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. randal sexton says:

    So, as someone endowed with an overactive curiosity, and a pretty limited math and physics background, I find myself awed, excited, confused, amused, baffled and boggled by this sort of thing- but if I can ask a few questions and get any kind of response I would be very grateful – Question 1- The inflation – I have been thinking of this inflation as the idea that space itself was expanding, not that the ‘things’ ( things being matter, and radiation I suppose) were expanding. If I was standing next to Fred, who was 1 foot away from me, and some inflation happened, would we suddenly be 2 feet apart? Without Fred or I experiencing any acceleration? Is that the idea, that more space was injected between us ? What about the space between the molecules of my body ? Would that space have expanded as well? Would the tape measure in my pocket give me a different answer after this expansion ?

    Question 2 – The hot/cold/dark energy condensation part – So when this HUGE expansion was happening, Fred and I might not have really been able to check distances with our tape measures, because there was no matter yet? I have read that only at some point of expansion, the dark energy which was driving it, condensed or converted into matter/radiation, a huge phase change like event ? That slowed down the expansion somewhat, but not entirely. Did all the Dark Energy do this ? Are Fred and I condensed Dark Energy ? ( Is Dark Matter also condensed Dark Energy ? ) Is there still some Dark Energy running around still pushing stuff apart ? Question 3- The gravity waves – I can think of the ‘waves on a string’ notion of a wave causing me to move up and down orthogonally to the direction of the wave, or a compression style wave, that makes me move towards and away from the direction of the wave, is this a useful way to think of a gravity wave ? In any case, it seems like anytime there is a wave like this it really is transmitting energy – are gravity waves transmitting energy ? ( I would really like to have some nice anti-gravity boots please. ) . Well, many more no doubt moronic questions I have but this is probably long enough post anyways.- Thanks in advance for your indulgence.

  2. Kyle says:

    I have a hard time visualizing what is meant when someone describes the universe as having a definite “size”. My (layman’s) impression was that the shape and geometry of the universe is unknown other than it having very low local curvature. Is the current thinking that the topology of the universe is “closed”, like the surface of a sphere? Was it different during the inflation period?

  3. John Barrett says:

    The first time I read about Planck Length and Planck Time, I just knew that it would end up having something to do with the moment of The Big Bang. It is nice to see that new evidence is always pointing more and more closer to this idea.

    The idea that this could be proof of gravitational waves is very troubling though. We would just have more indirect evidence of it’s existence while still having no way to know how to find it in the laboratory. I couldn’t help but wonder if the left and right handed signals they picked up could have just come from particles traveling in two different directions once The Big Bang occurred.

  4. Pat Ridley says:

    Great post. I love the poetic last paragraph!

  5. “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.”

    Right. The Hubble constant is the change of the scale factor with time divided by the scale factor itself. So, if H is constant, one has acceleration. This is the de Sitter model and the model which our universe will asymptotically approach. It is also roughly the law of expansion during inflation itself.

    Note that there is no proven connection between inflation and the cosmological constant, even though both are connected with exponential expansion.

  6. John says:

    I love hearing Guth lecture, although his jokes often times fall flat as can be.

    Say quantum fluctuations caused the inflaton field to expand initially, what caused it to level out and then start to pick up again about 5 billion years ago? It can’t be quantum fluctuations again, right?

  7. “Say quantum fluctuations caused the inflaton field to expand initially, what caused it to level out and then start to pick up again about 5 billion years ago? It can’t be quantum fluctuations again, right?”

    Again, there is no proven connection between inflation and the cosmological constant, even though both are connected with exponential expansion.

  8. “there is no proven connection between inflation and the cosmological constant, even though both are connected with exponential expansion.”

    Also, nothing picked up 5 billion years ago. You are probably referring to the time when acceleration set in and/or the energy densities of Omega and lambda (matter and the cosmological constant) were the same. Nothing fundamental happened then. They have a different dependence on the scale factor, so with time the relative strength varies, but there was no event associated with it.

    There is something similar with matter and radiation, but when the density of radiation dropped enough, it did cause other events, like the universe becoming transparent. But this drop itself was not caused by anything other than the different dependencies on the scale factor.

  9. “I have a hard time visualizing what is meant when someone describes the universe as having a definite “size”. My (layman’s) impression was that the shape and geometry of the universe is unknown other than it having very low local curvature. “

    You are right. However, the observable universe (that within the particle horizon) does have a finite size. Sometimes people aren’t as correct with terminology as they should be.

  10. J Duffield says:

    I’m afraid I’m with Peter Coles on all of this. I think he sounds the right note. He says a primordial signal should not vary as a function of frequency, but there was no detection of the B-mode signal at 100GHz on BICEP1.

    All the more so because IMHO inflation is looking like a solution without a problem these days. We now know that space is “flat”. It wasn’t curved a billion years ago, or a billion years before that. It never ever was. So why do we need inflation to make it indistinguishable from flat today? Magnetic monopoles can’t exist, we don’t need inflation to make them rare. And the CMB is very uniform, but so what? The evolution of the universe can in some respects be likened to pulling away from a black hole, and the coordinate speed of light is zero at the event horizon. That’s uniform. Plus there are other possible causes of B-mode polarization such as self-attraction of the CMB photons and cosmological defects.

    All in all I would urge some caution during this great time for reason and science.

  11. “So why do we need inflation to make it indistinguishable from flat today? “

    First, how do you know what the universe was like that long ago. Second, your statement reflects a serious misunderstanding. In this context, “flat” means “radius of curvature large compared to the Hubble radius”.

  12. Sean– So these reverse gravity waves which drove inflation are not the origin of the dark energy which now pushes the galaxies apart? –or rather, has no connection between the two been established?

  13. Ray says:

    isn’t it grossly misleading to refer to inflation as being 10^-34 or whatever seconds after the big bang. It was my impression that we have no clue how long inflation lasted or what (if anything) preceded it.

  14. Alvin says:

    Possible dummy question that’s been eating at me for a while:

    If the “bekenstein bound” / holographic principle set a limit on the information density of space, how could the universe have been compacted into a smaller volume and still contain any entropy? Shouldn’t it have contained basically zero entropy when it was compressed to the scale of a planck length?

  15. As you said in the post, the idea of inflation was proposed by Alan Guth. But other scientists have made contributions as well, such as Andrei Linde. So what exactly was the role of Guth and Linde (and others) on the theoretical prediction that, it seems, have been confirmed by BICEP2?

  16. Alvin says:

    Related question that also bugs me: As I understand it quantum information is always conserved, and the laws of QM are symmetric in time. So the “arrow of time” only seems to show up at the macro scale. Fair enough.

    But if quantum info is conserved and time symmetric, then how could the universe have ever had a radius smaller than the Bekenstein bound radius implied by its current entropy?

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  18. Daniel Tung says:

    Hi Sean,
    I wonder what’s the implication of this to the search of quantum gravity, both the theory and the experiment?
    Does it also increase the possibility of multiple universe?

  19. James George Neil says:

    The two biggest discoveries in Science in the past year are the confirmation of the Higgs mechanism/boson and inflation.

    Does the evidence for inflation theory also tell us anything about how the Higgs field is formed? How long after the Big Bang did the HIggs mechanism come into being? Or are the two completely unrelated?

  20. Simon says:

    When will the Planck team release their data von B-Mode polarization? Does anyone know?

  21. James Gallagher says:


    According to a quote from Planck team member Olivier Doré in New Scientist, results are due October 2014:

    Forthcoming data from Planck should help resolve the issue, and we may not have long to wait. Olivier Doré at the California Institute of Technology is a member of the Planck collaboration. He says that the BICEP2 results are strong and that his group should soon be adding their data to the inflation debate: “Planck in particular will have something to say about it as soon as we publish our polarisation result in October 2014.”

    This seems to have crept up from previous estimates of “early 2014”

  22. J Duffield says:

    Phillip: re So why do we need inflation to make it indistinguishable from flat today?

    1) We don’t know exactly what the universe was like 13 billion years ago, but we see some galaxies as they were 13 billion years ago. See this report.

    2) When you say “flat” means “radius of curvature large compared to the Hubble radius” you’re missing the point. Which is that there is no radius of curvature, and there never ever was.

  23. Bill Bunting says:

    I’ve just watched (in awe) the Andrew Lange talk and have a better idea of what is going on in this mind blowing research. I have one nagging question. Was the Higgs field created in the big bang, or is it a natural feature of empty space?

    In my mental model (which I happily revise with better information) is that there are 2 (or 3 or 4) types of energy which I am calling dynamic energy (matter) and static energy (the Higgs Field) . Then there is dark energy and dark matter. Dynamic energy acts against static energy and in that way takes the form that we experience. I’m not suggesting that this is the way things actually are, this is just the model that helps me make sense of this amazing transition of understanding the universe that is underway right now.

    So the question again, is the Higgs Field a natural property of space before the big bang or is it an outcome of the big bang?

  24. Robert cattle says:

    The vacuum of space is referred to, as well as time past, time present (phew that went fast!) and seriously time future.
    I really want to know if “Nothing” exists or more properly when that particle becomes smaller and smaller past the Planck ten to the minus 34, does that non entity ( which is NOT a particle) have any time.
    Forget particle, wave, field, force and imagine the new entity ” Nothing”
    Surprisingly it has properties. Can you guess what they are?
    My Nobel prize is just around the corner!

  25. Bill Bunting says:

    I got some clarification over at the Matt Strassler site. I have been merging mass with gravity, which is not correct. So I have a lot of reading to do. At least I am asking the right questions now. My mental model needs a major over haul. This universe has been put together in a confusing way. It is not the way I would have designed it, but its too late to change it now. Its all out there.