Aliens invaded three days ago and they have been slaughtering us, but now we might have information to fight them.

Many soldiers have died to bring you this information use it well,

The aliens also called mimics are large quadrupeds formed out of ductile metal with long feelers they use to strike at their foes. They can also launch high speed explosive projectiles, that are fast enough to even target aircraft. They are damage resistant but can be killed with high caliber bullets. They can also burrow for concealment and surprise. They are organic EMP did not effect them.

This is not the worst - We believe they can reset time.

During the initial landing in eastern Europe we launched several sets of nuclear strikes against them and each time before we even launched the missiles they all burrowed underground, or by impossible luck managed to intercept the missiles.

There is a subspecies called alphas that we believe reset time when they die

Many troops record fighting alphas but no one has ever successfully killed one.

It appears that time is reset the most recent dawn, and no farther

The Russians laid a massive ambush out around the city of Kursk, with 1/4th of the worlds artillery and thousands of tanks. The mimics blissfully continued walking into the trap for two days until the dawn of the day when the trap was going to be sprung. At dawn, they suddenly turned tail and fled out of the kill zone then they counter-attacked. Since they only reacted on the last day it implies they could not have reset multiple days back and destroyed our ambush even worse.

We believe the number of resets is limited

The mimics have made some mistakes that they could have fixed by resetting the day, this makes us think that they can only reset the day so many times, and so have to let some small mistakes stand.

The armies of the world have united to fight this foe, a fact we would have thought impossible just days ago. China and Russia are preparing defensive works around the City of Stalingrad, Joint NATO forces are preparing defenses along the Marine, the CMEEF (combined Middle Eastern Expeditionary force) is advancing into northern Italy. We have used about 1/5 of our nuclear arsenal, both NATO and Russian lost almost 1/3 of their forces during the initial Mimic landing in Eastern Europe.

We have troops but how do we fight an army that can reset time???

PS one Scientist suggested injecting Alpha blood into a human to give him the ability to reset the day but we have never been able to kill one, and it also sounds like a crazy idea anyway.

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    $\begingroup$ Isn't this pretty much exactly the plot for Edge of Tomorrow? $\endgroup$ – Aify Apr 25 '16 at 2:37
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    $\begingroup$ Kill the Omega? $\endgroup$ – Xandar The Zenon Apr 25 '16 at 13:46
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    $\begingroup$ Send in Tom Cruise with a sword. $\endgroup$ – Serban Tanasa Apr 25 '16 at 14:16
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    $\begingroup$ I'm pretty sure North Korea would not be the only one pledging alliance to the allies. And you should also count those who will silently wait to see who wins, in the meantime trying not to interfere. You know, this kind of bastards who join the war when it is almost at it's end, and then scream how brave and valiant they were. $\endgroup$ – gaazkam Apr 25 '16 at 20:08
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    $\begingroup$ Send wave after wave of your own men at them until they reached their reset limit and shut down. $\endgroup$ – Headcrab Jan 23 '18 at 3:36

10 Answers 10


Greg Egan's novel Teranesia posits a similar situation: DNA is a quantum computer, and natural selection is drawing on many worlds. Any counter you can conceive of has already been tried and adapted to from a parallel universe. How do you fight disease that has already adapted to your cure?

The answer is that DNA's predictive power is short sighted. It can only "see" so far into the future. It's vulnerable to being trapped in a local maxima. If you offer it a very beneficial environment, say a jar of nutrient water, it will happily settle there and be trapped.

The same can be applied here. If the aliens can only reset to the previous dawn, then you must make sure they only realize their mistake when it's too late. Lure them past the point of no return, make them think they had a good day, and only after 24 hours let them find out they did not.

The other option is to make every alternative move a worse one, like the strategy from chess known as pinning. Give them a Hobson's choice between a rock and a hard place. A change to save one army loses them another.

Use deception and counter-intelligence to make them burn resets. Make them think a day went poorly when it actually went well. Make them think they could have done even better.

Finally, if there's no other option, use randomness. Defeat their predictions by acting truly unpredictably. Make strategic decisions by flipping a coin, rolling a die, or looking at quantum fluctuation... anything where a tiny change will produce a different result. Every time they reset humanity will act differently at a strategic level, and they gain no advantage. Instead of grand strategy, the war will be decided by thousands of small unit actions, and the actions of millions of individuals. Without their strategic precognition, they may fall to our small-unit tactics.

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    $\begingroup$ Also known as the Kaizo Trap. Retreat, let them take over the city, only to find out the next day that you stuffed it full of bombs. Bonus points if you can convince them to make it their new home base and bring their leader there first. $\endgroup$ – IndigoFenix Apr 25 '16 at 5:58
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    $\begingroup$ Maybe. But, given that so far, quoting the OP, We have used about 1/5 of our nuclear arsenal, both NATO and Russian lost almost 1/3 of their forces during the initial Mimic landing in Eastern Europe and we have never been able to kill one [an Alph] the situation seems harsh enough even without the time resetting thingy. This could've worked if humanity had advantage at everything bar the time resetting thingy, and this seems not to be the case. $\endgroup$ – gaazkam Apr 25 '16 at 15:20
  • $\begingroup$ @gaazkam I've assumed that's because of their strategic foreknowledge, and that's the interesting part of the question. The question doesn't have enough military and tactical information to answer what happens next, nor should it as that would be a whole other question. I've just given them a fighting chance. $\endgroup$ – Schwern Apr 25 '16 at 16:57
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    $\begingroup$ +1 issue each commander a RDMD (random decision making device) of either the 25 or 5 cent variety $\endgroup$ – sdrawkcabdear Apr 25 '16 at 17:01
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    $\begingroup$ @sdrawkcabdear There's the risk that the commander will experience not even the slightest change before they make their decision, so I'd to go with a device based on quantum fluctuations, a cheap CCD in a dark can is enough. $\endgroup$ – Schwern Apr 25 '16 at 17:27

Infect them all with a virus/bacteria that takes longer than a day to show any symptoms- they can reset time all they want, but they're still infected and going to die.

The only thing the time-resetting would help with is developing a cure... maybe. If possible, try to infect all the aliens at the same time so you only need a single viral strain. If that's not feasible, you'll probably have to engineer a couple viruses/bacteria to get rid of more than just a local population. You can toggle between the lytic and lysogenic cycles to get maximum impact.

Idea courtesy of H.G. Wells

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    $\begingroup$ Bonus points if it includes some form of neurological impairment as one of the symptoms. $\endgroup$ – Joe Bloggs Nov 8 '17 at 8:29

If the reset is triggered by the death of an Alpha (as in the movie), you could try to run them out of resets by laying (nuclear) traps and triggering one just after dawn, so that the day would only reset a few minutes, not enough time for the Alpha to escape.

This is a very dangerous tactic, because it is possible that the number of resets is not finite, but the Mimics simply decided to accept some losses to further some strategic goals. In that case, you may lock the world into an infinite loop.

To implement the traps, hide suicide commandos with nukes at strategic places that are in the path of the Mimic army. The commandos are then to hide while the human armies retreat, listen to certain coded radio signals that indicate the detection of an Alpha and/or pop out of hiding just after dawn each day to check for themselves. If they don't find anything, they must lock up their hiding place again and wait a full 24 hours.

  • $\begingroup$ I like using nukes to force a very early morning reset and limit the effectiveness of their look ahead. $\endgroup$ – sdrawkcabdear Apr 25 '16 at 17:04

Being able to reset the game to a saved state is pretty much like being able to choose the best move to begin with. If there's no randomness involved, they are the same and it's just a lazy way to avoid the computation.

So behave like you do in any strategy game: set traps that prevent the opponent from having any winning move.

Make it more like a pure strategy game, removing sources of randomness when you have a winning strategy. But add randomness when you don't, because it might hurt them.

With the limited number of resets, it approaches a pure strategy game in theory. (With an unlimited, they can just keep resetting until one side or the other died spontaneously due to quantum events.)

The time limit in resetting is just like a look-ahead implementation limit in deterministic strategy.

If things go well, and when you lay a piece of an eventual trap, stall the play and get past the reset horizon. On the other hand, when things go poorly (or intentional random things don't give the right outcome) force the opponent to reset, to your benefit.


I think everyone is mistaken. The aliens can't choose when time resets, we do. This makes resetting time when an Alpha dies an advantage for us humans. We could be on the verge of total, utter defeat, and as long as we kill one single Alpha we get to try again. All we need to do is use non-lethal weapons on Alphas.

So we fight against the other aliens, and if it looks like they're winning, we execute one of our Alpha prisoners and try again.


Don't concentrate on killing them - try to drive them crazy. Since the aliens revive with all memories of an alternate timeline, some part of their "mind" cannot be fully recovered upon reset.

You could try wiping out their memories, causing some sort of amnesia. If succeed, the alphas would revive without any memories of previous attempts. Wipe out all alpha's minds in one day (and kill one to trigger the reset), and this day will be looped and repeated until aliens run out of resets and lose.

But causing amnesia in an alien specie sounds unlikely. Their brain should have different structure and chemistry, it might operate on something other than electricity, etc. So, just try disrupting it as strongly as you can.

How? Idk. You say some omega aliens have been killed, so people could try to figure how aliens' brains function. Try overloading their brains with their own signals (electricity or whatever), try chemicals that simulate their "neurons", try chemicals that break connections between them. Just try everything and hope that "unrecoverable" part of their mind gets damaged.


As with my answer to the very similar How do you assassinate someone who is protected by precognitive people? my answer would be to lure the mimics into a trap where there is no escape regardless of knowing the outcome.

To do this you need to lure them into a trap which was sprung more than 24 hours prior so that, by the time the trap is sprung, resetting to dawn wouldn't save them.

For example: You bury nuclear landmines throughout a very large area and detonate them only once the mimic army has spent 24 hours inside the killzone. Some of the army at the edge of the zone will be able to groundhog back to the beginning of the day and escape, but hopefully enough of the army will remain trapped in the killzone and unable to escape in time.

  • $\begingroup$ A 48 hour flight time implies putting them in a very, very visible orbit which still leaves the aliens 24 hours to get out of the way. $\endgroup$ – Schwern Apr 25 '16 at 16:58
  • $\begingroup$ @Schwern We're dealing with fighting a war against groundhog-day capable aliens. Maybe they're stealth ICBMs or something. $\endgroup$ – evilscary Apr 25 '16 at 21:43
  • $\begingroup$ You don't just paint something black and call it stealth, especially not a 60 foot tall, 80,000 lb, three stage rocket. It requires careful shaping of the object to scatter radar, usually at the expense of aerodynamics and stability which a rocket cannot spare. If you managed that, the flash from the launch is visible from space. The light and heat from the rocket motor can be visibly tracked or on infrared. Humans are already very good at this, space-faring aliens would probably chuckle. $\endgroup$ – Schwern Apr 25 '16 at 21:55
  • $\begingroup$ @Schwern I didn't suggest painting them black. But point taken; I've removed that suggestion. $\endgroup$ – evilscary Apr 25 '16 at 22:01
  • $\begingroup$ You nuke the aliens, they reset time, and after the reset, look for and disarm the nukes. $\endgroup$ – Monty Wild Apr 25 '16 at 23:22

It appears that time is reset the most recent dawn, and no farther

7:04 am and 2 seconds.

sunrise https://www.nasa.gov/multimedia/imagegallery/image_feature_2047.html

Your nuclear strike flies just before dawn and hits 2 seconds after the sun peeps over the horizon. Resetting time 2 seconds will not allow the aliens to escape the missiles 500 meters over their heads.

But they could enjoy those 2 seconds over and over again. Which is a nice thought, because it is a pretty sunrise.

  • $\begingroup$ This idea was suggested in other answers already, though yours puts it succinctly, humorously, and with a pretty picture so +1 anyway. $\endgroup$ – Loduwijk Nov 7 '18 at 22:50
  • $\begingroup$ This isn't a great idea, because we'll be stuck reliving those 2 seconds as well. $\endgroup$ – Ryan_L Nov 7 '18 at 23:49

Play the hostage game, what do the aliens want? If they want to conquer the planet maybe we need to nuke it all so they'll know if they cross the line no side we have anything left. I don't know maybe they'll retreat, otherwise they would have just lunched orbital strike and killed us all long time ago.
Edit- I may explain myself a little further:
If aliens don't use nuke-like weapons in our world means that our world is something they want or something in it.
We nuke our world.
Aliens can see the future. 24hs Ahead we destroyed the world.
There is not much they can do to stop nukes all around the world.
Since the world is in ashes and there is no much left to obtain they may retreat instead of keep wasting their resources.

  • $\begingroup$ Hello, Nahuel Perales, and welcome to Worldbuilding.SE! Please take our tour and visit the help center to learn more about the way the site works. Have a nice day! $\endgroup$ – Gryphon Jul 18 '18 at 20:50
  • $\begingroup$ Hello Nahuel. You may want to re-read the question. The aliens can reset time (per the movie Edge of Tomorrow). Without explaining how your answer solves the problem of aliens resetting time, it's not a complete answer. Thanks! $\endgroup$ – JBH Jul 18 '18 at 21:11
  • $\begingroup$ Oh I thought it was clear, I mean if you see your future and always see the entire world in doom you may think you are defeated somehow since there is nothing you can get from there. Accepting defeat and retreating will be less expensive than fight for nothing $\endgroup$ – Nahuel Perales Jul 19 '18 at 13:22

I don't think this is that much of a problem. While the aliens have a ludicrously powerful advantage the key for the human forces is live intelligence gathering.

Imagine an Alpha who gets into a soldiers crosshair at position X. He dies to the soldier and near the end of the day when the Mimics have gathered as much data as possible the day is reset.

With the new knowledge the Alpha moves to position Y, but he's still in the soldier's crosshairs as the soldier just uses the information he has now, the fact that he does not know anything that happened in the previous timeline does not matter to him.

On the battlefield you just need to use a larger scope of intelligence. If for example you do an artillery bombardment you don't do a random one, you have people guide the artillery strike towards the enemies. If they do something different because they saw what happened the previous time the artillery strike will be guided differently and still have a high likelyhood of getting on-target.

It is also smart to assume the Mimics know your exact army composition and position at any point in time as they'll likely have seen it before they did the reset. So you always have a group of "counter commanders" who look at potential ambushes or attacks that could happen if they knew the entire army position (which these commanders should have). Based on that they can predict potential attacks and counter them prematurely.

As a way to reduce the effectiveness of the Mimic reverse time ability, you can try to wait to finish off some Alpha's just after the reset time has passed. This way you can fool whatever central intelligence uses the time reversal that there were less Alpha deaths and it might think it has lost too little Alpha's to warrant a reset.


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