4
$\begingroup$

Right at twilight, the sun stops setting. It just stays in the same spot in the sky permanently.

What would have to happen in physics for this to happen? Would there need to be an event prior to this? Maybe it moves erratically as it moved into a "stationary orbit" that allowed for it to sit in the same position of the sky?

EDIT:

  • Happy to hear answers that point towards humans grossly misunderstanding physics and new models of physics being defined.

  • Also happy to hear answers where the sun slows down to that point or has erratic movement before it stops

  • Considering this happens on an "Earth-like" planet.

$\endgroup$
10
  • 2
    $\begingroup$ Does it stop instantly? Or gradually slows down? $\endgroup$ – Alexander May 7 at 20:32
  • 5
    $\begingroup$ I assume the explanation "We are in the Matrix!" is not accepted as a physical one? $\endgroup$ – Alexander May 7 at 20:33
  • 1
    $\begingroup$ you are aware that it's not the sun that's orbiting earth? $\endgroup$ – ths May 7 at 21:18
  • 3
    $\begingroup$ So you want the planet to become tidally locked to the star? I'm not sure how long that takes, but it would meet your description. en.wikipedia.org/wiki/Tidal_locking Perhaps some rogue body passes through the system, arresting the momentum of the planet. Only it would be pretty devastating to happen suddenly. $\endgroup$ – DWKraus May 7 at 22:02
  • 3
    $\begingroup$ What does the rest of the world see? You do realise that the sun doesn't rise or set simultaneously in all time zones? If the sun has paused while setting at one point, has it paused while rising at another? Frozen at high noon halfway between? $\endgroup$ – nzaman May 8 at 5:35

14 Answers 14

15
$\begingroup$

Giant mirrors in space.

(Assuming you want a reasonably non-apocalyptic way of making "the Sun stand still", and a technological level within the current millennium)

A large (sort of) statite is placed in the L1 Sun-Earth Lagrange point. Also, a Fresnel mirror is placed just beyond the Sun, focusing a stream of sunlight towards a third mirror in a powered orbit around the Earth at a distance of about 1.5 million kilometers, with a speed of around 110 km/s.

Solar light wavelength will not match exactly and diffraction and Doppler effects will be more than enough to reveal what's happening to any equipped laboratory (not to mention SOHO readings, or the Moon becoming permanently dark), but to the naked eye, you can simulate a Joshua event quite faithfully.

The solar shield appears briefly in Arthur C. Clarke's Childhood's End, while giant mirrors are featured both in John Ringo's Troy Rising and, less technically as "focusing fields", in the Lensmen series by E. E. "Doc" Smith.

Other useable methods in literature involve "shifting momentum through hyperspace" (used in Peter F. Hamilton's Night's Dawn series to stop a lorry, but I imagine it could be scaled waaaaay up to harmlessly stop a whole planet from spinning - long-term effects are still catastrophic unless the momentum loss is carefully crafted and spatially modulated in order to maintain Elsasser invariance of the Earth's geodynamo) and instantaneous space portals (one with one end again in L1 and the other in a powered Earth orbit as above; if large enough, the Moon keeps its phases. This time, the sleight of hand is slightly harder to detect. This kind of portal is also featured in another Hamilton series, the Salvation Sequence, and again would require massive scale-up).

$\endgroup$
1
  • 2
    $\begingroup$ why would the Moon get permanently dark? Since we already have one giant optical device to hide the sun and two more to illuminate it from a new angle, why not just widen the beam enough to also illuminate the Moon from the same direction? This wouldn't be the full Joshua event, because the Moon would keep moving - but simulating the moon as well shouldn't be too hard - just sneak a giant optical device to the GEO. $\endgroup$ – John Dvorak May 8 at 10:20
14
$\begingroup$

On Earth, the planet would need to suddenly stop spinning.

At the equator, that's roughly 1000 mi/hr "just" to a dead stop. Woe betide the billions of people close enough to water to be drowned in the ensuing tsunamis. Not that most would notice, having already been pulped by buildings falling upon them or shredded by 1000-mile-an-hour winds. The shattered crust of the planet will no longer contain the mantle, and the few conscious survivors will be consumed by the the rising lava before they have time to worry much about why the sun has apparently stopped.

$\endgroup$
11
  • 4
    $\begingroup$ XKCD What If examines this in terrifying but amusing detail. Anyone at the North or South Poles will take a little while to find out that they are almost the only survivors on the planet. $\endgroup$ – KerrAvon2055 May 8 at 0:31
  • 15
    $\begingroup$ Why is something capable of stopping the earth's rotation limited only to the solid portion? $\endgroup$ – Mary May 8 at 1:12
  • 4
    $\begingroup$ Nitpick, I know, but you don't want to slow the Earth's rotation to a dead stop, but to where it rotates once per year, thus always keeping the same face to the sun. Just as the moon keeps the same face to the Earth by rotating once a month. $\endgroup$ – jamesqf May 8 at 5:05
  • 4
    $\begingroup$ HG Wells thought of this 120 years ago in The Man Who Could Work Miracles. A character discovers that he has supernatural powers. He decides to order the Earth to stop spinning. All hell breaks loose. “he had made no stipulation concerning the trifling movables upon its surface .... Every human being, every living creature, every house and every tree – all the world as we know it – had been so jerked and smashed and utterly destroyed.” $\endgroup$ – Michael Harvey May 8 at 14:31
  • 3
    $\begingroup$ @AlexP: Ah, but if we have handwavium tech sufficient to stop the Earth from rotating, we also have the tech to siphon off the heat energy in some other form, perhaps as electricity to power our hyperspace drive. See for instance how flywheels are used to provide large electric currents: $\endgroup$ – jamesqf May 8 at 16:44
3
$\begingroup$

Some hyper-advanced race deployed a vast number of gravity projectors around the planet and used them to bring it to a stop--it's now tidally locked in that position.

You'll need a vast number to make the field even enough you don't tear the world to pieces in the process and you'll have a big problem handling the energy involved without spilling enough to kill the inhabitants.

$\endgroup$
3
$\begingroup$

"The fool on the hill sees the sun going down, And the eyes in his head see the world spinning round."

The sun largely is motionless in the sky. The observer on earth is on a moving platform. The earth rotates on its axis once a day, and revolves around the sun once a year. But that's not what common sense tells people. They feel like the earth is stable and unmoving, and the objects in the sky are attached to giant invisible spheres that cause them to go around once a day, and for the planets to move a little every day.

From Aristotle up to Copernicus, deep thinkers agreed with what common sense tells us. But Copernicus, Galileo, and Newton among others came up with a model where the earth is a moving platform, as I said.

What if people like Newton were just plain wrong? What if they were seduced by mathematical convenience into a mathematical model based on supposed laws of motion and gravity, that are just a way of reconciling observation with our model.

In the alternative model, Aristotle got it right. The sun is attached to a giant crystal sphere, and all of its motions can be explained that way. The crystal sphere stops moving, and the sun no longer sets. Easy.

What isn't easy is explaining all the data we've gotten from earth orbit satellites, the ISS, solar orbiters, mars missions, and capsules we have sent into the sun.

$\endgroup$
4
  • 2
    $\begingroup$ If people can believe the Apollo program was a fake (and some of them still do) believing that "all the data we've gotten from earth orbit satellites" etc is a fake is no big deal. In fact, academic institutions are really just lunatic asylums and government funded "space research" really comes from the healthcare budget, as occupational therapy for the inmates. $\endgroup$ – alephzero May 8 at 13:44
  • $\begingroup$ I came here to say something like this, but you did a nice job. I would have also point out that the Aristotlian model is probably closer to the model we have hardwired into our brain for catching prey on earth, i.e. some like "an object in motion will slow down and come to rest unless acted on by an addition force that keeps it moving". $\endgroup$ – Mike Wise May 8 at 14:05
  • $\begingroup$ Nor is it easy to explain the sudden loss of momentum of the giant crystal sphere. $\endgroup$ – Damian Yerrick May 9 at 14:18
  • 1
    $\begingroup$ The concept of momentum is part of Newton's laws of motion. The crystal sphere need not have any momentum at all. $\endgroup$ – Walter Mitty May 9 at 18:03
2
$\begingroup$

Gravitational lensing.

Unknown to humans, dark matter is a very real force in the universe, and a large amount is going through the solar system. This has set up an orbital circle around the earth and the sun. Dark matter doesn't impact matter but does impact light, and so the light of the sun is being focused along a particular track by the intense gravitational pull.

The dark matter stream takes a while to lock into the dark matter at the core of the earth, so it takes a while till twilight is reached, with the sun's light meandering around the earth erratically as it snaps into place.

$\endgroup$
8
  • 2
    $\begingroup$ Won't work. Dark matter can't form very dense bodies or dark solids - research Noether's theorem (I think). Or something. Basically the same properties that mean EM radiation can't detect it, means it also can't lose energy like regular matter does, and that's essential to forming dense volumes of matter. Also its not "unknown to humans". We know it's a very real form of matter. We know there's a lot of it (80-90% of the matter in the Milky Way for example, going out maybe 10x as far as the rough galactic radius). We just don't know what its made of. $\endgroup$ – Stilez May 8 at 16:42
  • 1
    $\begingroup$ Also worse for this idea, any amount of matter (of any kimd) large and dense enough, and positioned suitably, to cause lensing of the sun as seen on eartb , would create a far bigger problem than the sun appearing to stand still. Like, orbital perturbation of the earth, or destruction of earth (or of earth as we know it). TL;DR this idea wouldn't work in any way at all. $\endgroup$ – Stilez May 8 at 16:56
  • 1
    $\begingroup$ The author explicitly said "Happy to hear answers that point towards humans grossly misunderstanding physics and new models of physics being defined." so sticking to established models of physics are unnecessary. $\endgroup$ – Nepene Nep May 8 at 18:33
  • 1
    $\begingroup$ That's true, but logical inconsistency isn't. The question welcomes new physics, not in-universe logical inconsistency. If matter is dense enough to lens light, the answer will also need to include new physics how it can be gravitational enough to.lens light but not affect the earth any other way. If a new physics explanation of that is added, sure. But overlooking it isn't new physics, it's just not a workable answer as it stands. $\endgroup$ – Stilez May 8 at 19:35
  • $\begingroup$ Yes, new physics is allowed. We don't know how dark matter works reliably, so it's a great area for vague technobabble physics tweaks. $\endgroup$ – Nepene Nep May 9 at 11:20
2
$\begingroup$

Artificial mega-structures encasing the planet.

This is just the initial display for an artificial sky on a giant shell around the planet with artificial lights on the inside as a preliminary step in turning the planet into an intergalactic spaceship. The sun will start "moving" again once the engineers are sure they've got the rest of the shell's environmental systems working, and this time it'll be by fusion-powered lights turning on and off in sequence.

Yes, it's theoretically possible to turn a planet into a spaceship. It's not going to be accelerating very fast (you'll be measuring it in micro-gees), but you could get it up to a modest fraction of the speed of light (say 10%), and the thousands of years that would take are going to be a drop in the bucket compared to the tens of millions of years you'll be spending coasting between galaxies.

For a more in-depth discussion of the topic, Isaac Arthur on YouTube has done a video on it: https://www.youtube.com/watch?v=oim7VvUURd8

$\endgroup$
1
$\begingroup$

As I understand it, either the planet's rotational velocity must match the planet's constant gravitational orbit (and the associated indirect rotation) around the sun, so that it always faces the sun at the same angle, or the planet is not moving nor rotating at all.

$\endgroup$
1
$\begingroup$

The sun just powered up a reactionless drive and is now circling the still rotating earth - but this doesn't work with known physics.

Could perhaps be a flyby from a rogue black hole, but that wouldn't permanently fix the sun in position. The orbit is non-longer a circle. Winter is coming.

$\endgroup$
1
$\begingroup$

There are already some good answers here about how to get the sun to stop. I'd like to talk a moment about what the effects of that would be.

Initially, huge gee forces

Right when it stops, as @user535733's answer says, you've got huge inertia problems where anything not fixed to the Earth is suddenly moving at supersonic speeds. Great.

But there are also huge forces involved in the stopping itself that would instantly crush anything on the wrong side of the Earth and, I would imagine, fling everything on the other side completely off. After all, it would likely be dozens or even hundreds of gees to have such a sudden stop, compared to Earth's 1.

Imagine you have an apple and you cover it in honey. We'll imagine the apple is the Earth and the honey is everything on it. Get in the car and hold it out of the window, slowly driving up until you're moving fast. You may need to be in a vacuum to avoid wind from affecting the experiment. Then slam on the brakes as hard as you can. (The author disclaims all responsibility if you take this out of the realm of a hypothetical situation.)

Okay that diverged quickly. BUT my point is that you're going to have some serious problems with all the atmosphere flying off the Earth completely, not just moving at supersonic speeds.

I haven't even talked about what would happen to the Oceans. They'd be all over the place, mostly probably also flying off, but the rest going all over the land.

Searing heat

Your end result is basically tidal locking of the Earth and the Sun. If you heeded what I said about the air being stripped off, you now have an airless planet where one side is mercilessly being bombarded with solar rays, while the other is in shadow. It'll be like the Moon's 28-day Day/Night cycle, but with it never cycling.

If the atmosphere is still there, you might have a similar effect to Venus, where the super-long day means one side gets heated and rushes over to the other, creating huge storms and fast-moving winds. Even if that doesn't happen, you still have huge temperature gradients.

Either way, not great.

Responses to other answers

First off, they're all great ideas. I do, though, want to evaluate the results.

  • Zokka's answer about tidal locking I already addressed above.
  • Walter Mitty's answer is an ingenious way to get everything attached to the Earth to seem motionless. I'm not sure what would happen to the atmosphere, though. Or if it even matters. If the platform is moving to exactly counter the Earth's rotation, you have what is empirically the same as the tidal locking scenario. Everything on the surface is motionless, so it still has one side constantly in day and the other in night.
  • Jasen's, as they said, isn't really under known physics. But if the end result is that it looks like the Sun is motionless, you have, once again, the tidal locking scenario. (If I understand N-body physics correctly, because the Sun and Earth are actually orbiting a center of mass of the system that happens to be inside the sun, there's no difference between the Earth orbiting the Sun and the Sun orbiting the Earth--at least not with our laws of Gravity.)
  • Loren's addresses the problem of trying to cushion everything on the Earth so nothing flies off and addresses it ingeniously-- since everything on the Earth is pulled equally, there is no observable gee force on the inhabitants. But you still have the tidal locking problem.
  • LSerni and Nepene's answers both involve reflecting or deflecting the light (and, I assume heat) in such a way that it appears that the sun is steady when it isn't. While yes, this means you don't have insane gee forces slowing down the Earth, but since all the light and heat is still redirected to one side of the Earth, you have the massive overheating of that side in the same way as the Tidal Locking scenario.
  • user535733's answer I addressed. I mostly just clarified that all the atmosphere and things would likely fly off the Earth because of inertia and would like to point out the effects afterward from tidal locking.

Conclusion

Tidally locking the Earth probably isn't a good idea in a hard science world, no matter how you do it.

My suggestion: Take one of the solutions that slow down the earth without causing problems for the inhabitants. I personally like Loren's where you have gravity projectors. Then you need some sort of heat distribution system. If you've already got a deflection system like in LSerni or Nepene's answers, you can use it to regulate how heat is equitably distributed around the planet. You'd probably want some sort of mirror that is permeable to light but reflective to heat. I don't know if we have something like that already-- it's worth a google. You can use those to distribute the heat and keep the light going right on its normal path.

It's complicated, but I'm sure you can figure out a way to work it in; people like you always wow me with your creativity. ;)

I hope this helps.

$\endgroup$
1
$\begingroup$

The sun is part of a binary system with a dark object of similar mass, such as a black hole. The planet orbits around the centre of mass of both the sun and the dark object. The sun and dark object are sufficiently close that their orbital period is similar to the planet's rotation period (i.e. the length of a day). As a consequence, the sun's apparent motion through the sky is equal to its apparent motion due to the planet's rotating reference frame, plus its actual motion due to the sun's orbit around the dark object. Occasionally, these terms are approximately equal and opposite, causing the sun to appear motionless in the sky for a short while.

In the simplest configuration, your planet's sunsets and sunrises have always exhibited this behaviour. If you want this to be a rare event (like total solar eclipses are rare on Earth), you could either have the dark object in a very elliptical orbit around the sun such that it only occasionally causes visible motion, or you could have the sun plus two dark objects in a chaotic ternary system. The dark object could also be on a parabolic or hyperbolic trajectory which gets close to the sun just once, if you want the event to be a one-off. However you do this, the sunset is only temporarily delayed - the sun won't permanently stand still in the sky.

$\endgroup$
0
$\begingroup$

So if the sun needs to set at twilight, it will only be twilight on a small sliver of the earth if it's round. On other parts it would be dark, and others it would be forever afternoon.

The earth is actually rotating due to inertia of the planet when it was born 4.5 billion years ago. You can read that here. Another interesting fact is that the earth is slowly slowing down by itself due to the tidal friction caused by the moon. So eventually the earth should stop on it's own, but before that happens the sun will blow us up in 4 billion years.

Can we slow it down faster? Answer is yes. But we need a bigger moon. If there is a gravitational pull strong enough it would slow us down quicker. I don't know the maths for this but it's bound to be interesting. We might need a moon bigger than the size of the earth before we start to notice it.

Can we slow it down all at once? Answer is yes. But this will wipe all life as we know it. There is no way it wont. The amount of energy used to slow down the earth should be enough to vaporize all organic life forms. It could be a meteor, or an enormous volcanic eruption (like yellow stone park, but bigger) but I doubt even having a deep deep underground bunker would keep you safe from this apocalyptic event.

Is there any other it could happen by itself? So apparently the earth shows evidence of flipping it's magnetic field around. When this happens the earth would start rotating erratically. It's plausible that if this process would somehow really get screwed up, it could potentially stop our planet from spinning normally, maybe even stopping it all together.

What if we break physics? Easy. Just stop the flow of time.

$\endgroup$
0
$\begingroup$

Your planet could become tidally locked to the sun! We always see the same side of the moon because it is tidally locked to the earth, so there's no reason why your planet couldn't become tidally locked to your star.

Just looked into it as well, and apparently the earth could eventually become tidally locked to the sun, but it'll take a long time due to the sun's low gravitational influence on earth's rotation.

$\endgroup$
0
$\begingroup$

If you want twilight everywhere, you would need a disk-shaped mega structure with a hole in the middle that the sun sits in. That way, it is always twilight (or sunrise?) everywhere on the disc.

$\endgroup$
0
$\begingroup$

The mythogoly

"Helios (also Helius) was the god of the Sun in Greek mythology. He was thought to ride a golden chariot which brought the Sun across the skies each day from the east (Ethiopia) to the west (Hesperides)" ~https://www.worldhistory.org/Helios/

Your earth-like civilization may have experienced certain geopolitics along the way (in butterfly effect fashion), which resulted in a civilization still under Greek rule and ideologies. They developed a different understanding of "what we think of as" physics - which still models the old Greek mythology.

Adopting from Norse mythology's 'Ragnarok'... the legend foretells the events of this civilization's 'Heliotelos' - where the God Helios' fate ends with his demise from an accident with his chariot at twilight. As a result, the Sun hangs, suspended.

The physics facts

  • The earth-like planet is heliocentric.
  • The sun rises from the east and sets in the west.
  • The sun stopping references the folklore 'Heliotelos' - the demise of Helios
  • How? A gravitational 'blip' halts the rotation of the earth-like planet ~https://journeynorth.org/tm/mclass/SunriseSetAns.html
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.