A Great Time for Reason and Science

Here I am at an extremely stimulating meeting on gravity and quantum spacetime in Santa Barbara, but I skipped yesterday’s afternoon session to talk on the PBS News Hour about the new inflation results:

There’s a great parallel (if the BICEP2 result holds up!) between Monday’s evidence for inflation and the Higgs discovery back in 2012. When talking about the Higgs, I like to point out the extraordinary nature of the accomplishment of those physicists (Anderson, Englert, Brout, Higgs, Guralnik, Hagen, Kibble) who came up with the idea back in the early 1960’s. They were thinking about a fairly general question: how can you make forces of nature (like the nuclear forces) that don’t obey an inverse square law, but instead only stretch over a short distance? They weren’t lucky enough to have specific, detailed experimental guidance; just some basic principles and an ambitious goal. And they (independently!) proposed a radical idea: empty space is suffused with an invisible energy field that affects the behavior of other fields in space in a profound way. A crazy-sounding idea, and one that was largely ignored for quite a while. Gradually physicists realized that it was actually quite promising, and we spent billions of dollars and many thousands of scientist-years of effort to test the idea. Finally, almost half a century later, a tiny bump on a couple of plots showed they were right.

The inflation story is similar. Alan Guth was thinking about some very general features of the universe: the absence of monopoles, the overall smoothness and flatness. And he proposed an audacious idea: in its very earliest moments, the universe was driven by the potential energy of some quantum field to expand at an accelerated rate, smoothing things out and diluting unwanted relics like monopoles. Unlike the Higgs idea, inflation caught on quite quickly, and people soon realized that it helped explain the origin of density perturbations and (potentially) gravitational-wave fluctuations. Inflation became the dominant idea in early-universe cosmology, but it was always a wild extrapolation away from known physics. If BICEP2 is right, the energy scale of inflation is 0.01 times the Planck scale. The Large Hadron Collider, our highest-energy accelerator here on Earth, reaches energies of 0.00000000000001 times the Planck scale. We really have (had) no right to think that our cute little speculations about what the universe was doing at such scales were anywhere near the right track.

But apparently they were. Over thirty years later, thanks to the dedication of very talented experimenters and millions of dollars of (public) funding, another bump on a plot seems to be confirming that original audacious idea.

It’s the power of reason and science. We tell stories about how the universe works, but we don’t simply tell any old stories that come to mind; we are dramatically constrained by experimental data and by consistency with the basic principles we think we do understand. Those constraints are enormously powerful — enough that we can sit at our desks, thinking hard, extending our ideas way beyond anything we’ve directly experienced, and come up with good ideas about how things really work. Most such ideas don’t turn out to be right — that’s science for you — but some of them do.

Science is a dialogue between the free play of ideas — theorizing — and the harsh constraints of empiricism — experimental data. Theories are a lever, data are a fulcrum, and between them we can move the world.

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53 Responses to A Great Time for Reason and Science

  1. Ben Goren says:

    Indeed, those who find the power of prophesy persuasive should be absolutely bowled over by the success of both the CERN team and, we hope, BICEP2.

    I feel so lucky to live to see these discoveries made, and I can’t wait to see what comes of them.


  2. Pingback: Sean Carroll explica la importancia del modelo de la inflación cósmica | Por Amor a la Ciencia

  3. Kieran Garland says:

    Ben Goren: “I feel so lucky to live to see these discoveries made, and I can’t wait to see what comes of them.”

    I couldn’t agree more; in terms of our understanding of the universe, it’s an almost unbelievably magical time to be alive.

  4. Don Goldsmith says:

    If we consider the amazing efforts that led to these discoveries, and to how carefully scientists must analyze their data to exclude systematic and other errors, we can appreciate the enormous difference between science’s take on the cosmos and the quick-and-dirty approach that evolution has given us. Richard Feynman spoke of this eloquently in the PBS interview “The Pleasure of Finding Things Out,” and it is worth taking a look at his essay “Cargo Cult Science,” easily available on line, to admire the joy and energy he put into searching for real answers in the real world.

  5. Kieran Garland says:

    Indeed, though perhaps we could stretch the conceit by saying that evolution gave us science, too (you know, eventually).

  6. Björn says:

    During the discussion about the multiverse theory on World Science Festival 2013 Alan Guth says that the expansion doesn’t really accelerate but inflation keeps it from slowing down (http://www.youtube.com/watch?v=2Qt-eGKa34M&t=32m30s). In your post you say the expansion accelerated, and it seems as whenever you read about inflation the acceleration seem to me to be central. Am I confusing the terms? How should a layman think about inflation and acceleration?

    On another note I would just like to thank you for speaking clearly about this things and making a medical student interested in physics.

  7. Björn says:

    Double post, sorry!

  8. Mark Caragio says:

    Sorry for the laymen question here, but what is the difference in the type of “space,” whereas prior to the big bang it was “empty space,” like you mention above, but now while our universe is expanding, new “space” is being created as it does so*. Is the empty space in our universe (that devoid of any matter/energy) different from the empty space that existed prior to the Big Bang?

    *per a comment I heard on Radiolab from Brian Greene

  9. Ben Goren says:

    Mark, this is a perfect example of where our human-scale intuitions quickly fail us.

    Naïvely, one might think of the Big Bang and the subsequent expansion of the Universe as akin to a bubble in your beer that keeps getting bigger and bigger…but it’s still expanding within the beer itself. Unfortunately, that analogy breaks down the instant you start thinking of the bubble being within the beer.

    Rather, space isn’t expanding into something; it’s simply expanding, period. There isn’t any outside, no medium that holds space, or anything like that.

    Your intuition will rebel against that…but it’ll do so in much the same way that Aristotle’s intuition would have rebelled against the idea that the planets move without being moved upon by a Prime Mover. In everyday experience, once you stop pushing on something, it stops moving, and thus our intuitions are tuned to that type of motion; Newtonian mechanics is, indeed, rather counter-intuitive. (What? You mean that, when I push on this wall, it’s pushing back? How is it that the wall can push? It has no muscles!)

    The expansion of the Universe (and of spacetime itself) is another example of that same basic idea. Just as, yes, nothing moves the planets and, yes, the wall is pushing back, yes, space itself is expanding even though it’s not expanding “into” anything.



  10. Mark Caragio says:

    Thanks for the reply Ben. To be clear, I recognize the intuition problem, and of course suffer from it.

    But since I don’t have the theoretical background to answer the question I had, I was hoping to get a better understanding of the empty space that the Big Bang sprung from, and if/how it differs from empty space inside our universe. Since the Higgs particle was found inside our universe, is it conceivable then that the space in which the Big Bang occurred is similar/identical to empty space in our universe?

  11. Sean Carroll says:

    Björn– It’s a little counterintuitive. There are two different ways to characterize the expansion rate of the universe: the Hubble parameter H, and the apparent velocity between two galaxies (or points) at distance d, given by Hubble’s law v = Hd. When we speak of “accelerated expansion,” we usually mean that the velocity v is increasing. But we usually don’t mean that H is increasing; all you need is that H is decreasing sufficiently slowly that the increase in d is most important. So when Alan says “the expansion doesn’t really accelerate” he just means that H is not increasing — but v would be, so it’s actually still okay to say the universe is accelerating.

  12. Tom Anderson says:

    I couldn’t agree more or phrased it better. Tom A

  13. Charles Murray says:

    I keep hearing it said that the universe inflated a trillion, trillion, trillion times in the first 10^-34 seconds or numbers of that order. To me, this seems like it would far exceed the speed of light. How is this possible?

  14. Ben Goren says:

    Charles, not only are you correct that the early Universe expanded faster than the speed of light, it’s still to this very day expanding faster than the speed of light.

    The reason this is possible is because it’s space itself that’s expanding. The speed of light only applies to “stuff” within the Universe itself, and space isn’t “stuff.” A bit more precisely, the speed of light applies to the propagation of waves in the various fields, but not to the fields themselves.

    See my response to Mark above about how it is that space is expanding without actually expanding into anything.



  15. Charles Murray says:

    Ben, thank you. It is fantastic that space is expanding faster than the speed of light. I love that!

  16. Agron says:

    The space-time is a quantum field, which means it moves with the speed of light. But that doesn’t mean that universe is expanding. The Hubble Law is not true it is an misunderstanding of movement of quantum field. Think about it!

  17. Ori Vandewalle says:

    Does anybody know if this result lends support to any particular model of inflation? It’s always been my understanding that we’re a little hazy on the mechanism of inflation, that we know what inflation has to do but not how it does it.

  18. Andrew Fredriksen says:


    Great response to Gwen Ifill’s theology dig.

  19. Neo says:

    Alan Guth only?
    Typical Americans; they behave like they own the world ignoring everyone else…

  20. M DJ says:

    A little-known fact, perhaps, is that Demosthenes Kazanas was the first to publish this sort of “thing”; see
    http://bit.ly/1gI5AA8 “Dynamics of the Universe and Spontaneous Symmetry Breaking” (see also: http://bit.ly/1nEOcl9 “Cosmological Inflation: A Personal Perspective”)

    It is shown that the presence of a phase transition early in the history of the universe, associated with spontaneous symmetry breaking (believed to take place at very high temperatures at which the various fundamental interactions unify), significantly modifies its dynamics and evolution. This is due to the energy ‘pumping’ during the phase transition from the vacuum to the substance, rather than the gravitating effects of the vacuum. The expansion law of the universe then differs substantially from the relation considered so far for the very early time expansion. In particular it is shown that under certain conditions this expansion law is exponential. It is further argued that under reasonable assumptions for the mass of the associated Higgs boson this expansion stage could last long enough to potentially account for the observed isotropy of the universe.

  21. Fantastic job on the News Hour, Sean!

  22. Sid says:

    Sean, great post. A minor quibble though (and I know that you know this):

    When you point to the Higgs and the BICEP results and say that the theory is vindicated by tiny bumps in the graph, I think you underplay the importance of how many theory and experiment modules needed to be imported into building the theories and experiments behind the Higgs or inflation, and how well-tested these modules needed be before you could say that if you build this giant particle accelerator or this giant telescope, then you’ll see the tiny bumps in a graph.

    In other words, the tiny bumps in the graphs mean so much because we know that the referents of the quantities being plotted have a very stable ontic status. For the inflation results, we needed to have a very clear picture of how the universe evolved and what the CMB is and what the different patterns in the CMB mean and many, many other pieces of knowledge, even going all the way back to GR and electromagnetism and quantum mechanics. Thus the vindication of inflation rests not just on the tiny bumps in the plot, but on the strength of the connected web of knowledge that has been built before the BICEP experiment even conceived.

  23. Zetopan says:

    You passed up a golden opportunity to explain what a scientific theory actually means when you were asked “How do you go about proving a theory not to be a theory …?”
    Gwen Ifill appears to be using “theory” in a non-scientific context (i.e. as in a speculation, such that valid scientific theories somehow become facts). At that point you could have pointed out that scientific theories are not idle speculations, they are actually one level above facts since they explain facts. Since there are multiple inflationary theories explaining the same set of facts, scientists test the predictions of each of these theories against new data to determine which, if any, of these theories is the more accurate.
    In the end, the winning inflationary theory will still remain a scientific theory and not anything like a fact. A fact is what the non-scientific public imagines to be the end goal of a valid scientific “theory”. Hence the misguided notion that evolution is “only a theory” and not a “fact”, and similarly for inflationary theory.
    If Gwen had asked “How do you go about invalidating [or validating] a theory?” I would not have brought this matter to your attention. But the manner in which the question was asked very much fits into the general public’s misunderstanding of “theory”, which has very little to do with the actual scientific usage of that term.

  24. Glenn says:

    Sean, you nailed the News Hour interview. You hit the key points in a limited time format.

  25. Do you have a taste for crazy-sounding ideas? You should get familiar with my ideas. I have a collaboration ongoing aimed to generate electron annihilation with low energy electrons shot head-on from two (anti-parallel) spin polarized (on line connecting) electron guns.

    Naturally, the same can be generated with protons, but the outcome is much more impressive. We surely are living exciting times!