Michelson Morley And Gravitational Lensing Question

[A-wal]

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.

Why? Inertial objects follow straight lines in four dimensions, accelerating objects follow curved paths.

[engcat]

Why? Inertial objects follow straight lines in four dimensions, accelerating objects follow curved paths.

 

You don't know that.  Object follow whatever paths and you do not know whether they are accelerating or moving at constant speed along those lines.  

Is the Sun an accelerating object, does it rotate at constant speed, or is it stationary?  You do not know. Whatever you say, I can say something different, and my claim is just as good as yours, it's a guess.

[A-wal]

You don't know that.  Object follow whatever paths and you do not know whether they are accelerating or moving at constant speed along those lines.  

Is the Sun an accelerating object, does it rotate at constant speed, or is it stationary?  You do not know. Whatever you say, I can say something different, and my claim is just as good as yours, it's a guess.

You need to define a coordinate system and then you can talk about the paths that objects follow. If that coordinate system includes the gravitational effects of a massive object then it will cause objects to follow curved paths, but each object will be following what is locally a straight path. It's not a contradiction or a paradox, it's just a why of describing gravity that works.

[Mutex]

Thanks for the answer, I am looking at various space density theories now. The both concepts are interesting.https://www.researchgate.net/publication/228736243_Proving_that_Space_Density_Theory_is_Different_and_More_Complete_than_Spacetime

 

Thankyou, the reference to RSD was from a paper I read awhile ago where they were talking redshift/distance attributed to the big bang and they were exploring how it is more reasonable to accept the redshift is from gravitational shift (or Einstein shift), of light as a function of the relative masses of the objects observed (galaxies). 

So they were referring to 'relative space density' total 'density' of the matter in that region of space due to the amount of matter in that region, so if the RSD was higher to galaxy would look more red. 

 

This goes against the Hubble constant where the redshift is a function of distance, not relative mass (and with Doppler relative velocity). Which puts into question if redshift is a function of distance, and if it is not, then no big bang! (which I expect is the case). 

 

I read that abstract, I'm not sure what 'spacetime theory' is, in my model of relativity time (the length of time) is an emergent property of space length, as is the length of space is the length of time. (otherwise c would not be constant). 

 

If my space length model, matter makes space longer (and everything in that space bigger), that means more matter present in the system the lower the space density (it's longer so lower density). 

 

Here is something to think about in regards to density or space and matter, think about the various states of matter can only exist in that state in a narrow range of space length. 

 

Low mass objects has shorter length and can have binding forces able to makes solids, earth exists in this region.

Higher mass and you may only be able to have weakly bound liquids and gases, these would be gas giants, they have enough mass that the local space density is too high for the length of the binding forces for solids.

 

Step up to lots more mass, and you get the Sun, very low density (1/3 the density of the earth), so much mass that now not even electrons can bind and you have the state of a plasma.

 

BLACK HOLES: Do they follow this trend? If the RSD so low that neutrons and protons can no longer stay bound? Does that make active galactic nucelli mini matter to energy to matter big bangs?

 

The big shock from the observation of M-87 was how freaking HUGE it is, far larger than expected, not the compact massive object but the HUGE massive object, because all that mass makes for very long space!

 

This is all the e=mc^2 matter (energy into space length), to energy (space length to energy)… This is a balance, black holes when large enough convert matter to energy by making space length shorter (extracting the energy from the length of space itself, because that is what energy as matter is). then creating high energy matter (jets), that is the creation of new matter.

 

It makes a lot of sense to me at least !! 

[Mutex]

I still only have the abstract from research gate it is messing me about for some reason.

 

I am interested in any theory not involving big bangs as origins of the universe, although I suspect inflation could produce matter and cause a big bang.

 

The accepted view is redshift is a function of distance, the more red shifted the further away they are due to space expanding between objects. Explaining the Hubble not so constant constant

 

If light is leaving a gravitational field it will lose energy and so be red shifted. 

 

Are you suggesting galaxies at the limit of the visible horizon have much more mass than previously thought?

 

How do you balance red shifted galaxies with huge blue shifted ones like Andromeda. Would you agree its still coming this way? 

 

I am guessing you think Hoyle was on the ball, how does your view of space deal with creation of matter? Why isnt new matter being created today.? 

 

Does space have a definable shape/limit in your model?

 

The length of space (density) varying around objects could perhaps be equated to quantum inflow theory, by Reg Cahill. 

 

and a whole heap of other questions ??????????????????????? 

 

The abstract messed with me too, some idea's and terms used there that don't sit too well yet.. Anyway

 

I liked your post because you are asking the same questions I have been asking (mostly), and I have some good news for you :)

 

 

I am interested in any theory not involving big bangs as origins of the universe, although I suspect inflation could produce matter and cause a big bang.

 

First, I'm not really interested in what did happen or how the universe got here, if it is not a big bang 13.8 BY ago, then I think the question is beyond an answer, I think it IS here, it has probably always been here, and it has always been EVERYWHERE, it's not contained, there is no 'beyond' there is NOTHING BUT Universe. (and it is history and not science). How or why it exists I will leave up to philosophers, religions and wild speculation. We don't know, and I don't think we can know that.. 

Inflation is one of those things to 'fix' some other problem with the BB models, and of course it created many more problems.

 

 

 

The accepted view is redshift is a function of distance, the more red shifted the further away they are due to space expanding between objects. Explaining the Hubble not so constant constant

 

The accepted view IS correct, there IS a redshift with distance relationship that Hubble observed, that is a fact.... BUT, what is not a fact at all is that this redshift is the consequence of 'space expanding between objects'. That's the problem. 

 

Space expanding between objects would not produce a redshift! There is no relative velocity so it is not Doppler shift, so if space expands between when the photon leaves the source and arrives at the destination that will only produce a longer path so a greater transit time, but no shift in light frequency.

 

Light is 'uncoupled' to space, as far as light is concerned space (and time) do not exist, as such with no coupling or interaction with space the light cannot 'give up' it's energy to space or have that energy taken away from it by gravity.

 

 

If light is leaving a gravitational field it will lose energy and so be red shifted. 

 

This is for me what is so beautiful about understanding that matter (gravity) gives space a fundamental length property, and we live in a universe where we are that is the SUM of all the space length contributions of all the masses as a function of the mass and the distance from that mass.

(you could also say that about 'gravity', we exist in all the gravity influences of all the mass as a function of the mass and distance to that mass). 

 

SO instead of thinking about 'light losing energy' to be redshifted, think about it as relative size or relative length or space between the object and the observer.

 

So what we want to achieve here is a redshift with distance relationship using a known, tested and somewhat understood mechanism.

We only have two to choose from Doppler shift and Gravitational shift, (BB inflation/expansion shift is unknown and untested and no understood).

 

WE can rule out Doppler shift it is a real shift but it is not a redshift/distance function, it is relative velocity. So not Doppler shift (although it is often stated as such, but people who should know better IMO).

 

So that leave the only other KNOWN physics to account for a redshift/distance relationship. (I am discounting for now diffusion and particles that give up a red sunset because that is a filtering process not a shift process). 

That know effect is Gravitational shift or Einstein shift, it's the same thing just called two different things.

 

Einstein Shift produces a redshift with distance effect in a homogeneous and isotropic universe that is BIDIRECTIONAL. That is in BOTH directions the further away you are the redder the object will appear.

 

Before I describe a simple model to explain this, IF the universe was perfectly homogeneous and isotropic the Hubble constant would be absolutely constant and the plot of distance to redshift would be perfect, as you stated, it is a complete mess, there data is all over the place, and the more precisely we look the worse it gets, this is a part of the 'crisis in cosmology', the big bang model is falling apart. (I'm starting to rant !!!).. 

 

OK, lets have a very simple universe and look at Einstein Shift... JUST THE EARTH, that is the universe right now and here we are on it. No other mass except the earth and somehow it is just like this earth in terms of space and time length.

 

The earth is matter and a ball, the center of the earth is the points where there is the most amount of mass as a function of distance, that point is the point of longest space length (highest gravity). That point is ALL the way down, if you are there every direction is up, every direction puts you into shorter space.

 

The length of space and time on the surface of the earth is a little bit shorter, because you are further away from the points of most mass to distance. 

 

The amount of length change is very small something like 2.5 and 4.5billion, so it is a slight slop straight line. 

Now we put a spaceship some distance away from the earth (everything is stationary here, so disregard orbits of velocity or doppler shift). 

 

What the ship is at the surface of the earth it sees not redshift the ship is in the same length space. 

Now the ship is 10,000Km away from the earth, the ship is in shorter space, you are in the ship and you see that the earth is REDSHIFTED... 

 

You go 20,000km away, and the earth is even more redshifted, but this is NOT light losing energy because of it leaving a gravitational field.

You are observing the earth getting redder because you are in shorter space away from the earth and you are in a higher energy state, relative to you the earth is at a lower energy, it is in a higher 'gravity well', or for me, you are shorter (smaller) looking at something relatively longer (bigger). 

 

You are in shorter space looking into longer space:

 

OK, this only gives us a single direction redshift to distance relationship, the ship will see the earth has redshifted, but the earth will see the ship as more blue when it is further away. 

 

This is because the only significant source of matter to give the length (gravity) property to space is the earth, the ship is low mass and contributes far less.

 

I really have to learn how to post diagrams here, because it is so much simpler to diagram out.

 

Now replace the ship with a second identical earth, then you will so no shift at all to an observer on the NEAR side of earth, the contribution of space length (gravity) will be equal, you will both be at the same 'level' in the gravity 'well'. No shift at all regardless of the distance.

 

But if you go to the FAR side of one of the earths and look at the other earth, it will be redder, for either observer on either earth bidirectionally as a function of the distance between the two earths. 

 

This is because there is an asymmetry of matter between each observer, if you are on earth 2 on the far side the mass of your earth is contributing more to earths 1 length and at the point you at. You are in shorter space relative to the distant object, because your local objects contribute more to making the distant object larger..

 

It's hard to explain, but it is trivial to show with a simple diagram example. So that is how you get redshift/distance in both directions without a big bang.. 

 

 

Are you suggesting galaxies at the limit of the visible horizon have much more mass than previously thought?

 

No, not at all, in a perfectly smooth and uniform universe with evenly distributed equal masses evenly spread out then the redshift distance Einstein shift would be perfect and useful for measuring distance. BUT IT'S NOT. It's pretty blotchy, and things are different sizes and masses, and on top of that things are moving about, frankly it's a mess!

 

That's why if you look at Hubble's paper and his Hubble constant plots they are all over the place, it's a VERY poor data fit, Even Hubble did not think it was from expansion. 

 

So a more distant galaxy will be redder, but so will a more massive galaxy. 

 

 

How do you balance red shifted galaxies with huge blue shifted ones like Andromeda. Would you agree its still coming this way? 

 

You ask the best questions!

 

Exactly, This is the same effect as I explained above, there is a redshift with distance because of the 'shared' masses both locally and to the observed object. 

The local galaxies contribute more to our length so we are relative to them 'bigger' (in longer space) and locally they are relative to use 'smaller', Light from shorter space is blue shifted.

 

So Andromeda might be moving towards us and it's doppler shift, or it might not be and it's just local Einstein shift.. 

 

Light from longer space is redshifted. 

 

 

I am guessing you think Hoyle was on the ball, how does your view of space deal with creation of matter? Why isnt new matter being created today.? 

 

Not sure that Hoyle says LOL... 

 

I think active Galactic nucelli and probably quasars are matter/energy/matter recyclers, breaking up matter into some fundaments energy/matter state (with very long space length), and exchanging that energy for space length (distributing energy over space and time). I think new matter is being created all the time.

 

Galaxies are universes, they create matter and space (for that matter), that gives the universe it's length property.

 

 

Does space have a definable shape/limit in your model?

  

No, it has no shape, it cannot have a shape and it has no limit, it also does not have a size!, there cannot be a multiverse, IF you created a universe that has space in it, it WILL become THIS universe, that's why I see galaxies are Universes, self contained except they share 'space'.

 

Even for our universe that is only the earth, the further you go away from the earth the shorter the length of space, eventually all you will really have is your own length from your own mass, but the length contribution from the earth is never be zero. 10,000Km on the surface of earth might be 1mm where you are very far away from earth, your speedo might say you are going 10,000km/h but I am on earth seeing you go 1mm per hour.

 

Single earth universe, the earth is the only mass contributing to space length, now start removing mass from that earth, as you do the length of space to become shorter it will approach zero length as you approach zero mass. 

 

You take out that last unit of lass, you have a universe in your lab that is infinite in extent if you were in it you could go in any direction at the speed of light,, forever. 

But the length of space is zero so the distance between every points is zero, an event will occur everywhere all at once. Any energy is infinite (dissipated over zero area in zero time). This is zero length infinite energy no mass universe. 

 

Put a unit of mass in that zero length universe, and you have NON-ZERO length universe, finally you get away from infinite energy, you have some place some space to put things like matter and energy.. Now we live in a universe that is a balance between matter and energy moderated by space length. (that gives us space based time or 'spacetime).

 

Now we are all happy with places to go, and things to do and time to do it.. A happy universe... 

[AnssiH]

deleted - posted to wrong thread

Edited July 6, 2020 by AnssiH

[Vmedvil2]

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.

GAHD is correct and anyone that disagrees with that statement is wrong.

Edited July 6, 2020 by VictorMedvil

[GAHD]

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.

After revisiting this, I thought it would be useful to point out that "time" is measured in frequency. If there is more "space" in a give area/volume, that frequency is "slowed" because it takes longer for it to move across that "more-space area/volume."

 

A lot of time dilation can be explained with frequency changes in that physical way. I'm still waiting on a recovery of a long-term atomic clock from orbital-frame to see if the decay rates also change along with the frequency-counter adjustments we use. First principles really matter in this kind of interaction. The nature of dilation being from "momentum-over-area frequency change" or from actual "entropy acts differently in these conditions" is an important FP that changes a lot of the resulting (in/de)ductions.

[Mutex]

After revisiting this, I thought it would be useful to point out that "time" is measured in frequency. If there is more "space" in a give area/volume, that frequency is "slowed" because it takes longer for it to move across that "more-space area/volume."

 

A lot of time dilation can be explained with frequency changes in that physical way. I'm still waiting on a recovery of a long-term atomic clock from orbital-frame to see if the decay rates also change along with the frequency-counter adjustments we use. First principles really matter in this kind of interaction. The nature of dilation being from "momentum-over-area frequency change" or from actual "entropy acts differently in these conditions" is an important FP that changes a lot of the resulting (in/de)ductions.

 

This is really interesting, it's a subject I have had stuck in my mind for the past 4 or 5 years. (specifically this subject or what space and time is from first principles)

 

And how space and time work in terms of gravity and relativity. (I want to do a full thread on this but I would like to post some diagrams with it first, and it's hard to word..)

 

 

 

I thought it would be useful to point out that "time" is measured in frequency. If there is more "space" in a give area/volume, that frequency is "slowed" because it takes longer for it to move across that "more-space area/volume."

 

What I had a lot of trouble with, and others do as well, is the idea that time is measured in frequency. Someone asked on reddit or somewhere if we could take advantage of the 'higher frequency of altitude' and would a computer produce output faster in 'higher frequency space'.

 

So would a computer on top of Everest produce results faster than one in the center of the earth, where time is a 'lower frequency' ?

 

You put the same question with nuclear decay, would a particle decay faster in higher frequency time?

 

This is a testing of the 'twins paradox', you have two people of identical age, send on orbiting a black hole for some time and when they come back they have aged much less than the person on earth.

 

This is where I think the mainstream treatment of relativity at best paints a confusing picture/model. 

 

The 4 Dimensional geometric model of relativity treats time as a frequency.

 

You run an experiment with two clocks, you end up with two different numbers on each clock, one clock might say 5 and the other 10 (seconds or whatever). 

You started and stopped the clocks at the same time in the same location, so how do you calculate and justify the different readings?

 

In the geometric treatment, you draw a curve (a worldline, or geodesic or a 'like path'). In this case you curve the 10 so that the start and finish match that of the 5.

Curved space and time.

 

Frequency is not fundamental! it's a function of two different terms, the number of somethings over the number of something else. (cycles over seconds or whatever). 

 

This for me was very confusing, they talk about time slowing down and even stopping with mass or in a black hole. So if time slows or stops does that imply infinite frequency?

 

So, what if what if time is not a frequency or measured in frequency, but is measured as a period 1/f ?

In this case in the experiment where two clocks show 5 and 10 you do not curve the 10 to match the start and end points in a curved geometrical model. 

 

Instead, you understand that time is a period, it has a fundamental length property (or if you like a duration), it is as such a variable and not a constant.

 

It's locally constant (in your frame of reference) but it is relatively variable.

 

This is a non-geometrical treatment, you have two flat lines starting and stopping at the same time (and reference frame), but the clock that displays 5 has simply been in time where time is twice as long as the clock that displays 10.

 

They both could the same (local) time, one counts 5 longer seconds and the other counts 10 shorter seconds. 

 

Time is a variable its length varies from place to place (we observe that from relativity tests).

 

The speed of light is constant in every reference frame (so regardless of the length of time).

 

SPEED is the length of some unit of space over the length of some unit of time. So, if the speed of light is constant and the length of time is a variable, then the length of space also needs to be a variable fixed to the length of time.

 

You could consider this a volume or an area, but what you need to get your head around is that it is not more miles or kilometers or seconds, it's LONGER (or shorter) miles or kilometers or seconds.

 

AM I CORRECT???

IF my model is correct, I would make a testable prediction that we will not measure any spacetime curvature (we'll I win that one), but also this: The twins paradox is wrong, the twin will come back and will have aged the same amount as the one left behind. AND, the nuclear decay of the atomic clock will be no different that one on earth.

 

WHY? 

Because the same amount of work is being done. The time is longer but the length of space is equally longer, you have more time but you have to cover a greater distance.

 

Or in shorter time, you cover less distance but do it faster, you use the same amount of energy either way. 

 

Light is a waveLENGTH, it is not a frequency, so a photons LENGTH is a function of how much time it takes to create the photon, this is the length of space and time measurement we see with Gravitational/Einstein shift of light. Bigger photons from bigger space, or smaller photons from shorter space.

 

IF time was a frequency we would not see blue shifted light from the ISS, we would see a brighter signal from the ISS (a higher frequency of photos, as opposed a frequency of higher photons).

 

(WOW, WHAT!!)

 

You would see a higher number of UNSHIFTED photons, not the same number of shifted photons.. (I hope that makes sense).. 

 

(I will stop now).. Thanks for any comments.

[Dubbelosix]

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?

 

Funnily I tend to agree so long as gravity is the aether. Notice that their experiment ruled out a very narrow class.

[Dubbelosix]

Einstein also revised his statement saying that light was only a constant in a vacuum devoid of gravitational fields, hence he came to realize it did indeed spatially variate.

Edited July 9, 2020 by Dubbelosix

[engcat]

Einstein also revised his statement saying that light was only a constant in a vacuum devoid of gravitational fields, hence he came to realize it did indeed spatially variate.

 

And that's the point.  So, if the the light accelerates in gravitational field, what is the point of Lorentz transformations and special relativity? Do those have any real application?

I mean, we normalized everything to constant speed of light because it is invariant based on MM experiment, and that is the universal coordinate system in which we use Lorentz transformations, but in real life where light indeed bends, special relativity and its math gymnastics are meaningless.  We could've just stayed with our own frame of reference and use Galilean transformations.  It's the same thing as tying everything to speed of light which is arbitrary.

[Mutex]

And that's the point.  So, if the the light accelerates in gravitational field, what is the point of Lorentz transformations and special relativity? Do those have any real application?

I mean, we normalized everything to constant speed of light because it is invariant based on MM experiment, and that is the universal coordinate system in which we use Lorentz transformations, but in real life where light indeed bends, special relativity and its math gymnastics are meaningless.  We could've just stayed with our own frame of reference and use Galilean transformations.  It's the same thing as tying everything to speed of light which is arbitrary.

 

Yes, the constancy of the speed of light is the very foundation of relativity, if that is wrong, you have nothing to work with. Also, there is no such thing as anything 'devoid of a gravitational field' in our universe. 

 

The reason why there is an apparent change in the speed of light in a non-vacuum is due to the longer path the light travels (at c), not the value of c changing. 

 

It's sort of like the Hubble constant, if it is not constant and changes from place to place then you might as well throw out the whole model, because everything stops making sense. 

[Dubbelosix]

And that's the point. So, if the the light accelerates in gravitational field, what is the point of Lorentz transformations and special relativity? Do those have any real application?

I mean, we normalized everything to constant speed of light because it is invariant based on MM experiment, and that is the universal coordinate system in which we use Lorentz transformations, but in real life where light indeed bends, special relativity and its math gymnastics are meaningless. We could've just stayed with our own frame of reference and use Galilean transformations. It's the same thing as tying everything to speed of light which is arbitrary.

Well sure, in the sense that it can take light longer to reach a point in spacetime depending on the bend in space and time, but this will still require non Euclidean transformations. We also have to remain aware that no matter what inertial reference frame we take, the peculiarities of relativity states that we should always measure the speed of light as a constant.. But yes, given the right set up, light does vary in the gravitational field.

[engcat]

You need to define a coordinate system and then you can talk about the paths that objects follow. If that coordinate system includes the gravitational effects of a massive object then it will cause objects to follow curved paths, but each object will be following what is locally a straight path. It's not a contradiction or a paradox, it's just a why of describing gravity that works.

 

In GR, by definition, by a rule, which is the equivalence principle, a light that follows a curved path is in an accelerated frame. Gravitional lensing proves.

In SR, by definition, light cannot be in an accelerated frame. it follows a straight line!

 

Which is it? It cannot be both.

Edited July 21, 2020 by engcat

[Mutex]

In GR, by definition, by a rule, which is the equivalence principle, a light that follows a curved path is in an accelerated frame. Gravitional lensing proves.

In SR, by definition, light cannot be in an accelerated frame. it follows a straight line!

 

Which is it? It cannot be both.

 

Good question, which is it GR 'straight lines (paths) in curved space or SR curved lines in flat space. Is space curved or is something else going on. 

 

First there is a big problem in relativity and physics in that we cannot measure ANY curvature of space at all, on any scale, this is sometimes referred to as 'the flatness problem'.

 

We only assume space is curved, we have not been able to confirm that it is.

 

It turns out that you do not need curved space in order to get the gravitational lensing effect, the same effect will occur with flat space that is not curved but is relatively longer (and shorter). 

 

That is, the light path itself is not longer because it is a curved path (because c is constant), but the path is longer because the 'length of distance' is longer. 

 

Either effect will result in a lensing effect, but one requires curved space and one requires flat space.

 

In longer space (space being made longer as an effect of 'gravity'), you have the same distance (number of kilometers), but the meter is longer (close to a source of gravity), so light does not have to be in an accelerated from (it cannot be as you say), it's just in a frame that we externally (relatively) see as being a longer length.

 

It is the same principle that a glass lens works by, except that the longer path is a function of the speed of light in the glass (refractive index, or velocity factor), and in space it is the length of space that changes not the speed of light.

 

It is no different in principle, (and effect), except that it makes GR space flat, so it is 'curved lines through flat space'. 

 

You have no doubt seen the typical model of a sheet of rubber with mass curving the space around it, and light following that curved path.

 

Instead of that curved rubber model, you stretch the rubber (but keep it flat) with the mass, more stretched closer to the mass, and less stretched further away, and the plot of the light path will still curve around the massive object, IN FLAT SPACE, because of GR. 

 

 

Just as a side note: if you are buying curved space then I can sell you are flat earth!! (I can easily argue that the surface of the earth is flat according to it's position in curved space (the equivalence principle), but I actually believe the evidence (observations) indicate that the earth is a ball and also that space is flat.

 

As a second side note: the equivalence principle does not really hold anyway, it states that if you are in a box you cannot tell from within that box if you are in a gravitational field and stationary or in an accelerated frame.

 

BUT: you can tell by making a simple observation, if you place an atomic clock on the floor and one of the roof the 'tidal forces' will be observed if you are in a gravitational field and not observed if you are in an accelerating frame. In a gravitational field the clock on the roof will measure shorter time and the clock on the floor will measure longer time. 

 

Because time is shorter the further away you are from the source of gravity and the speed of light is constant, you know that space is also shorter the further away from the mass you are.

 

And longer the closer you are, it's the length of space, so in that space the length of space corresponds to the length of space (c is constant), it takes light longer time to move through longer space (at a constant speed), and that like a glass lens changes the transit time of light which gives the observed lensing effect.

[Dubbelosix]

In GR, by definition, by a rule, which is the equivalence principle, a light that follows a curved path is in an accelerated frame. Gravitional lensing proves.

In SR, by definition, light cannot be in an accelerated frame. it follows a straight line!

 

Which is it? It cannot be both.

This has different interpretstions , but the general consensus is that light can accelerate. If you want me to go into more details let me know. Edited July 22, 2020 by Dubbelosix