Gary Stephens This is a very good question. If light were a particle then you would expect it to behave as you suggest.

If light were a wave in a medium you would expect the wave to travel at a fixed speed in the medium regardless of the velocity v of the source.

What Special Relativity tells us is that the velocity of light is the same in every inertial frame of reference. This goes against both of the above possibilities.

In my view, the answer to your question is that the postulates of SR are not correct:

Preprint Special Relativity thought experiment

Then in my view, light travels as a wave disturbance in the medium of space and its velocity as measured by an observer travelling with velocity v relative to the medium will depend on v.

Preprint Space Rest Frame (March 2022)

Richard

From a pure hypothetical geometric model of space-time point of view, through which light has to propagate in vaccum (irrespective if one likes or dislikes the use of the physically as of today burned word "ether" - or whatever one might call any mediumlike vaccum - so be it), I would like to suggest the following, which is based on a heaxgonal gear like model of spacetime as already proposed (and graphically depicted) in a paper of Maxwell (it can e.g. be found well explained in the book Malcom Longlair, Theoretical Concepts in Physics, p.93ff, ISBN 0-521-52878-X):

Lets assume some hypothetic 2D spacetime plane would consist of hexgonal interlocked rotational doors (like typicaly in shopping centers, where light has to pass through), then nothing would be able to move faster than light when such doors would rotate gear wise perfectly interlocked with an angular speed of exactly the speed of light at its outer radius.

This way everything passing the doors can enter such doors and rotate with them multiple times (ending out slower than the speed of light) but never faster. One enters such a say clockwise turning door on the left and is guided by such rotational door to the right entry of the next cell entry rotating anti-clockwise (and so on).

It was at the time of Planck suggesting this be thought of an unphysical model, but as such gears would lock up itself no longer being able to move - but this is valid only for a 3D space assumption. If such gears would rotate to synchronize itself perfectly in a say 6D subspace, each direction in 3D would have a degree of freedom in 6D not to get stuck, with perfect synchronization (starting from hypothetical big-bang to today keeping to be in sync locally and on cosmic scale at the same time).

Now while this seems to be a far fetched model, it would explain a lot of other things, like how light is accelerated from 0 (zero) speed to speed of light in 0 (!) seconds which is physically impossible. But if the actually emitting part of light of the atom - the electron - would its combined orbital spin-speed be already the speed of light, nothing would need to be accelerated. Emission process would be as simple as a child on a carussell opening its hand and a ball (the light in particle form) flying tangentially away when doing so.

Another thing is when such rotational doors woule be made of a transparent material for other waves/particles than light - while light would have to take the limit of such rotational doors, frequencies which would see such doors as transparent could go straight through with the speed - which could then exceed the speed of light (no longer bound to the door frequency).

You say - ok, so what? Its all just a speculative model. Right, but you asked (so you/one possibly did not know either any better). Constraints are what to be found and imposed experimentally (on all things physics, for that matter). And the imho best constraints are right in front of every (lab) physicists eyes - constants of nature themselved (like c, e, h, alpha, me, re, a0, Rinfinity, G just to name a few).

And it happens that iSpace-theory is able to calculate an exact value and full symbolic dependency for all such constants (both in iSpace-SI aka MKSA/SI and iSpace-IQ unit system, the first of its kind to get away without any human artefact whatsoever. And for logical integer-geometric reason iSpace proposes (or requires) a 3D (space) + 6D (subspace) + 1D (time) so 10D spacetime structure (as does some form of string theory, but for completely different mathematical reasons).

If you want to step out from here into the world of iSpace, which has some really impressive integer-geometric results on why constants of nature do what the do - and exactly how geometrically - have a look at my RG home papers and project (and sorry for my long answer, being slighty off topic by now but everything is furtunately related to each other):

Overview and RG log of iSpace project on constants of nature:

https://www.researchgate.net/project/iSpace-Exact-quantum-geometric-value-of-primary-constants-of-nature

Method iSpace - Quick check of α and Φ0 from Markoulakis & Antonidakis

Conference Paper iSpace - Exact Symbolic Equations for Important Physical Con...

Conference Paper iSpace - Deriving G from α, e, R∞, μ0 and Quantum of Gravita...

and many more to be found as published on my RG profile home:

https://www.researchgate.net/profile/Christian-Wolf-20

One of our mistake is. we model nature, and we think light (flashlight ) is the same as Sunlight.

Sunlight can not have constant speed, but flashlight in vacuum has. .

Article Title: Science is wrong on…Light & Photon

Wrong question: the observer does not send the light

If Christian would be right, Boltzmann would have succeeded in building a mechanical model of electromagnetism.

One of the considerers has mentioned that "the observer does not send the light".

The words of the question were carefully chosen so as to reflect the circumstance that an observer holding a torch in motion relative to some fix frame (say a plank of wood) would see light speed away from him at light speed.

Similarly another observer watching from the sidelines (the stationary frame) would also see the light speed away from the observer (holding the torch) at light speed.

The question is, how can these two statements be reconciled. By what mechanism?

Because it is the assumption of relativity.

No, it is not an assumption, it follows from the Lorentz transformation. And that follows from, (i), the homogeneity and isotropy of space and time when space is empty and, (ii), Galilean relativity (all inertial systems are physically equivalent). It's purely kinematic matter. In turn, it is classical mechanics which makes an additional assumption. E.g.,

i) is time the same in all inertial systems, or

ii) the change of the momentum of a body subject to an external force is independent of its current value (Newton, 2nd axiom), or

iii) the change in the velocity of a body subject to an external force is independent of its current value (Euler, Mechanica, Nos. 111, 131).

Relaxing Euler's assumption, one is led to special-relativistic mechanics and the Lorentz transformation (Suisky & Enders 2005).

All these are assumptions.

IMHO, the homogeneity and isotropy of space and time when space is empty is a consequence of the principle of sufficient reason. Galilean relativity is an assumption. The point is this: Special-relativistic mechanics follows from two assumptions which are made within classical mechanics. The second assumption is this (sorry for having forgotten it in my foregoing text): There is three-dimensional space and one-dimensional time. They can be equipped with three- and one-dimensional coordinate systems, respectively.

Imagine, if the earth wiped from universe, our Time (second, minute) ges with it.

How could Time get one dimension for something that made?

All the argument is pseudoscience...

Time is relative, and does not get any dimension, and universal-time is different from ours,

https://www.academia.edu/38071066/Time_is_Relative

In special relativity, space and time are operationally defined. This definition is an assumption. A more important assumption is that the collection of space/time measurement can be organized in a manifold, i.e. it is integrable. The speed of light and all its properties are part and parcel of the operational definition. Actually is constancy is not an assumption but a convention.

So no one knows why this is the case. It just is the case : It's a fact of Nature, and however paradoxical, it cannot be explained. It just "is" ... ?

Science is wrong on speed of sunlight. Sunlight cannot be constant.

Article Title: Science is wrong on…Light & Photon

What exactly means "cannot"? Do photons have the possibility to choose something?

Thanks to Einstein and as a consequence of Einstein's wave-particle duality,light is made of photons that are massless and consequently can only travel at light speed,no more,no less,and thus the velocity-addition formula is inapplicable to light and the speed of light measured by a moving inertial source is the same as that measured by a stationary inertial observer.Photons also can never be at rest,else they cease to exist and there will be no more light.Since physics is special cases of mathematics and about applied mathematics,when deriving Lorentz transformations,  there is a constant or group-theory parameter that appears and has the dimension of velocity and is also an upper limit for velocities,else Lorentz factor becomes imaginary.Einstein called it universal and postulated that that constant is the speed of light and thus the same in all inertial frames.All that has been experimentally verified to be true for decades,proving that Einstein was right.Einstein went further and developed his theory of general relativity where gravity either as effect or wave cannot travel faster than light,and this has also been observed and experimentally verified through direct detection of gravitational waves,proving once again that Einstein was right. It also lead to an indirect confirmation of the existence of gravitons and the quantization of gravity through general relativity and perturbation theory,resulting in a quantum field theory of gravity considered by many physicists to be the most successful quantum-gravity theory of all quantum theories of gravity including the string theories of gravity. 

Is it the case that the constancy is the speed of light for all observers, is something that cannot be analysed further, and so we must just accept it, as "a given".

There has emerged, in the current epoch, a difficulty in separating out the observer from the observed. This is most widely known in Quantum Mechanics. What is less well known, or less discussed, is that the same difficulty also arises in Special Relativity. For example the constancy of the speed of light in vacuo is, in reality, a consequence of the interaction between the observers (cf. Preprint The Reason for the Constancy of the Speed of Light in the Sp...

First things is, what is light and what is sunlight ?

All of the test has been done by artificial light, like flashlight, not sunlight.

Flashlight has no room it science, but sunlight does.

Article Title: Science is wrong on…Light & Photon

We must open our eye. and see these two are different from each other.

Thank you very much for your kind invitation to answer this question. My gratitude.

The principle of light speed invariance is obtained by solving Maxwell's equations simultaneously, and is confirmed by Michelson Morey experiment.

And Special Relativity Theory take the principle of light speed invariance as one of its basic postulates and deduced many valuable conclusions.

In my humble opinion inside this article:

A DISCUSSION ABOUT THE NATURE OF TIME

https://zenodo.org/record/7079721#.Y7pkz8h3KnE

https://doi.org/10.5281/zenodo.7079721 Light propagation in medium, such as water, crystal, vacuum, etc, but not in the void(Vacuum is not void, vacuum are filled with gravitational fields and gravitational fields are physical existence. Thus vacuum is full but not empty).

Therefore, the speed of light depends on the medium, but irrespective of the motion of the torch issuing the light ray.(if light travels in water, it is multiple medium, water plus gravitational field, so it might be more complicated?)

inside this article, I wrote, light does travel in ether,

"ether should be gravitational fields. This is logical because it is known to all that vacuum gravitational fields, in which light can travel, can interact with electromagnetic wave and can bend light, as transparent crystal, in which light can also travel, can also interact with electromagnetic wave. That’s why, when we measure light speed on the surface of the earth, the light speeds are the same in every direction, because light travels at the same speed in the same gravitational fields"

Just for your kind reference.

BR

Recent SS post in https://www.researchgate.net/post/Speed_of_light_independent_of_the_speed_of_the_source_or_constant_for_all_observers/9 is relevant to this thread question.

Cheers

There has emerged, in the current epoch, a difficulty in separating out the observer from the observed. This is most widely known in Quantum Mechanics. What is less well known, or less discussed, is that the same difficulty also arises in Special Relativity. For example the constancy of the speed of light in vacuo is, in reality, a consequence of the interaction between the observers (cf. note "The Reason for the Constancy of the Speed of Light..").

Light particle is a minimum known particle in the whole Universe, it has limited speed about 300,000 km/second. The light speed still low speed as compared to the size of a Universe because light particle faced to resistance of dark matter particle in space, it means that the space is not vacuum 100%, it is faced to hidden objects are dark fabric particles. Sincere Sabir Sadiq