What is Fire?

Fire is a chemical reaction.  Fire is quantum mechanics.  Fire is awesome.  As a very lay scientist I'm going to do my best to describe what is happening in this reaction.

Starting ingredients for fire:  fuel, oxidizer (like oxygen), and heat.

First we need to heat the ingredients to a sufficient energy to start the cascade--think spark, etc.

This heat is used to break the bonds of molecules.  With gasoline or wood the large hydrocarbon molecules are broken up into their subsequent parts.

Counter to what you might think it takes energy to break bonds.  Making bonds produces energy.  This is where things get exciting.  The gas produced by the chemical reaction then reacts with an oxidizer (like oxygen) to produce new bonds.  The act of producing these new bonds creates an enormous amount of heat.

This heat does several things.  First, it perpetuates the reaction.  The heat causes more bonds to be broken, which causes more bonds to be made (since there is more raw material then), which causes more bonds to be broken, to be made, to be broken...

Heat has another by product, though--molecules collide more often and with greater energy.  Since atoms aren't just balls of stuff, they also have charges (like the negative charge for electrons and positive for protons) they don't just hit with each other--they react with each other.


I'll fully admit this analogy may be incorrect since I found pitifully little on it online, but I almost understand these interactions to be like sloshing.  One atom/molecule bombards another atom/molecule causing their negative charges to repel each other.  At some point these interactions cause an electron to jump up an orbital.  In my mind I think of it as being on the opposite side of the atom as the bumping of negative on negative happened (This may be completely wrong and probably is. hehe).  This excitation of electrons to an outer orbital is  only temporary and the electron eventually relaxes back into its ground state and as it does something mysterious happens--a photon is thrown off with a certain amount of energy/frequency (based on how high it fell from and what kind of orbital it was/is in).  That's how light is produced in fire.  And, no, this makes no sense whatsoever.  We don't know why going down an orbital produces a photon.  It just does, okay!

If you think about it, fire producing light isn't as weird as you initially think...Or, actually it is just as weird as it ever was, but it's much more common than we generally appreciate.  Take for example--infrared.   As you well know from spy shows we are constantly emitting infrared electro-magnetic radiation.  Let me remind you what that means: we're emitting photons of energy just below the visible spectrum all the time--and so is just about everything else above absolute zero.  Ever have someone say you look like there's a glow about you?  That you look radiant?  You are!  Literally!  Heat up something and the photons emitted start to have more and more energy until they finally start to reach an energy level that we can see in the visible spectrum.  Fire produces light for the same exact reason that incandescent light bulbs do, lava, heated metal, your toaster/oven does--heat (the bombardment of atoms and the subsequent excitation of electrons and then relaxation which produces a photon).  The heated substance, however, in this case is soot and gas.

You're like Dr. Manhattan, but redder--infraredder.

In summary:

The making of bonds produces heat.

The heat produces light by atoms colliding causing electrons to become excited and then return to a ground state emitting a photon.



Other neatness:  

The first fossil record of forest fires is from 420 million years ago towards the end of the Silurian period.  The things that were missing prior to that were plants on land (470 mya) and then for oxygen levels to be above 13%.

Fire goes up because the heated gas is less dense than the surrounding air.  What would happen to a candle flame if there was little to no gravity??

Pictures from here, here, here, here, here, here, here, here, and here.

Works Sighted [sic]:

http://en.wikipedia.org/wiki/Black_body_radiation
http://en.wikipedia.org/wiki/Thermal_radiation
http://en.wikipedia.org/wiki/Planck%27s_law_of_black-body_radiation
http://en.wikipedia.org/wiki/Fire
http://en.wikipedia.org/wiki/Combustion
http://science.howstuffworks.com/light4.htm
http://science.nasa.gov/science-news/science-at-nasa/2000/ast12may_1/http://gizmodo.com/#!5199243/nasa-testing-next-generation-firefighting-gear-for-fires-in-spaaace
http://www.reclusland.com/compass/2009/02/05/space-fire/
http://www.straightdope.com/columns/read/2425/what-exactly-is-fire
http://en.wikipedia.org/wiki/Fire
http://www.pbs.org/wgbh/nova/fire/onfire.html
http://en.wikipedia.org/wiki/Oxidizer
http://www.youtube.com/watch?v=td38NCj0MZ4
http://www.youtube.com/watch?v=8PwttI30PI8

Infrared "Vision" in Snakes

Seeing in the dark is (and is not) pittsville for snakes.  It's been so great that it's evolved more than once in pit vipers and in pythons.


Here's the organ:

Facts of note about the pit organ:


"Essentially, it allows these animals to “see” radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes"


"The facial pit actually visualizes thermal radiation using the same optical principals as a pinhole camera, wherein the location of a source of thermal radiation is determined by the location of the radiation on the membrane of the heat pit. However, studies that have visualized the thermal images seen by the facial pit using computer analysis have suggested that the resolution is actually extremely poor. The size of the opening of the pit results in poor resolution of small, warm objects, and coupled with the pit's small size and subsequent poor heat conduction, the image produced is of extremely low resolution and contrast. It is known that some focusing and sharpening of the image occurs in the lateral descending trigeminal tract, and it is possible that the visual and infrared integration that occurs in the tectum may also be used to help sharpen in the image. In addition, snakes may deliberately choose ambush sites with low thermal background radiation (colder areas) to maximize the contrast of their warm prey in order to achieve such a high degree of accuracy from their thermal “vision”."


"he organ is used extensively by them to detect and target warm-blooded prey such as rodents and birds, and it was previously assumed that the organ evolved specifically for that purpose. However, recent evidence shows that the pit organ may also be used for thermoregulation. In an experiment that tested snakes' abilities to locate a cool thermal refuge in an uncomfortably hot maze, all pitvipers were able to locate the refuge quickly and easily, while true viperswere unable to do so. This suggests that the pitvipers were using their pit organs to aid in thermoregulatory decisions."
http://en.wikipedia.org/wiki/Infrared_sensing_in_snakes#cite_note-KM-0


"Take a whiff of mustard or wasabi and you’ll be hit with a familiar burning sensation. That’s the result of chemicals in these pungent foods hitting a protein called TRPA1, a molecular alarm that warns us about irritating substances. The same protein does a similar job in other animals, but rattlesnakes and vipers have put their version of TRPA1 to a more impressive and murderous purpose. They use it to sense the body heat of their prey.

Pit vipers are famed for their ability to detect the infrared radiation given off by warm-blooded prey, and none more so than the western diamondback rattlesnake. Its skills are so accurate that it can detect its prey at distances of up to a metre, and strike at objects just 0.2C warmer than the surrounding temperature. Against such abilities, darkness is no defence.

Like all pit vipers, the rattlesnake’s sixth sense depends on two innocuous pits located between their eyes and their nostrils. With two pits on either side of its head, the snake can even ’see’ heat in stereo. Each pit is a hollow chamber with a thin membrane stretched across it, which acts as an “infrared antenna”. It is loaded with blood vessels, energy-harvesting mitochondria and dense clusters of nerves. The nerves connect with the visual parts of the snake’s brain, allowing it to match up images of both heat and light."

"A single gene that encodes the TRPA1 protein was 400 times more active in the pit nerves than the spinal ones.

In humans, TRPA1 is activated by allyl isothiocyanate, the chemical that gives wasabi and mustard their kick."

"Two other groups of snakes, the pythons and boas, can detect infrared radiation, although their technology is 5-10 times less sensitive than the sophisticated viper hardware. They also have pits but theirs are spread across their snouts, are simpler in structure and have fewer nerve connections. But Gracheva and Ingolia found that they have independently co-opted the same molecule in their pursuit of hot sensory action, even though their ancestors diverged from those of vipers 30 million years ago."
http://blogs.discovermagazine.com/notrocketscience/2010/03/14/wasabi-protein-responsible-for-the-heat-seeking-sixth-sense-of-rattlesnakes/#more-853


"The membrane is only 15 micrometers thick and hangs freely suspended in the pit organ so that it is isolated by the air. Heat sensitive cells from the membrane react to differences in temperature of only a few millikelvins."


It's also interesting to note that some scientists think that the snake's brain might clean up the blurry images similarly to our brain scrubs out our blind spot, flips our eye's lens image reversal and how our mind accentuates borders.  

http://www.bccn-munich.de/news-views/bccn-research-news/catching-prey-in-darkness