https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=2A0A%3AEF40%3A1424%3AC301%3A4E4E%3AD770%3A9AAD%3A1CD7explain xkcd - User contributions [en]2026-05-23T17:05:17ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=3146:_Fantastic_Four&diff=3900073146: Fantastic Four2025-11-02T11:08:07Z<p>2A0A:EF40:1424:C301:4E4E:D770:9AAD:1CD7: /* Explanation */</p>
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<div>{{comic<br />
| number = 3146<br />
| date = September 24, 2025<br />
| title = Fantastic Four<br />
| image = fantastic_four_2x.png<br />
| imagesize = 343x388px<br />
| noexpand = true<br />
| titletext = One perk of being born at 0.88c is that your birthday is over two days long.<br />
}}<br />
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==Explanation==<br />
{{incomplete|If you have watched the movie, check the actual citation needed and remove it if it is correct, and add a note. Also, explain why Oberth effect is related <!-- didn't we already have that, from several contributors, but it got edited out? -->}}<br />
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The comic is a pun on the {{w|Oberth effect}}, which causes orbital maneuvers to be more efficient when deep into a gravitational well.<br />
The movie referenced is ''{{w|The Fantastic_Four:_First_Steps|The Fantastic Four: First Steps}}'', released in 2025. The comic says that there is a boost because of the propulsion produced by the baby (a 'birth', rather than a 'berth'). In the movie, they do indeed go around a black hole, and she does give birth to a baby while on board, but doesn't do that to get a boost.{{Actual citation needed}}<br />
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This effect is probably zero, as the change in the centre of mass of the ship and crew would not constitute a form of effective reaction-based propulsion.{{cn}} <!-- Although, together with a combination of tidal and relativistic effects, it technically ''could'' mean all the difference, on top of actual spacecraft thrust at, in an ''extremely'' finely tuned attempt to escape a gravity well. --><br />
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The title text states that being born at 88% the speed of light results in a birthday that's over two days long. This is due to {{w|time dilation|time dilation}}: from the perspective of Earth, at 0.88 c, the dilation factor (γ) is 2.1. So one day is 2.1 days seen from Earth. The day of one's birthday has many perks, such as celebrations.<br />
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The Oberth effect was also mentioned as a key to escaping Origin in [[2765: Escape Speed]].<br />
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==Transcript==<br />
:[Ponytail is facing Cueball with one of her hands out, facing up and towards Cueball.]<br />
:Ponytail: In the new ''Fantastic Four'' movie, their ship doesn't have enough fuel to get home and Sue Storm goes into labor, so they slingshot around a neutron star and fire their engines at periapsis — as Sue has her baby — to get a boost.<br />
:Cueball: Ah yes, the Obirth effect.<br />
{{comic discussion}}<noinclude><br />
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[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Movies]]<br />
[[Category:Physics]]</div>2A0A:EF40:1424:C301:4E4E:D770:9AAD:1CD7