The Speed Of Sound

[jnorman]

bassguy, others - you are missing a true fundamental of the nature of reality here. C does NOT change via different mediums. it is not affected by refraction, etc. even in a bose-einstein condensate, C is C. for example, when light enters a denser medium, it is merely absorbed and re-emitted more often, and appears to be slower - however, as each photon moves between atoms, it is always moving at C. in the extreme conditions of a bose-einstein condensate, the atoms are so lethargic, the absorption-reemission process is greatly slowed down, but the photons, when finally re-emitted travel at C until they are reabsorbed. i have spent the last 30 years studying QED, and can point you at any number of references to verify my comments, if you are interested.

[Addix Metzatricity]

I think this is where, as in most sciences, theory and practicality seperate. In theory, you may be correct. But for all practical purposes, light (as a whole, maybe not individual photons) speeds up and slows down when traveling through various mediums.

[Sylver]

I just like to say that, though I found this an interesting thread, YOU GUYS ARE A BUNCH OF GEEKS! I guess since I found it intersting, I'm a geek too.

[D. Gauss]

<> is much faster than a 1976 ford pinto. -d. gauss

[Addix Metzatricity]

Would that be before or during the fuel tank explosion?

[Rod S]

[quote]Originally posted by BassGuy21: [b]Light has a much shorter wavelength (THz) than sound (Hz-KHz) does, and thus requires vastly less power to move it.[/b][/quote] [quote]Originally posted by BassGuy21: [b] [quote]Originally posted by jnorman: [b]in fact, there isnt anything that will either accelerate or decelerate photons - they move at C.[/b][/quote]Unfortunately, that is not correct either. I deal in light. Optical telecommunications. There is a medium that will excite infrared photons called Erbium. There is another, more recently discovered substance that will excite photons in the visual light spectrum, but alas, I cannot remember what it is called. In fact (this is an afterthought) many things slow light. Especially water. It's called refraction.[/b][/quote]Your original statement is wrong. You can't compare an electromagnetic wave with a pressure wave. However, the later part is correct. The speed of light does change. Every media has something called index of refraction (for visible, IR, and UV, for other electromagnetic waves it's the dielectric constant that is used), which is basically the ratio of the speed of light at that media to that in vacuum (Aprox 300,000 km/seg) Erbium will not excite photons, and it's not the medium either. Erbium, in ion form, is doped into a crystal (YAG, YLF, etc), forming the 'heart' of solid state lasers such as the Er:YAG. When excited by a source of light of the correct wavelength, it will emit photons (resulting from the atomic transition) either thru spontaneous emission (at the absence of photons at the emission wavelenght), or stimulated emission. And yes, I do work (or have worked, rather) with fiber optics too, on the design end. Several such ions can be used, holmium, neodymium.. ahhh the rest escapes me.

[doug osborne]

[quote]Originally posted by BassGuy21: [b]Light has a much shorter wavelength (THz) than sound (Hz-KHz) does, and thus requires vastly less power to move it.[/b][/quote]but the acoustic impedance of our atmosphere is much higher at audio vibrational frequencies than at visual vibrational frequencies. For the answer to all things in life, consult the "Big Note" theory of one F. Zappa.

[Addix Metzatricity]

[quote]Originally posted by Rod S: [b]Your original statement is wrong. You can't compare an electromagnetic wave with a pressure wave.[/b][/quote]I've always understood the electromagnetic spectrum to encompass every type of wave (light, sound, RF, etc.) Maybe I misunderstood. [quote][b]Erbium will not excite photons, and it's not the medium either. Erbium, in ion form, is doped into a crystal (YAG, YLF, etc), forming the 'heart' of solid state lasers such as the Er:YAG. When excited by a source of light of the correct wavelength, it will emit photons (resulting from the atomic transition) either thru spontaneous emission (at the absence of photons at the emission wavelenght), or stimulated emission.[/b][/quote]So then, when the erbium is excited, the light is AMPLIFIED rather than ACCELERATED. Correct? Another misunderstanding on my part.

[jnorman]

rod - inre: "The speed of light does change. Every media has something called index of refraction..." - i addressed this earlier, but will repeat, refraction does not alter the speed of light, which remians constant at C. refraction, and transmission through various mediums, only alters the speed of the transmission of the wave front through a specific medium. each individual photon will travel at C from atom to atom within any given medium. it is just the fact that the photons get absorbed and re-emitted so many times within a medium that the wave front is delayed.

[Rod S]

[quote]Originally posted by jnorman: [b] C does NOT change via different mediums. it is not affected by refraction, etc. even in a bose-einstein condensate, C is C. [/b][/quote]It's affected by the dielectric constant of the medium, which varies. [b]for example, when light enters a denser medium, it is merely absorbed and re-emitted more often, and appears to be slower - however, as each photon moves between atoms, it is always moving at C. [/b] Re-emitted? 3 processes occur : transmission, reflection, and absorption - usually a combination of these. You can get deeper with specular and diffuse reflection, and so forth. Re-emission is pretty interesting.. care to elaborate? I gotta admit, I'm not much of a Physics guy - my are is engineering, so I don't know too much about the little details of physics. I can tell that I've never heard what you're talking about, and I did know what I'm talking about half of the stuff I've designed wouldn't work. :D But I can tell that yes, c is constant in vaccuum, but changes with the medium. [b]i have spent the last 30 years studying QED, and can point you at any number of references to verify my comments, if you are interested.[/b] I am interested. I've designed plenty of photonics devices, majored in this shit and can tell you that the speed of electromagnetic propagation does change. ;) I'll admit I've read Feynman's QED book, and although interesting, I couldn't give a shit about half of the stuff he says. I would have lost my job wondering about the implications of everything he talks about instead actually implementing what is commonly accepted about electromagnetic theory. It's all mental masturbation, if you ask me - an academic exercise at best.

[Rod S]

[quote]Originally posted by Addix Metzatricity: [b]I've always understood the electromagnetic spectrum to encompass every type of wave (light, sound, RF, etc.) Maybe I misunderstood. [/b][/quote]Yes, you did. Electromagnetic radiation encompasses all electromagnetic phenomena, xrays, gamma rays, uv, visible light, infrared, microwave, and RF. Sound is a pressure wave- different phenomena. There's nothing electromagnetic about it, it's just displacement of gas particles. 20Hz - 20KHz is what called sound, above that ultrasound, for instance. 18 kHz Typical limit for Man 25 kHz Typical limit for Dog 50 kHz Butterfly 100 kHz Whale 'SONAR' 175 kHz Bat 'SONAR' (Echolocation is english, I think) [b]So then, when the erbium is excited, the light is AMPLIFIED rather than ACCELERATED. Correct? Another misunderstanding on my part.[/b] Right. Basically a new photon is created. Spontaneous emssion - a photon is created from the spontaneous decay from a higher atomic energy level to a lower. Stimulated emission. A photon is created by the stimulated decay (by antoher photon), from a higher energy level to a lower.

[Rod S]

[quote]Originally posted by jnorman: [b]rod - inre: "The speed of light does change. Every media has something called index of refraction..." - i addressed this earlier, but will repeat, refraction does not alter the speed of light, which remians constant at C. refraction, and transmission through various mediums, only alters the speed of the transmission of the wave front through a specific medium. each individual photon will travel at C from atom to atom within any given medium. it is just the fact that the photons get absorbed and re-emitted so many times within a medium that the wave front is delayed.[/b][/quote]Alright, this seems like the mental masturbation that I was referring too. (With all due respect to you, but I always speak my mind) I will check in my Physics book and get back to you. I never really cared to get this deep into it to really think about this at the atomic level. Still never heard of photons being absorbed and re-emitted - I will concede that this theory may exist. But then again, as far as I'm concerned it's useless beyond an academic exercise. I'll let Physicists battle it out.

[Rod S]

[quote]Originally posted by Doug Osborne: [b] [quote]Originally posted by BassGuy21: [b]Light has a much shorter wavelength (THz) than sound (Hz-KHz) does, and thus requires vastly less power to move it.[/b][/quote]but the acoustic impedance of our atmosphere is much higher at audio vibrational frequencies than at visual vibrational frequencies. [/b][/quote]no no no no It's pointless to tie electromagnetic waves to sound waves. They are completely different phenomena. Electromagnetic waves will travel in vacuum, so trying to argue acoustic impedance is meaningless, there's not such thing as acoustic impedance in electromagnetic theory. It amazes me how many books try to address these two things as being the same phenomena. The're only similarity is that both are waves and follow a vaguely similar mathematical treatment.

[big K]

sorry , read the next post. .|. \.|./ .\./. ..|..

[big K]

[quote]Originally posted by big K: [b] [quote]Originally posted by BassGuy21: [b]I think this is where, as in most sciences, theory and practicality seperate. In theory, you may be correct. But for all practical purposes, light (as a whole, maybe not individual photons) speeds up and slows down when traveling through various mediums.[/b][/quote]This is right, as far as I know, the speed of light is a constant, C, but- light only travels this fast in a vacuum. Light in out atmosphere and water and anything else is slowed down (via the optical density)... The speed of sound is related to young’s modulus. Basically more dense = faster... this is why the speed of sound is faster in cold water then warm water. And faster in cold air then warm air, and faster in steel then air. The reason temperature effects it is because temperature changes the density ( this is how hot air balloons work). Also it is effected by pressure so it is different at sea level then up at the top of the mountains, and up high in the atmosphere (this is where the mach numbers come in, it is the speed relative to sound SO you can be flying the same speed, at 2 different highest and have 2 different mach numbers). Light is a different animal... though if I am not mistaken light does have inertia. It is a EM (electro magnetic wave) .. totally different from sound water (mechanical) It is like comparing a wave pool to an radio antenna, yes they are both waves, and mathematical you can express the phase and amplitude with sin and cosine even do Fourier transforms and other need tricks with them , but they are fundamentally different in the way they work. This most basic difference is in the wave type, .. the EM wave is a transverse ware, it oscillates perpendicular to its wave velocity. Pressure waves are the opposite. They are longitudinal they oscillate in the direction of the motion.. [/b][/quote]

[Joachim P. Dyndale]

As long as you're all discussing physics here... Anyone know anything about quantum physics? It's extremely facinating! I read an explanation once that said something like: In quantum physics you can have one single photon that you can make travel two paths at once, and then merge again into the same path. So basically the same photon is in two places at the SAME time. People are studying this for use in computers. I believe there are a few algorithms for such computers. Basically you deal with qbytes, qwords etc. You can do one single operation on all 256 qbits at the SAME time. One qbit can be on AND off at the SAME time. Amazing :) Anyone know more about this? Enlighten me! :thu: