Morgan, Jon, and the Mystifying Balloons

Morgan Freeman appears on the Daily Show to chat up his new movie, but Jon Stewart just wants to ask questions about physics and physicists. They are both fans! (Hat tip Megan Parlen.)

Freeman doesn’t get all the details right, but his enthusiasm is genuine and infectious, and it’s clear that he’s picked some stuff up from hanging around with scientists (and making Through the Wormhole, of course). The poor man has clearly fallen prey to the dreaded balloon analogy for the expansion of the universe. More harm than good, that little bit of metaphorical imagery has done. It makes you think the universe is expanding into something, which it’s not (as far as we know). Much better to think about the real universe, with galaxies all around you and moving away.

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24 Responses to Morgan, Jon, and the Mystifying Balloons

  1. John Wilkins says:

    Tonight I heard Lawrence Krauss use the balloon analogy. Want to take him to task? 😉

  2. Enry says:

    the balloon analogy truly is horrible. But it’s the only way to really describe it to those without any understanding of the subject. If I say that an expanding and contracting Hoberman sphere ball is better, nobody knows what I’m talking about. A drop of water boiling into steam would also be better, with molecules representing galaxies.

  3. Thomas Stone says:

    I tell people that a one dimensional analogy of the universe is an infinitely long rubber band. If, at a given time, there are tick marks every inch, and then the rubber band is stretched so that the tick marks become two inches apart, during that stretching, marks that are further apart recede from each other faster than marks that are closer together. The key is that the rubber band is still the same length, infinite.

    If people are still confused by infinity, I tell them that if I have a bucket with an infinite number of balls in it and I throw two more balls into it, there are still an infinite number of balls in the bucket. Similarly, infinity times 2 is still infinity.

    So now I have painted a picture of an infinite universe that is expanding but stays the same size.

  4. Alex Songe says:

    As I understand it, the balloon analogy works fine as long as you accept that the entire universe is the balloon’s membrane. Then again, asking people to pretend that 3 dimensions can be hand-waved to 2 dimensions takes some convincing.

  5. Gerald says:

    John: “Tonight I heard Lawrence Krauss use the balloon analogy.”

    To be fair, and assuming it’s the same program I listened to*, Krauss did mention that people would usually think of the balloon in the context of a room, and that instead the surface of the balloon should be imagined to be all there is, without anything around it (paraphrasing).

    Another analogy he talked about was an infinitely-sized stretchable bed sheet that gets pulled from all directions, so everything on it gets further apart from the rest, but the bed sheet doesn’t change in size.


  6. Wayne says:

    To balloon, or not to balloon. That is the question. But seriously, just the fact that he’s engaging Idiot America about cosmology in an enthusiastic manner is priceless.

  7. C.F.T. says:

    Good Grief, what a bunch of hooey.
    @Wayne, just the fact that you called the people of my country “Idiot America” in your very own ‘enthusiastic manner’ does not put you in any enlightened position whatsoever. Please stop channeling Sheldon Cooper’s ego and reel in your contempt a wee bit.
    @Thomas Stone, please stop making very bad analogies with rubber bands of any length in relation to the structure of the universe. The universe is hardly one or two dimensional in nature, and no actual evidence exists of it ever having been so. It took thousands of years for humanity to figure out the planet wasn’t two dimensional, now you want to screw around one dimensional analogies of the universe?? Also, your ‘bucket of golf balls’ analogy to infinity is ridiculous and wrong. You apparently don’t know what infinity is yourself if you think you can add or subtract, multiply or divide it like a finite sum or real number. Do you think you can divide by zero as well? If you do, don’t despair, You will fit right in with the rest of the black hole true believers in ric=0 la la land.

    @Everyone else,
    the public is confused about what to think about the structure of the universe (expanding balloons? boltzmann brains? stretchable bed sheets?? rubber bands and silly string analogies??) because the people teaching the ‘science’ and ‘physics’ are confused as well, and quite frankly, have no real consensus amongst themselves. It is not hard to see why the layman has so little interest in ‘science’ when the people who are supposed to be experts do such a piss poor job of explaining what they actually do know, and have serious problems admitting when they don’t know. Making crap up with overly complex mathematical methods or stupid analogies that play sophomoric logic games with the data and then smugly looking down your nose at those who look perplexed is not helping anyone understand anything except what human hubris looks like.

  8. FrankL says:

    Not being a cosmologist, I’m interested in what is wrong with the balloon analogy. Or the infinite string (=1-d version of infinite sheet) analogy. It seems to me the string and sheet apply to a universe of infinite volume, the balloon to a universe of finite volume. Do we know whether the universe has finite or infinite volume? (Well, “know” is a strong word – is there a favored model?). Where do these analogies break down, as all analogies do?

  9. Doug says:

    The problem with the balloon analogy is that after telling them “the balloon is all there is, don’t think about the center of the balloon or the room it’s expanding into,” people do anyway. It’s like telling juries to disregard evidence that’s been stricken. So it makes it a bad tool for explaining things not because you wind up saying wrong things, but because the people listening will walk away thinking wrong things.

  10. C.F.T. says:

    “The Problem” as you call it with the balloon analogy is that it is meaningless, it doesn’t work even as an analogy. A balloon is a three dimensional object with a finite mass existing in a three dimensional space or volume. The balloon may or may not be elastic in its composition, but regardless, its mass is fixed. When a balloon is inflated it is acting much as a container being filled with some actual substance. The inflation of the balloon puts tension on the substance of the balloon which may to a greater or lesser degree increase the apparent surface area of the balloon. The elasticity of the balloon will determine if the surface area of the balloon changes very much at all, compared to the volume of the balloon which will definitely be changing as the balloon is inflated. All these physical manipulations of the balloon take place in three dimensional space in the presence of entities other than ‘just the balloon’ (which is as meaningless as ‘just a black hole’ math without an actual object to act upon). None of these manipulations is possible with less than three spatial dimensions in which to occur. Even the observation of the surface area of the balloon is only meaningful in three dimensional space, since objects don’t actually exist in less than three dimensions (if you can name a truly two dimensional physical object that exists outside of abstraction, please let me know.) After using the physical properties of a three dimensional object as the basis of your ‘Balloon Analogy’, you can’t then turn the balloon into a two dimensional construct sans three dimensional properties and physics and complain about how ‘people listening will walk away thinking wrong things’, the ‘wrong things’ is your bad analogy, not their thinking. If you want a good analogy to teach people about the structure of the universe we actually live in, start with models that can actually contain physical objects (like you) within a volume, because without them, you literally have nothing to talk about.

  11. Doug says:

    You sound hostile. Why? This is precisely what I am saying!

    The problem with the balloon is that you want something to think of a 2d model of a thing which expands, but because of their familiarity with the physical properties of a balloon, most audiences do not imagine the balloon in the limited role in which you are trying to talk about it. So it is a bad analogy. You try to introduce caveats, “I’m not really talking about a 3d balloon, I just mean the surface, blah,” and they don’t register. Bad analogy.

    But you also seem to have a bug up your butt about black holes so who knows.

  12. FrankL says:

    I thought the balloon was expanding in the time direction. So it’s sort of like a spatial dimension is suppressed. Supressing it IS the analogy, it doesn’t destroy it. The analogy does break down because the whole thing takes place in a four dimensional spacetime, not a four dimensional Euclidean space, so the idea of what constitutes the surface of the balloon (i.e., the spatial universe now) depends on the inertial frame of the observer, etc. Every analogy breaks down somewhere, otherwise it wouldn’t be an analogy. Every analogy is in that sense misleading. My question is, does the balloon analogy simply break down eventually, as all analogies do, or is it wrong from the get go?

  13. Neil says:

    I do not share your distaste for the balloon (or any stretching surface) analogy. When I learned it in school, it helped me understand why the fact that all galaxies are receding does not mean we are at the center of the universe. Later, when my dimensional understandings were better developed, I figured out why the universe did not have to be expanding into anything.

  14. C.F.T. says:

    I’m thrilled you have no problem with bogus balloons or rubber sheet analogies that cant hold water, but tell me,
    if all galaxies are receding or moving apart, then Andromeda must not be a galaxy…maybe it’s just a smudge on a telescopic lens… that mysteriously grows larger? Sheesh. Ok, we know Andromeda is approaching the Milky Way Galaxy, so what gives? Oh yeah, all galaxies are moving apart…except when they aren’t due to….(fill in the B.S. blank). Real predictive theory that, you’ve covered all the bases without even trying to avoid the obvious glaring logical contradiction…and apparently galaxies do collide and merge as well all over the place…all while ‘receding’ from each other…err…after they have collided and merged or passed through each other.

    Is contradiction the new logic or some such new math? As for your ‘dimensional understanding’ becoming better developed… what pray tell is that? Can you explain what you are referring to as a dimension because it is hard to understand the meaning when people use three dimensional spatial parameters interchangeably with theTwilight zone or the Inseam of one’s pants.

    (First, Google Stephen Crothers, follow his math and arguments before you sneer)
    My hostility towards imaginary ‘black holes’ (in relation to this 2D ballon universe hooey) stems from the recognition of the nonsense that originated ‘the black hole’ within a purely mathematical space defined by ric=0, and only by allowing a purely flat Euclidian space containing no matter to contain an infinite gravitational mass with zero extension (Even Wikipedia admits this, which is unusual), made possible within the flawed math only by allowing division by zero, which is still the basis of all black hole theory from back then to this day.
    This same nonsense latter encouraged mathematicians and physicists to engage in extra-dimensional loopiness which pretends objects can materially exist (and interact with actual matter, energy, and gravity) with a zero cross section, like a point, a line, or a plane. Modern Physics and mathematics seems to have completely lost track of the difference between what a surface and a plane are. Surfaces can exist in reality, they are the exterior of an actual object which has more than zero extension in height, length, and width. Planes (such as a two dimensional plane) do not exist in actual reality, they are merely a geometric abstraction with a zero ‘z’ extension or cross section and can not physically interact with anything in the known universe, except as an abstract (or imaginary) cross section or point of reference. The fact that physicists today seriously think a physical length (like an inch, a meter, a light-year) can actually have a tensile strength in any way shape or form whatsoever (Superstring Theory) or that dimensional hand-waving the universe into a two dimensional plane (Brane anything theory) can prove anything exists (much less other actual universes), or pop this universe out of a zero point (singularity) without even a moment of time (Big Bang) shows what happens when smart people A.)lose their grip on reality, B.) what happens when you do multiplication by zero, and C.) Forget basic arithmetic and try to divide by zero… and then brag about how ‘accurate’ and ‘beautiful’ the answers are, and D.) Pile complex math on top of flimsy explanations to make any theoretical challenge nearly impossible, even by other experts in most cases. Some folks have been on to this fraud for some time and made light of it, check out or ‘Google’ The Space Child’s Mother Goose “This is the theory that Jack Built”. Check out the copyright date of the book. This trend has been in motion since before the beginning of the twentieth century.

    I’m a tad hostile because the ‘experts’ and ‘elites’, the ones we should trust to guide and educate us, have betrayed their very vocation to an unquestioning belief in incorrect arithmetic, bad logic, and dogmatic nonsense. Wish I could tell you why, because I sure don’t know why anyone would want to try adding even one more line to this little “Theory that Jack Built” for fear of it crashing down before they retire and are long buried.

  15. Brett says:


    I don’t think you are willing to give the leading ideas a chance. I think that’s why you are so angry; because you don’t understand how physics is explained by math and you don’t seem to know anything about information theory or Boolean Algebra; you’re understanding is restricted to geometry but you seem to know nothing about advanced algebra. Your complaints are very typical of someone who is cognitively lazy and expects everyone to ‘make’ them understand while they don’t want to put in the actual effort to understand. For this reason, I don’t believe there is an explanation out there that you will accept. There is a big difference between Popular Science and Science. Just as there is a big difference between Popular (Pop) Music and Music. The popular form of somethng tends to be extremely dumbed down so that someone who hasn’t studied it for 15 years+ can understand the fundamental concept. If a person wants to fully understand it, then they need to put in some effort to understand the concepts at a deeper level. Do you know the notes and tetrachords of a Hungarian Minor scale? No? So music is complete bullshit and musicians of all genres are doing a horrible job? If you disagree with the current theories of cosmologly then that’s fine, but I don’t see you doing anything to further your cause/opinion. When you leave out certain details of Inflation theory to try and prove your point, it just makes you seem less trustworthy. People tend to ignore those who attempt to deceive.

  16. Brett says:

    I checked out Stephen Crothers and stopped reading after I read the following and realized he was so insane that it made the Sheldon Cooper character look tame,

    “Anyone who was rude or otherwise behaved as a smart-arse I responded to bluntly. And I still do, since I refuse to turn cheeks, having discovered that the majority of people understand only the power of money and the persuasiveness of force. So if it’s a fight they want then it’s a fight they’ll get. Pasty-faced softies however, cloistered away in universities are not much of a challenge; but there are so many of them, like cane toads in the breeding season. And so I now make no bones about how I view blokes who, like K. Thorne and Ned Wright, prance about with long pony tails and matching sandals, or wear earings and otherwise dress and behave like girls (most “male” physicsts nowadays). “

  17. max says:

    Brett, the great thing is that there are plenty of smart physicists out there. If we ignore all of the assholes, we’re still left with plenty of smart physicists. Good job on giving up on this Crothers fellow and saving me a round trip to google.

  18. Brett says:


    yeah, the guy is completely insane. He thinks there are 2 shadow governments in Australia working to inhibit scientific progress. He is an amazing freak show to watch because he was in contact with some of THE biggest names in physics and cosmology today, and absolutely imploded and destroyed any possibility of a career other than appealing to other conspiracy cranks. Referring someone to his ideas is like defending your views on modern western civilization by referring someone to Osama Bin Laden or the Westboro Baptist Church.

  19. Mark P says:

    It seems to me that the balloon analogy can do a reasonable job of explaining how stars can get so far apart that they are more light years distant from one another than can be explained by the age of the universe. That is, they are not speeding away from each other at the necessary speed relative to some fixed point in the universe; instead, the universe itself is expanding. But it doesn’t do a very good job of explaining how the universe can expand without expanding into something.

  20. Brody Facoum says:

    “But it doesn’t do a very good job of explaining how the universe can expand without expanding into something.”

    Well, we can lift coordinate choice and equivalencies from classical GR…

    Stretching the (transparent!) latex medium of the balloon so that “pinchy” or “bunching” opaque defects embedded in that medium observe the other defects’ recession velocities to be proportional to their distance when looking through the (clear!) latex medium is roughly equivalent to adding in more clear latex uniformly everywhere at some reasonable distance from each defect.

    Now consider the views of observers embedded (which get called “we” below, sorry) in the medium seeing only along the medium and using a system of polar coordinates (azimuth, radius, time) and calculating intervals as (ds)^2 = (dr)^2 + (r da)^2 – (dt)^2. For convenience the conversion factor between radius and time has been set to unity, so we can measure both radius and time in seconds. For objects with a constant azimuth [(r da)^2 = 0] we can interpret a measured recession (ds -> -0) as strictly an increase in dr, or equivalently strictly a decrease in dt, or equivalently a combination of the two. Moreover, since the medium is transparent, the principal observable of the medium is simply that measurements of ds approach 0 from below more strongly with visible defects that we “know” are further away (for example, because they are a common size and so subtend smaller azimuthal angles at larger radiuses) than those which are close, but not in our “pinching-together bunch”. So we can say that the medium is growing spatially, increasing the amount of space uniformly everywhere outside of the pinchy bunches, or the medium is contracting temporally, slowing down clocks uniformly everywhere outside of the pinchy bunches, or some mix of the two. Because the (ds)^2 = … equation is a metric equation, we call the observation a metric expansion; if we interpret it as an increase in the amount of space everywhere with time behaving normally, it gets called the usual metric expansion of space.

    The “real” expansion of the model balloon produces the same observable: intervals at greater distances from observers embedded in the balloon and constrained to particular views along the thin medium of the balloon really do become more lightlike as the balloon inflates.

    The analogy is not *complete* for a variety of reasons, but it is also not a bad one.

    You are right that it does not explain “expan[sion] without expanding into something”. It simply offers up a reason for the lack of explanation: the views of the particular observers are too constrained, in this case mostly by the exigencies of the analogy.

    That in turn suggests that our ability to explain the mechanism of our real universe’s metric expansion of space is also hobbled by observational constraints, although those are probably more driven by issues of technology than anything else.

    Apologies in advance for any sign errors or other picayune mistakes. 🙂

  21. Thomas Stone says:

    Sean’s point of people visualizing the balloon as expanding into something is valid. The average person has a great deal of difficulty comprehending the concept of infinity. Don’t even start to explain countable versus uncountable infinities or how a countable infinity times 2 is still a countable infinity. It takes a bit of training to accept these ideas.

    I had a guy get extremely angry at me when I showed a proof for why 0.9999 (ad infinitum) is precisely equal to 1. It is not just arbitrarily close to 1, it is 1. He accused me of attempting to trick him and he “knew” there was something wrong with the proof. He was physically trembling from his anger. He was also an engineer.

    So if C.F.T. brushes aside the notion that anything can be added to infinity, how do you expect him to believe that an infinity large universe can expand?

    People keep sticking to the idea that the big bang started as a point (in something!) that expanded and grew (like a balloon). When I correct them by saying that the universe was infinitely large and the big bang happened everywhere, they are disbelieving.

  22. Charon says:

    Sean, do you have any evidence about your distaste of the balloon analogy? Like, actual physics education research? Because my anecdotal experience is that astro 101 students presented simply with the idea that the Universe expands will then immediately ask what it’s expanding into. And told the Universe was once arbitrarily small, and then expanded, they’ll ask where the Big Bang (the “center”) was. The balloon analogy doesn’t create these misconceptions. But again, it appears that’s my anecdotes v. yours.

    I just find your claim of simply not using any analogies to be… dubious. I was in a differential topology class as an undergrad with a number of very able math majors, and they had noticeably more difficulty understanding differential manifolds defined intrinsically compared to defined embedded in a higher-dimensional space. It is actually a more mathematically complex thing to do. I don’t believe the general public at one of your talks will grasp this. Heck, in grad school I TA’d astro 101 for a smart, capable PhD astronomer who didn’t grasp this.

  23. Charon says:

    I just wanted to add that I know you’re a good teacher, Sean. I was in an undergrad GR class you taught at the U of C back in the day, and you were one of the best teachers I’ve ever had. But I’m curious if you’ve ever taught astro 101, and if so, if you’ve done it since grad school. Public lectures are entirely different beasts, and you get no real feedback about how well your audience really understood what you were saying.

    In fact physics/astro education (PER/AER) research shows that often even professors teaching a class wildly mistake how much their students are learning. So I’d caution you to stop knocking the balloon analogy (used in AER) until you have any evidence of a more effective strategy.

  24. Latverian Diplomat says:

    How do people feel about the raisin bread analogy?

    The galaxies are the raisins they don’t expand, the dough is space, as the dough rises the galaxies get farther apart.

    It’s three dimensional which is nice, and the raisins don’t expand, unlike ink dots on a balloon. It still has the “expanding into” and center problems, and arguably introduces a boundary issue? the surface of the bread as the “edge” of the universe?