My hero lived his ordinary life until recently, when he realized that Magic actually exists. So far, he has been granted levitation for a short period, and invisibility for several hours.

Both worked perfectly fine. Now, he has received a third gift from a magician.

My hero was told, that the immortality works like this:

  • The only thing that can actually kill you is getting your head cut off completely or starving to death.
  • Other injuries will still hurt, but everything else will recover itself without the need for surgery.
  • To recover, your body will need extra energy to heal. So if you are hurt, you have to eat and drink like crazy.
  • The immortality works on the principle of "quick, flawless regeneration". Each cell in your body is regenerated perfectly without any pesky side effects, aging included.
  • You cannot drown or suffocate. However, your body will need extra energy to work underwater or in unbreathable gasses.
  • Extra objects inserted into your body (like bullets or daggers) will eventually be absorbed by your body. And yes, that's extra energy cost.
  • You cannot get fat. If you overeat, your body temperature will increase to get rid of the excess energy.
  • The magician will check your progress in life after 250 years.

As you can guess, the magician disappeared after telling my hero these basics.

My hero is a 30-year-old male who has never had any type of operation which leaves something in the body (like hip replacement or a bone fracture, which needs screws to hold the bone together).

He tried to cut himself, and it hurt as usual. The scar seems to be healing quicker than my hero is used to.

My hero still does not believe in magic. Also, he does not trust this magician. However, if he is really immortal, he can make some long term plans.

So, how to test if you are immortal? Yes, you can put a dagger to your heart ... but if the magician was lying (or immortality does not exist) that would be a really stupid test.

Edit: This is happening in current world, current time, in one of First-World Second-World countries. Apparently, Czech Republic seems to be still on the list of Second World countries...

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Tim B Oct 18 '17 at 9:02
  • $\begingroup$ Any further comments added to this question will be deleted. Please take it to chat. $\endgroup$ – Tim B Oct 18 '17 at 9:03

24 Answers 24


Start with the simple stuff

Well you have written a bunch of rules and most of them are non fatal if tested, so you start with the simple and "safe" stuff, and then you move down the list.

Objects are absorbed

Well I have a slight objection to that one: absorbed as in encased and kept indefinitely or dissolved and excreted?

Test: Push a sewing needle into your arm.

Success: Needle is gone after some amount of time.

Failure: Needle causes discomfort, infection, inflammation or otherwise hurt you.

Keeping safe from failure: Visit a doctor and have the needle extracted.

Cannot drown

Test: Jump into a pool at the shallow end and crouch down. Bring a buddy if you wish for extra safety.

Success: Still alive after 10 minutes with no ill effects.

Failure: Feeling the usual feelings of panic and discomfort of not being able to breathe. Starting to get grey-out and tunnel vision.

Keeping safe from failure: Stand up and breathe.

Cannot get fat

Test: Eat excessively. Monitor your body temperature

Success: You do not get fat. Body temperature rises.

Failure: You gain weight.

Keeping safe from failure: Stop over-eating.

Fast healing 1

Test: injure yourself lightly. See how long it takes to heal and if that varies depending on how much you eat.

Success: Wounds heal without scarring or discoloration, and they do so depending on your food intake.

Failure: Scarring results. Wound do not heal any faster compared to what they would normally.

Keeping safe from failure: Stop injuring yourself

Fast healing 2

Test: Cut off some part of yourself, like a centimeter wide flap of skin, as if say removing a birthmark or a mole. That cannot heal on a normal person without scarring.

Success: The cut is healed without scarring.

Failure: The cut is not healed without scarring.

Keeping safe from failure: Sorry, you will have to put up with that scar.

Fast healing 3

Test: Donate blood five days in a row. No normal person reacts well to losing five pints of blood in that short amount of time.

Success: You do not experience dizziness or other signs of low blood pressure.

Failure: You start to feel the symptoms of blood loss.

Keeping safe from failure: Stop donating blood as soon as you feel the least bit ill.

Fast healing 4

Test: Cut off the tip of a finger

Success: The finger heals without trace of injury

Failure: The fingertip does not regenerate

Keeping safe from failure: Again, sorry, it is gone... but a fingertip is easy to live without.

Fast healing 5

Test: Stab yourself in the lung

Success: You heal without sign of injury

Failure: You start experiencing great difficulty to breathe

Keeping safe from failure: Call emergency services and have them patch you up at the hospital. Blame a mugging or something like that.

Fast healing 6

I think you get the idea by now...

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Tim B Oct 8 '17 at 15:56
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    $\begingroup$ Great answer. Perhaps also worth testing the aging thing: Test: get a detailed physical from your most trusted GP, keep the records. Wait ten years, living your life as you previously did, then get another detailed physical. Success: Both tests show you to be in practically identical condition. Failure: The second test is consistent with you having aged roughly ten years. Keeping safe: Nothing you can do about it if you fail, but if you continued living your life as usual, you haven't really lost anything. If you succeed, spending ten years on this test is nothing. $\endgroup$ – Steve-O Oct 11 '17 at 3:32
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    $\begingroup$ A fingertip can be surprisingly hard to live without. I'd suggest a toe-tip instead. It's more easily concealed as well. $\endgroup$ – timuzhti Oct 12 '17 at 1:28
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    $\begingroup$ Any tests you do could only prove the hypothesis of immortality wrong but never correct. Even coming back to life would prove only that you had another life left. $\endgroup$ – Thaylon Oct 12 '17 at 15:06
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    $\begingroup$ Any tests you do could only prove the hypothesis of immortality wrong but never correct. This is generally true for all tests is it not? E.g. in all the years since Einstein's theory of general relativity it has been tested time and time again and was never proven false. But still it is not and can not be proven correct. We just keep testing it in more and more clever ways. As long as it does not fail it's most probably correct but never certainly. $\endgroup$ – Stijn de Witt Oct 13 '17 at 19:06

If all the rules have been explained to the hero I would suggest he goes out and gets a piercing.

If I understand your rules correctly he would absorb the part of the piercing that is encased in his body and the hole will seal itself. This is not how normal healing would work at all, and if the wizard was lying (he isn't, but the hero doesn't know that) the hole would grow shut on its own again once the piercing is removed.

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    $\begingroup$ This is interesting in the same way as the knitting needle through the arm. If the piercing's shaft or stem or whatever were to be absorbed, then you'd think that the pieces that were not inserted into the body there would just fall off. harder to detect if absorption takes a while of course. Also, if this is really just "super fast cell regeneration", I wonder if the rate of healing varies with the amount of blood flow to the area. Would a helix piercing heal as fast as a lobe? Pierce them all, and test! $\endgroup$ – ghoti Oct 6 '17 at 11:57
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    $\begingroup$ Tattoos are another option in the same vein... Ink is a foreign object. Also might be interesting if he had pre-existing tattoos and they disappeared because of the rapid healing. $\endgroup$ – aslum Oct 6 '17 at 14:07
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    $\begingroup$ This certainly testing the rapid perfect healing part of what the magician offered. But if that's all he gave the person. The man might still age, be vulnerable to disease, and be mortal. This is a good answer and was upvoted accordingly. It's hard to know how to test immortality which stops you from dying without trying to kill yourself. A well reasoned answer. $\endgroup$ – a4android Oct 7 '17 at 1:23
  • $\begingroup$ This doesn't actually answer the "How to safely check if you are immortal?" question. Healing/dissolving a piercing only shows your body abilities were altered somehow. It doesn't prove immortality. $\endgroup$ – enkryptor Oct 13 '17 at 12:27
  • $\begingroup$ @enkryptor: True, the core of my answer is to see if there is any validity to what the wizard is claiming without inflicting permanent harm or extreme pain. It might be argued that testing for complete immortality is hard or even impossible, e.g. ageing not appearing to happen might just mean it was slowed by a factor of 1000. $\endgroup$ – Mara Oct 13 '17 at 19:46

This is simpler than might appear to be the case. The person is now immortal or, at least, so he's been told. When if anyone lives long enough eventually they will die except, of course, if you're immortal.

Essentially sooner or later anyone will be faced with circumstances that will kill a normal mortal person. Therefore, the best way to test your putative immortality is to continue living, preferably as if you're mortal, and when that fatal day comes and you're involved in a car accident, fall off a cliff, caught in a fire, drowned while swimming or whatever fatal incident occurs and you're still alive then you've tested your immortality.

Basically if you're immortal you have all the time in the world to test your immortality. The odds are in your favour. Something fatal will always occur to everybody. If the test fails and you're not immortal you haven't lost anything (except your life and that happens to all mortals). You will have lived your life taking all the normal precautions of staying alive. Good luck to you fellow for doing so too. If, of course, it turns out you are immortal and you aren't dead, now you can begin to enjoy your immortality in style.

Living normally long enough itself will be the best test for immortality.

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    $\begingroup$ I'll vote this up - while I stand by my answer (you can't), your approach (simply wait and see) is logical enough given a long enough time-frame - I just interpreted the question as requiring a somewhat quicker solution. I think yours is the better answer. $\endgroup$ – Lee Leon Oct 6 '17 at 15:46
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    $\begingroup$ It does, however, occur to me now that immortal is not necessarily the same as not aging. $\endgroup$ – Lee Leon Oct 6 '17 at 16:15
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    $\begingroup$ That's not testing it, that's just providing an opportunity for it to be tested. Those are completely different things. Also, the most common causes of death are things like cancer, heart disease, etc. Failing to get cancer after 100 years would provide credence to the magician's claim, but leaves the hypothesis that one is immune from disease, but not injury, as a significant possibility. And even if one is injured, there aren't many ijuries that are guaranteed to be fatal without immortality. For instance, people have survived jumping off bridges. $\endgroup$ – Acccumulation Oct 6 '17 at 18:46
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    $\begingroup$ @Revetahw Exactly. So when the magician said he'd be back in 250 years, that's an immortal's equivalent of be back in five minutes. $\endgroup$ – a4android Oct 8 '17 at 10:10
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    $\begingroup$ @ a4android Statistically speaking, it would take 10,000 years for an average American to have a fatal car accident. And again, as I said, it's not enough for it to be something that would have killed, it has to be something that you know would have killed you. And fast healing doesn't prove that the rest of what the magician said is true. And no, just because someone is immortal, that doesn't mean they're patient. $\endgroup$ – Acccumulation Oct 11 '17 at 3:27

You can't.

It is clear from the OP that not only does the hero not trust the magician, but also that the purpose of any test is to prove whether or not the magician is lying.

The magician may well be telling the truth with respect to any non-life threatening injuries (or behaviour such as over-eating), but any improved healing, even if proven and no matter how magical it may appear, does not prove immortality. Immortality can only be proven in such a situation in which the hero would be dead, otherwise.

In other words, if the hero can avoid otherwise unavoidable death, then he is immortal and there can be no alternative proof.

Furthermore, the hero has only been granted magical powers previously for limited periods of time - maybe the magician cannot grant any powers permanently. Immortality only makes sense if it is permanent (or at least significantly beyond a normal lifespan) - it cannot be temporary.

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    $\begingroup$ @MichaelK The OP said that the hero had been told this, presumably by the magician - if the OP just explained that this is how immortality worked then I would agree, but to assume the magician may be truthful in one respect, but not in another (hence the test) is simply inconsistent. $\endgroup$ – Lee Leon Oct 6 '17 at 12:01
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    $\begingroup$ Completely agree with this. I have thought about this on my own several times and the only way you COULD, would be if you were able to directly know and understand the mechanism and its effects, and control it -- a scientific basis, essentially. Otherwise you have to accept things on trust and therefore you can't know, if there is some additional thing you are not being told, which changes everything. $\endgroup$ – Gnudiff Oct 6 '17 at 14:37
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    $\begingroup$ The magician's offer of immortality might be a cunning plan to kill the person. By getting them to kill themselves while testing their immortality. This adds a whole new meaning to the phrase "murder-suicide". I like your answer & it has been upvoted. $\endgroup$ – a4android Oct 7 '17 at 1:17
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    $\begingroup$ Even raising from the dead n times does not necessarily mean you are immortal. The magic might exhaust itself after n+1 times. $\endgroup$ – Thaylon Oct 12 '17 at 15:10
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    $\begingroup$ I like this answer, since there's always the issue of the magician making you only 99% immortal. Since there's already two caveats -- beheading and starving -- who's to say there isn't another? Say, someone ripping your heart out, or feeding you to piranhas. Due to the arbitrary nature of the existing exclusions to the rule, additional invisible fine print in the immortality contract may exist. Any reasonable doubter of wizards would therefore assume that they must exist. $\endgroup$ – Rick Moritz Oct 15 '17 at 17:22

Cut off your little toe as a quick test

It will hurt a lot. But you will see whether it regenerates. It should not regenerate and if it does you know that magic exists and you can be magically healed. That lends credibility to the story of the wizard. Either that or the toe will not regenerate, which is inconvenient but not really a big problem. People survive every day with far bigger problems. And most importantly: with the right precautions you should be able to survive this little test.

Monitor your health over the next couple years

Once this is confirmed you can just try to monitor your health as much as possible. You shouldn't see any difference in the upcoming 5 or 10 years, but you would expect something to happen if magic didn't exist. You can combine this with trying to get fat as hard as you can. This shouldn't really be a big problem to check. Even naturally thin people would get fat when eating nothing but chocolate for a prolonged time.

Assume you are not immortal in the beginning

Until the first real checks in a few years you should live your life as if magic does not exist. This is pretty much a safety net for you in case something normally deadly would happen to you.

Expand your definition of "long-term" regularly

After a few years your character will see that he can survive longer than others and he can expand the time horizon he is looking at. He is immortal, so it doesn't really matter when he starts.

Every couple dozen years he can then increase what he perceives as "long-term".


All in all your character just thinks he has a very long life span. Not really immortal as he will never test that willingly. Maybe he will realize his immortality if some accident happens that would kill a normal human being. But that is certainly not his goal.

Additional benefits

This also prevents your character from going mad because of boredom. He does not perceive himself as immortal - he just thinks he has a very long life span. He still has to care for himself, monitor his health regularly in a very rigid fashion and look out to the end of his life. After all he can't be sure that tomorrow the magic is still there. He can just assume that he probably will live far longer than other people based on his experience up until that point.

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    $\begingroup$ This is exactly what Claire Bennet did in Heroes to test her regenerative powers. On that note, make sure nobody sees you do this or it'll raise some awkward questions. $\endgroup$ – F1Krazy Oct 6 '17 at 9:39
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    $\begingroup$ I'm not so sure about "cut XXX part of your body" solution for it's quite difficult to do so because of the pain it causes. Sometimes it's not even easy to do something guaranteed safe, e.g. jumping with parachute or being under some common surgical operation - it's still scary. The part about waiting for a couple of years makes perfect sence, though. If it were me, I would just live as usual until I notice I'm not getting old or not getting new deceases. $\endgroup$ – user2851843 Oct 6 '17 at 9:58
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    $\begingroup$ @user2851843 Just ask someone to cut it for you... or pay them. There are crazy people for everything in USA. $\endgroup$ – An old man in the sea. Oct 8 '17 at 17:41

Well, he could do it like in Flatliners: have a doctor to stop his heart and wait if his body comes back online before the "safe" amount of time for the brain to exist without oxygen passes. If it does not, the doctor resuscitates him. Of course, that could still mean there just wasn't enough time for him to heal the damage and then he'd have to find a different way.

This method is both fatal and reversible.

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    $\begingroup$ +1 without seeing your answer, posted the same thing. Deleted it an upvoted yours. Highlighting your post so no one else will miss it. $\endgroup$ – Cem Kalyoncu Oct 6 '17 at 19:42
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    $\begingroup$ The "fatal" part of that last sentence is accurate, but "reversible"? Do you realise that the success rate of cardio-pulmonary resuscitation is less than 50%, and even when the patient survives there are often long-term negative effects? $\endgroup$ – Peter Taylor Oct 9 '17 at 20:08
  • $\begingroup$ The heart wouldn't stop, or rather, the heart would restart itself. The only thing that kills is starvation and decapitation. This would go some way to proving you are immortal... the trouble would be finding the crazy doctor to do this. $\endgroup$ – josh Oct 11 '17 at 12:43
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    $\begingroup$ @PeterTaylor I assume this stat is for patients with existing health issues, not normal, health adults or immortal super heroes. Even in heart operations the death rate is down at 3.4% and that requires the controlled stopping of the heart. $\endgroup$ – josh Oct 11 '17 at 12:48

You cannot get fat. If you eat too much, your body temperature will increase to get rid of excess energy

Just eat an aweful lot of calories and see if that holds true. Unless your hero already has a very fast metabolism or a genetic disposition for not taking on too much excess fat he will fatten like a piggidy-pig in a few weeks.

As he can already levitate and make himself invisible getting money to pay for the foods (or the foods themselves without inconvenient middle-men1) shouldn't provide any big hurdle.

1Including but not limited to: Bakers, Butchers, Confectioners, etc.

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    $\begingroup$ @user2534 would you mind pointing out why it does not provide an answer to the question? Many thanks in advance $\endgroup$ – dot_Sp0T Jan 6 '18 at 9:11
  • $\begingroup$ @WaterBearer Are you thinking about a different answer? This particular answer answers the question quite well. $\endgroup$ – The Daleks Nov 12 '20 at 0:21

There are a lot of good ideas here, little things like testing the healing factor, and I really like the pool test. But the really smart thing to do is to do nothing overt.

The problem with some of the more severe overt testing methods is that they will be noticed. If you punch a hole in your lung and you don't want to die, you need to get in front of a doctor, and that means another person you have to convince to keep your secret. Drawing attention to yourself is likely to be worse than stabbing yourself in the lung. Attention means scrutiny, possibly from the authorities. That means long term plans are going to be harder to deal with.

So maybe after a couple of checks that do not rely on somebody else getting involved, stop destruct testing and live your life as an almost mortal man. As a long term check, start taking "before and After" photos of yourself and someone you know. keep this up so you can compare the aging process.

Start some long term planning. Diversify portfolios, start long term investments, get some swiss bank accounts. Bearer bonds. That sort of thing. None of these things is dumb for normal people, so this isn't going to attract attention.

After about ten years, carefully comparing the aging photos, start looking into ways to move your wealth around. Keep on top of tech trends. Also, start looking into setting up false identities. After 20 years, start planning your death and orderly transfer of assets.

Repeat as necessary, and try not to lose your head.

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    $\begingroup$ +1 Excellent point about having to trust a doctor to keep your secret. $\endgroup$ – Henry Taylor Oct 6 '17 at 14:04
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    $\begingroup$ I thought the idea of the "hole in the lung" test was that you see the doctor only if the test fails, in which case you have nothing to keep secret--a hole in the lung is life-threatening to you just like to everyone else. I'm not sure that idea is fully justified by what the magician said, but that's a separate issue. $\endgroup$ – David K Oct 8 '17 at 23:19
  • $\begingroup$ @DavidK if you put a hole in your lung and are not healing, by the time you get to a doctor, it may be too late. Not impossible, but risk vs reward is too slim $\endgroup$ – Paul TIKI Oct 11 '17 at 15:06
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    $\begingroup$ The person who suggested that technique seemed to think you would feel OK immediately, in which case you are OK, or you would feel like you're dying, in which case the magician lied and you call emergency services--which arrive quickly since you're in the parking lot for the ER. I think there may be a third possibility (you feel like you're dying, but you will get better if you wait) and I agree that case isn't well covered by that test. $\endgroup$ – David K Oct 11 '17 at 16:07
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    $\begingroup$ That could work, but to be honest, I cannot think of any circumstance where putting a hole in my lung would be in my list of things to do today. $\endgroup$ – Paul TIKI Oct 12 '17 at 14:04

Over Exercise

A simple ongoing test of a altered state would be to excercise at a level that is going to leave you really sore the next day.

You get to stay really fit and you can test every day without too much long term problems.

No proof possible

My understanding of the scientific method you cannot prove what the magician said was true. That you can only be killed by the methods outlined. All you can do is find a method that will kill you and then unfortuantely you are dead. There is no absolute proof only disproof or running out of tests.

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    $\begingroup$ That was really clever, I like it. Exercise does wear on the body and normally it needs time to recuperate. $\endgroup$ – MichaelK Oct 10 '17 at 13:10

Hire someone to kill the magician. If he can make people immortal, he would do it to himself.

Also, you aren't really immortal, are you? Anything that destroys your head, throat or stomach will kill you. so, if the magician wanted to do you harm, he doesn't need to trick you at all.

But really, what would be the purpose of testing it? What suicidal thing would you regret not having done because you mistakenly believed it would be fatal? Saving someone you weren't willing to risk your life for?

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    $\begingroup$ Presumably, something that mucks up the GI tract will still heal, he'd just be really hungry afterwards. $\endgroup$ – Matthew Oct 13 '17 at 15:43

Since the hypothesis to be tested is "I am immortal", there is no way to skip the "try to kill yourself" step.

Since sticking the fingers in the plug, or whatever quick "suicide" attempt, in case of failure it is obviously stupid.

Therefore the only way to test the immortality of the hero is to put him into some "slow killing" path.

He can i.e. starts drinking heavily super alcoholics. This in a normal human would quickly damage the liver. After 1 year of this regime, the hero can have his liver checked. If it is still fit and healthy, he got the prove. If his liver is damaged, he can still quit drinking and go rehab.

  • $\begingroup$ A ruined liver and an alcohol addiction are not the things that I would want to live with for the rest of my life in case that I'm not immortal... $\endgroup$ – cmaster - reinstate monica Oct 11 '17 at 12:25
  • $\begingroup$ @cmaster, I agree. But you would live longer with those than with a bullet in your skull... $\endgroup$ – L.Dutch - Reinstate Monica Oct 11 '17 at 13:04
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    $\begingroup$ @cmaster You might be immortal and still have to live with that ruined liver ... $\endgroup$ – Thaylon Oct 12 '17 at 15:17
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    $\begingroup$ @Thaylon Which would prove the magician wrong in a funny way: Immortality without full self healing... $\endgroup$ – cmaster - reinstate monica Oct 12 '17 at 15:29

You can never be sure by testing it using self inflicted injury. It could be a healing rather than immortality spell, or wear off after some time (years?), or not provide the full protection described to him

After all, if you were the magician wouldn't you want a hero who, when you reappeared 50 years later to tell him actually he can be killed using something not obvious, and you plan to do so unless he does exactly what you ask?

Also crossref the Norse myth of Baldur and Loki - Baldur was made immortal and all his friends spend their evenings tryingto kill him for fun. The one thing that could kill him was a weapon made from mistletoe (a small plant). Unfortunately Loki didn't see a need to tell him or anyone else that minor fact, before passing such a weapon to one of the people playing the game of "use your weapon on Baldur" ......

Your hero's first quest (before or after whatever else he has to do) should be to find someone else learned, who he can trust, and who can tell him what's been done to him.

I would suspect that whatever it is, is not known, in the whole cosmos, by only one person.....

  • $\begingroup$ That didn't end too well for Loki, if I recall $\endgroup$ – Paul TIKI Oct 11 '17 at 15:07

Especially if he's as skeptical as you make him sound (doesn't believe even after a rapidly healing cut), the most sensible strategy for him would be to just wait. If he isn't immortal, he puts himself at no extra risk and lives a normal life. If he is immortal, then after several decades he should have more than enough experience proving the truth of his immortality: no aging, fast recovery from injuries, etc. At that point he can make his long-term plans. And since his lifespan is infinite, the decades he waits to confirm his immortality are completely insignificant.

Edit: Wait, I re-read your question, and you start by saying that your hero believes in magic because he has been given the powers of flight and invisibility, and saw that they worked. Then you say he still doesn't believe in magic after being granted immortality. So I'm not sure what level of skepticism I should be reading in this.


Can you still get sick or ill? I'm assuming from the various other conditions you've listed (can't get fat) that you don't.

In which case there is one quite easy method of testing this that shouldn't be fatal if it goes wrong;

Eat some raw chicken.

If you get food poisoning and are violently ill then you're not immortal, if you don't you may have just got lucky so try again. Repeat at least five times, if you don't get ill at all then the magician was telling the truth.

The advantages to this are food poisoning is awful and very obvious, reasonably easy to self inflict but shouldn't be fatal or have any lasting effects on a healthy adult.

Other things you could try (with various degrees of success depending on vaccinations etc.) are contracting chicken pox, measles, thrush or other skin conditions (admittedly some of those can have more nasty results if caught as an adult) or even attempting to contract a mild STD (not AIDS or HIV, just something like chlamydia or syphilis).


Wait, the only really sure check that is entirely "risk free", as in no more risky than his existing life, is to simply wait and see if he ages. He will probably run into situations which prove or disprove some or all of the rules he has been given by the wizard who has cursed him with immortal life but the ultimate test of his immortality is time. Anything else only proves he can heal not that he'll live forever, twenty or thirty years with no signs of aged decline should be convincing enough for even the staunchest cynic.

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    $\begingroup$ The point about testing quickly is to shift your situational analysis: If you know you are immortal, you can act very different from a mortal being in exceptional circumstances. Say, you come into a situation where you stand a chance to save your son's live if you know that you are immortal (by getting him out of a sinking ship that's already below the water line), but no chance at all if you are not. You definitely want to be sure of your status. $\endgroup$ – cmaster - reinstate monica Oct 11 '17 at 12:34
  • $\begingroup$ @cmaster No you don't, you do it anyway, I would at least. Plus even if you can't drown that only proves one of the other "rules" it doesn't prove you're immortal, only living forever can prove that, not invulnerability. $\endgroup$ – Ash Oct 11 '17 at 12:44
  • $\begingroup$ @cmaster Also, if you are immortal, you'll start thinking about life differently, yours and everyone else's. Acting immortal now verses acting immortal 50 years from now is not a big difference if you are going to live ages more. $\endgroup$ – frеdsbend Oct 11 '17 at 17:13

In some sense, we're all immortal - until we're not. That is, we've grown up with a set of rules that help us stay alive (and stay complete) for the longest possible time. Those rules say things like "don't ride a motorbike without a helmet and thick leather jacket" and "don't jump off cliffs" and whatnot. We learn these rules because people tell them to us, but also because we test them out when we're kids (falling out of a treehouse and breaking an arm, for example).

Your hero just has a new set of rules - and even if he trusted the magician, he'd still have to go and discover those rules for himself. @MichaelK gives a good logical course of action to re-learn the rules of self-preservation, but even those won't really tell your hero what he can and cannot do.

Over the hero's (now extended) life, he'll try more and more things and gradually find out what he can and can't do. For example, he might jump out of an upstairs window - for most of us that's survivable, but our hero seems to be able to do it with extreme ease. You and I would think "wow, that was close, lucky I only broke a leg - glad it wasn't worse than that". Our hero thinks "hmm, that was no big deal, let's try jumping out of a 5th story window now". So it goes on, until our hero works out what his new limits are. Presumably jumping out of a 100th story window would lead to such complete injuries that whilst survivable, our hero would still have a long recovery time. That might convince them that jumping out of an aeroplane without a parachute isn't worth the 'cost' of the recovery, even if it's survivable - especially if there's another way down, which may appear more difficult or impossible at the time.

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    $\begingroup$ Actually, there's no big difference in the injuries from a 100 story dive and an airplane dive: In both cases you'll hit the ground at approximately 200 km/h as the air resistance will slow you down to that speed. (Assumption: 1 story = 3m. So free-fall in vacuum would yield a terminal velocity of about 270 km/h, which is already significantly higher than the maximum free-fall speed in air.) $\endgroup$ – cmaster - reinstate monica Oct 11 '17 at 12:46

Testing the drowning part is rather simple: just hold your breath. If you cannot suffocate, you will be able to hold your breath indefinitely, if you can suffocate you will pass out and automatically start breathing again with no ill side-effect beside a headache. (Pro-tip: do not try this at home! It's really uncomfortable if you are not immortal)

An easy test for the invincible part would be to get infected with the common cold. If the wizard spoke the truth, then the infection should be defeated without any effects other than a major hunger. As that illness is highly infectious, not getting it if you really try is close to impossible. Asking someone to cough in your face might however cause socially awkward situations.

Another test would be to find a sharp object and cut into the tip of a finger with it just deep enough to injure the skin. That part of the body is highly sensitive (it really hurts) and therefore measuring the time it takes to heal becomes very obvious as you get constantly reminded of the state of the injury. It usually takes about a week for such a skin penetration to heal completely, so if it is gone by the next day, that part seems to be true as well.

Testing for true immortality like driving a knife through the heart I would simply skip. There is no logical reason to test that. Sooner or later there will be a situation where someone will test that for me anyways. And if it still hurts like crazy there is no need to know, because I would want to avoid such situations at all cost anyways. There is also the risk that I might pass out from the pain, and while my body would dissolve the knife I might not be able to eat/drink enough to support it, and then I'd die despite being otherwise immortal.

The hunger part should be a dead-giveaway alone, as a sudden overwhelming hunger would be quiet obvious. As my body approximately heals that way - sadly without the immortality and perfect recovery part - I got some experience with that, if I get ill I eat about twice as much on the day before (my friends keep calling me Frostmourne). Excessive drinking would only be necessary if your body actually needs to replenish fluids, but not for skin/bone/organ regeneration. Or if the body would try to flood out an infection, which probably won't happen with this type of immortality as such infections would be dissolved magically.

This form of immortality might result in the following side-effects:

  • Excessive fear of starving, because you need food to survive, but can't store it, because the body dissolves it.
  • Excessive fear of blade-like objects, because they could cut off your head.
  • Allergy-like reactions when the body tries to dissolve otherwise harmless particles like spores or car emissions.
  • Immunity to any form of drugs and/or medication, even those which could be helpful.

How to safely check if you are immortal?

Please, excuse me sir, but it is impossible! There is not a safe way to check if you are imortal or not! It is plain logical think. Do you want to know if you are imortal or not? Jump inside a active volcano, place your head straight in the path of a magnun 45 bullet or similar. Smoking for 50 year or more and dont have a lung disease is not a prove you are imortal, it is not even a prove you are immune to the cigars quimical. Some things are the way they are, basead on logic. Some times there is not a shortcut :) .


Get infected from diseases, such as Cholera or TB for which medicine exists.

But don't take any medicine. If it cures by itself you are immortal. If the disease increases daily you should start taking the medicine.


Visit a Hypobaric Chamber

Hypobaric chambers are routinely and safely used for training people to cope with the effects of a high-altitude/low-oxygen environment:

A hypobaric chamber, or altitude chamber, is a chamber used during aerospace or high terrestrial altitude research or training to simulate the effects of high altitude on the human body, especially hypoxia (low oxygen) and hypobaria (low ambient air pressure).

One of the powers the magician claimed to bestow is:

You cannot drown or suffocate. However, your body will need extra energy to work under water or in unbreathable gasses.

In theory you no longer require oxygen as long as you have food (I assume that's what "extra energy" means). So all you need to do is visit any high-altitude training center with a hypobaric chamber, and pay them to take you and your dinner for a ride.

Have them take you to an impairing but not-immediately-life-threatening altitude to start with, like say 25,000 feet. You sit and enjoy your dinner and you either start rapidly becoming impaired from the low oxygen levels (in which case the lab technician repressurizes you, or you grab the nearby oxygen mask, or whatever) or you don't. If you don't, the technician can gradually increase the altitude even further. Eventually you reach an altitude where a normal person would lose consciousness and rapidly die from lack of oxygen. If you remain conscious and unimpaired, then congratulations; you may not be fully immortal, but you do seem to be immune to suffocation and no longer required to actually breathe!

Why it's safe

Someone else operates the chamber for you and observes you the entire time. If anything goes wrong, they can rapidly restore pressure and give you supplemental oxygen. If they're quick you probably won't even suffer any permanent brain damage from the hypoxia. Just try not to break your nose when you pass out and fall over.

You're also not exposing yourself to any exotic of potentially toxic atmospheres. You're just slowly removing O2 from the environment, and immediately restoring it the moment anything goes awry.

What are the risks?

Maybe the tech is incompetent or hates you for some reason. They lock you in the chamber, take you to 50,000 feet (good luck forcing the door open with the chamber under that much negative pressure), and go play Tetris for a few hours. You'd better hope you're really immortal.

Or maybe the chamber suffers a technical fault, and depressurizes too much or cannot be repressurized when something goes wrong. Probably these things have failsafes built in so that things like that mostly never happen.

What are the limits?

With this method you only find out if you're immune to suffocation as long as you have a source of extra energy. It's possible that this aspect of the spell works as advertised, but others do not. I wouldn't suggest you do this, and then move on to the "shoot myself in the face" test. Better to do it, wait 10 years, and confirm that you're not aging instead. And then you just assume you'd pass the "shoot myself int he face" test, without actually trying it.

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    $\begingroup$ Problem with that is, that technician is going to look at the plan - and possibly the results - and go what the heck?. Ending with him or her knowing, if not about the immortality, then at least that something's up with this person. Alternate option: take some kind of opaque mask in, so the "test" is about, say, some kind of new oxygen mask. If the person suffers from low oxygen, clearly the "mask" prototype failed, if it does work, it was a test of a technology(commonish) not a inherent ability (rareish and interesting). $\endgroup$ – Megha Nov 26 '17 at 3:03

You can't, and he's not. You can't because he's not.

The only way to prove that he is not immortal is to die. As the wizard said there are conditions in which he can die, he is presumably not immortal - otherwise the wizard would not have felt the need to explain things that could kill him, unless the wizard is lying not about the immortality, but the mortality. This is just fast regeneration.

  • $\begingroup$ Being "immortal" usually means not dying because of age, and in this case includes other types of wounds. Not being able to die at all, is called to be "eternal", which is f.e. claimed for the christian god. $\endgroup$ – Thaylon Oct 12 '17 at 15:25
  • $\begingroup$ Then why does he still need food? $\endgroup$ – Stackstuck Oct 13 '17 at 19:27

Ever see Flatliners? Get a medically trained buddy to stop your heart and see if it starts up on it's own, otherwise attempt resuscitation. The only way to test immortality is to die, there isn't a "safe" way to do that.

How is this [magic] energy gathered/replenished to heal or survive underwater? If it's through food, hence starvation being a cause of death, magic typically requires a lot more calories than a person can eat. If it's replenished some other way, why would they need food to survive? Or a body for that matter? as long as they can gather magic energy they should be able to survive as only a head since biological processes aren't necessary to survive, evidenced by surviving underwater.


Why not just wait until the hero accidentally injures himself? Then he could eat a lot and see his body temperature and injury.

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    $\begingroup$ I don't think this is a very helpful answer. What you are suggesting, effectively, is ‘do not check for the condition’. That's not what the question needs — unless you can explain how it would work better than anything else. $\endgroup$ – can-ned_food Oct 7 '17 at 9:45

Since his body only need extra energy to work in an ambient filled with unbreathable gasses, he just need to close himself in a garage with a car engine turned on.

If after some minutes/hours he only feel tired, then he is an immortal, if he start to not breath well (or feel some of the symptoms of the CO2/CO poisoning) then he can exit the garage and he is not an immortal.

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    $\begingroup$ That one is very dangerous because hypoxia degrades your ability to determine that you are in any kind of danger. See this example from hypoxia training. That one is NOT a safe way of testing. $\endgroup$ – MichaelK Oct 6 '17 at 12:00
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    $\begingroup$ @MichaelK I suppose there is not a safe way to test if you are an immortal since you are trying to kill yourself (or provoke a seriuos damage) anyway. And before to die from CO poisoning he can have a lot of warning signal as the concentration raise. $\endgroup$ – Gianluca Oct 6 '17 at 12:49

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