, the whole universe.

Musser: Yeah, forget the world, the universe. The thing about these little black holes—and this is actually something I talk about [a] lot in the book and which is essential to unifying physics—little black holes, you've [got] to think of them very differently from the big ones. They are all black holes, but the little ones aren't the monsters that the big ones are; they are kind of tortured souls. They are, kind of, they come on[in] to this world and they wink out almost as fast as they appear. So you shouldn't think of the little black holes as these, kind of, cosmic monsters or[that can] just, kind of, tear you apart.

Steve: It's not the doomsday machine.

Musser: It's not [a] doomsday machine. These are just going to form and they go pop; they form and pop; and they don't pose any threat to us, because in order to be created, that very fact that they can be created in the laboratory necessarily implies that they would also go pop and they would also destroy themselves almost instantly.

Steve: So we'll see some, you know, within the next couple of years, we are going to start to see some very interesting things or not come out of the collider. But let me ask you, there is this search for unification. It's been really this dream of physics now for, you know, a pretty much a century. Why do physicists believe that there is unification to be found? How do I know that that's the way the universe is and how do I not know that, well, as you said at the beginning of our conversation, this is just the way it is and you have to deal with it? How do I know that this isn't just the way it is and I can't unify gravity with the other fundamental forces, and I just have to live in a universe that is aesthetically unpleasing that goes on its merry way without unification?

Musser: I think there is [are] really three ways. One is just that nature itself is a unity. There don't seem to be lines in the sand drawn around natural phenomena in the world. Everything seems to just click together, so it suggests that underlying the natural world is a unifying set of principals. Second is really historical example—that in the past, every time we had seen disparate phenomena and that we think of just, "Oh completely different," they turn out to have a common cause; they turn out to stem from some unified description of them. And third, there are particular sign posts up ahead that tell us that there seems to be a unity to the particles and even to gravity and particles. For example, if you extrapolate the strengths of different forces of nature, they still vary; they are not constant. Electromagnetism strengthens a little bit as you probe to higher and higher energies; to strong force seems to weaken a little bit as you probe to higher and higher energies; gravity seems to strengthen as you probe to higher and higher energies. These trends among the forming forces of nature all converge; they all converge on a point up near this plank scale I was telling you about earlier. It happens about 10-35 meters; it is the distance or equivalent energy—because those two concepts are related—at which all the forces of nature seem to be unified.

Steve: And what we mean by that is: it's not that there is a single set of equations that describe them all so much as they are all the same.

Musser: Right.

Steve: At the point of the big bang, gravity is electromagnetism, is the strong force, is the weak force. They are force X, they are all exactly the same, and it is only when we get that expansion, then the forces themselves also start to separate from each other.

Musser: Exactly, exactly, exactly. So, at the dawn of our universe—and I have to emphasize our universe, because there could be others—so, dawn of our universe, physicists think there was one type of force, one type of matter and that as the cosmos expanded, as space expanded, it cooled and things started to condense out like snow flakes, and over time that single force broke, it differentiated; and something similar happens in the human body as we develop from a single cell; we differentiate, different tissues form in our bodies, different layers of tissues. Something similar happened, physicists think, in our universe, that over time this single force somehow differentiated into the four forces that we know today. The two nuclear forces—gravity and electromagnetism—and in turn electromagnetism seems to differentiate into electricity or magnetism, depending on our own velocity, for example; depending how we perceive what our perspective on that force is. So the idea is that because the forces seem to converge in strength it is taken as a clue as a sign post that they are actually manifestations of a single force. It's not proved, but it's, you know, go to battle with the army you have; you have to see what's you have got here and it seems to be a clue; what's interesting in particular about that clue is that the two components of it—namely gravity on the one side and the three quantum forces, electromagnetism, and the nuclear forces on the other—act independently in their convergence. For instance, the forces of electromagnetism and the nuclear forces seem to converge and there are laws of quantum mechanics that dictate that convergence and they actually are fairly modest in their variation with scale, with energy. So they just, kind [of], lackadaisically they come together to a point and meet. Gravity, which varies hugely with a scale of with a scale of energy that you probe it out, just kind of swoops in from afar like a falcon and lands exactly where this[these] other three forces are. That is a coincidence rather than something that had deep meaning rather then, "Boy, God has really played a trick on us".

Steve: (laughs)

Musser: So the indications are there. There seems to be some unity to nature. It's coming out in the measurements that scientists can now take.

Steve: Well, these are certainly interesting times to be a physicist or to follow physics.

Musser: I think so. I mean, everybody thinks to live in a special time, wouldn't that be great, to see Einstein's theory proved in 1919, demonstrated in 1919; and today we have something similar. So as we see these results come from the Hadron Collider, we are going to see something new, and I think most physicists would like to speed it up, if they were wrong, because that it would open up new doors for them.




Steve: Now its time to play TOTALL....... Y BOGUS. Here are four science stories; only three are true. See if you know which story is TOTALL....... Y BOGUS

Story number 1: A species of chameleon has been found whose eggs, while the chameleons are in them developing, can change color to match their surroundings.

Story number 2: Historians have dated Caesar's invasion of Britain to August 26th and 27th in the year 55 BC, but a new analysis by astronomers shows that the actual invasion dates had to be earlier.

Story number 3: Keeping a food diary doubled the pounds taken off by participants in a weight loss program.

And Story number 4: After suffering from a stroke, an Ontario woman started to speak with a Newfoundland accent.

Time is up.

Story number 4 is true. An Ontario woman sounded like a "Newfie" after a stroke. So-called foreign accent syndrome affect[s] some people who suffer brain damage. Their speech changes to something that listeners think sounds like a foreign accent. In this case, however, the changes are more reminiscent of maritime Canadian English. The case was reported in the Canadian Journal of Neurological Sciences.

Story number 3 is true. A study of participants in a weight loss program found that those who simply wrote down everything they ate lost twice as much as those people who just tried to follow the program. The researchers published in the American Journal of Preventive Medicine; for more check out the July 11th edition of the daily podcast, 60-Second Science.

And story number 2 is true. Because of gravitational forces exerted by the sun and moon, the English Channel would have been flowing the wrong way on the dates usually given for Caesar's invasion of Britain. Caesar's own descriptions of the tides along with the new astronomical calculations indicate that he probably invaded Britain four days earlier than the accepted dates of August 26th and 27th 55 B.C. The research appeared in Sky & Telescope magazine.

All of which means that story number 1, about a chameleon whose eggs exhibit color mimicry, is TOTALL....... Y BOGUS. But what is true is that a species of Madagascar chameleon has been discovered to spend three-fourths of its life span inside the egg. It then lives free for only four or five months. No other known four-legged animal has such a rapid growth rate after hatching or birth along with such a short life span.


Well that's it for this edition of the weekly SciAm podcast. Visit for the latest science news, content from our magazines and all our podcasts. For Science Talk, the weekly podcast of Scientific American, I'm Steve Mirsky. Thanks for clicking on us.

Click below to watch a brief version of Steve's interview with George Musser about his new book, The Complete Idiot's Guide to String Theory. Listen to the complete audio podcast above.











Science Talk is a weekly podcast, subscribe here: RSS | iTunes

Share this Article:


You must sign in or register as a member to submit a comment.

Starting Thanksgiving

Enter code: HOLIDAY 2015
at checkout

Get 20% off now! >


Email this Article