All observers in inertial frames will measure the same speed of light, regardless of their state of motion, why?
@ Aleš Kralj
my dear Aleš Kralj thank you....
so we mean it is just an experimental fact rather than a cause?
i agree with an effect (experimental fact).....my intuition is if we find secret behind same speed of light may have some hidden surprises....
Relativity explains it as being a consequence of the hyperbolic geometry of spacetime. Any massless particle travels at that speed.
The speed of light is tightly coupled to properties of matter caused by the charge of electrons and nucleons. If the speed of light would depend on an absolute speed, the chemical properties of all molecules on earth would depend on their orientation, on day time, and on the season. This couldn't be good for life.
The speed of light is NOT invariant. The Shapiro Time delay proves that light slows down when traveling through a strong gravitational field. However, c is always the same when ‘measured locally’. This is explained in more detail on my page: http://pcmhahn.wixsite.com/foamyether/introduction-1
Think of a long stretched elastic band; the tension along this band may vary due to local distortions. However, ‘measuring’ the speed of a wave traveling along this band, at every point, would always give the same result because your clock varies.
Also… Einstein himself was considering a variable c. You may be interested in reading Alexander Unzicker’s book “Einstein’s Lost Key”.
@ Peter Hahn
my dear Peter Hahn thank you....
may be lights slow down .......the question here is, All observers in inertial frames will measure the same speed of light, regardless of their state of motion, why?
The real question is why electromagnetic waves propagate in vacuum.
Indeed, we know that the speed of waves propagating in a medium, depends on the speed of the receiver with respect to the medium, but does NOT depend on the speed of the emitter with respect to the medium. Therefore, if electromagnetic waves propagates in vacuum, its speed has nothing to depend on.
@ Aleš Kralj
my dear Aleš Kralj , why these theories, obviously can't explain something they are based on?
everyone agree we have experimentally observed invariance ... but why invariance?
at those time everyone know experimentally apple falls down from a tree....but Newton only asked a question; why apple falls down from tree?
why apple falls down? answer is due to gravity....
why speed of light is invariant? no answer !!!!!!!
"why speed of light is invariant? no answer !!!!!!!" ???
The answer is: "Invariant properties of molecules require an invariant speed of light". (On a molecular scale only vacuum is relevant.)
@Wolfgang Konle....
My dear Wolfgang Konle, do you mean due to Invariant properties of molecules require an invariant speed of light, All observers in inertial frames will measure the same speed of light, regardless of their state of motion?
Can you please elaborate this I am not getting your explanation?
@ Aleš Kralj...
My dear Aleš Kralj, on what proofs you are claiming we can not derive it mathematically out of any fundamental theory?
May be there is a scope to unlock still more fundamental.....
@shs hussainsha
the speed of light results from the interaction of magnetic and electric fields. If there would be any dependency (e.g. on an absolute speed in space) , this would also lead to dependencies of interactions in electron shells of molecules.
We can say that only a invariant speed of light allows the existence of matter with invariant properties.
The answer is therefore, the speed of light is invariant, because life needs matter with invariant properties. With other words, we would not exist in a universe with a non invariant speed of light.
We even can assume that stable matter cannot exist in a universe with a non invariant speed of light.
There are several possible answers to this question.
In classical electrodynamics, the speed of light in the vacuum is expressed by the well known relation derived by Maxwell:
$$c={1\over {\sqrt{\mu_0\epsilon_0}}}$$
According to the textbook: "Formal structure of electromagnetics" by E. J. Post (1962), $\mu_0$ and $\epsilon_0$ are the properties of the vacuum which are the same in all coordinate systems independently on their relative motion. The speed of light in vacuum is therefore constant.This property automatically determines the hyperbolic geometry of the time-space. The proof of this statement is in the first chapter of the textbook by Landau and Lifshitz: The Classical Theory of Fields.
The second answer based on the quantum properties of vacuum is elaborated in the paper "The quantum vacuum as the origin of the speed of light" by Urban et all (2013)
https://arxiv.org/pdf/1302.6165.pdf
It is shown that $\mu_0$ and $\epsilon_0$ may originate from magnetization and polarization of continiously apperaring and disapearing fermion pairs. The corresponding model of light propagation is based on transient captures and relases of a photon by these ephemeral pairs. The speed of light in such a model is not constant.
Dear Aleš Kralj, Thank a lot for your comment underlying the role of the experiments and that of the mathematics: Well, first, mathematics is our invented, .
We ask, why are things as they are. A general answer is, that we would not exist, if basic constants of nature would't be exactly as they are.
(Invariant speed of light, electron mass and charge, proton mass and charge, gravitational constant ...)
The invariant speed of light is only a small part of the question why exactly the known and obviously balanced set of natural constants allows the existence of life.
But even if we find out that only exactly that set of natural constants allows life, we never will know if nature performs experiments with different sets of constants. May be there a many disjoint universes with different sets of constants, but these universes don't have observers asking questions.
Dear Wolfgang, If we suppose that the interactions are the result of grains of very small mass having the speed c, then the stability is the result of the stability of the quantum state “see Quantum state and periodicity”. Indeed the exchange of very small grain mass make easy the stability of the quantum state given by the stability of the action measured in h the Plank constant for all the occupied states, in all the atoms as exhibited with the periodic table. The stability of the QS is confirmed with magnetic momentum see on my ResearchGate site: “Total angular momentum and atomic magnetic momentum” published with Lochak. Is it in agreement with your approach Wolfgang?
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1. The velocity of light depends only of the properties of the medium and no on the kinematics of the observer or emitter. Thus it is not so strange that it remains constant independently of the state of motion for one observer.
2. Michelson and Morley found it experimentally many years ago. It is one experimental fact as the one that the electric charges of the same sign reppel while the ones with opposite attract.
3. In optics the indices of refraction n is constant following the Snell's law. In agreement with the dependence only of the permittibity and permeability of the medium.
4. The spectral degree of coherence of the scattered electromagnetic field may demonstrate identical distribution when certain conditions between two media are satisfied. The dispersion law might affects only to the phase velocity but not to the group velocity of the electromagnetic wave in different media (Poynting momentum conservation and energy density).
Dear Xavier,
"Grains of small mass with velocity c" is something I never heard about.
I am more familiar with standard QM, QED , SR, GR.
But I would not exclude a completely different aproach if it is able explaining as many observations as the standard theory does.
Dear Wolfgang,
I wish to underline one aspect of the action. According to Sommerfeld and to Dirac it is the action which is quantified.
Now according to Einstein “physical laws should be independent of the place of observation”, the exchange of mass in the form of very small grains with the speed c, seems to be the alone way to have the same law for the interaction if we consider the motion from the proton or from the electron. On the same way of approach it must be the mass which induces the orbital and spin motions, “see: The quantum state and Periodicity”.
Thus whatsoever are the interaction in an atom with several electrons and belonging to a crystal or a molecule, the variations of mass allow to keep constant the action along the trajectories of the different electrons. As a result the stability of the quantum properties of the different atoms put in view in the periodic table.
Now when a photon is emitted, we have flux of grains all traveling in the same direction. If we consider a plane perpendicular to the direction of the photon, the grains cross it in different point which are a projection of the orbit of the electron. As a result during the absorption they grains will communicate an angular or linear momentum corresponding to one unit of action h. Now this momentum according to this approach is the result of the absorption not an intrinsic property of the photon.
Xavier
Dear Sheng Liu: The Sommerfeld and Dirac equations are based on the Lorentz transformation and give excellent theoretical result when compared to the experiments. They applied at the differential scale this indicates that the motion is the result of exchange of small gains mass.
It’s important to recognize that speed of light `C’ is always associated with respect to material object like photons, though C itself appears to be independent of any other properties of those objects. In other words, independent of material reference, C has no meaning by itself.
If we think that the creation in Nature has two independent entities like space and matter, then it’s impossible to argue why C is a constant. Space and matter are intimately related in such a way that space-time gets so adjusted to maintain C constant. Another reason one can see is that, speed of an object with respect to space can’t be defined (though it’s defined in the space), b’cos it’s a material property and different objects can move with different relative speeds such that no speed is a privileged one. Each object has its own space-time (these different space-times are again related by Lorentz transformations which reflect the uniqueness of the universe) such that C remains a constant which is needed in such a way that with respect to it the laws of nature can remain universal (or) the creation is due to some unique universal law and C reflects that universality. We don’t have to use different laws for different observers b’cos after all the universe is an indivisible one. In special relativity, the actual relation between the space-time and matter is rather indirect, only through C but in general relativity (GR) its relation is direct via Einstein’s field equations.
According to my recent findings (Ref:- arXiv: 1710.09270 [physics.gen-ph]), even quantum systems share this common property of having related to its own space-time and hence suggesting that the more fundamental underlying law of Nature must have the universality property. My belief is that from microscopic to macroscopic manifestations of Nature, both matter and space-time are intimately related to each other in exactly the same way (like the case in GR), which give raise to a hope of identifying the underlying unified description of Nature.
Dear Xavier,
may be you misunderstood Sommerfeld and Dirac. Quantification is not absolute in the sense, that everything is quantized.
If you compare free and bound electron states, then you see that free electron state solutions are a continuum. Applied to that continuum your small grains of mass would shrink to mass zero, or with other words, they would vanish.
Dear Wolfgang, the following comment was to focus the attention of the need of experimental result before to fight something giving agreement with experiment. “Dear Sheng Liu: The Sommerfeld and Dirac equations are based on the Lorentz transformation …”
About the free electrons I do not see what about you refer, what is a free electron? In metallic conductivity the electrons are not really free. On the other hand what you mean by continuum. Generally this notion is a source of misleading. For me there is nothing in vacuum.
Dear Xavier,
we compare solutions of the Schrödinger equation, for a hydrogen atom. There are bound states with an energy smaller as the ionisation limit. The bound states are discrete. The possible states beyond the ionisation limit are continuous. We neither use Lorentz transformations for describing interactions with such electrons nor small grains of mass.
I agree with N. Gurappa when he wrote: “Each object has its own space-time (these different space-times are again related by Lorentz transformations which reflect the uniqueness of the universe) such that C remains a constant which is needed in such a way that with respect to it the laws of nature can remain universal (or) the creation is due to some unique universal law and C reflects that universality.”
But in my opinion space and time are not elements of nature but elements of our thinking about nature.
1. Each object is observed at a specific place, it takes a certain position relative to the other objects. The collection of all possible places is called the “space” and an observer experiences his own Being as a ”being-in-space”. In line with this definition the space is conceived as a three-dimensional, homogeneous, isotropic, unlimited and empty continuum. It is a construction of our intellect that cannot be manipulated nor observed. It is the imaginary framework for an efficient description of “spatial characteristics” (such as shape, extent, …) of objects; and for the adequate expression of “spatial relations” (such as distance, orientation, …) between their places and between their spatial characteristics. The space is Euclidean. That means that what spatial can and what cannot - what is possible and what is not possible - is described by the Euclidean geometry. The Euclidean geometry is the expression of the logic behind the spatial characteristics and relations of present-at-hand objects. It provides the tools that we need to mathematically describe spatial characteristics and relations.
2. The objects appear to the observer in the context of phenomena. A phenomenon manifests itself as a sequence of appearances that, via the present, cross from the future into the past. Each appearance divides the phenomenon in two parts. The first subsequence contains that what preceded the appearance and the second that what came later. Each appearance has its own “place” in the sequence: it has its own “moment”, it is “datable”. This means that an observer is experiencing his Being-in-the world as a continuous sequence of moments. That continuous sequence of moments is called “time” and an observer is ”in time”. Each phenomenon takes time: it has a certain extent, it shows itself during a limited set of moments, it has a “duration”. Durations can be quantified using a “standard-clock”. The indication (in second) of a standard-clock unrolls the sequence of the real numbers in ascending order and creates an unequivocal relation between the set of the moments and that of the real numbers. It generates a steadily increasing reel quantity “t” that we call the “(standard)time”. It connects to each moment a defined value of t and to each duration a defined time period.
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By linking a reference system O(x, y, z; t) to a particular material object we can describe the universal physical reality and we can locate each place and date each event in an objective and unambiguous way relative to O (a mental construction). If we link the reference system to another material object the description of the same reality will take another form (Lorentz transformation). It is evident that quantities that characterize intrinsic properties of the material objects (as rest mass and electric charge) don’t depend on the choice of the reference object. The same should apply to the speed with which “information” (carried by EM- and gravitational waves) propagates if we assume that the speed c is an intrinsic characteristic of the constituent element of that kind of information.
https://www.researchgate.net/post/Are_space_and_time_elements_of_nature_or_are_it_elements_of_our_thinking_about_nature
@ Antoine J.H. Acke
my dear Antoine J.H. Acke , it is nice view towards nature of physics.....
The local speed of light is defined to be fixed constant for measuring physical things based on the electromagnetism. That explanation is all enough.
Do not ask the why of a postulate of SRT
But you can analyze the evidence for it.
@ Juan Weisz
my dear is that anything crime if i ask?
can you please elaborate evidences? and whats wrong if we ask postulates of SRT?
Are distances as electromagnetic wave structures questionable? That's the issue. By Maxwell they are the basis.
@ Esa Säkkinen ...
my dear Esa Säkkinen , yes questionable.....because though there is full evidence, asking a question is nothing wrong for the development of physics and sharing knowledge with each other......we all know very well that without why, what, how development is impossible.....
@ s h s hussainsha
Then your first job is to reveal what is wrong with Maxwell's equations.
@ Esa Säkkinen ...
my dear Esa Säkkinen thank you for your valuable suggestion......do you collaborate with me to reveal what is wrong with Maxwell's equations?
Because you only suggesting or you only thinking there is something wrong with Maxwell equations means you may have answer to reveal what is wrong with Maxwell's equations.
Dear Esa thank for your comment,
You say: “The local speed of light is defined to be fixed constant for measuring physical things based on the electromagnetism. That explanation is all enough.”
Yes the speed of the light is constant but the fixed constant can change according to the accuracy of the measurements. The question was: “The speed of light is invariant, why?” The implication is that the vacuum does not has any mass in it and cannot be a place for the waves.
The vacuum could be considered as decreasing entropy of quanta and the matter as increasing entropy of quanta.
So there can be a physical field tangenting with Higgs scalar field. The dynamical equilibrium prevails because matter needs low-entropy quanta from vacuum and vacuum needs high-entropy quanta from matter.
The quantum of light is vacuum portion (wave packet) when propagating and matter portion (photon) when emitting or absorbing.
Hence, the light it's not matter-like waving - it's signalling of positions for matter field. On the other hand, matter it's not vacuum-like volume but singularities of excite states.
(little accociating freely)
I see no need to scrutiny Maxwell's work - it's seems to be ok.
"..the vacuum does not have any mass in it and cannot be a place for the waves"(??)
Electromagnetic waves intrinsically contain energy and therefore also mass.
A relevant question is: Does poton/photon interaction exist?
Dear Wolfgang,
I agree with the vacuum with no mass.
You write “Electromagnetic waves intrinsically contain energy and therefore also mass.”
I prefer: Electromagnetic Field intrinsically contain energy and therefore also mass.
According to the approach with grains mass of course I think so.
“Does photon/photon interaction exist?” I do not know but it seem to me I would already heard if it exists.
A stationary electric or magnetic or gravitational field is something directly linked to particles in the near vicinity. They have a zero frequency and therefore no "photon" energy and no "gravitational wave" energy.
The energy of a stationary field therefore belongs to the multi particle object, which generates the field.
Electromagnetic waves/photons or gravitational waves are something else.
Though generated by particles, those waves exist on their own. Particles can create waves without changing their properties. And the waves can exist far away from the particles. In fact they move away from the particles with the speed of light.
It seems that the key for really understanding nature is understanding the fundamental difference between particles and waves.
Actually, there is a possible ans., but not in style with srt.
The thing is that as soon as light leaves the source it is in a specific
medium(vacuum), so you have a specific wave in a speciic medium; so why should that not indicate a specific speed? As in sound waves in air say.
Research Was Einstein in need to impose the stability of the speed of...
The speed of light is tightly connected to detailed properties of atoms and molecules. The world would be absolutely strange, if the intrinsic properties of matter would depend on its movement, (on its velocity vector relative to the velocity vector of an arbitrary celestial object).
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