ronse@prlb2.UUCP (Christian Ronse) (02/03/88)
As I am thinking about differences between vision and audition, I would like
to know the difference of behaviour between light waves and sound waves which
manifest themselves at our everyday (Newtonian, non-quantum) scale. For
example: longitudinal/transversal waves, superposition and interference of
waves, diffraction, refraction, reflection, and absorption of waves by
objects. Don't explain me special relativity!
Pointers to serious books or papers appreciated. Follow-up to sci.misc.
Christian Ronse maldoror@prlb2.UUCP
{uunet|philabs|mcvax|...}!prlb2!{maldoror|ronse}
``Stars were born of the sky.
Not the stars of glass,
but those of chrome steel.''firth@sei.cmu.edu (Robert Firth) (02/08/88)
In article <413@prlb2.UUCP> ronse@prlb2.UUCP (Christian Ronse) writes: >As I am thinking about differences between vision and audition, I would like >to know the difference of behaviour between light waves and sound waves which >manifest themselves at our everyday (Newtonian, non-quantum) scale. For >example: longitudinal/transversal waves, superposition and interference of >waves, diffraction, refraction, reflection, and absorption of waves by >objects. Don't explain me special relativity! First, apologies for not having any references to hand - except Hal Clement's 'Cycle of Fire', which has some aliens who "see" using sound waves. Both vision and hearing are sensitive over a wide amplitude range - vision from magnitude +25 or so down to -7 or so; hearing from 120dB to a small lower bound I can't remember. In both cases, perceived brightness/loudness is proportional to the logarithm of the amplitude; this is the Weber-Fechtner law. However, there are really major differences between how we see and how we hear. Some instances (a) We can perceive barely one octave of visible light (4000..8000 A), but over 10 octaves of sound (15..20000 Hz) (b) We can perceive the pitch of sound accurately, but have very imperfect colour perception. For instance, we can't tell many colour "chords" from pure monochromatic light. (c) Visual location uses parallax, by binocular vision. Aural location uses phase difference, by binaural hearing. We cannot perceive either phase or polarisation of light. (d) We seem to have a far better linear memory for sounds than for colours. That is, we find it much easier to duplicate a sequence of tones than a sequence of colours. Try that Simple Simon game both ways. This may of course be learned rather than innate. (e) Finally, of course, we can generate sounds as well as perceive them; we can't generate colours. I don't know enough to speculate on the extent to which these differences are necessary, given the nature of light and sound. But note that some creatures have a wider range of vision, can perceive polarisation, and perhaps can perceive true colour "pitch".
daveb@eneevax.UUCP (David Bengtson) (02/09/88)
In article <4110@aw.sei.cmu.edu> firth@bd.sei.cmu.edu.UUCP (Robert Firth) writes: >In article <413@prlb2.UUCP> ronse@prlb2.UUCP (Christian Ronse) writes: >>As I am thinking about differences between vision and audition, I would like >>to know the difference of behaviour between light waves and sound waves which >>manifest themselves at our everyday (Newtonian, non-quantum) scale. For For me, the most obvious diffrence is that light is electromagnetic in nature, and as such is governed by Maxwells equations, while sound is a physical vibration in the material that the sound propogates through. Other than that, the wave equation applies to both, and ( I assume ) is solved the same way. Except, of course, with sound, one must take material constants into account, while with EM, vacuum is generally assumes. > >(e) Finally, of course, we can generate sounds as well as perceive them; we > can't generate colours. Actually, we can 'generate' colors. Color generally refers to our perception of specific wavelengths of Optical frequency radation, and as such, can be generated easily. Just think of paint, neon tubes, colored light bulbs, etc. David Bengtson If you think that I speak for Laboratory for Plasma Fusion the University, I've got a Bridge University of Maryland to sell you :-) College Park Md 20742 {your keyboard} !uunet!mimsy!eneevax!daveb eneevax.umd.edu
csm@garnet.berkeley.edu (02/09/88)
In article <4110@aw.sei.cmu.edu> firth@bd.sei.cmu.edu.UUCP (Robert Firth) writes: >In article <413@prlb2.UUCP> ronse@prlb2.UUCP (Christian Ronse) writes: >>As I am thinking about differences between vision and audition, I would like >>to know the difference of behaviour between light waves and sound waves which >>manifest themselves at our everyday (Newtonian, non-quantum) scale. For ... >(b) We can perceive the pitch of sound accurately, but have very imperfect > colour perception. For instance, we can't tell many colour "chords" > from pure monochromatic light. Some of us are more adept at naming colours than chords. >(e) Finally, of course, we can generate sounds as well as perceive them; we > can't generate colours. Well, I hope you weren't blushing when you wrote that. A stick breaking under foot generates a (sonic) shock wave (chaotic behavior due to parts of the stick moving faster than the speed of sound ?) -- I don't think there is analogous light behaviour in the everyday world (aurora borealis?). -- Brad Sherman I don't know what I like, but I know art when I see it.
fiddler%concertina@Sun.COM (Steve Hix) (02/09/88)
In article <6917@agate.BERKELEY.EDU>, csm@garnet.berkeley.edu writes: > In article <4110@aw.sei.cmu.edu> firth@bd.sei.cmu.edu.UUCP (Robert Firth) writes: >>In article <413@prlb2.UUCP> ronse@prlb2.UUCP (Christian Ronse) writes: > ... >>(b) We can perceive the pitch of sound accurately, but have very imperfect >> colour perception. For instance, we can't tell many colour "chords" >> from pure monochromatic light. > > Some of us are more adept at naming colours than chords. > >>(e) Finally, of course, we can generate sounds as well as perceive them; we >> can't generate colours. > > Well, I hope you weren't blushing when you wrote that. > > A stick breaking under foot generates a (sonic) shock wave (chaotic behavior > due to parts of the stick moving faster than the speed of sound ?) -- I > don't think there is analogous light behaviour in the everyday world > (aurora borealis?). Cerenkov light? The energetic particles causing the cerenkov glow underwater are initially moving faster than the speed of light in water, aren't they? (Maybe that was just in that old movie I thought I slept through...) seh
greg@mind.UUCP (greg Nowak) (02/09/88)
In article <6917@agate.BERKELEY.EDU> csm@garnet.berkeley.edu.UUCP () writes: }A stick breaking under foot generates a (sonic) shock wave (chaotic behavior }due to parts of the stick moving faster than the speed of sound ?) -- I }don't think there is analogous light behaviour in the everyday world }(aurora borealis?). I doubt that the generation of an aurora borealis involves anything moving faster than the speed of light. :-) Arthur C. Clarke used to give a puzzle: "What was the first man-made object to move faster than the speed of sound, and when did it first happen?" The answer, of course, is several thousand years ago, when the first whip was cracked. -- greg
tim@ism780c.UUCP (02/11/88)
firth@bd.sei.cmu.edu.UUCP (Robert Firth) writes:
< (e) Finally, of course, we can generate sounds as well as perceive them; we
< can't generate colours.
I knew a girl whose parents showed up for a surprise visit at school.
She had recently just moved in with her boyfriend. When her mother
walked into the room, her face generated several different colors. :-)
--
Tim Smith, Knowledgian tim@ism780c.isc.com
"Who needs sex, drugs, and rock n' roll when you've
got Missile Command?" -- Anon.tan@ihlpg.ATT.COM (Bill Tanenbaum) (02/12/88)
< A stick breaking under foot generates a (sonic) shock wave (chaotic behavior < due to parts of the stick moving faster than the speed of sound ?) -- I < don't think there is analogous light behaviour in the everyday world < (aurora borealis?). ------ There is analogous light behavior. It's called Cherenkov radiation. It occurs when particles travel through a transparent medium faster than the speed of light in that medium. It occurs in the everyday world, but not so as you'd notice. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan
Wasser@cup.portal.com (02/14/88)
I believe the radiation in the previous article is due to Auger (Oh-zhay) electrons.......
t-peterw@microsoft.UUCP (Peter Williams) (02/20/88)
>There is analogous light behavior. It's called Cherenkov radiation. >It occurs when particles travel through a transparent medium faster >than the speed of light in that medium. It occurs in the everyday >world, but not so as you'd notice. >-- >Bill Tanenbaum As far as I know the only thing that travels faster than the speed of light is the Starship Enterprise. As a high school student, I spent a summer working in a reactor. The workers used to laugh because the guides that would occasionally come through would say that the blue aura around a sample of radioactive cobalt in a bay (ie water bay) was caused by EM waves travelling faster than the speed of light in water. I believe the real cause of Cherenkov radiation is that the speed of light in the emitting medium is greater than that of the water so when the EM waves enter the water they release enery (in the form of blue light) as they assume the speed of light of the water medium. Please correct me if I should err. --------------------------------------------------------------------------- Peter Williams University of Waterloo coops like to move, and move, Microsoft Corp. and move, and move, and move,... Redmond, WA
UE4@PSUVMA.BITNET (Dan Schultz) (02/22/88)
In article <1181@microsoft.UUCP>, t-peterw@microsoft.UUCP (Peter Williams) says: > >>There is analogous light behavior. It's called Cherenkov radiation. >>It occurs when particles travel through a transparent medium faster >>than the speed of light in that medium. It occurs in the everyday >>world, but not so as you'd notice. >>-- >>Bill Tanenbaum > >As far as I know the only thing that travels faster than the speed of >light is the Starship Enterprise. As a high school student, I spent a summer >working in a reactor. The workers used to laugh because the guides that >would occasionally come through would say that the blue aura around >a sample of radioactive cobalt in a bay (ie water bay) was caused by >EM waves travelling faster than the speed of light in water. I believe >the real cause of Cherenkov radiation is that the speed of light in the >emitting medium is greater than that of the water so when the EM >waves enter the water they release enery (in the form of blue light) >as they assume the speed of light of the water medium. > >Please correct me if I should err. You are in error. Cherenkov radiation occures because of nuetrons travelling in the water faster than light travels in the water. SR says nothing can travel faster than light in a vacuume. Since EM radiation travels slower in water than a vacuume, particles can move faster than light IN THE MEDIUM. EM waves moving from a material of one index of refraction to a material of another index of refraction do not emit other EM waves (or any other enerty)-- they change direction and wavelength. ------- Daniel B. Schultz "A _better_, more _compact_ form of humanity" J. C. Kilgannon.
jfc@athena.mit.edu (John F Carr) (02/22/88)
In article <1181@microsoft.UUCP} t-peterw@forward.UUCP (PUT YOUR NAME HERE) writes: }As far as I know the only thing that travels faster than the speed of }light is the Starship Enterprise. As a high school student, I spent a summer }working in a reactor. The workers used to laugh because the guides that }would occasionally come through would say that the blue aura around }a sample of radioactive cobalt in a bay (ie water bay) was caused by }EM waves travelling faster than the speed of light in water. I believe }the real cause of Cherenkov radiation is that the speed of light in the }emitting medium is greater than that of the water so when the EM }waves enter the water they release enery (in the form of blue light) }as they assume the speed of light of the water medium. } }Please correct me if I should err. If this were the cause of Cherenkov radiation then you would see a blue glow coming from glass, which has an index of refraction similar to that of water. Energy = h*frequency, and frequency does not change as radiation changes media. The blue glow is the result of massive (i.e., not massless) particles losing energy as they slow to the speed of light in water. --John Carr (jfc@ATHENA.MIT.EDU)
przemek@gondor.cs.psu.edu (Przemyslaw Klosowski) (02/22/88)
In article <1181@microsoft.UUCP> t-peterw@forward.UUCP (PUT YOUR NAME HERE) writes: >>There is analogous light behavior. It's called Cherenkov radiation. >>It occurs when particles travel through a transparent medium faster >>than the speed of light in that medium. It occurs in the everyday >>world, but not so as you'd notice. >>-- >>Bill Tanenbaum > >As far as I know the only thing that travels faster than the speed of >light is the Starship Enterprise. As a high school student, I spent a summer > >Please correct me if I should err. ^^^^^^^^^^^^^^^^^^^^^^^^^^ >Peter Williams University of Waterloo coops like to move, and move, OK here it is. The speed of light IN VACUUM (c) is indeed a fundamental barrier nott to be taken lightly (unlike '55 mile limit'). Now in the dielectric medium (everything that contains atoms is dielectric) EM wave interactions with the electrons in an atom cause those electrons to vibrate and emit their own EM radiation. This radiation sums with initial wave and changes its phase continuously. It looks like the total wave slows down a fraction of a wavelength each cycle, and travels with a speed of c/n (n is the refractive index). You can calculate n based on the parameters of the electrons (simple case is to assume that electrons are free wrt atoms---this is plasma). Now nothing prevents charged particle from travelling in this dielectric with speed greater than c/n (but OF COURSE smaller than c). This is when Cerenkov radiation sets in---how does it do it is another story. Your reactor sages were right: EM radiation cannot travel faster than the speed of light (EM radiation itself) in the medium. In fact it travels with its own speed all right :^) przemek@psuvaxg.bitnet psuvax1!gondor!przemek
Wasser@cup.portal.com (02/23/88)
The thing to remember when discussing Cerenkov radiation is this: "c" is the only "magic velocity" that cannot be exceeded (or even attained by objects which have rest mass.) Light only travels "at c" in free space. In water, for instance, light "travels" at about roughly 0.7 times "c". Particles being emitted from decaying nuclides can certainly exceed 0.7 times c. Charged particles can be accelerated through a high potential difference at least as high as 0.9 times c. So if you have beta particles, for instance, traveling through water at greater than 0.7c, they set up point disturbances that spread out to form a cone of radiation, akin to that of a supersonic object forming a shock cone in the atmosphere. A large portion of the cone's energy falls in the visible light range. Due to the dispersion effect, different colors of light have different indices of refraction, and it just so happens that Cerenkov radiation shows up as bluish. The half angle of the cone can actually be measured and used to determine the energy (and thus the speed) of the particle causing it. That would likely make a physics prof turn green, but, put in simple words, there is nothing sacred about "the speed of light". However, the constant "c" is another story. Cheers, Wasser What Descartes really said was "I Drink, Therefore I Am." His students quietly changed the quote to read as we know it today.
jeric@tybalt.caltech.edu (J. Eric Grove) (02/24/88)
In article <3129@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >The blue glow is the result of massive (i.e., not massless) >particles losing energy as they slow to the speed of light in water. > > > --John Carr (jfc@ATHENA.MIT.EDU) Note that this statement is misleading. Charged particles lose about 3 orders of magnitude more energy in ionizing the medium they are traversing than in generating Cerenkov radiation. Typical ionization energy losses for relativistic particles are ~2*Z*Z MeVcm2/g, while typical energy losses to Cerenkov radiation are ~Z*Z keVcm2/g. Mr. C's radiation is only a minor player in energy loss. J. Eric Grove jeric@tybalt.caltech.edu ...rutgers!cit-vax!tybalt.caltech.edu!jeric
carl@aoa.UUCP (Carl Witthoft) (02/25/88)
In article <5537@cit-vax.Caltech.Edu> jeric@tybalt.caltech.edu.UUCP (J. Eric Grove) writes: >In article <3129@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >>The blue glow is the result of massive (i.e., not massless) >>particles losing energy as they slow to the speed of light in water. >Note that this statement is misleading. Charged particles lose about 3 orders >of magnitude more energy in ionizing the medium they are traversing than in >generating Cerenkov radiation. Typical ionization energy losses for > J. Eric Grove What's going on here? I thought that the whole point of Cerenkov radiation was that it is a "bow wave" of light given off by a particle moving faster than the speed of photons in the present medium. The radiation is somewhat like a sonic boom. -- Alix's Dad ( Carl Witthoft @ Adaptive Optics Associates) {ima,harvard}!bbn!aoa!carl 54 CambridgePark Drive, Cambridge,MA 02140 617-864-0201 "People unclear on the concept: 'Nah, I don't want to windsurf, I wanna do more C-programming.' "
jeric@tybalt.caltech.edu (J. Eric Grove) (02/26/88)
In article <98@aoa.UUCP> carl@aoa.UUCP (Carl Witthoft) writes: >In article <5537@cit-vax.Caltech.Edu> jeric@tybalt.caltech.edu.UUCP (J. Eric Grove) writes: >>In article <3129@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >>>The blue glow is the result of massive (i.e., not massless) >>>particles losing energy as they slow to the speed of light in water. >>Note that this statement is misleading. Charged particles lose about 3 orders >>of magnitude more energy in ionizing the medium they are traversing than in >>generating Cerenkov radiation. Typical ionization energy losses for >> J. Eric Grove >What's going on here? I thought that the whole point of >Cerenkov radiation was that it is a "bow wave" of light given off >by a particle moving faster than the speed of photons in the present >medium. The radiation is somewhat like a sonic boom. > >Alix's Dad ( Carl Witthoft @ Adaptive Optics Associates) Yes, I should have been more specific. Certainly the blue glow is Cerenkov light, and certainly the charged particles are losing energy to this radiation; however, the slowing down is dominated by ionization of the medium. It is also true that if the charged particles are electrons, then in this relativistic regime, energy loss to bremsstrahlung is also quite large. The classic text on Cerenkov radiation, _Cerenkov Radiation and its Applications_, by J. V. Jelley is an excellent source (as you might have guessed from "classic"). The introduction provides a nice summary which I think should be approachable by anyone with a little physics, and chapter 2 presents the classical theory (understandable if you've done some E&M). J. Eric Grove jeric@tybalt.caltech.edu ...rutgers!cit-vax!tybalt.caltech.edu!jeric