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It's my first time writing an original story and I have this idea, but I don't know if it could be scientifically feasible. My story would be medieval fantasy with magic, but I wanted to add a twist in it: at the end it becomes clear that the setting isn't another world, it's earth after the sun has gone out and became a white dwarf, which didn't happen because of natural causes but due to magic/fantasy things. So yeah, it's going to be a mix.
Anyway, I didn't want to make it too scientific, what I wanted to do was that humanity barely survived the red giant phase of the sun with technology (it doesn't matter what kind, the people that now live on earth don't know what technology is anyway), and then adapted to live in a world much colder than before and slowly life began again. But I read online that to be habitable, a planet must be really close to the white dwarf. Would it be too far-fetched if the earth was somehow pulled towards the sun with technology or some other thing?
What do you think, is this idea too crazy and unbelievable? Thank you for your help!

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    $\begingroup$ If you are willing to use magic, you could put the whole planet in a magic bubble if you want. But the scientific answer is NO. $\endgroup$ – A. C. A. C. Aug 4 '17 at 15:45
  • $\begingroup$ it's magic. If well written pretty much anything goes. $\endgroup$ – Hyfnae Aug 4 '17 at 15:51
  • $\begingroup$ Earth won't survive red giant phase as Sun will expand beyond Earth orbit, adsorbing it before it will become a white dwarf. $\endgroup$ – ZioByte Aug 4 '17 at 16:08
  • $\begingroup$ With sufficiently advanced technology, you could keep the Earth safe from the latter stages of the Sun's lifetime (namely by preventing the red giant phase altogether via Star Lifting), but once the sun is truly depleted it will no longer provide enough light for the Earth to be habitable as we traditionally see it. If you somehow moved the Earth closer, like within 0.05 AU, it might be habitable, but that would be hard to do even for a civilization capable of star lifting. $\endgroup$ – MozerShmozer Aug 4 '17 at 16:25
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    $\begingroup$ What you could do is say the Ancient Civilization, while in the process of star lifting, was also collecting power off the sun with some sort of megastructure like a Dyson Sphere or something similar, and were storing the energy on the Earth for later use. After the sun is depleted, this energy is tapped to maintain the habitability of the planet. It could also be what is providing the energy for the magic to work, if you wanted. $\endgroup$ – MozerShmozer Aug 4 '17 at 16:34
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If the Earth is moved by the same magic that turned the sun into a white dwarf (or by some technological means), then maybe. The same methods used to move away from a red giant would also work to move closer to a white dwarf.

The luminosity of white dwarfs varies enormously, so you can tweak this a good deal, but a typical white dwarf will have a luminosity around 1% that of the sun. That means the Earth needs to be 1/10th as far away to get the same amount of light, which means the year is going to be about 9 hours long, assuming the sun retains the same mass. That's might be a bad assumption, though; white dwarfs formed through natural processes lose about half their original mass, in which case the year would be a little over 12 hours long. Somewhat coincidentally, the white dwarf sun would end up at almost the same angular size in the sky as the sun is right now! The reduction in the radius of the sun and the radius of Earth's orbit just about cancel out. The Earth would almost certainly also be tidally locked, so one side is always in daylight and the other is always in night. Otherwise, there would be pretty darn impressive tides! And by "impressive" I mean "probably catastrophic". Fortunately, tidally locked worlds can still be habitable, but they have some pretty weird climates. There's a pretty large body of literature on this subject, but a good starting point would be Climate model studies of synchronously rotating planets. A 3:2 spin-orbit resonance, such as Mercury has, might also be stable, though, in which case, with the 12-hour year around a reduced-mass sun, the solar day would end up just a smidge over 24 hours! How convenient!

And if there's a planetary nebula surrounding the new white dwarf sun, night times, whether eternal or not, could look pretty spectacular!

The sunlight would be much bluer--the whole world would look like an indoor scene lit with bright halogen bulbs--but our eyes would adapt to that just fine, and as would most plants; the wavelengths they need for photosynthesis would still be there, after all, just in slightly different proportions. The major issue would be a large increase in the amount of UV light the planet has to deal with, but that's not a total deal-killer. It just means you need a thicker ozone layer, and people get sunburnt more easily if they're outside without protection. Dark skin would be an evolutionary advantage much farther away from the tropics than it is now.

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Maybe if the magic/technology let them move the orbit out a ways during the red giant phase, and then in much closer as it became a white dwarf

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