Thread: Can GR produce an illusion of light travelling superluminally

Alternatively can light travelling in a straight line away from you travel less than 1 light year in 1 year?

I think the answer is yes for both but want to make sure.

Of course as with all of my other questions we need to start with a black hole.

The key to the following logic is that C ( the speed of light ) is constant however neither time nor space is constant. By that I mean that in different reference frames two clocks wont necessarily stay syncronized. So if an observer passes through a strong gravitational field the speed of his clock relative to a clock in empty space will signifigantly vary. If the speed of his clock varies and his perception of distance varies then the distance that he traveled in the past can appear differently to what he currently percieves.

Here is the example.

You are hovering very close to the event horizon of a black hole. You shoot lasers then wait a few seconds then hit your boosters to travel in the direction that you shot the lasers. Peculiarly you notice that the lasers are now much farther away than they should be. In fact after a year you may notice that the light travelled 20 light years away from you.


So now you find that strange shoot 2 move lasers in the same direction and then put your ship into reverse back to hovering near the EH. You see that these lasers after a year really are only 1/2 a light year away from you.

However at any moment if you measured the speed of the lasers away from you they will be travelling at the speed of light away.

They key here is moment. Within a year ( or even a second ) the percieved flow of time can change as one passes into or out of a gravitational field. While this is happening percieved distances are also changing. What was your last year was really 20 years to everything else that is in your current gravitational well.

However at an instant light never travels away from you at any other speed than C.

Are you taking into consideration the SR effects of your movements? You have to move yourself at speeds approaching C in order to even hypothesize on this. What I was taught is that the speed of light is a constant in all media, and in all reference frames.

Good stuff Tom,

To the last response...the way light moves (C) is consistent, but the environment is not. Light bends and shifts around strong gravity fields, or is even trapped (black holes). Certain materials can slow light way down as it passes through.

Another interesting tidbit, At any given moment, the speed of light is constant...But! As the universe continues to expand, C is slowly changing. The constant, C, is a manifestation of the given space within which light travels (i.e. the whole of the universe as it is). But it has been found that as the universe changes, so too does this constant C (among other things)

Originally Posted by krueger1

Are you taking into consideration the SR effects of your movements? You have to move yourself at speeds approaching C in order to even hypothesize on this. What I was taught is that the speed of light is a constant in all media, and in all reference frames.

Really I guess what is confusing is that how can SR even be taken into account? What are we moving relatively to? If you are talking about the light itself ... we are always moving at c away from the light ... So in a universe with just us and a photon of light there really is no SR to take into account.

What i think I am talking about is more GR ... say we used to be in a gravitational well ... but no longer are ... the way we used to see the universe is very different than how we see it now ... at any point in the past light has always been travelling at c away from us ... however if you were able to take the real distance of the photon and divided it by the time that we observed we may record different time than C. the tricky part is ... how do we accurately measure the distance of the photon away from us and how do we measure time from a point in the past, in a gravity well to now.

Originally Posted by arcshade

Another interesting tidbit, At any given moment, the speed of light is constant...But! As the universe continues to expand, C is slowly changing. The constant, C, is a manifestation of the given space within which light travels (i.e. the whole of the universe as it is). But it has been found that as the universe changes, so too does this constant C (among other things)

I am interested in learning more about this. Can you please discuss this a bit more?

One problem with the question: You cannot OBSERVE the 'laser light' unless you catch it or it comes around to you! OBSERVED speed of light is always C, but the real constant is the 4 dimensional interval between two space-time points. So my answer is that any of many computed speeds for light are possible.

Also: remember, C is the speed of light in empty space. It can be observed to slow slightly in refractive media like glass. The environment of a black hole probably refracts.

So my answer is learn the math if you want observable answers to questions like this one. But I'm not an expert, just an amateur.

Amatuer,
Studying physics is a joy. Studying physics from qualified individuals to learn the secrets of nature is something that takes discipline, dedication and time. A physicist separates what is true from what is false and teaches his/her students to do the same. A physicist is someone who possesses the keys of knowledge. Enroll yourself in a university physics program, and you will reap the benefits for the rest of your life. Get on the Einstien train, er railroad car (insider joke).
Light travels the same speed in ALL reference frames, and in ALL media. This is the principle that we must accept, as it is observable fact. Light is observed to slow slightly in various materials, proportionally to the optical path length. When the path is longer, it takes longer for the light to pass, but speed C NEVER changes. Getting back to the previous question....

Look up cherenkov radiation. Light given off when electrons traveling slower than C but faster than light wavefronts in water. Saw it two days ago with own eyes. Only explanation is local light travelling slower than vacuum C in the water!

One of current physics main problems stems from Einstein's inference that time was relative. Einstein's special relativity, which concepts he expanded in his General Relativity, was an attempt to reconcile the theory with the constency of the speed of light as measure by the Michelson-Morley experiments.

But the relative time inference was not axiomatically sound and though General Relativity seem to be confirmed by observations, it collapses when applied to a larger domain of reality.

General Relativity implies, for example, that if two observers move at different speed relative to one another, then as that relative speed approaches the speed of light, from the first observer's point of view, the time of the second observed will appear to slow down (proposition 1). But, from the second observer's point of view, it's the first's observer's time that slows down (proposition 2).

From a mathematical standing, those two propositions exclude each other. Formal logic would conclude that since both propositions can not be true and since GR implies they both are, then GR is wrong, and both propositions are wrong. General Relativity demands that we suspend mathematical rigor and that leads to a number of similar paradoxes.

As I mentionned in another post, Quantum-Geometry Dynamics proposes a theory of fundamental reality that is complete and is consistent with all observational and experimental data. It shows, among other things, that there is no such things as event horizon or the space-time continuum, that space is discrete and finite, and explains interactions at both the fundamental and cosmological level or reality. It also accounts for black matter and black energy, the Cosmic Microwave Background Radiation and much more. It does so because the theory is axiomatically sound.

I'm not competent to check the consistencey of Quantum-Geometry Dynamics . To get it across it needs to explain observed physics better, either easier or with improved predictions. That space/time is somehow quantum is starting to be obvious. Which competing theory doing this prevails remains to be seen. And saying things actually observed cannot happen won't help. Do Google "Cherenkov radiation (also spelled Cerenkov or Čerenkov)". "Light travels the same speed in ALL reference frames, and in ALL media." observed not true for all MEDIA. Observed true in all REFERENCE FRAMES. You argument for what may be a good theory is harmed by your misstatements of observations. Sorry about that.