Tsung-Dao Lee, physicist who challenged a law of nature, has died
nytimes.com
nytimes.com
- "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?"
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."
Thinking about it, ironically I think the direct mention of Ursa Major might have played a part in that.
Very interesting thought experiment while drinking my coffee this morning!
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.
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?
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
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.
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.
See the problem? :)
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.
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)
BOOM annihilation
Ah, the alien was made from antimatter, where the spin is different. Oops.
"left is the handedness of the rotation of the neutrino"
Steve Mold and 3b1b have videos on the subject.
(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).
neutrinos (the only ones we can detect), however, are left handed.
https://physics.stackexchange.com/questions/240502/why-only-....
We simply point to the neutrino. left v right solved?
Was fascinated by this. His advisor, Fermi, made Lee teach him stuff, not the other way around!
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.”
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.
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.
My PhD advisor worked with Wu at Columbia. He held her in very high esteem.
https://www.amazon.com/Symmetries-Asymmetries-Particles-Jess...
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.
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 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."
Also, this comes to mind: https://www.youtube.com/watch?v=AL8chWFuM-s