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Post by duwayne on Sept 26, 2017 16:53:27 GMT
Some posters have expressed a desire to broaden their understanding of photons. That goes for me as well and I started this thread with that in mind. Let me begin by posting a slimmed down version of the definition of a photon from Wikipedia which is undoubtedly technically correct but not very user friendly. Later I'll post my own layman’s description which focuses on the features of photons that relate to climate science. Wikipedia……
“A photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and always moves at the speed of light within a vacuum.
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. The photon's wave and quanta qualities are two observable aspects of a single phenomenon, and cannot be described by any mechanical model.
The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical wave model of light. The benefit of the photon model was that it accounted for the frequency dependence of light's energy, and explained the ability of matter and electromagnetic radiation to be in thermal equilibrium. The photon model accounted for anomalous observations, including the properties of black-body radiation, that others (notably Max Planck) had tried to explain using semiclassical models. Although these semiclassical models contributed to the development of quantum mechanics, many further experiments[3][4] beginning with the phenomenon of Compton scattering of single photons by electrons, validated Einstein's hypothesis that light itself is quantized.[5][6] In 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles.[7] After Arthur H. Compton won the Nobel Prize in 1927 for his scattering studies,[8] most scientists accepted that light quanta have an independent existence, and the term photon was accepted.”
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Post by nautonnier on Sept 26, 2017 17:38:53 GMT
Good idea Duwayne. The one thing I would add is that an infrared photon cannot not have a temperature it is radiant energy. IF that energy is absorbed by a molecule/atom of matter then it may convert to kinetic energy and the molecule move faster and/or vibrate. The energy cannot however be lost.
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Post by duwayne on Sept 27, 2017 14:52:16 GMT
Here is my attempt to provide a layman’s description of photons in a way that is useful for understanding global warming.
Photons have properties of both particles and waves. I like to think of a photon as a discrete particle of energy which travels in a wave pattern.
Here are some of characteristics…..
Photons travel at 186,000 miles per second (rounded) in a vacuum, and a slightly slower speed in air but the speed still rounds to 186,000 MPS.
Photons vary widely in energy content but an individual photon can’t be subdivided. At a given energy content, the photon will travel in a specific wavelength. You can calculate the energy content by measuring the wavelength and vice versa.
All photons with the same energy content have the same wavelength. Some wavelengths are several miles long and some are less than the diameter of a hair and the energy content varies accordingly.
They have no (at rest) mass.
They are zipping around everywhere.
If a photon of the right wavelength hits your eye, a protein in the eye will send a message to the brain and you will be able to “see” the photon. Its color will depend on its wavelength. Photons that we can see are called light.
Molecules absorb photons and emit photons, but each gas type (water, oxygen, nitrogen, etc.) can absorb only photons with certain ranges of energy content (and therefore certain wavelengths) due to the molecule’s individual molecular structure.
The energy content and therefore the wavelengths of a photon emitted by a blackbody are indicative of the temperature of the blackbody. The warmer the blackbody, as might be expected, the larger the energy content of the photons emitted. The larger energy content photons have shorter wavelengths. The relationship between a photon’s energy content and wavelength is exact.
Photons emitted by the sun do not all have the identical energy content but in general they contain considerably more energy than those emitted at the lower temperatures of the earth. Accordingly, they have a distribution of wavelengths representative of a hot sun. And most but not all are visible. The “invisible” wavelengths are infrared (longer wavelengths) and ultraviolet (shorter).
A photon’s life is “forever” as it travels in a vacuum at 186,000 MPS. When they hit a molecule they either bounce off, travel on through the open space in the molecule or are absorbed. The energy from an absorbed photon can be emitted, but it is often of a different wavelength due to temperature and therefore the photon can have a different energy content.
Photons don’t have a measurable temperature. Their energy can be transformed to heat when they strike a molecule.
“New” photons can be generated by converting mass to energy per Einstein’s E=MC squared. Nuclear reactions like those in the sun are the source of massive amounts of photons.
Photons are an important part of some chemical reactions. Photosynthesis, the basis for plant life depends on photons.
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Post by duwayne on Sept 27, 2017 15:54:28 GMT
When I’m talking to kids and trying to get them interested in science, I like to talk about photons. For some reason they don’t get their fair share of discussion in the schools. Here are some of the things I say.
Photons are little pieces of energy which fly everywhere. The room you are in is filled with trillions of photons zipping around at unbelievable speeds. They can go from here to Grandma’s or wherever in a fraction of a second.
If one of a certain size hits your eye you can “see” the object that they came from. They are the fastest things in the universe. If it weren’t for photons there would be no daytime. The earth is warm enough to live on because photons bring heat from the sun.
Perhaps most important, photons bring the messages to your IPhone and carry the messages to your friends. And photons heat up your food in the microwave.
If it weren’t for photons you’d have no food since plants need photons to grow. And so on..
And for the younger kids… fairy dust is made out of photons and the little sparkles flying off the magic wands are photons.
And for the older kids you can talk about how photons get converted to signals from the eye to the brain and your brain paints a picture of where the photons came from.
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Post by acidohm on Sept 27, 2017 16:11:39 GMT
Great explanations Duwayne. Personally I'm playing catchup in this area....any further explanations welcome.
Like what is being emitted by matter in a dark cave 🤔
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Post by nautonnier on Sept 27, 2017 17:15:47 GMT
All good explanations. Duwayne Only a minor quibble - probably a typo. Speed of light is 186,282 miles per second.
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Post by acidohm on Sept 27, 2017 18:16:28 GMT
All good explanations. Duwayne Only a minor quibble - probably a typo. Speed of light is 186,282 miles per second. 😲😲😲 unacceptable inaccuracy!!
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Post by duwayne on Sept 28, 2017 20:26:25 GMT
All good explanations. Duwayne Only a minor quibble - probably a typo. Speed of light is 186,282 miles per second. Thanks. I, like everybody else did know it was miles per second even though I typed MPH 3 times.
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Post by Ratty on Sept 28, 2017 23:25:50 GMT
All good explanations. Duwayne Only a minor quibble - probably a typo. Speed of light is 186,282 miles per second. I'll second that.
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Post by duwayne on Oct 2, 2017 17:26:26 GMT
Previously, I described photons (packets of energy) and how they are absorbed (amount of each wavelength photon absorbed dependent on the molecular structure) and emitted (the warmer the molecule, the larger the photon emitted and the more photon power emitted).
When the photons are absorbed by molecules, for the most part, their energy is converted to heat. When photons are emitted, molecular heat leaves as a packet of energy with no measurable temperature until it is absorbed again.
The sun produces massive numbers of photons via nuclear reaction and emits photons in all directions. When a small portion of these photons strikes the side of the earth facing the sun, some are reflected, some pass through the edges of the earth’s atmosphere unaffected but a significant portion is absorbed by molecules in the air or the earth’s surface thus heating those molecules.
Meanwhile, the molecules in the atmosphere and at the earth’s surface are emitting photons and cooling the atmosphere and the surface.
All the while the earth and its atmosphere are experiencing all sorts of physical events which transfer and mix the heating and cooling.
Since the earth is surrounded by a vacuum none of the heat escapes (or is gained) through contact with matter outside the earth and its atmosphere. Likewise, because of the effect of gravity, none of the heat comes or goes due to molecular transfer. The only way for heat to enter or leave the earth and its atmosphere is as energy onboard a photon.
Photons are continually coming from the sun. Photons are continually leaving the earth. If the sun were to increase its photon output to a new level, the earth’s temperature would increase. But since higher temperatures cause more photons to be released from the earth, the temperature would stabilize at the point where the additional photon power coming in from the sun was offset by the increased photon power leaving the earth.
Since the earth’s average annual temperature is quite stable, this means that the photon power incoming equals the photon power outgoing over the course of a year or at least pretty nearly so.
More to follow…….
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Post by nonentropic on Oct 2, 2017 18:20:07 GMT
I think this is a cul-de-sec.
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Post by duwayne on Oct 3, 2017 17:07:19 GMT
For the earth the overall photon power coming in equals the photon power going out or close to it.
It’s probably obvious but the photon power in/out isn’t the case for all parts of the earth. It’s the overall totals entering and leaving that are in balance.
If for some reason, the earth and its atmosphere absorbs more photons, the earth’s temperature will rise which increases photon emissions. When the incoming/outgoing are in balance, then the temperature will stabilize.
Here is an analogy which isn’t perfect by any means, but it may help to understand the earth’s photon balance.
You are in a rowboat and the water is slapping against the side of the boat but none is getting into the boat. (This is similar to a case where the earth is surrounded by mirrors and all photons are reflected away. The earth doesn’t require any temperature to emit zero photons.)
Then the boat hits a rock which results in a hole in the bottom of the boat. To keep the boat afloat you need to bail some water from the boat. (This is similar to the case where not all of the photons are reflected away. Some are absorbed and the temperature begins to rise. The rise in temperature causes increased molecular activity and an increase in photon emissions. When the emissions outgoing equal incoming the temperature stops rising.)
Now an ogre comes along and catches some of the water being bailed out of the boat and throws it back in. You have to bail harder. This is similar to what a carbon dioxide molecule in the atmosphere does. Carbon dioxide, because of its molecular structure, absorbs photons of specific wavelengths. Those specific photons are present in the infrared photon mix which is emitted from the earth’s surface. As these photons head towards outer space at 186,000 miles per second, carbon dioxide absorbs them and then emits photons which travel in all directions.
Those photons which are emitted back to the earth’s surface are mostly absorbed thus increasing the earth’s temperature. This, in turn, causes the emissions from the earth’s surface to increase and the temperature rise stops when the incoming/outgoing is back in balance.
That’s the “Greenhouse Effect”.
I haven’t said anything on this thread about how much the earth’s temperature will warm due to the greenhouse gas effect, but in previous posts on the “Global Warming Predictions” thread, I have made specific predictions with the rationale which extend out to the end of this century and I report every 6 months or so on the actual temperature vs my prediction.
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Post by missouriboy on Oct 3, 2017 19:41:51 GMT
I will post this article as it seems to be a reasonably detailed treatise on CO2's ability to absorb, hold and radiate electromagnetic radiation (photons). I'm working my way through it and haven't detected a 'slant' yet. Actually the article is rather short, but the responses are very long. clivebest.com/blog/?p=1169
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Post by Ratty on Oct 4, 2017 0:11:24 GMT
[ Snip ] I haven’t said anything on this thread about how much the earth’s temperature will warm due to the greenhouse gas effect, but in previous posts on the “Global Warming Predictions” thread, I have made specific predictions with the rationale which extend out to the end of this century and I report every 6 months or so on the actual temperature vs my prediction. Will you be using cryogenics, Duwayne?
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Post by nautonnier on Oct 4, 2017 0:58:05 GMT
Another interesting paper around the subject... Abstract Increases in CO2 and other greenhouse gases will not be able to bring about significant climate disruption in the next 75-100 years. The main problem with the Anthropogenic Global Warming (AGW) theory is the false treatment of the global hydrologic cycle which is not adequately understood by any of the AGW advocates. The water vapor, cloud, and condensation-evaporation assumptions within the conventional AGW theory and the (GCM) simulations are incorrectly designed to block too much infrared (IR) radiation to space. They also do not reflect-scatter enough short wave (albedo) energy to space. These two misrepresentations result in a large artificial warming that is not realistic. A realistic treatment of the hydrologic cycle would show that the influence of a doubling of CO2 should lead to a global surface warming of only about 0.3°C – not the 3°C warming as indicated by the climate simulations. The global surface warming of about 0.7°C that has been experienced over the last 150 years and the multi-decadal up-and-down global temperature changes of 0.3-0.4°C that have been observed over this period are hypothesized to be driven by a combination of multi-century and multi-decadal ocean circulation changes. These ocean changes are due to naturally occurring upper ocean salinity variations. Changes in CO2 play little role in these salinity driven ocean climate forcings. tropical.atmos.colostate.edu/Includes/Documents/Publications/gray2012.pdf
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