| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
24 Feb 2006 10:32:19 AM |
| Object: |
the "forces" behind light? |
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
Given
F = mA
and
E = mc^2 ,
we can quickly derive
F = EA/(c^2)
which tells us that, maybe, there is force (or something like it)
associated with light and similar energies. At least there's a
formula!
But acceleration is involved. Acceleration is the second derivative of
location with respect to time. That's fine for continuous
accelerations. But quantum physics, if I understand correctly, posits
instantaneous (i.e. discontinuous) changes in values. E.g., a photon
is emitted from an atom, leaping immediately to light speed from a
"rest" state. So the formula above might not apply, in its present
form. The Dirac delta function comes to mind, but that still doesn't
answer the original question.
Can someone please de-muddle me? Thank you very much!
Ted Shoemaker
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| User: "srp" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 11:55:09 AM |
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a écrit :
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
Given
F = mA
and
E = mc^2 ,
we can quickly derive
F = EA/(c^2)
which tells us that, maybe, there is force (or something like it)
associated with light and similar energies. At least there's a
formula!
But acceleration is involved. Acceleration is the second derivative of
location with respect to time. That's fine for continuous
accelerations.
Well, there is continuous acceleration implied even in the plane wave.
Continuous transverse acceleration of the two orthogonal fields since
they cyclically intersect as they oscillate to and from between max
amplitudes.
It is even easy to define a transverse acceleration constant for
EM energy = hc = 1.98644544E-25 J.m which could be seen as a
distance based counterpart to Planck's constant. Say we name it H.
If you divide it by a wavelength and then further by the related
amplitude, you have F=H/lambda *1/A)= (something * acceleration)/A
But the vectorial resultants of both orthogonal fields can only be
orthogonal to the direction of motion by nature. So the question of
what force makes the light move forward instead of pulsating
stationary remains.
What if say half the energy of a photon would simply be kinetic,
pushing both local EM filds in the direction of motion?
But quantum physics, if I understand correctly, posits
instantaneous (i.e. discontinuous) changes in values. E.g., a photon
is emitted from an atom, leaping immediately to light speed from a
"rest" state. So the formula above might not apply, in its present
form. The Dirac delta function comes to mind, but that still doesn't
answer the original question.
Can someone please de-muddle me? Thank you very much!
Ted Shoemaker
André Michaud
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| User: "" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 11:46:02 PM |
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wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
Given
F = mA
and
E = mc^2 ,
we can quickly derive
F = EA/(c^2)
which tells us that, maybe, there is force (or something like it)
associated with light and similar energies. At least there's a
formula!
But acceleration is involved. Acceleration is the second derivative of
location with respect to time. That's fine for continuous
accelerations. But quantum physics, if I understand correctly, posits
instantaneous (i.e. discontinuous) changes in values. E.g., a photon
is emitted from an atom, leaping immediately to light speed from a
"rest" state. So the formula above might not apply, in its present
form. The Dirac delta function comes to mind, but that still doesn't
answer the original question.
Can someone please de-muddle me? Thank you very much!
Ted Shoemaker
As you have been thoroughly "muddled" by the posts,
I will try to "de-muddle" you.
1. Imagine a mesh consisting of many impedances and batteries.
2. A "potential difference" will exist between various
places in the mesh.
3. An electrical current will flow between various points in the mesh
depending upon the potential difference.
4. Next, imagine making this mesh larger and finer,
and the sources (Batteries) and the sinks (Impedances)
tend to clump together and form composite
source/sink objects.
5. Next consider that there is a smallest quantity of ACTION,
and that is one unit of Planck's Constant.
6. Next consider that the maximum transfer of ACTION
occurs when the source impedance equals the sink impedance.
7. Next consider that at the lowest potential level,
the maximum ACTION is also the minimum ACTION.
8. So in order for a single quantum of ACTION to flow
the source impedance equals the sink impedance and this
MUST equal the impedance of the fine space mesh.
The impedance of this mesh (Space) is 377 ohms.
The bottom line is that flows of action
(Current, matter, light, etc.) are constantly occurring
in the universal mesh between points of high ACTION potential
to points of low ACTION potential, and the paths followed
are paths where the various impedances are equal.
So to answer your question,
what travels is ACTION,
and what makes ACTION travel is a different of ACTION potential.
That said, the real quantity involved is the second radiation constant
(ACTION * C).
Visit my web site, download the PDF file,
and have your daughter read it.
--
Tom Potter
http://no-turtles.com
http://photos.yahoo.com/tdp1001
http://spaces.msn.com/tdp1001
http://tom-potter.blogspot.com
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| User: "Richard Herring" |
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| Title: Re: the "forces" behind light? |
01 Mar 2006 09:38:41 AM |
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In message <1140846362.060383.133320@v46g2000cwv.googlegroups.com>,
tdp1001@gmail.com writes
1. Imagine a mesh consisting of many impedances and batteries.
2. A "potential difference" will exist between various
places in the mesh.
3. An electrical current will flow between various points in the mesh
depending upon the potential difference.
4. Next, imagine making this mesh larger and finer,
and the sources (Batteries) and the sinks (Impedances)
tend to clump together and form composite
source/sink objects.
5. Next consider that there is a smallest quantity of ACTION,
and that is one unit of Planck's Constant.
Potter's understanding of action is only rivalled by that of Lester
Zick. I doubt if he can even define it, and he wouldn't know a
Lagrangian if it bit him. There's a smallest quantity of _angular
momentum_, which happens to have the same dimensions but is otherwise
rather different.
6. Next consider that the maximum transfer of ACTION
occurs when the source impedance equals the sink impedance.
Nope. Maximum transfer of energy. Action is a measure of the change in a
system, not something that can be transferred between parts of the
system.
7. Next consider that at the lowest potential level,
the maximum ACTION is also the minimum ACTION.
Meaningless. At the lowest potential energy, the _potential energy_ is
(surprise!) the minimum potential energy. There's no coherent way you
can work action into that sentence.
8. So in order for a single quantum of ACTION to flow
the source impedance equals the sink impedance and this
MUST equal the impedance of the fine space mesh.
Gibberish.
The impedance of this mesh (Space) is 377 ohms.
The bottom line is that flows of action
(Current, matter, light, etc.) are constantly occurring
in the universal mesh between points of high ACTION potential
And Zeus only knows what Potter thinks he means by "ACTION potential".
"Action potential" is a technical term from electrochemistry or
neurobiology, in which "action" has nothing to do with its meaning in
physics.
to points of low ACTION potential, and the paths followed
are paths where the various impedances are equal.
So to answer your question,
what travels is ACTION,
and what makes ACTION travel is a different of ACTION potential.
That said, the real quantity involved is the second radiation constant
(ACTION * C).
Visit my web site, download the PDF file,
and have your daughter read it.
She might enjoy a good laugh.
--
Richard Herring
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| User: "" |
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| Title: Re: the "forces" behind light? |
26 Feb 2006 05:42:41 PM |
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Tom Potter wrote:
Visit my web site, . . . .
--
http://no-turtles.com
http://photos.yahoo.com/tdp1001
http://spaces.msn.com/tdp1001
http://tom-potter.blogspot.com
I'll be glad to. Which one?
Ted Shoemaker
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| User: "" |
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| Title: Re: the "forces" behind light? |
26 Feb 2006 08:24:41 PM |
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wrote:
Tom Potter wrote:
Visit my web site, . . . .
--
http://no-turtles.com
http://photos.yahoo.com/tdp1001
http://spaces.msn.com/tdp1001
http://tom-potter.blogspot.com
I'll be glad to. Which one?
Ted Shoemaker
http://no-turtles.com will do, but
the URL below will take you directly there.
http://home.earthlink.net/~tdp
Tom
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| User: "PD" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 01:03:18 PM |
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wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
Given
F = mA
and
E = mc^2 ,
we can quickly derive
F = EA/(c^2)
which tells us that, maybe, there is force (or something like it)
associated with light and similar energies. At least there's a
formula!
But acceleration is involved. Acceleration is the second derivative of
location with respect to time. That's fine for continuous
accelerations. But quantum physics, if I understand correctly, posits
instantaneous (i.e. discontinuous) changes in values. E.g., a photon
is emitted from an atom, leaping immediately to light speed from a
"rest" state. So the formula above might not apply, in its present
form. The Dirac delta function comes to mind, but that still doesn't
answer the original question.
Can someone please de-muddle me? Thank you very much!
It's a little different than a bullet from a gun. You might ask what
what pushes sound through a 2x4? What's at work here is the
"connectedness" of one slice of the board to the next slice of the
board. It actually involves a ratio of the strength of the elastic
bond between one two adjacent chunks of wood and the inertia of each
chunk of wood. This ratio determines how fast the sound signal
transmits through the board.
"Yes," you say, "but I accelerate the end of the board when I smack
it." True, but the speed of the signal does not depend on how hard you
smack it; i.e. the acceleration you apply to the end chunk of wood. The
rate that the signal travels is strictly determined by the coupling of
one piece of wood to the next and the inertia of that wood.
A similar thing happens with light, except that the coupling that
happens is between the electric and magnetic fields that make up light.
The change in one produces a change in the other, which in turn
produces a change in the first, and so on. The speed depends strictly
on this coupling, and is independent of the size of the "force" that
originated the original disturbance.
PD
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| User: "SCW" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 11:51:19 AM |
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wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
<snip>
Acceleration occurs in the generation of the photon - similar to a
bullet from a gun.
It travels according to Newton's First Law: "Every object in a state
of uniform motion tends to remain in that state of motion unless an
external force is applied to it."
i.e. just like a bullet, it keeps going until it hits something - then
things start getting weird and you can forget Newton. But that isn't
the question your daughter asked!
Sam's answer is, as far as we can tell, correct, but not helpful (sorry
Sam!)
SCW
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| User: "Sam Wormley" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 01:08:15 PM |
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SCW wrote:
Acceleration occurs in the generation of the photon - similar to a
bullet from a gun.
The concept of acceleration is not tp photons... they only exist
at the speed of c.
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| User: "SCW" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 03:02:46 PM |
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Sam Wormley wrote:
SCW wrote:
Acceleration occurs in the generation of the photon - similar to a
bullet from a gun.
The concept of acceleration is not tp photons... they only exist
at the speed of c.
Hi Sam
I only say this because I have two daughters (11 & 7), so a bullet from
a gun analogy would be accepted!
I know that you know your stuff and I'm learning from you!
Best regards
SCW
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| User: "Sam Wormley" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 03:20:30 PM |
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SCW wrote:
Sam Wormley wrote:
SCW wrote:
Acceleration occurs in the generation of the photon - similar to a
bullet from a gun.
The concept of acceleration is not tp photons... they only exist
at the speed of c.
Hi Sam
I only say this because I have two daughters (11 & 7), so a bullet from
a gun analogy would be accepted!
I know that you know your stuff and I'm learning from you!
Best regards
SCW
I think the most important point to make to the girls is that
because light particles have no mass, the don't have to be
"accelerated".
Push the button an a laser pointer and the light leaves at c.
One and a half second later, it's all the way to the moon.
Round trip to the moon and reflected back is just under three
seconds. Shorter times for shorter distances.
-Sam
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| User: "tj Frazir" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 08:53:50 PM |
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the photon changed direction and fell into the gravity of the atom then
exchanged energy with the electron and then some energy changed
direction again and leftthe atom because it cant slow down or speed up
and is still at c.
maybe I didnt BUST you this time ..but you should know how it works by
now.
Im shure a few of you felt the heat.
when you leat exspect it ...
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| User: "tj Frazir" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 08:52:46 PM |
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the photon changed direction and fell into the gravity of the atom then
exchanged energy with the electron and then some energy changed
direction again and leftthe atom because it cant slow down or speed up
and is still at c.
maybe I didnt BUST you this time ..but you should know how it works by
now.
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| User: "Andy Resnick" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 01:00:27 PM |
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wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist.
"Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
We can think of force as applying an acceleration to a mass. Since
mass and energy are different forms of the same thing, hers is a
reasonable question.
<snip>
As you have seen, applying the concept of 'force' to light is not
simple, mostly because light does not have a rest mass. The simple
answer to your daughter is 'no'. (Smart girl, by the way- keep
encouraging her to ask questions!)
"energy" and "momentum", on the other hand, are perfectly suited to
describe light: energy relates to the frequency, and momentum to the
wavelength. The propogation of light is simply the flux of energy. The
absorption and emission of light involves momentum and energy transfer.
One other thing to keep in mind: Physics, and science in general,
doesn't answer 'why' questions, only 'how' questions. Physics cannot
tell you why light propogates, but it can tell you how it propogates.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
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| User: "Sam Wormley" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 10:56:41 AM |
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wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist. "Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
But it is an answer to the question.
Light is a force carrier. A photon a massless particle that always
travels at the speed of light. The electromagnetic force (just about
everything we experience other than gravitation) is mediated by
photons.
See: http://particleadventure.org/particleadventure/frameless/chart_cutouts/particle_chart.jpg
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| User: "Spaceman" |
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| Title: Re: the "forces" behind light? |
24 Feb 2006 11:27:29 AM |
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"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:dVGLf.788292$x96.613593@attbi_s72...
But it is an answer to the question.
Light is a force carrier. A photon a massless particle that always
travels at the speed of light.
And it completely ignores all relative motion to do so!
LOL
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| User: "Y.Porat" |
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| Title: Re: the "forces" behind light? |
01 Mar 2006 10:14:08 AM |
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Sam Wormley wrote:
shoemakerted@yahoo.com wrote:
My daughter asked me a question that I can't answer. I'm not a
physicist. "Isn't there a force that makes light travel?"
I can tell her that "it is light's nature to travel fast", but that
doesn't answer the question.
But it is an answer to the question.
Light is a force carrier. A photon a massless particle that always
travels at the speed of light. The electromagnetic force (just about
everything we experience other than gravitation) is mediated by
photons.
idiot parrot!!
a photon cannot be a mediator of Em forces since it travels
in straight lines!!
2 the photon does not need a foce to keep it moving
since it has a constant velocity.
3 the photon has mass because itr has energy and momentum
Y.Porat
-------------------------------
See: http://particleadventure.org/particleadventure/frameless/chart_cutouts/particle_chart.jpg
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