Atoms: Building Blocks of Molecules | Of Particular Significance


Of Particular Significance Conversations About Science with Theoretical Physicist Matt Strassler

s: Building Blocks of Molecules

sler [December 7, 2012; updated December 9]

es — the main structures that are involved in chemistry — are the words from which all of the materials around us are built, then he letters, the building blocks for molecules. Just as there are words of all lengths, a typical molecule may contain a few or a

r even a hundred thousand atoms. A molecule of table salt (NaCl) contains two atoms, one of sodium (Na) and one of chlorine (Cl); a

of water (H2O) has two of hydrogen and one of oxygen; a molecule of table sugar (C 12H22O11) is made from twelve atoms of carbon,

oxygen and twenty-two of hydrogen in a very particular arrangement.

e know atoms exist? In some cases, we can “see” them, much as we can see the molecules that they can form… not with our eyes, but

advanced “seeing” devices. One method involves a “scanning tunneling microscope”, which can show the atoms inside a crystal, or

e them around one at a time. Another method uses our ability to trap ions (atoms which are slightly altered, as explained below). Here

showing evidence of three ions being trapped simultaneously. [Light is shined onto the ions, which is then absorbed by the ions tted. The re-emitted light can be detected, allowing us to “see” where the ions are, in a way somewhat analogous to how a

of light off a tiny but shiny diamond allows us to find it.] types of atoms are there? The types are called “chemical elements”, and the precise number depends on how you count, but let us

moment that the atomic alphabet consists of about a hundred chemical elements; we’ll return to the counting subtleties later. Just

d associate the letters in the alphabet, A to Z, with the numbers 1 to 26, every element is given not only a name but also a number,

atomic number, and often written “Z”. The simplest atoms are those of the element hydrogen; it has atomic number 1. The most

toms found in abundance in nature are those of the element uranium, which has atomic number 92. Others include oxygen (8),

7), calcium (20), krypton (36), lanthanum (57), platinum (78). You can find the full list here, in the “periodic table of the chemical

Which element an atom represents determines its chemistry — how it behaves inside molecules — just as the member of the

hat a letter represents determines how that letter can function inside various words.

s a list of questions you might ask about atoms:

at are atoms made of?

at is the meaning (if any) of the atomic number?

at is the main source of the difference in chemistry between an atom from one element and an atom from another element?

what degree are all atoms of a particular element similar or the same?

at makes the parts of an atom stick together?

y do atoms stick together to make molecules?

t that all of these questions are best answered by starting with question number 1: what are atoms made of? Atoms are made of

ually called “subatomic particles”. [Unfortunately the term is somewhat misleading, as we’ll see, for these “particles” have some

that aren’t very particle-like at all.] Specifically, atoms consist of a set of tiny featherweight electrons surrounding a very small

atomic nucleus that contains most of an atom’s mass. The nucleus is made of other “particles”, which are made of yet other ; we’ll get to them in future articles. on Atom

ee cartoon pictures of atoms drawn on chemistry books, advertisements, and warning signs. An example is given in Figure 1. It

he very rough idea of what an atom is like: it has a certain number of electrons (drawn here in blue) on the outside, in orbit around a mic nucleus. The nucleus is a cluster of protons (drawn red) and neutrons (drawn white). n answer question 2: what does the atomic number Z mean? It is simply protons an atom has. Oxygen has atomic number 8, so its nucleus has 8

simplest circumstances (see below), the atomic number is also how many

an atom has. (The number of neutrons is a more complicated story, to be

ter.) Electrons have a negative electric charge (an amount we call -e) while

ve a positive charge (+e); neutrons are neutral (i.e. carry no electric

When the number of electrons and protons is equal, the charges of the nd protons exactly cancel, so that atoms have no electric charge — they

cally neutral. t is not unusual — in the process of forming molecules, for instance — for

gain or lose one or more of its outermost (or “valence”) electrons. In this

ectric charges of the electrons and protons don’t cancel, and the resulting

y-charged atom is called an ion.

ealistic Atom

the cartoon in Figure 1 vaguely captures the overall architecture of an

is true that there are electrons on the outside and a nucleus made of

d neutrons in the middle — it profoundly fails to convey the real shape ter of an atom, because (1) it’s not at all to scale, and (2) we live in a

world, in which objects often behave in ways that are hard to draw or

Fig. 1: A cartoon of an atom, showing electrons (e) on the outside orbiting a nucleus, made from protons (p) and neutrons (n), at center. The numbers of protons equals the “atomic number”, often denoted “Z”; in its simplest, electrically neutral state, the atom has the same number of electrons as protons.

1) can be partly dealt with through the somewhat more accurate (though still highly imperfect) image shown in Figure 2.

Fig. 2: A more accurate depiction of an atom, showing it is mostly empty space (grey area) traversed by rapidly moving electrons (blue dots, drawn much larger than to scale) with the heavy nucleus (red and white dot at center, drawn larger than to scale) at center. Its shape is like that of a rural community, with expanses of uninhabited land, a few scattered farm houses, and a small village with closely packed houses at its center.

plain what I’ve tried to convey through this image. First, electrons are very, very tiny, so small that we have never been able to eir size — for all we know they are point-like, with zero size, but certainly they’re at least 100,000,000 times smaller in diameter

s. Second, the nucleus (and the protons and neutrons that make it up) is also very tiny, though larger than the electrons; its size has

ured, and is about 10,000 to 100,000 times smaller in diameter than its atom. An atom is in some ways like a small rural community. think of the protons and neutrons that make up the atomic nucleus as somewhat larger houses that make up the village in the center

munity, and the electrons as the far-flung farmhouses scattered around the village. Most of the land of the community — analogous

m of the electrons — contains crops but no houses. Although the territory that is considered part of the town may be quite large, the

ount of area occupied by houses is very small, as is the area occupied by the village at the center of the town.

gy only goes so far, since the electrons, unlike the farmhouses, are in rapid motion, moving through the greyish region in the figure

d the nucleus at speeds that are typically about one percent of the speed of light. Note also that the territory they tend to cover, the

ical cloud, is not accurately drawn; it often has a more complicated shape, and not all of the electrons travel in the same region.

arned you, Figure 2 still isn’t really accurate. First, I’d have to draw the nucleus thousands of times smaller, and electrons millions of

ler, than I have, in which case you wouldn’t see them on the picture at all. For scale, if an atom were the size of your bedroom, its

ould be the size of a speck of dust (unless you’ve got a really big bedroom.) Compared to the size of the objects out of which they

atoms are huge! In a sense (but see below) atoms are mostly empty space!

d, much more profound and subtle, the figure does not convey the murky nature of quantum mechanics. We use the equations of

mechanics to describe and predict the behavior of molecules, atoms, and subatomic particles, and those equations tell us that can have very strange and counter-intuitive properties. Even though electrons are point-like in one sense (for instance, if you try to

o electrons off each other, you will find you can get them arbitrarily close together without them revealing that they have any

there is a way in which, when left alone, they can spread out like a wave, and fill out the entire grey area in Figure 2. If that sounds

s not because you’ve misunderstood; it is strange, and hard to think about. I certainly don’t have an ideal way to draw it that

be misleading, and experts still argue about what is the best way to think about it. So please just accept this as a strange fact, for

he electron’s size (if it has one) is too small to measure, and its mass is so small that the electron can spread out over a whole atom,

s, on the contrary, has a measured and well-known size, and its mass is so large — more than 99.9% of the whole atom’s mass — that

preads out at all. The nucleus mostly just sits at the center of the grey area as the atom moves about.

and Its Chemistry

t way to describe an atom that I can come up with is this: most of an atom’s mass is carried by the small nucleus that sits at its center,

ich extremely tiny electrons, with much smaller mass, are spread out (through the weirdness of quantum mechanics) in a most un-

ke way, filling the grey area in Figure 2. ze of the nucleus relative to the whole atom, and its tendency to sit at the center of the atom, explains why it plays a relatively

in chemistry. Chemistry occurs — molecules form and change — when atoms come close together, and that happens when the

(“valence”) electrons from one atom come close to those of another atom — when the edge of the grey region of one atom comes neral vicinity of the grey region of another atom. In chemical processes, the atomic nuclei remain at the centers of their atoms, and

e anywhere near each other, relatively speaking. The main roles of the nucleus are providing the positive charge that holds the

n the atom, and providing most of the atom’s mass (which determines how easy it is for other objects to push the atom around.)

s gives us the answer to question 3: what determines an atom’s chemistry is (mostly) the details of its outermost (“valence”)

These details can be determined (in a somewhat elaborate way, using quantum mechanics equations) from its atomic number Z.

pursuing chemistry itself, a subject for a whole college course, we’ll continue on down to the subatomic particles, addressing along

e other questions that are still unanswered. Here are the ones we dealt with and the ones that we still have to get to:

at are atoms made of? Answer: Electrons on the outside and an atomic nucleus (made from protons and neutrons) at dead center.

at is the meaning (if any) of the atomic number? Answer: it is the number of protons in the nucleus of the atom, which under simple

umstances equals the number of electrons that surround the nucleus.

at is the main source of the chemical difference between an atom from one element and an atom from another element? Answer: the

perties of its outermost electrons, which are determined by the total number of electrons for each element, i.e. the atomic number.

what degree are all atoms of a particular element similar or the same? Answer: Click here for a discussion of isotopes, and click here arn about how all atoms of a given isotope are truly identical.

at makes the parts of an atom stick together? Answer: Click here to learn about the role of electric forces and quantum mechanics.

y do atoms stick together to make molecules? Answer: Click here [coming soon] to learn about the role of electrons and electric

es in building molecules out of atoms.

s another that may have occurred to you, based on Figure 2: atom is mostly empty space, how is it that any objects can seem solid? Why can’t I just put my hand right through my computer

en, if the screen is made from atoms which are mostly empty?



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k: New Article on Atoms and Their Structure | Of Particular Significance

nox | December 7, 2012 at 11:47 AM | Reply

nd why you’re describing the atomic number in terms of the electron count, because it’s what matters for chemistry, but

me it opens up the possibility of a lot of confusion when it comes to ions. People might think that a -2 oxygen ion with

ns and a neutral neon atom with 10 electrons should behave similarly…

Strassler | December 7, 2012 at 12:20 PM | Reply

an interesting point. You’re right, that’s a flaw. Will think about it.

stón E. Nusimovich | December 7, 2012 at 6:16 PM | Reply

outer layer of electrons of atoms (valence electrons) have many interesting behaviours, and all of these behaviours are

ted to chemistry.

se behaviours determine the types of bondings that a given atom may have when binding to other atoms to form

ecules and other arrangements (like lattices).

types of possible bondings that some kind of atom may have are determined (in a rather complex way) by the atomic


ure always behaves in such a way that it is always looking the most stable state that could be achieved under current

ditions. The available types of bondings for a given kind of atom are related to this tendency to look for the most stable

e that can be achieved by a given atom under current conditions. mistry is all about this tendency to look for the most stable state that could be achieved under current conditions, and

er certain conditions, the formation of ions is the most stable state for a given kind of atom.

ctrons are fermions, which means that they are affected by Pauli’s exclusion principle. What that means is that on a

en atom, each electron has a unique set of quantum numbers, and they “want to stay as far away” from any other electron

hey can. To be able to “stay as far away as possible” from each other, electrons are arranged within certain “slots” called tals.

se “slots” are not precise places, but rather fuzzy regions where it is more probable that certain electron with certain

rgy level could be found (quantum mechanics rules, so everything is about uncertainty and probabilities!).

electrons in an atom are organized by energy levels, and for a given level, there is an arrangement of electrons that is the

st stable. The most stable arrangements is achieved by a certain kind of elements, the noble gases (like Hellium, or

on, just to name two such noble gases).

hese elements present the most stable arrangements, they do not have a very strong need to bind with other atoms to

k for a more stable state (because they already are in a confortable enough state). Atoms of other kinds of elements that

e too few electrons or too many electrons in the outermost layer (valence electrons) are very close to the stable state of

noble gases, so it is very easy for these atoms to either shed their valence electrons and be similar to a noble gas (when

y have too few electrons) or to “steal” electrons from some other atom to complete the electron count to emulate a noble

atoms that behave this way (either shedding electrons or stealing electrons to emulate noble gases) are the ones that can

ome ions under certain conditions.

just like Prof Strassler described, chemistry is all about the behaviour of the valence electrons (and all electrons behave

ording to quantum mechanics).

d regards, Gastón

ecember 7, 2012 at 12:03 PM | Reply

r your continued articles. I have a pedagogical quibble, however. I read reddit’s AskScience section, and people often

atom is truly mostly empty space, then why don’t atoms just pass through each other? What am I touching when I touch

face?” Another question that gets asked is, “Why don’t electrons fall inside the nucleus?” For this reason I think the

the atom as empty space with tiny electrons is not really helpful. It’s at this point that quantum physics has to be

d (as it was by the physicists themselves at the turn of the century).

wrong about this because I’m not a physicist, but I’d like to suggest that maybe it’s better to present the electrons as

aving the shape of the orbitals that they occupy. It answers the first question (the atom is filled with the orbitals) and it

e second (the lowest orbital is centered on the nucleus, and the other ones can’t get lower because of the Pauli exclusion

But then you have to also have the caveat that the electron behaves like a point particle under some circumstances.

with an analogy for this. Matter is like a tent, composed of tent poles (the nuclei) and the tent fabric (the electrons). The

themselves don’t occupy much space but they “pin down” the tent fabric and give it shape. The tent fabric, on its own,

e shaped like a little ball, but when you stretch it on the poles, it begins to occupy space. This can be readily extended to w the orbitals in some solids become essentially distributed throughout the whole material, and the Rutherford

t that initially created the idea that atoms are mostly empty space.

mething from your series on particles as ripples in fields could be brought in here to explain orbitals in a more


Strassler | December 7, 2012 at 12:19 PM | Reply

edagogical quibble is well taken: these are indeed questions that always get asked and that I have to answer in these

. I was going to answer them later, but your point is that probably I need to bring them up — at least pose them, with

o answers — in this article directly. I think you are right, and I will make a revision.

that if you say the electrons have the shape of their orbitals, you will generate all sorts of problems later in explaining

e physics. You definitely do not want to say that an electron is the same size as a hydrogen atom. At some level this is a

mental problem in explaining quantum mechanics and the nature of particles… and indeed I am in danger of stency within the website. Will ponder. nt fabric analogy is an interesting one.

s for your comments. It’s a challenge, definitely, to put in all the pictures and caveats in the right order.

Goldhor | December 7, 2012 at 3:21 PM | Reply

le, Matt. It does seem to be one of those situations where the only way to the truth is through a number of carefully-

, half-truths. I like Figure 2 very much, but a variant of it showing the balloon-like shapes of the orbitals might be a

mpanion. I would also echo Jon Lenox’s caveat–I too was worried that people might think you could perform alchemy by

toms. (In fact, it raises the rather interesting question about why that DOESN’T work. We all know that singly-ionized esn’t turn into nitrogen, but I’m not sure I could state simply, clearly, and correctly why it doesn’t…as opposed to

g on at great length!)

u | December 8, 2012 at 12:35 AM | Reply

ionized oxygen is very close to nitrogen, it will readily bind three hydrogen atoms to produce an ammonia shaped

molecule and will pair up into strongly bonded O2.2+ molecules. Likewise O2- is very much like a noble gas atom. ctric charge on ions often acts as a modifier more to their physical properties than their chemical ones; and there are

ing situations where this can be almost completely cancelled, carbon monoxide is much like nitrogen and boron nitride

st in both graphite-like and diamond-like polymorphs.

ael | April 29, 2014 at 7:44 PM | Reply

root of two truths?

rassler | December 7, 2012 at 3:42 PM | Reply

nk you folks enough for your wise comments. I have (at least temporarily) taken the ions out of this entry; I will put where else. And I’ve got my first attempt at dealing with the issue of orbitals up. It certainly won’t be the last version.

ing about whether additional figures would help or hurt.

E. Nusimovich | December 7, 2012 at 7:45 PM | Reply erspective of chemistry, the atomic number for a given kind of atom is determined by the amount of protons in the

that type of atom. In such a way, you can avoid the “ion problem”, or what happens when an atom of a certain type in

ome other atom (the arrangement of valence electrons in molecules is somewhat different, but the atoms remain being of


ds, GEN

E. Nusimovich | December 7, 2012 at 7:58 PM | Reply

balloons is an analogy that might work up to a point, but when you consider hybridization of orbitals and molecular e analogy might be confusing.

E. Nusimovich | December 7, 2012 at 8:02 PM | Reply

ce, the molecular orbital for the benzene ring is one single orbital but it looks like two balloons.

December 8, 2012 at 12:30 AM | Reply

nt piece that prompts a few questions.

ther trivial one, but as a physicist what is your take on treating the neutron as element zero?

what is size exactly? Minute Physics recently produced a video on ‘What is touch?’ that concluded that perhaps touch

eing close enough to interact, and from this article I gather you suggest that the size of an object is the area of space that

cles will interact with it, bouncing off but possibly also including other interactions like scattering or fusing? Then the

roton would be given by the scale at which particles stopped scattering off the ‘proton’ and began to interact with the

quarks within it?

this relate to point particles? Are they just an idealization?

this relate to density? Obviously something of a given mass is denser if it is smaller, so does this limit how small an

y be (An object of sufficient density would be a black hole would it not?)

Strassler | December 9, 2012 at 12:19 PM | Reply

on as element zero”; I would say this is physically not an atom, because, lacking an electron, it is not in the same class as

er atoms. For one thing, it is 100,000 times smaller in radius than any atom. It is, instead, in the class of nuclei, being

by near-symmetry to the hydrogen nucleus.

his turns out to be an astonishingly complicated business. That’s indeed why I’m struggling with it in this article. Size is

haracteristic of an object; it is a characteristic of the interaction between a probing object and the object that it is being

d , and it often comes with ambiguities. This is one of the very important things one learns in quantum particle physics.

is is very counter-intuitive, because in ordinary life it isn’t often true. I need a good analogy for this.

ning size, radius, point-like objects, density, etc. is something that turns out to be precise only with careful technical ons, and ambiguous because there are different possible definitions that depend on what experiment you are carrying

famous example is that the proton size effectively grows (not a lot) as you increase the energy of the particles that you tering off of it. Another is that if you scatter an electron off of a magnetic monopole of a certain type, the monopole will

to have a definite and finite size; but if you scatter a monopole off a monopole, they will act as though they are point-

s well understood why, but that’s at least two or three articles deep to explain it.

aise Pascal | December 10, 2012 at 1:22 PM | Reply

you have a reference to the monopole-scattering experiments? I’d like to read those papers.

derson | December 8, 2012 at 2:44 AM | Reply

s not quite correct to say that the nucleus is not involved in chemistry, because the mass of the nucleus is sometimes

Not so much that a single neutron makes much difference in a chemical reaction, but there are general trends in

due to mass. For example, see how heavy metals interact with polysaccharides.

r Laia | December 8, 2012 at 6:55 PM | Reply

-transfer reaction rate are quite sensetive to mass. Deuterium effects are well known, normally these reactions are slower.

on’t forget NMR spectroscopy, where these aspects are crucial to elucidate the structure of molecules (e.g., Carbon 13

Strassler | December 9, 2012 at 12:10 PM | Reply eed to write that with more care, yes.

December 8, 2012 at 5:52 AM | Reply

chemistry or physical chemistry? Certainly I think it blurs the lines between the two.

r Laia | December 8, 2012 at 6:57 PM | Reply

al Chemistry is a branch of Chemistry, while Chemical Physics is a branch of Physics. I guess it is really blurry…

ecember 8, 2012 at 1:46 PM | Reply

gy with Letters, words, sentences is a great one, I enjoyed it. However, maybe you are enforcing it a bit too much,

y speaking. In my experience its better to just tell it once and then let the reader make the analogy for himself.

e to the part after the electron radius, I personally also would leave out remarks how weird or bizzare or hard to

d something is, because with that, you are creating a kind of “thinking-barrier” – at least for some people. (The thinking

Oh ok this is weird! I cannot possibly understand it!) Also generally judgements, conclusions, meta stick most. One

ell emphasize how perfectly natural a certain behaviour is.

are quibbles. I cannot thank you enough for your great articles, I enjoy reading you a great deal.


Strassler | December 9, 2012 at 11:59 AM | Reply

s for your comments!

ll struggling with the issue of the electron radius. About the weirdness: The problem is that if you make statements that izarre and you don’t say “yes, this is weird”, that confuses one set of people; and if you say “yes, this is weird” that

the thinking-barrier you mentioned. So what’s the best approach? I am trying “yes, this is weird — and it’s ok if it seems

o you, because it seems weird to me too.” But I’m not confident that this is best. So you have added to the many voices

head that push and pull in different directions.

an amazingly difficult article to pull off; it’s supposed to be just a stage along the way to particle physics. It’s not an

nt that the atom article took over six months to write after the molecule article.

December 10, 2012 at 3:50 PM | Reply

spect it would be much easier to write about atoms if you do not try to explain QM simultaneously. You refer to protons

neutrons with proper abstractness and you should not be afraid to do the same with electrons, regardless of the fact that

y are elementary particles. The composition and the basic properties and ordening of the constituents are more important

understanding the atom casually.

ncerning the size of an electron, could you simply not mention it and merely give the mass ratio between a nucleus and lectron as some kind of measure, and cross your fingers?

ofscience | December 8, 2012 at 6:29 PM | Reply se explanation of how Chemistry occurs!

mber 9, 2012 at 10:33 AM | Reply

if you’ve addressed this in another article, but I remember being taught that electrons were point-like, having zero size.


Strassler | December 9, 2012 at 12:30 PM | Reply o be quite careful in my wording, don’t I! No, what you learned wasn’t really wrong, but it wasn’t complete.

hen someone says to you “an object has zero size”, what they really mean is that “if this thing has a size, it is too small

o currently observe.” After all, everything we *know* comes from experiment. All we can do is look to see if the size

measured; if we can’t observe any effects of a finite size, we know the object is smaller than we can measure with that

lar experiment. So the correct statement is not quite that “electrons are point-like” but that “electrons are not known not

oint-like”. It’s an subtle but important distinction, because the first statement might prove to be wrong (we might

ay run an experiment good enough to detect the electron’s size, if it has one), while the second statement is a correct and

ble statement about current knowledge. , in quantum mechanics the notion of point-like particle is inherently confusing. The idea that something is point-like

tatement that if and when you try to break it apart or detect its finite extent by banging something into it, you fail. But if

-like object is left to its own devices to wander around a proton inside a hydrogen atom, there is a sense in which it

s out around the hydrogen atom in a nice spherical shape. Now the problem is that what is really going on does not have

uitive picture to go with it, and people interpret it differently. Should one say it is the electron that spreads out? Should

y that it is a wave that describes the electron that spreads out? Is it only the probability to find the electron that spreads

one of these is really entirely accurate as far as it describes the equations we use, and we don’t know the equations are

us quite the right picture for what nature is doing. Physicists and philosophers are still arguing, even today, over the

ords to use. So my challenge (and yours) is to figure out how to sidestep this and move on. This website is not intended

m I prepared with the right pedagogical tools) to try to explain quantum mechanics to the public; and I think that’s too t a problem for anyone to solve, at least with current knowledge.

December 9, 2012 at 8:30 PM | Reply

for your reply. I hope one day to read these articles as they sound like they would be very enlightening on this topic,

ur brief explanation does make perfect logical sense.

k: New Attempt at Atomic Article | Of Particular Significance

ember 10, 2012 at 1:16 PM | Reply

had a physics course so can only follow your simpler descriptions, but I have a strong interest in these things and have

al books over the years. Something you’ve said above confuses me, and I’m sure I must have a hole in my

ding. You describe the electron as being like a wave that fills the entire gray area. I thought the wave was not a physical

instead a mathematical construct describing the probability of finding the electron in a given position within the atom.

u | December 10, 2012 at 3:43 PM | Reply

something even the experts argue over. It is often said that this wave is the probability of finding the electron in a

lar place, in which case we could possibly say yes, the wave is math and the electron is ‘really’ whizzing about in one

lar place at a time, but this is not entirely accurate. We can also imagine the electron itself smeared throughout that

or as the cloud, again not entirely accurately. As the professor states it’s a tricky area where our usual notions can easily

e us.

h | December 10, 2012 at 4:56 PM | Reply

s makes me think of the blades of a fan rotating quickly. At rest you can see them as simple objects. When running they

m to be a cloud of metal.

Strassler | December 11, 2012 at 12:05 PM | Reply

er the wave is a mathematical construct or something to be treated as physical is very subtle, and people don’t

arily agree on the matter. I am going to have to write an article about this in future, but I want to make sure I do it right.

case, the equations we use give correct predictions for atoms and how they behave; the issue in question is how you

et what the equations signify, which is inevitably ambiguous.

Benish | December 10, 2012 at 1:44 PM | Reply

y years as a physics student I have gotten the impression that, for all the lip service paid to the contrary, the three least

ords of most physicists are “I don’t know.”

Strassler’s above post gingerly leans toward being an exception, but the hesitancy speaks volumes. I would suggest that

to and the difficulty in “explaining” the behavior of atoms is that we really don’t know what it is. We have no

answer to the question, “how big is an electron?”

ons and their reliability with respect to a wide range of predictions provide useful clues. But we are nevertheless at a

how to “explain” this success because of the irreconcilability of the facts into a story that consistently supports our

tions. Neither chunk-of-stuff-like particles nor fuzzy wavy particles make sense across the board.

nd it convincing to blame the failure to explain these things on the mathematical limitations of the audience. The truth

math does not answer some of the biggest questions. It is a veritable cliche borne of quantum theory’s founding fathers

er an understanding of atomic reality based on quantum theory is to reveal one’s ignorance.

h circumstances the most fruitful approach, it seems to me, is to be very humble and be very receptive to new ideas.

he ultimate explanation will be of a less mathematical character and a more artistic or intuitive character. Maybe all the

arried along with the word, “particle” is an obstacle to a deeper understanding. Maybe the problem has to do with our

ully understand gravity.

Strassler | December 11, 2012 at 12:13 PM | Reply

the challenge is to explain what we do know and what we don’t. That’s what’s behind my hesitancy; I don’t have the

n this article to be clear. If one says “we don’t know” in a general way, important details get lost : that we can predict

roperties of the electron to one part in 10^12, that we can predict how electrons scatter off each other to one part in

hat we can predict how muons decay to electrons with comparably great precision, etc. And we can measure that the

n’s radius (as defined by how differently it behaves from a quantum point-like particle) is smaller than 100,000,000

maller than that of a typical atom. Now, that represents a huge amount of knowledge. And we know, therefore, that

ns are very well described as quanta of the electron field, just as other elementary particles are. That does not represent

e knowledge, and there are things we don’t understand… as there always are.

her problem is that quantum mechanics language is not quite the same as quantum field theory language. This is another

for my being hesitant. One has to be very careful if one is to be accurate.

an | December 10, 2012 at 3:34 PM | Reply

ine and enlightening. Thank you Professor.

this relate to density? Obviously something of a given mass is denser if it is smaller, so does this limit how small an

y be (An object of sufficient density would be a black hole would it not?)/- Kudzu.

tmosphere and freedom of movement allowed in space arround nucleus: Two completely different particles (the electron

ti-positron) are swapping back and forth(create mass). What does this mean? The physical thing which is propagating ace is a mixture of the two particles. When you observe the particle at one point, it may be an electron, but if you

a moment later, the very same particle might manifest itself as an anti-positron! This should sound very familiar, it’s the

e story as neutrino mixing (or, similarly, meson mixing). m of movement allowed is due to the “pull” created by the density of the nucleus, not by the Higgs vev?

“vev”(spontaneous electroweak symmetry breaking – occupying lower potential energy)- is same as back and forth

um of photons(mass?) inside a closed system(black holes).

n cannot contain “speed of the light”. In Black holes, the spacetime dimension is ruptured – the light had free fall into


et the “mass” because it cannot escape closed system created by Big bang temperature(after cooling).

ere massless because it already escaped closed system- but cannot escape the Roller coaster of spacetime metric.

sed system mass is conserved. But Higgs(h) mass is not conserved only for a while(abruptly zero) – thus react with

metric for a while. ?????

December 10, 2012 at 4:16 PM | Reply

em is, QM is a very vital, nay fundamental aspect of how atoms work, so there’s really no way to avoid mentioning it. It’s

ve a section on the cartoon atom (Looking very classical) and the more realistic atom (Looking far more quantum l.) our fingers is problematic too, many readers will have their own questions raised elsewhere or will be smart enough to

hen reading this article.

n E. Nusimovich | December 11, 2012 at 8:21 PM | Reply

y, as in the density of water at 5 °C, is the end result of the interaction of billions of billions (“a la Carl Sagan”) of water les.

hat specific meaning of density, it makes no sense to speak about the density of an electron. gards, GEN

ecember 10, 2012 at 6:19 PM | Reply

r “Yes, this is weird” approach. As a science student trying to come to grips with all this 25 years ago I would loved to

your article back then. Keep up the good work!

nje | December 10, 2012 at 8:34 PM | Reply

ks very much for your efforts on this very useful project. It is helpful for the student to have a broad outline description scape as you are providing. The fact that there are difficult/mysterious problems ahead is one of the attractions of this

ising that at the start you keep the student engaged and up to speed whilst you gradually advance towards the problems.

(@Oaktree_) | December 11, 2012 at 12:24 AM | Reply

ke to know your opinion on aperiodic crystals. Do you think the are a freak of Nature or a Nature’s natural progression

s to order?

rödinger was wrote:

s we have dealt hitherto only with periodic crystals. To a humble physicist’s mind, these are very interesting and

ed objects; they constitute one of the most fascinating and complex material structures by which inanimate nature

s wits. Yet, compared with the aperiodic crystal, they are rather plain and dull. The difference in structure is of the same

at between an ordinary wallpaper in which the same pattern is repeated again and again in regular periodicity and a e of embroidery, say a Raphael tapestry, which shows no dull repetition, but an elaborate, coherent, meaningful design

he great master.”

ger’s focus on what makes progeny from parent, on an as yet unknown crystalline molecule within the chromosome,

to a scientific prediction of the nature of the gene. It would take James Watson and Francis Crick ten years to unravel gs of this “aperiodic crystal”—and identify the hereditary, helical molecule as deoxyribonucleic acid—DNA. …”

eak of Nature or was the DNA inevitable every since the first Bose-Einstein condensate popped into existence?

usness the end goal of all this orderly transformations of energy we see all around us in the universe?

uestions so little time … I wonder why Einstein ended his quest so prematurely?

u | December 11, 2012 at 9:11 PM | Reply

dic crystals are as inevitable in our universe as periodic ones. Their existence is dictated by the same laws of nature.

er asking whether the universe has a goal or purpose in dangerous territory. What would set the goal? Th universe itself?

You would need some sort of consciousness to do so. You may wish to check out this brief screed by Neil deGrasse

ktree (@Oaktree_) | December 12, 2012 at 1:15 AM | Reply

sh I sketch that fast, …

l deGrasse makes for good TV but I am afraid he failed in convincing me that there is no purpose in the majestic dance

see all around us. You see, he made the cardinal mistake of ending his sequence of questions short, short of the goal,…:-

e based the universal goal to humans as the end goal, far, far from it. Consciousness, universal consciousness, is the end

l because that would, I contend, would close the loop. From absolute chaos, the singularity, the Big Bang, to universal

sciousness that could control it’s own destiny. ckout my post below.

E. Nusimovich | December 11, 2012 at 11:44 AM | Reply

crystals have an ordered structure and symmetry, the point being on the fact that that ordered structure is not based on al symmetry, which is the basis of traditional crystallography.

crystals present more complex types of order and symmetry, and it is because of this order and symmetry that they


as happened before with Physics, it was first that mathematicians found some “funny” properties with geometrical

th no special relation to nature, and then it took some time for the physicists to realize that those “necessary

ns” found by mathematicians were useful to solve certain theoretical physics problems.

ce, Riemann discovered the metric tensor, differential geometry and non euclidean geometry (then to be extended by

Levi-Civita), and then it took a while for somebody (Einstein) to realize that that “funny” stuff was the math trick

avitation (General Relativity).

0s, mathematicians discovered aperiodic tilings, and it took a while for physicists to realize that these kinds of tilings

math trick” behind quasi-crystals.

e the relation between aperiodic crystals and Bose Einstein condensates (BECs require very low temperatures to be

and they happen only with composite structures that present a specific quantum state, that is, composite bosons, while

als are produced at temperatures much closer to standard room temperature, and they are just normal atoms organizing

to geometrical lattices).

ds, GEN

ree (@Oaktree_) | December 11, 2012 at 9:06 PM | Reply

ve the underlining theme is exactly what Schrödinger was inferring to, chaos to order, “a masterpiece”.

er there is a “DNA” embedded in Nature’s laws which leads to higher and higher states of energies is hard to decipher, as

But this is growing evidence that may suggest that order is not just a consequence of more complex structures which in-

e a consequence of certain variables changing one way or another, i.e. entropy, universal cooling, etc.

a post in another article on this website which expands on this theme and, in my opinion may very well lead to some dence of universal consciousness.

Prof Strassler will not be upset if I repeat it one more time.


niverse may grow like a giant brain, according to a new computer simulation.

ults, published Nov. 16 in the journal Nature’s Scientific Reports, suggest that some undiscovered, fundamental laws vern the growth of systems large and small, from the electrical firing between brain cells and growth of social networks xpansion of galaxies.

ral growth dynamics are the same for different real networks, like the Internet or the brain or social networks,”]said study

hor Dmitri Krioukov, a physicist at the University of California San Diego. ” … NBC

months ago I posted this same observation but with a twist, that may have caused a negative impression, GOD. Of course,

not what Dr. Krioukov is suggesting but he does like it open to conjecture.

my post …

s God then did God create the universe or did the universe create God?

created the universe then that would be very problematic w.r.t. causality, what caused God? However, if the universe

God then that would be well within the realm of our real universe all our questions both from evolutionism and

nism would lead to a common goal.

all that we know about our universe and ourselves:

t could God be?

would there be a need for God in the first place?

could God control the universe, which created Him? us observation is as the structures, atoms and molecules, become more complex the outcome, evolution of the universe,

o life and beyond to consciousness, (we are very high up in the overall scheme of existence).

ve a consciousness which is very difficult to define and formulate with the same math we use to formulate physical

mena. Below is a very interesting video of a 3D formulation of what the known universe looks like. As you can see it has

ng resemblance to the structure of our brain, the structure that gives us consciousness.

ou believe that a universal consciousness (God) can exist given this data?

our own consciousness can control our brain’s motor functions and hence our body functions, could the universal

ousness (once it “turned on”) create the more complex physical fields from the fundamental field (gravity or something

the strong field) and hence drove the primordial chaotic universe to one of order and expanding, i.e. the expansion of

verse is not related to the initial conditions at the big bang but rather the universal consciousness is reinforcing and

ng to a higher and higher state. A principle of conscious advancement as the driving force for everything. No

vation laws need to be violated or invalidated.

the universal consciousness created by the magnificent structures of our universe, see the video below.

cember 11, 2012 at 2:06 PM | Reply

bably quite a bad analogy but I was thinking in terms of these differing behaviors as being similar in structure to a

in the electron field (as it would be in water) – the spread out ‘field’ being the aperture at the top, and moving towards a

nd narrower focus at the ‘bottom’ as higher energies are utilized until reaching the terminal ‘point’ particle at the end (or

e able to currently determine as the end, since it could extend further beyond our ability to ‘reach down’ that far).

the idea further: the ‘downward’ terminus of the funnel can move about, just as the particle element of an electron can

ut within its waveform probability; the ‘downward’ nature of the funnel is negative charge whilst an inverted ‘upwards’

could be seen as a particle with positive charge. (Maybe even the direction of whirlpool spin could be, well, spin or


is has problems with any attempt to make it fit mathematically (in that it wouldn’t at all) and so only works as well as

ommunity description, though I suppose this would be true of any analogy for a complex phenomenon that has no

rld’ equivalent.

December 11, 2012 at 9:50 PM | Reply

what I was wondering when I asked the question was how the energy of the electron was distributed through space. With define a certain volume of space and state that a certain amount of mass (thus energy) is present in it, the density being

t divided by the volume.

wondered if I could define a certain volume of space that contained the electron with a known amount of energy. The

s volume of space was, the more energy per arbitrary unit it would contain. A point particle would then be infinitely

king a finite amount of energy into an infinitely small volume.

s far as I understand it currently was to assume that these measurements of ‘size’ were evidence of a particle’s energy

pletely contained in a space. On reflecting on what it is that size may or may not mean however I have come to

d that it is a vague concept, especially when dealing with small entities.

December 11, 2012 at 10:01 PM | Reply

lts are very interesting, but I would hesitate to draw the conclusions you do from this data. This is possibly due to the le, which, in the usual manner of such press release is not entirely accurate.

imulation shows is that the same laws govern large and small systems. This is not obvious, but not surprising either. We

n nature phenomena that do not change with scale. The emission of plasma from the black holes in the center of galaxies

identical to the squirting of ink by a squid, and is governed by similar laws (A high speed fluid slowing down as it

with surrounding matter.)

headline focuses on two examples, and the most eye catching, we could equally say the universe is like the internet, a

congealing on a plate of leftovers. Rather than assume that the entire universe is somehow imitating a small lump of

e bodies of a few billion apes on a tiny rock in space, might we rather infer that our brains grow not by some sort of

nsciously directed means, but via the same simple laws that govern the collection of cold gas clouds?

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Anderson | April 18, 2013 at 4:00 PM | Reply

tutorial. 1) A better pictorial would be an animation where the electron is a pixel at jumps around the nucleus 10 times . Then point out that the animation is slowed down 10^43:1. Fast chemical reactions may occur on attosecond time

from the electron’s standpoint this is 10^26 time steps. You underteach if you don’t point this out. 2) re: your reply to

“..sense in which [the electron] spreads out around the hydrogen atom in a nice spherical shape.” This is the shape of the

re the electron hangs, not the shape of the electron.

bott | May 5, 2013 at 2:44 PM | Reply

said that “electrons … are in rapid motion, moving … around the nucleus at speeds that are typically about one percent d of light.” That would suggest that electrons have lots of kinetic energy. Is there any way to tap that energy? Thanks.

u | May 5, 2013 at 9:35 PM | Reply

ns do indeed have a massive amount of kinetic energy on a weight-by-weight basis. Sadly, just because something is

oes not mean it can be used. The electrons are in their ‘ground state’; the lowest energy they can possibly be, so there is

of getting that energy out. It is similar to the fact that a single iron nail, if converted to energy, would power your house

years; there is just no way to actually convert it, to get the energy out. (Short of throwing it into a black hole.) ingly one exception is ‘k-capture’ radioactive decay where an electron is adsorbed by a nucleus. This happens in you

time, it is how potassium, a vital component of organic life, decays into argon.

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