Editing 1758: Astrophysics
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+ | ==Explanation== | ||
+ | {{incomplete|Are there other theories than MOND and the new paper? Seems like there must have been many examples to get such a motto? It would make general relativity more complicated is not good evidence of MOND not being a good model}} | ||
− | + | The theory of gravity produced by {{w|general relativity}} is generally very accurate—it predicts the orbits of planets precisely, even details like the {{w|Two-body problem in general relativity#Anomalous precession of Mercury|precession of Mercury}} which Newton couldn't fully explain. However, the predictions for the behavior of galaxies are wrong—{{w|Galaxy rotation curve|the galaxies seem to spin at the wrong rates}}. | |
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+ | The standard explanation is that there is something else filling these galaxies, which has mass (and therefore exerts a gravitational pull) but which can't be seen with current telescopes. This is called {{w|dark matter}}, and most astrophysicists believe it exists—either in the form of {{w|Massive compact halo object|an unknown type of star that is too dim to see}}, or {{w|Weakly interacting massive particles|an undiscovered subatomic particle}}. | ||
− | However, | + | However, an alternative theory which gets proposed regularly is {{w|modified Newtonian dynamics}} (MOND). In MOND, gravity doesn't simply follow the {{w|inverse square law}} but has more complicated behavior. Usually, the extra behavior is either to say that gravitational force can be affected by the acceleration of the particle, or that it goes from inverse-square to just inverse at large distances. It "sounds good" because it's relatively simple—it just changes our understanding of Newton's law of gravitation, rather than requiring entirely new forms of matter or unknown stars to exist—and because it has some nice side-effects, such as explaining why there seems to be a limit on the density of galaxies. |
− | + | Unfortunately, as the sign says, MOND doesn't fit all the scientific data. One famous counterexample is the {{w|Bullet Cluster}}—two colliding galaxy clusters that are ripping through each other, and from which the mass distribution can be inferred through gravitational lensing. The collision, and the differing ways that ordinary and dark matter interact, have separated the dark matter from ordinary matter to a certain extent, which can be seen in the mass distribution. Another counterexample is MOND's incompatibility with observations of the motion of galaxies in galaxy clusters. Even if MOND ''is'' correct in some way, we still need dark matter to explain the Bullet Cluster. More generally, MOND isn't compatible with general relativity—which has a huge amount of experimental data in its favour—and a MOND-compatible general relativity would be very complicated and ugly. | |
− | + | The specific impetus for this comic may be [https://arxiv.org/abs/1611.02269 this] recent publication by {{w|Erik Verlinde}} (see popular description of the paper [http://phys.org/news/2016-11-theory-gravity-dark.html here]). It was released on-line three days before the release of this comic. Verlinde's theory ({{w|entropic gravity}}) isn't MOND—rather, it's derived from {{w|thermodynamics}} and {{w|quantum information theory}}—but it has a lot in common with it. The paper got a lot of "This will prove Einstein wrong" coverage (see [[1206: Einstein]]), even though it's just a {{w|pre-print}} and hasn't been peer-reviewed or experimentally verified yet. Verlinde's theory also doesn't match the data—[http://motls.blogspot.de/2010/01/erik-verlinde-why-gravity-cant-be.html it disagrees with experimental results showing how particles interact with gravity]. | |
− | + | Apparently, whoever put up this sign was getting tired of news agencies stating that dark matter has been "disproven". | |
− | + | The title text lists the text on a similar sign standing outside the Department of {{w|Neuroscience}}. Their motto is "If I hear the phrase 'mirror neurons' I swear to God I will flip this table." {{w|Mirror neurons}} are brain cells which trigger when watching someone else do something. Experiments claim to have found mirror neurons in humans and apes, and there are theories that make mirror neurons the foundation of learning, empathy, language and consciousness itself. However, {{w|mirror neurons#Doubts concerning mirror neurons|the evidence for mirror neurons is still patchy}}, and even if they exist, it's very simplistic to try to attribute so much of human behavior to a single type of relatively simple cell. In light of this, the motto of the neuroscientists at the department may reflect their frustration and even rage, over what they see as a common misperception. | |
+ | [http://knowyourmeme.com/memes/flipping-tables Flipping tables] is a common depiction for expressing extreme outrage. It is used also as a pun because mirrors flip the image in front of them. | ||
+ | A similar story of a paper questioning science and leading to press coverage was mentioned two days before the release of this comic on the YouTube channel Space Time from PBS Digital Studios in their newest video with the title [https://www.youtube.com/watch?v=7UNLgPIiWAg Did Dark Energy Just Disappear?]. This was based on the press coverage of the paper [http://www.nature.com/articles/srep35596 Marginal evidence for cosmic acceleration from Type Ia supernovae]. The conclusion in the video is that dark energy is still the best explanation. Note this is about the existence of dark energy rather than dark matter. The two are not related! | ||
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Science papers with results that supposedly disprove solidly founded theories have been the subject before in [[955: Neutrinos]]. | Science papers with results that supposedly disprove solidly founded theories have been the subject before in [[955: Neutrinos]]. | ||
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{{comic discussion}} | {{comic discussion}} | ||
− | [[Category: | + | [[Category:Astronomy]] |
[[Category:Science]] | [[Category:Science]] | ||
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