Slashdot Mirror
Measurement Shows the Electron's Stubborn Roundness (scientificamerican.com)
OneHundredAndTen writes: A new article in Nature reports of a new, extremely precise measurement of the electric dipole moment of the electron. The conclusion is that, within the margin of error of the measurement, the electron remains a perfect sphere. This implies that supersymmetric theories keep running out of corners to hide, that another nail is driven into their coffin, and that string theory looks less and less compelling. By lighting up the molecules with lasers, "the scientists were able to interpret how other subatomic particles alter the distribution of an electron's charge," reports Scientific American. "The symmetrical roundness of the electrons suggested that unseen particles aren't big enough to skew electrons into squashed oblong shapes, or ovals. These findings once again confirm a long-standing physics theory, known as the Standard Model, which describes how particles and forces in the universe behave."
Well, if electrons are so perfect, that only makes me wonder is Feynman's One-Electron postulate is actually true....
because it was not Feynman who postulated it?
I do not think they are claiming anything of the sort. They are saying that, as alternative theories become less likely, there is more reason to believe the Standard Model could be correct.
Yes.
I'm trying to think of the last time an experiment to try to prove supersymmetry actually worked, and I honestly can't remember one. I do remember a solid handful over the past couple of decades that didn't pan out, though. AFAIK the best argument for supersymmetry at the moment is that someone thinks it would be awesome if things actually were arranged that way. That's pretty much it. At this point I think even string theory is more plausible than supersymmetry, and those guys are as wacky and as out-there as it gets!
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
The abstract:
"The standard model of particle physics accurately describes all particle physics measurements made so far in the laboratory. However, it is unable to answer many questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories that contain particles and interactions beyond the standard model, such as models that incorporate supersymmetry, may explain these phenomena. Such particles appear in the vacuum and interact with common particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which could explain the cosmological matter–antimatter asymmetry, can give rise to an electric dipole moment along the spin axis of the electron. No electric dipole moments of fundamental particles have been observed. However, dipole moments only slightly smaller than the current experimental bounds have been predicted to arise from particles more massive than any known to exist. Here we present an improved experimental limit on the electric dipole moment of the electron, obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field. The sensitivity of our measurement is more than one order of magnitude better than any previous measurement. This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider."
Bingo. You answered the apparent contradiction yourself.
Electrons are point-like particles -- meaning they're so small as to not have a well defined size if any. You describe the electron density for the orbitals of electrons -- which can be many shapes. That's more about the probability of where to find an electron in relation to the type of atom or the molecular bond between atoms.
This article is about the magnetic moment of the electron. So, if an electron were in a known position, this experiment shows that it doesn't matter from what direction in 3-D space another particle approaches this hypothetical electron, it will still get the exact same response. So, the field force-lines around the electron are perfectly spherical in strength.
This was important because electrons have a magnetic moment (like a bar magnet) that we call spin -- either spin up or spin down... which you're likely familiar with in chemistry as the rule that 2 electrons can share the same orbital as long as they are opposite spins. Some alternate theories propose that this means some parts of the electron are more charged than others or that the shape was more like a spinning charged ring instead of a sphere.
We've long known that nothing is actually spinning to create "spin." It's just a label for a quantum property that was somewhat useful as an analogy long ago. Yet, there remains this strange source of angular momentum. This experiment just confirmed that even though there is a magnetic dipole moment, that property doesn't mean the particle itself is distorted in order to express the property.
What's even weirder is that "spin" being a quantum property, is in a strange superposition state until measured and the spin axis can change depending upon the experiment.... with no intermediary direction for the spin. It's a binary choice -- spin up or spin down for any axis tested.... and seemingly random.
TL,DR -- this test just showed that the particle we call an electron is the same when approached from all angles - same charge, same interaction. So, it's "spherical" even though it's point-like. The probability distribution of an electron's location in atomic orbitals or molecular bonds is a different subject.
It does mention the word "sphere" 13 times though. The words "Cube" or "Pyramid" are not present either.
Now if only the Standard Model were an actual theory, instead of a list of empirical observations.
In many scenarios electrons are not well-described by point particles. Their de Broglie wavelength is in the order of one Angstrom, depending on how fast they move. That means you have to take their wave nature into account and the only reasonable description is via the Schroedinger equation (for non-relativistic velocities), or the Dirac equation (for relativistic velocities).
Every end has half a stick.
Everyone always wants to talk about the little tennis balls, but no one ever talks about the tiny little golden retrievers chasing them around.
They are saying that, as alternative theories become less likely, there is more reason to believe the Standard Model could be correct.
The Standard Model IS correct. It has been tested and the once a theory is tested the results cannot be unproven. Now it might be that the Standard Model only works for certain conditions or it might be a subset of a more comprehensive theory. Newton's laws of motion very correctly describe large objects moving slowly but the theory was subsumed into Einstein's theory of general relativity. Newton's laws fall out of relativity under certain conditions to a high degree of accuracy and utility. We might come to a better and more comprehensive understanding of the universe but what we have already proven about the Standard Model will stand forever.
Now we know that the Standard Model is an incomplete understanding of the universe. But what it has been shown to describe it describes very accurately and that will always remain true no matter what else we learn in the future. It makes testable and correct predictions about the behavior of some bits of the universe so QED it is correct for at least those phenomena.
Now if only the Standard Model were an actual theory, instead of a list of empirical observations.
It is a theory that made testable predictions (like the Higgs boson) that were later proven to be correct via experiment. If that's not a theory then nothing is.
Now if only the Standard Model were an actual theory, instead of a list of empirical observations.
There's plenty of theory behind the Standard Model. It's the core of modern physics. Observed results are explained mathematically, those models make predictions, and the predictions keep being verified. It's a very solid theory.
No one like it, because it's not elegant. There are just too many seemingly arbitrary fields and quantum numbers, and the math is nearly intractable. It's a big stinking mess that keeps successfully predicting all observations.
It's very clear now that string theory has failed at every level. It started as a quest to simplify the Standard Model, but the math is even worse, it has even more tunable parameters, and it keeps failing to predict anything. Perhaps we'd have a better alternative to the Standard Model if decades of brilliant minds weren't wasted chasing string theory nonsense.
Socialism: a lie told by totalitarians and believed by fools.
Scientific theories can never be proved to be correct.
They most certainly can be proven correct and are routinely. You are confused about what being falsifiable means and what being correct means. Being falsifiable means that we can state what data would cause us to declare a theory to be incorrect. It does not mean the theory cannot be proven correct. Correct in the context of a theory means it provides useful predictions. Arguments to the contrary are nothing but philosophical masturbation about whether we really know anything for certain.
To give an example I can make a prediction with effectively 100% confidence that the Earth will rotate on its axis causing the Sun to rise somewhere to the East of me tomorrow. That theory has been tested daily for millions of years and it IS correct for any meaningful definition of the word correct. I also can tell you what data would cause me to declare my sunrise theory incorrect which means the theory is falsifiable. But falsifiable does not mean incorrect. If I have overwhelming confirmatory data and no data contradicting my hypothesis then the theory is correct until such time as contradicting data is found.
They will agree with experiments, and they will make predictions that are later verified, but that doesn't imply that they are correct.
If a theory makes a prediction that is verified by experiment then the theory is correct. If the theory does not agree with experiments then it is incorrect. There is no third option. If a future theory provides a more accurate model of what is happening that does not render the previous theory incorrect insofar as it has been verified by experiment. Correct simply means it provides a verifiable prediction.
They are useful, that's all. Newton's theory of gravity is (extremely) useful, even if it is known NOT to be correct.
Newton's theory IS correct. You can use it to predict the motion of many objects to a very high degree of precision. It is just useful/correct only for certain conditions of speed and size. General relativity did not render Newton's theories false. It just showed that they are a special case of the theory of general relativity much like the theory of special relativity is just a special case of general relativity.
Are you saying.. they've been stringing us along? I guess they're at the end of their rope now.
Ughh.. I won't be here all week.
Look back up at my post, now look back down, you're on the Internet. Now look back up. I'm a signature.
Good question. I found this helpful: https://www.quora.com/How-does-refraction-work-If-a-photon-interacts-with-matter-it-is-absorbed-but-it-passes-through-a-transparent-material-Therefore-it-is-not-absorbed-therefore-it-does-not-interact-So-what-happens-to-slow-the-speed-of/
Strange things are afoot at the Circle-K.