In 1676 Roemer estimated the speed of light by timing the orbit of Jupiter’s moon Io, noting that as the Earth approached Jupiter, Io emerged from behind Jupiter a little earlier every day, and as the Earth traveled away from Jupiter it appeared a little later every day, with the time of day varying by 22 minutes over a year. Knowing the difference between the two distances, he reckoned that light travels that distance in 22 minutes, or 227 thousand km/s. The actual speed is about 300 thousand km/s. Not bad!
I always appreciate these stories about how very specific observations that most people would miss can give away far deeper details of the universe that many wouldn't even consider. Eratosthenes using shadows and figuring out the size of the earth within a few percent is another well known one.
Another interesting thing about using the timing of moon eclipses:
> Galileo proposed a method of establishing the time of day, and thus longitude, based on the times of the eclipses of the moons of Jupiter, in essence using the Jovian system as a cosmic clock. The times of the eclipses of the moons could be precisely calculated in advance and compared with local observations on land or on ship to determine the local time and hence longitude.
Well, also knowledge of the distances between the objects involved (at least the Earth and Jupiter), which in turn depended on a series of further investigations.
Which is not to denigrate the achievement, but if I were to drop you on an alien world with only a telescope and an accurate time keeper, you're not going to be able to recreate it.
From what I've seen, talent is the tendency for a person to naturally develop a skill, if left alone to do so. It isn't some kind of intrinsic capability.
The speed of light, because it is so fast, is the most precise physical constant known
:
299 792 458 m / s. Less than 7/1000ths away from 300,000,000 m / s.
I am not going to sweat this in the least.
So light travels only 0.3 m / nano second, or 11.802 inches.
This is exactly it, the longer your traces (or any sort of write I guess) between processor and memory, the longer delay you have to have for things to "settle". Additionally increasing capacitance means that it takes more effort (read, even longer) for the line to settle.
Does make me realise I don't know so much about the super low level parts of it beyond electrons and holes. One end of the wire needs to be at a lower potential to encourage electrons to flow from that side to the other. Hmmm.
Armed with this fact thinking about electronic devices. How the front of the signal travels and how suddenly the distance matters. Was blown away when I first thought about this.
The second is (and has been) defined independent of length for a while. It's the time it takes for a certain number oscillations of a caesium atom.
The meter was redefined as the distance light travels in a specific time. So you could say that either the meter or the speed of light was redefined to make the speed of light a round constant, but not the second.
That reminds me of the Millikan & Fletcher oil-drop experiment [0], which measured the charge of the electron.
In short, microscopic atomized oil droplets had their fall-time through air measured to figure out their volume, and then a known electric field was used to levitate them. The calculated charge-per-molecule clustered around multiples of a smaller value, which would be the charge of an individual electron.
They tried a similar experiment first, called the water drop experiment. It was intended to work in the exact same way, except with the obvious parameter varied: they would use water instead of oil.
The reason the water drop experiment failed was that the bright lamps they used to look at the drops evaporated the water too quickly.[1] Such a relatable experience!
For that to happen, you would have to be very unlucky: all of your measurements would have to be 2e, 4e, 6e, etc. If a 3e or 5e sneaked in there, you'd realize that the charge was e, not 2e. With enough measurements, you can be confident that you've hit all the expected multiples of the quantum.
Not quite so. They did end up measuring a multiple of the fundamental electric charge. The experiment really measured 3e, 6e, 9e, etc. It turns out that the electron and proton have an electric charge 3× bigger than that of a quark. Since the experiment didn’t generate any free quarks, nobody noticed for years. Even today the mistake persists and school children are taught, unironically, that down quarks have ±⅓ of the fundamental indivisible unit of electric charge and that up quarks have ±⅔e.
No need to nitpick, the original comment states perfectly accurately that he was measuring the fundamental charge _of the electron_, from which the constant e is derived. We've been using e to mean _electron_ charge for a very long time. Where do you get the idea that constant has anything to do with quarks?
"I see a clock, but I cannot envision the clockmaker. The human mind is unable to conceive of the four dimensions, so how can it conceive of a God, before whom a thousand years and a thousand dimensions are as one?" -Albert Einstein
It would have revealed a lower layer of higher understanding.
No one has been able to calculate the mass of a quark:
"Nobody has seriously calculated theoretically a quark mass from first principles. So there is no issue of agreement with experiment. They are parameters in experimental fits, but sometimes remarkably consistent across a broad range of experiments-- and the QCD/EW calculations using them as inputs. If someone pretends to know their origin, he/she is bluffing."
In 1909 the results results were couched in some "elementary electric charge" quantity, since the now-familiar subatomic particle model (and the "electron") was still gaining acceptance.
I expect that the greater the number of trials, it becomes easier it is to detect a distinction between closer-multiples, and if at some point more trials stops changing the answer then you've likely converged on e, unless there's some new principle like "X-ray exposure only affects charge in in multiples of e greater than one."
The approximate value of the elementary electric charge had been known since 1874, when it was first computed by George Johnstone Stoney. After Stoney, other experiments had reduced the uncertainty with which the value was known, but it remained relatively high.
The importance of the experiments of Robert Andrews Millikan consists in the fact that the uncertainty of the value of the elementary electric charge obtained by this method was much smaller than by any previous method (he claimed that it was better than one half of one percent, but he used wrong values for the viscosity of air, so his actual result was off by more than that, but still by less than one percent from the correct result).
I love articles like this. I feel like too often in science education (at least my science education) that laws and theories are presented as just something that you need to memorize, when in my opinion the stories of how things were originally discovered and figured out is eminently more fascinating and inspiring. Like I remember having to learn all of these biochemical pathways, but I left school with nary a clue as to how these pathways were uncovered in the first place.
Thanks for submitting! Would welcome suggestions for any other publications on how scientific theories were first discovered.
Did you get your physics education in high school or university? I only had to take one physics class in the USA at college for my major, quantum electrodynamics for electrical engineering but my professor wrote the textbook and I recall he went over each experiment starting from the fundamentals of our understanding of the basics of the atom, Newton's understanding of light at the time, double slit experiment, to Maxwell's equations, the Michelson Morley ether experiment, to deriving then proving experimentally proving general relativity and decomposing GR into Newtonian physics/other laws of electromagnetism, I am still in awe at the people just figuring this stuff out from first principles.
Anyways, I haven't read this (have it on hold at my library) but someone recommended this book on reddit
How to Make an Apple Pie from Scratch: In Search of the Recipe for Our Universe, from the Origins of Atoms to the Big Bang
https://www.publishersweekly.com/9780385545655
What’s the name of that textbook? It sounds really interesting.
Isaac Asimov wrote a couple books that follow the narrative of science from the beginnings up until the 80s or so, which I highly recommend. One is called Atom and is more focused on how we got to our “present” understanding of particles. There’s also one that takes a broader view, it’s something like History of Science (? not at my bookshelf right now).
There’s several books in this genre for math as well. IMO it’s a much better structure for pedagogy since we can piggy back the education on our natural wiring to care about narrative and mystery/puzzles.
It's like 800 pages, I haven't read it but I think I'll keep that one. Seems like it might be hard to find another physical copy. He was definitely prolific on a number of topics.
"Asimov was so prolific and diverse in his writing that his books span all major categories of the Dewey Decimal Classification except for category 100, philosophy and psychology" - from his Wikipedia page.
He was also incredibly talented in phrasing ideas so that they stick in the reader's mind. I am right now sitting next to a dog Asimov named after him.
That was my Physics too, but Chemistry just completely glanced over the history. Same thing with Mathematics, no backstory of mathematicians. I guess that either 1. Physics History is short enough, well-recorded, or 2. Physicists really like teaching their history.
Physicists seem to be always seeking a deeper understanding of everything, more so than other fields like biology and sometimes chemistry, who have a tendency to get bogged down into to the idiosyncrasies of particular phenomena.
Yeah, in retrospect I think this aligns with my experience. But I'd even say that with the famous physics experiments I still remember often thinking "How did they get such precision with such primitive instruments?" I mean they would explain the experiments in very basic/schematic terms, but would have been nice to actually replicate I've to truly understand how it worked.
> to deriving then proving experimentally proving general relativity and decomposing GR into Newtonian physics/other laws of electromagnetism
Do you mean Special Relativity, which covers classical mechanics and electromagnetism? General Relativity covers gravitation and cosmology without electromagnetism (though Kaluza and later Klein devised a theory unifying gravity and electromagnetism by adding an fifth dimension to General Relativity, which can then be decomposed into 4-dimensional GR and Maxwell's equations).
I mis wrote, he talked about the experiments done to verify general and special relativity. Michelson-Morley was one of them that sticks in my mind along with some traveling atomic clocks. We never recreated the experiments like some of the other commenters did in their classes.
you only had to take one physics class, and it was quantum electrodynamics??? That sounds to me as if someone said "The only math class I've taken was differential equations."
I think I placed out of the physics prerequisites (everyone was expected to have some physics in high school and we went over that and more in a mechanical engineering statics/dynamics/fluids class we all took at the same time) and QED was a standard first semester sophomore year class in the electrical engineering curriculum, the professor made it a lot of fun though every class I remember him deriving equations for thirty minutes on the overhead projector as he explained things, and it was the largest class I had with fellow electrical engineering majors, there was an advanced calculus/diff eq class and linear algebra class during our freshman year.
We did it with several hundred volts (DC, scary) in college and it was pretty fun collecting the data and watching the numbers fall out in excel doing the analysis.
We also did it in uni, it was very exhausting. And after a full day of measurements noone ever had enough data to see the quantization of the charge of electrons.
I read Chasing the Molecule by John Buckingham recently and thoroughly enjoyed it! It give a good outline of the history of modern chemistry in a way that felt accessible but still thorough.
It also does a great job of explaining the different characters and their stories. Some little-known who moved chemistry forwards in profound ways, and others, very well-known, who through their loyalty to false theories ended up holding it back.
It's also a pretty short book when helps make it feel accessible.
Yes, often what is taught is taught in a manner that seems mysterious in origin, as if it were revealed, certain and final, and developing a sensibility like that concerning scientific matters is not good. You could argue that the viability of science as such rests on certain articles of faith, but the particular findings of science themselves are a matter of demonstration, interpretation of demonstration and argument making use of interpreted demonstration, as well as the making of certain working assumptions that do quite a bit of quiet heavy lifting. The last, I think, receives too little attention, but it also supports the idea that practical and pragmatic rather than theoretical motives and habits drive much of scientific activity.
Why assume "that the oil formed a single layer of molecules — a monolayer" ?
That is a very fundamental assumption, and could have been wrong as well (we know it is right, because the values match with more accurate recordings, but still...)
Yes! Not to get too political, but I saw a lot of this during the Covid debates, e.g. "Trust the science!" Noooo! Science is not just something you're supposed to "trust", but something that's supposed to be supported by evidence.
Yes, I definitely understand that most people don't have the training and background to understand complex scientific topics, and in some ways we do have to trust the scientific community if we're not a part of it. And I get frustrated by the common calls of "Do your own research!", which often means "Look at these YouTube grifters with absolutely no training who are just spouting stuff with no research of their own." But even the underlying problem with that is that most people aren't trained to evaluate the quality of data and motivations of people making it, and that is what scientific education should be about. For example, I may have to "trust" the scientific community when it comes to data about infectiousness of COVID because I'm not an epidemiologist, but how that data is translated into rules and regulations is a policy call, and that policy call is not necessarily one where the epidemiologists are the experts. I shouldn't be told to "trust the science" as though I should just accept policy recommendations even if I do accept the underlying data about transmissibility.
It isn't like "scientists" (whatever that means) don't also delegate to equipment or hardware manufacturers or (mathema|statis)ticians or compilers (or grad students, LOL). Sure they calibrate & cross-check, but while oil spread-out over water is easy to replicate at home in a few minutes with an oil dropper (maybe even with precocious (maybe pre-)pubescent kids not just Feynman Lectures on Physics Caltech Undergrads [1]), "more interesting/complex questions" usually have "full stacks" that are impractical to fully vet in general (see, e.g. Ken Thompson's _Reflections On Trusting Trust_). Epidemic disease coupled with human behavior is definitely getting into "holy crap complex" territory.
In its barest essence the problem is this - delegation affords so much that it is basically unavoidable, but trust sure is tricky. The https://en.wikipedia.org/wiki/Demarcation_problem - searches for how to demarcate trustworthiness. Sorry to say, but there is a long history of failure to get consensus. It's notably a competitive game and as long as anything has been deemed valuable there have been cheap knock-offs (e.g. Fool's Gold), but things like The News you seem to complain of (e.g. Crichton's Gell-Mann Amnesia [2]) or "conclusions", being more abstract than metal (often the metaphorically concrete), are trickier still to discern reliability.
It may be the single most central (in latitude-long's of WHAAA? coordinates) problem of today's human condition / experience. I think it's a https://en.wikipedia.org/wiki/Wicked_problem BUT the problem applies recursively to advice from anyone about trust/delegation (or about anything else). So, don't trust me. LOL. ;-) I don't think others can really answer these questions for someone. Part of life is learning to live with uncertainty, however precisely modeled. I'm just trying to share a perspective (and several relevant links!) on some of the principles involved with someone who seems interested in and frustrated by the questions.
So very true. The greatest science teachers understand the power that comes with the stories of scientific discovery.
Carl Sagan’s Cosmos and some of Richard Feynman’s best lectures come to mind as some of the most memorable examples, but I’m certain all the best teachers out there know to incorporate the historical and human aspects to bring the essential perspective and natural mnemonic anchors to otherwise “dry” subjects.
As part of 9th grade biology we had to read "Microbe Hunters". The grades ahead insisted that it was awful and boring but I devoured the whole thing in a weekend. So thankful that it was part of the curriculum.
How we derived the laws and theories is science. (Some of the other commenters are mixing this together with biographies of the scientists, which is not science but is sometimes interesting in its own right.) The laws and theories in isolation are just trivia, and any class that teaches just those cannot truthfully be called a science class. Demand a better education.
Both have their value, both the process and the results. And given the immensity of scientific knowledge, you can only learn so much of it in a K-12 education, or even in college.
I don't think it's a priori wrong to teach students our current understanding of the world, without going into the details of how we came up with it. I also don't think it's wrong to add those details, but the more details you add, the less of the full picture you'll be able to present. And I definitely don't think it would be a good idea to teach children how we do science, without teaching them what we actually learned from doing it.
I'd also say that the reality of some of the process is extraordinarily boring ("we kept meticulous records of precisely where on the sky various stars were each night, and how their position changed, for a few hundred years, and tried finding a function that matched those numbers; for a few hundred years, we kept adding more and more circles to correct things, until Kepler came up with some ellipses"). And that for many children, learning history is already a huge bore, learning the history of science in addition would make science classes much worse. For others, the opposite is true.
The results are useful in engineering, but the fact that the results are useful does not mean that a class that teaches just the results is a science class.
You don't have to include the boring bits of who paid for the research or the day to day lives of the researchers. That isn't science, and it doesn't help the student understand science. A mere description of the fact that Tycho Brahe kept meticulous records of the positions of the planets in the sky and a walkthrough of the math that shows this data matches elliptical orbits and the math that shows that Newton's laws lead to those elliptical orbits is sufficient. The fact that there is a discrepancy for Mercury motivates further developments.
The results are what science exists for, ultimately. If you're not going to go do science, you still benefit from understanding what the world is - not just for engineering, but as a basic human need for understanding the world you live in.
Most of the general public would be better served with more emphasis on the history of science. Knowing how and when it happened makes it seem less like magic dogma given to them from the elders, against which rebellion is appealing.
When I was a tutor, mostly doing math, when it came to polynomials and that range, I would trick my students into deriving the quadratic equation. It's not even a full page. Almost all of them finished with a strange expression, and then we had the little "it was always there, waiting for someone to find it" chat.
Some people care about the history, some don't. I find when people talk about astrophysics stuff, most of them do not know the history and ought to, because most of their interpretations fall into the "Yes, that was a question in the 1960s but eventually ..."
If you want one for relativity, I strongly suggest Was Einstein Right? by Clifford Will. It dates from 1986, so it is nearly forty years behind now, but it covers the many experiments and tests of relativities special and general.
>that laws and theories are presented as just something that you need to memorize
That's part of a larger problem in how science is presented. It is presented as something that is true, when it isn't. It is a model that describes reality. The models you are learning in high school and entry undergrad classes are mostly wrong models whose main use is that they are great building blocks to more complex models, as they work well enough in ideal conditions and correlate well enough with our exist. Yet even the best, most up to date models, aren't right. They work well enough in the places they are used that we can bet human lives on them, but that doesn't mean they describe what the universe is actually doing. Unless someone finds a way to crack open up the universe and check the "source code", we will never know exactly what the universe is doing and are limited to only ever improving models that approach the truth, like a sum that converges on a value at infinity but never equals that value for any finite sum of the series.
but chronological order of scientific discoveries does not imply conceptual linearity, so i kinda get why colleges and schools do not go for that kind of approach
Why "instead" ? they seem completely different from each other
Hunt for Vulcan is a fun history lesson with some interesting insights about human nature. It's history of science, not science. It took about 3 hours to read and I had a lot of fun with it.
"Rayleigh divided the volume of the oil by the area it covered, thus estimating the thickness of the oil film. Assuming that the oil formed a single layer of molecules — a monolayer — then the thickness of the oil film is the same thing as the length of one oil molecule.
This is how Lord Rayleigh became the first person to figure out a single molecule’s dimensions, many years before anyone could see such molecules."
This is fascinating, but wasn't it still a bit of a conjecture to assume the oil would spread to a minimum thickness of one molecule? Did he have any doubts, like that surface tension might keep it thicker? Or other clues hinting it was indeed a monolayer?
My question exactly.. I hope someone can chime in :)
EDIT: Thinking a bit more... I suppose it's a reasonable assumption that the molecules (mostly) wouldn't stack on top of each other. They all want to get lower and perhaps the resistance to the oil spreading out is much lower proportionately that the gravitational force encouraging the oil to flatten
I guess oil is repelled by water, so when it's poured on top of water it's more like floating on top. So the water pushes up, gravity pulls down and the oil molecules pull on each-other, there is no horizontal friction, allowing the oil to spread out this way. Whereas the oil does slightly stick to your plate, as can be observed when moving the plate around, so it won't spread as thinly?
There’s a couple of possible reasons. First, you probably spilled more oil onto the plate. In the experiment, 0.81 milliliters of oil spread out until it covered a circle with diameter 84 cm. Most spills would be more than a mL of oil, and most plates are much smaller.
Second, most plates aren’t flat. If you have an area of the plate that is at a lower elevation than the rest, the oil would pool up in that area.
Third, even if you fill the plate with water, you could have elevation changes due to surface tension of the water. If the water is concave up, the oil would float upward and form a ring around the edge. If the water is above the surface of the plate, held in just by surface tension, the oil would float upwards and form a bubble at the center of the plate.
Fourth, you could have something else on the plate that acts as an emulsifier. Whether a bit of egg, some pasta water, leftover detergent, these would break up the oil and prevent a film from forming.
The easiest way to have a flat surface is to do the experiment in the center of a much larger body of water, since any effects from the surface tension would be at the edge.
I believe this is at least part of the explanation. Although there might have been some further developments in the 100 years since this was published
Oleic acid on water forms a film one
molecule deep, in which the hydrocarbon chains stand vertically on the water surface
with the COOH groups in contact with the water.
Acetic acid is readily soluble in water because the COOH group has a strong
secondary valence by which it combines with water. Oleic acid is not soluble because
the affinity of the hydrocarbon chains for water is less than their affinity for each other.
When oleic acid is placed on water the acid spreads upon the water because by so doing
the COOH can dissolve in the water without separating the hydrocarbon chains from
each other.
When the surface on which the acid spreads is sufficiently large the double bond
in the hydrocarbon chain is also drawn down on to the water surface, so that the area
occupied is much greater than in the case of the saturated fatty acids.
Oils which do not contain active groups, as for example pure paraffin oil, do not
spread upon the surface of water
Perhaps he was observing the layer making sure it had integrity? Oil layers famously have an optical effect (iridescence from interference of reflections). This effect would transition as the layer goes from >= 1 molecule thick to <= 1 molecule thick (on average). It's likely possible to pinpoint this transition experimentally and then using the oil volume obtain the molecular layer thickness.
To me, the much more questionable assumption is that volume is preserved when a liquid spreads out to a layer one molecule thick.
There's no reason why the volume you get when each oil molecule is surrounded on all sides by other oil molecules should be the same as when each oil molecule has air above and water below. Can anyone explain why this is so?
there has to be some missing information on how he found the area of water that fully consumed exactly that amount of oil as it simply doesn’t make sense without that. for instance one can spread a teaspoon of oil over 1, 2, n square meters and at some point the oil goes from m later thick to one to less than one.
Such an experiment was described in a science book I read as a kid. They dissolved oil in alcohol so as to measure a very small quantity of oil, and then a a knitting needle was used to stretch the oil film across a plastic container filled to the edge with water (until the film breaks).
> Assuming that the oil formed a single layer of molecules — a monolayer — then the thickness of the oil film is the same thing as the length of one oil molecule.
How did he know that the film of oil was one molecule thick?
It feels like a huge assumption to me, but maybe this blog post left something out.
Rayleigh's experiment was actually trying to solve for the minimum thickness of oil required to stop some camphor shavings from moving around on the water. He never states it explicitly, but I think the assumption is that the minimum thickness required to stop the shavings' movement would be such that the oil volume 'just' covers the surface, ie. is 1 molecule thick everywhere and hence the shavings never touch water. I think he's specifically making a slightly more clever point about surface tension, but that's a little beyond me.
Reading the paper, there is no mention of sizes of molecules. Did Rayleigh actually make the connection between film thickness and molecular size at some point? Or is that just modern retconning?
Replying to myself, I found 1899 paper which is more explicit on the matter, and shows how Rayleigh was not all that certain about the results:
The comparison of the present with former results throws
an interesting light upon molecular magnitudes. It has been
shown (Proc. Roy. Soc. March 1890) that the thickness of
the film of olive-oil calculated as if continuous, which
corresponds to the camphor-point, is about 2.0 μμ while
from the present curves it follows that the point at which
the tension begins to fall is about half as much, or 1.0 μμ
[...]
If we accept this view as substantially true, we
conclude that the first drop in tension corresponds to a com-
plete layer one molecule thick, and that the diameter of
a molecule of oil is about 1.0 μμ
XXXVI. Investigations in Capillarity:—The size of drops.—The liberation of gas from supersaturated solutions.—Colliding jets.—The tension of contaminated water-surfaces
If we assume that the "about 2.0 μμ" value is just the previously mentioned 1.63 nm value rounded up, then that throws a wrench into the story, in particular this bit from blog post
> Rayleigh’s final result was 1.63 nanometers. Olive oil is mainly composed of fat molecules called triacylglycerols, and we now know that they measure about 1.67 nanometers in length, implying that Rayleigh’s “primitive” estimates were off by just 2 percent
is more of a numerological coincidence, the actual estimate that Rayleigh gives is half of that!
"The thickness of oil required to take the life out of the camphor movements lies between one and two millionths of a millimetre, and may be estimated with some precision at 1’6 micromillimetre."
Looks like a primary guess to me, even if the table lists more data points.
It's really (really) quick but the first line of the second para is:
> In view,
however, of the great interest which attaches to the determination of
molecular magnitudes, the matter seemed well worthy of investigation...
So it seems like his main goal was to understand the size of molecules via his film-thickness measurements
If you try the experiment lots of times with drops of different sizes you find the oil layer always has roughly the same thickness. That's an interesting observation that calls for some kind of explanation, and the hypothesisis that the thickness of the oil layer is the length of one molecule is perhaps the most obvious and plausible explanation. Then one would look for confirmation, of course. (What was the next thing to confirm this, historically?)
It feels intuitive that a thin fluid on a low-friction surface (like water) would spread out "as much as possible" given enough time. There certainly may be confounding factors, but it seems like a reasonable thing to pin as an "assumption" in a hypothesis. I.e. he didn't have to "know" - assumptions are OK, and I don't feel like this one is huge.
> It feels intuitive that a thin fluid on a low-friction surface (like water) would spread out "as much as possible" given enough time.
Most fluids do not behave this way in most circumstances, because of surface tension, so it's really not intuitive.
This experiments is one of the few ways you can get an accurate measurement. Many other fluids will either mix or end up as bubbles/blobs many orders of magnitude thicker than a molecule.
I'm confused, the blog wrote "known amount of water," so was it a closed little area like a bathtub? If you added a ton of oil wouldn't it spread out as much as possible aka 600 molecules thick or whatever?
My understanding is that the actual body of water was larger, but that the oil would only spread out to one molecule of thickness. So you start with a larger area of water, and measure the diameter of the resulting oil slick.
Scientists frequently have to make assumptions in order to make progress.
Famous example is Darwin figured out that traits are inheritable by natural selection, and this is the driving force of evolution, without having any concept of the physical nature of DNA, or how genes could change (eg. by DNA mutation) to develop adaptations and thus make an organism more fit.
This is why I guess I was never really interested in scientific experiments personally and decided to study mathematics. These assumptions don't seem justified to me. At least in mathematics you always state these assumptions or hypotheses very clearly, or make them into axioms.
I don't know if anybody challenged Darwin on that point. It's an interesting question.
The simplest explanation is that he deduced such a physical mechanism must exist but the science and technology available at the time could not locate it.
If there were multiple layers of molecules then the film would spread out over a wider area. With repeated experiments it would be clear that films are always an integer multiple of this thickness and never thinner.
Except that you could have part of the surface covered in 1 molecule, and another portion covered in 2 molecules. Since you never directly measure the thickness, this would produce the same apparent thickness as a uniform 1.5 molecule thick layer.
That's not how fluids work. The molecules spread out to form an even surface everywhere, so you can't have local high spots. You'd have to put in enough oil to cover the entire surface, and then put in more.
Yeah and the point is that there is more embedded knowledge about surface tension here. For example if I put a small drop of water onto my desk, it does not spread out into a thin film of one water molecule thick. It remains a droplet due to surface tension.
And if you put an oil drop into that little bead of water it will spread out because it destroys the surface tension. That's why Rayleigh was playing around with it to begin with, and the reason why a thin film of oil calms the surface of water.
The molecular scale was well estimated (at least for the gaseous phase of matter) by 1865 (25 years earlier not 5 as the incorrect HN title would suggest) https://physics.stackexchange.com/questions/13757/how-was-av... (and guesstimated by just "following your nose" in Gandalf-of-Lord-Of-The-Rings-ese in 1646!)
Rayleigh's experiment is just accessible requiring very little training / background to describe. To interpret as a monolayer is honestly probably not so accessible at all, though, and a weakness of the atomsonly.news piece and seemingly not even done by Rayleigh himself. Modern retconning as zokier says elsewhere.
Perhaps at the time it was sufficient to define "molecule of oil" as "the height of the amount when spread maximally across the surface of water", and it just so happens that height is only 1 actual molecule
An idea: if oil forms a two dimensional shape, ie a single layer of molecules, then adding 2x amount of oil would give you twice the area. If it is three dimensional, say oil makes a bubble, then it would look smaller.
Of course this also fails if the oil formed a disc of X layers of molecules
> Seems questionable that Rayleigh would have known that oil molecules are hydrophobic on one end and hydrophilic on the other.
That's not a true thing, so it kinda doesn't matter. Surfactants (soaps, emulsifiers) have hydrophobic and hydrophilic ends. Oils are just straight up hydrophobic and nonpolar and don't have a water-loving end.
He certainly knew oil was hydrophobic. I don't think the hydrophilic nature was necessary for the logic.
If it was, I'm sure he knew that soap oils are both hydrophobic and hydrophilic and had ways of figuring out that soap oils consist of a single type of molecule and aren't a mixture.
If that's true, then the ChatGPT answer isn't wrong, at least for the specific case of olive oil.
I love how a few self-appointed guardians of hackerhood are able to declare certain resources as haram, even when they propose a plausible answer to a question that went unanswered more than once in the thread. Instead of embarking on a discussion that leaves us all a bit better informed, the literal messenger is attacked. Does that gratify intellectual curiosity? Really?
No the idea that Rayleigh knew the film was one molecule thick, let alone why it was one molecule thick, is clearly made up. The paper makes it clear that he was reporting the thickness, and thought this might provide information on molecule size.
Whatever possessed you to post that bilge, despite finding it fishy, is beyond me. In the future, you might choose to keep such interactions to yourself.
Agreed, although it does make me wonder whether the number of mistakes chatgpt comments make would truly be greater (or at the least more harmful) than the outstanding number of folk who are confidently wrong in a way only obvious to domain experts. It’s easier to be skeptical of a bot.
I would have loved to have had a course in school about "The Design of Scientific Experiments." One that described the processes of landmark historical experiments from antiquity onward, and challenged students throughout: "Given this set of constraints, how would you design and execute an experiment to estimate the size of the Earth? Disprove phlogiston and luminiferous aether? Measure the speed of light?"
I don't think many people today would be able to propose the Michelson Morley experiment and then actually do it. It was truly heoric (and Michelson was a genius).
We did this oil/water experiment in freshman physics or chemistry lab. It was rushed, everybody just did the minimum, the teachers barely explained any of it, and then we moved on.
I agree. The Michelson Morley experiment reminds me of some difficult algorithms: simple only in hindsight, and implementation is _hard_ to do correctly.
Experiments are HARD. There is a joke among physicists that theoreticians are washed up by 35 but experimentalists don't even get started until 45.
To make a physics experiment work you have to be ridiculous about recording details and have a strong intuition. You have to design the experiment such that you can differentiate between "hypothesis wrong" and "equipment doesn't work" because you don't know the answer.
(For example: When they turned on LIGO for the first time, they almost immediately caught a great event. Huge victory party, right? Nope. They promptly ignored it assuming that something was wrong with the machine. And it was only after significant post analysis and correlation that they decided that it was a real event.)
And this is my sticking point with a lot of "Science skeptics" around that have skepticism as their personality
Make no mistake, I do take scientific discoveries and knowledge very serious, and knowing the stories make it appreciate more the efforts and the work it took to get there
But a lot of times people think the experiments give a very clear-cut results, when it's more like "one line is squiggly down and the other is squiggly up" with data being barely over 5 sigma
The title of this thread appears to be wrong, because the parent article says
"But a little experiment that Rayleigh performed in 1890, inspired directly by Franklin's observations, is not nearly as well-known."
Therefore Rayleigh computed the size of molecules in 1890, not in 1870 (in 1870 Rayleigh was young and not known yet for any original research).
While Rayleigh has devised a novel method for determining the size of molecules, it should be noted that the first who has succeeded to determine the size and weight of molecules was Johann Josef Loschmidt, in 1865.
The publication of the weight and size of air molecules by Loschmidt is one of the most important milestones in the history of physics.
Until that moment in 1865, the theory of atoms revived by Dalton could still be considered as some kind of fictitious model that explained some features of the chemical reactions and of thermodynamics, but which might have been wrong and which would probably be replaced by some better model.
Starting from that moment, the atoms and molecules could be weighed and counted, so their reality was no longer questioned.
The determination by Loschmidt of the size and weight of air molecules was enough to determine the sizes and weights of any other known atoms and molecules, making use of the relative atomic weights that could be determined from chemical reactions and which were already known.
Moreover, a few years later, in 1874, George Johnstone Stoney has used the results of Loschmidt together with the theory of the existence of an elementary electric charge published by Maxwell one year before, in 1873, to compute the value of the elementary electric charge. Some years later, Stoney has given the name "electron" to the elementary electric charge, which has been the source of a very large number of words in modern science and technology, from electronics to hadrons.
We recreated this experiment in one of my university physics classes. It was a lot of work, and our results weren't nearly as good, but it was instructive and interesting. The equipment requirements were completely reasonable for an undergrad physics lab. I highly recommend giving it a try if you can.
Since January 2014, all ICANN accredited registrars (like Namecheap) have been required to verify the contact information (Registrant Whois) of customers registering domain names. This includes modifications to the contact details.
It's by a guy called Don Lincoln and it's about how we established things like the existence of atoms, the speed of light, and many other fundamental things that are good to know.
It's also an audiobook, though the lectures are easier to follow.
A few days ago, there was a HN post about surface acoustic wave filters, and a commenter mentions how inspired the inventor of it must have been(https://news.ycombinator.com/item?id=41604937).
Cool article. They somehow got the formula wrong though, the formula on the screenshot has an additional factor of 0.9 that accounts for the fact that 1l of oil is not 1 kg. Perhaps it's intentional, but for something so simple I don't think it needs to be dumbed down even further.
I went to a talk by a very old physicist. At the end of his talk, he said, recalling from memory, all of the great experiments of the past were done by nothing. If an experiment costs more than $100, I am out.
His setup has mud in a jar and bacteria in it which you can see with a simple microscope or handheld lens.
That's a bit harsh. To give one counterexample, the Michelson-morley experiment put the figurative nail in the coffin of centuries of speculation about the "luminiferous aether". The experimental apparatus was a table-sized precision carved slab of sandstone floating in a huge vat of mercury, holding the highest precision optical equipment of the day. I suspect it cost rather more than $100 even in the 1880s.
Ten years earlier and she didn't publish it right away. That really goes to show how much more difficult it was for a woman to become a scientist back then.
These are the best kind of posts, where there's something I've never even heard of before. I never knew 'oiling the seas' was a thing, or that it (apparently?) works.
Luckily it wasn't my grade that got this experiment as the practical exam in one of the National Physics Olympiads I went to... :) poor souls, most got answers orders of magnitude away.
> I love this story because it shows, at least anecdotally, how deep scientific insights can emerge from the simplest of experiments. It's a testament to the idea that you don't always need sophisticated equipment to unlock the secrets of nature — sometimes, all it takes is a drop of oil and a bit of ingenuity.
The credit for proving the existence of atoms is more often associated with Einstein's explanation of Brownian motion and Jean Perrin's experimental confirmation, even though earlier work by Lord Rayleigh, Benjamin Franklin, and others hinted at the molecular structure of matter.
> and he charted the Gulf Stream’s course across the Atlantic ocean, noting that ships traveling from America to England took longer than those going the opposite direction
?? Has the Gulfstream changed direction in the intervening years?
The page is timing out for me, but is it the inverse problem of the time when Steve Mould/Matt Parker measured the unknown quantity π, but already assuming a size of the molecules? Presumably Lord Rayleigh already had a at least a good order-of-magnitude approximation of pi...
By 1870 pi was known to several hundred decimal digits, for something like this calculation where you have other large sources of error Archimedes approximation from 2 millennia earlier would probably be fine. (<1% error)
Its not ancient times, some of the most accurate measuring instruments of that time are of a precision that you'd still need a few hundred or thousand dollars to buy today. The tooling wasn't primitive by any means.
That's funny, thanks for sharing. I was watching his video where he's saying "you can see it right there, look how much calmer it is, it looks like ice" and was thinking "I don't know what he's talking about I don't see ... oh, that ice patch is water"
We did this same experiment in school, with a tiny pinprick of oil, estimating the volume of the drop as a sphere, and a small water tank, and then estimated the area of oil slick as a circle.
The actual manuscript from Rayleigh [1] explains it better: the area is the entire area of the vessel the oil was placed in, and the thing actually being measured was how much oil was required for it cover the whole area.
He used a fixed area (a 33 inch diameter bowl) and measured the weight of oil required to just about calm the entire water. That turned out to be 0.81 milligrams.
Some powder is added to the water, which covers the surface of the water but not the oil patch (which is circular). Then the oil patch diameter is measured.
When we did it in high school (70's) we just used compound that had a long chain (soap?) and only one end dissolved in the water. It was very easy to measure and calculate the size of the molecule . We had a series of these simple experiments. Another I recall was measure the speed at which certain volatile compounds moved through the air.
I definitely learned that all science doesn't have to involve complex equipment.
The original way was to cover the surface of a round bowl with oil. It certainly makes a lot more sense to me than trying to measure a floating disk of oil.
We performed this experiment in high school chemistry and it has remained with me as one of my deepest aha moments.
It has become fashionable in foodie circles to mock the idea of adding oil to boiling pasta so as to prevent stickiness. The argument against seems to be that oil floats and cannot possibly affect the pasta, unless you add so much that the pasta becomes slimy. But I maintain that a drop of two in boiling water is enough to coat all the pasta in a single layer of molecules. The agitation of the water spreads the oil evenly as a kind of colloidal suspension.
All these fancy restaurants with elaborate methods to avoid sticky pasta.
>"not more than a Tea Spoonful," according to his diary — Franklin poured it onto the agitated water. The oil spread rapidly across the surface, covering "perhaps half an Acre" of the pond and rendering its waters "as smooth as a Looking Glass."
