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# Michelson Morley And Gravitational Lensing Question

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Hey everyone!  Where are Dave and Modest and all the dudes from the old forum?

I cannot wrap my head around something.  If light path "bends" in presence of gravity, gravitational lensing.  This is observed.  Then, it follows, the speed of light will change according to coordinate system.

On the other hand, there is Michelson Morley experiment that says the light does not bend, and consequently Einstein said the speed of light is constant.

How do we explain this paradox?  Am I wrong or what?  Does the speed depend on gravity (coordinate system) or does it not depend on gravity?

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Yes gravity slows the speed of light, it would have to through time dilation and length contraction.

The speed of light is always c locally, and then only to interial observers.

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Yes gravity slows the speed of light, it would have to through time dilation and length contraction.

The speed of light is always c locally, and then only to interial observers.

Thank you.  So the speed of light does vary with the coordinate system, or the observer.

How can then both special relativity which sets speed of light at a constant, and general relativity which acknowledges the rate of change, both be correct?

Which one of these theories is then strictly local?  Because, one of them has to be.  They cannot be both "relativity" theories.

Edited by engcat
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SR deals specifically with local coodinate systems and inertial observers. That's why it's special, not general.

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Hey everyone!  Where are Dave and Modest and all the dudes from the old forum?

I cannot wrap my head around something.  If light path "bends" in presence of gravity, gravitational lensing.  This is observed.  Then, it follows, the speed of light will change according to coordinate system.

On the other hand, there is Michelson Morley experiment that says the light does not bend, and consequently Einstein said the speed of light is constant.

How do we explain this paradox?  Am I wrong or what?  Does the speed depend on gravity (coordinate system) or does it not depend on gravity?

Dave, and Mod, and Alex, and even that freak FreeThinker are missed. Haven't seen hide nor hair of most of the old crew in a long time.

On your question: One intuitive way to grasp it is that Gravity can pack more "space per area."

Light still travels at C, but there is more distance-per-area for it to travel when there's more stress on space itself so it takes more time for it to get past that area.

That's drastically over-simplified, but it's an intuitive way to grasp at the invisible forces at play.

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On your question: One intuitive way to grasp it is that Gravity can pack more "space per area."

Light still travels at C, but there is more distance-per-area for it to travel when there's more stress on space itself so it takes more time for it to get past that area.

That's drastically over-simplified, but it's an intuitive way to grasp at the invisible forces at play.

That's length contraction but that's only half the picture. Gravity also 'packs more time per volume'.

I assume you meant volume, not area. I know your a righty but I don't think you're uneducated enough to think that gravity is a two dimensional effect. :)

Edit:

Actually I suppose that would be gravity also packs less time per volume, time moves slower the more gravity there is. More space, less time.

Edited by A-wal
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That's length contraction but that's only half the picture. Gravity also 'packs more time per volume'.

I assume you meant volume, not area. I know your a righty but I don't think you're uneducated enough to think that gravity is a two dimensional effect. :)

Edit:

Actually I suppose that would be gravity also packs less time per volume, time moves slower the more gravity there is. More space, less time.

I do mean area, the SURFACE of a sphere(or complex equivalent but spheres are simple and I'm trying to keep it a bit simple to help them intuitively grasp) is an AREA, and because gravity changes the closer you get to barycenter you have to think in slices of area, not a homogeneous volume.

Edited by GAHD
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But gravity packs more space into an entire volume, it packs specific amounts into areas of that volume. ;)

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SR deals specifically with local coordinate systems and inertial observers. That's why it's special, not general.

Good.  So we extend SR generally, and call it GR.  The consequence of that is, in GR the speed of light is constant by definition. (We extended our preferred coordinate system generally to all coordinate systems, and we call them geodesics, and to track those we invented tensors.)

Now in GR we now the light bends based on lensing.  Which equivalence principle takes this GR evidence of gravitational lensing and accounts for it in special relativity, local frames?  More precisely, how is Michelson Morley explained locally if light follows geodesics under constant speed?  Does it not follow the geodesic?

Edited by engcat
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Good.  So we extend SR generally, and call it GR.

No, gr isn't simply extrapolated sr. The whole point of sr needing to be a local and inertial coordinate system means that you can't do that.

The consequence of that is, in GR the speed of light is constant by definition. (We extended our preferred coordinate system generally to all coordinate systems, and we call them geodesics, and to track those we invented tensors.)

It's always c locally to inertial observers, even in a gravitationally field. Geodesics in gr are curved paths in spacetime, bad naming convention because geodesic means straight.

Now in GR we now the light bends based on lensing.  Which equivalence principle takes this GR evidence of gravitational lensing and accounts for it in special relativity, local frames?  More precisely, how is Michelson Morley explained locally if light follows geodesics under constant speed?  Does it not follow the geodesic?

The light follows what is locally a straight path, but a curved path if you use a coordinate system that includes a gravitational field with a strength that varries over the coordinate system, creating a curved path.

Edited by A-wal
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The light follows what is locally a straight path, but a curved path if you use a coordinate system that includes a gravitational field

You do not think that's a paradox?  That's a self consistent explanation?

Edited by engcat
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Hey everyone!  Where are Dave and Modest and all the dudes from the old forum?

I cannot wrap my head around something.  If light path "bends" in presence of gravity, gravitational lensing.  This is observed.  Then, it follows, the speed of light will change according to coordinate system.

On the other hand, there is Michelson Morley experiment that says the light does not bend, and consequently Einstein said the speed of light is constant.

How do we explain this paradox?  Am I wrong or what?  Does the speed depend on gravity (coordinate system) or does it not depend on gravity?

I have a different model or idea that explains what we observe as relativity but does not treat space as warped or curved and that space itself is not a geometrical entity at all, that there is no X,Y,Z (directional) properties to space.

It is a little hard to get you head around initially (because we all grew up being taught that space is 3 dimensional and curved or warped), but once you do start to think about it in this way many things start to make much more sense.

First, what is space? On a fundamental level space is the 'gap' or the 'length of space' between two points in space.

General relativity (matter and distance from that matter) determines (or establishes) this fundamental length property (you can almost call this length value or property 'gravity').

So you have a lot of mass and as a function of that mass the fundamental length of a point is space is longer than it would be will less mass or at a great distance from that mass.

In 3D space, the amount of matter determines the curvature of space or one or more X,Y,Z directional dimensions of that space.

This is what is used to explain gravitational lensing, that you are asking about.

It is saying you are seeing light go in a straight line through curved space.

You get statements like "Matter tells space how to curve, and space tells matter how to move"

The Flatness problem - We simply do not observe curved or warped space, this is a problem for big bang cosmology and for relativity, within the limits of our observations on any scale we do not detect ANY curvature properties of space.. We only observe space as being FLAT.

So how can we explain what we DO observe about relativity in a flat (non-geometrical) space, and what fundamental property does space need to have for space if curvature is not observed. (to explain what we do observe about things and light moving through space)?

Space has a fundamental property of LENGTH, that length property is a relative property determined by your position in that space and dependent on your local sum of all the 'gravities' (or length contributions) from the masses of the universe determined by the amount of mass and the distance from that mass.

Everything that needs space, is bigger or smaller as a function of the fundamental length of the space that that object is in.

That means if you are in longer space that I am, I send you a 1 meter ruler and I measure the length of that rules from my space length I will measure that ruler as longer than 1 meter. But you will measure the length of the ruler to be exactly 1 meter, and if you sent it back to me and I measured it locally it will be exactly 1 meter.

The local length of space is always 1, it is only in a relative context would you notice a relative variation.

As is space IS time - We have a common fundamental understanding of space and time that is so second nature that we do not really seem to think about it. (I do, but I'm a weirdo).

LENGTH of Space and LENGTH of time: I could say you live 20km away from me, I am defining a length of space, a fundamental property of space, that is, "space is the 20km gap that exists between you and me"

The other length we deal with in our universe is the length of time 1 hour a length of time.

So we are ok with understanding the space and time have a fundamental property of length.

3D relativity tries to justify that relative variation in the length of space and time by placing the differences into curves, called geodesics or 'worldlines' and you get terms like "light like paths" and "space like paths".

This is the classic 3 dimensional (plus 1 of time) geometric treated of warped of curved space and time.

So what if space has a single, literal DIMENSION of length?

Then you would observe that space is FLAT, we would treat the dimension (length) as a true dimension (it's length value).

Our observations would show that space if flat (our observations who that space if flat).

As the length of time is a direct function of the length of space we would observe that the speed of light is constant (length of space / length of time = 1)

What else would we observe?  And are those things observed?

It turns out that we would observe the same things as we would if space was curved, but by a different mechanism (or different treatment of the same mechanism).

So Gravitational lensing: So is the light you see as bent taking a straight line through curved space, or taking a curved line through flat space? The observed effect will be exactly the same, the lensing effect.

Transit or travel time through space: We know the speed of light is constant

On the other hand, there is Michelson Morley experiment that says the light does not bend, and consequently Einstein said the speed of light is constant.

How do we explain this paradox?  Am I wrong or what?  Does the speed depend on gravity (coordinate system) or does it not depend on gravity?

You are right, light does not bend and the speed of light is constant.

As light has a fixed and finite speed, the only thing left to consider is that the length of space varies as a function of matter and proximity to that matter, Transit time.

So how does a simple glass convex lens work to 'bend' light?

It's simple optics, we know that light propagates through glass slower than through air, so what a lens does it 'line up' the travel times of the light falling on the lens to be the same total time, the light going through the thickest part of the lens will be delays the longest and the thinnest part of the lens will be delayed the shortest.

Such that the light will be focused in space and at the focal point of the lens.

Gravitational lensing works the same way, the massive body gives the space a length property that is longer the closer you are and shorter the further out you go, same as the glass lens.

We observe gravitational lensing as the result of this, it takes LONGER for the light to travel at c through longer space. The result is that the speed of light is constant, space is flat and the transit time of that light varies (but not by varying speed, or taking a longer curved path).

The light takes a longer path, but it is not because the road is curved, it's just the road is longer, the number of meters are the same, the length of the meter varies (relatively).

Shapiro Delay:

Another observation that is explained by a flat space and time of relativity varying length is Shapiro delay. A radar pulse will take longer to return off an object (measuring it is further away) if there is a massive object near the path of the radar signal.

This is easily explained if you understand that matter gives space's fundamental property of length, and that length is longer in the presence of mass.

It's not curved, it's just longer.

It also explains general relativity time dilation, we observe shorter time on a GPS satellite, and longer time at the center of the earth, the length of time varies will 'gravity' or matter.

So do we observe straight lines moving through curved space or curved paths moving through flat space.

Functionally equivalent models that are conceptionally very different. But I think the NON-observation of curved space indicates to me that the space length model makes more sense, is simpler and explains what we do observe..

I do have a reddit on this subject where I try to flesh this out a bit more it's R Spacetime_relativity

Sorry for making you put up with my ramblings !!

(one last thing).

I am considering space as non-geometrical as I would consider a color as non-geometrical, it has a property (color or length), but it does not have a shape, you can have shapes or geometries IN IT, it itself it is not geometrical,

With color the property is its color, with space the property is its length.  (neither has the property of shape)..

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The light follows what is locally a straight path, but a curved path if you use a coordinate system that includes a gravitational field

You do not think that's a paradox?  That's a self consistent explanation?

Of course it's not a paradox! If you walk in a straight line it's straight to you but someone outside the gravity of Earth would say that you're following a curved path.

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Of course it's not a paradox! If you walk in a straight line it's straight to you but someone outside the gravity of Earth would say that you're following a curved path.

What do you think of Flat Earth theory?  It's flat to me, but to someone outside of mu frame of reference it is curved. Is it valid that the Earth is both flat and curved?

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What do you think of Flat Earth theory?  It's flat to me, but to someone outside of mu frame of reference it is curved. Is it valid that the Earth is both flat and curved?

What is a straight line locally can be curved in a wider context, it's not a paradox, it's just an arbitrary choice of how you want to define your coordinate system.

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Are you sure, ref your fundamental property of length ? Can the same argument not be conducted with density of space, if you move in a specific direction things will be blue shifted in that direction etc

Yes, in many ways it is about 'space density' I have seen the term 'RSD' related to this subject that stands for 'Relative Space Density', but what it is, is more like 'relative matter density' in that point in space.

If space (length) is longer 'down' and shorter 'up' due to 'gravity' or the presence of matter then the 'relative density' of something 'up' in short space is higher than something 'down', the matter is at a higher energy level/potential when it is in shorter space. (it is what 'potential energy' is), it is why it takes energy to put and keep something in shorter space. It is also why matter that wants to be in the lowest state possible tries to 'conserve' space length.

Matter wants to be in long space, it wants to be 'down' as much as it can, it takes energy to be 'up' and being 'up' in shorter space is a 'concentration' of matter (energy/matter from e=mc^2).

Doppler shift is just another aspect of the same thing, with doppler shift you 'consumer' or use more of the available length of space over time so you make that space you are in 'longer' this is a function of special relativity, where the direction of 'down' is still the direction towards longer space, but that object is making (or seeing) the direction of longest space to be in the direction it is going.

So that is how an object would be in an orbit, it is in continuous free fall around the earth, because in the direction it is going it sees that 'down' is the direction to longest space length, and that length is a function of its velocity in that direction.

This also explains a mechanism for how we experience 'gravity', it shows how gravity works (not just that it works), once you get your head around a unit of length (like the meter) is still 1 meter but that meter is longer below you and shorter above (relatively speaking).

Then you can see that by going at the same speed (number of meters per second) that you will be accelerating if the length of the meter increases (in your direction of travel).

You will accelerate but not feel acceleration (free fall), if you are doing 10 meters a second and the length of a meter is getting longer I will observe you are accelerating, you are still doing only 10m/s but the length of the meter gets longer.

Same in the opposite direction, you throw a rock up, due to it's velocity it sees longer space in the direction you throw it, but it is moving into shorter space length, so it decelerates loses velocity and at a certain point 'down' is again the direction of longest space.

In the direction of travel the faster you go the longer the space (you experience over time), from velocity and special relativity, and with gravity (when falling into longer space) the longer the space the faster you go..

In our universe, every unit of mass contributes to your local total length of space value, but it is the predominate (local) mass (in our case the earth) that determines the direction of up and down.

But if you were going to the moon, at some point the Moon would be the predominate contributor to your local length of space and you would be 'captured' by the moon and the direction of the moon would be the direction of longest space.

It is much easier to visualise if you just consider a simple systems such as a universe with only the earth in it, where the center of the earth is 'all the way down' and is the longest space length in that universe, and as you go away from the earth the length progressively gets shorter (it never reaches zero length).

So in an earth only universe, you could imagine space getting very short relative to its length on earth at some vast distance away from the earth. Light would still go at 300,000 km/s but the length of the meter would be very short.

But if you sent a space ship (made of matter) into shorter space, the matter of the ship itself would end up being the predominate matter contributor to your local space length, you bring the universe with you!.

As matter contributes to this length, is the reason why matter cannot go at the speed of light, as you cannot have a velocity relative to your own space length contribution, your own length contribution subtracts from the maximum speed you can go. Unless you are light (energy) that does not contribute to that length property and that means you must go at the speed of light (you use all the length of space in the shortest time).

Be careful, once you get this model in your head it all makes sense and you will find there is no going back!

The universe must work on a very basic and simple set of rules and principles, with this model for relativity you don't need any 'action at a distance', 'down' is just the direction of longest space. Up is shorter space and higher energy, and as you pointed out higher relative matter density (therefore higher energy density).

The water in a dam on top of a mountain is in shorter space and has potential energy its not at higher pressure and it does not take up less volume (not locally), but relativity it is higher density that water at sea level.

So the length of space of a flat line but also a gradient (a very, very small gradient) from longer to shorter.

If the center of the earth is 2.5 years 'younger' than the surface of the earth, over 4.5 million years, then the gradient of the slope of length from the center to the surface of the earth is 2.5 in 4.5 billion. (not much but not nothing). So 4.5 billion golf balls on the surface of the earth would take up the volume of 4.5 billion + 2.5 golf balls at the center of the earth. This tends to agree with how very weak 'gravity' is if considered a force on its own.

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What is a straight line locally can be curved in a wider context, it's not a paradox, it's just an arbitrary choice of how you want to define your coordinate system.

Then there is equivalence of straight and curved lines.  The question is then, why is there acceleration in local frames?  If everything follows curvelinear lines of motions, there should be no acceleration.

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