I never quite understood this type of logic. You live out your day as your brain organically modifies itself through your external senses (memories are formed). You then are exploded into little pieces, including your brain.

You then wake up restarting your timeline of the day with everything back to what it was at the start of the day, or in the case of Edge of Tomorrow, just before being dumped into an incredibly difficult fight. Except, for some reason, your brain's organically modified state is retained, like a save spot in a video game, so you aren't entirely how you were when you started. If you were exactly the same, you wouldn't remember of course.

Please explain how this works in this movie as I'm making assumptions obviously not seeing the movie yet or reading the book. This is akin to Ground Hog Day with Bill Murray in a similar fashion but I'm sure has completely different explanations for this happening.

  • Added the tag for the original book.
    – user1027
    Dec 12 '13 at 21:26
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    Your handle is warranted. Dec 12 '13 at 21:27
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    It's not just the brain. Cage gets better in combat over his many incarnations -- which suggests the rest of his body is changing, he is at least developing new reflexes and possibly becoming stronger and faster as well. None of this is explained beyond some vague handwaving about tachyons. What it really comes down to is mind/body dualism -- the film is drawing on the pre-scientific idea that the mind is some sort of immaterial spirit. Jun 26 '14 at 20:14
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    I have to add this comment, I saw the movie and I absolutely loved it from start to finish. This is one of the best Cruise movies to date. It was so entertaining, I didn't care the whys and hows. Jul 6 '14 at 2:16
  • I ended up seeing this again on a search result and checked back. Since then I have delved into physics more and have a new concept of "entropy" under my belt. It sadly renders my beloved "Back in Time" movies to silliness but I'm sure someone clever will dream up an entropy-based sci-fi movie. Feb 16 '18 at 17:55

The movie is based on the short story All You Need Is Kill by Hiroshi Sakurazaka. While – as far as the upcoming movie is concerned – we only know the line from the trailer things are a bit different in the novel. Rita has gone through a time loop as well and she's the one to tell Keiji how to end the loop.

In the book,

Mimics can - if they're about to die - emit some kind of tachyon pulse. This signal travels back in time to the past and appears in the memory of the Mimics as some kind of vision. The mimics receiving that vision are able to modify their actions which allows them to change the outcome to their advantage. Keiji, like Rita before him, somehow tapped into this signal when he killed a Mimic and that's why he's stuck in this "loop".

Judging from the line in the trailer the time loop mechanic seems pretty close to the book. The author doesn't exactly bludgeon the reader with science talk – it would be quite a feat on the meager 168 pages – and leaves a lot to the reader's imagination.

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    Checked. That makes the most sense except, time doesn't loop. The signal was going to the past which exists already as space-time is the same thing and exists just as a geolocation exists. After getting input from the future, the past then goes forward with differently weighted probabilities in every possible permutation. I just don't understand the tachyon part of sending things to the past but I see a reference to it in wikipedia sci-fi as being just that. Dec 13 '13 at 17:30
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    Yeah, well, tachyons have appeared in many works of fiction as the go-to mechanism for anything time travel related. Since hypothetical tachyonic particles are always moving faster than light they're predestined to turn up in many sci-fi works, most notably in the Star Trek universe. Regardless of the technology behind that unique experience, it is referred to as time loop in both the trailer and the book. I didn't change that. :)
    – JC2k8
    Dec 13 '13 at 17:58
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    @Jason Sebring - there's a basis in physics for thinking that if tachyons existed, according to the theory of relativity they would allow for information to be sent back in time, see en.wikipedia.org/wiki/Tachyonic_antitelephone
    – Hypnosifl
    Jun 26 '14 at 16:55
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    @JasonSebring, time doesn't loop....except that it does in the movie. Oct 14 '15 at 23:16
  • @PaulDraper good point. It is fictional after all. But usually that's not good to admit here. :) Oct 22 '15 at 1:21

One thing to note is every point in time that he jumped back to he's asleep. So one could wager that the information comes to him in his dreams. That in addition with the mechanics described by JC2k8 would give us as clear of a picture as we're likely to get. Somehow while sleeping the human brain can receive said signal and translate it into a dream.

  • What's wrong with my answer to deserve the downvote?
    – Dagonis
    Jun 19 '14 at 19:01
  • i didn't down vote you. Jun 27 '14 at 15:56
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    Neither did I but references and evidence are preferred over wild speculation. Nov 17 '14 at 12:12
  • I just read this again and up voted you because of the dream comment. He was always asleep I noticed after reading that. Good catch. Jun 12 '15 at 15:47

This is how it works in the book, on which the movie is based, "All You Need is Kill".

An "antenna" alien on the battlefield emits tachyons to the other "recevier" aliens. Tachyons can travel backwards in time. Any being that can recieve the tachyons from the battle antenna will learn in the form of a hyper-realistic dream of the day in question in order to gain an advantage on the battle field. It will feel like a 30-hour loop. They are so difficult to defeat because they have already seen each battle, assuming they couldn't win it on the first try.

The main character accidentally gains this power in battle, and realizes that super soldier Rita once did so too. She teaches him how to escape the loop the only way she knows how...

And that's how that piece of science fiction works. I recommend the book. It was a very fun read.


There's a line in the trailer that Emily Blunt's character says in the trailer that indicates this is a capability that the aliens that they're fighting have.

You hijacked their power.

She also says that Tom Cruise's character is undergoing something that happened to her, so at some point in the past she did the same thing. So presumably the aliens either naturally or through technology have a similar ability to do this "Groundhog's Day" sort of time looping.

Since this isn't something that actually happens in reality, the rules of how it works are up to the author. In the film, the aliens seem to naturally have this ability. The Omega manages the science-fictiony mechanics of resetting the time loop. The death of an Alpha (or Cage, for the bulk of the film) is the trigger that causes an Omega to reset the time loop.

The film takes on the perspective of the humans, and their limited knowledge of the aliens. The humans figured out some of the mechanics of the alien time loops, but not every detail. So, we don't know how the Omega resets time while allowing the aliens or Cage to remember past loops.

  • Wasn't there a book about this? Dec 12 '13 at 21:52

The movie explains this in a very hand-wavy manner. The omega mimic can control time, this power can be controlled by the high level mimics. If bathed in the blood of the high level mimic, one essentially gains control of that power, and can loop things backward in time. Rita indicates that when she had this power she wasn't able to control it, it simply triggered on her death automatically.

This, of course, causes continuity problems, because in the second, and many other later loops, the main character wasn't bathed in the blood of the higher level mimic, so if this really is a form of going back in time, then, physically, the main character never obtained the power a subsequent loop, and the mimics should have won merely by restarting time prior to that power transfer.

The manga hinted at what was going on, but the book delved into it further.

Rather than a form of time travel, or reversal of time, only memories were transferred from the future. This implies parallel universes.

The main character lives the first day, but by killing the strange mimic they gain the ability to "radio" (tachyon waves) their memory back to their prior self . There is a distinct "beginning" time, though, that can't be altered - the memories are sent back to the person at one point in time, so one can't send memories further back.

So essentially a hundred or more parallel universes split off from that point in time, each one sending back the memories created from that universe to the original character. The character's body, therefore, and brain receive all these memories, and it appears to them that they've lived them sequentially, but the reality is that they haven't at that point. Their brain is just trying to make sense of it. In the book/manga this results in headaches, the more memories are given. In the movie there's "visions" and nose bleeds.

Note, also, that the manga indicates the mimics are actually terraforming bio-robots with little intelligence of their own. If you think of memories as merely computer data being radioed back via tachyon pulses (which are theorized to travel back in time) and robots of the past receiving and acting on future data, it might make more sense. The difficulty is accepting biological robots with this capability, and further accepting that humans are biologically compatible enough to also be turned into receivers and transmitters of the same method.

I don't know that there's a good explanation for how things work in the movie, but you could adapt the same kind of technique. The omega mimic can send memories back, once connected, the connection only grows stronger and it can't resist sending memories of its own back. The characters could be wrong about whether it's time travel, or simply memory sending.

In the book it's the fact that the human killed the important mimic - the mimic somehow imprints on the human. Perhaps the extraordinary strong tachyon pulse it emits on death is involved in getting the human to send one of their own back to their own biological body in the past. Note also that the human doesn't die at this point, he continued to fight, and eventually died from another mimic.

At any rate, to the person experiencing it, it feels like time travel. In the book and manga, it's clearly not time travel, but simply sending memories back.

Since both stories are told from the point of view of the main character, and their understanding is obviously limited, then it is likely that we can theorize forever and never come to a real understanding in either case.

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    This rambling explanation brought to you today by Procrastination! Try some Procrastination today, it's procrasterific!
    – Adam Davis
    Jun 18 '14 at 20:28

A comment was raised regarding why not have a single entity be both the server and the antenna...

If an entity is both an antenna and a server, and is fighting against an enemy server (e.g., rogue server), then the antenna/server entity may end up looping forever... because as an antenna/server, the antenna/server would still be 'standing' to transmit the pulse of the enemy server it kills (assuming they are in range of one another; for example, Rita as an antenna each time transmitted the pulse of the Mimic Server, even though they are not on the same side)... resulting in both the enemy server and server/antenna to loop. On the other hand, if the server/antenna dies, it will loop (assuming it can send the pulse back to itself). So, an antenna/server entity would be stuck in an endless loop.

As the loops increased, more and more tachyons would meet both the server/antenna and the enemy server at the start of the loop. For humans, the increase in tychyons resulted in strain, felt as a headache. At some point, with enough loops, the server/antenna and/or server may become overwhelmed - either unable to function or unable able make sense of the enormous amounts of tachyons - at which point, the information going back to them becomes useless - and without new usable information - the present will then proceed forward the same way every time. Another alternative might involve some physical limit on the number of tachyons that can be in the same area at a time --- go above or approach that limit on the number of tachyons in the same area at the same time, and the communication may fail.... resulting in no further (or none at all) information arriving at the start of the loop... so the loop again proceeds the same way each time.

Thus, being a server/antenna when going up against another server (e.g., a rogue server) would not necessarily be a better strategy than the current one of servers and antennas being separate (with the ability of the server to 'jump' to an antenna).

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