Science Questions

How does light change speed?

Mon, 15th Jun 2015

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Question

Robert de Vos asked:

We know that light is composed of photons that move at 300,000 km per second in a vacuum. If I shine a light though a 5cm sheet of glass, it will slow down and also heat up the glass as it passes through. As it leaves the glass, it then speeds up again, Now where does the energy come from to speed it back up to 300,000 per second?

 

One could assume that the continuous flow from the source achieves this, but what would happen if one directed a single photon through the glass sheet?

 

Would it still lose energy to the glass as it passes through and then as it emerges, how could it find the energy (from nowhere) to speed back up to 300,000 km per second?

 

Answer

We put this question to Cambridge University physicist Zephyr Penoyre...

Zephyr - When it goes into the glass, it’s moving slower. But also, Spectrum of a Light Bulbbecause the frequency has to be the same, the same waves have to be coming into the glass at the same rate as they're coming out, otherwise you’ve lost waves somewhere along the way…

Chris - And it’s changed colour.

Zephyr - And that’s because wavelength has changed. So, the energy of the light is to do with the wavelength of the light. So, as it slows down, the energy gets higher - because the wavelength has shrunk - so the total amount of energy passing through the glass is exactly the same as it was going through the air, it's just moving at a slightly different speed.

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Photons never move at other than light speed the apparent slowing down is due to the tortuous path they take being absorbed and re-emitted by atoms en route.
When they leave the materiel this effect ceases and their normal speed becomes apparent.
I know that this a simplified version but the gist is correct.
syhprum, Thu, 13th Mar 2014

Re the speed of light in general - I have asked elsewhere on this forum about the scientist who has slowed down light and even stopped it at one point, and why this is not being celebrated/discussed/questioned/debated/explored more. Is this scientist's discovery (Lene Haus) not that important after all? I thought that showing Einstein was wrong would be a big deal. annie123, Fri, 14th Mar 2014


Einstein's theories have been remarkably resilient at large scales. (Relativity does not address the quantum scale, although his work on the photoelectric effect does.)

We routinely slow down light slightly by shining it through a transparent medium like glass - this is how lenses work.

Slowing light to a walking pace or slower does not violate Einstein's theory of relativity, which takes the speed of light in a vacuum as a speed limit for matter.

These demonstrations of slowing light uses light of a very specific wavelength, and a medium which is carefully primed to put it in the right quantum state.
It is definitely not a vacuum... evan_au, Sat, 15th Mar 2014


What do you mean? There is a relativistic theory of quantum mechanics. PmbPhy, Tue, 16th Jun 2015


The work of Lene Hau is being celebrated but it would be a mistake to conclude that it shows Einstein to be wrong. It is also a mistake the think that Einstein said light speed is constant in all circumstances, the constancy of light speed as described by Einstein is for a vaccum. Dr Hau's work was on light in dense, indeed very cold, media eg sodium, for which she has received significant and well deserved accolades. Colin2B, Tue, 16th Jun 2015


This seems to be talking about the energy density of a beam of light, eg measured  Joules/m3 or similar

However, when you are talking about an individual photon, its energy remains the same in vacuum, air or glass.

Unlike objects having a rest mass, light does not gain or lose energy when its speed changes, so it doesn't need to gain energy when it exits the glass. evan_au, Wed, 17th Jun 2015



Yes, quantum mechanics has been adapted to consider relativistic effects such as c being a speed limit, time dilation and gravitational red shifting, etc. All these can be tested on Earth, for example by accelerating subatomic particles to nearly the speed of light in a particle accelerator, or by flying atomic clocks around the Earth in a GPS satellite.

However, I have not seen a well-tested quantized theory of relativity. To test this would require close study of the behaviour of subatomic particles close to the event horizon of a black hole. If scientists attempted experiments on a reasonable-sized black hole here on Earth, I fear that they would not live long enough to publish the paper. evan_au, Wed, 17th Jun 2015

It doesn't. Light which exits the material it's not the same light which enters and which is inside: the em field which exits is generated by the last charges inside the material.

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lightarrow lightarrow, Wed, 17th Jun 2015

At the event horizon of a black hole the gravitational field exhibits a critical density like a 'perfect' medium. Perfect in respect of its ability to stop light. The photon's energy is effectively canceled exactly at the horizon. At this point the electromagnetic and gravitational fields are at equilibrium. Not in the sense of a stationary point but in the balance of energies. This does not help unless observational data can be collected from the immediate environment surrounding a black hole. A collision with the horizon of Sag A* is the best chance of obtaining this data. jeffreyH, Wed, 17th Jun 2015



Explanations often say, or imply, that it is not a single photon that travels through the medium (e.g. glass); it is a succession of new photons, created at each new emission from atoms in the glass.  If this were what actually happened, then the absorption spectrum would be discrete because atoms have only discrete energy states. Yet, in glass for example, we see almost the whole visible spectrum being transmitted with no discrete disruption in the measured frequencies.

The reason for this is that a solid is composed of a network of ions and electrons fixed in a "lattice".  They have what is known as "collective vibrational modes", or phonons. These are quanta of lattice vibrations, and it is these vibrational modes that can absorb a photon. 

If a photon has an energy beyond the phonon spectrum, the solid cannot sustain this vibration, because the phonon mode is not available; so the lattice does not absorb this photon and it is re-emitted but with a very slight delay. 
Bill S, Thu, 18th Jun 2015



Explanations often say, or imply, that it is not a single photon that travels through the medium (e.g. glass); it is a succession of new photons, created at each new emission from atoms in the glass.  If this were what actually happened, then the absorption spectrum would be discrete because atoms have only discrete energy states. Yet, in glass for example, we see almost the whole visible spectrum being transmitted with no discrete disruption in the measured frequencies.

The reason for this is that a solid is composed of a network of ions and electrons fixed in a "lattice".  They have what is known as "collective vibrational modes", or phonons. These are quanta of lattice vibrations, and it is these vibrational modes that can absorb a photon. 

If a photon has an energy beyond the phonon spectrum, the solid cannot sustain this vibration, because the phonon mode is not available; so the lattice does not absorb this photon and it is re-emitted but with a very slight delay. 

Yes, this is also what I quoted from another forum in this one some years ago. Infact I haven't written that a photon is absorbed by an atom's material then ri-emitted and so on.

Nontheless a photon entering the material is not the same photon exiting from it: the em field, entering the material, let's say glass, excites it and the glass generates in turn another em field, which interacts with the first and with glass itself. Photons are constantly created and destroyed in the resulting field so their individuality is lost at the end of the path.

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lightarrow lightarrow, Sat, 20th Jun 2015



You are right, of course.  These thing always seem to get more complicated, the closer you look at them. Bill S, Sat, 20th Jun 2015

Reading through the views expressed, there seemed to be three alternative explanations put forward.

1. The ‘bus stop’ theory, where like a bus stopping at every bus stop, a light photon stops at every electron it meets on its route through the translucent material.
2. The ‘spring’ theory, where the photon acts like a spring which becomes more tightly coiled on its passage through the translucent material.
3. The ‘water surfer’ theory, where like a surfer skimming the wave tops of water, the photon is swept through the translucent material carried on the top of the internal wave motion of the material’s ‘electron sea’.

The arguments raised against each particular theory were along the following lines:

The ‘bus stop’ theory needs to explain how all visible light photons are absorbed and emitted by electrons on their passage through the translucent material. Particular elements such as silicon, have a specific absorption and emission spectra, so some visible light frequencies would not be affected and pass through at the speed of light without hindrance.

The ‘coiled spring theory’, raised the question of where the frequency of a photon of visible light changes to a higher value. Is it upon contact with one or multiple electrons on its passage through the translucent material? And interestingly, if an infra-red photon passed through the translucent material would it be visible on its passage as ‘red light’?

The ‘water surfer’ theory makes the assumption that there is a ‘standing wave’ within the ‘electron sea’, which carries the photon along without absorption and emission. (This is articulated much more cogently as the collective vibrational modes (phonons) of the ions and electrons located in their lattice structure.) The speed of passage of the photon through the translucent material riding this vibrational lattice must be presumably less than the speed of light, but the photon itself is unaffected and emerges at the speed of light again.

All three theories are plausible, but it does seem to me that our understanding of the photon and its interaction with the electron is at best sketchy. If we understood the commonality of the energy structures of the photon and the electron, we would know how the photon is absorbed and released by the electron, (bus stop theory), receives and releases energy, (coiled spring theory) and hitches a lift without energy being exchanged with the electron lattice (water surfer theory).


RTCPhysics, Thu, 25th Jun 2015



No, the frequency determines the "color," and that does not change from medium to medium. The wavelength must change, but ultimately it is the frequency (energy) that registers as the color in our eye.

If you consider the eye as the detector, then it doesn't matter what material the light passes through, ultimately the refractive index of the eye where the light is absorbed determines the "observed wavelength", but we can design an experiment to probe the color of light in other materials:

Say we have two solutions that each contain the same concentration of a dye that absorbs at a very specific frequency, but the two solutions also contain different amounts of some other dissolved species that changes the refractive index substantially (many additives could allow us to tune the refractive index by 10-20%, without changing the behavior of the dye). If the spectrum of light coming out of the solution is independent of the refractive index, that proves that the frequency determines color, not the wavelength (and if the absorbed light shifts with refractive index, that proves the wavelength is the important factor) chiralSPO, Thu, 25th Jun 2015



I disagree. The explanation that the reduction of the velocity of visible light in a translucent material is effected by a reduction in wavelength but not frequency, implies that the sinusoidal wave model of a single photon is incorrect. With the sinusoidal model, the wavelength and frequency are related, one being the inverse of the other.

The only way I can see to explain the reduction of light speed upon entering a translucent material from say, air, is if the amplitude of the sinusoidal wave is increased at the boundary between the media, but its frequency and wavelength remain unchanged. The higher amplitude increases the three dimensional distance travelled by the photon's new sinusoidal wave form and hence its velocity through the medium. On emerging from the translucent medium back into air, the amplitude reverts to its previous level, giving the photon the energy it needs to return to its previous velocity.

Reading the results of experimental tests upon the functioning of the eye, their results all refer to the wavelength of the visible light as being the important factor in the colours that the brain observes, not frequency.

Absorption and refraction are two different phenomenon, not to be confused. Refraction or bending of light occurs at the surface boundary between the two media. Absorption of a particular frequency of light by electrons can happen anywhere within the receiving medium. In the experiment you described, adding the dye to the change of refractive index would only shift the whole light spectrum to one side. The absorption frequency of the translucent solution would be unchanged within this spectrum, proving nothing. Except that the added dye does not absorb light of the particular frequency used in the experiment. I'm assuming that the absorption line did not move! RTCPhysics, Fri, 24th Jul 2015

I have never read anywhere that wave amplitude is a factor. Do you have any references for that? jeffreyH, Fri, 24th Jul 2015



They are not quite inverses, they are inverse AND related by the velocity: wavelength = speed / frequency (wavelength * frequency = speed ; meters per cycle times cycles per second equals meters per second) Therefore, to maintain a fixed frequency when light slows down, the wavelength must decrease. This can be (and has been) experimentally shown by performing interferometry (which depends on the wavelength, not the frequency) in media other than vacuum, and comparing against the energy of the photon (which is a function of frequency, not wavelength).



I don't think amplitude has anything to do with this. The sinusoidal wave is not the "path" that the photon takes. It is a representation of the electromagnetic oscillation of the photon. More photons = greater amplitude (if they're in phase).



Almost everybody talks about the wavelength of light rather than frequency, but it is implied that they mean the wavelength in a vacuum. The wavelength changes based on the refractive index of the medium the light is in (see above), but the frequency (energy) remains constant. The eye detects light by virtue of rhodopsin, which is the adduct of an enzyme (opsin) and a small molecule called retinal. The light isomerizes retinal, causing a conformational change in the rhodopsin, which sends a signal to the nerve, etc. etc. There are a few different variants of opsin (called photopsins) that can modulate the energy required to isomerize the retinal (this is how we see different colors). The key here is that the differentiation of different "wavelengths" of light is due to little protein devices that respond very selectively to certain energies (frequencies) of light.

(https://en.wikipedia.org/wiki/Rhodopsin)
(https://en.wikipedia.org/wiki/Photopsin)



This is exactly my point! If the absorption line did not move, and the whole spectrum shifts to one side, the light that gets absorbed depends on how much of a shift there was!!!  chiralSPO, Fri, 24th Jul 2015

"Translucent"? it's not the correct term."sinusoidal wave model of a single photon"? It doesn't exist. Maybe you intended something else.No, as others already wrote, in an electromagnetic wave, not only wavelength λ and frequency f are related, but radiation velocity (precisely phase velocity vp) too:

λ = vp/f

frequency f doesn't change inside the material, so if vp decreases, also does λ.


... your personal and wrong theory.

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lightarrow lightarrow, Sat, 25th Jul 2015


I heard a very practical example of the fact that the wavelength of light changes when it enters a material of higher refractive index:

Obtaining the light spectrum of stars and planets is a powerful tool for astronomers - it allows them to determine their chemical composition without actually traveling there to take a sample.

One of the common ways to break light up into a spectrum is to use a diffraction grating - very fine lines etched on a flat surface, which breaks up the light into a rainbow of its constituent colors.

Astronomers studying the infra-red need to put their instruments above the atmosphere, ideally in a satellite, but volume is at a premium in a satellite.

Some instrument makers recently "reversed" the usual diffraction grating design - instead of shining light onto the diffraction grating in a vacuum, they shone the light through the back of a silicon wafer onto the diffraction grating, so the light was passing through silicon, rather than through a vacuum when it hit the grating.

The refractive index of silicon is about 3-5 times higher than a vacuum in the infra-red region, so the wavelength of light is correspondingly shorter.

This allowed them to separate the wavelengths as effectively as an instrument about 4 times longer (and wider & high), so they reduced the volume of the instrument by a factor of about 60, which is a significant saving in a spacecraft! 


Maybe I'm just nitpicking here, but...
I would call a photon an em field which propagates through space, as per Maxwell's equations.

To me, it doesn't matter whether the em field at point X is the same em field that exists 1 meter (or 1 micrometer) away. What matters is that it is the same quantum of energy that is propagating (as per Einstein's explanation of the photoelectric effect). To me, the photon that enters a glass block is the same photon that exits a glass block (assuming it isn't absorbed in-between). evan_au, Sun, 26th Jul 2015

Presuming light has a speed and it is not something in space that is being energized at a speed such as CBMR. Thebox, Sun, 26th Jul 2015


Light definitely has a speed, as measured by Ole Rřmer in 1676, Fizeau & Focault around 1848 and many more modern measurements.
In Physics, we call this speed "c", and it is about 300 thousand km/s in a vacuum.

See: https://en.wikipedia.org/wiki/Speed_of_light#Measurement


Visible light happens in space because of things like stars, bouncing off things like planets, Moons and clouds of dust. It does not rely on the CMBR to power it (the CMBR is far too weak to have much effect on visible light). evan_au, Sun, 26th Jul 2015


Maybe I'm just nitpicking here, but...
I would call a photon an em field which propagates through space, as per Maxwell's equations.Aha! 90 yars of quantum mechanics thrown away! 😊
Sorry but a photon is something much more complicated than that!Then an electron or a photon is the same, for you 😊 Prove it, if you can.

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lightarrow lightarrow, Sun, 26th Jul 2015


No, an electron does not obey Maxwell's equations (in particular, it cannot travel at c); a photon does.


I don't think it is a matter of proof. I think it comes down to how it is defined.

I don't know what would be an authoritative definition, but in this one: "a photon is a discrete bundle (or quantum) of electromagnetic (or light) energy", ..the focus is on the photon as a quantum of energy, rather than on the photon as a localized disturbance in the em field.

More authoritative definitions & interpretations are welcome! evan_au, Sun, 26th Jul 2015


No, an electron does not obey Maxwell's equations (in particular, it cannot travel at c); a photon does."An electron does not obey Maxwell's equations..a photon does"? Not very correct, because it mixes classical and quantum description.
An electron AND a photon are described by QED = Quantum ElectroDynamics.
I don't think it is a matter of proof. I think it comes down to how it is defined."A state with n = 1 of the quantistic hamiltonian of the electromagnetic field in absence of charges" is a definition nearer to the concept than your definition.My God! That would be "an authoritative definition"? It seems a popular book!At this point you are perfectly right! But it's very difficult to find a correct definition of "photon" because it's a very technic concept.

While I'm looking for a link with that definition, have a look at:
http://www.sheffield.ac.uk/polopoly_fs/1.14183!/file/photon.pdf

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lightarrow lightarrow, Mon, 27th Jul 2015


No, an electron does not obey Maxwell's equations (in particular, it cannot travel at c); a photon does.You are mixing classical and quantum concepts here. If you want to talk of Maxwell's equations, then forget the word "photon".
If you want to call for a quantum description, then BOTH electron and photon are described by QED: quantum electro dynamics.
I don't think it is a matter of proof. I think it comes down to how it is defined.
I don't know what would be an authoritative definition, but in this one: "a photon is a discrete bundle (or quantum) of electromagnetic (or light) energy",And from that how can you deduce that the photon which exits a piece of glass is the same which entered?
If it were so simple, Einstein wouldn't have had the need to say something like: "50 years of thoughts about the subject didn't bring me closer to understand what a light quantum is...but nowadays every Bob and Alice thinks to know what it is..."
A photon is a much complicated concept. Have a look here:
http://www.sheffield.ac.uk/polopoly_fs/1.14183!/file/photon.pdfIt's very difficult to find one because it's a very technical subject, despite the fact we always talk about it as if we knew it well...
Here is one from an extract of a discussion in other forum (and I admit not to have completely grasped it ):
Given a free electromagnetic field (that is without electric charges) a photon is (something alike) the subspace with n = 1 of the hilbert space of quantized field's states, where n are eigenvalues of the operators "number of particles" N which gives the hamiltonian of the field when multiplied by ħω, which gives the field energy when applied to the state.

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lightarrow lightarrow, Mon, 27th Jul 2015

I'm about to start reading up on Hilbert spaces. jeffreyH, Mon, 27th Jul 2015

When you calculate the path and speed of a photon through a block of glass, you must do a calculation at the boundaries of the glass block, because the conditions change (ie glass has a higher refractive index than air), and this affects the speed of the photon. It does not matter whether you are using classical optics or infinite-dimensional Hilbert spaces to do the calculation.


The fact that QED is able to unify the behaviour of photons & electrons makes it better than classical physics; maybe one day we will have a theory that includes gravity too, and that will be even better than QED.

But the existence of a "better" theory does not necessarily render the old theory invalid. The new theory is only considered valid because in the "classical limit", it predicts the same results as the experiments which had already been successfully explained by the classical theory.

So in selecting a method to solve a particular problem, it is important to know how accurate an answer do you need?

All design calculations are approximations; will the approximations of a given method yield an answer which is "good enough" for the problem at hand? This means you must understand the domain of applicability of the different theories:

Where they will give essentially identical answers

Where they will give answers that are "close enough", and you can build a prototype and tweak it to correct the discrepancies that occur because real objects are never exactly the same as even the best theoretical models.

Where they give divergent answers, and you must use the more complex theory (but you still need to build the prototype!). 


In cases 1 & 2, the selection is essentially made on pragmatic grounds like simplicity and accuracy (the proverbial "back of the envelope calculation" may be all you can afford in the middle of a discussion). 

For myself, my maths classes did not go beyond eigenvectors on finite dimensional vector spaces, so I don't have all the mathematical tools needed for determining the eigenvalues of infinite-dimensional Hilbert spaces.

However, I would argue that you do not need these advanced mathematical tools to calculate the path and speed of a photon through a glass block, because this is in the domain of classical optics. The answers are "close enough", provided the size of the block of glass is much larger than the wavelength of light, and the size of the atoms in the glass is far smaller than the wavelength of the light. You just need to recognize that the classical term "a ray of light" is an approximation to "a stream of photons" in quantum theory.

Undoubtedly, a grand unified theory which includes gravity (or even a small extension of current theories which is able to explain why calculations on Feynman diagrams work so well) will require additional, even more complex mathematical tools in your toolkit.

You don't always need a sledgehammer to crack a nut...
evan_au, Tue, 28th Jul 2015

One thing that is significant about the answers given here is that they either tend to ignore physical facts as in the posts favouring the propagation of light through a substance in accordance with  Maxwell’s equations or they  give static answers which ignore the dynamics present. Too often (almost exclusively) the emission and absorption of photons by electrons in an atom is treated as a one off case, an electron within the atom absorbs and then emits an electron, this does not fit in with the observed data Firstly the definition of spectroscopy is as follows:

Spectroscopy is a scientific measurement technique. It measures light that is emitted, absorbed, or scattered by materials and can be used to study, identify and quantify those materials.

In order for the above to be true it is implicit that electrons in the atoms comprising the substance must be absorbing and emitting light of a given frequency at precisely that same frequency. (i.e., If green light at 540 THz is being observed it means that the electrons are oscillating at that same frequency of 540\times 10 ^{12} THz  and absorbing and emitting electrons in those same numbers.

Next examining Lene Hau’s experimental results on the slowing down of light, it is found that while the results wholly substantiate the emission and absorption theory the results equally completely rule out Maxwell’s electromagnetic field, interacting with the fields of the atoms in the material while allowing the light to pass through only slightly slowed down.

Again what makes  an object transparent or opaque? An opaque material such as wood will absorb all or most of the visible spectrum of light releasing the extra energy as heat, while a transparent material such as glass will absorb and re-emit most of the  visible spectrum, resulting in the passage of light .  A photon is characterized by its energy which is directly related to the wavelength of the light when the radiation is considered as a wave. This relation is :

E_{ph}= \frac{hc}{\lambda}

A large amount of photons make a ray of light, this ray of light can be characterized by its wavelength, intensity and the variation of this intensity over time. This translates in the particle domain to the amount of particles crossing an imaginary surface per unit of time. Particles interact with each other by exchanging particles or energy. A photon interacts with other particles by transferring its energy to the other particle (absorption). This exchange of energy happens if the maximum energy that the photon can bring is at least equal to the smallest quantum of energy that the other particle can accept.

In a transparent material such as glass the photons of all frequencies are transmitted by being absorbed and re-emitted, since this represents a longer path than the light would experience while travelling through air it results in a slowing down of light and a speeding up once again as it exits the medium.  Also since the speed of light undergoes a change it is obvious that the wavelength must also increase according to the relation \lambda = \frac{c}{\nu}.
McQueen, Wed, 29th Jul 2015

Good. Let me know what you grasped (or not).

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lightarrow lightarrow, Wed, 29th Jul 2015

No, if you use classical optics and/or classical electrodynamics you calculate the path, speed, phase, etc, of a light beam or of an em wavefront, not of a photon, because "photon" is a quantistic concept which have to be treated quantistically. Infact in all of these discussions we could better never talk of photons at all; to talk of photons it's a sort of "trend".
The fact that QED is able to unify the behaviour of photons & electrons makes it better than classical physics; maybe one day we will have a theory that includes gravity too, and that will be even better than QED.
But the existence of a "better" theory does not necessarily render the old theory invalid. Certainly, I'm the first to say that, in most of the cases, we could and should better talk of classical electrodynamics only. But it was you to write "No, an electron does not obey Maxwell's equations (in particular, it cannot travel at c); a photon does". In case it's the opposite...
But anyway is an incorrect statement for what I've already written.I agree with you, but as I said, we can't answer the question "the photon which enters the glass is the same which exits?" without using QED, at least I'm pretty sure it's impossible to do it with Maxwell's equations only.I wish it were enough!Do you agree, at least, that a photon is an excitation of the em field and that the field outside the glass is not equal to field inside?

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lightarrow lightarrow, Wed, 29th Jul 2015



It was the absence of references that caught my attention. All the diagrams of the electro-magnetic (e-m) spectrum, that I have seen, have always shown each photon as having the same amplitude, whatever the wavelength. But if, in practice, photons can vary their amplitude, then it is reasonable to conclude that photons interacting with the electrons on the surface of a denser ‘isotropic’ medium, conserve their energy by exchanging velocity for amplitude upon entry and  amplitude for velocity upon exit, rather than increasing or decreasing their wavelength.

But if it is a fact that the wavelength of a photon changes, then how does this actually happen? Relativity is one possibility. For a photon to hold its energy level constant, measured in cycles per second, upon entering an isotropic medium implies that the intervals of time that it experiences remain unchanged, but the shortening of its wavelength to slow it down implies that it experiences a reduction in the distance intervals of space as it traverses through the isotropic medium, reverting back to its original velocity upon exit. However, this explanation of the reduced velocity by the application of relativity theory to photons is another with no references!

As you will have read by now, there are many more informed and interesting replies which rebut the logic of an amplitude variation in the photon, restricting its role to interference effects, so unless there is a path to rebutting them, amplitude variation remains what it is, a personal idea. RTCPhysics, Sun, 2nd Aug 2015


The wavelength of any wave is directly related to the velocity: v=nλ, where:

v: velocity (=c for light in a vacuum)

n: frequency in Hz

λ: Wavelength in m


If the frequency remains the same, then reducing the velocity as a photon enters a block of glass causes a proportional reduction in wavelength inside the glass. This is explainable using classical optics, without reference to relativity.


The photon's energy is exchanged between an electric field and magnetic field as it propagates through space (as per Maxwell, applied to a single photon).

Inside a block of glass, the permittivity ε≈4ε0, which results in a higher refractive index for glass.

We can draw analogy with another case where ε>ε0, which is a capacitor. The energy stored in a capacitor is E=˝CV2; the higher the dielectric ε, the larger the capacitance (for the same physical arrangement of the plates).

If you apply the same amount of energy to a capacitor with vacuum as the dielectric, and also to a capacitor with glass as the dielectric (εr≈4), you find that the strength of the electric field inside the glass dielectric is halved, ie the amplitude of the electric field is halved.

The energy of the photon does not change as it enters, transits or exits a block of glass. If the above analogy holds(?), the amplitude of the photon's electric field is reduced when it enters glass.

On the other hand, normal silica glass is almost non-magnetic, so the permeability μ ≈ μ0, and the amplitude of the magnetic field of the photon is not really affected while propagating through glass.

The velocity of the photon is determined by both the permeability & permittivity of the medium. evan_au, Sun, 2nd Aug 2015

Good. Let me know what you grasped (or not).

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lightarrow


At the moment I am reading through quantum physics. I now understand the double slit experiment and the relationship between photon wave length and measurement. Also exactly why position and momentum cannot be measured together. I have started on complex vector spaces and bra ket notation and am up to complex conjugates. When I get further I may have questions. jeffreyH, Sun, 2nd Aug 2015


Surely you mean a proportionate increase in wave - length ? McQueen, Mon, 3rd Aug 2015


Surely you mean a proportionate increase in wave - length ?


no, a reduction of wavelength would be expected when light enters the glass from air or space (or water). chiralSPO, Mon, 3rd Aug 2015


Surely you mean a proportionate increase in wave - length ?

λ=v/f
f doesn't change, so if the light slows wavelength reduces. Colin2B, Mon, 3rd Aug 2015



I happened upon this most interesting thread by chance, but nearly fell off my chair when I read this post!  You have made comment on my thread about there being limits to my understanding.  I want you to know that I have long since read through quantum physics, "Quantum" by Manjit Kumar as well as touching on the subject in the dozens of physics books I've read over the last 5 years.  I've also studied complex vector spaces and bra ket notation and complex conjugates with Professor Susskind on YouTube on ""The Theoretical Minimum Lectures, I'm on lecture 8 of the GR lectures at present.  I want you to know that I understand mathematics but I just don't have a flair for the notation in much the same way that I can understand musical notation but am incapable of playing unless by ear.  The concepts of the physics themselves I find really rather simple.

Can I ask you please not to underestimate my understanding? timey, Mon, 3rd Aug 2015

It has been mentioned above as to an exchange of energies between the light and the medium it is passing through affecting frequency.

IF... (I have my ideas, but I'll say 'for whatever reason')... If the length/rate of a second is not a constant then Planck's h constant can actually be considered as a variable.  If velocity is measured by seconds that are not constant then the length measurement is affected.

We know that mass and a gravity field affect the phenomenon of time dilation...

IF we can view the experience of time from the perspective of the quantum world as being of a different length/rate of second in relation to our own experience of time, then Planck's h constant becomes an inadequate tool in the measurement of lengths/frequencies.

IF the quantum world experiences time at a rate much slower to our own experience, Planck's h constant would actually be 'blocking' the view of quantum activity.

The implications of this notion are that the quantum world may not be granular but may in fact be as smooth as the macroscopic world, and if Planck's h constant were to be variable in accordance to the variability of the length/rate of a second... then perhaps it would be possible to measure both location and velocity simultaneously.

Under the remit of this notion, the energies exchanged between the light and the medium of the glass would be time related. timey, Tue, 4th Aug 2015

You are misunderstanding what a photon is and how it travels, if you look on my post TOE fun you will I have demistified it and that includes the slit experiment apparent wavelike effects as well and much more. Aquarius, Tue, 4th Aug 2015

Erm...Nope,sorry I am not misunderstanding the photon or how it travels.  What I am doing is extrapolating a notion regarding Planck's h constant with regards to measuring frequency and relating it to quantum light theory...but I'll gladly check out your thread. :) timey, Tue, 4th Aug 2015



Poppycock. jeffreyH, Tue, 4th Aug 2015



I do so hate it when people quote a portion of your presentation as if that portion was going to make sense when not attached to the rest...and then insult it without providing an explanation of their discordance.

JefferyH, are you saying that there is no varition in the length of a second?  Or are you saying that Plancks h constant takes into account variations in the length of a second?

Oh wait...that's right, you're not really saying anything at-all are you? timey, Tue, 4th Aug 2015



Poppycock.


No it was the statement that you may be able to measure position and velocity or more properly momentum simultaneously. You say you understand quantum physics and yet your statements indicate the opposite. jeffreyH, Tue, 4th Aug 2015

As a start you need to read and understand these two pages.

https://en.wikipedia.org/wiki/Dirac_delta_function
https://en.wikipedia.org/wiki/Momentum_operator
jeffreyH, Tue, 4th Aug 2015

As far as I am aware JefferyH, I am not questioning the mathematical structure of the Dirac delta function or of the momentum operator.  These are  considerations that were formulated after Plancks discovery of quanta and his dirivation of the h constant which is an action of a time or a length, whereas Planck tried, to no avail, to iron out the quantum nature of his findings.

Now if you could actually relate the first half of the post that you didn't quote, to the part that you did quote - then we might even be in danger of having a proper conversation! timey, Tue, 4th Aug 2015



You may be confusing proper time with coordinate time. Proper time runs at a constant rate and is always in a local frame of reference. Coordinate time changes when viewed from remote frames. Planck's constant is just that, a constant. You cannot consider it as a variable. That is what the term constant means.



I have no idea why you should choose the word affect in this context as they are the very reason for time dilation.



If you are writing in terms of Planck's constant then the second is the wrong base. You then need to be thinking in units of Planck time. You can't mix the two and hope to get meaningful answers.



The rest is unsubstantiated speculation. jeffreyH, Tue, 4th Aug 2015

Nope, I'm not confusing these relativity/space time related considerations of proper time or co-ordinate time.  I do have my own ideas on time - but this thread is not my thread, nor is it in the new theories section...therefore for the purposes of this conversation I think it within the remit of accepted physics to say that we have time as a measurement and, as a separate issue, that we observe the occurrence of the phenomenon of time... and that this time is subject to change in the rate of its occurrence due to changes in the gravity field.

Of course my post/posts are entirely speculative, :) , is there something wrong with that?

IF we can view gravity fields on a smaller scale, as in our own personal gravity field, ie: if we get fatter we feel heavier, if we go to the moon we feel lighter... on the basis that a black hole will change the rate of time fairly drastically, 'maybe' the gravity fields of the quantum world are 'differently oriented' in relation to to time dilation.

The smallest quantum package is delivered at an unbelievably small fraction of a 'second'.  Clearly Planck has used a time measurement factor in the derivation of this constant... But IF the quantum world is operating within a time structure that is different, ie not occurring at the same rate as our own, the time measurement that Planck has used to derive these units of Planck time as constant would be rendered inadequate in measuring the entirety of the quantum world.  The gaps between the quantum leaps being the point of relevance here. timey, Tue, 4th Aug 2015



Well now you are clearer in meaning and actually saying something interesting. jeffreyH, Wed, 5th Aug 2015

JeffreyH :) You wouldn't be the first person to say I have trouble expressing myself.  Thank you very much for the positive comment! timey, Wed, 5th Aug 2015

A further point of interest might be found in the consideration of whether or not the changes in the rate of time themselves are delivered in quantum packages...

(Edit: Light traveling through changes in the gravity field being the main point of relevance here) timey, Wed, 5th Aug 2015

Anyway, since no one wishes to 'engage' in actual discussion about my speculations, I will make this my last post here on the subject.  I do monologues in my head all day long.  It's boring.

I just want to point out that although it may seem as though I am arguing in favour of classical physics in my questioning of the mathematical structure of Planck's h constant, whereas it is a logical consideration that 'perhaps' the quantum nature of his measurements "may" be ironed out by my suggestion - it is also just as logical to assume that any re-measuring of Planck's derivation of the h constant, under the remit of the quantum worlds own time structure and rate of time, could 'also' result in evidence of a quantum nature...but 'perhaps' a more 'readable' quantum nature than we have now.

IF it did become clear that the quantum world is subject to 'differently oriented' time structure/s, logical process denotes that this avenue of investigation through time dilation considerations could 'perhaps' either lead to quantum being united with classical physics or quantum being united with gravity. timey, Wed, 5th Aug 2015



I think I see what you are suggesting here, but you may have to come up with a sound argument in favour of 'differently oriented' time structure/s in order to spark the interest of the experts, or even the general run of posters. Bill S, Wed, 5th Aug 2015

Well yes... The best I can do is re-iterate a passage from an earlier post...

"IF we can view gravity fields on a smaller scale, as in our own personal gravity field, ie: if we get fatter we feel heavier, if we go to the moon we feel lighter... on the basis that a black hole will change the rate of time fairly drastically, 'maybe' the gravity fields of the quantum world are 'differently oriented' in relation to to time dilation." 

And point to the suggestions of questioning Planck's h constant and looking at the changes in the rate of time being quantised as to being avenues of potential investigation.

NIST have been stringently testing time dilation.  Of course it is a matter of what tests they run and why, I have not heard of any further tests planned.

One is either inspired or not, I guess.  Thanks for the reply Bill.
timey, Wed, 5th Aug 2015

Bill... I've been giving some thought to your comment on coming up with a sound argument in favour of the quantum world being subject to a different time structure or different time structures than our own, ie: a different rate or different rates in the occurrence of time.

There is conclusive evidence via NIST that even the slightest change in a gravity field will change the rate time occurs at.  When one is dealing with such minuscule fractions of a second such as Planck's h constant, the tiniest change in the length of a second will indeed affect the measurement of a length (edit: if that length measurement is in relation to momentum.)

We are inured, due to current thinking and experimentation as of date, to only consider the change in a gravity field due to 'elevation'.  Admittedly, it is very hard to make tests on a gravity field.  However... the phenomenon of time dilation 'could' prove to be an excellent window into the subtleties of the gravitational phenomena.

IF one were interested in reconciling the world of quantum with classical physics, in examining the gaps between the quantum leaps one 'might' try stretching or shrinking the length of a second until the quanta are delivered smoothly.  Taking the length of the second that this is achieved at and relating it to the NIST experiments, this 'may' unlock further secrets of the gravitational phenomenon.

On the other hand, IF one were interested in uniting quantum mechanics with gravity, then one 'might' examine the possibility of the changes in the rate of time being quantised, and look at the changes of the frequency in light being caused by the changes in the rate of time. (photon with no mass)

Whichever takes your fancy... Fact is that if you mathematicians can get your heads around using different lengths of a second when appropriate in your equations, then your mathematics will gain more depth and transform from being 2 dimensional to 3D. 

Mathematics gone IMAX, if you like...
This giving your maths much more 'reach'. timey, Sat, 8th Aug 2015


Thanks for that link. Over the past week, I have read these 6 essays on “What is a Photon?”. I learnt quite a lot about the quantum nature of light, and where the boundary is drawn between classical and quantum representations of light.

As I now understand it:

Maxwell’s  equations allow light to carry any energy at any frequency.

However, quantum theory tells us that there is a minimum energy for light, E=hf. This minimum quantum of energy is called a photon.

Maxwell’s equations work for high intensity light as it is propagating through space (or glass); in this case you can ignore the quantisation of energy.

Maxwell did not predict photons – but someone forgot to tell the photons. A photon still obeys Maxwell’s equations as it is propagating through space (or glass).

A photon is described by its energy, spin/polarization and momentum (where momentum is a vector, giving the photon’s direction).

There was an interesting discussion about why quantum descriptions of the photon don’t ascribe a definite position vs time to the photon (apparently, this is beyond the usual fuzziness described by Heisenberg?).

The characteristics of entangled photons or parametric down-conversion is not described by classical optics.

Nor are photons which can take multiple paths through an optical bench.

Clearly, quantum representation of light is a more complete description of light than classical optics. 


This example does not involve entangled photons, mirror mazes, Lamb shifts or Bose-Einstein condensates, so I don't think we need the full power of a quantum representation to crack this particular nut (mainly Planck’s hypothesis which quantizes the energy of a light beam into a stream of photons).

From classical optics, we can measure the polarization of a beam of photons striking a detector. In addition, using classical particle physics, we can determine the energy and position vs time of bunches of photons or individual photons (subject to diffraction limits and Heisenberg’s limits), allowing us to determine the path of a beam of photons on either side of the glass block.

A photon exiting a sheet of glass has the same energy, spin and momentum as the one which entered*. In the quantum world, if these parameters are the same, it is the same photon.

*The reverse is not necessarily true, because not all photons approaching a glass sheet will exit it towards the detector, due to classical effects like partial reflection, scattering and absorption.
evan_au, Mon, 10th Aug 2015

If we move away from photons for a second and consider particles with rest mass we can propose something interesting. I will state straight away that a particle with rest mass, if it could travel at c, cannot possibly have angular momentum. This is because the velocity of angular momentum would be summed to the straight line velocity giving an overall value > c. This reduction of angular momentum should relate directly to time dilation and should also be present in a gravitational field. jeffreyH, Mon, 10th Aug 2015

This brings up the possibility that in the total absence of gravitation the photon would have no angular momentum. jeffreyH, Mon, 10th Aug 2015


Thanks for that link. Over the past week, I have read these 6 essays on “What is a Photon?”. I learnt quite a lot about the quantum nature of light, and where the boundary is drawn between classical and quantum representations of light.
As I now understand it:

Maxwell’s  equations allow light to carry any energy at any frequency.

However, quantum theory tells us that there is a minimum energy for light, E=hf. This minimum quantum of energy is called a photon.

Maxwell’s equations work for high intensity light as it is propagating through space (or glass); in this case you can ignore the quantisation of energy.
Ok.The problem is you cannot describe a photon as an electromagnetic wave, so, maybe what you say is true but I don't know how we apply Maxwell’s equations to a single photon.Quite. A photon never has an exact momentum and an exact energy, it's always in a superposition of states with different momentums and energies. A photon of a very collimated and monochromatic laser beam will have more precise momentum and energy, but a photon emitted from an excited atom will have less definite momentum and energy.I only know that it's very difficult to define a position operator for a photon, because of the fact it's impossible to find a frame of reference in which the photon is stationary.
This example does not involve entangled photons, mirror mazes, Lamb shifts or Bose-Einstein condensates, so I don't think we need the full power of a quantum representation to crack this particular nut (mainly Planck’s hypothesis which quantizes the energy of a light beam into a stream of photons).

From classical optics, we can measure the polarization of a beam of photons striking a detector. In addition, using classical particle physics, we can determine the energy and position vs time of bunches of photons or individual photons (subject to diffraction limits and Heisenberg’s limits), allowing us to determine the path of a beam of photons on either side of the glass block.

A photon exiting a sheet of glass has the same energy, spin and momentum as the one which entered*. In the quantum world, if these parameters are the same, it is the same photon.
In this sense, yes, but what I intended is: if an object enters a "black box" and it exits as (seemingly) the same, can we be sure that it wasn't destroyed somewhere inside the box and then re-created? In my opinion it's exactly what happens but I don't know QED enough to have a definite answer.
Nontheless you can be the one who is right.

--
lightarrow lightarrow, Tue, 11th Aug 2015




Ok, I've left you to think about that one for a bit, but for me it becomes clear that the 'reasoning' is a catch 22.  Because if light has no angular momentum in a 0 gravity field, the implications of this are that the speed of light is only constant to the strength of a gravity field.  We experience the speed of light as we do in our gravity field and we appreciate that light 'can' move slower.  What happens in a gravity field that is greater than our own?

For me this leads to questioning the fact of the speed of light being the uppermost speed limit of the universe, but if you 'do' consider this, then it requires a complete re-assessment of the current view of the mechanics of the universe... But that's just my humble take and I'd be interested to know what 'takes' others may have... timey, Tue, 11th Aug 2015

But it can't, so every consequence of an incorrect assumption have to be incorrect.This is not true, velocities composition is not a mere sum, relativistically.

--
lightarrow lightarrow, Tue, 11th Aug 2015

But lightarrow, what if they could?

What IF relativity has its place in describing motions relative to each other in relation to the observer but is inadequate when describing the universe. (There is evidence of this)

IF a particle 'can' travel faster than the speed of light, then I suspect that we have just arrived back on the doorstep of the importance of using the appropriate length of a second to calculate momentum, and we can go on to see that the 'distance travelled' then becomes quite 'interesting'. timey, Tue, 11th Aug 2015

Do you mean if you can accelerate a massive object to light speed without having to use infinite energy? And what if we all were blue angels with green wings and bright eyes? If physics doesn't count, everything is allowed, isnt'it?
Of course physics is not "static", it evolves and maybe what you say could even be true in a remote future, but in this forum we should talk of what we know and of what is possible, not of any idea which we can have in our mind, in my opinion.Not if its mass is different from zero (and real).

--
lightarrow lightarrow, Wed, 12th Aug 2015

Erm, no lightarrow... what I was thinking about (in relation to Jeff's 'experimental speculation') with regards to particles with rest mass - was a situation where a very massive body (black hole) jets very small bodies of mass (particles) into space - potentially at a rate faster than the light speed we experience on earth. This being on the basis - (again in relation to Jeff's 'experimental speculation' on light experiencing no angular momentum in a 0 gravity field) - that the speed of light, in relation to a more massive body of mass than earths, 'may' (speculative) be going faster. This being 'a' logical progression of such speculations...and that these particles in that situation would have no trouble reaching 'our' speed of light, but would not be able to reach the faster speed of light of their own reference frame (this being the black hole), for the same reason that the same particles could not reach the speed of 'our' light in our reference frame of earth.

These 'speculations' are born of the 'very real' possibility that the mathematics of quantum are operating minus an important factor - this being time dilation.  IF this is true, (speculative) then logically speaking the implications of this 'may be' that the changes in the rate of time are 'responsible' for the changes in the frequency of light - rather than current view which is that  the changes in the gravity field itself are responsible for redshift/blueshift. This current view actually being based upon the 'speculative' basis of a photon having 'relativistic' mass.

Of course to think in 'these alternative terms' does require one to consider the phenomenon of time as a 'force', (a phenomenon that does something).  And to conduct a rethink as to the current view of time dilation and how it works.

I take on board your comment about 'real physics', and point you in the direction of Lee Smolin's book, "The Trouble With Physics".  Physics is very far from being in possession of the whole picture.

Perhaps it might be better if I took my speculations back to my own thread... I'm open to suggestion... however I myself would find this to be a shame... There is some good 'form' written above and so long as everybody is 'aware' that these consideration are but 'speculations', I think we are ok...personally.

I think it also worth mentioning that 'most' people are not aware that a lot of the concepts that are being discussed as "proper physics" are in fact hardly based on anything but speculation and supposition themselves. timey, Wed, 12th Aug 2015


Superluminal jets have been known since the 1970s. They are believed to be associated with black holes, but it is thought that they are explainable within relativity.


Einstein's relativity was well-known by 1920. From the late 1920s, efforts were made to integrate relativity (including time dilation) into the new field of quantum mechanics.

With particle accelerators like the LHC operating so close to the speed of light, and the collision debris also travelling near c, particle physicists have to consider relativistic effects on a day-by-day basis (and their computers need to deal with it many times per microsecond). evan_au, Wed, 12th Aug 2015

True enough... However the stark, in your face facts remain that quantum, all these years later is not reconciled with gravity, relativity, all these years later does not 'fully' describe the universe, and Planck's h constant was derived before it was possible to 'measure' time and time dilation with such great accuracy... And LHC, despite its multitude of funding, hasn't really brought the situation much further along at-all considering...

So...where do you go from there?

Can you explain what the efforts made to integrate time dilation into quantum mechanics consisted of?  Were they successful?  And why is it that time dilation is thought to be relativistic?  It's an actual phenomenon of the universe and does not need relativity to explain it... timey, Wed, 12th Aug 2015



Can you give some concrete examples of where quantum falls short? I don't mean "it's not elegant" or "it doesn't make sense" or "disagrees with gravity or relativity." In which situations do they disagree? How much different are their predictions, and which one is right? (if "neither" you have to explain how the correct answer was determined).

Then we focus our attention on those descrepancies. chiralSPO, Wed, 12th Aug 2015

But it can't, so every consequence of an incorrect assumption have to be incorrect.This is not true, velocities composition is not a mere sum, relativistically.

--
lightarrow


We use imaginary and complex numbers as a way to determine eigenvalues. Those numbers don't exist and yet they are used. We use the impossible to find the possible so why not use the impossible with respect to the speed of light? If you take a spiral, it moves along a straight line path as well as an angular path. If we project each infinitesimal point from the spiral path onto the straight line path we can see that the path of the spiral is moving faster than the straight line path is indicating. It travels a greater distance. We need to add the difference to get the correct result. This is very like the change in wavelength of light in a gravitational field. As the length in the direction of travel contracts then so the energy path through space increases as if light still has to travel a set distance in another way to compensate. This is an unproven speculation but it answers some questions about how real the wave function might actually might be. jeffreyH, Thu, 13th Aug 2015



Ok, quantum gives a description of everything except gravity and relativity is a theory of gravity.  Relativity 'needs' the so far unknown and unseen (there are perhaps hints in The Bullet Cluster, unproved) additions of dark matter to make it work outside the solar system... and dark energy to expand the universe.  It falls short at black holes, where the time vector has to be swapped with a distance vector in the space time matrix.
If relativity could be reconciled with quantum, apart from the other niggly matters, we'd be close to a fully operational and unified theory, except for the fact of what happens inside and before the Big Bang.

Unfortunately relativity cannot be reconciled with quantum.  If it could, I'm pretty certain that after the 100, give or take a few, years since the discovery and progression of quantum, that the means to do so would already have been discovered by now. (Hence, I imagine, the emergence of the hugely funded String Theory saga)

The suggestion that I made in post 49, bottom of page 2, IF relevant, 'could' give an insight into either reconciling quantum with gravity or reconciling quantum into the sphere of classical physics.

The 'proposed' discrepancy being: In the questioning of the mathematical structure of Planck's h constant in relation to there possibly being a time dilation factor within the quantum region and exploring how this 'could ' affect or change our perception of the phenomenon of light with regards to energy and frequency in relation to time dilation, and time dilations relationship with the gravitational field.

(Sorry, I'm not sure about the 'predictions' aspect of quantum, so I won't comment there)

(Edit: The predictions of relativity have been pretty right on so far, therefore I don't think that there is 'all' that much wrong with it... although clearly, considering the non-unification of both working hypothesis, quantum and relativity, there must be some aspect of it that 'is' slightly off.  Personally I feel that the time dilation aspect of relativity is misconceived, at fault, and in need of further investigation.) timey, Thu, 13th Aug 2015

No, you are wrong. They exist as numbers, but not only! Quantum description of nature is impossible without them and this suggests they are more deeply "ingrained" with reality.You are making a big mistake. What is real is the result of a measure of an observable; since observables are associated with hermitian operators and these have (mathematically) real eigenvalues, the result is a real number (not a complex one).But, be it a spiral or what you want, in relativity, and I've already wrote it, velocities don't sum up.

--
lightarrow lightarrow, Thu, 13th Aug 2015

Well lightarrow, to say so I'm going to reply to your post above even though it isn't directed at me, because that is something I can do, in the hope that Jeff is busy doing some mathematics, which I can't do.

Your reasoning is coming over as slightly cockeyed.  It is, as Jeff stated, perfectly normal to use imaginary numbers (and therefore imaginary concepts, which are actually also mathematical in practice) to equate and then renormalise, whether dealing with quantum or classical physics.  I believe it is actually the basis of Gauge theory. (although I do stand to be corrected, as I'm otherwise unfamiliar with Gauge theory.) The link below is quite interesting with regards to rest mass and the photon.

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

If Jeff is considering rest mass then he 'is' operating within the region of quantum, and your reasoning does not hold.  If imaginary numbers can be used to determine the reality of the hidden quantum world, then logic derives that imaginary concepts may also be used in a similar fashion.

We can no more 'prove' that a particle of any kind can or cannot reach the speed of light in a reference frame of a greater gravity field than our own, than we can prove if a photon has mass or not.  Therefore, as with the photon, any concept can be 'experimented' with, so long as one keeps track and renormalises as appropriate.  It may even turn out that to do so 'could' reveal some other hidden reality of our universe as indeed you have stated using imaginary numbers reveals the reality of quantum!

You say that velocities do not sum up, I don't pretend to understand 'exactly' where you are coming from with this - I'm sure I might not be the only one, could you please explain? timey, Thu, 13th Aug 2015

Yes you are correct that in relativity it is more complex.

https://en.wikipedia.org/wiki/Velocity-addition_formula

However I am attempting to gain a better understanding of some issues. jeffreyH, Thu, 13th Aug 2015

Imaginary numbers exist, as numbers; what do you mean with "imaginary concepts"? In physics we can talk of what we know, not of what we don't know. But physics evolves and if now we say that a photon is massless, it doesn't mean "it's established that it will be so forever"! Physics (differently from phylosophy or else) can only describe what is known at the moment; everything else is speculation and not physics.It may turn out everything, so this reasoning is meaningless.If an object moves with velocity v1 with respect to a frame of reference S and S moves at velocity v2 with respect to another frame S' (v1 and v2 be parallel) then the object moves with respect to S' at velocity:

V = (v1 + v2)/(1 + v1*v2/c2)

As you see it's not a mere sum.
Try with v1 = v2 = c (or one of them = c and the other non zero) and then tell me what is V (you don't need to put numbers, you can leave the letters, the computation is immediate).

--
lightarrow lightarrow, Thu, 13th Aug 2015

Ok, well dark matter (which may have been observed - as yet unproven) and dark energy are imaginary concepts based on mathematical necessity.  It is only 'when' we observe their reality that they will come out of the 'theoretical' region.  Anything unobserved is an imaginary concept.  Any imaginary concept can have a basis in mathematics whether is becomes necessary as a result of mathematical necessity or as a theoretical necessity.  For instance we observe redshift and we have theorised that the fact of redshift means that a light source is moving away from us.  Although this concept is widely accepted as fact, this being because it is 'the' most logical reasoning in relation to our current understanding, but it is still an imaginary concept non-the-less.  Other theories concerning redshift have been extrapolated...I really can't be bothered to relate them here :) , suffice to say there are other imaginary concepts attached to the observation of redshift.  I could go on...and on :).

Yes, I agree, we can talk about what we know. (Edit: or what we think we know). In fact its all people ever do, I'm literally bored to tears over it!
If there had been no speculation about black body radiation we wouldn't have a quantum theory.  Logically speaking speculation is an absolute 'must' if progress is to be made, and the reality is that we 'actually know' very little, although we have 'theorised' immensely.  And we have taken the concepts of this theorising, the real and the proven concepts along side the theorised, and the therefore imaginary concepts and attached mathematics to them.  Mathematica isn't fussy you know, it's quite capable of calculating all manner of wrongness as well as wonderfully illuminating the right and the real.

The maths you have included (I'm not good with maths) are related to a particle or wavelength in relation to the momentum of another particle or wave length.  I don't see how this relates to a path taken by light round a spiral as opposed to a path taken by light in a straight line.  I didn't read it that Jeff was measuring 2 situations in relation to each other, just that if light took one path that it would not be the same as if it took the other, but I'll state again that I'm not at-all that mathematically adept and I may have misconceived his intent.  I stand to be corrected.  In a situation where the speed of light 'may' be slowed, or speeded up, when adding the concept of time dilation, for me it is the distance travelled that becomes interesting. timey, Thu, 13th Aug 2015

Firstly Timey I didn't say that light took a spiral path. Secondly you cannot simply use speculation to formulate hypotheses. Most of the discoveries in physics followed on from experimentation where the equations were derived to understand the mechanism at work. Not the other way round. Thirdly don't follow me. I am untrained and this is just a hobby for me. The way I do things is not the correct way as understood by professional physicists. I have studied the areas I need to for those things I am interested in at the time. If you have an interest in quantum physics then try to find out why \sigma_1 n_1 + \sigma_2 n_2 + \sigma_3 n_3 is important and what it means. It is to do with the electron. Also try to find out what <a|b><a|b>* means. It is to do with probability. These are not difficult and are just linear algebra (matrices). It will surprise you. You will also learn what a complex conjugate is and how it relates to the complex plane. jeffreyH, Thu, 13th Aug 2015

Firstly Jeff, I'm not 'following' you.  LOL !!! ...did you think you were guru type material???

Secondly, I am perfectly aware that speculation cannot be used to form a hypothesis. 

Thirdly, most of the 'experiments' conducted were conducted because """someone""" speculated a reason that they should be conducted.

My understanding of quantum is sufficient for my purposes.  I have also read extensively in my area of interest, thank you.  Why is is that it is always assumed when one makes a suggestion that this is based on a misunderstanding of the subject matter???  I do NOT understand maths.  I need a description in words.  I am well acquainted with Heisenberg's principle.  I think I mentioned earlier in this thread that I have read Quantum, by Manjit Kumar and am in fact reading it again at this present time.

P.S . I did not say that you said that light follows a spiral path.

Keep it civil - Mod. timey, Fri, 14th Aug 2015

To sum up the world of quantum, on a basic level there isn't really a lot to it.  Particles have spin, spin can be oriented.  If you orient a particle it's spin will remain oriented in that direction.  Therefore, we can harness the electron to our purpose.  We have to take round the houses methods in order to calculate quantum through probability because p x q does not sum up to the same as q x p, this being because when attempts are made to measure simultaneously a pair of conjugate variables: position and momentum or energy and time, the limitations of these concepts become evident.

Anyone else wish to condescend me? timey, Fri, 14th Aug 2015

Look Jeff, having evened my temper with an egg and bacon sandwich, and a cup of tea, I am back to tell you that you are right in the fact that I read your posts.  But I also read a lot of other peoples posts too.  It's not everybody's posts that I come back to though.  Interestingly enough it is for the very reasons you say I should stay away, that I do come back to your posts.  My only complaint being that you do not include more written explanation of your intent, direction, and findings in words.  I think even a mathematician 'might' agree. timey, Fri, 14th Aug 2015


Sorry, late reply, been away.
I always felt that imaginary numbers were misnamed as they relate to real things.
Take AC voltage current, normally inphase but in an inductive load complex numbers give us the phase relationship between the 2. Similarly, in Fourier Analysis they can show the relationship betwen frequencies and phase. These are not unreal relationships. Colin2B, Fri, 14th Aug 2015



I meant following my example. You do pick up the general idea which is good. The mathematics is the interesting part of the physics. Without a clear understanding you can miss the subtleties. jeffreyH, Sat, 15th Aug 2015

Which is why I have been using the internet extensively to visit places like Stamford University to study advanced mathematics with the benefit of explanation in words.  However...yes... I'm sure that I 'have' missed some of the subtleties of, in particular, the GR field equations.  But Jeff, it's one thing to understand these mathematics and quite another to then turn them to one's own purpose...

Sometimes one has to accept the imitations (Edit: That should be 'limitations' but I'll leave it in for humours sake :). ) of ones own abilities.  This therefore being my reason for posting my ideas to see if I can inspire any interest.  I know... :) , you're busy, we've established that!

I'm sorry I flew off handle and wish you all the best. timey, Sat, 15th Aug 2015

Actually, on reflection I think it fair to tell you that it was the fact that your post suggested that I should further my idea through investigation of the calculation of quantum probability that I found annoying, as this is entirely contrary to the very nature of my suggestion.  However it does occur to me (slowly, I admit) that the implications of my notion have perhaps evaded you... timey, Sat, 15th Aug 2015

What notion would that be then? jeffreyH, Sat, 15th Aug 2015



Well that would be the notion laid out in post 49, bottom of page 2, that you answered saying:

"Well now that you are being clearer in meaning you are saying something interesting"

Good job I have a photographic memory because you have somehow completely deleted that post, but it is evident that you made this reply in the fact of my reply, now classed as post 50, top of page 3, teaching me a valuable lesson in the relevance of "quoting" :)

(Edit: Your exact wording was "Now you are clearer in meaning and are saying something interesting") timey, Sat, 15th Aug 2015



I'm sorry, I cannot think of one instance whereas I 'have' followed your example.

To re-iterate a couple of points that got edited out of post 76, this time minus the scathing sarcasm:

I'd like to remind you that it was you who came speaking to me on my thread where I was asking for mathematical help.  You encouraged me to "bounce your ideas off me", these being your very words.

You have now, despite my explaining to you more than several times that I need a full explanation of mathematical process in words, 3 times posted me maths equations without explanation.
This is in as much as my speaking both English and Spanish, whereas I know you speak only English, and my posting supposed answers or suggestions to your posts in Spanish without translation.  I'm sure you would consider this to be an act of, if not rudeness, then severe illogicality!

The fact that your response to my notion in post 49 has been deleted is also an illogicality.  Illogicalities raise red flags in my book.  They spell the existence of an incomplete picture!  Now that the "notion" in question has been identified, do you have a response?

For what reason, under the remit of the nature of my suggestion, would your suggestion of my necessity to study the mathematics of quantum probability, (outside of the fact that p x q does not sum up to q x p), actually be 'relevant' to my cause?

... because it would seem to me that studying the Planck unit in relation to particle mass would actually be a much more logical approach, wouldn't you agree? timey, Mon, 17th Aug 2015


I don't understand this. What do you mean by p x q does not sum up to q x p?

In quantum mechanics, if p and q are operators, "x" is the cross product then p x q does not equal q x p. Is this what you meant? PmbPhy, Mon, 17th Aug 2015

Yes. Heisenberg's uncertainty principle to be precise. timey, Mon, 17th Aug 2015


That's incorrect. In anycase I wanted to know what you mean by "p x q does not sum up to q x p"?

Heisenberg's uncertainty principle is not directly related to the fact that in general operators corresponding to observables don't commute. However sometimes they do. Here's why: two operators are said to commute if AB = BA. The commutator of A and B, denoted as , is defined as

= AB - BA

If A and B commute then = 0. It can be shown that delta A * delta B >= (1/2)|<>| where <Q> is the expectation of Q and |a| is the magnitude of a. Therefore if = 0 then delta A * delta B = 0.

For these reasons I once again ask what you mean by "p x q does not sum up to q x p"? PmbPhy, Mon, 17th Aug 2015

"The uncertainty discovered by Heisenberg is an intrinsic feature of reality.  There could be no improvement, he argued, on the limits set by the size of Planck's constant and enforced by the uncertainty relations in the precision of what is observable in the atomic world.
The fundamental equation of quantum mechanics, pq-qp=ih/2(symbol I can't include), where p and q are the momentum and position of a particle.  It was the inherent uncertainty of nature that lay behind non-commutativity - the fact that pxq does not equal qxp."

Quoted directly from Manjit Kumar's book "Quantum". timey, Mon, 17th Aug 2015

Yeah, I know that all too well as any physicist would, i.e. it's the canonical commutation relation for position and momentum (which are canonically conjugate observables). However it's not Heisenberg's uncertainty principle. It's barely related to it either. The only connection is as I'll explain below.

Note: I assume the symbol you're referring to is\pi, right? I'm going to use \hbar = h/2\pi

Question:You didn't know the name for pi? pi is a Greek symbol which you can include here by using Latex.

The commutator for position, p and momentun, q, is pq - qp = . Therefore

= i\hbar

We place this into delta A * delta B >= (1/2)|<>| and we get the Heisenberg uncertainty principle (it's really a theorem because it can be derived), i.e.

delta A * delta B >= (1/2)|<>| = (1/2)|<i\hbar>| = h/4\pi or more simply put

delta A * delta B >= h/4\pi

Again I ask - What do you mean by "p x q does not sum up to q x p?"

Can't you simply explain what you meant when you posted that comment? I.e. please define the phrase "does not sum to". Do you mean "Does not equal"? If so then that would make a great deal of sense. If that's the case then it was a language barrier problem. PmbPhy, Mon, 17th Aug 2015

I'm sorry Pete, but I actually did answer your question of "do I mean "equal?"...
In England "sum" can mean add".  If something doesn't add up, they are not equal.  So what I was saying was that pxq does not add up to, sum to, or equal the same as qxp.  Ok?
So when I replied "yes" in post 87, that was indeed what I was saying yes to!

However, I am experiencing a weird sense of symmetry going on here with regards to my posts, whereas Jeff seems to have completely lost his tongue simultaneously to you having just found yours...therefore, thank you for pointing out the finer details of the Uncertainty Principle, but perhaps you would care to explain to me, under the remit of my notion set out in post 49, why Jeff's suggestion:



...would be relevant in the furthering of my cause?

P.S.  Yes, of course I know the name for 'pi' and what 'pi' is, and now I can relate that to the symbol.  If I come across that symbol again and have to describe it, now I'll know what to say, so thanks.  Learn something new everyday, aye! timey, Mon, 17th Aug 2015

But it's not true the opposite, infact you can sum up something which is not equal, for example 2+5. In our case we have the operator pq which is not equal to the operator qp. Does it mean they don't sum up? No! Infact they can. Theyr sum is called "anticommutator of p and q" and is a well defined operator.

--
lightarrow lightarrow, Mon, 17th Aug 2015

Lol!  Are we actually debating the definition and use of words here???

What about the question in hand? (she growled) timey, Mon, 17th Aug 2015


As I said, it's a language barrier. If there is a next time then when someone asks a question like

Then just say "they aren't equal" rather than all that stuff you replied with.

Note: A bit of friendly advice; If this happens again then just explain what you meant directly. Here you could have simply said from the beginning "they aren't equal".


As I said; language barrier.


But when you followed that by an irrelevant reference to Heisenberg's principle it lost its meaning.


This was an unfair suggestion by Jeff since he didn't defined his terms. The sigmas remind me of the Dirac notation but that comment doesn't bring anything to mind. It's not as if people readily remember everything from all fields unless they spend a great deal of time working with/studying that field. PmbPhy, Mon, 17th Aug 2015

Thanks!  Advice taken, 'sum up' has now been banished from my vocabulary with regards to mathematical definition of 'equal'.  We could get into a discussion about the term 'equals' in relation to a 'summing up', but you know...perhaps there 'are' better things we could do with our time...

(Tried quoting but it's not working)

I'm sorry, but I don't really think one has to spend a great deal of time studying a field to realise that a suggestion that questions the mathematical structure of Planks h constant, due to a possible factor of quantum time dilation actually relates only as far as Heisenberg's uncertainty principle, and that any investigation into calculating quantum probability is totally and utterly irrelevant and has no bearing whatsoever on the structure of Planck's h constant.

In fact one of the the most logical approaches would be to study the Planck unit in relation to particle mass.

May I suggest you partake of a hot chocolate with brandy and let Jeff answer for himself? timey, Mon, 17th Aug 2015


I don't understand this comment. What is it that you are referring to? Was it something I said?


Of course. However I never suggested that I was going to do otherwise. All my comment was for was to say that I think that wasn't a helpful suggestion from Jeff to you. I.e. I was agreeing with you. PmbPhy, Mon, 17th Aug 2015

I cannot seem to "quote" you any more...

You said:

""This was an unfair suggestion by Jeff since he didn't defined his terms. The sigmas remind me of the Dirac notation but that comment doesn't bring anything to mind. It's not as if people readily remember everything from all fields unless they spend a great deal of time working with/studying that field.""

I said:

"I'm sorry, but I don't really think one has to spend a great deal of time studying a (edit: 'this') field to realise that a suggestion that questions the mathematical structure of Planks h constant, due to a possible factor of quantum time dilation actually relates only as far as Heisenberg's uncertainty principle, and that any investigation into calculating quantum probability is totally and utterly irrelevant and has no bearing whatsoever on the structure of Planck's h constant.

In fact 'one' of the the most logical approaches would be to study the Planck unit in relation to particle mass."

Hopefully that makes more sense now I've added what you said.

Hot chocolate with brandy is 'nice', I do it a lot when appropriate.  Sorry, I didn't mean to sound so sharp, yes you were agreeing with me in a 'sort of' fashion. :) timey, Mon, 17th Aug 2015

Look Jeff, you haven't responded, which surprises me because logically speaking it is your only move.  A move that, it may surprise you, would be received amenably by me.
I consider myself to be an emotional environmentalist and at least 'try' to take care not to leave my footsteps floating in someone's head.
I actually have quite a lot of respect for you in most instances.  When someone speaks to me here, (or I develop an interest), I make a point of reading a lot of their posts in order to get a measure of them.  (I read incredibly fast). Pete's statement, (which I would spend the considerable time locating to quote him were it not for the fact that I seem unable to quote Pete anymore,) ... however it stated "Jeff is quite a bright boy"... and I do feel this 'is' a valid statement.
I cordially invite you to perhaps pm me so that we can bury the hatchet. Nothing would give me greater pleasure than to put my 'little lawyer' back in my breast pocket and problems 'always' have solutions if one changes ones perspective. timey, Tue, 18th Aug 2015



I have just read this last post but can't remember what the comment was that you wanted me to respond to. Can you post it here and I will try to respond and make sense. I am currently fixing system issues and working late so it might not be this evening. jeffreyH, Wed, 26th Aug 2015

Oh, you know what Jeff... forgetta'bout'it!  ...It's all past tense far as I'm concerned. :) timey, Wed, 26th Aug 2015

Lee Smolin's book "The Trouble with Physics"...page 255-256

Quote:
"While there is today an exciting sense of progress among quantum-gravity theorists, there is also a strong expectation that the road ahead will bring at least a few surprises.  Unlike string theorists in the exhilarating days of the two superstring revolutions, few of the people working on quantum gravity believe they have their hands on a final theory.  We recognise that the accomplishments of background-independent approaches to quantum gravity are a necessary step in finishing Einstein's revolution.  They show that there can be a consistent mathematical and conceptual language that unifies quantum theory and general relativity.  This gives us something string theory does not, which is a possible framework in which to formulate the theory that solves all five of the problems I listed in chapter 1.  But we are also fairly sure that we do not yet have all the pieces.  Even with the recent successes, no idea yet has that absolute ring of truth.
When you look back at the history of physics, one thing sticks out: When the right theory is finally proposed, it triumphs quickly.  The few really good ideas about unification appear in a form that is compelling, simple, and unique; they do not come with a list of options or adjustable features. Newtons mechanics is defined by three simple laws, Newtonian gravity by a simple formula with one constant.  Special relativity was complete on arrival.  It may have taken twenty five years to fully formulate quantum mechanics, but from the beginning it was developed in concert with experiment.  Many of the key papers in the subject from 1900 on either explained a recent experimental result or made a definite prediction for an experiment that was shortly done.  The same was true of general relativity.
Thus, all the theories that triumphed had consequences for experiment that were simple to work out and could be tested within a few years.  This does not mean that the theories could be solved exactly - most theories never are.  But it does mean that physical insight led immediately to a prediction of a new physical effect.
Whatever else one says about string theory, loop quantum gravity, and other approaches, they have not delivered on that front.  The standard excuse has been that experiments on this scale are impossible to perform - but, as we have seen, such is not the case.  So there must be another reason.  I believe there is something basic we are all missing, some wrong assumption we are all making.  If this is so, then we need to isolate the wrong assumption and replace it with a new idea.
What could that wrong assumption be?  My guess is that it involves two things: the foundations of quantum mechanics and the nature of time.  We have already discussed the first; I find it hopeful that new ideas about quantum mechanics have been proposed recently, motivated by studies of quantum gravity.  But I strongly suspect that the key is time.  More and more, I have this feeling that quantum theory and general relativity are both deeply wrong about the nature of time.  It's not enough to combine them.  There is a deeper problem, perhaps going back to the origin of physics."
Unquote:

...and I reiterate this particular sentence in relation to my post, post no 49.

""My guess is that it involves two things: the foundations of quantum mechanics and the nature of time."" timey, Sat, 29th Aug 2015

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