6 ms·
It's important to keep in mind that there are always plenty of outstanding experimental anomalies in physics. At the moment, this is one of ~40 roughly equally
by knzhou 7y ago
It's important to keep in mind that there are always plenty of outstanding experimental anomalies in physics. At the moment, this is one of ~40 roughly equally credible hints towards new physics, and it's more likely than not that all of those hints will fade away over time. That isn't anybody's fault either: it has always been like this, and it happens because experiments are difficult and subtle.
Personally, I still find this extremely exciting, even though history tells us it has less than a 1% chance of panning out. A 1% chance of revolution is still meaningful. But don't be too surprised if we land in the 99%.
- beaner 7y agoAny chance you know of a list of such anomalies?
- est31 7y agoMaybe this? https://en.wikipedia.org/wiki/Category:Hypothetical_elementary_particles https://en.wikipedia.org/wiki/Category:Hypothetical_elementa...
- MrEldritch 7y agoI do not, but I can think of a few off the top of my head - the muon g-2 anomaly, the Antarctic upward-moving particle anomaly, the Hubble constant tension, the proton radius puzzle was one until quite recently (but is now largely resolved), the (not statistically significant yet, but they've been in the data since 2013 and they keep not going away) hints of lepton universality violation at the LHC...
- knzhou 7y agoLet's also add the PVLAS anomaly, the white dwarf cooling hint, the 'too big to fail' problem, the cusp/core problem, missing satellites, the DAMA/LIBRA anomaly, the MiniBooNE excess, the Valentine's day monopole, the reactor neutrino anomaly, the Hooperon, the AMS positron excess...
- dodobirdlord 7y agoPerhaps these two lists will be of interest? https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_p... https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model#Phenomena_not_explained https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Mo...
- knzhou 7y agoYou can go straight to review articles, which are generally available for free on the arXiv. Or if you want the firehose, you can scan for papers whose abstracts contain words like 'hint', 'anomaly', 'excess', 'discrepancy', and so on [0]. No individual has made a global list across all fields, because this would be a thankless and kind of pointless task; nobody has the time to be interested in every anomaly. 0: https://arxiv.org/search/advanced?advanced=&terms-0-operator=AND&terms-0-term=anomaly+OR+excess+OR+hint+OR+discrepancy&terms-0-field=all&classification-physics=y&classification-physics_archives=all&classification-include_cross_list=include&date-filter_by=all_dates&date-year=&date-from_date=&date-to_date=&date-date_type=submitted_date&abstracts=show&size=50&order=-announced_date_first https://arxiv.org/search/advanced?advanced=&terms-0-operator...
- PhantomGremlin 7y agoOne of my favorite "anomalies" is dark matter. Not much explanation for it so far. One of my favorite quips on HN put it thusly: GR only matches observation because you added in 20x more stuff that is undetectable other than as a deviation from the predictions of GR. https://news.ycombinator.com/item?id=19537192 https://news.ycombinator.com/item?id=19537192
- knzhou 7y agoThat's a witty quip, but it's witty because it's unfair. We don't grade theories based on what fraction of the stuff is obviously visible. If that were true, even electromagnetism would be a terrible theory because the vast majority of the spectrum we consider is invisible to human eyes. What always matters is how well the theory predicts given how simple its assumptions are, and dark matter is great at that.
- ryacko 7y agoDark matter is a fudge factor.
- knzhou 7y agoYou can call anything a fudge factor. One person's fudge factor is another's elegant explanation.
- jacquesm 7y agoFudge factors are natures Magic Constants. There's a #define in there somewhere.
- dogma1138 7y agoIsn’t the cosmological constant the OG fudge factor in GR? AFAIK we need dark matter to explain any theory of gravity, the observations don’t match what we would expect form classical mechanics either which is still the go to theory for things like galaxies. MOND was introduced initially to fix the observations mostly in regards to how we understand Newtonian mechanics, the relativistic versions of MOND can be used as an alternative to GR but these have been more or less debunked with the observations of gravitational waves since afaik all the versions of MOND have “instant gravity” just like Newtonian mechanics.
- CabbageRice 7y agohttps://en.wikipedia.org/wiki/Axis_of_evil_(cosmology) https://en.wikipedia.org/wiki/Axis_of_evil_(cosmology)
- Akababa 7y agoHow do physicists control model parsimony, so that the number of particles doesn't keep growing indefinitely? Would it be reasonable to think of the "true model" of the universe as having infinite complexity, and we are trying to approximate it by adding features and interactions stepwise? And then some of the non-standard models (ex. string theory) tear much of it down and start over?
- _Nat_ 7y agoLooks like you have some good questions for [SE.Physics](https://physics.stackexchange.com/ https://physics.stackexchange.com/)! @knzhou's profile shows that they're a member there. Short version's probably that we don't quite have enough data to compellingly argue for excessively elaborate descriptions. I mean, yeah, every time there's any little observation -- even one that's not anywhere near statistically significant -- there's technically a tiny bit of information in it that could, in principle, be used to better inform a model than a model that excludes it. But at current, folks don't tend to care; too much mental/computational overhead for too little payoff. Cows in Physicsland aren't spherical because physicists couldn't conceive of more precise descriptions, but rather because non-spherical cows were too much work.
- knzhou 7y agoYour question could deserve a book-length treatment, but one quick thing I can say is that the system is self-correcting. The more bells and whistles you add onto the Standard Model, the less anybody else will want to build upon it. And complexity doesn't rise steadily over time. Because of the LHC results, many models these days are a lot simpler (at least to me) than 10 years ago. It is true that in addition to bolting on correct features, you occasionally need syntheses that simplify the whole thing, like how the zoo of mesons and baryons were explained by quarks. But at the moment, we're very far from having that problem...
- perlgeek 7y agoThere is no formal process for assessing the complexity of a theory or an interpretation, which leads to some interesting disagreements. Consider the Many-Worlds Interpretation[0] of quantum mechanics. Its proponents say you need just a pretty small assumption (the Universe branches under certain conditions), and its critics say assumption is a huge deal, because it postulates an astronomically high (erm, cosmologically high) number of Universes that we can't observe. [0]: https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation > Would it be reasonable to think of the "true model" of the universe as having infinite complexity, and we are trying to approximate it by adding features and interactions stepwise? Nobody knows. So far, we have very successful theories (general relativity, quantum field theory) that rely on a small number of equations with a small number of terms each. That gives hope that at least the laws that govern the Universe are not infinitely complex, but we cannot really know for sure.