Feynman wrote a exceptionally clear explanation of this experiment and what it meant:
- "To illustrate the whole problem still more clearly, imagine that we were talking to a Martian, or someone very far away, by telephone. We are not allowed to send him any actual samples to inspect; for instance, if we could send light, we could send him right-hand circularly polarized light and say, “That is right-hand light—just watch the way it is going.” But we cannot give him anything, we can only talk to him. He is far away, or in some strange location, and he cannot see anything we can see. For instance, we cannot say, “Look at Ursa major; now see how those stars are arranged. What we mean by ‘right’ is …” We are only allowed to telephone him."
- "Now we want to tell him all about us. Of course, first we start defining numbers, and say, “Tick, tick, two, tick, tick, tick, three, …,” so that gradually he can understand a couple of words, and so on. After a while we may become very familiar with this fellow, and he says, “What do you guys look like?” We start to describe ourselves, and say, “Well, we are six feet tall.” He says, “Wait a minute, what is six feet?” Is it possible to tell him what six feet is? Certainly! We say, “You know about the diameter of hydrogen atoms—we are 17,000,000,000 hydrogen atoms high!” That is possible because physical laws are not invariant under change of scale, and therefore we can define an absolute length. And so we define the size of the body, and tell him what the general shape is—it has prongs with five bumps sticking out on the ends, and so on, and he follows us along, and we finish describing how we look on the outside, presumably without encountering any particular difficulties. He is even making a model of us as we go along. He says, “My, you are certainly very handsome fellows; now what is on the inside?” So we start to describe the various organs on the inside, and we come to the heart, and we carefully describe the shape of it, and say, “Now put the heart on the left side.” He says, “Duhhh—the left side?” Now our problem is to describe to him which side the heart goes on without his ever seeing anything that we see, and without our ever sending any sample to him of what we mean by “right”—no standard right-handed object. Can we do it?"
Ha, I remember this from an old Open University TV lecture. They suggested looking at the spin of a particular particle. So eventually the alien arrives and it goes to shake hands/tentacles, but it’s not holding out the right one as it has been taught is customary …
BOOM annihilation
Ah, the alien was made from antimatter, where the spin is different. Oops.
“Try to teach an alien on a telephone about left and right” actually sounds like a fun game to try with a class full of kids.
I would solve this particular circumstance by using the andromeda galaxy (“the closest galaxy”) as a reference, but it definitely stumped me for a bit.
"He is far away, or in some strange location, and he cannot see anything we can see. For instance, we cannot say, “Look at Ursa major; now see how those stars are arranged. What we mean by ‘right’ is …” We are only allowed to telephone him."
The rest of the story about developing a way to communicate with the alien is a significant part of Andy Weir's Project Hail Mary, which is also a good book for kids.
I would love to try it, but I think the problem is hard enough to explain to an adult. I think it's difficult to describe the constraints. I've tried to explain this problem to adults and they just didn't really get it and the problem sounds like either a riddle or a bunch of nonsense rather than a physics problem with deep implications for the laws of nature.
As long as he exists within a planet instead of unknown dimension, we can simply give them a slightly modified version of Wikipedia (removing arbitrary data, arbitrary metadata; language does not matter given it is a plaintext we can encode into transmission). They will eventually figure it out.
Why couldn't we just tell the aliens to observe the direction of the field lines of electromagnetism? We could define for them "lower potential energy direction" by describing gravity, then use that phrase for describing the motion of the electrons in a conducting wire around a magnetic coil.
No, the electrons actually move in the same direction always, just as a free falling object always moves towards the locally dominant mass. We could call the direction of electron movement "right".
It's the magnetic field that has the arbitrary sign convention. You can't determine the direction of a magnetic field from observations without using the right hand rule.
You don't have to know the sign, you could tell which way the electrons are going.
We tell the aliens: you take all sorts of organics with liquid inside (on earth we typically use a lemon, but other organics will do), and put a stake of element 29 in one side and a stake of element 30 in the other. You then connect them with a length of element 29. Keep trying different organics until you find one that works. They might not have lemons, but there is a good chance that something will eventually work.
You'd need to predefine what the atomic numbers mean and some other things, but we're already assuming some level of communication already being established so this aspect is not far-fetched.
Now arrange the apparatus such that the element 29 side is near you, and the element 30 side is far from you. Additionally, ensure that the wire is up (further from the locally dominant gravitational mass). Now place an election between the "lemon" and the wire. See which way the election moved? That was right (or left, I don't remember).
Edit: if you make the electron move, it will move towards or away from the wire, depending whether it's moving in the same or opposite direction as the electrons in the wire.
Set up whatever apparatus you like, you can always set up its mirror image, and then the electrons are going in the opposite direction. So which is right and which is left?
Remember you haven't yet established with the alien what you mean by right and left, so you won't be able to instruct it to set up your apparatus rather than its mirror image, and of course you can't appeal to the right-hand rule.
This problem has no solution because electromagnetism is right-left symmetric. You would need to use the weak decay (and assume that your alien is made of matter rather than antimatter)
I addressed that. We know which way the electrons flow from the anode to the cathode. I specifically chose this example because of the right-hand rule.
... but we can determine left and right via the chirality in chemistry? sugar water in a tube has a 'right-handed' chirality (where it twists polarized light to the right)...
"left is the handedness of the rotation of the neutrino"
The inverse enantiomers of sugar function exactly the same way, with the correspondingly inverted enzymes. The chirality of sugars isn't a universe-wide property inherited from fundamental physics, but just a path-dependent quirk of the evolutionary history of biochemistry on Earth. "Universal" for Earth-life only.
(The strength of the weak force is very certainly far too... weak... for it to have plausibly influenced this selection process. It was 100% chance).
I thought about this for a bit. One easy to use explanation for left and right is a number line. Smaller numbers are on the left and larger numbers are on the right. It's still an assumption that alien species would count that way.
There's nothing you possibly draw on paper that answers the question, in isolation. A diagram on paper means exactly the same thing if you simultaneously (i) flip it, and (ii) flip your mental interpretation if it.
Or: if you run a software program on a raster image, there exists a different program that returns identical output given an input image which is mirror-flipped copy of the first one. (It's just the first program, plus a pre-processing step that flips its input (which is computable). If f is a computable program, and f(img) = "left" and f(flip(img)) = "right", there exists a computable program g=f∘flip such that g(img) = "right" and g(flip(img)) = "left").
Similarly: there's nothing you can do in complex analysis that can distinguish the case where all +sqrt(-1)'s are swapped with -sqrt(-1)'s. Nor can you invent any math whatsoever that has an isomorphism to the plane, that works differently if the plane is mirror-reversed.
But we can distinguish i and -i by convention and keep consistent right? Akin to sending the distant alien a sample? It’s in the abstract that we can’t really tell them apart. But as soon as we are given any kind of starting point to form a convention, like the first mathematical textbook tells us which is i and which is -i, we have enough?
I think of an unlabeled, unconnected graph of two vertices. If I just pick one and call it A say by pointing to it, that’s enough. The trick is to do it for limited communication partners like the alien right?
Have them project an imaginary line from where they stand and in the direction they are facing. Have them mark the numbers 1 2 3 in the ground as they walk forward. Now have them stand facing the number two. Now you say if you are standing left side of the line looking left to right the numbers would go 3,2,1 if you are standing on the right side looking left to right the numbers would go 1,2,3
Edit: it's a bit silly though,
I think if they could understand our language well enough to convey complex scientific ideas like an atom and its size, then smart people could probably find a good way to convey direction
> it's a bit silly though, I think if they could understand our language well enough to convey complex scientific ideas like an atom and its size, then smart people could probably find a good way to convey direction
You completely missed the point of the original thought experiment. The whole experiment already assumes that the Martian understands the concept of direction perfectly. That's the premise of it.
The hard part is to convey which direction is which. It's a completely different thing from the concept of direction.
It's not about Martians is so stupid and we need to try very hard to make them even understand what direction is. It's about whether there is a universal and fundamental (as fundamental as elementary particles) reference to distinquish left and right.
> Now you say if you are standing left side of the line looking left to right the numbers would go 3,2,1 if you are standing on the right side looking left to right the numbers would go 1,2,3
The Martian doesn't know how to "looking left to right". He doesn't know which side is left. That's the whole point.
Is the number line even universal among humans? Do cultures that read top-to-bottom or right-to-left still conceptually sort the larger numbers to the right?
I think this still illustrates the problem, though: where is the start of the number line? Perhaps this alien species has a right-to-left written language. Or top to bottom. How would one help orient the alien to the left to right numbering system used in this language?
Very interesting thought experiment while drinking my coffee this morning!
> Lee became Dr. Fermi’s sole doctoral student in theoretical physics, meeting with him every week. It was an extraordinary learning experience, partly because of Dr. Fermi’s teaching technique, which Dr. Lee explained in the 2007 interview with the Nobel Institute. “‘You see,’ he said, ‘there are things that I would like to know,’” Dr. Lee recalled Dr. Fermi saying. “‘Lee, why don’t you look up and give me a lecture next week.’” “I was very happy to teach Fermi,” Dr. Lee added. “Of course, this is an excellent way of building the student’s confidence. And then he would ask me questions and I would have to answer.”
Was fascinated by this. His advisor, Fermi, made Lee teach him stuff, not the other way around!
> Fermi, made Lee teach him stuff, not the other way around!
In grad school, one of my profs said something to the effect of, "We expect you to aggressively eradicate any ignorance you have on the whatever papers we assign to you before lecture."
Then we were Socratically interrogated in lecture. For me, it was a great way to learn, even if I'm not remotely in the class of Fermi and Lee.
Fermi’s “intuito fenomenale” — phenomenal intuition — and his near infallibility in predicting the results of experiments were characteristics that prompted colleagues at the University of Rome to designate him “the Pope.”
I met Lee briefly, along with a few other Nobel laureates, in 1991 at a weird symposium in Japan. Unlike some of the others, he was very friendly and relaxed. RIP.
Chien-Shiung Wu, who conducted the experiment that proved Lee’s (and Yang’s) theory didn’t share the Nobel Prize with them in 1956. When I read people lamenting the fact that Rosalind Franklin didn’t get the Nobel due to sexism I wonder why Wu is not mentioned. For more information on the circumstances see https://physicsworld.com/a/overlooked-for-the-nobel-chien-sh...
> the fact that Rosalind Franklin didn’t get the Nobel due to sexism
The primary reason why Rosalind Franklin didn't get a Nobel is that she died in 1958. It's maybe not easy to speculate what would have happened in the alternate timeline where she had lived until the Nobel nominations started to happen.
In his memoir of their discovery, The Double Helix, James Watson suggests that, had Franklin not died due to cancer a few years after their ground-breaking research, she might have shared their Nobel. He further speculates that since her protege Aaron Klug later won the Nobel in chemistry for his X-ray crystallography work (techniques she introduced him to), it wouldn't be far-fetched to imagine her having been a double laureate.
The primary reason Franklin didn't get the Nobel is that she didn't contribute the key component of the discovery: that DNA is a double helix that is antiparallel.
I believe a large part of it is that DNA is a famous discovery, and lots of people have heard of the double helix story. far fewer would know about Lee and Yang or understand the first thing about what they discovered.
“subatomic particles, contrary to what scientists thought, are always symmetrical.”
This cannot be called challenging a law of nature. He questions what his colleagues generally believed. He challenges a convention of physics profession not a law of nature. But we know that media must exaggerate to sell papers.
No. What he challenged was an assumed law of nature. All laws of nature are assumed, as you cannot prove them, or only proof them in the context of a theory (which you then have to assume). It was not a convention.
So, before Lee made his discovery physicists believed (or assumed, or conjectured, or theorized) that “the laws of physics were identical whether observed directly or as a mirror image." Lee and Yang proposed that this did not always hold. Their proposal was later confirmed by experiments.
So, what physicists believed before Lee, was not a law of nature. Lee challenged what his colleagues believed to be true.
But you are right all so called laws of physics are provisional.
"for discovering that subatomic particles, [...] are always symmetrical."
"for overturning what had been considered a fundamental law of nature — that particles are always symmetrical"
The first sentence from the subhead is wrong. The second sentence is correct. "the laws of physics are not identical when observed directly or as a mirror image."
Is it just me or does anyone also get this odd feeling when people use phrases like "challenged a law of nature". Makes it sound like he did something that is physically impossible when he actually attempted something that was believed to be impossible or highly unlikely
Yes, it's not only you, it'll less confusing and more accurate statement should be who challenged the understanding of natural laws but then the headline would not be sensational. Anything that challenged law of nature can be considered miracles for biblical examples the creation of Adam and Eve without parents, and Jesus virgin birth.
