Questioning the Universal Constance of the Speed of Light.

So maybe someone can explain this to me.

How do we know that the speed of light is Universally Constant?

We see that light is affected by gravity, that it can be bent (gravitational lensing), it can be stopped outright by a black hole. But common wisdom is that the speed of light is not slowed by gravity.

But how do we know that?

Humans have never experienced or sent probes out far enough to experience actual zero gravity. Yes, astronauts experience "zero gravity" on the space shuttle or on their way to the moon. But that's not because they were outside of Earth's gravity, it's because of the constant falling nature of an orbit.

Yes, we've sent probes past Pluto. But in all those cases, we/our equipment was still very much inside the gravity well of our Sun. There are bodies further out that are still reacting to the gravity of our Sun. Comets go way out past Pluto, but they return.

Earthbound experiments with the speed of light could be flawed because they are Earthbound. And the affects of gravity on C are minimal over such short distances (measuring the speed of light towards the Sun vs. away from the sun would only be quadrillionths of a second even across the diameter of the Earth. Do we even have uquipment that could process that fast?

And maybe it doesn't matter if you are headed towards the Sun or away from it, just being a relative fixed distance from the Sun slows all light down. And at the diameter of our orbit, it's slowed down to 300million KPS no matter what direction you are going. Perhaps gravity acts on light like friction or a viscosity.


What little I know of physics or astrophysics, it seems like a good portion of our current theories on physics depend on C being constant. So if C is not constant, how much of what we understand about the Universe would change?

Objects that are super distant are not as old as we think? The universe not expanding as fast as we currently believe?

Dark matter? Maybe what we are grappling to understand as "dark matter" is really just a ghost left in an equation of mass because we are plugging in what we think is a constant which is actually variable.

Maybe the hard part of interstellar travel is getting beyond the Sun's gravity well. Maybe once you get out in interstellar space, you can travel much faster than the 300million KPS we accept as the limit now?


I pose this all as a question because I know virtually nothing about Physics. Just enough to be embarrassingly wrong. But I know a nuclear physicist and when I asked him he said "The speed of light is a universal constant because it's universally constant. It has to be." or some such - close minded sounding to me - nonsense.


So maybe somebody here can point out something I'm not seeing.

To me it seems like we base a lot of our "knowledge" on an unverifiable constant that could be a variable, and maybe looking at it as a variable tie up a lot of loose ends.


TL;DR : That's how the little green men got here.

 

The trick about gravity is though, that there is no way to actually increase the pull of gravity with out something more massive than the Earth.

Like when a jet fighter pulls a 10g turn, that's not the same as a gravitation field 10x stronger than the Earth. It feels like 10x the gravity, but it's really just momentum.

The pull of actual gravity feels the same, but it's not. It's not momentum, it's some kind of actual attraction.

In order to get real gravity stronger than Earth's, you'd need a body more massive and/or dense than the Earth. And that's just for the relatively small gravity of the Earth. To make something that out-pulls the Sun, you'd need something more massive and dense than the Sun.

That's why I say, we accept it as Universal, but we don't really know.

Maybe that's what they are working on with the Hadron Collider. I've heard they are trying to create super dense particles like mini-black holes. Maybe close to those particles, there will be enough actual gravity to do tests.


And yeah, this would totally scale out to inter-galactic dimensions. Like maybe in deep interstellar space you can get up to 10x what we currently accept as the speed of light, but further out from the galactic center or in intergalactic space you can get up to 100x or 1000x the currently accepted C.



The first person to observe proof that the speed of light was less than instantaneous (like a finite number, not infinite) did so by observing phases of one of Jupiters moons. He deduced that Jupiter's moon phase was something like 22 minutes shorter when the Earth was in the part of it's orbit where it was approaching Jupiter then when it was in the part of it's orbit where it was moving away.

And the speed of light that he calculated from that was off by 26%. And 26% slower, so that would seem to contradict the idea of light moving faster if it's further away from the Sun. But then there is also Jupiter's mass to factor in.

He also was doing it with 1700s technology, so 74% accuracy is actually pretty damn good.

That also seems like something that students would do in a college Astronomy or physics lab, so I'm sure it's been repeated over and over and someone would have caught on if it demonstrated a different than expect result.