In a parallel universe, death is physically impossible so nothing can ever die but this universe has lots of life. It is also physically impossible for any life form in this hypothetical universe to be harmed or feel pain. In this hypothetical universe, death, pain, and harm being impossible is as fundamental a law of physics as conservation of energy and momentum in our universe.

How could the physics of this hypothetical universe be different from ours to make death and harm and pain impossible?

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    $\begingroup$ I'm not a physics expert, but I think the answer is either "It's impossible" or "Bad things follow." $\endgroup$
    – Frostfyre
    Jan 20, 2016 at 0:13
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    $\begingroup$ It is impossible, but for the sake of the story, disregard that. I vote bad things follow. $\endgroup$ Jan 20, 2016 at 0:30
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    $\begingroup$ Could you be more specific? What happens when you're trying to harm someone? $\endgroup$
    – enkryptor
    Mar 14, 2016 at 7:59
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    $\begingroup$ Define "harm". When I restrict someone's movement, do I harm them? When I insult someone verbally, do I harm them? $\endgroup$
    – enkryptor
    Mar 14, 2016 at 8:10
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    $\begingroup$ The universe is actually a simulation. $\endgroup$ Nov 4, 2016 at 17:16

9 Answers 9


Fundamental concepts

To attempt to summarize your question, in two points:

  1. First, you posit a universe whose fundamental laws preclude death, harm, or pain to any life form.

  2. Second, you ask how to structure the fundamental laws of the universe such that the first point holds.

In short: things are going to get weird...

Entropy (a.k.a. "everything dies")

Although it's a complicated concept related to the Second Law of Thermodynamics, suffice it to say that we believe our universe is approaching a state of maximum entropy, which means, over time, the energy in the universe approaches a state where it is evenly distributed, and the closer we get to that state, the less possible it becomes for arrangements of energy (and matter) to be able to perform work. Importantly, entropy never decreases (Maxwell's Demon is a fun way to look at this), so the process is irreversible.

If you made it through that link-dense paragraph, the good news for you is that there are model theories that either avoid the heat death altogether, or have the universe spontaneously perturb itself to decrease entropy on extremely long timescales, on the order of $10^{{10}^{56}}$ years. In the meantime, however, your immortal beings wouldn't be "alive" as such, unless you really start to stretch the definition!

Speaking of which...

What is "life"? "Pain"? "Harm"?

These are philosophical terms that have no universal definition.

Life: Is your universe created with your life forms from the beginning, or are they created/formed/born later in the timescale of the universe? If they evolve, they obviously can't evolve their immortality/invulnerability traits, because their predecessors would violate your First Law of Immortality.

Thus, your First Law of Immortality must be a fundamental property of the universe. It is impossible to build it constructively from simpler definitions of "life".


The concept of "lower" life forms would be difficult to reconcile with your universe, since no life form dies, not even bacteria, or grass. Thus there is no competition, no cause to fight, but also nothing to eat, in a conventional sense. Your life forms would have to feed exclusively on inorganic matter and energy.

Where does that leave us?

Honestly, I have no idea.

To avoid paradoxical situations, some of our most hallowed laws of classical physics, such as the conservation of momentum, mass-energy equivalence, atomic theory, etc., all pretty much have to be thrown out the window:

  • With conservation of momentum, it follows that if I swing an axe at your head hard enough, that axe will tend to want to keep moving through your brain pan. OK, so maybe your life forms are made of gas or energy somehow.
  • Mass-energy equivalence and atomic theory? It follows that if I get a critical mass of radioactive material in a small enough space, it makes one hell of a big boom. Even for, say, pure energy life forms, you'll have a lot of explaining to do if they can sit at ground zero unscathed.

This has been an interesting question, and to answer it completely, I feel like I'm tiptoeing on the edge of having to expanding it to include enough material to fill an entire lecture series. If ever there was a loaded question.

Thus, in short, I strongly suggest you define a dimensionless hand-waving constant of the universe!

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    $\begingroup$ This. Entropy is one of the most important (if not the important) thing(s) here. $\endgroup$
    – HDE 226868
    Jan 20, 2016 at 2:15
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    $\begingroup$ Yes. I'm not sure if the reality is quite this extreme. You have to define how it all works. Like if someone hits you in the head with an axe, does it just bounce off? Pass through your hard harmlessly? Cut your brain in half but it quickly grows back? Your soul migrates to a new body? Etc. I'm always cautious about saying that something is impossible just because I can't think of a way to do it. But the idea creates many questions. $\endgroup$
    – Jay
    Jan 20, 2016 at 5:34
  • $\begingroup$ Extending the whole 'what do things eat' bit, if it's possible for a life form to not eat food, then not eating food can't cause harm or pain to that being. Every life form could live forever without ever eating, though food could still be used for reproduction. $\endgroup$
    – ckersch
    Nov 2, 2016 at 23:47
  • $\begingroup$ What if the living beings are the fundamental particles of the universe? What then? $\endgroup$
    – user64742
    Jun 2, 2017 at 5:22
  • $\begingroup$ I'm not opposed to this answer, low rank as I am, but shouldn't the middle section of this answer be in the comments of the question in the form of the following? "Please approximate a definition for: Life, Pain, Harm, and Food." $\endgroup$
    – William C.
    Jun 2, 2017 at 6:53


Since the majority of life sustains itself by eating other life, and that this action is destructive to the creature(s) being eaten, it follows that creatures in your universe will not eat each other. Thus, they must create all of the building blocks necessary to grow from scratch. Note, however, that they do not need to engage in maintenance, because that would imply that a sufficient lack of repair might result in death.

The main problem with this world is that life is a kind of "creative force", but one which is balanced against the "destructive force" of death. More importantly, it is very likely that death is not, in fact, a necessary outcome of living beings in our universe. Rather, death occurs because it is optimal for life. That is, creatures grow old and die so that nature can start over with something potentially better in each generation. This allows the creatures to adapt over time.


In your universe, adaptation is not necessary, because nothing can kill life. Thus, life will compete on the only thing that it can: resources to grow. Living things will figure out how to convert non-living matter into living matter at an increasing rate, and this will be the only form of evolution, except for composition.

Composition means not just eating another creature, but hosting it symbiotically. For instance, one creature might be able to consume nitrogen easily, while another might be able to incorporate carbon. Working separately, they will only grow quickly in environments rich in their native resource. But as a hybrid, they will grow in both environments. Thus, life will also coalesce into bigger and bigger creatures, because this is one of the most effective ways to increase resource consumption.


Eventually, life will send itself out into the stars, consume all of the inert matter into life, and burn out the universe by consuming every last matter and energy store. By then, it will likely be a giant conglomerate of initial creatures--a kind of biological Unicron eating the universe. Then the universe will die, because this creature is all that will be left.

This is the biological counterpoint to a runaway strong AI turning the universe into Computronium. This could make for an interesting story, but the inevitability of the outcome will remove all suspense for anyone who deduces the rules.


You're pushing an extreme type of universe which will push an equally extreme philosophy.

First off, you'll need to define what it means to "die." While we generally have a decent intuition of what dying is, the corner cases are tricky. Is someone who is "brain dead" "dead?" What about a rock that gets broken in half, does it "die?" Can an idea "die?" In our world, these are considered corner cases. The intuitive concept of death is sufficient for us. However, in your world where things cannot die, very few situations will fit into our neat intuitive box. We'll have to define death.

Feel pain/harm are also phrases which get very difficult when you take things to an extreme. We generally understand what it means to feel pain. Harm is harder. Does a surgeon cutting into a patient do harm to them? Is the pain felt by a masochist the same thing as the pain we feel? These are also corner cases which are usually not important for our intuitive concepts of pain and harm, but become very important when you describe a universe that has no pain.

The easiest way to do all of this is to walk away from the physical universe entirely. It's remarkably hard to define life/death/pain/harm in ways such that it is physically impossible for them to occur without them being remarkably dissimilar to our intuitive concepts. We could, however, have a world governed by idealism. Under idealism, there is no physical world, only a mental substance (compare to physicalism which defines all to be physical and mental is built on top of physics, and dualism, which believes there's two substances: mind and matter). It would be trivial to define an idealist world where entities can live forever without pain. In fact, many descriptions of an afterlife are described in this way.


Maybe have a different concept of time.

In computer science, you can have systems where the state doesn't change by updating values, but rather the new state is separate and the old still exists. This is used in revision-control systems like git, reliable file systems like ZFS, pure functional languages like Haskell, and languages that employ the concept for multi-threading like Clojure.

If I delete a file under such a system, the “present” shows it is missing, but every previous state is still there and it was not actually altered on disk. Likewise for corrupting or changing a file: each version is present and usable.

If physics and time worked on the pure-functional system, interactions might be like lenses in Haskell, and you can interact not just with the “present” but with things as they existed in the past.

You can go visit Grandpa when he was your same age and play with him as kids together. This creates a new equally-valid timeline for him, too. How can you say he dies if he still continues to have new experiences, forever? Everything that ever existed can be found again as long as there is a path to get there.


Inspired by JDługosz answer and the works of Greg Egan, I've come up with an idea that approaches the stated goals.

As far as we can tell, our universe has three dimensions of space and one dimension of time with an opposite eigenvalue to that of the spatial dimensions.

In Greg Egan's Orthogonal universe, time has the same eigenvalue, so the speed of light is dependent on its frequency, and it is possible to be living either forwards or backwards in time relative to another, as well as being able to travel infinitely fast.

To take this idea a step further, we can imagine a universe where we have two time dimensions, both with the same eigenvalues as the spatial dimensions, with a very low (average) speed of light such that the life-forms that live there can significantly change their own time-vectors.

We then have a universe in which beings aware of their own existence can have the ability to change their own 'futures'. In the event of injury, these beings would have the ability to back out of that future and head off down a different timelike path, in which the injury does not take place.

This is not to say that injury or death is unknown or impossible, just that it is an option that need not be taken, and most creatures would evolve to not take that option - those that did, wouldn't get to evolve further.

Inanimate objects could be broken and non-aware lifeforms on the order of bacteria or moulds would of course be able to be injured or die, as they have insufficient processing capability to plot a safe timelike path back from injury. However, any lifeform with sufficient brains and size - and believe me, with this kind of advantage, most lifeforms will have evolved sufficient brains and size - will be able to back out of almost any injurious or potentially lethal situation.

This is not to say that actual death or injury could not occur, just that in general, it won't (at least not without being reversed). If sufficient injury was delivered sufficiently quickly to an entire organism, the organism could be terminated so fast that it wouldn't be aware that it needed to back out of that timelike path, however, the equipment needed to do this would likely be large and obvious to anything with more than half a brain, making it unlikely to work more than a few times unless very cleverly disguised, on anything approaching sentience. It would also most likely be a technological device, and hence it's inventor could be said to have invented death.

The physiological state of being unaging is not such a stretch of the imagination - some organisms in our universe also have that trait.

This universe would have an interesting biota. There would be no predators that preyed on large organisms, as most potential prey would be smart enough to be able to back out of a predatory encounter, and since autotrophy is cheap - just emit light in a controlled way - most organisms will supply their own energy needs, and consume minerals or primitive organisms only to obtain raw materials.

Some additional features of this universe would be that electricity would be impractical, and photonics would be more likely to be used by both lifeforms and technology. Emitting light would result in an increase in an object's kinetic energy, not a decrease as in our universe. The universe itself would tend to get hotter rather than colder. There would likely be no degenerate matter or black holes.


The simplest answers are always the best it would seem. I can actually give several examples of answers. You'll catch my drift eventually.

Attempt 1

Take Super Mario for instance. Delete all of the lava. Patch all of the pits with terrain. Disable the results of stomping and make all of the enemies NPCs.

Result: Infinite lag due to spawning pipes producing far too many enemies for the system.

Attempt 2

Take Pokemon for instance. Remove the ability to go into battles.

Result: Success.

Attempt 3

Take Pong for instance. Give them both infinite paddles.

Result: Success

Simply put, your world will ultimately resemble that of a video game, but where the win and lose conditions have been either made unreachable or downright removed... which basically describes 90% of the flash games being perpetuated by 'amateurs'.

What does this mean scientifically?

Well, if your living beings enjoy bouncing around the universe and love to slam into other members of their various species like bumper cars then the answer is staring you dead in the face:

This is life!

Oh you wanted biological life?

Guess what, it's the same difference. I remember having this debate with someone about what constituted a universe (with my general opinion being anything dissimilar to a video game or simulation essentially, but without actually being in a computer). My response (to be quite absurd) was that there is a theoretical universe out there (I don't believe in alternate universes) consisting of nothing but koopas and goombas bouncing around resulting in complex systems developing. In other words, super mario could literally constitute a universe, with the namesake plumber being, in essence, the violation of the law of mass conservation.

So your answer is really the obvious. You need to build your universe so that your complex organisms are the building blocks of your universe. They cannot be neither created nor destroyed, as they are the fundamental masses of the universe. And why can they not be intelligent? It's just in their science that they are intelligent particles. Why can they not be?

So really I would imagine this universe to either be one built on absurdity (if you consider the idea of a universe built from googles of koopas and goombas to be absurd) or a computer simulation. The latter is technically wrong though as failure from the outside universe results in mass extinction and general destruction.


Other answers cover most aspects wonderfully, but for pain there is actually a very simple solution:

Pain is simply nerve signals. There is considerable debate over whether or not plants experience pain, and if so, in which way.

The evolutionary purpose of pain should be clear - we'd all be running into everything, breaking bones and poking out eyes constantly if it didn't exist.

However, it is not unthinkable to have life without pain. For example, harm-preventing reactions could be completely localised and the central brain only gets factual information after the fact. While the hand moves away from the hot plate all the same, the brain would never experience a pain sensation, because there is no necessity for one.

Secondly, if you solve "harm", then "pain" becomes simply unnecessary and it would not evolve. If you cannot be harmed, there is no reason to experience pain.

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    $\begingroup$ There are individuals who cannot feel pain. They have all sorts of problems because of it. $\endgroup$
    – JDługosz
    Nov 3, 2016 at 14:27

Depending on how we define life, death, harm, and pain, your universe may be fairly similar to Earth's own primordial sea, where early life fed on abundant chemicals.

For the purposes of this argument, I am defining 'life' as any self-replicating structure capable of holding itself together against entropy, accumulating the resources it needs to grow and replicate, and the ability to seek out these resources. Using this definition, I am conviniently avoiding the issue of abiogenesis (i.e. lipid-membrane protocellular "bubbles" don't count), as well as the issue of intrinsically non-viable mutants - if an organism is incapable of keeping itself alive even when provided with abundant resources, it does not count as 'life' and its inevitable death does not count.

The main thing this universe requires is infinite accessible matter, energy, and living space - an infinite sea of nutritious chemicals and an ever-present light emanating from everywhere. This is, practically speaking, impossible in our universe, but let us presume it exists in some magical handwavian plane. It is the scarcity of free available energy that drives living organisms to break down their fellow organisms for food. As long as every living organism has access to all the energy it needs, there is no need to go through the trouble of breaking another living organism apart.

Evolution can occur in this universe, but not natural selection - the earliest, most primitive life forms will continue to endure. Effectively, every 'species' will have an infinite population. However, organisms which could harvest energy more efficiently and reproduce faster will eventually become more common in the infinite sea.

Complexity can evolve in a manner similar to how the first complex cells developed - by one cell engulfing another, without harming it, or by multiple cells attaching to each other and forming a biofilm. If two cells can grow and reproduce more effectively by working together rather than alone, they will become more common. Life in this infinite sea will be incredibly diverse, with an infinite variety of weird mutants that would not cut it in our world, but the most common organisms will still be ones that make sense - not 'survival of the fittest', but 'abundance of the fittest'.

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    $\begingroup$ So it will be like a giant probability distribution? $\endgroup$
    – user64742
    Jun 24, 2017 at 17:50

Excluding the possibility of death basically means that certain classes of physical structures and processes cannot be permitted to to degrade, or to be altered outside of some species-specific set of allowable parameters.

That give you two options:

  1. Living things are not special, and the universe is steady-state, with a fixed number of complex, macroscopic entities that cannot be created or destroyed, and have a limited (though possibly continuous) range of possible states.

  2. Living things are special. This comes in two sub-flavors:

    2a. All living things are immutable entities as in option 1, but there is additional mutable stuff in the universe that can be interacted with and undergo arbitrary alterations under some set of laws comparable to those of our own universe, but cannot be permanently integrated into a living thing. 2b. Living things are not a unique kind of matter; they're made out of collections of simpler bits of normal matter just like unliving stuff, matter which normally obeys laws comparable to our own. But, once some collection of matter ends up organized into a form that counts as living, new rules come into effect that prevent it from degrading outside of a species-specific range of allowable variation.

All of these options, but most obviously option 2b, constitute a magical universe, in the strict technical sense- i.e., a universe in which the laws of physics are sensitive to specific macroscale scenarios, which cannot be explained in reductionist terms by the interaction of more fundamental laws. If you find yourself in a magical universe, there is a very good chance that it is the result of a computer simulation. After all, all three of the above scenarios accurately describe the workings of some variety of gaming physics engine! And in that case, the "real" universe is pretty unconstrained; it can have any sort of physics that permits arbitrary computation.


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