Could gravity waves be faster than light?

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Could gravity waves be faster than light?

Postby ralfcis on September 20th, 2017, 4:28 pm 

Light is an electromagnetic wave travelling through the electromagnetic medium (or field) of space. It's speed is limited by the permittivity and permeability constants which are analogous to a mechanical medium's properties of inertia and elasticity that allow mechanical waves to propagate through matter. But gravity waves probably depend on analogous gravitational constants that allow the gravitational wave to propagate through the gravitational medium of space. So why would a gravitational wave whose speed depends on other constants, somehow be coincidentally the same as the speed of light? And for that matter, why would the speed of light be necessarily the same as the max speed limit the universe sets?

The Standard Model states for every field there is a corresponding particle. The Em field has photons. I assume the denser the concentration of photons, the greater the field strength. Would not the constants of permeability and permittivity then change for different field strengths as they do when different types of matter are introduced. Would the field strength be less in intergalactic space as there are fewer photons there and so wouldn't the speed of light be faster because the two constants seem to diminish when mass is vacuumed out of space. Has there been an experiment to verify the speed of light is the same through stronger EM fields? I say it should be slower.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 1:25 am 

ralfcis » 20 Sep 2017, 22:28 wrote:Light is an electromagnetic wave travelling through the electromagnetic medium (or field) of space. It's speed is limited by the permittivity and permeability constants which are analogous to a mechanical medium's properties of inertia and elasticity that allow mechanical waves to propagate through matter.

'Analogous', but not equivalent. There are big differences between a mechanical medium and the spacetime that light propagates through, which I think you are aware of.

But gravity waves probably depend on analogous gravitational constants that allow the gravitational wave to propagate through the gravitational medium of space. So why would a gravitational wave whose speed depends on other constants, somehow be coincidentally the same as the speed of light? And for that matter, why would the speed of light be necessarily the same as the max speed limit the universe sets?

GW's are changes in the curvature if spacetime that propagates as ripples through space, tending to alternately stretch and compress space, almost like an earthquake on earth does to the ground. The "speed of gravity" comes from deep down in the math of GR, which points towards propagation at the universal speed limit, c.

The two LIGO stations received the one clear event that we had so far at roughly a time difference compatible with a propagation speed c. When we have more of the sensitive detectors online, that observation is expected to converge on c as more events are recorded.

On photons: the standard meaning is a quantum of e.m. energy and these photons do not travel. Light is emitted as packets of energy (photons) which then propagates as e.m. waves through spacetime and are again absorbed in packets (photons). Now e.m waves can interfere with each other, can lose energy, but never has any change in their propagation speed been observed, except when passing through solid transparent media, like intergalactic gas. We also know that light of different wavelengths (energies) all propagate at c, measured astronomically and locally.

In cosmology, we had intense radiation energy density very early on, but all observations indicate light an g.w.'s have stuck to the universal speed limit with exquisite precision.
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Re: Could gravity waves be faster than light?

Postby bangstrom on September 21st, 2017, 2:58 am 

ralfcis » September 20th, 2017, 3:28 pm wrote:Light is an electromagnetic wave travelling through the electromagnetic medium (or field) of space. It's speed is limited by the permittivity and permeability constants which are analogous to a mechanical medium's properties of inertia and elasticity that allow mechanical waves to propagate through matter. But gravity waves probably depend on analogous gravitational constants that allow the gravitational wave to propagate through the gravitational medium of space. So why would a gravitational wave whose speed depends on other constants, somehow be coincidentally the same as the speed of light? And for that matter, why would the speed of light be necessarily the same as the max speed limit the universe sets?

The Standard Model states for every field there is a corresponding particle. The Em field has photons. I assume the denser the concentration of photons, the greater the field strength. Would not the constants of permeability and permittivity then change for different field strengths as they do when different types of matter are introduced. Would the field strength be less in intergalactic space as there are fewer photons there and so wouldn't the speed of light be faster because the two constants seem to diminish when mass is vacuumed out of space. Has there been an experiment to verify the speed of light is the same through stronger EM fields? I say it should be slower.

In the Newtonian theory, the speed of gravity is instant so the Earth is attracted to a point where the sun is ‘now’ which keeps the Earth in a stable orbit. If gravity had a slower propagation speed, such as the speed of light, the Earth would be attracted to a point where the sun was 500 seconds ago because there is a 500 second delay between the Earth and the sun and the Earth’s orbit would slowly spiral into the sun.

In General Relativity, gravity propagates at light speed but gravity creates a distortion in spacetime, as visualized in the old bowling ball on a water bed example, and the Earth is attracted by the ‘slope’ of the spacetime distortion to the point where the sun is ‘now’ and not where it ‘was’ so the planets are able to maintain stable orbits as predicted by Newtonian theory despite having a slower propagation speed for gravity.

You are right that the speed of light is faster in the lesser gravitational density of intergalactic space. Light slows in the presence of a dense gravitational field. Gravity has been described as curvature of space and time but it is hard to visualize how either one could curve so I prefer to think of gravity as shorter space and slower time since that is the effect of gravity on spacetime.

Einstein said, “Special relativity is founded on the basis on the law of constancy of the velocity of light. But the general theory of relativity cannot retain this law. On the contrary, we arrived at the result that according to this latter theory the velocity of light must always depend on the co-ordinates when a gravitational field is present.”
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Re: Could gravity waves be faster than light?

Postby bangstrom on September 21st, 2017, 3:40 am 

BurtJordaan » September 21st, 2017, 12:25 am wrote:
ralfcis » 20 Sep 2017, 22:28 wrote:Light is an electromagnetic wave travelling through the electromagnetic medium (or field) of space. It's speed is limited by the permittivity and permeability constants which are analogous to a mechanical medium's properties of inertia and elasticity that allow mechanical waves to propagate through matter.

'Analogous', but not equivalent. There are big differences between a mechanical medium and the spacetime that light propagates through, which I think you are aware of.

Ralfcis did not claim they were equivalent.

In Maxwell’s Laws, the constants of permittivity and permeability are constants of free space and they limit the speed of electromagnetic signals through the vacuum. This is the spacetime through which light propagates.

'Ralfcis' said the vacuum constants of permittivity and permeability are analogous to inertia and elasticity in a mechanical medium. This helps to clarify what permittivity and permeability are for those not familiar with the terms.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 10:36 am 

bangstrom » 21 Sep 2017, 08:58 wrote:In General Relativity, gravity propagates at light speed but gravity creates a distortion in spacetime, ...

I suppose that you have meant gravitational waves propagate, because it is only changes to the gravitational field that propagate.


You are right that the speed of light is faster in the lesser gravitational density of intergalactic space. Light slows in the presence of a dense gravitational field.

You need to be more precise with this. In GR, the speed of light in vacuum is locally exactly 'c' everywhere, even close to a black hole. It is only when you consider the propagation rate in a frame other than the "local inertial frame", that you get a different value. Ditto for gravitational waves.

The piece that you have quoted from Einstein only gives an answer in a certain context, because it is not true in general.
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 11:33 am 

On photons: the standard meaning is a quantum of e.m. energy and these photons do not travel. Light is emitted as packets of energy (photons) which then propagates as e.m. waves through spacetime and are again absorbed in packets (photons).


Well this is interesting. So the wavefunction is created then collapses to create photons. This makes sense because in the SM, particles denote position while the wave denotes motion. So Bangstrom's theory is almost correct; the photons appear at the source and destination but their wave function provides their velocity between the two. Of course I'm just spitballing.

Also I suspect GR doesn't actually derive a value for c, just that c exists. Otherwise there'd be a mathematical way to use the GR derivation o derive the values of perm&perm from gravity which would link gravity and electromagnetism. But do these GR equations say c is the same for gravity and light waves?
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 12:40 pm 

ralfcis » 21 Sep 2017, 17:33 wrote:Well this is interesting. So the wavefunction is created then collapses to create photons. This makes sense because in the SM, particles denote position while the wave denotes motion.

In the standard quantum model, the wavefunction is just an interpretation and it is probably wrong to assign physical concepts like 'motion' to it. In SR/GR there are no photons or wavefunctions and we can observe the physical motion of e.m. waves at will - and is done practically every day. There is hence not much left to 'interpret'. This is where Bang and I differ, mostly interpretative, but that's another topic.

But do these GR equations say c is the same for gravity and light waves?

Yea, SR/GR does not predict the value of c, it simply says that it is the same for both types of wave. The actual value is determined by experiment. We have very accurate measurements for e.m. waves, but still need some progress with measuring g-waves. They are not readily available to experiment with!
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Re: Could gravity waves be faster than light?

Postby Braininvat on September 21st, 2017, 1:02 pm 

Can anyone recommend a good semi-layman's explanation of permittivity and permeability out there? I can limp through most of the physics here, had a bit of college training in math/physics, but my background is more life sciences and medicine. I am not fully getting the analogy of inertia and elasticity, partly due to having trouble thinking of the vacuum having either of those qualities.
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 1:22 pm 

They appear in the electrical equations for capacitance and inductance. Mechanical systems can be modeled as electrical circuits with capacitance representing mass and inductance representing a spring. A Higgs field fills space so why not EM and gravitational fields. Ed Witten won a nobel prize for proving empty space is not empty but is a quantum foam. Space is a substance with measurable properties. A non-substance would not have measurable properties.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 1:24 pm 

Braininvat » 21 Sep 2017, 19:02 wrote: I am not fully getting the analogy of inertia and elasticity, partly due to having trouble thinking of the vacuum having either of those qualities.

Yea, I should have warned readers that it is a pretty poor analogy used by Ralf (and somewhat defended by Bang), because the 'vacuum' cannot be compared to a mechanical system in any conceivable way. I do not have the reference handy now, but Einstein himself warned against it!

The Wiki articles on permittivity and permeability of space are pretty OK, though.
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 1:39 pm 

Sorry Jorrie I took an entire course on it in university. The electrical properties of space can be modeled as a mechanical system. Light propagates when the electrical and magnetic fields create one as the other collapses. The electrical field is space's capacitance and the magnetic is space's inductance which are analogous to a mechanical system's imertia (mass) and elasticity (springiness). Would you like me to find you the name of this course or would you like to google it. I remember "physical" was in the title. Here's the first link I found:
lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 3:14 pm 

ralfcis » 21 Sep 2017, 19:39 wrote:Sorry Jorrie I took an entire course on it in university. The electrical properties of space can be modeled as a mechanical system.

Such analogues can be used to model non-relativistic systems, but do you really think it can be used to model relativistic spacetime with respect to e.m. or g.w. propagation?
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 3:25 pm 

The Maxwell equations don't lie. Space as an electromagnetic medium propagates light in a similar way a slinky propagates a transverse wave. Compare the equations and you'll see the exact same structure. Even if you don't see I hope you won't protect the readers from making up their own minds.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 21st, 2017, 4:56 pm 

ralfcis » 21 Sep 2017, 21:25 wrote:The Maxwell equations don't lie. Space as an electromagnetic medium propagates light in a similar way a slinky propagates a transverse wave. Compare the equations and you'll see the exact same structure. Even if you don't see I hope you won't protect the readers from making up their own minds.

But we don't want to fool readers into thinking that a set of pre-relativity equations can give them answers to the OP question on the speed of g-waves, do we?

It is fine to start a tutorial there, but then we must qualify the inaccuracy of the analogies that we use and build them up to the correct ones. It will be a long tutorial, because gravitational waves are lurking quite deep in the solutions to the equations of GR.

We have already discussed the short answer: according to relativity, no. They have the same speed in every single frame.
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 5:09 pm 

I've given my evidence, you say there's more. I don't think they're too dumb not to understand that. That shouldn't stop them from investigating the analogy because it is more interesting than no answer at all which is obstructionist to the conversation in my view.
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Re: Could gravity waves be faster than light?

Postby ralfcis on September 21st, 2017, 5:56 pm 

Ok can I be blunt. No I really mean can you be blunt. I'm going to paraphrase what you said. Maxwell's equations are now antiquated crap so you can't extrapolate any modern theory from them. I instead see his calculations still stand up today modeling space as an EM wave medium for EM waves which behaves similarly to a mechanical wave medium for mechanical waves. (Yet, as a side note, you'll stick by Einstein's 19th century clock sync method, even though you call it a gamble that has still paid off to this very day, instead of endorsing the much cleaner atomic clock method which is based on the universal accuracy of atomic clocks.) You say we don't have the right answer, you won't ell us the right answer and I assume you will prevent us from further discussing the "wrong" answer. Feel free to move this thread and put Maxwell under personal theories as well.
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Re: Could gravity waves be faster than light?

Postby mitchellmckain on September 21st, 2017, 9:28 pm 

ralfcis » September 20th, 2017, 3:28 pm wrote:Light is an electromagnetic wave travelling through the electromagnetic medium (or field) of space. It's speed is limited by the permittivity and permeability constants which are analogous to a mechanical medium's properties of inertia and elasticity that allow mechanical waves to propagate through matter. But gravity waves probably depend on analogous gravitational constants that allow the gravitational wave to propagate through the gravitational medium of space. So why would a gravitational wave whose speed depends on other constants, somehow be coincidentally the same as the speed of light? And for that matter, why would the speed of light be necessarily the same as the max speed limit the universe sets?

According to QFT there is no coincidence. Particles are either massless and travel at the speed of light or they have mass and they do not travel at the speed of light but at a variable speed according to their kinetic energy. Furthermore, the speed of light is not a speed limit. You can travel as fast as you like and get to your destination in as short a time as you want. The speed of light is just how an infinite speed looks to observers because of the structure of space time. Thus you misunderstand if you think this means a particle travels at a certain speed just because of the type of particle it is as your talk of coincidences imply.

HOWEVER, it is possible that gravitons DO NOT travel at the speed of light. A theory by Ahmed Farag Ali and Saurya Das has proposed that gravitons could have a very small but non-zero mass and this would not only explain why we have nonzero cosmological constant without resorting to dark energy but also explain why the cosmological constant is so small.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 22nd, 2017, 12:27 am 

mitchellmckain » 22 Sep 2017, 03:28 wrote:Furthermore, the speed of light is not a speed limit. You can travel as fast as you like and get to your destination in as short a time as you want. The speed of light is just how an infinite speed looks to observers because of the structure of space time.

This a rather bold statement, considering that the speed of light is defined locally in an inertial frame. Did you not mean "The speed of light is just how an infinite rapidity [w = artanh(v/c)] looks to observers because of the structure of space time."

A non-zero mass graviton can obviously not be ruled out totally, but since GR predicts propagation at exactly c and dispersion analysis of the LIGO signal points at that value too, it looks to be (almost) settled. [https://dcc.ligo.org/P1500213/public]
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 22nd, 2017, 1:25 am 

ralfcis » 21 Sep 2017, 23:56 wrote:I'm going to paraphrase what you said. Maxwell's equations are now antiquated crap so you can't extrapolate any modern theory from them.

Instead of writing such nonsense, rather read up on what the modern forms of Maxwell's eq's look like. A good starting point could be:
https://en.wikipedia.org/wiki/Covariant_formulation_of_classical_electromagnetism

For an answer to your OP question, try:
https://en.wikipedia.org/wiki/Gravitational_wave#Basic_mathematics,

which will give some part of answer under the subsection:
https://en.wikipedia.org/wiki/Gravitational_wave#Advanced_mathematics.

For more, you should consult the ample references given in those articles. When you are finished, please tell me how you would have answered the OP question in a few posts here. I know of no correct answer that can avoid the advanced math.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on September 22nd, 2017, 2:44 am 

Braininvat » 21 Sep 2017, 19:02 wrote:Can anyone recommend a good semi-layman's explanation of permittivity and permeability out there?


This is the most practical, accessible and complete classical (non-relativistic) description that I could find:

Basics of Measuring the Dielectric Properties of Materials
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Re: Could gravity waves be faster than light?

Postby Odal on October 17th, 2017, 8:44 am 

ralfcis » September 20th, 2017, 3:28 pm[/url] wrote:In the Newtonian theory, the speed of gravity is instant so the Earth is attracted to a point where the sun is ‘now’ which keeps the Earth in a stable orbit. If gravity had a slower propagation speed, such as the speed of light, the Earth would be attracted to a point where the sun was 500 seconds ago because there is a 500 second delay between the Earth and the sun and the Earth’s orbit would slowly spiral into the sun.

In General Relativity, gravity propagates at light speed but gravity creates a distortion in spacetime, as visualized in the old bowling ball on a water bed example, and the Earth is attracted by the ‘slope’ of the spacetime distortion to the point where the sun is ‘now’ and not where it ‘was’ so the planets are able to maintain stable orbits as predicted by Newtonian theory despite having a slower propagation speed for gravity.
[/i].”
[/quote]

I might be off topic, and if that is the case then I apologize.

I have been wondering about the following issue for quite some time, and your remarks about light and gravity have (re)awakened my interest.
If Earth reacts to the actual position of the Sun, and not to its position as indicated by light speed, couldn't the same be said of our vision?
The reason I dare ask is because of this: when we are looking at an object, say, the sun, through a powerful telescope, are we seeing it where it is at that moment, or where it was when the light rays/waves left it to reach out to us?
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 17th, 2017, 9:11 am 

You could never get a powerful enough telescope to see where a distant star is now. The telescope doesn't reach farther into space to catch light before light would hit a pair of binoculars beside the telescope. Only moving telescopes closer to the distant star would allow one to see the star where it is now but the delay of televising those pictures back to earth, still wouldn't allow people on earth to see where the star is now.
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 17th, 2017, 9:16 am 

I guess this latest result with Ligo and the two neutron stars looks quite convincing that gravity waves probably travel at the same speed light does. The reason I say this is because the event is far enough to have possibly allowed the telescopes that turned to the source of the event to have caught the explosion after the gravity waves were detected.The ligt from the start of the explosion had already occurred before they could catch it.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on October 17th, 2017, 9:24 am 

Odal » 17 Oct 2017, 14:44 wrote:If Earth reacts to the actual position of the Sun, and not to its position as indicated by light speed, couldn't the same be said of our vision?
The reason I dare ask is because of this: when we are looking at an object, say, the sun, through a powerful telescope, are we seeing it where it is at that moment, or where it was when the light rays/waves left it to reach out to us?

No, light is emitted continuously by the sun as e.m. waves that have to travel to us all the time. So we see it where it was relative us about 8 minutes ago. The gravity that holds earth in orbit around the sun does not have to be transmitted any more - the gravitational field is there all the time and earth experiences it where it is. It is only changes to the gravitational field that that propagates as gravitational waves.

To be complete, the sun/earth system orbiting each other do emit gravitational waves, but they are undetectably small. They are just 'feeble' little ripples in the sun/earth gravitational field that travels away outside of earth's orbit.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on October 17th, 2017, 9:37 am 

ralfcis » 17 Oct 2017, 15:16 wrote:The ligt from the start of the explosion had already occurred before they could catch it.

Correct, but I would not describe the merger as an explosion, just the creation of an extraordinary hot, large neutron star, that will 'shine' in many wavelengths for many days (or longer). They have already measured the cooling down in the first day or so, according to the articles that I have seen so far.
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Re: Could gravity waves be faster than light?

Postby Odal on October 17th, 2017, 10:08 am 

@BurtJordaan

Ramesh Raskar, the femotography specialist at M.I.T, takes pictures of light as it progresses from one location to the other. The distances are very small, and the exposure times are in picoseconds.
As far as I could see, all pictures were taken from aside, the beam progressing horizontally.

Imagine now looking at the progression of the beam through the scene from the end. Theoretically, you would expect the scene to light up completely at the same instant.
we would never be able to see the progression of the beam towards us?
Am I wrong?
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 17th, 2017, 10:30 am 

Sure if it's a series of pulses.
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Re: Could gravity waves be faster than light?

Postby Odal on October 17th, 2017, 10:32 am 

[quote="Sure if it's a series of pulses.[/quote]

Could you please elaborate? I am assuming that it is a continuous beam of light, as I think Ramesh does.
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 17th, 2017, 1:48 pm 

Google his stuff on youtube, he films pulses of light and none get length contracted.
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Re: Could gravity waves be faster than light?

Postby Odal on October 17th, 2017, 2:44 pm 

ralfcis » October 17th, 2017, 6:48 pm[/url] wrote:Google his stuff on youtube, he films pulses of light and none get length contracted.


You are obviously speaking of something else. What I have in mind has nothing to do with contraction.
When the light beam starts its travel towards us, it illuminates gradually everything in its path, and we see the objects only after they have been revealed by the beam.
But since the light has to reach our eyes before we see the objects, by the time it does we will see the whole scene as illuminated, and not the gradual illumination that is seen from the side.
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