Over the past week or so, there has been unnecessary confusion created about whether or not there’s some relationship between (a) the Higgs particle, recently discovered at the Large Hadron Collider, and (b) the Big Bang, perhaps specifically having to do with the period of “Cosmic Inflation” which is believed by many scientists to explain why the universe is so uniform, relatively speaking. This blurring of the lines between logically separate subjects — let’s call it “Cosmic Conflation” — makes it harder for the public to understand the science, and I don’t think it serves society well.
For the current round of confusion, we may thank professor Michio Kaku, and before him professor Leon Lederman (who may or may not have invented the term “God Particle” but blames it on his publisher), helpfully carried into the wider world by various reporters, as Sean Carroll observed here.
[Aside: in this post I'll be writing about the Higgs field and the Higgs particle. To learn about the relationship between the field and the particle, you can click here, here, here, or here (listed from shortest to most detailed).]
Let’s start with the bottom line. At the present time, there is no established connection, direct or indirect, between (a) the Higgs field and its particle, on the one hand, and (b) cosmic inflation and the Big Bang on the other hand. Period. Any such connection is highly speculative — not crazy to think about, but without current support from data. Yes, the Higgs field, responsible for the mass of many elementary particles, and without which you and I wouldn’t be here, is a spin-zero field (which means the Higgs particle has zero spin). And yes, the “inflaton field” (the name given to the hypothetical field that, by giving the universe a lot of extra “dark energy” in the early universe, is supposed to have caused the universe to expand at a spectacular rate) is also probably a spin-zero field (in which case the inflaton particle also has zero spin). Well, fish and whales both have tails, and both swim in the sea; yet that doesn’t make them closely related.
[Aside: Spin is a tricky concept which you don't need to understand for this post, but in case you want to know something, here's a sketch. Unlike the electric or magnetic field, which (at each location in space) has a magnitude (i.e. size) and a direction in which it points, a spin-zero field doesn't point; it just has a magnitude at each location. And unlike a particle with spin, which in some ways behaves as though it is rotating, a spin zero particle doesn't behave this way.]
The main issue I’m concerned with in this post isn’t the science itself (though I will say some things about it), but how it is communicated to non-experts. Personally, I think it very important for scientific experts to be clear, when they speak in public, about what is known and well-established, what is plausible and widely believed but still needs experimental checks, and what is largely speculative and could very well be false. (For example: The Higgs particle and field are nearly established; inflation is increasingly plausible; any connection between them is speculative.)
Clearly scientific integrity and clarity are enormously important in subjects such as climate change, applied genetics, and nutrition. Are they important in particle physics and cosmology? Well, it seems to me that when particle physicists, string theorists and cosmologists get in the habit (or, in some cases, can’t get out of the habit) of stretching the truth to make headlines bigger and eyes wider, then not only our own credibility, but also that of our colleagues in other research areas, is undermined. Many non-scientists have somehow come to that believe science is just about tossing wild ideas around, and that just as in politics, it’s simply a matter of one person’s opinion against another’s. I meet many people who think scientific research is all about money and fame, with the search for knowledge and understanding no more than window dressing. To turn this trend around, it seems important to me that there be a code of ethics, written or unwritten, that governs scientists speaking to the public about scientific knowledge. And those who won’t abide by it need to be pointed out by their colleagues.
Just as we widely agree the Higgs particle must have zero spin, and that the inflaton is quite likely to have zero spin, I’d like to see a consensus emerge that public communication of particle physics, string theory and cosmology should also have zero spin. Too bad that’s still a rather speculative idea.
Now Some Details
Back to the Higgs and inflation. Let’s look at the logical options, and evaluate them.
- Might the Higgs field and the inflaton field be one and the same? Yes.
- Might they be closely related fields, perhaps members of a larger family? Yes.
- Might they be very weakly related, perhaps with just a vague resemblance? Yes.
- Might they be completely different types of fields, completely unrelated? Yes.
In other words, nothing is known for sure — and among these options, there isn’t even a favored possibility. In my view, no popularizer of science should be going around giving the impression that the situation is otherwise. It is especially weird, if not irresponsible, for anyone to say that the Higgs particle is important because the Higgs field might be the inflaton field, or might be closely related to it. The importance of the Higgs field and particle is certainly not predicated on some speculative idea, one that might be false, about the distant past of the universe! Independent of what happened during or before the Big Bang, if the Higgs field weren’t doing what it does right now, right here, then much of the stuff from which we, and our planet, and all ordinary matter are made wouldn’t exist. Isn’t this important enough? And discovery of the Higgs particle confirms the Higgs field really is doing this, and opens a new window through which we can learn about the Higgs field in unprecedented detail.
Just to give you confidence that what I’m saying about the Higgs field and the inflaton field isn’t merely a matter of personal opinion, I invite you to take a look at one of the papers (admittedly rather technical) made public by the members of the collaboration who operate the Planck satellite, which reported data just last week. In their new paper entitled “Constraints on Inflation”, http://arxiv.org/abs/1303.5082, the Planck collaboration considers various suggestions theoretical physicists have made for how inflation might have occurred, and looks to see if those suggestions are consistent with the data that they’ve obtained. Here are some things they found (though you should keep in mind that some aspects of their results have not been confirmed yet by any other experiment.)
First and foremost, the Planck data are completely consistent with some form of inflation having occurred. (See section 4.1, paragraphs 2 and 3, of the Planck paper.) Essentially, what they see is that the distribution of non-uniformities in the nearly smooth cosmic microwave background [CMB] (the after-glow from the Big Bang) agrees with what one would expect had cosmic inflation occurred. Since inflation is currently the leading theory of how the universe became so large and relatively uniform, and there aren’t widely accepted and clear alternatives, this new data gives inflation additional plausibility. That said, we can’t really regard the Planck data as a direct proof (in the way that the discovery and study of the Higgs particle is a direct test of the idea of the Higgs field) but it is a big step forward. Direct proof may be a long way off, I’m afraid.
Second, many specific ideas for how inflation might have occurred are now excluded by the data; others are perfectly consistent with it, and still others are now a bit borderline. This is partially discussed in section 4.2 and Figure 1 of the Planck paper (and there are discussions of even more models later in the paper.) I’ve reprinted their Figure 1 here. The Planck authors spend three pages (small print) going over a wide variety of theoretical ideas, and as you can see in the figure, quite a few of the various ideas make predictions (dots connected by short lines, or curved swathes) that are found within the outer edge of the light-blue-shaded area, which means they are reasonably consistent with the Planck data combined with other measurements. In fact, there are more theories studied there than it might appear, as certain ideas that differ quite dramatically in their origin give similar predictions, and are represented by a single dot. And here’s the point: among the dots and swathes found inside the shaded area you will find speculations in which the Higgs field and the inflaton are (a) identical, (b) perhaps closely related, (c) possibly vaguely related, and (d) completely unrelated with no resemblance at all.
For instance, the notion that the Higgs and the inflaton fields are the same gives (if you trust the calculational methods) almost the same result as the orange dots in the figure, which are inside the blue region and are thus allowed by the data. But also allowed is a part of the purple-shaded area [referring to a theory called "natural inflation"] which has an inflaton field similar to the pion field, a type of spin-zero field that (unlike the Higgs field) is very common in nature and quite familiar to scientists. [It's called a pseudo-Nambu-Goldstone boson; Nambu won a Nobel prize for work on this subject, while Goldstone was passed over.] Other theories with more complicated inflatons also appear on this figure. Thus, despite what some have said on other websites and to journalists, it simply isn’t true that discovery of the Higgs particle makes inflation more plausible, because for all we know today, the inflaton might be a type of field that is quite unlike the Higgs field. To say otherwise is conflation on a cosmic scale.
I would be remiss if I didn’t point out that Planck’s data could have strongly disfavored the idea that the Higgs field is also the inflaton field. It didn’t. The value of the Higgs particle’s mass, measured for the first time as the particle was discovered in July, could also have strongly disfavored the idea, but didn’t. So the suggestion that the two fields might be one and the same has more credence now — though I hasten to add that there are still big theoretical problems with the idea. Perhaps what is more important for the non-expert to know is that the Higgs field’s average value during inflation, if it were serving as the inflaton, would have been trillions of times larger than it is today (when it has a value of 246 GeV, thus assuring the known elementary particles can have masses no larger than about 1000 GeV.) And we have no idea, from any experiment we’ve ever done, how the Higgs field would really behave if its value were so large. So this is an interesting idea worth thinking about and investigating, but if we’re going to talk about it on national television, we should probably point out how speculative it remains at this point.
Speculation — in particular, grounded speculation, involving that special combination of creativity and mathematics that turns conversation over beer into a serious scientific theory, with detailed predictions — is an essential part of physics, and of other branches of science. I have nothing against speculation! It’s part of my job. But it’s important, when talking to non-experts, to distinguish well-established facts and consensus beliefs from speculations that may well prove false and are viewed with skepticism by most people in the field. Journalists and the public already find it challenging to understand our discoveries and their significance, so how can it be wise to confuse them? Unnecessary forms of cosmic conflation frustrate those who wish science well, and deliver ammunition to those who don’t.