Hey, I Uploaded a Video

By Sean Carroll | August 15, 2007 11:41 pm

Just got back from a great trip to Beijing, very enjoyable if a bit tiring, where much musing was done on the Primordial Existential Question, about which more anon. But I also mused a bit about what this blog needs, and I came to the conclusion that must have been obvious to everyone else long ago: more videos of me.

So, here you are. Thanks to some heroic efforts on the part of folks who would just as soon lurk behind the scenes, we now have video captured from the C-SPAN broadcast of our science panel at YearlyKos. Here is my talk, conveniently divided into two pieces to appease the YouTube gods. They are a little fuzzy, but you get the idea. I used the mysterious beauty of dark matter and dark energy as an excuse to make some didactic points about science and rationality and politics. (If I weren’t an atheist, I would have made a good preacher.) You can also find videos of Chris’s talk and Ed’s talk at their respective sites; Tara, who felt sorry for me for being given the impossible task of making the universe sound interesting, has the Q&A up as well.

But! Behind the fold, the true payoff!

Those talks of mine are inspiring and educational and all that, but they’re not truly art. For that, you will have to check out this series of videos by Dylan King. Here is a taste.

For our slower viewers, I’ll explain: this is a series of trumpet improvisations, recorded over (and inspired by, I like to think) my appearance on Art Bell’s Coast to Coast AM. A confluence of science and music, radio and the internet, that can only be described as unique.

CATEGORIZED UNDER: Personal, Science
  • Dima

    LMAO great talk, I enjoyed it immensely (especially the comic parts 😛
    I wanted to ask you Sean two questions:

    1) What do you think of the Simulation Argument?


    2) What do you the role of consciousness is in the universe? You mentioned in your talk the oft-cited observation that our planet is a very insignificant speck on the vast expanses of the cosmos and I was wondering how can this be reconciled with the age-old question of solipsism whereby we cannot prove that anything or anyone other than us exists and from our point of view, when we die, we drag the entire universe with us.

    So what do you think consciousness is if, on the one hand, it is nothing on the scale of the cosmos (whether individual or collective), but on the other hand, it is everything?

  • Mike Saelim

    Sweet talk! It reminds me of one of the dark matter lectures we were given at the CERN Summer Student program this year, including its discussion of the Bullet Cluster. In fact, I hear that you lectured for the program a couple years ago – some of my friends went and watched your talk from then, which is also online. I believe it was about neutrinos?

  • Tom Ryan

    Sean, you were blessed with two gifts (and by that I mean fortunate enough): Cosmology and Public Speaking.

    You and the team here are brillant thinkers and I love reading every thought you all have, and LOVE the science you explain to the non math inclinced, but I was enthralled by your speech. I knew most, if not all the data and facts you presented, but you were captivating, funny, and knew how to draw you audience in. Hell, if you can make an average joe laugh a number of times during a science lecture that’s a pretty good barometer of how effective you are at public speaking.

    ~Thomas Francis Ryan III

  • jw

    Nice talk! Just a nit – in the second video you say that we should approach the universe with no preconceptions. All well and good, but that in itself is a preconception 😉 And most scientists do indeed have preconceptions.

  • http://tyrannogenius.blogspot.com Neil B.

    Sean and associates: Great! I wish I had caught you on C to C. How goes the work of getting liberal/progressive politics and the science folk together on mostly the same page? I say mostly since for example I respect but don’t agree with atheism (but for different reasons: it is just as dumb to put all non-atheists together as to have only two political categories.) We philosophical theologians often feel like libertarians at a debate between ordinary Republicans and Democrats, and our mutterings about existence not being a predicate, Goldilocks constants, existential sufficient reason, modal realism etc. are indeed the sort of thing that may appeal only to stoned listeners! (Realizing that there’s no strictly logical way to define non-mathematical, substantive “existence” or flowing “time” either is indeed mind-blowing.) However, I agree that reasoning is the way to find out what to do, especially in policy, not any “revelation” supposedly supplied us from above. I particularly despise anyone who thinks God granted them land, and empowers them to take it from others regardless of worldly claims.

    Dima: Good question, and I have talked about the simulation argument directly or (mostly) indirectly on appropriate threads here and sometimes Backreaction etc. Here’s a quote from “Unusual Features of Our Place …” to get you thinking:

    As I have explained before, existence is not a predicate and cannot even be logically defined, such as could separate described model universes into “the ones that exist” and the ones that don’t. Check “modal realism” on Wikipedia etc. Ironically I don’t actually believe in MR. It’s just that either “everything exists”, or, something outside logical necessity must be responsible for the limited set of existing things being as they are. You can imagine that “something” as you wish.

    One point: the platonic multiverse is really all descriptions, which is a bigger set (and perhaps not even well-defined) than “simulations” run by specific programs. The latter is just one way to get something, interesting because the results are mostly more orderly than the big mess of all configurations.

    To me consciousness is a “realness” maker for which possible universes are real versus not. I experience this, so it’s real in some sense, whereas if no one can or does experience a 23-dimensional space with different laws (or even a cartoon world per modal realism) then it isn’t “real.”

  • Michael T

    I would argue the point that in the “last ten years we know what the universe is made of”. All you can really say is “something” is exerting what appears to be gravitational influence on the small portion of known matter in the universe. I mean really now, dark energy/dark matter is not an explanation of anything.

    In light of todays sad news of the passing of Ralph Alpher it is clear to me that the real pioneering work in cosmology was done decades ago by people little known in the public sphere. I think the best we can say about the current state of cosmology may be along the lines of Chou En-Lia’s famous comment about his thoughts on the French Revolution, “It’s too early to tell”

  • brad

    Given the jazz touch, it might be appropriate to note the sad passing of Max Roach today.

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  • http://orbum.net/mark Mark

    I really appreciated your humanistic interjections in the presentation. I know such things can be unappreciated both within science, and without. But it seems good to remind people of the always larger things, than what we currently find ourselves within. I wanted to thank you for your courage, in that.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Thanks everyone, I’m glad people seem to have liked the talk.

    Dima, I don’t think much of the “Simulation Argument,” if by that we mean the suggestion that we are likely to be a simulation rather than “real.” For one thing, if there is truly no way to tell the difference, then I think the idea is strictly meaningless. (If there is a way to tell the difference, then of course it’s meaningful.) For another, this paper by Hartle and Srednicki convinced me that you can’t make predictions by assuming that we should be a typical intelligence in some large ensemble. I’m not sure what the correct way to make such predictions might be, though.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Mike (#2), sorry for not replying before. Yes, I did give the CERN academic lectures — you can find them here. They weren’t about neutrinos; just an overview of cosmology for particle physicists.

  • http://tyrannogenius.blogspot.com Neil B.

    Sean: I sympathize with lack of appeal for a scientist of a concept (like simulation of reality) that can’t be distinguished experimentally from the “real” thing. Ironically, to the hard-core foundational philosophers, that’s exactly the problem when you start speculating about further implications. If there’s no difference, then other conceptual simulations (of the “all possible chess games” sort) should be equally real as well. Max Tegmark says he believes that they all are, but doesn’t appreciate what a mess that makes.

    I believe the distinction is, I am conscious (say, nauseated, a quale) therefore I am, since cognition, thinking, is a simulable program – a platonic ideal world without “substance” can run a thinker going through the description, “I think therefore I am.” But from the scientific perspective of looking for empirical distinctions (definable consequences of actions) it is reasonable to put such thoughts aside as playthings for philosophers as such, and the stoned.

  • Dima

    Max Tegmark believes a lot of things, that’s for sure 😀
    Anyway, I have never experienced any worlds of the “modal realism” (augmented with various multiuniverse theories) category, other than video games, movies, etc and I assume they don’t count 😉

  • Praedor Atrebates

    I personally consider the simulation argument interesting and fun to play with but beyond that…crap. It is the latest fad or fashion, if you will. Before computers (and quantum physics) the universe was considered something of a mechanical device. In much earlier times, it was literally considered a mechanical device with gears, pinions, etc. The reason was rather simple and twofold: limited human intelligence (in general, and as true today as yesteryear…we ARE slaves to our limited, evolved brains afterall) and the tendency to try to organize things in mode with the ‘latest’ thing. Back yonder, the top of technical sophistication was precision mechanical devices, driven by steam, springs, water, etc. Naturally, that being the peak symbol of technical sophistication, it was the prism through which the nature of the universe was viewed. NOW we have digital computers. Fantastic and useful devices…seen as a pinnacle of technical sophistication and, once again, the prism through which many view the world around them. BETWEEN the mechanistic and the digital, we had the drug-induced psychedelic-based idea that the universe was a creation of our own minds…you know, how do YOU know that what you see around you, and everyone and everything in it, is not simply a creation of your own mind and that none of it exists outside your imagination? Of course, this applied to everyone across the board leaving open the question of which one of us was the supergenius actually individually responsible for, well, EVERYTHING.

    Basically, the “crude” mechanisms of yesteryear are now superceded by the the “technically advanced” computers of today. Just as we create gods in our own image, we also (often) create models of the universe in our own image. The universe itself is either seen as a computing device itself (go figure) or what we call the universe is merely a simulation run on some pimply-faced teen’s dual-core computer somewhere elsewhere.

  • Praedor Atrebates

    Here’s MY question (involving a bit of mental masturbation). Dark matter…is it thought that there is only one type of dark matter, a dark matter particle, or could there be a family of related dark matter particles similar to the Standard Model for normal matter? From there I wonder if dark matter could interact with other dark matter in a manner akin to how regular matter interacts (closely)? From THERE I wonder if there could be dark matter stars, planets, and even dark matter life that would essentially be, for all practical purposes, forever separate and virtually invisible to us (and vis versa)?

  • Praedor Atrebates

    Thank you Sean for the link to the article on “typicality”. It was useful, in particular (for me) when considering the Doomsday Hypothesis. This is itself an interesting and “fun” mental/imaginative exercise that comes to mind now and again…

  • Levi_the_Oracle

    I am not a professional astronomer, but I have some basic science education and have been wrestling with the questions of the big bang and the expanding universe as a personal hobby. My question is, if the universe is expanding at an expanding rate, is matter also expanding and if so at an expanding rate?
    The observational data certainly shows that the universe is expanding and that that expansion is accelerating. What I want to know is if that expansion is occurring at the molecular level or even at the atomic level. I realize this goes from the macro level of science to the micro level, and this may not be your particular discipline, but I believe that the answer to this question is very important to the understanding of the nature of the expansion of the universe.
    If the space within molecules is not expanding, but space is, then the relationship between matter and space is very confusing. I expect that, if it is possible to even measure something like molecular expansion, we will find that matter at the molecular, atomic and even subatomic levels will be expanding at the same rate as the rest of the universe. Unfortunately, I am not privy to the people and the equipment necessary to validate, or invalidate my theory.

  • Jason Dick

    Praedor Atrebates,

    As for the possibility of multiple species of dark matter this is definitely possible. In fact we’re certain there are multiple species of dark matter: there are, after all, neutrinos, though they make up only a small fraction of the dark matter.

    However, just from looking at the numbers, it is difficult to construct theories where it is natural for more than one species of dark matter to be dominant (by dominant, let’s say greater than 90% of the dark matter or so). This doesn’t mean there isn’t more than one species, naturally, it just means that the numbers seem to indicate it would be unlikely. I’m not sure that we’ll be able to say anything definitive one way or the other, though, until we know what particle or particles make up the dark matter. But I do suppose that structure formation observations have a chance of finding evidence for more than one species of dark matter too.

  • Jason Dick


    No. The expansion is driven by gravity. Once you start getting bound gravitational systems (galaxy clusters, galaxies, globular clusters, solar systems, etc.), the local gravity no longer drives expansion. Thus it only makes sense to speak of the expansion of the universe on large scales. How large of scales depends upon how dense the local area is.

    Consider, for a moment, that the average expansion of the universe is in the range of 70 km/s/Mpc. If we are in or near a galaxy cluster with peculiar velocities on the order of 1000km/s, then clearly the expansion starts to dominate once you reach distances of about 14Mpc, or about 47 million light years. The further away you observe, the more dominant the expansion of the universe becomes over local effects.

  • Praedor Atrebates

    Levi_the_Oracle…that expansion idea you asked about sounded so familiar to me. It took me a while to hit where I’ve heard it before. Are you referring to a particular “theory” of gravity, by chance? Or is this truly an independent question you have come up with.

    There was some guy a couple years ago who claimed to have “solved gravity”. Basically, he said there was not “gravity” per se, but that what we perceive as gravity is actually akin to (well, it wouldn’t be akin to, it would BE) inertia. This guys claim was that the universe is expanding, but so are all particles, and thus, everything made of said particles. Because of the expansion of space AND MATTER (including the earth, for instance) we felt “gravity” when, he says, what we are actually feeling is inertia on the surface of the expanding earth (etc).

    I assume you are asking an independent idea/question you had rather than getting around to asking in some way about this guy’s “theory” of gravity…

  • Levi_the_Oracle

    Since I am not well read in the various theories out there regarding the expansion of the universe, I came up with my concept independently. I am loathe to call it a theory yet because I have not resolved many of the issues, and I need some evidence to either support it, or shoot it down.

    I find it interesting that “some guy” claimed to have solved gravity through the concept of inertia. As Jason Dick mentioned, the expansion of the universe is not constant, but relative to the distance involved. I am willing to accept this based on observational evidence. The converse, however, then must also be true. The closer the relative distance between the observer and the observed, the smaller the relative expansion. At the molecular level, distances are MUCH smaller so the relative expansion is incredibly tiny; Perhaps beyond our current observational threshold.

    If we assume for a moment that the space matter occupies is expanding, and the matter within that space is also expanding, then molecules would “push” against each other. This might explain molecular cohesion in a manner other than the traditional. It might also explain gravity as a matter of perspective. That being, stuff sticks to the planet because the planet it pushing against the stuff, and the stuff is pushing back. I will have to think about that for a while and see if it explains how stellar bodies exert gravitation force against one another.

    I have always been perplexed by gravity. We know it exists, and we can measure it, but I still have not seen once decent theory as to why matter exerts a force upon other matter. I believe current theory just explains gravity away as “a property of matter” but does not explain why matter has this property. Please correct me if I am wrong. I would love to hear the bleeding edge explanation of why matter has the property of gravity. In my opinion, humanity will make a huge leap forward if we can understand why the apple falls from the tree.

    I wanted to babble a little about my thoughts on dark energy. Dark matter doesn’t surprise me much. We have known about the Oort cloud for a long time. I believe that there is a vast amount of matter that simply does not radiate light or any other detectable radiation. I find dark matter do be a very good name for matter that does not radiate anything we can observe (except for its gravitational effects). Dark energy, on the other hand is a horrible name.

    If I understood it correctly, we have now been able to measure how much force, per cubic centimeter of space, exists and we call it dark energy. We know there is a force there, but we do not know why it exists or where it is coming from. It is just a mystery background force. I would hypothesize that the dark energy we are observing is just another manifestation of gravity. Lets assume for a moment, that all the matter, both light and dark matter, came from a central location at the point of the big bang, and began expanding outward. I refer to the outside edge of the expanding universe of the event horizon of the universe. I have a strong suspicion that there is a lot more dark matter beyond the edge of the event horizon of the universe than there is matter inside the event horizon of the universe.

    I propose that the universe is not expanding from the energy of the big bang, but is actually being torn apart by the gravitational attraction of an infinitely large field of dark matter. In a normal explosion, the rate of expansion is fastest immediately following the explosion, and begins to decrease after that. Unfortunately, the universe is not following the rules of physics regarding how explosions work at the human scale. If the universe is being torn apart by “dark energy”, I suspect it is only “dark” because the matter causing it cannot be observed. We have measured how much force per cubic centimeter this outer universe of dark matter exerts upon the inner universe so we should be able to map the dark matter outside of our universe in much the same way we have mapped the dark matter inside our universe.

    I realize this quasi theory of mine is probably just so much amateur nonsense, but I am searching for answers to a universe that modern theories simply do not describe very well. I am not willing to accept that empty space has a background energy that is causing the universe to expand. We have not observed any background energy other than gravity, therefore, I am inclined to believe that dark energy is just gravitational in nature, but our perspective makes it appear to come from nowhere.

  • http://blogs.discovermagazine.com/cosmicvariance/mark/ Mark

    #16 – dark matter doesn’t cluster the same way that regular matter does and so one doesn’t expect the same kinds of structures. this is because it needs to be so weakly interacting to work in the correct way for structure formation to match observations.


    I have always been perplexed by gravity. We know it exists, and we can measure it, but I still have not seen once decent theory as to why matter exerts a force upon other matter. I believe current theory just explains gravity away as “a property of matter” but does not explain why matter has this property. Please correct me if I am wrong. I would love to hear the bleeding edge explanation of why matter has the property of gravity. In my opinion, humanity will make a huge leap forward if we can understand why the apple falls from the tree.

    We have such a theory – General Relativity – and it is one of the best tested theories we’ve ever had; far better than decent. While the concept of matter exerting forces on other matter can help in certain circumstances, in GR gravity is very well understood (including explaining the scales on which expansion makes sense and those on which it doesn’t) by mass and energy warping the geometry of spacetime. The motion of other matter or energy on that background i what we mean by gravity.

  • Jason Dick


    Sorry, perhaps I didn’t explain properly. The expansion rate itself is constant, independent of distance. The relevant point is rather that it’s an average. That is to say, on average, the universe as a whole is expanding everywhere at the same rate. But when you start looking closer, you find that local structure mucks things up. Since the expansion is driven by gravity, and since local structure generates gravitational fields, once you get to small enough scales, dependent upon the mass of the local structure, the local structure dominates over the average expansion of the universe.

    On small scales, you’re not averaging over much area, so the local structure is more important. On large scales you’re averaging over much more area, so it isn’t so much, and we see the expansion. Thus, no matter how detailed your experiment, you simply cannot measure the expansion of the universe, say, in the vicinity of our solar system.

    The comparison of velocities I gave earlier was an attempt to show how much area you have to average over before the average expansion of the universe becomes the dominant gravitational factor.

  • Martin

    Though of course you’re correct to say that Brooklyn is not expanding, it’s thoroughly misleading to say that the expansion is ‘driven by gravity’, IMO. The large-scale dynamics of the universe at the present day are determined by gravity — mostly, with a significant and increasing role for dark energy — but gravity alone doesn’t cause expansion: in fact gravity acts against expansion. Einstein’s equations give you a set of possible solutions for the evolution of the scale factor that include an expanding universe, a contracting universe, or even a static (but unstable) one. The fact that we live in an expanding universe, while observationally true, can’t be deduced from a consderation of gravity alone.

  • http://www.mikeschuler.com Mike Schuler

    Levi_the_Oracle on Aug 17th, 2007 at 9:51 am
    I am not a professional astronomer, but I have some basic science education and have been wrestling with the questions of the big bang and the expanding universe as a personal hobby. My question is, if the universe is expanding at an expanding rate, is matter also expanding and if so at an expanding rate?

    This has been my question for several years. If space is expanding as evidenced by Hubble’s consistent red shift in every direction, space is expanding from every point in the universe. Let’s build a model that assumes that matter is also expanding from the center of each individual particle in the universe. The expansion of space and matter is perpetual. As each object expands, the space between each object also expands, and everything stays relative. The only thing though is, you’ll get this strange illusion that material objects are being attracted to each other by some invisible force, or it will seem like the presence of matter is causing a curve in space-time that causes things that think they are moving in straight lines to move in curved lines.

    Inertia is the tendency of mass to resist acceleration. If each atom or sub-atomic or primordial particle of matter is expanding in volume, that means the entire Earth is expanding. No matter what the rate of expansion is, the surface of any object would be accelerating away from the center of the object. That means that the surface of the Earth is accelerating upwards at a constant rate. That’s what we perceive as gravity.

    Levi, all I know is, I pay a shit load of taxes so the NSF can dish out grants, and while they will seriously debate simulation theories and string theories, they constantly miss the point about perpetually expanding matter. No, you can’t measure the expansion of matter because your ruler is made of matter. That doesn’t mean that matter is not expanding. If you build your model based simply on matter that expands at the same constant rate everywhere, you will find that you don’t need dark energy anymore.

    The idea that now is the time in history that will be looked back upon as the time when we figured out what the universe is made of, is just like the time they thought the patent office should be closed because everything had already been invented.

  • aatish

    wow. great talk. you’re awesome. You’ve blown me away with science, yet again. Also, I esp. like the little bit near the end about science and honesty. what the bleep is hilarious (that was my reaction when i first saw it), until you see that it has continually been an annual top seller at amazon.com. Then things start to get depressing. Oh well, as you say, there’s still hope for us all. Cheers!

  • Jason Dick


    Well, I suppose to be more precise I should say that gravity is instrumental in changing the expansion, while the initial conditions of our region of the universe are also important. But whichever way you slice it, the expansion goes away once you’re in an orbit around anything. And furthermore, the existence of acceleration in the expansion indicates that gravity is decidedly not working against the expansion, except on small scales.

  • Martin


    I would say that dark energy is not gravity: wouldn’t you? Take the cosmological constant out of Einstein’s equations and you will see that gravity certainly is working against (acting to decelerate) the expansion.


  • http://tyrannogenius.blogspot.com Neil B.

    Here’s an interesting link about dark matter surprises. I think it’s recent but don’t see a release date:
    Analyst Magazine

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  • http://3quarksdaily.com Abbas Raza

    Sean, brilliant talk!!! Thanks for posting the video.

    By the way, I prefer T.S. Eliot over Portishead to the trumpet over you: http://www.hyperlexic.com/ts_eliot_portishead.php

    Check it out. It’s pretty cool. And greetings to JO…


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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .


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