Why C (LightSpeed) Does Not Violate Thermodynamics Laws

[krab]

I've already made my points very clear
if you read them point by point and still don't follow the logic

Still that patronizing tone... maybe you are getting defensive.

try to bounce a single laser pulse for a sustained period at it's (sic)initial energy level in your reflective superconducting cavity and tell us about the result

Type "fabry-perot" into google. Here's a good site

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fabry.html

It's an interferometer whose operation depends exactly on the feature you claim is impossible; many reflections between two mirrors. As an undergraduate, I did these experiments with white light and also laser light.

 

[energia]

if you look at the link you posted
you will see at the lower left where it illustrates an incident light source

now take away the incident laser light source and see what happens

 

[energia]

now please go and produce a perpetually reflected laser pulse bewteen 2 mirrors
removing the incident laser source after the initial pulse
and let me know how long the beam hangs there at a constant intensity

when you've done that - then come and report your results

 

[krab]

So it is your position that if you suddenly turn off the light source, the light that is already between the plates will no longer continue as before, reflecting and partially transmitting at each mirror, but instead will suddenly what? evaporate?

 

[swansont]

I've already made my points very clear
if you read them point by point and still don't follow the logic

then don't take my word for it

do the experiment...

and then watch your jaw drop in amazement as the laser pulse vanishes almost as quickly as it's interrupted by mirror A

because that's exactly what will happen
whether you like it or not
whether it agrees with whatever you've been taught or not

The experiment that starts with "assuming 100% reflectivity were possible"?

You are arguing two sets of conditions. If you assume 100% reflectivity, you get one answer. If you do a real experiment you get a different answer.

Nobody's jaw would drop in amazement, since what you describe would not happen. It violates conservation of energy, for one. And the behavior you deny has been observed (as noted in another post), whether you like it or not.

 

[energia]

perhaps someone can find a link to such an experiment somewhere

meanwhile, I will do my best to come up with a better explanation


if all of you don't follow my thought experiment

then I have to blame myself

it's obvious you all have a good working knowledge of photonics
so it's just to find the right expression

 

[Gokul43201]

perhaps someone can find a link to such an experiment somewhere

meanwhile, ... if all of you don't follow my thought experiment.

Here's where the problem lies : You propose a "thought" experiment - one that can not be duplicated in practice because of the non-existence of 100% reflectors - and then support your argument with claims that a "real" experiment will not work because of your "entropy philosophy". Do you see the inconsistency ?

A photon has a certain energy, no matter where it came from. To make the energy disappear is a violation of energy conservation. In reality, the photon does disappear, but it's energy goes into the mirrors. This is not allowed by your 100% reflectors. So, in your thought experiment, there is no place for the energy to go. Hence, the beam lives forever !

 

[russ_watters]

Here's where the problem lies : You propose a "thought" experiment - one that can not be duplicated in practice because of the non-existence of 100% reflectors - and then support your argument with claims that a "real" experiment will not work because of your "entropy philosophy". Do you see the inconsistency ?

That appears to me to be precisely the problem: energia, you won't accept any experiment given to you, only one that matches your criteria, criteria which you specificy to make the experiment imposssible to conduct in reality. And even then, every now and then you make a mistake and suggest one that is possible to do or has even already been done, then you change your requirements to correct that.

energia, whether you like it or not, the experiments that have been done fit the theories we use. Period. You can't ask anything more from a theory.

 

[energia]

b*tch



haha just kidding - you're absolutely right of course, the conditions for my argument have been allowed to morph into obscurity ..I apologize

I've been trying to design a thought experiment that would test the 100% reflectivity premise for a perpetual laser beam pulse with no incident source

logic suggests that it's not possible to have a hanging laser beam with no laser tube to power it - the beam should vanish as soon as the source is cut off since a beam of photons scatter without being amplified and focused
perfect reflector or not

now do you see what I'm suggesting?

bouncing photons don't violate entropy since electric fields and magnetic fields balance each other out

however a laser beam is highly focused and amplified
and it's the continuity of the highly focused and amplified state that I'm calling into question

 

[russ_watters]

logic suggests that it's not possible to have a hanging laser beam with no laser tube to power it - the beam should vanish as soon as the source is cut off since a beam of photons scatter without being amplified and focused perfect reflector or not

now do you see what I'm suggesting?

I'm not sure at all what you are trying to prove here. A laser beam continues independent of its source for the duration of its existence, fancy experimental setup or not.

How about just turning off the laser before the beam hits/bounces back from the target? In the lunar ranging experiments, the time lag between the beam being turned off and reflected back would be noticeable on a human scale (3sec or so, IIRC).

Is that all you're interested in?

 

[energia]

Is that all you're interested in?

no, not exactly

but let me ask you a more specific question
since you work with lasers (yes?)

lets say that we use the world’s most powerful laser: the 60-beam Omega
at LLE which draws energies in the 300 TeraWatt range during a
1 nanosecond pulse

and we use mirrors equal to the reflectivity of those used on the Hubble Space telescope (the most reflective that exist)

these are technologies which exist in the real world

assuming a near perfect vacuum (let's say in a 150 m EM shielded tube)

the mirrors are adjusted perfectly parallel
the mirror nearest the laser is synchronized to rotate 180^o in such a way that a hole on 1 side of the circular mirror is aligned with the pulse at the precise moment

so when the 60-beam Omega fires a 1 nanosecond pulse
1 microsecond later the pulse has returned and is again reflected
this time by the mirror nearest the laser, with it's hole now rotated away

the question is...

how long will this 300 TeraWatt pulse reflect (unchanged) between the 2 mirrors?

that is precisely what I''m intersted in

 

[Gokul43201]

The beam intensity decreases geometrically with each reflection as

I = Io*R^n, where R is the reflectivity.

If the distance between mirrors is d, then the time taken for each traversal is d/c = T, say.

Then n=[t/T],
So I = Io*R^[t/T]

This tells you the change in beam intensity as a function of time.

 

[energia]

The beam intensity decreases geometrically with each reflection as

I = Io*R^n, where R is the reflectivity.

If the distance between mirrors is d, then the time taken for each traversal is d/c = T, say.

Then n=[t/T],
So I = Io*R^[t/T]

This tells you the change in beam intensity as a function of time.

thank you for brilliantly illustrating my point

so, as you can see the laser pulse does not reflect for infinity at it's original intensity, but in fact decreases geometrically with each reflection

entropy wins again

 

[russ_watters]

thank you for brilliantly illustrating my point

so, as you can see the laser pulse does not reflect for infinity at it's original intensity, but in fact decreases geometrically with each reflection

entropy wins again

That's it? Couldn't you just have come out and said that before? We already know this (several people have explained it already). So what?

And btw, this is also quite different from your assertion that a photon from a laser behaves any differently than any other photon when emitted.

 

[energia]

a single photon (as I stated before) does not behave differently from any other single photon

however a high energy laser beam is not a single photon

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

that's my main argument

 

[Integral]

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

Just what do you mean by focused here? How is a laser beam broken? Once again your terminology does not lead one to believe that you have depth of knowledge in these matters. It is not clear that you fully under stand the term "amplification" when applied to a laser.

 

[energia]

perhaps you should read my earlier post...

we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it

a basic solid state laser assembly consists of:

1. a polished aluminium reflecting tube (laser tube)
2. a 99. 9% reflective mirror
3. a 95% reflective mirror
4. a quartz flash tube (the photonic inductor coil I mentioned)
5. a ruby crystal (natural or glass)
6. a power supply

theory of operation:

first: a high voltage power supply causes the photonic inductor coil (quartz flash tube) to emit an intense burst of light, exciting atoms in the ruby crystal to higher energy levels

above a critical energy level, these atoms emit (initially unfocused) photons. traveling in all directions

the photons from one atom stimulate emission of photons from more atoms and the light intensity is geometrically amplified

the 2 mirrors reflect these photons, resulting in stimulated emission and amplification

the photons reach a critical excited and amplified state and finally are ejected out the 95% reflective mirror - in the form of a laser beam

besides solid state lasers, there are also gas, liquid, and semiconductor lasers

the most powerful lasers are solid state
the 60 beam Omega is a solid state laser


so, do you still question my knowledge of lasers?

I've built a laser myself - have you?

It is not clear that you fully under stand the term amplified

it is not clear that you understand the meaning of the terms 'focused' or 'amplified' since you question their meaning

I design and build amplifiers professionally - I know the meaning of term 'amplified' better than you will ever dream of knowing it

 

[swansont]

a single photon (as I stated before) does not behave differently from any other single photon

however a high energy laser beam is not a single photon

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

that's my main argument

Then how is it possible that a pulsed laser works? That's a bunch of "broken" beams.

 

[energia]

Then how is it possible that a pulsed laser works? That's a bunch of "broken" beams.

this is the area of misunderstanding

you are referring to propagation
and I am referring to reflection

 

[Integral]

What you posted sounds as if it were copied from a High school textbook.

http://www.cohr.com/products/index.cfm?fuseaction=Interfaces.Part&PCID=23&PLID=34&PDID=300&PTID=DPSS0002 is what I work with every working day. I am responsible for the maintenance of 18 of these things. The only barely resemble your description. Lasers come in many different varieties your general description is every much wrong as it is right. Further it still does not convey any true understanding, on your part, of how a laser operates.

 

[swansont]

this is the area of misunderstanding

you are referring to propagation
and I am referring to reflection

I think an area of misunderstanding is that you keep changing the question. But a pulsed laser can be reflected, and is, inside of the laser - the gain medium is just a small section of the overall device - and yet it seems to work just fine.

 

[Integral]

I design and build amplifiers professionally - I know the meaning of term 'amplified' better than you will ever dream of knowing it

Does this mean you are an Electrical Engineer?

If so that explains a lot right there.

Simply because you build amplifiers does not mean that you understand or even know the basics of LASER operation. The fact that you claim a laser beam is "focused" means that you do not understand laser beams. The fact that you somehow separate the the beam from the generation means that you do not understand lasers.

The fact that you seem to think that reflection is somehow different for lasers then any other source of light means that you do not understand light. It does not appear to me that you understand enough of these topics to carry on a meaningful converstion. And that explains a lot right there.

 

[energia]

my description of laser operation was given at it's most basic level
I don't need to write an essay on the operational theory of all lasers

since you work with lasers - you must understand the energy states of the electrons that make them work

lasers are possible because of the way light interacts with electrons
the photoelectric effect

(btw. Einstein was awarded the Nobel prize in 1921 for his theory on the photoelectric effect )

the electrons of each atom and molecule exist at specific energy levels
which orbit a nucleus

outer orbital electrons are at higher energy levels than inner orbital eletrons

the energy levels of electrons can be AMPLIFIED by the injection of photons

as an electron drops from an outer to an inner orbit, it loses energy in the form of light

the wavelength (colour) of the emitted light is relative to the amount of energy released. specific wavelengths of light are absorbed (exciting the electrons) causing specific wavelengths to be emitted as soon as the electrons return to their original energy level

and that's how a laser operates - any laser, whether solid state, gas, liquid, whatever

and yes I'm an electronics engineer - with a firm foundation in Maxwell equations and semiconductor physics

if physicists think they're somehow above engineers - let me remind you that it's engineers who provide the means to take physics from theory to reality
and many engineers are also physicists

 

[energia]

now back to the point

I'm suggesting that - at the moment of reflection, the photoelectric effect occurs between the striking photons and the electrons orbiting the nuclei of the atoms of the reflector, resulting in a net energy loss (entropy)

now do you see my point?

 

[swansont]

the energy levels of electrons can be AMPLIFIED by the injection of photons

The "Amplification" is the increase in the number of photons, from stimulated emission. That is, one photon induces an atom to de-excite and emit a photon (in phase), so now you have two photons. You have amplified the light signal.

 

[Integral]

Obviously you have not had even basic Quantum Theory. You need to stop lecturing about things outside of your expertise and start asking questions. Your knowledge of the fundamental functionality of lasers is woeful.

I am sorry the photoelectric effect is not the place to start.

my description of laser operation was given at it's most basic level
I don't need to write an essay on the operational theory of all lasers

In reality your description did not get anywhere near the core of the physics of a laser.

the energy levels of electrons can be AMPLIFIED by the injection of photons

as an electron drops from an outer to an inner orbit, it loses energy in the form of light

the wavelength (colour) of the emitted light is relative to the amount of energy released. specific wavelengths of light are absorbed (exciting the electrons) causing specific wavelengths to be emitted as soon as the electrons return to their original energy level

This also describes a light bulb. Or even a reflection off of a wall. What is different in a laser? You did not mention population inversion, nor did you touch the idea of stimulated emission. These are the keys to a laser, the rest is window dressing.

 

[Integral]

now back to the point

I'm suggesting that - at the moment of reflection, the photoelectric effect occurs between the striking photons and the electrons orbiting the nuclei of the atoms of the reflector, resulting in a net energy loss (entropy)

now do you see my point?

The photoelectric effect does not enter into this. In the photoelectric effect an electron is IONIZED, simply not the case in common reflections.

Give this up, I would like you to change your approach, rather then assuming that you have a full understanding, assume that you have only a partial understanding and attempt to ask questions to help us guide you to a better understanding. As long as you maintain the delusion that you understand this field you will find it impossible to learn.

 

[energia]

You did not mention population inversion

you want to discuss population inversion? fine

first we create two photons from one
then an amplifier must produce millions of photons
adding increasing numbers of atoms to the upper metastable state
and holding them long enough to store energy and allow the production of lorry loads of stimulated photons

the longer lifetime states allow the rate at which atoms are raised into one of these states to exceed the rate at which they leave

atoms can be excited into and held in the upper state leaving an almost empty state below them

atoms can stay in this metastable state without de-exciting while the population is being raised

a population inversion occurs when more atoms are in a higher state of excitation than in the lower state

NOTE: this violates entropy

nor did you touch the idea of stimulated emission

we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it

here is my quote again

as you can see I've already stated the process with these terms alone

"Light Amplification by Stimulated Emission of Radiation"

notice the terms "Stimulated Emission of Radiation"


and I've had far more than basic QED (Euler-Lagrange equations) thank you

 

[energia]

in any case...

i've already demonstrated my point - which is that a laser beam cannot be sustained indefinately between 2 reflectors without a constant source

not using current technology - not even using emerging technology


why can't you just admit that it can't be done (?)


the whole argument is that it can't be achieved because it violates entropy

 

[swansont]

this topic has become tiresom

i've already demonstrated my point - which is that a laser beam cannot be sustained indefinately between 2 reflectors without a constant source

not using current technology - not even using emerging technology


why can't you just admit that it can't be done (?)


the whole argument is that it can't be achieved because it violates entropy

What the? Who has disputed this, if you use real mirrors?

What has been disputed is the notion that laser photons somehow know whether the laser is still on or not.