Our Cosmology and The Big Picture: An Interview with Sean Carroll

Doing a PhD as an international student has its perks. You get to attend fancy conferences, interact with a wide variety of scientists, and most importantly meet some your idols that inspired you to study astronomy. I attended the 228th American Astronomical Society Meeting in San Diego this summer (my first ever) and had a chance to do all three!

Astrobites at the 228th AAS Meeting!

Astrobites at the 228th AAS Meeting!


Jim Peebles, Leonard Susskind, John Carlstrom, Joseph Silk and Sean Carroll were all there (something I didn’t know when I signed up to be a member of the press at the meeting as part of the newly-formed AAS-Astrobites partnership). In my capacity as a graduate student and an Astrobites writer, I had the utmost pleasure of not only attending the fantastic Limits of Scientific Cosmology session, but also having the courage to ask Sean Carroll for ten minutes of his time. At Astrobites, we believed that an interview with Sean (one of the leading theoretical cosmologists of our time) about his new book The Big Picture, his outreach efforts with his blog The Preposterous Universe, and his current research would be extremely insightful for our readers. Let’s see how it went:


Gourav Khullar: Thank you for doing this, Sean. I apologize in advance for all the fan-boying that I am about to do. Your Spacetime and Geometry and The Cosmological Constant review have saved my life multiple times in undergrad and grad life.

Sean Carroll: Thank you very much!

GK: I would start off with congratulating you on two counts. One, for giving such a fantastic talk yesterday as part of Limits of Scientific Cosmology. Second, for the great reviews of your new book The Big Picture! I am curious to know how you feel about this emphasis on writing, this transition per se. Do you get enough time for research these days?

SC: Thank you! It’s gratifying to see the reviews. I think that research is still my primary focus – there’s no question – but still once every few years I can write a book, and I really enjoy writing books! The ability to stretch yourself for a hundred thousand words or more, and get things right, and explain things the way they should be explained – I think that’s something I adapt very naturally to. There are friends of mine who are writers who hate writing books because they just can’t go that long, but for me it’s a lot of fun! And this is something that I want to keep doing.

GK: Your books are very lucid and entertaining. I am currently about quarter-way through The Big Picture. You invoke the concept of ‘poetic naturalism’ in your discussion. For our readers, could you give us a one-line snippet of what that entails?

SC: Sure! Naturalism is the basic idea that there is only one world – the natural world. The world that obeys the laws of nature, the world that we can explore using the methods of science. Poetic Naturalism is a statement about what is real within that world. In particular, lots of different kinds of things can be real. There are also lots of different ways of talking about the universe – thus poetic. If all these ways of talking about the universe serve the purpose at the moment , these can be thought of as describing real things. So atoms are real, but tables and chairs are also real. Similarly, moral principles can be real to the person who invents them given their initial moral inclinations.

A must read.

A must read.


GK: Bringing something up from the theme of your session now, I would like to know of your current opinion on how we are progressing in the field of precision cosmology these days. We are on the verge of actively using big data to quantify our understanding of the universe. My question is, once the hose turns on with the 3rd generation telescopes and the gigantic datasets, when do we stop? For example, what if we don’t see a major deviation from Lambda-CDM or what if CMB-S4 does not see cosmological B-modes?

SC: That’s an easy one. We should never stop! I say this because we don’t have a theory that predicts a threshold, that says that beyond this boundary there is nothing interesting that we can possibly see. All cosmological parameters are continuous in nature, and we could be surprised at any time. So the question shouldn’t be when we should stop, but how do we balance the cost of doing something like [LSST or CMB-S4] or doing something else. Living in a world with finite resources, it might not be worth the money to do it. I don’t think we are at that point yet, but it could be a possibility in the foreseeable future.

GK: You raised the idea of the multiverse as a theory in several contexts during your talk. I am sure you are asked this a lot, but how far do you think we are from a robust theory of the multiverse?

SC: Honestly, I don’t have an idea. I am not trying to avoid the question here, but I don’t think we are close at all. I don’t think we understand quantum gravity or inflation well enough, or even the initial perturbations [of the early universe]. These things are so far away from stuff we can directly detect or test, that theoretical progress is slow, naturally. But it will happen – I do it myself – and we should not be impatient.

It was an experience listening to Sean's session on alternatives to falsifiability in the scientific method, and about our universe in general.

It was an experience listening to Sean’s session on alternatives to falsifiability in the scientific method, and about our universe in general. Image credit: The Preposterous Universe blog.


GK: Thanks, Sean! I am going to close with a question about your outreach efforts in the past and present. Astrobites would really like to thank you because on your blog The Preposterous Universe, your mentions of Astrobites and ComSciCon a few years ago drew a lot of initial readership to our blog. In which direction do you think a platform like Astrobites, and more importantly your own blog should head in? What future do you see for The Preposterous Universe?

SC: Oh, great! I am glad to hear that. I am a big believer in a big wide ecosystem of science communication. Especially when students are involved, because they have insights that we old folks don’t have! I think technology has allowed people to communicate and interact in new ways, and I think we are nowhere near equilibrium yet. We are closer, and certainly closer than we were ten years ago when I started my blog, a time when things were changing very rapidly. It has now become a little more clarified and professional with media like Twitter, Facebook, Instagram and blog platforms – a whole new set of tools that people can use to convey their own excitement and knowledge to a wide audience. I don’t think we have figured out what’s the best way to do it yet, and I am not in the vanguard about that these days. I was in the vanguard back in the past, but now there are other people using these media and making new videos, animations and it’s all very exciting!

GK: Thank you Sean! It’s been a pleasure interacting with you. Thank you so much for your time.

SC: My pleasure. Thanks. Good luck!


Please Note:

To know more about Poetic Naturalism, see Sean’s blog post.

To know Sean’s views about the multiverse, see his recent TED talk.

To read more about the session Limits of Scientific Cosmology at AAS this year, see this astrobite.

About Gourav Khullar

Grad student at UChicago. I look at the fantastic phenomenon engulfing galaxy clusters that is gravitational lensing. If that sounds cheesy and/or weird, wait till you hear me talk about science, chocolate chip muffins and comic books.


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