🚀 go-pugleaf

>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}

	Let me try a couple of things, first about human perception
of light and sound.  Your eyes let you see over only a small
band of frequencies of the electromagnetic spectrum, the part
of the spectrum that we call light.  On the other hand your ears
let you hear over several orders of magnitudes of frequencies of acoustical
disturbances, those that we call sound.  I also know for a fact that
your ears are very sensitive over a large range of sound intensities,
many orders of magnitude.  I suspect that your eyes are not sensitive
to several orders of magnitude of light intensity (how bright or dim),
but I am less sure of this.
	Physically, assuming the air is your propagation medium, light
waves are transverse waves and acoustic waves are longitudinal waves.
Specifically for light the electric and magnetic field vectors are perpendicular
to each other and to the direction of propagation.  For sound the
displacements of fluid are along the direction of propagation.  In just
about every case, linear propagation theory correctly describes
light wave propataion.  This means that the principle of superposition
works well.  For acoustics, however, superposition breaks down for
very loud sounds.  Some everyday examples of this are jet aircraft
noise, certain types of helicopter noise, or the noise of explosions.
For sounds less loud, linear theory holds and you get the same 
reflection, diffraction, and refraction effects as you do for light,
just that the scales of things are different.  Remember light travels
at 3x10**8 m/sec and sound at about 343 m/sec.
	I don't know much about the properties of light other than what
I got in sophomore college physics.  Physics texts may help you here.
For basic books on sound and acoustics some good ones are:
		Musical Acoustics -- Donald Hall
		???		  -- A. Benade
		Fundamentals of Acoustics - Kinsler, Frey, Coppens
						and Sanders
For a deeper look at acoustics:
		Theoretical Acoustics -- Morse and Ingard
		Acoustics -- Allan Pierce

Good luck,
Vic Sparrow
sparrow@osiris.cso.uiuc.edu

In article <4100002@osiris.cso.uiuc.edu> sparrow@osiris.cso.uiuc.edu 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. 
>
>  I also know for a fact that
>your ears are very sensitive over a large range of sound intensities,
>many orders of magnitude.  I suspect that your eyes are not sensitive
>to several orders of magnitude of light intensity (how bright or dim),
>but I am less sure of this.

No, you're mistaken about this...the full moon is about 1,000,000 times
brighter than the faintest stars that are visible without optical aid;
typical sunlit terrestrial scenes are brighter still, by perhaps another
order of magnitude.

>For sounds less loud, linear theory holds and you get the same 
>reflection, diffraction, and refraction effects as you do for light,
>just that the scales of things are different.  Remember light travels
>at 3x10**8 m/sec and sound at about 343 m/sec.

This manifests itself in several observable ways...for example, the
Doppler effect is significant for sound, but not light.  ("But officer,
that traffic light looked *green* to me...must have been the Doppler 
effect!" :-)  And the difference between the speed of sound and the speed
of light gives you something interesting to do if you're stuck in a
thunderstorm....

-- Jim Lewis
   U.C. Berkeley

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".

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

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.

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 

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

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.

< 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

I believe the radiation in the previous article is due to Auger (Oh-zhay)
electrons.......

In article <4809@ihlpg.ATT.COM>, tan@ihlpg.ATT.COM (Bill Tanenbaum) 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?).
>
> 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

Isn't one instance of this the bluish glow given off by water-bathed
nuclear reactors, or more precisely, by the emitted particles moving
faster than the speed of light in water?  

What is the mechanism behind this?  Particles travelling faster than
c in *any* medium bothers me just a bit ... I mean, what if (physical
non sequitor approaching) we found a meduim wherein the speed of 
light was greater than it is in a vacuum?  What consequences could this
have?

-- 
Mike Sellers                           ...!tektronix!sequent!mntgfx!msellers
Mentor Graphics Corp., EPAD            msellers@mntgfx.MENTOR.COM
"Never confuse motion with action." -- Ben Franklin

>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

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.

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)

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

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.