Imagine you are a petite, high school girl named Brooklyn. You also happen to be a superhero, and your power is speed.

You were on a mission to investigate a suspicious politician with your best friend since kindergarten Amanda and her boyfriend Brian (a shape shifter and heat controller respectively).
It turns out that the politician is up to no good, and you are captured. Your friends are sedated, to keep them from escaping, but you are contained more easily; just shackled to the wall. You can't get out.
A timer for a bomb starts to tick down. At super speed, ten seconds seem like a long time. There is no hope of escaping without help.
6.75 seconds left, and the impossible happens. Someone runs in, so fast even you can't see her properly, and frees you and your friends. You escape in the nick of time (your friends were carried out too), and pass out as the building explodes dramatically behind you. Your last thought is that your rescuer looks oddly familiar...
You wake up in a motel room. Brian is still asleep, but Amanda is up, and she has tied the rescuer to a chair. She has good reason to be suspicious; the claim your rescuer is making is far-fetched even by your standards.
She claims to be you, from about 5 years in the future. So far as you know, time travel is the stuff of science fiction.
She looks the part. For half a normal second, you thought she was a younger version of your mom. She remembers everything you do about your childhood. You ask her to try to predict something, but she can't. She says all her memories since a couple hours ago were suppressed, to keep her from changing the future to badly. She says she came back to rescue you, and then do something else that she can't remember.
Amanda thinks that she's a telepathic power mimic that shape shifted to look like an older you.

How can she prove she's not?

- You don't want to risk untying her (but it might be necessary)
- You can't call in for help, since you've discovered from the news on room's TV that you and your friends are being blamed for blowing up the building
- You should avoid leaving the room or getting separated from your friends
- She couldn't bring anything back from the future
- You all your cool gadgets were confiscated when you were captured

This question is different from How do you prove you're from the future? because that question assumes you have lots of resources to prove yourself with, while in this situation you have very few. I don't think any of the answers fit within the limits here.

  • $\begingroup$ By "suppressed memories" I mean that they all feel like they're on the tip of her tongue. If she sees someone or something that she will have a really positive experience with, she'll feel good about them, but she won't know why. She retains muscle memory. Not sure if this is important. $\endgroup$ – Mary ML Apr 30 '15 at 6:05
  • $\begingroup$ DNA test is the most straight forward evidence just swipe some sample of saliva or puck a few strains of hair will suffice. $\endgroup$ – user6760 Apr 30 '15 at 6:34
  • $\begingroup$ @user6760 I don't think that they would be able to preform a DNA test in a hotel room... otherwise this would be easy $\endgroup$ – Mary ML Apr 30 '15 at 6:43
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    $\begingroup$ I knew it would eventually come to this no problem let's just check the molar(tooth) against each other please don't tell me one of you lose all the teeth. $\endgroup$ – user6760 Apr 30 '15 at 7:19
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    $\begingroup$ @Ghanima, as a possible power mimic, future-Brooklyn could mimic Amanda's power and shape-shift the exact same message onto her own arm... $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:38

Use logic.

Supposing she were a power mimic, why would she mimic Brooklyn? Why would they not instead mimic Amanda or Brian? She'd point out that Amanda is being inconsistent, that if she really did believe that about her, then simply tying her to a chair would be rather useless (she would instead have to be sedated, like Amanda had been while captured) - thus she must already believe that she had only the same super-speed ability Brooklyn has. If she was really telepathic, she also would have surely made up a much more logical lie, knowing that Brooklyn did not believe that time travel is possible. Indeed, if people with such powers did exist, then who is to say that the Amanda or the Brooklyn in the room right now is the real Amanda or Brooklyn?

The choice is up to them, either they think this person is so far above them in power and ability, and could just escape and kill them at any time, and is merely toying with them for no clear reason whatsoever... Or they can take her at her word.

Even if they don't want to believe what she says, then whether or not she is actually from the future doesn't actually change a thing: she did rescue them, in the end, and that's the main, big reason to trust her. Would Amanda have tied up an anonymous, unknown rescuer who didn't happen to look like Brooklyn? Future-Brooklyn could also be evil and untrustworthy, for all they know. So there's no obvious reason to keep her tied up, at least.

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    $\begingroup$ Wow, this is really the best answer here. $\endgroup$ – Aarthew III Apr 10 '16 at 5:11
  • $\begingroup$ Actually, you could then go one level deeper than this. If this 'logic' is what Amanda, Brian and now-Brooklyn would be using to decide whether or not to free her, a telepath would know all this from reading their minds. And all he/she has to do would be to mimic Brooklyn, make up this lie about time-travelling (precisely because it sounds illogical), and then 'rescue' them, so the trio would think all these things mentioned in the above answer, and free her. The basic problem, is that this still depends too much on trust and 'what ifs'... $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:26
  • $\begingroup$ The point is there isn't any way out of this dilemma without trust. Brooklyn still has to trust the Amanda standing next to her, after all, a trust she has no reason to hold if what Amanda says is true. The fact of the matter is that what Amanda is saying is really illogical and inconsistent. $\endgroup$ – Fhnuzoag Apr 11 '16 at 13:23

Just look at her finger prints. If they are identical to Brooklyns, then she is likely to be Brooklyn.

I don't know what my fingerprints look like exactly so a mind reader wouldn't be able to extract that information from me like that.

It would also be too small of a detail for one to see to replicate.

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    $\begingroup$ I think that would depend on the extent of shape shifting in this setting. It may well be possible to duplicate a person down to their fingerprints, retina, etc. $\endgroup$ – Fhnuzoag Apr 30 '15 at 13:14
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    $\begingroup$ Also, since they had just been captured, it would have been easy to collect biometrics from them for the purpose of duplication. $\endgroup$ – Fhnuzoag Apr 30 '15 at 13:24

There are 2 things I can think of:

  1. Watch for her habits and quirks.

Whilst a telepath could read a person's mind, and they would have all of the information about the person's history, that doesn't mean that they have lived that person's life.

So after a while looking for specific things, it would be easy to spot, like looking for tells when someone is bluffing in poker.

You could see if future Brooklyn bites her nails when she's nervous, or cracks her knuckles, or scratches that specific point on the back of her head when she's thinking about something that present Brooklyn does.

Someone pretending to be her would not know to do these things in the middle of a conversation, because they are done without thinking. An imposter would be going through memories trying to look for the correct information to questions about her life, the real future Brooklyn would be thinking whilst maintaining the same unthinking habits that we all have.

  1. Watch for a spontaneous reaction.

You could get Amanda to go in the bathroom, shape-shift into someone/something that Brooklyn is afraid of/fond of (I'm not sure how the shape-shifting works, but it could be a childhood friend or pet for example), and watch the reaction of future Brooklyn when Amanda reenters the room in this form.

It would take at least a second for a telepath to identify from Brooklyn's memories what she is seeing and react appropriately. A telepath would simply know these facts about Brooklyn, she would not have assimilated them into her own life.

There would be an ingrained response to something so profound in Brooklyn's childhood memories that someone wouldn't be able to fake the correct reaction within the quarter second that they should do, so her face lighting up seeing fluffy again or recoiling at the childhood fear of her aunt's grandfather clock would tell present Brooklyn everything she needed to know.

So Brooklyn isn't looking for what this person claiming to be from the future knows about her life, but rather that she has lived the same life as her, and would do things in the same way that an imposter would not know to do without thinking and considering.

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    $\begingroup$ For number 2, this might not be very accurate, considering the future-Brooklyn is 5 years older. Though her memories for those 5 years may have been suppressed, the very fact that she is older means some subconscious things may have changed. For example, now-Brooklyn may have a morbid fear of spiders, but future-Brooklyn may not anymore. She may remember that she used to be afraid, and not know why she isn't anymore, but subconsciously, that part of her would already have changed. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 15:16

"I'm going to remember this moment very well. I'm currently thinking a certain word. I will remember it, and in the future - when I'm back from the future to this moment, and tied to the chair, I am going to whisper that word to my past self's ear. So, dear future me, what is that special word I'm thinking about?"

(the only alternative to time travel would be that the person tied to the chair can read my mind... but in that case, screw it, I'm willing to set her free.)

Edit: I came up with an idea how to overcome the telepaths.

"My dear past self, so if this is a stable loop, I'm gonna do everything the same as you did in the past, right? Well then." I pull a box of cigarettes out of my pocket, covering the 'lid' with my palm. "Give me the digits."


I read the serial number on the excise tax band. It ends with 656.

No background check could go this deep. We're surrounded with millions of random numbers: barcodes, serial numbers, expiration dates, manufacturer's phones. It's impossible to predict what I'll use as my random number generator, it's only important the number is decided even before I ask about it - but completely lost through the deterministic, but impossible to trace in their entirety processes, like which batch of cigarettes reaches the shop where I buy them. If the time loop is rock-stable, I might get away with rolling dice and asking what's the result before revealing them, but interaction with future self might introduce minuscule loop instabilities. If I pick an unknown, but already determined random number, there will be no instability. I'm gonna remember it, and repeat it when the time comes. And no telepath and no spy can guess it before I read it.

  • $\begingroup$ How does that work against a telepath? $\endgroup$ – Xavon_Wrentaile Apr 10 '16 at 3:56
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    $\begingroup$ @Xavon_Wrentaile: As I said: screw that. The alternative is that she's simultaneously a telepath, a shapeshifter AND super-fast, plus had some nefarious motive behind saving our lives. And without a telepath in our midst (and if we had one, how would we tell the telepath is not another shape-shifting stand-in?) there is no way to tell. Once you bring in shape-shifting telepaths who can also mimic our superpowers into the equation, this becomes a ridiculous shitfest of paranoia. And the only way out is to judge by actions: she might not be me but she still saved our lives. $\endgroup$ – SF. Apr 10 '16 at 4:33
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    $\begingroup$ ...never mind that - a'la Total Recall - who's to say the me in the future doesn't cross over to the dark side? Instead of proving she is "me", we should be more interested in proving she isn't evil. The proof she's future me is pretty much useless for our current needs. $\endgroup$ – SF. Apr 10 '16 at 4:37
  • $\begingroup$ @SF. yes, very true, and a very good point. But the question asked was how to ascertain future-Brooklyn is who she says she is... $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:33
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    $\begingroup$ «all her memories since a couple hours ago were suppressed, to keep her from changing the future to badly» so the future girl would not remember the answer, anyway. $\endgroup$ – JDługosz Feb 2 '17 at 6:26

A few different options:

Proof by additional time travel:

Brooklyn will decide that, if time travel is real and possible, she will time travel again, to this room, 2 minutes from now. For example, she looks at her watch and it's 10:03 PM. At 10:05 PM, another future version of Brooklyn appears in the room, says, "Yes, time travel is real. Yes, that's also me. No, I can't tell you anything else or Bad Things happen. Bye!" and disappears in a flash of temporal light.

Proof by interrogation:

Presumably telepaths have some limits. Instruct Now-Brooklyn to start thinking of an earworm (favorite song, The Song That Never Ends, etc). This should make it harder to read her mind. Now her friends should interrogate Future-Brooklyn on stuff only she should know until they're satisfied.

To make this more effective, you should distract Future-Brooklyn during the interrogation to make it harder to concentrate. Pain would probably be the most effective, but since you might be beating up your friend, tickling is an alternative that will make it harder for her to lie/read minds while answering questions.

Proof by past knowledge:

If for whatever reason neither of the above two options will work, we need to try some separation to negate the telepathy. It should work like this:

Ashley writes down some instructions without showing them to anyone else. She hands the instructions to Brian, and sends him and Now-Brooklyn to another room (out of telepathy range, whatever that is).

Brian's instruction is to hand the rest of it to Now-Brooklyn.

Now-Brooklyn is told to think of a question/answer from her past that only she knows, and is hard to remember, then to write it down without showing Brian. She dredges her memory, comes up with a childhood event, and writes down the question and answer on separate pieces of paper. She then folds them up and hands them to Brian, and tells him to go back to the room.

Once Brian gets back, we can now ask Future-Brooklyn the question, and no one in the room will have the memory of the answer, so she can't read any minds to answer it. It has to be the real Future-Brooklyn.

  • $\begingroup$ For 'Proof by interrogation', future-Brooklyn might not be able to read now-Brooklyn's mind, but if Amanda and Brian ask her a question, they would of course think of the answer, so future-Brooklyn could read their minds. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:18
  • $\begingroup$ For 'Proof of past knowledge', a telepath's skills may not be confined solely to the room. She may still be able to read now-Brooklyn's mind as she writes the answer down. And to take now-Brooklyn far away enough that the future-Brooklyn can't read her mind would be impossible because they've been blamed for blowing that place up, so they effectively can't leave the room/building without getting spotted and arrested. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:21

I have actually prepared for this very situation by deciding on a code phrase in case I ever encounter time travel. Back in the early '90s, while pondering far too heavily on time-travel related SF, I decided that the easiest way to convince me that I was me was to have a simple catch phrase that nobody else knows. If a me from the future ever shows up and doesn't know the phrase, well, they're not really me.

What, the rest of you haven't done this?

This answer is actually in all seriousness: somewhere around 1991 or 1992, I came to this conclusion - I've just never encountered a need (nor do I ever expect to encounter a need) for the phrase. Think of it as preparing for something that will never, ever happen... unless it does.

Oops! I completely missed a line in the question:

Amanda thinks that she's a telepathic power mimic that shape shifted to look like an older you.

The "telepathic" part of that quite possibly negates my answer. (Thanks to @not store bought dirt for pointing this out.) The only way this answer would still stand is if the telepath could only read surface thoughts, and not deeper memories: if the telepath didn't know a catch phrase was necessary in the first place.

  • $\begingroup$ @notstoreboughtdirt do not think about the white monkey. It actually might work, you do not think about all your passwords each time in any situation, but when time comes to use them you recall them. So mind reading not a problem there unless the reader might read memory without person recalls events. Hm, but I'm not sure it should be called mind reading then. $\endgroup$ – MolbOrg Feb 2 '17 at 1:29
  • $\begingroup$ When I say, "hi future me." I think <if he doesn't say 'white monkey' he's fraud.> Unless you can do hashes in your head a challenge/response doesn't work if the other side can read from your script. $\endgroup$ – user25818 Feb 2 '17 at 5:44

As someone said in the comments: DNA test or alternately, you can have both them have a scar from a fight... Something which could have been formed in a unique circumstance... They could match that.

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    $\begingroup$ I figured that shape shifter would be able to replicate a scar, see above comments about DNA $\endgroup$ – Mary ML Apr 30 '15 at 6:44
  • $\begingroup$ How about the scar then ?? Something they got in a fight... $\endgroup$ – user96551 Apr 30 '15 at 6:46
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    $\begingroup$ The scar could be replicated by a good shape shifter. Even if it's a scar that isn't visible normally, a mind reader could discover it's presence if anyone thought of it. $\endgroup$ – Mary ML Apr 30 '15 at 6:50
  • $\begingroup$ If it's a scar on the person's back (covered by clothes) a shapeshifter could not replicate it without seeing it, and if the person never had a good look at it due to its location (on their back) then a telepathic shapeshifter could not extract its exact shape from the person's mind. It's a lot of "if"s but it could be possible. $\endgroup$ – Alexandre Aubrey Jul 10 '18 at 14:49

Interrogation process in a few simple steps:

  1. Separate future-Brooklyn from now-Brooklyn. If the two Brooklyns are together, and someone asked future-Brooklyn a question, now-Brooklyn would also hear it, and she would subconsciously think of the answer. Since future-Brooklyn is suspected to be telepathic, she would be able to hear the answer in now-Brooklyn's head and say it. So, put now-Brooklyn somewhere else, where she wouldn't even hear it if future-Brooklyn were shouting at the top of her lungs. If it's impossible to physically separate them, give now-Brooklyn a pair of headphones and tell her to watch TV/listen to music while staring at the wall, or just knock her unconscious for a while. Just make sure she has no way of knowing what questions future-Brooklyn is being asked.

  2. Have both Amanda and Brian collaborate to ask future-Brooklyn questions that neither of them know the answer to, and those questions have to be factual. Nomatter how far you travel, how old you are, or how many things you've experienced, the answer cannot change, and both Amanda and Brian cannot know the answer. For example: During vacation when you were 10 years old (assuming now-Brooklyn is about 15), what colour was your toothbrush at your hotel? She wouldn't have considered it necessary to share that information with anyone, and the toothbrush will remain the same colour in her memories, nomatter what. Or What was the last thing you said to your mother and/or father when you last saw her/him/them? It would be personal enough that she wouldn't have shared it with anyone, and apart from slight forgetfulness, her feelings, opinions, beliefs and experiences would not have changed the fact. By the way, future-Brooklyn would have to answer the questions truthfully. 20+ questions should be enough.

  3. Amanda and Brian, not knowing if the answers are right or wrong, would have to write them all down. But they must not let now-Brooklyn see the questions or the answers.

  4. Let now-Brooklyn back into the picture, with absolutely no idea what questions were asked and what was answered. Amanda and Brian will ask now-Brooklyn the exact same questions, in the exact same order, etc. And still do not let her see future-Brooklyn's answers: you do not want her to be influenced by what she sees written down. Now-Brooklyn also has to answer truthfully, and Amanda and Brian can check her answers with future-Brooklyn's answers.

  5. Cross-reference the answers. If both Brookylns gave the same answers to most (well, actually, should be all) of the questions, then you know that future-Brooklyn is legitimate. If there is a large discrepancy, or if it looks like future-Brooklyn was guessing, you know she's a phony.

The good thing about it is that it makes all future-Brooklyn's powers completely redundant. Speed and power mimicking would not help her here. And, if she really were a telepath, there would be nothing useful to pick up in other people's minds, because neither of them would be thinking of the answers. Amanda and Brian would not know the answers, and now-Brooklyn would not even hear the questions, until after future-Brooklyn has already given all her answers. By then, it's too late to change her answers if she realises it was wrong.

Also, by asking factual questions, it would not matter how old either of them were or what happened to future-Brooklyn in those 5 years. For example, if you were to ask a opinion question, like If you were to see your first, most beloved pet, Jack the dog, would you be happy or sad?, now-Brooklyn might say she would be happy, because she loved that dog. But future-Brooklyn may have let's say watched her friend get viciously attacked and eaten by a dog during those 5 years. Though the memory would have been suppressed, subconsciously, she would have developed a phobia of dogs, without knowing why right now. So she might say, she'd be frightened, cos she's scared of dogs. And this would cause errors in the cross-referencing of answers, unlike the factual questions above. Nomatter what happened to you, if your toothbrush was blue, you will always remember it to be blue.

  • $\begingroup$ I'm assuming that this is normal telepathy, where most telepaths can only read people's thoughts at that current moment. If the person is not thinking it right now, they would not be able to read the thought. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:13
  • $\begingroup$ @ASG: That's a far-fetched assumption. Never mind the fact if you asked me today about my toothbrush when I was 10yo, I'd be completely clueless. There are very few facts that one simultaneously remembers that long, keeps secret that long and are such that others may guess one still remembers them. $\endgroup$ – SF. Apr 11 '16 at 18:51
  • $\begingroup$ @SF. The assumption is quite logical, actually. Most telepaths I've heard of can read your mind in a sense that they know what you're thinking. But that doesn't necessarily mean they can see all your memories. Only one telepath I've heard of can do that, and then again, he wasn't able to to do it from a distance. $\endgroup$ – ASH-Aisyah Apr 12 '16 at 0:33
  • $\begingroup$ Plus, those examples are just that: examples. The whole point is that Amanda and Brian don't know the answer, and it's a factual question that cannot be coloured by emotions. There are many other possibilities: What's the colour of your bedroom wall (assuming neither Brian nor Amanda have been to her house), what's the pattern on your bedspread, what was grandma's favourite food, what did mom live to sing at night, etc. Emotions won't change the answers, and it's not likely Amanda or Brian would know. I certainly don't know these details of my friends' lives. $\endgroup$ – ASH-Aisyah Apr 12 '16 at 0:38
  • $\begingroup$ Seems like stuff a thorough background check of the subject would provide. Bugging the house, taking photos of it, a channel of communication and an agent to dictate the answers from the file. Find the bedroom photos, tell wall colors. Mother singing recording. Grandma's dietary habits. All on file. If anything's missing, it can be chalked up to "I forgot, it's been such a long time." $\endgroup$ – SF. Apr 12 '16 at 4:45

Have Brooklyn go out and buy a newly released book that none of them have read. A big, thick textbook. She can use her speed to avoid getting recognized (blurring her face) or caught.

Have future!Brooklyn read it at super speed. Have Brooklyn take the book across town (again, using her speed to avoid being seen or caught), and quiz future!Brooklyn on it over the phone.

Of course, it doesn't sound like multiple powers are particularly common, so the fact that future!Brooklyn has demonstrable super speed makes it dubious that she also had the proposed telepathy and shape-shifting.

  • $\begingroup$ I don't understand. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:27
  • $\begingroup$ 1) They can't go out to buy a book or go across town, cos they've been accused of blowing that place up, so they'd be arrested if they left the room. 2) How would quizzing future-Brooklyn about what she read in the book from over the phone prove anything? 3) Even if you meant let now-Brooklyn read it, and quiz future-Brooklyn to see if she remembers the book after 5 years, future-Brooklyn is also telepathic, and may just pick up all the info from now-Brooklyn's head. 4) Multiple powers are possible. Already it has been suspected that future-Brooklyn is telepathic and a power mimic. $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:27
  • $\begingroup$ Sorry, I meant have Brooklyn go across town. Speedsters are pretty hard to catch. And as for buying the book, she could blur her face with her speed, or just outright steal it. $\endgroup$ – Xavon_Wrentaile Apr 10 '16 at 16:32
  • $\begingroup$ Hmmm, ok, yup, that would make more sense... 1) She wouldn't be caught (hopefully). 2) It would prove that future-Brooklyn really remembers something now-Brooklyn experiences. 3) Since now-Brooklyn is all the way across town, a telepath wouldn't be able to read her thoughts from so far away. Yup, I guess the only problem now is if future-Brooklyn would remember the book details after 5-years... $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:45
  • $\begingroup$ by the way, would you mind editing your answer slightly, so I can re-vote? $\endgroup$ – ASH-Aisyah Apr 10 '16 at 16:46

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