Editing 2186: Dark Matter
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==Explanation== | ==Explanation== | ||
− | [[Megan]] and [[Cueball]] are talking about {{w|dark matter}} | + | {{incomplete|Created by a DARK MATTER SQUIRREL ON A SPINNING BIRD FEEDER. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}} |
+ | In this comic, [[Megan]] and [[Cueball]] are talking about {{w|dark matter}}. Megan states that dark matter's density across the solar system is 0.3 GeV/cm<sup>3</sup>, as claimed by, for example, [https://arxiv.org/abs/1205.4033 Bovy and Tremaine (2012) "On the local dark matter density" in ''Astrophysics of Galaxies''.] Since Cueball likely does not have a science background, he does not understand what this means, so, to clarify, Megan explains that 0.3 GeV/cm<sup>3</sup> equates to one squirrel's worth of dark matter for the volume of the Earth. For the last two panels, Cueball conflates this with dark matter actually ''being'' a squirrel for comedic effect, enraging Megan. | ||
− | The {{w|gigaelectronvolt}} (GeV) is a unit of energy that can be converted to a mass using {{w|Mass%E2%80%93energy_equivalence|Einstein's formula}} ''E'' = ''mc''<sup>2</sup>. It is typically used for subatomic particles, such as {{w|weakly interacting massive particles}} (WIMPs), one of {{w|Dark matter#Composition of dark matter: baryonic vs. nonbaryonic|several contending possibilities}} for the still-open question of the composition of dark matter, and one which Megan's uniform density figure | + | The {{w|gigaelectronvolt}} (GeV) is a unit of energy that can be converted to a mass using {{w|Mass%E2%80%93energy_equivalence|Einstein's formula}} ''E'' = ''mc''<sup>2</sup>. It is typically used for subatomic particles, such as {{w|weakly interacting massive particles}} (WIMPs), one of {{w|Dark matter#Composition of dark matter: baryonic vs. nonbaryonic|several contending possibilities}} for the still-open question of the composition of dark matter, and the one which Megan's uniform density figure assumes constitutes most of it. For example, the mass of a proton is 0.938 GeV/''c''<sup>2</sup>. However it is frequent to omit the ''c''<sup>2</sup> factor and to represent masses in GeV (or MeV). A mass represented as 0.3 GeV is equal to 5.35 × 10<sup>−25</sup> grams [https://www.wolframalpha.com/input/?i=0.3+(GeV%2Fc%5E2)+in+grams]. This implies a {{w|squirrel}} has a mass of 580 g [https://www.wolframalpha.com/input/?i=(0.3+(GeV%2Fc%5E2)%2Fcm%5E3)+*+(volume+of+earth)+in+grams] (about 1.3 lb), which is a typical mass among several species of common squirrels. |
− | + | The title text imagines using a spinning bird feeder like a {{w|particle accelerator}}, colliding hydrogen atoms at relativistic speeds to detect new and exciting particles like the {{w|Higgs boson}}. Note, however, that accelerating even [https://what-if.xkcd.com/1/ one squirrel] to relativistic velocities would destroy the feeder and be deadly to any birds near the feeder (not to mention the squirrel). | |
− | + | [[:Category:Squirrels|Squirrels]] are a recurring topic on xkcd, but are not a serious alternative to WIMPs as a scientific explanation for the composition of dark matter. Since the September 2015 detection by the {{w|LIGO|Laser Interferometer Gravitational-Wave Observatory}} (LIGO) and subsequent confirmation by the {{w|Virgo interferometer}} of gravitational waves from an unexpectedly large number of merging {{w|black hole|black holes}} larger than those produced by stellar collapse, {{w|primordial black holes}} (PBHs) have become a popular alternative explanation to WIMPs (and squirrels), attracting [https://arxiv.org/abs/1605.04023 proponents at NASA,] and [http://www.buchaltercosmologyprize.org/#announcements other cosmologists] for [https://arxiv.org/abs/1711.10458 several reasons.] However, PBHs remain controversial, because if they constituted more than a very small portion of dark matter, [https://iopscience.iop.org/article/10.1088/2041-8205/720/1/L67 alternative explanations would be almost entirely excluded.] | |
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==Transcript== | ==Transcript== | ||
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[[Category:Comics featuring Cueball]] | [[Category:Comics featuring Cueball]] | ||
[[Category:Squirrels]] | [[Category:Squirrels]] | ||
− | [[Category: | + | [[Category:Astronomy]] |
[[Category:Physics]] | [[Category:Physics]] |