shevek:

Bilge wrote:
shevek:

One possible answer is that massive particles become unstable upon
reaching superluminal velocities and emit Cherenkov radiation. Such a
phenomenon acts almost like the "aether resistance" that Vern is
advocating.

But, we don't observe that.




Yes, that's what I've been trying to tell Vern.

However, how do you explain Cherenkov radiation?


The same way you explain all electromagnetic radiation - scattering
of one charge from another charge. The only difference between what
superficially appear to be different radiation processes is the
approximation you can apply in particular conditions. What kind of
picture would you like?

Autymn D. C.:
Bilge wrote:
The particles don't have imaginary mass-enery in glass.
The ether is supposed to be a medium, so why should the
mass-energy be imaginary?

what particles? Your question is self-explanatory.

Non-repsonive.

wrote:
A speaker cone moves quickly and this motion is coupled to the gas
particles which take on some of the motion. No sink or source is
involved.

I know that is the standard explanation of how a speaker works, but
there may be an alternative explanation. If in the standard
explanation the motion is coupled, as you say, to the gas particles,
and they take on some of that motion, then there must be a mechanism
for that coupling and transference of the motion. This requires
something more than just random collisions.

And yet you can do the actual statistical calculation and
find out that this does NOT require anything more than just
random calculations.

If I'm not mistaken, a
superfluid has only elastic collisions, yet sound will travel through
it. Given a medium of only particles with elastic collisions, do you
think it is possible to have a wave or waves?

Of course. Do you think that the collisions in an ideal
gas are inelastic?

The problem I see with
the standard description of a wave is that if it depends on the
elasticity of a medium or if the motion of the particles is somehow
carrying the wave along,

In a pressure wave, it is variations in pressure that are
propagating, even if individual particles are not moving
very far.

then there is an assumption of a forward and
backwards motion. If that is the case, then there is no net momentum,

Hand waving. Compress a bunch of air behind a valve. Open
the valve. "No net momentum?"

Inflate a balloon. Pop it. The compressed air rushes
out in a spherical front, so that on average there is no
net momentum. Yet every part of the wavefront has a
momentum.

You are declaring impossible, things that are not only possible
but simple to describe.

- Randy

Randy Poe wrote:
wrote:
A speaker cone moves quickly and this motion is coupled to the gas
particles which take on some of the motion. No sink or source is
involved.

I know that is the standard explanation of how a speaker works, but
there may be an alternative explanation. If in the standard
explanation the motion is coupled, as you say, to the gas particles,
and they take on some of that motion, then there must be a mechanism
for that coupling and transference of the motion. This requires
something more than just random collisions.

And yet you can do the actual statistical calculation and
find out that this does NOT require anything more than just
random calculations.

I assume you meant to say "random collisions" instead of "random
calculations." AFAIK, the mechanical wave theory assumes that the
kinetic energy of an oscillator is supposed to be transmitted by the
simple back and forth oscillation of the particles of the medium. This
requires a restoring force. Also, AFAIK, based on the kinetic theory
of gases, there are no restoring forces in a medium where the particles
are undergoing only elastic collisions. Therefore, there is a conflict
between the mechanical wave theory and a wave model based on the
kinetic theory of gases.

If I'm not mistaken, a
superfluid has only elastic collisions, yet sound will travel through
it. Given a medium of only particles with elastic collisions, do you
think it is possible to have a wave or waves?

Of course. Do you think that the collisions in an ideal
gas are inelastic?

Shevek made the statement that collisions between the particles in a
medium are not required for waves to propagate through the medium. I
was asking him whether, conversely, he believed that waves could
propagate _only_ due to the collision between particles in a medium. I
think we both understood that the collisions being discussed were
elastic.

The problem I see with
the standard description of a wave is that if it depends on the
elasticity of a medium or if the motion of the particles is somehow
carrying the wave along,

In a pressure wave, it is variations in pressure that are
propagating, even if individual particles are not moving
very far.

Shevek stated, "If you add some motion in one area, the particles
move away from the area and the region with extra motion spreads out
like a wave." I had stated that a wave is not caused by adding
motion, but instead by creating a sink or a source in the medium which
in turn causes a change in the average collision free distance between
the particles.

then there is an assumption of a forward and
backwards motion. If that is the case, then there is no net momentum,

Hand waving. Compress a bunch of air behind a valve. Open
the valve. "No net momentum?"

Isn't that just free expansion?

Inflate a balloon. Pop it. The compressed air rushes
out in a spherical front, so that on average there is no
net momentum. Yet every part of the wavefront has a
momentum.

Shevek said, "A speaker cone moves quickly and this motion is coupled
to the gas particles which take on some of the motion. No sink or
source is involved." I could not understand a mechanism for that in
an ideal gas. If by "coupled" he meant "transferred," then the
speaker cone would be initiating a compression pulse. Again, AFAIK,
the mechanical wave theory is based on the particles of a medium
performing simple harmonic oscillations. Since, from a fluid dynamic
perspective, compression pulses are different from rarefaction pulses
and an ideal gas medium has only elastic collisions, there is no
mechanism for backwards momentum or restoring forces, therefore simple
harmonic oscillations are not possible in an ideal gas. What may be
possible instead is that waves are a train of periodical individual
compression pulses.

You are declaring impossible, things that are not only possible
but simple to describe.

Mechanical wave theory uses a lot of analogies such as stretched coil
springs, waves on elastic strings and stationary elastic ribbons and
uses descriptives such as restoring forces, simple harmonic
oscillations and "mechanical waves are characterized by the transport
of energy through the propagation of a disturbance without any
corresponding bulk motion of the medium itself." With respect to the
actual motion of the particles of a medium, statements such as "the
displacement of some portion of an elastic deformable medium from its
normal position, causing it to oscillate about an equilibrium
position" and "a back and forth movement of the particles" is
described with the motion being in the same direction in which the wave
propagates in the case of longitudinal waves and "each particle
oscillates transversely to the direction of propagation of the waves"
in the case of transverse waves. On the other hand, the Kinetic Theory
of Gases, dealing with the movement of the particles in ideal gases
relative to flow patterns, resistance, pressure, etc., has the kinetic
energy in the medium transmitted solely through the collisions between
the randomly moving particles. Therefore the method of transmission of
sound energy should be able to be described by the kinematics of the
dissipation of local disturbances through an ideal gas like medium.

Vern