Suppose an world in the . Then aliens come and decide to play a mischievous trick on this world on an epic scale. The goal is to disrupt Earth's time by 18 minutes. Specifically, they wish to make the time on Earth 18 minutes slower within 24 hours. It's a one-off prank, just to show they can.


Assuming the aliens have very advanced technology, but are still confined to the known laws of physics, what relativistic feat would accomplish their goal?

Further Clarifications

  • Goal: slow down time on Earth by 18 minutes
  • Quality Metric: the more perceptible to the Earthlings the better (if the Earthlings don't even realized they've been pranked, where's the fun in that? However, direct perception of time slowing down might not be possible and I'm willing to live with that. So the other component to the quality metric is if there were simply some glaring clues for the victims to realized they were time-pranked recently, that would also be favored by the quality metric.)
  • Technology: The exact limit of the Alien's technology is uncertain, but what is known is the technology must comply with known laws of physics
  • Timeframe: The 18 minutes must be slowed down in the span of 24 hours. You may assume a lengthy preparation phase prior to the implementation of the prank if necessary.
  • Nature of Prank: The prank is not intended to be permanent. The idea is we are taking one Earth day and slowing it down by 18 minutes; a one-off.

Note: Changing the rotational speed, while not overtly out of scope, would not get to the heart of my problem, since we are dealing with perception of time as a quality metric.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Sep 11, 2018 at 14:52

13 Answers 13


Nothing we know of could achieve that.

There are two things that distort time:
velocity and gravity

18 minutes per 24 hours is a dilation factor of 1.0125. ($\frac{24hours + 18minutes}{24 hours} = 1.0125$)


Velocity is out of the question as you can't just accelerate the planet and have it keep a stable orbit around the sun. Also you would heavily quicken the year as your position around the sun would change drastically. You can not use $$T_0' = \sqrt{1-\frac{v²}{c²}} \times T_0$$ without changing lots and lots of other things on earth.

Also time dilation by velocity is not a simply thing and works both ways. Relativity is not just spacetime-bending, but also mind-bending. Takes a while to wrap your head around that.


Time distortion by gravity is a very tricky thing. And it would come with loads and loads of side-effects that are probably unwanted. You would need a very heavy mass near earth to distort time to that extend. It would just have to pop up and disappear, too. And not change the path of earth at all.

For reference:

Time Dilation Effects on Earth

A picosecond is 10^-12 of a second. So a tiny fraction of a second. What you want is for a span of a day to gain 18 minutes. You want 12.5 milliseconds per second.
In this image you can see that earths gravity distorts time by less than a nanosecond per second. So you would need something incredibly more massive directly near earth.

Also, as I mentioned, it would entirely screw up your orbit and everything.

A note:

Spacetime is a weird thing. You can't just delay or slow time, by means we know of. It is always an interaction of things that works both ways. Without heavily altering something in spacetime you can not heavily alter spacetime. (1.0125 time dilation is a heavy alteration to a balanced system of orbits)

  • $\begingroup$ Another way of thinking of picosecond per second is that it's equivalent to one part per million (10⁶) million (10⁶) = 10⁻¹², or one part per thousand (10³) billion (10⁹). $\endgroup$
    – user
    Sep 10, 2018 at 20:31
  • 2
    $\begingroup$ "Velocity is out of the question as you can't just accelerate the planet and have it keep a stable orbit around the sun. Also you would heavily quicken the year as your position around the sun would change drastically." That doesn't make sense. If they're powerful enough to increase the Earth's velocity, they are powerful enough to keep in orbit. And this happens over a day, so the length of the year would only be changed by the 18 minutes. $\endgroup$ Sep 10, 2018 at 20:53
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    $\begingroup$ Why only move the planet? Move the whole systen and don't worry about keeping orbits. $\endgroup$
    – 8192K
    Sep 11, 2018 at 6:53
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    $\begingroup$ @Acccumulation my point was not that they could not do it, but altering the velocity to 0.15c to achieve the wanted distortion would change earths perception of the solar system so drastically, it's insane. Also you'd have to handwave the ridiculous acceleration for this onetime thing. $\endgroup$ Sep 11, 2018 at 6:59
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    $\begingroup$ @Sebastian preceisly that is what is being discussed below Ash's answer. Then nothing within the solar system changes. Just everything outside of it. Only it's perception of the outside and the outside's perception of it would change. I highly doubt that OP was asking for that. $\endgroup$ Sep 11, 2018 at 7:01

As others have pointed out, messing with spacetime here on a scale that doesn't screw up earth's orbit, etc etc would make time seem slower for people observing us from a different frame of reference. Since we want as many people as we can to notice we can:

Alter spacetime around the objects we use to measure time

One could argue that most people tell the time by their phones and computers, not whatever the sky says. Computers sync their time from several servers, that get their time (in part) from 400 highly precise atomic clocks that determine International Atomic Time. By screwing with the devices that the entire species has decided to use to keep time, we will, for a lot of people, effectively slow down time. People will have to work longer if they are following a digital clock to check out of their shift, banks will open just slightly latter than they should, pissing off a bunch of people, etc.

How to achieve it

Bend spacetime locally (around each clock) so they seem slower from the perspective of everybody else. Since we're not changing gravity for the entire planet, just the clocks, we could probably achieve it without messing too many things up by placing a very dense dark matter-like material close to each clock. You could use less mass if you were to solely warp spacetime around the of the clock Caesium.

This can be done by either casually teleporting in and out the material, or by using advanced stealth devices that the aliens have.

Hopefully that's clearer! :)

  • $\begingroup$ Hello, welcome to Worldbuilding! I really enjoy this idea, but it could use more information and content. For example, could you talk about the impact it would have? Thanks! $\endgroup$ Sep 10, 2018 at 18:04
  • $\begingroup$ Did my best to expand the idea, I'll try to figure out numbers for the large mass on my next break. Cheers! $\endgroup$ Sep 10, 2018 at 18:42
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    $\begingroup$ Maybe you don't even need to warp the entire clock, just the relevant caesium cloud. Or just glitch our primitive, electronic circuits to make the clock think time has passed. Bonus points if you tilt observatories to make it seem the sun has moved until someone double checks them. $\endgroup$ Sep 10, 2018 at 20:15
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    $\begingroup$ @thatotherguy I love the idea of tilting all the towers. Every amateur astronomer in the world says "The stars agree with my microwave, not my smartphone. Better go online and tell everyone—wait a second, all of the real observatories say the stars agree with my smartphone after all? Well, I'd better adjust my telescope…" And then, a few hours later, after people have figured out that all of the towers had tilted and all of the amateur astronomers were right… "Screw it, I'm selling my telescope and changing hobbies. How's action figure collecting?" $\endgroup$
    – abarnert
    Sep 10, 2018 at 21:36
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    $\begingroup$ You don't really need to change something complicated to achieve it this way, maybe you'll find this interesting: theguardian.com/world/2018/mar/08/… $\endgroup$
    – ChatterOne
    Sep 11, 2018 at 7:18

A long-term and harder version of some of the "illusion" pranks... Also, to pull it off in "near future", they would have to have already started preparations.

The aliens get a giant (and I mean GIANT) lens - ideally something fairly flat, like a high-tech Fresnel lens - then position & keep it between the Earth and the Sun. When the lens is straight on, no problem - but, by moving it sideways and angling it slightly (relative to the Sun/Earth line), they can bend the light from the Sun, causing it to appear in a subtly different part of the sky.

If they move it enough to make each day approximately 0.05 second shorter then, after about a 10 years, the day will have been shifted by about 18 seconds. After about 600 years, the day will have been shifted by 18 minutes, and leap-seconds/minutes etc will have been added to "correct" time such that Noon is Noon.

Then, one day, they just remove the lens - jump it to FTL during a Solar Eclipse or something. Boom, that day is suddenly 18 minutes too long/slow.

  • $\begingroup$ I like it. I like that this gives the impression that they're, say, outside of our culture, our value system, outside of the normal perception of the time value of doing a prank. They're in it for the long game; they're not just doing it on a whim. Think Trading Places imdb.com/title/tt0086465 $\endgroup$ Sep 11, 2018 at 13:26
  • $\begingroup$ I also appreciate the long game feel of this answer... however, are the aliens prognosticians or actively involved in culture growth? 600 years is a long time generation-wise, but does not always equal expected technological advancements in human cultures. They may need a few restarts to hit the right age if no one at 600 years in is using sophisticated enough time measurements to notice. $\endgroup$
    – N2ition
    Sep 17, 2018 at 22:17
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    $\begingroup$ @N2ition Once it's in place, you can leave it there. Perhaps they were aiming for 30 minutes, but we got too close to detecting the lens? Plus, we've had suitable clocks since at least the 14th century (and clocks in general for hundreds of years before that), so it might just be something they do when a species reaches a certain dependency on timekeeping $\endgroup$ Sep 17, 2018 at 23:58

A less technical solution:

Have the aliens simply do it the old-fashioned way, and hack into all electronic timekeepers, set them such that their time runs slow/fast by 18 minutes (adjusting their perception of the length of one second so they don't notice immediately). Yes, this would be really hard, but easier than speeding up the whole planet or something, and this gets really easy if most Earth timekeeping devices use the internet to update their time. It'd be really funny when tides stranded boats and stuff and sunset times were off and the like. Plus everyone's metronomes would no longer have 60bpm as one beat = one second when they checked with their clocks, but only on that day.


This is not making time itself slower, but making the rotation of the Earth slower, stealing 18 minutes from a day:

Push a large amount of water from the poles to the equator, slowing down the rotation of the Earth. I am not going into the formulas to calculate the amount of water need for the size of the effect nor the increase of sea level at the equator.

An alternative method to achieve the same effect is to push a lot of mass into the atmosphere (preferably around the equator).

  • $\begingroup$ I think this is not what OP asked for. OP asked for time dilation for 18 minutes, not for slowing earths rotation to make a day 18 minutes longer. $\endgroup$ Sep 10, 2018 at 15:29
  • $\begingroup$ As you have demonstrated in your answer this is virtually impossible, even with very superhuman technology. $\endgroup$ Sep 10, 2018 at 15:30
  • $\begingroup$ You could melt the caps completwly and you wouldn't achieve that effect. $\endgroup$ Sep 10, 2018 at 15:51

Our current knowledge of physics allows us to travel forward in time, but not backwards, so the aliens would be able to slow down time, but not revert. But as already stated, you can slow down the rotational speed of the Earth by moving the moon closer to Earth until it's just a few minutes slower.

This will not take 24 hours though ¹ but this will allow you to build up suspension:

  • Astronomers would notice quite quickly but would be too afraid to publish as this is quite impossible
  • Governments would try to suppress the information because
    • The military's smart bombs would stop working
    • GPS-based ankle bands would stop working
    • ...
  • Governments would not be able to hide it any more because people's own GPS systems would start to glitch ²:
    • Cars driving into rivers and off bridges
    • Airplanes landing on the wrong runway
    • Back to sextants for nautical navigation!
    • People's satellite TV dishes would be out of alignment! (No! More! T!V!)
    • Satellite Internet would stop working
    • The moon is getting bigger!

The reason for the practical joke? It's just a stunt of one of their TV 3-V stations doing a Reality 3-V show back on their planet showing the misery of planet Earth!
The misery is stopped in 24 hours by moving all geosynchronous satellites back into alignment.

Note ¹: I need a cosmologist's help to calculate how long it would take.
Note ²: Geosynchronous Satellites would be out of alignment (the old ones) or run out of fuel pretty quickly (GPS satellites)


Using astronomical amounts of positive and negative mass

If aliens construct a massive shell around the Earth, they will indeed slow the time on it, without causing any gravitational damage inside if the shell is spherically symmetric (because of the Birkhoff's theorem). However, for a sufficient time dilatation, the shell would have to be very massive, so massive that it would mess-up the Solar system.

Solution: Bring equal amount of negative mass.

By constructing two concentric shells, one made out of positive mass, and the other one made out of the same absolute amount of negative mass, the same effect can be achieved, depending on relative radii of the shells. As before, there would be no additional gravitational field inside the smaller shell, but now there would also be no additional gravitational field outside the larger shell, because they would cancel-out. Only the space between the shells would have extremely strong gravitational field.

These two shells would be the gravitational analogue of a spherical capacitor.

Because aliens want to slow down the time, the negative mass shell should be larger, and the positive mass shell should be smaller. Otherwise, they would speed-up the time. Time dilatation is proportional to the gap between the shells, so for a smaller gap, the shells should be even more massive and negatively massive, but this shouldn't be too big problem, because the total mass is zero.

The problem is creating and maintaining such megastructure (because energy conditions should be violated for negative mass and the immense gravitational fields would threat to tear the megastructure appart), but let's assume that aliens figured that one out. Other problem is the light and other EM radiation passing inside and outside. If aliens make their megastructure simply transparent, there would be a gravitational redshift/blueshift, not detectable by naked eye, but certainly detectable by spectrometers. If your aliens fine with it, than this is all they need. If not, they would have to make the superstructure slightly more complicated by installing cameras and screens which would stop redshifted/blueshifted EM radiation, and emit the "corrected" EM radiation.


The problem I think is that the question is basically trying to un-prove relativity. Because time is always relative to the inertial frame of reference there wouldn't be any way for anyone to actually even notice that something had changed.

Of course, assuming that you don't want the solar system to come flying apart from the massive gravitational changes required to dilate time around just the Earth, you are left with dilating time around the entire solar system.

Then assuming that the aliens can somehow (casually for a joke remember) generate the insanely huge amounts of energy required to accomplish this you would still have the problem that no one would probably notice.

Perhaps astronomers might notice that the position of a nearby star is off by 18 minutes of time, however over that great a distance, it doesn't seem that it would be noticeable.

  • $\begingroup$ 18 minutes is 1/80th of a day. That translates to 4.5 degrees. Astronomers certainly would notice if stars are 4.5 degrees away from where they're supposed to be. $\endgroup$ Sep 10, 2018 at 20:49

18 minutes is 1/80th of a day. Being next to the event horizon would stop time completely, so this is in some sense 1/80th the effect of a black hole, which is a massive amount of distortion. However, it would not be enough to put 1/80 of a black hole next to the Earth. That would produce so much gravity that humans wouldn't notice the 18 minutes, because they would be distracted by the whole "crushed to death" thing. If you are equidistant between two black holes, the time dilation of the black holes will reinforce each other while the gravity cancels out. So maybe they can do something similar. However, that raises the issue of tidal forces. Putting the mass further away reduces tidal forces, but also increases the mass the aliens need to use.

Another issue is whether all this matter will block out the sun. So maybe the aliens are using dark matter. Of course, dark matter, by definition, interacts very weakly with normal matter, so this will raise the issue of how the aliens are manipulating it.

So the best candidate would be a massive shell of dark matter surrounding the Earth carefully manipulated somehow to avoid large gravity gradients in space or time.

What about accelerating the Earth to a high speed? Well, for low speeds, we have the approximation $\gamma = 1+\frac{v^2}2$. So for an effect of 1/80, we'd need $v=\sqrt{\frac{1}{40}}$, which is about 0.158. That is, Earth would have to be accelerated to .158 of light speed over 24*60*60 seconds, for an acceleration of 5km/sec/sec, 500 times Earth's gravity. And that's not even taking into account that you would have to decelerate back down to normal speed, and that you would have to accelerate to a higher speed to account for the fact that you're not spending all the time at top speed.


Could the aliens trick the human population into believing time has changed? A mass hallucination, caused by something in the air or water.

The best part of the prank is that you're not going to get everyone to be affected - the aliens could use those people as "the rational ones" who end up getting more and more frustrated by the rest of the world who are not realising something is wrong. Hilarity ensues.

This shows off the aliens technical abilities (able to poison an entire planet, able to create a poison for people that only affects them for 24 hours and - aside from the hallucinations - is completely harmless).

  • 2
    $\begingroup$ Do you perhaps mean mass hypnosis rather than mass hallucination? A hallucinatory effect of a substance that targets specifically ONLY time perception, much less specifically 18 minutes of time dilation is going to be hard to believe. A hypnotic effect that specific, however, is more believable, especially as some people seem to be resistant to hypnosis. Method of delivery could perhaps come in the form of flashes of lights or colors or EM or other wave pattern pulses of certain sequences and frequencies. Anyone shielded somehow could be the unaffected ones. $\endgroup$
    – N2ition
    Sep 17, 2018 at 22:58
  • $\begingroup$ That sounds even better :-) $\endgroup$
    – James
    Sep 17, 2018 at 23:45

If a sun is like a proton on an atom nuclei, every planet would logically be exactly as an electon's field! Assumption 1: slightly concave "flat disc" shaped planets, clouding around a common proton plasma emitter! THEN apply a torus shaped movement between the 3 main toral moments! Electrons and electronic clouds do this.. an electron gets bigger and further away from the proton as temperature rises and will get smaller and closer to the proton when temperature drops! NOW you get a couple examples for each of the torus 3 moments: super-dense sphere like Mercury or Venus Separation moment: when the sphere turns to a donut with almost a whole, but still closed like earth and mars And finally the donut phase. When the planet grows so much that actually gets a whole in the muddle! The donut planet theory almost address the point, but misses it widely by assuming the crust would be the outside of the donut, when in fact, the crust would be the horizontal plane of a the vertical midsection cut... Therefore being perceived as mountain and ice on superdense sphere state, plainny and w/liquid water like earth or mars and scarce, gassy and with a whole in the middle like saturn Uranus & Neptune... The gassy nature of the plane is just but a misinterpretation of data! Where we assume the planet is, there is in fact nothing but the north central vortex aka light whole! We perceive the whole to be the planet because exclusively of the gas atmosphere! Which is easy explained considering a torus donut planet with a gassy atmosphere covering ALL: hole, water and rock around! Fact the gas planets with belts have rock and water/ice on the belts and nothing but gas in the central area...

Check the link for a few basics on torus https://en.m.wikipedia.org/wiki/Torus

So, answering your question: there are no aliens, the earth is simply decreasing ray, cooling and getting shorter days... We call it ice ages, but virtually no one has a clue why! You will have discrepancies in time loss depending on how far north on the planet you are... Difference should be more discernible far south, losing more day time!

Put some black suits at my door if you're interested in the whole picture :)


Really REALLY brute force. Slow down time for the entire solar system with a really big distortion of space-time. The only people who notice it are astronomers studying the timing of stuff outside the solar system. For example, the folks watching the signal from the Pioneer probes. Or people studying pulsars. Semi-empirical models of pulsars can identify and predict individual pulses to a really wonderful degree of accuracy. When dozens of astronomers start complaining about the missing 18 minutes, people start to put things together. When both Pioneer probes are 18 minutes "fast" people really start to joggle the old almonds.

Also, the stars will look a really weird color for a while. All at once all over the sky.


Okay for a one-off slow down of 18 minutes you need a space-time disruption of some sort, you aren't messing with Earth's rotational period in any way but rather the way the world experiences time. This would make a single day 18 minutes longer for the world than the one before or after it. That will throw every clock dependent technology completely out of calibration, including but not limited to satellite communications and GPS systems.

How would you do such a thing? I can only think of one effect which would be to artificially accelerate our frame of reference, objects travelling at higher speeds experience time dilation such that they take longer to experience the same amount of "real-time". If you accelerated, and then decelerated (to get things back to normal), our reference frame sufficiently we would experience 18 extra minutes. That's an ASB feat though, I can't even begin to quantify the energy you'd need to pull it off. There would be some longterm ramifications, including but not limited to the fact that stellar navigation would be messed up until all new co-ordinate tables were created because our relative position in the galaxy would get a sharp jolt.

  • $\begingroup$ where would you accelerate things? And what exactly would you accelerate? Earth? The solar system? $\endgroup$ Sep 10, 2018 at 15:15
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    $\begingroup$ @ArtificialSoul At a minimum the solar system I should think but part of the reason I can't even begin to quantify the energy necessary is that I'm not sure how wide you'd need to go to do the job effectively, ASBs all the way. $\endgroup$
    – Ash
    Sep 10, 2018 at 15:18
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    $\begingroup$ If we accelerated, we would not notice days taking longer. Observers looking at us would see that ehat used to take some time for us is taking a bit longer. We would notice the same about the rest of the universe. But a day on Earth would still seem to take ~24 hours for us. $\endgroup$ Sep 10, 2018 at 15:27
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    $\begingroup$ No, nothing on earth would change. If you accelerate all of the solar system equally then from within the solar system NOTHING changes about the solar system. Just everything else outside it is different. $\endgroup$ Sep 10, 2018 at 15:34
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    $\begingroup$ @Renan No it doesn't because I never see the sun rise, or set, at all, I'm only up at night after it goes down and I'm always inside, one way or another when it comes up. I live in a rather small town and there isn't a property within miles where you can see the true horizon at ground level without buildings or vegetation being in the way. I know of no-one who can, without knowing the time, tell you with any degree of accuracy where the sun should be in the sky when they walk out the door which is what you're suggesting. $\endgroup$
    – Ash
    Sep 10, 2018 at 16:12

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