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

  • Thread starter drudkh
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  • #26
It must also be undetectable.

Matheinste.
Yeah, and that is a bit of rub for any theory; makes the search for magnetic monoples and stranglets look downright hopeful.
 
  • #27
TCS
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It is kind of like saying a bed sheet isn't detectable. Even though we only interact with threads, we could infer the existence of a bed sheet from the behaviour of the threads. Likewise, you could say that the metric that defines the distance between vectors in space time implies the existence of the "ether". Although, there may be other explanations for those metrics.
 
  • #28
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I just don't believe in empty space. I think that there is energy density everywhere and that the wavelength of the photon is dependant upon the enrgy density of the space it is passing through.
I think that is true - that there is "energy density" but that would not stop packets of energy either.

Who the hell knows?
 
  • #29
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If you define the ether as having a zero velocity for all observers
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.
 
  • #30
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Then it is not related to the usual aether concept in any fashion other than its name.
DaleSpam -

If there were energy density, and if the universe were expanding, wouldn't this "density" "bleed off" to zero - eventually?

Or, if the universe expands to a point then recontracts, I guess that would be an alternative scenario.
 
  • #31
TCS
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DaleSpam -

If there were energy density, and if the universe were expanding, wouldn't this "density" "bleed off" to zero - eventually?

Or, if the universe expands to a point then recontracts, I guess that would be an alternative scenario.
I'm thinking that if the energy density gradient is high enough or you have enough energy with respect to the local neighborhood, like in a black hole, then instead of just constraining the expansion (hyberbolicity) of space, the space becomes eliptical so that the energy crunches in on itself until it reaches a point of maximum focus where the energy is redistributed into a flat distribution(once the energy or all of the vector segments are contracted to minimum size or a point then there is no longer an energy density gradieint so there would no or very little gravity) and then starts to spread and form a new fabric with it's own time and that the universe allows for infnite levels of rescaling, but that it just speculation.
 
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  • #32
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In classical physics, if energy level is uniform, though NOT zero, no work can be done. It takes a difference in energy level to get work done:

Sadi Carnot, 1828

Q = (T2 - T1)/T2

where Q = efficiency, T2 = higher temperature, T1 = lower temperature.

Of course this is thermodynamics but I think the concept is more universal.

By the way, to those of you who know me... I taught Sadi Carnot
 
  • #33
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I agree with TCS and Austin on one point. I think it could very well be a medium which we 'perceive' as space. It doesn't have to have a flow as was the basis of the M-M experiment. And matter could be the perceivable 'complement' of space.
 
  • #34
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The speed of sound through water doesn't depend upon the speed of the boat emitting it or the submarine listening to it. It does depend upon the relative velocity of the submarine to the water....
Ok so, two situations:
1] Both the boat and the submarine is at rest
2] The boat is moving in the -x direction and the submarine is moving in the +x direction.

Wouldn't the speed of sound be different in the two cases?
 
  • #35
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Ok so, two situations:
1] Both the boat and the submarine is at rest
2] The boat is moving in the -x direction and the submarine is moving in the +x direction.

Wouldn't the speed of sound be different in the two cases?
Between 1) and 2) I would say yes

Case 2) Boat and submarine could disagree on measured speed.
 
  • #36
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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
 
  • #37
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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!?'
 
  • #38
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there's no reason, it's an assumption
 
  • #39
TCS
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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.
 
  • #40
what about red/blue shift?
 
  • #41
TCS
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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.
 
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  • #42
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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 physic instructors. That was the 1950s and early 60s.
 
  • #43
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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
 
  • #44
TCS
85
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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 physic 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.
 
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  • #45
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:smile:Ha! Ha!:smile:
 
  • #46
TCS
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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.
 
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  • #47
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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)
 
  • #48
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do not convince me yet pal, maybe a mathematical proof will work
 
  • #49
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Wait so if there's a light source shining light in space, and I'm travelling 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)?
 
  • #50
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Wait so if there's a light source shining light in space, and I'm travelling 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.
 

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