Why is the speed of light independent of a frame of reference?

[stevmg]

Then it is not related to the usual aether concept in any fashion other than its name. We already get into enough problems re-using words, e.g. "spin" and "particle" and even "mass". Labeling what you described "aether" is a bad idea.

DaleSpam -

We have a criss-crossed chain of posts here which has messed up this "blog."

It Just happened 1255 EST or 1755 GMT.

Stevmg

 

[rod_worth]

Back when Michelson and Morley conducted their experiments it wasn't 'completely' known whether or not the speed of light was truly constant, or if it could vary a little, which is what their experiment would have told them if this was true. Their 'null' result needed an explanation. 'Part' of the reason Einstein became so famous was that he was bold enough to propose that the speed of light was a constant; special relativity you could kind of say 'fell out of' that assumption, if you will (I say that very loosely). As more and more experiments were conducted to test special relativity, the experiments all pointed towards Einstein's bold proposal as being correct. Today, the speed of light is considered a well respected 'constant of nature'. This means 'c is c' NOT 'v + c'.

I personally like to reserve the 'why' questions for the philosophers; physicists are 'generally' more concerned with 'how' and 'what'. If you want to know 'why' the speed of light is what it is then I recommend consulting __________ (insert religious figure here). There is a saying, and I can't remember where I heard/read it that goes, 'nature is what it is, does what it does, and who are we to say otherwise!?'

 

[Sybren]

there's no reason, it's an assumption

 

[TCS]

there's no reason, it's an assumption

If a photon always travels the entire path length from it's creation to it's observation within the receiving particle, then all receiving particles can have the same C because the recceiving particle is the medium of oscilation.

 

[Quantum-lept]

what about red/blue shift?

 

[TCS]

what about red/blue shift?

Since the particle extends through space, it will be expanding with time and that expansion will provide the red shift. Also, there will be relative motion during the brief period of interaction.

If you think of an interaction as a shear in the time energy dimension, then the situation is analogous to an Earth quake. The energy of the interaction travels though each layer at the layers own speed regardless of the properties of the other stratigraphic layers, although pressure impossed by one layer can affect another. Even if a river is flowing over a stratigraphic layer, it won't change the Earth quake wave speed through the layer. However, if the layer has been bent by stratigraphic forces, some of it could be bent deep into the Earth and very it's properties through that region. Accordingly, if particles could were like stratigraphic layers, then they would all see light at C as a constant.

The ocean would be an even better example. Each particle is like a separte layer of ocean flowing at it's own speed in it's own direction in an ocean that is heating up.

Although, in reality, it couldn't be quite as simple as my anologies. It would have to be the quantum mechanical possibilities that travel through the particle.

 

[stevmg]

I understand the Michelson–Morley experiment and its result; but what I don't know yet is the REASON.
Example:
A torch in free space is moving at a velocity [v] w.r.t me. Considering the material nature of light, shouldn't the speed of photons emitted from the torch be [v+c] w.r.t ME?
According to the experiment, it's not so.
I know how relativistic velocities are formulated (Lorentz transformation, Einstein's Addition, etc.). But all these calculations are based on the accepted norm that light speed in invariant. WHY? What's the scientific explanation of this (if any)? Is it still a mystery?

I've seen other posts regarding the speed of light, but couldn't go through them all. So, apologies if this topic already exists.

I do believe that when drudkh asks "why" he doesn't mean the philosphical "why." I believe he is referring to the nuts and bolts "why." These questions were addressed by the many posts on this topic.

I believe the Michelson-Morley series of experiments were the major scientific approaches to this subject along with Einstein's generalized conjecture which, so far, has not been disproven.

When I first studies physics and that was many years after Einstein they still discussed the "ether" or something like it. The Aristotlean view or Newtonian view had not been cleared from the thinking of secondary school or basic entry college physics instructors. That was the 1950s and early 60s.

 

[stevmg]

I understand the Michelson–Morley experiment and its result; but what I don't know yet is the REASON.
Example:
A torch in free space is moving at a velocity [v] w.r.t me. Considering the material nature of light, shouldn't the speed of photons emitted from the torch be [v+c] w.r.t ME?

To elucidate on this point in particular, the invariance of the speed of light in his situation is taken up by time dilation and length contraction. They do work opposite to each other but one offsets the other. What should be an increase in closure speed as you posit is enhanced by the length contraction yet offset by the time dilation so that, relative to you, things "slow down" back to light speed.

Am I clear? I hope I got it correct. It took me a long time to figure this one out. Chapter 2 of Spacetime Physics, the first edition in the 1960s by Taylor/Wheeler goes into it (by discussion the maintenance of momentum/energy between different frames of reference which means different underlying velocities) but you have to read it slowly and over, over and over again and work the problems, which they give.

stevmg

 

[TCS]

When I first studies physics and that was many years after Einstein they still discussed the "ether" or something like it. The Aristotlean view or Newtonian view had not been cleared from the thinking of secondary school or basic entry college physics instructors. That was the 1950s and early 60s.

To Aristotle, Metaphysics was just the chapter in his book that came after physics. He described what he could of the operation of the universe using physics and he used metaphysics for the rest. Over time, as physicists have devloped better models, much of what was in the metaphysics chapter has shifted into the physics chapter. I think that it is a valid goal of physicists to try and make the metaphysics chapter as small as possible and to explain everything with physics.

 

[stevmg]

Ha! Ha!

 

[TCS]

Why is the speed of light independent of a frame of reference?

It might be because, the photon will always follow the geodesic (the shortest path) and the shortest path to you is the geodesic through a medium traveling in your reference frame (which would be expanding with time along with the rest of space), since the space is hyberbolic.

 

[Austin0]

To elucidate on this point in particular, the invariance of the speed of light in his situation is taken up by time dilation and length contraction. They do work opposite to each other but one offsets the other. What should be an increase in closure speed as you posit is enhanced by the length contraction yet offset by the time dilation so that, relative to you, things "slow down" back to light speed.

. Chapter 2 of Spacetime Physics, the first edition in the 1960s by Taylor/Wheeler goes into it (by discussion the maintenance of momentum/energy between different frames of reference which means different underlying velocities) but you have to read it slowly and over, over and over again and work the problems, which they give.

stevmg

Hi ...As length contraction is the same in both directions (-x) and (+x)
and dilation is of course without direction ,,how would this explanation work with a light coming from behind (c-v)

 

[maritz]

do not convince me yet pal, maybe a mathematical proof will work

 

[Red_CCF]

Wait so if there's a light source shining light in space, and I'm traveling at exactly the speed of light away from the source (in space), then the light from the light source will still have a velocity of c with respect to me (assuming light is shined in the direction I'm travelling)?

 

[Bussani]

Wait so if there's a light source shining light in space, and I'm traveling at exactly the speed of light away from the source (in space), then the light from the light source will still have a velocity of c with respect to me (assuming light is shined in the direction I'm travelling)?

This seems a little obvious to point out, but you can't travel at exactly the speed of light. If you picked a speed like 0.999c instead, then yes, the light would still be c with respect to you.

 

[Kometkaj]

Try and see it from the photon's point of view:
Its entire mass is dependent on it's velocity.
If it had a different relative speed, it would also have a different mass, and masses can't really change or appear/diappear.
Thus the speed HAS to C, in order to maintain it's mass.
Then forget about the space reference or third party point of view, because he and space CAN observe two particles meeting each other at the speed of C+C=2C.

Thus remains only the contradiction between the photon receiving parties's measurements, and the third party observers observation (which can only be an observation and not a direct measurement).

I think it's easier to see the difference this way.

/Best regard

Henrik

 

[yoron]

I understand the Michelson–Morley experiment and its result; but what I don't know yet is the REASON.
Example:
A torch in free space is moving at a velocity [v] w.r.t me. Considering the material nature of light, shouldn't the speed of photons emitted from the torch be [v+c] w.r.t ME?
According to the experiment, it's not so.

I'm wondering about that one too. You could assume that it a direct result of SpaceTime existing, maybe? That anything 'existing' needs a metronome, and the best metronome we have is light. The arrow of time we refer to macroscopically 'ticks', to me that is, with the speed of light :) Plank time is often said to be the limit for any observations that makes physically sense to us, and the way we defined it, or Plank defined it, is that one Plank time is the time it takes for light to travel in a vacuum, one distance of Planck length.

It seems as a natural choice for the arrow to me. If it is so then it follows that for this to work over a whole SpaceTime you will need light to behave exactly as it does. Giving you the same 'speed' locally in all 'frames' possible. That means that although you will find other frames of reference change relative you (mass, energy, gravity), the 'frame' you define by existing, never change intrinsically. Meaning that if you had a life defined in yards, and we agreed on it being ten yards, you would nowhere find those yards to 'change', measuring it by your own yardstick.

Often the idea of 'clocks' is used to describe different 'frames of reference'. Those 'clocks' will vary with the gravitational potential ('static' as on a planet) and with motion and invariant mass. Then you have the idea of 'energy' as a process too, but that one is defined by 'interactions', so I will just mention it as a possible interference. There has been simple experiments done with extremely sensitive 'atomic clocks' where you have two synchronized on a table and then by moving one to the floor desynchronizing them, elegantly showing that there are no 'frames of reference' that can be said to be the exact same. This is more of a assumption from my side as they were synchronized on the table, but I would expect all positional points inside SpaceTime to differ slightly, which in a way makes it rather hard to define where that own 'frame of reference' should be situated. But we all have one as I think of it, even if it's only conceptual.

And as far as I know this is correct. The time 'measured out' for you, in your own 'frame of reference', where and whatever that may be, does not change. What changes is the relations you have, relative all other 'frames of reference', and that it do with gravity, invariant mass and motion (and 'energy' as an idea). And acceleration is a 'must' for any motion to exist, as far as I know, so that assumption is sort of 'baked in' into any motion defined, relative something else.

But there is also the fact that all uniform motions in a sense (black room scenario) is equivalent, meaning that there is no experiments you can do in there defining that 'motion', no matter what 'speed' you believe yourself to have relative some origin. All uniform motions can be seen as being 'at rest' relative 'gravity' giving you a geodesic. If we would find a possible definition of being 'still' relative SpaceTime, all of this would be wrong though but as it is any uniform motion, including a uniform constant acceleration becomes ambivalent phenomena, and only a non-constant acceleration will prove to you that it is you 'moving' without doubt in Einsteins universe.

If you use the definitions full out then all invariant masses, as planets and suns, are, as far as I can see, gravitationally 'accelerating phenomena, giving 'motion' a whole new meaning to me :)

Although, this is how I see it. And even though I believe it to 'fit' with the theory of relativity there might be others that see those clocks in another way. In a accelerating frame you can use those 'clocks' to define light as having different speeds by setting them up inside that spacecraft accelerating and then measure the 'time' the light takes from A to B and then from B to A. But that is all about the equivalence of acceleration with 'gravity' to me, and as we all know that light always take the path of least (no) energy expenditure that is no proof to me of different 'speeds'.

 

[yoron]

There is one definition of being 'still' that one could consider though. The one in where you find no 'gravity', being 'at rest' with it as you are in a geodesic. Einstein defined 'gravity' as the metric of SpaceTime as I understand it. And then, if we define uniform motion as being of 'no gravity', the metric could be seen as 'gone'. But as uniform motion will take you from A to B that can't be correct.

Which leads me to my other notion. that this in fact, is a somewhat roundabout proof for his idea of space needing gravity to 'exist'. Because we know that, even though falling of a ladder on Earth becomes a momentarily geodesic, that doesn't mean that 'gravity' as such stopped to exist. It just mean that you're 'at rest' relative it, for that short moment.

So Space is defined by 'gravity' to me. That doesn't state that 'invariant mass' and uniform constant accelerations is what 'gravity' must be. It is two properties we know of that according to Einstein can be seen as equivalent with a 'gravity', including the concept of 'energy' too as a guess :)

There might also be a possibility of the coupling to be more of SpaceTimes restricting than 'creating' gravity, as another wild guess :)
==

But, in a very weird way, I can't help but wonder about if you could use this being 'at rest' versus 'gravity' as a definition of a 'null speed'? I'm actually considering it, which proves me to be slightly wacky I'm afraid. Then again, if Einstein was right? 'Motion' becomes a very wacky phenomena too :)