Why is the speed of light constant?

[ABierman1986]

Another thread on this forum got me thinking about the speed of light. Maxwell's equations (a vector calculus form of four other genius' laws to give credit) form the foundation of our understanding of E&M. Quantum physics has given us equations to relate the nuclear forces with the electromagnetic force. So now physicists work on their GUT. So more to the point;

I'm not going to try and argue any of what we have verified about light or the theories surrounding it, I'd rather work within this framework assuming our observations are correct than worry about other options at this moment, other than options that might explain my question.

Why should light travel in the way that it does? What characteristic of spacetime is the root cause of relativistic consequences? The entire argument of relativity is that time, mass and length are relative to observers frames of reference. So something about the act of moving at relatively very high speeds causes spacetime to react in a way that light travels the same speed for both perspectives.

Gravity has proven to 'bend' spacetime, and light will react to this curvature. My thoughts are that perhaps its the motion of the gravity wells that causes the relativistic effects, gravity is thought to travel at the speed of light, but so little is known about the mechanisms of gravity that I wonder what unknown effects it might have.

I have read papers theorizing gravity as a manifestation of a higher spatial dimension, but I'd like to hear responses to this. Since increased mass implies increased gravitational effects, and gravity may be associated with higher spatial dimension is mass an indicator of the effects that 4th dimensional motion has on our perception? (I know, the logic here is very faulty, but its the line of thinking I went through to try and disprove) And could the relative movement of two bodies in this higher dimension have the consequences of relativistic effects? I know this is borderline philosophical, but I'd like to hear theoretical contradictions to this idea as I'm not as well versed in this as I'd like to be.

[Tiberius]

The speed of light isn't constant. The speed of light through a certain material is constant, but the speed of light generally can vary massively.

The speed of light through a vacuum is believed to be the speed limit of the universe (i.e. the fastest you can go relative to space-time). However if a light photon goes from a vacuum into water, it will slow down. Scientists can even stop light momentarily: http://news.bbc.co.uk/1/hi/sci/tech/3308109.stm

No sure how this affects your question; I just wanted to point out the correction.

[ABierman1986]

The speed of light isn't constant. The speed of light through a certain material is constant, but the speed of light generally can vary massively.

The speed of light through a vacuum is believed to be the speed limit of the universe (i.e. the fastest you can go relative to space-time). However if a light photon goes from a vacuum into water, it will slow down. Scientists can even stop light momentarily: http://news.bbc.co.uk/1/hi/sci/tech/3308109.stm

No sure how this affects your question; I just wanted to point out the correction.

Sure, I should have been more clear, I am strictly speaking of light in a vacuum being constant, more to discuss what this might be a result of, and moreover the root cause of all of those actions.

[AnunZi]

I have read papers theorizing gravity as a manifestation of a higher spatial dimension, but I'd like to hear responses to this. Since increased mass implies increased gravitational effects, and gravity may be associated with higher spatial dimension is mass an indicator of the effects that 4th dimensional motion has on our perception? (I know, the logic here is very faulty, but its the line of thinking I went through to try and disprove) And could the relative movement of two bodies in this higher dimension have the consequences of relativistic effects? I know this is borderline philosophical, but I'd like to hear theoretical contradictions to this idea as I'm not as well versed in this as I'd like to be.

Are you saying that light in ALL cases is affected by mass/bodies along the 4th dimension? Or only in some cases thus resulting in the observable non-constant speed of light?

Or have I got the wrong end of the stick?

[ABierman1986]

I have read papers theorizing gravity as a manifestation of a higher spatial dimension, but I'd like to hear responses to this. Since increased mass implies increased gravitational effects, and gravity may be associated with higher spatial dimension is mass an indicator of the effects that 4th dimensional motion has on our perception? (I know, the logic here is very faulty, but its the line of thinking I went through to try and disprove) And could the relative movement of two bodies in this higher dimension have the consequences of relativistic effects? I know this is borderline philosophical, but I'd like to hear theoretical contradictions to this idea as I'm not as well versed in this as I'd like to be.

Are you saying that light in ALL cases is affected by mass/bodies along the 4th dimension? Or only in some cases thus resulting in the observable non-constant speed of light?

Or have I got the wrong end of the stick?

I'm strictly speaking of light in a free space, unimpeded by any medium. If we think of it as an Einstein thought experiment the idea would be two observers on spaceships (no light impedance through air or whatever), one moving very fast relative to the other in deep space. The moving one shines a flashlight straight up and the two observers measure the time it takes for the light to return. According to relativity the light will take a longer amount of time to measure based on the stationary observer than the moving one who shined the light. Also the mass of the moving ship will increase and the length will decrease.

My question is what is happening to the fabric of spacetime as one mass speeds past another, why does time slow down? An increased mass and shortened length would imply a more focused gravity well doesn't it? Since we know how light bends around gravity I thought that maybe the relativistic effects could be the result of a more focused gravity well. I'm not positive how this would correspond to the 4th dimension, but gravity's most promising contending theories that I've run across all seem to use a 4th spatial dimension. I'll try and find those papers so people can look at them.

[TheDarkestOfAngels]

Why should light travel in the way that it does? What characteristic of spacetime is the root cause of relativistic consequences? The entire argument of relativity is that time, mass and length are relative to observers frames of reference. So something about the act of moving at relatively very high speeds causes spacetime to react in a way that light travels the same speed for both perspectives.

Light travels the way it does because it does not have mass and anything without mass always travels at the speed of light. Gravity even travels at the speed of light even though it isn't so much a 'force' as it is a bend in space-time due to a massive object or whatever.
From what I understand, it's not a characteristic of space-time, but rather energy and matter or at least both.
I'm not sure if this answers your question, but this is the best answer I can give short of researching it myself.

Gravity has proven to 'bend' spacetime, and light will react to this curvature. My thoughts are that perhaps its the motion of the gravity wells that causes the relativistic effects, gravity is thought to travel at the speed of light, but so little is known about the mechanisms of gravity that I wonder what unknown effects it might have.

We actually know quite a bit about gravity but what we don't know is how massive objects cause gravity, exactly and the biggest frontier of 'shrug-shoulders' isofar as gravity is concerned is quantum gravity or gravity on the scale of atoms and light waves.

I have read papers theorizing gravity as a manifestation of a higher spatial dimension, but I'd like to hear responses to this. Since increased mass implies increased gravitational effects, and gravity may be associated with higher spatial dimension is mass an indicator of the effects that 4th dimensional motion has on our perception? (I know, the logic here is very faulty, but its the line of thinking I went through to try and disprove) And could the relative movement of two bodies in this higher dimension have the consequences of relativistic effects? I know this is borderline philosophical, but I'd like to hear theoretical contradictions to this idea as I'm not as well versed in this as I'd like to be.

There are a lot of theories about gravity's precise cause but unfortunately, the key to that understanding will probably have to wait until we discover the higgs boson, discover that the higgs boson isn't real, or something about quantum gravity will unlock, I think the answers you're seeking, but this is at the edge of physics research, as far as I understand it and right now there are more questions than answers for the time being.

I share your desire to understand more about it myself, but that'll have to wait some years I suppose.

[AnunZi]

My question is what is happening to the fabric of spacetime as one mass speeds past another, why does time slow down? An increased mass and shortened length would imply a more focused gravity well doesn't it? Since we know how light bends around gravity I thought that maybe the relativistic effects could be the result of a more focused gravity well

From what I understand of general relativity, its gravity it’s self that effects time. This is the theory of gravitational time dilation. Basically it states that higher gravitational potential causes time to slow down. This can be experimentally proven. Simply place 2 synced atomic clocks at differing altitudes (with a gravitational field) and over a period of time they will become out of sync.

My thoughts on this are that as space and time are (according to Einstein) one and the same thing, I.E Space-time then if you distort space with gravity you must also distort time.