Is fire life?

~~SpaceGuy50~~ · Mar25-09, 01:31 PM

Is fire a lifeform? Fire moves, grows, consumes, needs oxygen, gives off waste and can "die".

**Mapes** · Mar25-09, 02:41 PM

Fire doesn't fulfill at least one criterion I've seen, that life decreases local entropy.

**jambaugh** · Mar25-09, 02:49 PM

No. The critical properties distinguishing life is adaptation to changing environment and self replication of the information encoding the life process.

Fire does not change its process to adapt to its environment, e.g. moving toward more fuel or storing and conserving fuel when it is in short supply. Fire does not convey information via replicating as in genetic code. It is just a raw physical reaction.
Note that "killing a fire" and reigniting it is indistinguishable from just letting it continue.
This generally will distinguish life from non-life. If you kill a rabbit you can't recreate a rabbit just from the materials at hand.

BTW Many living organisms do not need oxygen and find it toxic.

Of course it is difficult to form a good definition of life given we only have the example of cellular organic life on earth. But within that restricted class I'd say viruses are right on the boundary. Some may consider viruses alive while others (me including) would define them as non-living phenomena.

Life is not an objective state but a process. Like other process phenomena such as "success" and "civilization" and "love" the definition is not going to be clear cut. The best way to define it is to let the definition be a bit ambiguous but refine it each time a borderline example comes along. The question "is it life" is both a question about the example and a question about the definition of the word... "shall we define life to include this case?".

**symbolipoint** · Mar25-09, 02:58 PM

Does fire have a property of Irritability? That is, can fire react to a stimulus? A long time ago, a biological science authority listed irritability as a property of life. For Fire, irritability may not be enough by itself. Besides, fire seems limited at best in how it might react to any stimulus.

**Danger** · Mar25-09, 04:25 PM

Fire is a by-product rather than a product. It consists of combustion gases. That makes it equivalent to the CO2 exhaled by animals, rather than to the animals themselves.

~~SpaceGuy50~~ · Mar25-09, 04:25 PM

Well I'm sure you would agree that fire meets some of the criteria for life, even if it's nonlife.

**mgb_phys** · Mar25-09, 04:39 PM

Originally Posted by SpaceGuy50

Well I'm sure you would agree that fire meets some of the criteria for life, even if it's nonlife.

It's a good example of why the old school book definition of life - respiration, reproduction, growth, etc, isn't correct.
You can find examples of things like fire or stars that meet some or all of these but aren't alive.

The modern definition of life is based around passing-on inherited characteristics.
This means some computer programs are also alive but we will worry about that once they demand citizenship.

**alxm** · Mar26-09, 11:44 AM

Deus creavit, Linnaeus disposuit.. so what would he say? :)

NATURALIA sunt corpora cuncta Creatoris manu composita, Tellurem constituentia, In Regna Naturæ tria divisa, quorum limites concurrunt in Zoophytis.

Lapides: corpora congesta, nec viva, nec sentientia.
Vegetabilia: corp. organisata & viva, non sentientia.
Animalia: Corp. organisata & viva, & sentientia, sponteque se moventia.

(Systema Naturæ)

So, nature is divided into three kingdoms.
Rocks - bodies which accumulate, are not alive nor sentient.
Plants - bodies which are organized and alive, but not sentient.
Animals - bodies which are organized, sentient and which may move themselves.

Fire doesn't fit into those categories. So by my 18th century definition it's not life or even part of the natural kingdom itself :)

**DaveC426913** · Mar26-09, 02:06 PM

Originally Posted by alxm

(Systema Naturæ)

So, nature is divided into three kingdoms.
Rocks - bodies which accumulate, are not alive nor sentient.
Plants - bodies which are organized and alive, but not sentient.
Animals - bodies which are organized, sentient and which may move themselves.

These are antiquated.

First, a clarification: Presumably, these are not the same "kingdoms" as in the kingdoms of life, since rocks don't belong. Also, there are more than two kingdoms of life - there are about five now - critters that are neither plant nor animal.

But even the definitions of the plant and animal kingdoms are ancient.
Many plants are capable of movement.
Many animals are neither sentient nor motive.

**Danger** · Mar26-09, 06:54 PM

So is Johnny Storm an animal or a fire?

**DaveC426913** · Mar26-09, 07:59 PM

Fire does not reproduce copies of itself except metaphorically. Thus, fire is life only in metaphor.

**alxm** · Mar26-09, 08:31 PM

Originally Posted by DaveC426913

These are antiquated.

You don't say?

Maybe I should've taken a hint from Linnaeus' mention of "the four elements" on the preceding page :)

First, a clarification: Presumably, these are not the same "kingdoms" as in the kingdoms of life, since rocks don't belong. Also, there are more than two kingdoms of life - there are about five now - critters that are neither plant nor animal.

Nope, they are in fact the same 'kingdoms', as it was Linnaeus who invented the whole classification system. Just in the original form. Since his classification system is the one still in use today, obviously there have been major revisions.

Just a historic curiosity. I think he considered mushrooms to be 'rocks' too IIRC.

**Savant13** · Mar26-09, 11:45 PM

Originally Posted by jambaugh

Fire does not change its process to adapt to its environment, e.g. moving toward more fuel or storing and conserving fuel when it is in short supply. Fire does not convey information via replicating as in genetic code. It is just a raw physical reaction.
Note that "killing a fire" and reigniting it is indistinguishable from just letting it continue.
This generally will distinguish life from non-life. If you kill a rabbit you can't recreate a rabbit just from the materials at hand.

Actually you could in principal make a new rabbit if you worked fast

**Danger** · Mar26-09, 11:48 PM

Originally Posted by Savant13

Actually you could in principal make a new rabbit if you worked fast

But that would be an unforgivable waste of a good stew.

**Ivan Seeking** · Mar27-09, 01:45 AM

I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image.

- Stephen Hawking

**Rade2** · Mar30-09, 06:03 PM

Life = Self generated action mediated by nucleic acids. Fire not = life.