Why are atoms mostly empty space?

By Phil Plait | December 28, 2011 7:00 am

Professor Brian Cox is a physicist in England, very well-known there as a popularizer of science. The reasons for this are many-fold, including his ubiquity across media (including podcasts, Twitter, and of course TV)… but also because he has an infectious enthusiasm for science coupled with a boyish charm.

This was all on display recently when he hosted a great segment on the BBC’s show A Night With The Stars, where he simply and effectively demonstrates why atoms are mostly empty space:

http://www.youtube.com/watch?v=Akc7ENCrXHU

Pretty cool, isn’t it? It helps if you can enlist Simon Pegg to help, too!

I like this demo a lot. On a very tiny scale, objects act like both particles and waves. On a big scale, like our solar system, we can think of planets as discrete particles, interacting through gravity only, and it works pretty well. Our semi-evolved brains want to think of electrons that way as well: little spheres whizzing around atomic nuclei. But that’s not the way the Universe works on the quantum scale; electrons act like waves, and that means they can interfere with each other. When a crest meets a trough they cancel, when a crest meets a crest they add together. If you have a wave bouncing around inside a box the result can be chaos.

I like to use the example of sitting in a tub, and rhythmically pushing your body along its length with your toes. It’s hard to do unless the rhythm is just right; otherwise the waves smack into each other chaotically and it’s a mess. But get the pattern timed just right and you’re in sync. That timing is just a simple multiple (like 1 or 1/2) of the time it takes a wave to move from one end of the tub to the other. You can actually feel it as you push; the correct timing just feels natural.

Electrons around an atomic nucleus work the same way. It’s more complicated than your bathtub, but the principle is the same. The electrons can only exist where the wave crests and troughs add up correctly. They literally cannot exist anywhere else. They’re like standing waves, as Brian shows.

We teach kids that atoms are like little solar systems, but that model is really bad! In principle, planets can orbit the Sun at any distance — give a planet more orbital energy and it’ll move away from the Sun and continue orbiting, happy as you please. But electrons can’t do that. They can only be at energy levels where they don’t interfere with themselves (and each other). It’s more like a staircase; they can only move up or down by discrete amounts. Once you figure this out, a ton of stuff becomes possible: lasers, semiconductors, fluorescent bulbs, atomic bombs… it’s quantum mechanics, and it’s a huge, huge field of science.

And it’s all because, as Brian demonstrates, a rope held at both ends won’t vibrate at any old frequency. Amazing, isn’t it?

Post script: can you imagine a show like this running on American TV? No, I can’t either, unless they had a toll number you could call to vote for atoms being a hoax perpetrated by Big Little Science.


Related posts:

Cox on TED
Astrologers jump on Cox
Symphony of Science: Onward to the Edge
UK science interest spiking? Blame Cox
TV as a source of science inspiration

CATEGORIZED UNDER: Cool stuff, Science, TV/Movies

Comments (56)

  1. SelfAwarePatterns

    One thing I’ve never grasped with this concept is waves of what?

    It would indeed be awesome to see this on American TV. Instead we get to see stuff about mediums and Bigfoot. Sigh!

  2. DrFlimmer

    Wow. That’s just brilliant! I have to remember it. Whenever I will explain the atomic structure to someone else, I will certainly use that picture!

  3. Steve

    Amazing isn’t it? This is the stuff PBS/NOVA should be doing for kids in the afternoons, along with Sesame.

  4. Mike

    Please, there really is a difference between England and Britain; as far as I know Brian Cox is very popular in Scotland, Wales and Northern Ireland as well as in England.

  5. serenity

    Sounds more like an explanation for the discrete energy levels and different orbitals! Still very interesting to watch, though!

  6. Anthony Cunningham

    Yes, I can imagine a program like that on US TV. It was called ‘Cosmos’.

  7. Timmy

    Why don’t we say “naught” here? It sounds so much more exciting than “zero”.
    Also, what would “A Night With the Stars” look like on US television? It would probably end with a drunken fist fight and there would definitely be no physics lessons.

  8. Alan

    I don’t think atoms really are mostly empty space! As Cox says, an electron is a wave, and the wave fills the atom, so there is virtually nowhere in the atom where the amplitude of the wave is zero.

  9. James

    I didn’t actually think this was Prof Cox’s best stuff – some explanations and necessary details were missing (maybe he was let down by the editing). Some of the stuff on interference was missing, the energy levels diagram was a little obscure and I was far from convinced about some of his claims about the Pauli Exclusion Principle.

    As serenity @4 notes, this is an explanation for why the orbitals are discretised, not why the atom is so empty. The proper answer to that is simply that the electron mass is much smaller than the Lambda_{QCD}, the scale of strong interactions (apologies to those who don’t grok LaTeX). Plus, the fact that the fine structure constant is small. Of course, those answers themselves raise further questions, but such is life, I’m afraid.

  10. Chris P

    Shout out to Jim Al-Khalili too (the guy on the other end of the spring to Simon Pegg).
    He also makes fantastic science documentaries for the BBC, too. A few of films well worth tracking down are ‘Shock and Awe: The Story of Electricity’, ‘Everything and Nothing’ and ‘Chemistry: A Volatile History’… and they’re just from the last year or so.

  11. You should check out Brian Greene’s four part NOVA special from Novenber, “The Fabric of the Cosmos”. Episode 3 “Quantum Leap” covers this topic in a way that I found to be easy to understand (well as easy as any QM explanation I’ve seen).

    The full episodes can be played online at PBS.org

  12. Grizzly

    If you follow the Youtube links afterwards there’s a link to the whole lecture, and it is a real treat. He has a great way of making things excitingly straightforward.

    I was looking for that page 127 moment, you know, the one in A Brief History of Time or similar books where you’re suckered in, nodding comprehension until BAM your brain explodes on something like “non real time”.

    There wasn’t a brain exploding moment in the video, but a few brain expanding ones, and that’s a tribute to Brian’s skill.

  13. Here’s a question for the physicists out there. If we have a thing in the universe that can act both as a wave and a particle, why haven’t we created some new nomenclature for it? Photons behave as both (as, apparently, do electrons and perhaps others), but we seem to be stuck in describing them as having properties of both waves and particles. Why not create some new term for these things (and socialize it) so we can start discussing this new thing (warticles or partives or whatnot) rather than confusing laypeople with saying something’s both “animal” and “mineral”.
    Perhaps this kind of thing already exists and just isn’t well known to the uninitiated. Can anyone chime in on this?

  14. Joe6pack

    The entire one hour lecture is available as well. It’s exceptionally well done (well, with the possible exception of the double slit experiment which I think is not made very clear) and very enlightening.

    I would love to see Mr Cox do something like this for American TV. The guy is so engaging and personable I couldn’t imagine it not being a huge hit here.

  15. Yacko

    Why is the universe mostly empty space? Take a large tree. Shred it. A much smaller pile. Implode it as dense matter and it takes up a fraction of the space. Is the universe merely a shape defined by waves – energy or mass? Perhaps we are entities who are the sum of our combined wave interference pattern. Is this why a holographic universe has been offered as an explanation?

  16. Austen Redman

    I remember Carl Sagan giving a series of Christmas Lectures in the same theatre back in 1977:

    http://www.youtube.com/watch?v=tpIjXuKCQHg

    He included the results of the Viking probes, which was very cutting edge at the time.

  17. Scott P.

    “Why not create some new term for these things (and socialize it) so we can start discussing this new thing (warticles or partives or whatnot) rather than confusing laypeople with saying something’s both “animal” and “mineral”.”

    There is the term “wavicle”, which was coined in 1927, but it’s not used all that much.

  18. Other Paul

    @BilldeVoe:

    I remember encountering the term ‘wavicle’ when I was a teenager, which is certainly last century (and some). The context was a science fiction short story (as it so often is) and I thought- at the time – it was just one of those made-up sciency-wiency sounding words you get in poorly written plots. But it turned out not to be the case, and it really was about the protagonist being schooled in QM. Can’t remember the author. But wavicle is certainly googlable.

  19. Malachi Constant

    @Bill DeVoe

    Speaking as a chemistry/physics undergrad, it’s often useful to think of photons and electrons as particles sometimes and as waves at other times. It’s not useful to keep their dual nature in mind at all times.

    For example, in chemistry we often say “This hydrogen atom donates it’s electron to this carbon atom”, or “The chlorine atom leaves, taking an electron pair with it”. This is a much more useful way to think about it. Trying to think of electrons as energy waves in those cases just obfuscates what’s really happening.

    If you’re studying light, however, it’s often more useful to think of photons as waves. For instance when you’re trying to understand how light gets polarized, and why those neat sunglasses you bought can block out reflected light, but not direct sun light. In that case thinking of photons as particles doesn’t make sense, you need to understand them as electromagnetic waves to figure out why it happens.

    It may just be a limitation imposed by our everyday experience, but we can’t really grok wave/particle duality in an intuitive sense. It’s more useful to think of them one way or the other (generally) to understand whatever phenomena we’re looking at. It’s just a handy model.

  20. If somebody out there wants to fund the making of such content for audiences here is the US, do keep me in mind as a producer. That is just the sort of programming I want to be doing. #ImJustSaying #PissingIntoTheWind #UsingHashtagsOutsideTwitterLikeAWanker

  21. march

    Bill, how about warves or parves?

  22. @Scott P, @Other Paul – thanks for the “wavicle” term. I recall now having heard in the term in college (I hung out with astrophysicists) but it seemed too nestled in my grey matter to be easily recalled. :)
    @Malachi Constant – I agree that there are instances where we need to think of the various independent properties, but I think your statement “we can’t really grok wave/particle duality in an intuitive sense” may be partly because we’re not using a single term. It’s sort of a nature/nurture thing – if the term exists and it’s used, we may be able to more readily grok the context. If it’s not, we’re going to be stuck in the same out-dated paradigms we persist today. People have tried to find new ways of explaining difficult concepts (I do it every day as a program manager with a technical background – interpreting technical and business concepts for the “other side”). I just think that if we used “wavicle” or similar we might begin to see the world in a somewhat new light. That’s how we’ve been doing it – pulsars, quasars, black holes, etc – are just terms we made for new understandings. Since photons are behave as both waves and particles but are neither, why should we continue to use both of those (inadequate) terms for them?
    Just my $0.02.

  23. Chief

    I was going to mention the video stopped too soon and didn’t go into the other orbits and the mechanics of the energy loss and gained with the jumping from level to level but other posters mentioned a longer video, have to pursue this tonight, thanks.

  24. Dragonchild

    @13. Bill DeVoe
    That has less to do with physics and more to do with human nature. It’s harder to undo a status quo than simply explain wave-particle duality.

    Heck, even “wave-particle duality” and “wavilce” are just variations thereof.

    The first epiphany of any student studying atomic physics is that reality itself is “fuzzy”. We’re used to energy levels being analog and one’s physical presence being discrete, but in quantum mechanics it’s the opposite — a particle’s characteristics (such as energy level) are well defined (quantized), but the “particle” itself isn’t much more than a cloud of probabilities, with no surface or location to speak of.

  25. edwardv

    Isn’t the reason for the space in the atom mainly due to the low mass of an electron? If it were heavier wouldn’t it be closer to the nucleus? And what does it mean to say atoms “have” empty space? Is there something else that could occupy the “empty space” between the nucleus and lowest state electrons?

  26. @Dragonchild – What you said that it’s less with physics and more with human nature is exactly the point I raised in 22. It’s the terms that we’re using that are persisting an inaccurate view of the universe. I’m hoping that if a new term would help break that paradigm.

  27. Wayne Robinson

    Well, actually the nucleons (neutrons and protons) are mostly empty space too, consisting of 3 quarks in a sea of virtual particles, which flash into and out of existence, and contribute most of the mass of the nucleon. When two protons are collided in the LHC, it’s only part of each proton that’s impeded, the rest just sailing along on its original course. The collisions scientists are interested in are those between the virtual particles, because they have most of the mass and hence energy to create novel particles.

  28. #6 Anthony:
    “Yes, I can imagine a program like that on US TV. It was called ‘Cosmos’.”
    But that was 30 years ago! Has anything comparable ever been made since?

    Phil:
    “Can you imagine a show like this running on American TV?”
    Sadly, there are far too few programmes like this on British TV! And the BBC could only manage this one, because in common with 95% of the stuff on our TV these days, it involved so-called “celebrities”! It was an excellent lecture by Brian, but why did it have to be given to an audience of so-called “celebrities”, most of whom obviously didn’t have a clue what he was talking about? Presumably, the producers thought more people would watch it if it involved “celebrities” – but those who were actually interested in the content probably didn’t give a monkey’s about the “celebrities”. ( For the record, I didn’t even have a clue who most of them were. )

  29. VinceRN

    I’d have learned a lot more in school with Brian Cox as a teacher, and had a lot more fun with Simon Pegg as the TA.

  30. tacitus

    Post script: can you imagine a show like this running on American TV?

    Well, can you imagine requiring Americans, by force of law, to pay $225 / year for the privilege of watching TV…?

    Nope…?

    Me neither. :(

    Three quarters of the BBC’s funding comes from the mandatory TV license fee, the non-payment of which results in about 100,000 criminal prosecutions each year. More Brits agree with this system of funding than not, but it’s fairly close. However, a large majority of Brits cite one of the BBC’s channels as their favorite.

    I’m an ex-pat, and would be supportive of similar public service broadcasting and funding here in the US, but I know that it is a complete non-starter here, given that anything funded through taxes is immediately condemned as communism and anti-American.

  31. As Alan says, this is bad physics. Atoms are not really are mostly empty space. I am happy if such falsehoods are not broadcast in the USA.

  32. Catalyst23

    Post script: can you imagine a show like this running on American TV? No, I can’t either, unless they had a toll number you could call to vote for atoms being a hoax perpetrated by Big Little Science.

    I’ve always been moderately flabbergasted by Britain – The BBC (And CBC) have excellent science programs. Surrounded by homeopaths and astrologers. Maybe it’s a distorted view of mine, but it seems that the excellence in educational programming in Britain is matched only by the vast amount of ridiculous pseudoscience claims in the country. Maybe they’re linked, maybe I’m totally wrong, I don’t know. What I do know is that I am eagerly waiting for Comcast to pick up BBC America. I am absolutely certain that if you give Americans the opportunity to see this type of program we would love it. I guess we’ll just have to wait until Cosmos: A Space-time Odyssey premiers on Fox in 2013. Can’t wait!

  33. Wayne Robinson

    Roger,

    You’re joking, aren’t you? If you are, then it’s a very funny joke.

  34. Brasidas

    @4 Mike

    We can’t really be too harsh on someone from the US being confused about how our country is named – most UK people don’t know either.

    We have Scotland, Wales, Northern Ireland and England which are the bits that make up our country, the UK. Great Britain is the island that has Scotland, Wales and England on it. The British Isles is the 4 bits of the UK plus Eire and some other islands.

    There is really no such place as “Britain” but people (even the prime minister) use it when they mean the UK. Actually there is a place called Bretagne (literally Britain, but we call it Brittany) but that’s part of Northern France!

    Even our Olympics team is called Team GB, but the team includes Northern Ireland which is not part of Great Britain, so it should be called team UK.

  35. If the electrons are like standing waves, then the atoms are not mostly empty space. The atoms are mostly standing waves. This whole discussion is very misleading.

  36. Messier Tidy Upper

    Post script: can you imagine a show like this running on American TV? No, I can’t either, unless they had a toll number you could call to vote for atoms being a hoax perpetrated by Big Little Science.

    Well, I’m not American but I can’t see why they couldn’t run something like this & have it work very well over in the States.

    Don’t you guys screen Mythbusters and a few other at least semi-sciencey things like … oh .. what was that show, Bad something or other by a certain Dr Phil P-something? ;-)

    Seriously, I think there are occassional good science related shows and references in popular
    culture incl. even talk shows such as Letterman which quite often has the odd astronomical reference mentioned such as the super-earth discovery Kepler 22b and the recent asteroid fly-by and the Space Shuttle missions to name just three I recall from this year.

    I think a good science show done well should be able to do well anywhere – because people are curious and if science is explained well it should get all humans anywhere and everywhere thinking and amused and astounded by it. It is human nature to want to understand and learn things incl. science after all! :-)

    Isn’t it? Shouldn’t it be the case? Or am I just naive or something here?

    Good demo there – Brian Cox is awesome. :-)

  37. This is an absolutely brilliant science TV concept. Think up fun demos and do them with celebrities. Now that I think of it, this is a little bit what TV magicians like Derren Brown or Luc Langevin in Québec do, but to extend the concept to science is just brilliant. If you’re going to be a public persona as a scientists, try to mix with other celebrities.

    This may not look like it, but this could be the start of a revolution in science popularization. The formula here is just perfect.

  38. runawayuniverse

    Before Discovery went full redneck with all their “reality” shows about swamps, loggers, guns etc. etc., I think something like this would have aired on the Discovery channel or at the very least, the Science channel.

    Now? Not a chance.

  39. SOLIDLY ETHEREAL
    — James Ph. Kotsybar

    We’re made of stuff that’s hardly even here
    composed of atoms that are mostly space.
    The solidity with which they appear
    happens because their trapped electrons race
    around the nucleus — near light speed fast –
    and always possess a negative charge
    that wont let other negative charge past.
    They also make the atom appear large.
    Around the nucleus, that is tiny,
    electrons blur to a far distant cloud.
    Were we their size, we wouldn’t even see
    the nucleus we’d remotely enshroud.
    The percent of empty space we define
    is ninety-nine point nine nine nine nine nine.

  40. Inky pinkie

    There is one part in the lecture (link to the full lecture video http://goo.gl/wlwrX ) that was mindblowing:

    «The Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the universe, and that if we does something to change the energy state of one group of electrons (rubbing a diamond to heat it up in his demo) then that must cause other electrons somewhere in the universe to change their energy states as the states of the electrons in the diamond change.»

    In other words it means that if you change the energy state of one electron than all electrons in the universe change slightly their energy states so that there won’t be two electrons with identical energy levels.

    Who wants to fire a match and play the game «I am a God»?

    It seems that a lot of physicists are sceptical about these statement too. On the physicsforums there is a thread discussing it and Brian E. Cox himself answered the critisism. For those who actually know what he is talking about here is a link to that thread http://goo.gl/CZG4m Look for the nickname «becox».

  41. StarGeezer

    There’s nothing like a little poetry to shed some light on the subject! Thanks James P. K!

  42. reidh

    Maybe its dark quanta, like Dark Quarks, Dark energy etc.

  43. Mark

    This is the reason why we Brits need to defend the BBC from funding cuts. Science programmes like this (or better) are aired on the BBC almost every day, but could be the first to go, if the BBC’s funding model changes, as many right-wingers want. The US system of only funding programmes which can attract mega audience numbers should teach us all a lesson – lowest common denominator programming. Hence the preponderance of reality TV, game shows, sitcoms and comedy series (albeit with some very good results). The other great thing about the BBC is that you could have watched the whole 1 hour show in the UK for free, without any interruptions from advertisements or channel placements.

    If US viewers demand such programming from the US networks, it will help to secure future commissioning of science programmes by the BBC.

  44. #34 Brasidas:
    “Even our Olympics team is called Team GB, but the team includes Northern Ireland which is not part of Great Britain, so it should be called team UK.”

    Also, the announcers and TV commentators – even our own – refer to our athletes as representing “Great Britain”, when it should be the UK.
    In fact, the full official name of our nation is “The United Kingdom of Great Britain and Northern Ireland”.

  45. Stathis Dimopoulos

    Someone was kind enough to upload the entire lecture from Prof. Cox on YouTube.

  46. Calum

    What’s more, Prof Cox is surely the only physicist working at CERN to have a UK chart topping single to his name, having been the keyboard player with D:ream.

  47. Tea For Me

    Sadly, there are far too few programmes like this on British TV! And the BBC could only manage this one, because in common with 95% of the stuff on our TV these days, it involved so-called “celebrities”! It was an excellent lecture by Brian, but why did it have to be given to an audience of so-called “celebrities”, most of whom obviously didn’t have a clue what he was talking about? Presumably, the producers thought more people would watch it if it involved “celebrities” – but those who were actually interested in the content probably didn’t give a monkey’s about the “celebrities”. ( For the record, I didn’t even have a clue who most of them were. )

    The reason for the celebrities is pretty simple. It was a fund raising exercise. The celebrities PAID to attend, and the proceedings were then sold to the BBC to raise money for the RI Christmas Lectures.

  48. Nigel Depledge

    Alan (8) said:

    I don’t think atoms really are mostly empty space! As Cox says, an electron is a wave, and the wave fills the atom, so there is virtually nowhere in the atom where the amplitude of the wave is zero.

    This is true only of the lowest-energy, or s-, orbitals.

    As orbitals of progressively higher energy are filled, they adopt specific shapes (the shapes reflecting the regions of space where 99% of the electron density associated with that orbital is located). Electron shells are numbered from the nucleus outwards, and each shell has a limit to the number of electrons it may contain. For example, shell 1 may only contain up to 2 electrons. Shell 2 may contain 8. Shell 3 may contain 18 and shells 4 and 5 may contain more (curses, I cannot remember how many f-orbitals there are). Edit, having looked it up – there are 7 f-orbitals, so the f-orbitals may contain an additional 14 electrons. Thus, shell 4 may contain 32 electrons.

    So, for instance, as we go from Lithium to Neon across the periodic table, the electron configuration goes He + 2s1 (Lithium), He + 2s2 (Beryllium), He + 2s2,2p1 (Boron), He + 2s2, 2p2 (Carbon), He + 2s2, 2p3 (Nitrogen), He + 2s2, 2p4 (Oxygen), He + 2s2, 2p5 (Fluorine) and He + 2s2, 2p6 (Neon). Since each orbital may contain only two electrons (of opposing spin and hence not violating the Exclusion Principle), there are three equivalent p-orbitals. These are roughly dumbell-shaped, with a zero at the nucleus, and are oriented at 90° to one another (and hence are designated px, py and pz).

    Between the p-orbitals the electron density is non-zero, but represents a total of 1% of the electron density for each of the p-electrons. So, from a chemist’s point of view, it is as near to nothing as makes no odds.

    Period 3 of the Periodic Table (from Sodium to Argon) starts with filling the 3s and 3p orbitals, and there are also 3d orbitals. But the 3d orbitals have higher energy than the 4s orbitals, so the 3d orbitals only start filling in Period 4 of the Periodic Table (Potassium to Krypton), after the 4s orbitals are filled. The d-orbitals are responsible for the behaviour of what are known as transition metals (in Period 4, these are Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper and Zinc).

    Three of the d-orbitals are kind-of X-shaped (again with a zero at the nucleus), fitting between the lobes of the p-orbitals (these d-orbitals are dxy, dxz and dyz). The other two are odd: d(x^2-y^2) has four lobes that line up with the px and py p-orbitals, while the dz^2 orbital has two lobes along the z-axis and a torus of electron density in the xy plane.

    In similarly awkward fashion, the f-orbitals are higher energy still, so the 4f orbitals (IIUC) only start to fill once 5s, 5p, 5d and 6s orbitals are filled. The f-orbitals are responsible for the behaviour of the Rare Earth elements, or Lanthanides.

  49. bob

    England was commonly used synonymously with, or indeed instead of, Britain up to the 2nd World War. The point being that we’d beaten all the other buggers…

  50. The problem here is that there is science and then there is explaining that science to, probably a large audience, who don’t know what the science is. Two very different subjects. In the real world of education, in the first instance, teaching or presenting a subject, can be very far removed from what the facts of that subject are, only because teaching is a separate skill. The same applies to presenting that subject on TV. It is only when the two come together that the idea clicks – which unfortunately doesn’t always occur for everybody involved! The mix up in the comments here is about this problem.

  51. Matt B.

    @41. StarGeezer:
    “There’s nothing like a little poetry to shed some light on the subject! Thanks James P. K!”

    Too bad the part about electrons traveling at near light speed is wrong. An electron in the 1st shell of a hydrogen atom goes about 1/137 c.

    @49. Nigel Depledge

    Yes, the p, d, and f orbitals are non-spherical, but they still technically occupy all space. Those shapes merely give an idea of where the probability density of the electrons in them is highest. The orbital shapes are all what are called spherical harmonics, and the solutions don’t have surfaces where they stop; they include all points in space.

  52. Anonymous

    Brian Cox is a genius. I love watching his shows! He explains everything so well and makes it easy to understand. Stuff like this is so interesting!

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