Why C (LightSpeed) Does Not Violate Thermodynamics Laws

[energia]

let's see if anyone can answer the question of why c (lightspeed) a universal unyealding constant does not violate the laws of thermodynamics - especially entropy

from what energy source do free photons in space draw the limitless power to travel at 299792458 m/s and no other speed?

what causes the apparent optical illusion of light slowing down 25% to 225000000 m/s in a tank of water - apparently losing energy (since c is constant it must be an illusion after all) and returning to 299792458 m/s upon leaving the tank? (apparently gaining energy)

what causes electromagnetic signals to slow down due to gravitational drag especially since gravity is supposed to propagate at lightspeed
(since c is a constant this must be an illusion as well)

why is light not able to escape a black hole?
if lightspeed is a constant and gravity propagates at the speed of light
why should light be stopped or slowed by gravity?
causing it to be blue or red shifted

if light is a wave how does it propagate in a vacuum?
if light is a particle, why does it behave like a wave, causing interference patterns in Thomas Young's double slit experiment ?

if a laser injected a single precisely perpendicular pulse between 2 parallel mirrors (assuming one mirror was a 2 way mirror) would the beam reflect for infinity at the speed of light - producing a perpetual floating light beam?
(according to entropy the beam must lose energy)

why does light traveling through a transparent solid cause the solid to heat up? as if the light were losing energy to the solid

if light (a photon) has no mass how can it push a solar sail?

 

[ZapperZ]

let's see if anyone can answer the question of why c (lightspeed) a universal unyealding constant does not violate the laws of thermodynamics - especially entropy

from what energy source do free photons in space draw the limitless power to travel at 299729458 m/s and no other speed?

It doesn't draw any energy. Via conservation of mass-energy, it has ALL of its energy in $$h\nu$$. If it draws any more energy, this conservation will be violated.

what causes the apparent optical illusion of light slowing down 25% to 225000000 m/s in a tank of water - apparently losing energy (since c is constant it must be an illusion after all) and returning to 299792458 m/s upon leaving the tank? (apparently gaining energy)

If you study a bit of a field of physics called optical conductivity, you will learn that photons do NOT lose speed in a dispersive material. The scattering-absorption-reemission of the material is what appears to slow down light in matter. It is the GROUP velocity that is measured, and it is this velocity that is found to have slowed down in matter.

what causes electromagnetic signals to slow down due to gravitational drag especially since gravity is supposed to propagate at lightspeed
(since c is a constant this must be an illusion as well)

why is light not able to escape a black hole?
if lightspeed is a constant and gravity propagates at the speed of light
why should light be stopped or slowed by gravity?
causing it to be blue or red shifted

Gravity warps spacetime metric. Light travels along such lines. Blackholes are thought to bend these spactime lines into itself. Thus, light follow these lines and never escape.

if light is a wave how does it propagate in a vacuum?
if light is a particle, why does it behave like a wave, causing interference patterns in Thomas Young's double slit experiment ?

Why would there be a problem of propagation whether it is a wave or a particle? It would be more unusual if something in free space doesn't move. What would make it THAT special that it shares the same reference frame with us?

if a laser injected a single precisely perpendicular pulse between 2 parallel mirrors (assuming one mirror was a 2 way mirror) would the beam reflect for infinity at the speed of light - producing a perpetual floating light beam?
(according to entropy the beam must lose energy)

I deal with a high powered Ti-Sapphire laser with roughly 8 ps pulse length. If you can find a "perfect" mirror that can do 100% reflectivity, give me a call.

why does light traveling through a transparent solid cause the solid to heat up? as if the light were losing energy to the solid

Because it does! Solids ALWAYS have phonons, which is partly responsible for what makes something transparent, and something else opaque.

if light (a photon) has no mass how can it push a solar sail?

Hint: solar sails works most efficiently if it has a metallic surface. Hint 2: how would you know there isn't another definiton of "momentum" that doesn't involved mass? p=hbar*k. Look that up.

Zz.

 

[energia]

I deal with a high powered Ti-Sapphire laser with roughly 8 ps pulse length. If you can find a "perfect" mirror that can do 100% reflectivity, give me a call.

let's start with this one...

assuming 100% reflectivity were possible
would you have a perpetually reflecting beam without a source?

 

[ZapperZ]

let's start with this one...

assuming 100% reflectivity were possible
would you have a perpetually reflecting beam without a source?

1. How would you have a beam already without a source?

2. By simply allowing reflectivity, it implies an interaction of the light with the plasmon states of the metallic surface. Unless you want to insist that (i) electrons should have zero mass and (ii) they don't scatter of each other and the phonons within the material, then we can't just weely-neely assume 100% reflectivity, because those are the two things that have to happen FIRST for you to have that.

Zz.

 

[energia]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

 

[swansont]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

Yes, if you had a perfect reflector you would get a perpetual beam.

You might get further if you drop the patronizing tone.

 

[ZapperZ]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

What do you think is a "reflectivity"? Light BOUNCING of a surface? If that is all that is, then why doesn't light bounces off ALL surfaces? Why does it bounce off metallic surfaces BETTER than dielectric surfaces? It is the interaction of the conduction electrons that participate in the retransmission of the incoming light AND the rest of the lattice recoiling via the phonons to preserve the conservation of momentum that ALLOWS for what you call "reflection" to happen! For there to be 100% reflectivity, you WANT zero electron mass, and for the object to be at 0K for there to be ZERO losses via the phonons.

Unless you live in a different physical reality than I do, I haven't seen both of those criteria ever being fulfilled.

If a child can answer your question, then why can't you answer it yourself?

Zz.

 

[Gokul43201]

In other words, you can not have your 100% reflectivity, unless you violate your favorite entropy law.

"If I only had a little humility, I'd be perfect." - Ted Turner

 

[energia]

since you can't just answer the question with a simple yes or no

I will answer it for you

the answer is: NO

it is not possible for a perpetual beam to reflect between 2 mirrors without a constant source

it violates the law of thermodynamics

there - that wasn't so hard was it?

You might get further if you drop the patronizing tone.

the patronizing nature of my tone is directly proportional to that of the tone I respond to - ZapperZ set the tone many posts ago

I will go back to my normal tone...

Now

 

[jcsd]

since you cannot just answer the question with a simple yes or no

I will answer it for you

the answer is: NO

it is not possible for a perpetual beam to reflect between 2 mirrors without a constant source

it violates the law of thermodynamics

that wasn't so hard was it?



the patronizing nature of my tone is directly proportional to that of tone I respond to

something to think about

whatever goes around comes around

It violates the law of thermodynamics, so what do we conclude about perfect refelectors then?

 

[energia]

the question was very hypothetical, since it would not be possible in reality

it was as much a question of logic as of entropy


it seems everytime a simple hypothetical question is asked

for example: if a 200KG piano is accelerating through space at 1 g at what speed does the piano's relative mass reach 400KG?

some brilliant physicist jumps into enlighten us to the fact that pianos cannot accelerate through space (wow! who would have guessed?)

Yes, if you had a perfect reflector you would get a perpetual beam.

respectfully - no, you would not get a perpetual beam

this violates entropy since you cannot draw more energy out of a system than goes into it

and it takes considerable energy for a laser beam to even exist
perfect reflectors or not

this is an excellent example of the difference between the modern scientific approach, and the classical (Natural Philosophy) approach

the modern approach relies almost exclusively on a set of accepted paradymes
and leaves logic out in the cold

the classical approach relied heavily on logic and reason - as well as experimental trial and error

which explains why the most prolific scientists lived centuries ago

 

[Gokul43201]

respectfully - no, you would not get a perpetual beam

this violates entropy since you cannot draw more energy out of a system than goes into it

and it takes considerable energy for a laser beam to even exist
perfect reflectors or not

this is an excellent example of the difference between the modern scientific approach, and the classical (Natural Philosophy) approach

What ?

 

[energia]

have you more to add to the discussion besides... what??

 

[Gokul43201]

Okay, so even if you had 100% reflectivity, you don't get a perpetual beam ! Either the clauses in this sentence contradict each other, or I'm missing something. Where does the lost energy go ?

 

[energia]

the energy would be lost as soon as the laser source were cut off
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

as soon as this source is cut off, the laser beam is also cut off
perfect reflector or not

there is nothing for free according to entropy

 

[Doc Al]

Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?

 

[GRQC]

from what energy source do free photons in space draw the limitless power to travel at 299729458 m/s and no other speed?

I generally find that anyone who must explicitly give the speed of light down to an integer value doesn't have a solid argument.

 

[energia]

Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?

to propagate.. no

to perpetually reflect...yes

I generally find that anyone who must explicitly give the speed of light down to an integer value doesn't have a solid argument.

oh? perhaps you think it's better (or maybe safer) to use the term 'c' rather than a precise value, since c can be any value we like within an equation

299792458 m/s leaves nothing to interpretation, and forces accountability

I was not even offering an argument, it was a question
and just for the record, I never start an argument without a solid basis

accepting something to be true as a paradyme does not make a solid argument, that approach is for the most timid and conservative scientists
and it's a shortcut to thinking

 

[Doc Al]

I asked:

Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?

You answered:

to propagate.. no

Then what was all this about?

the energy would be lost as soon as the laser source were cut off
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

as soon as this source is cut off, the laser beam is also cut off
perfect reflector or not

there is nothing for free according to entropy

to perpetually reflect...yes

Why?

 

[energia]

first of all it violates the laws of thermodynamics

secondly it violates common sense

and if these are not enough for you... perfect reflectors do not exist and cannot exist


perhaps you should attempt the experiment yourself
and report the results

the best metallic mirror absorbs a certain amount of light instead of reflecting. for focusing a laser beam, that's a serious problem. metallic mirrors reflect almost all wavelengths of light; for lasers you only want to reflect specific wavelengths

there's another kind of mirror that doesn't share these shortcomings. "Dielectric" mirrors use materials that selectively conduct electricity, stacked in a layer. If they're layered just right, they'll reflect almost all of a particular wavelength or wavelengths. Until recently, unfortunately, they've had one big drawback: they only reflect light that hits them at specific angles.

but for this experiment dielectric mirrors would work just fine

but you will have to inject the laser beam through a hole in one of the mirrors
and very quickly shift the hole in the mirror to one side before the light is reflected back, which means that these 2 mirrors must be a great distance apart

 

[krab]

to propagate.. no

to perpetually reflect...yes

Energia, you are quite wrong. Take an enclosed container with perfectly conducting walls. and a photon inside. This photon will bounce around forever. Experimentally, we come very very close to this situation. We have designed and built such cavities, by making the walls superconducting. Upwards of 10 billion bounces have been demonstrated. For normal conducting cavities, only 10000 or so is possible. Moreover, the finite number of bounces is consistent with the departure from ideal reflectivity.

 

[energia]

were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)

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

 

[Integral]

were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)

Really? What would the difference be?

 

[Doc Al]

first of all it violates the laws of thermodynamics

How's that?

secondly it violates common sense

It's your thought experiment.

and if these are not enough for you... perfect reflectors do not exist and cannot exist

But you're the one who said:

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

And you go on to say:

were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)

Please tell us the difference.

 

[energia]

the quick answer

photons exist free in nature and require no outside energy source to propagate

laser pulses do not exist free in nature... and do require an outside energy source to become amplified

 

[Doc Al]

the quick answer

photons exist free in nature and require no outside energy source to propagate

laser pulses do not exist free in nature... and do require an outside energy source to become amplified

The amplification takes place within the laser cavity. Once the pulse leaves the laser, it is just like any other set of photons. (Except for coherence, of course.)

 

[energia]

initially yes, but as soon as the source is removed the photons are on their own
and subject to dispersal after reflecting

what you would end up with a a bunch of scattered free photons
and not a perpetually fucused laser beam at a constant energy level

which would be impossible

imagine 2 dielectric reflectors, spaced 149864729 mm apart
mirror A is the source location - mirror B is the distant reflector location

a high powered laser pulse is injected towards mirror B
within 0,8 milliseconds mirror A is lowered into the path of the beam - in effect cutting it off and creating a secondary reflector

by this time the initial pulse has already been reflected off mirror B
and is near it's start point

after 1 millisecond the pulse has returned to mirror A after reflecting off mirror B 0,5 milliseconds earlier

at this time the laser source has been cut off by mirror A which is waiting to reflect the laser beam back to mirror B, and so forth, etc...

however as soon as the pulse is reflected it loses coherence
and there is no further laser source to refresh the losses in the intitial reflected pulse, so the pulse becomes more and more diffused
until it's photons disperse, and the beam vanishes

 

[Doc Al]

initially yes, but as soon as the source is removed the photons are on their own
and subject to dispersal after reflecting

As soon as the photons leave the laser cavity, they are on their own and the source is irrelevant.

 

[Antonio Lao]

My understanding of Light and entropy is the same as between order and disorder. The energy in entropy is useless (disorder and wasted) energy. The energy in a light beam such as a laser is highly ordered energy. Light waves of a laser are monochromatic and in phase although the linewidth still cannot be exactly zero.

Since the natural tendency of nature is toward higher entropy, toward higher disorder, laser lights are not found in nature, these lights have to be created by artificial process which requires high energy input at the outset.

 

[energia]

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

 

[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.