Good Answer?

We currently have different classes of posts. For the OP, there is the choice of Question or Discussion. For the responders there is the choice between Off-Topic, or On Topic. For the raters, there is the choice between Good Answer, and Off Topic.

As this is a scientific and Engineering forum, I propose that the creation of different classes or types of posts, in the first two categories. The philosophy of science talks a great deal about the Scientfic Method, as a means to convert observation into knowledge. Wouldn't it be interesting to be able to create/rate posts as belonging to these different classes? Wouldn't you like to know that something is agreed by many to be an extremely reliable piece of knowledge? Peer review is one of the best ways we have of correcting errors, or comparing hypotheses to reality or even of knowing accurately what reality is.

Here are some suggestions for types of posts:

Factual Data, Equation, Evidence, Observation, Prediction, Opinion, Procedure, Question, Discussion.

Consequently, the rating system could be altered to deal with the variety of types, and would be designed to review and rate for accuracy to international standards and understanding. Facts should be supported and evidenced...The whole system will show the evolution of the scientific and engineering knowledge, and ensure that the essential memes are well supported.

Chris

heres an example of a post filled with facts, each of which could be referenced from a separate archive of facts.. http://cr4.globalspec.com/comment/305544/Re-Why-Aren-t-Superconductors-Perfect-Mirrors

that way, when posting answers to questions, certain data could just be referenced instead of restated time and again. it would save time I think.

or is it reemission of new photons?)

Wow, I'm hooked........would not that place it in a whole new category of matter? Quantum matter?

Which blog was this in?

I'll get back to you on this.

milo

The simplest answer would be that the atom catches and throws the photon like a baseball player. without having to account for friction, or other subtractive values, the atom can store the energy absorbed when catching the ball, and use it to throw the ball. therefore, it is moot whether you call it new or old, because the quantity is the same.

I like it.

On the other hand what if the photon degrades the matter it is in contact with and by a process of absorption or deterioration transforms into an entirely new photon....a carrier of sub-atomic particles. There is a theory that the dark matter found throughout the universe might be photons that have lost their energy (which would account for the missing matter in the universe).

Photons, by their intrinsic nature, have zero mass. Their energy is proportional to their frequency, with the constant of proportionality being Planck's constant.

zero rest mass. if it was total zero mass, we wouldn't have a radiation pressure for solar sails and other phenomena to work with.

Zero rest mass means zero mass. Only for massive particles is the difference between rest mass and mass of interest. The solar wind is particles - if it were just photons we would simply call it light. That being said, photons, having energy also have momentum, and when they slam into something, they can impart that momentum. The momentum was given by de Broglie in his Ph.D thesis, which is the only Ph.D thesis to win a Nobel Prize:

p = h/wavelength

Fundamental physics: photons have no mass, and photons have both energy and momentum.

while I respect that what you are telling me represents the available answers in the physics community... an explanation of zero or the great nothing is not an explanation. its not an explanation that satifies anyway...maybe there is mass, but it is countered by anti-mass... and that is why there is momentum, but no mass Only the shadow knows...

Excuse me??? You are "unsatisfied"?

The fundamental physics of wave-particle duality, which was awarded a Nobel prize back in 1924 was presented to you. The explanation clearly shows that energy and momentum are tied to frequency, and are totally unrelated to mass. Einstein won the Nobel Prize in 1921 for explaining the photoelectric effect in terms of the energy of the photon interacting with electrons and liberating them from their atomic orbits.

All predicated on a zero mass photon. If the photon had mass, how could it move at the speed of light, when basic special relativity (1905) says that any object with non-zero rest mass will have infinite mass at light speed?

If you are "unsatisfied" with basic physical facts which were discovered nearly one hundred years ago, then maybe you ought to go back to school and get a physics doctorate, because it is going to take an awful lot of education and an awful lot of smarts to unseat Messrs. de Broglie and Einstein and all the other giants of the early 20th century who first explored the sub-atomic world.

don't take it personally. I do not know the answers. perhaps I'm probably not being as humble as I should. I do respect those whom you mention, and all others who dedicate their lives to scince. but you know as well as I that these equations and theories are simply the most accurate descriptions that agree with observation, to the limits of observation, to date.

maybe if we know what electricity, magnetism, mass, and time are, fundamentally, I would be more satisfied.

If you're not satisfied with the works I cited and all the other work based on that you are totally wasting your time here, and the time of others who try to explain these things. The only way you are going to be satisfied is learning it all for yourself and using what you have learned as a point-of-departure, and pressing on from there, on your own.

An engineering forum is not the place to question the fundamental laws of the universe. I am now un-subscribing from this thread.

Human nature dictates you'll be back....the law of gluon!

Photons have no mass at all. If they had the least bit of mass, they couldn't travel at C, the speed of light.

See http://en.wikipedia.org/wiki/Radiation_pressure#Discovery

Charlie

Charlie

by reading this I see that things have changes since I learned it 20 years ago. light travels at C, and has relatavistic mass Because it does so. that is what I was taught.

http://en.wikipedia.org/wiki/Mass_in_special_relativity

Chris

Special relativity and its relationship to light (photon mass, etc.) have not changed one jot since I was first taught it almost 50 years ago. However, my (still limited) understanding of it and its position within QM and GR took rather longer (and you will see from discussions on cosmology and dark matter that other aspects of fundamental physics are still developing)

As Einstein once stated, photons under certain conditions exhibit the properties of a stream of particles and under other circumstances exhibit properties normally associated with the behaviour of mechanical waves.

In other words if E=hf expresses the dual nature of light then this equation relates the energy of a photon to it's frequency. But if a photon is an independant, single particle, how can it have a 'frequency'?

because the photon has zero rest mass, it is not a physical object. However, if the alternation in the dimension(s) allows rotation or equivalent, then it can present the appearance of both particle and wave.

but for imagery think of a spinning coin, rotating about, and moving along its z axis. when it comes to an edge, where it is not absorbed, it can have its path altered bit the off-axis contact. the contact doesn't stop it because of the inertia it carries. in this way, it can behave as a wave. if it directly strikes someting, it can act as particle because all of the energy is absorbed in the transaction.

all photons move at the same speed because of their quantum nature, but the amount of energy contained could be seen as energy stored in a flywheel, or frequency/rotation. the energy and frequency are the same because size and speed are fixed geometrically.

the fact that higher energy light is refracted less is because of the gyroscopic effect of the particle. more energy equals a greater resistance to change.

thats just how i see it.. for what its worth. feel free to disagree.

It's not a matter of feeling free to disagree, that's just plain wrong. Higher frequencies are refracted more, not less. That's why the sky looks blue and the sun is yellow during the day but red at night. It's why a rainbow looks as it does: red on one end, and violet at the other.

okay. you are right on that point. thank you.

Pardon? Yes, if the loss is low, higher frequencies are generally refracted more than lower ones, and I agree that this is the reason that rainbows appear as they do (and that prisms split light).

But the reason that the sky looks blue (and the sun yellowish by comparison) is Brillouin scattering - the longer wavelengths are least affected by short-wavelength thermally-generated air-density variations. If the cause was just refraction, towards sunset the red light of the sun would be bent less than the blue, so you would see white sun with a blue tinge at the top and a red tinge at the bottom - and it would go bluish as it set.

Something went missing from my text. The dominant scattering is Rayleigh scatter, and was variously (and somewhat progressively) explained by Sommerfeld, Brillouin, and Einstein.

Apologies

Fyz

The photon IS a physical object: It can cause effects.

Einstein received a Nobel for his description of the photoelectric effect.

A photon supplies the energy (called the work function) that keeps an electron bound to an atom, thus enabling that electron to be free. Photovoltaic energy farms owe their operation to this effect.

see http://en.wikipedia.org/wiki/Work_function#Photoelectric_work_function

Charlie

I don't know.

http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/polref.html

this link is instructive about the whole deal. As far as degrading the atom.. I don't think that atoms leak energy.. they are too stable. each component in the atom structure is in its place, and each component contains a specific amount of energy. the structure is stable for the energy it contains.

if atoms could randomly lose energy to the dark side with photonic interaction, we would not see the obvious stability we see. because not only would photons cause it, but so would electrons, and even neutrinos on occasion. over time, the granite rock would deteriote to more porous structures. we don't see differences in new granite versus old granite do we? the canadian shield is pretty much the oldest rock on the planet.. a after a billion years or 2, we would be able to see differences as compared to new granite, don't you think?

but I do like the baseball player idea, and it is not negated by the polarization formulas. (imho)

I dunno either. I just wish those eggheads at Cern would stop blowing the thing up and answer once and for all whether it's all just illusion. Jeez!

That's very interesting. I had not heard that before.

Nor have I ("the theory that the dark matter found throughout the universe might be photons that have lost their energy"). On the other hand, the only 'interest' I find in the theory would be semantic or anthropological, because dark matter has rest mass and photons do not.

The closest that I have seen to a verbal theory is that "dark matter" is matter that has no charge-structure or spin as we know it, but that it may have some quasi-equivalent method of long-range 'radiation' (other than e-m or gravitational) that our matter does not (the 'radiation' would be a construct to account for mass in "dark energy" - and it is not (SFIK) at present 100% certain that this is necessary). If such 'radiation' exists, it would allow a co-existent body of material that interacts readily amongst itself - but will only interact with ours via gravitation or via close particulate interaction. If/when we understand more about Higgs we may be in a better position to start analysis.

A couple of personal notes:
Given that baryonic matter and radiation are believed to account for only about 4% of the mass of the universe, there is potential for a number of different forms of dark matter to exist, each of which behaves quasi-independently.
An alternative 'explanation' would be that our current interpretation of our observations is erroneous - specifically, the relationships between distance/time, velocity and red shift. Unfortunately(?) (again SFIK), no self-consistent interpretation has been proposed that does not require at least dark matter.

That's not quite the whole story - Sommerfield & Brillouin both showed that, during your "catching" process some of the energy is inevitably re-emitted as a precursor (at a much longer wavelength). The energy and amplitude of this precursor are inevitably small; in addition, analyses usually assume a continuous coherent wave which will cause re-absorption - but this is never true of the precursor that propagates at c ahead of the main wave.

More detail: any precursor will rapidly react with the medium and thereafter propagate at the velocity for its own wavelength, generating an even lower energy precursor at an even longer wavelength. For that reason, the energy in the total of the precursors 'decays' rapidly at times earlier than would be predicted by conventional dispersion. Indeed, in materials with absorption bands between the main wave and the precursor, most of the precursor can be delayed until after the original signal has arrived...

Given that both refraction and reflection are quantum resonance processes (QF Brillouin), I think we must accept that both involve re-emission. On the other hand, photons don't strictly have individual identity, so I'm not certain how to interpret the word "new".

Do go on!

milo

Wow. This is exactly why I am here!

Give us the link..I missed that one (I was watching a mouse hole)

Del

It's an impossible objective, because everyone has different notions of what is 'good'. Frequent visitors get to know what kind of stuff others will post, as well as their area of interest and knowledge. I don't often visit CR4 looking for something specific, but when I do, I usually know where to look and whos posts to look out for. The chat-like nature of CR4 also makes it more conducive to helping each other out. Maybe I'm a pig, but I'm more likely to try and be helpful to someone I feel vaguely familiar with, or whos posts I enjoy. The GA's can be useful, but it pays to scan all of a thread. It doesn't take that long on most threads to find the meat.

What the heck am I doing....I'm being topical !

....that's good.....I'm now at 6 off topic....c'mon who gave me the extra one ? Don't be shy, I like it

Yeah...but at least you know we all wub you...prrrr prrrr

'In the country of the blind, the one eyed man is King'
H G Wells wrote a good short story on that subject...
Cats like short sci-fi stories...trust me.
Del

That sounds like a good story. Despite finding some hilarity in the phrase (), I may get a copy. The Wiki, and it's link to Erasmus are interesting.

The picture of Erasmus is disturbing...
He appears to have a load of Squirrels hiding up his sleeves.

Maybe he couldn't get any cat

Here

Fyz

I'm impressed ! Thank you Fyz

Cute little buggers, hedhehogs. Too bad about the pricks.

ROFL ! Baaaad ducky .

In that case, what are you doing here?

"Oh, you can't help that," said Del: "we're all mad here. I'm mad. You're mad."
"How do you know I'm mad?" said Alice.
"You must be," said Del, "or you wouldn't have come here."

Fyz

*To see the original, substitute the remainder of Del's soubriquet

Lovely smoke rings Ducky - is that done with mirrors?

I dare ya to stare at it for two minutes while repeating "I'm the Cheshire cat".....

Alone, I might take you up on that just to see what happens. Although I suspect I might wake up here in the office in the morning (if at all) wondering wha' hoppin'. But the guy I share office space with would likely have me hauled off for drug testing before the two minutes were up!

Apparently some guy self-hypnotized looking at similar gizmo. Came out of it two days later. Wound up in therapy because image became persistant....sort of like a tune that keeps repeating itself in the mind.

I've heard of that happening. Could be OK if it's a tune you like, but how maddening if it were one you couldn't stand to start with!

http://www.youtube.com/watch?v=aslpeoZ0ibY _{(heh heh heh)}

That's a wonderfull piece of music. Everybody should hear it.

Damnit. why'd make me do that?!

So that's an old performance. Howd they get a camera in there back then. Did you notice everybody sitting, minding their P's and Q's?

No wonder....punk..... took off the way it did!

It's Enviro'mental

Back when computers started appearing on the factory floor instead of the computer room, one mechanic sat mesmerized by the spinning, turning, changing patterns of a screen saver. He sat there for the longest time, just staring until a supervisor snapped him out of it (after calling his name several times).

Can you make it go backwards? That might undo the effect.

^ _{(-|-|-|-|-|-|-)} ^ ←< Cheshire cat grin >

Massive Electro shock therapy 6/week for 6 months. No guarantee.

Stroking the EGOES of the engineers wil get you GA's sunking up works great on the workfloor and on the internet i am dazzled by your years of experience