Photon?

[quantum_wave]

GR is the best theory that fits the way that nature works, according to the collected observations and tests that people have done, at least since the 1600s.

It is often easier for us to use Newtonian mechanics, and we might not lose enough accuracy to make this worth our while. But even there, there is complete relativity according to whether or not the car is moving or the road.

It is usually easier for us to merely assume that the car alone is moving. But ease of use is not evidence for truth. It is far easier for us to assume that the road is moving when we are calculating the orbit of the Earth.

Agreed. However, are you saying that GR is truth, reality, and complete? Don't flame me for asking, because I said a few moments ago that motion is relative. But if GR is reality, doesn't that go against the concept that science is tentative? Couldn't future discoveries be monumental, like the presence of gravitons or gravitational waves between objects? It wouldn't change relativity, but wouldn't it change GR.

 

[PhysBang]

GR is definitely incorrect and incomplete. I have no doubt about that.

Yet for describing the motion of an object bigger than a marble, it's the best we have.

As far as I know, there is no good science of mechanics that identifies a real difference between the road moving and the car moving.

 

[quantum_wave]

GR is definitely incorrect and incomplete. I have no doubt about that.

Yet for describing the motion of an object bigger than a marble, it's the best we have.

As far as I know, there is no good science of mechanics that identifies a real difference between the road moving and the car moving.

Thanks. It is interesting to think that a person could confuse his particular relative motion so much as to really believe the entire universe was moving while he was fixed in place. No one is that detached from their surroundings and from cause and effect. You are saying that we can't tell, but are you saying we could be fixed and the universe is revolving around us; rhoterical question to make my point. Humans can misinterpret local observation and sensation, but only to a reasonable degree, lol.

 

[quantum_wave]

That's one way to say Einstein was wrong I suppose.

It sure is. And what's empirical, is that there isn't any time flowing through a clock. A clock features some kind of regular cyclical motion which is counted / accumulated and displayed as "the time". So what else is empirical is this: when the clock goes slower when it's lower it's because that motion goes slower. Even when it's a light clock. You will of course be familiar with the parallel-mirror light clock. It's an idealised clock, but nevertheless it's used extensively in relativity. For example, in the simple inference of time dilation due to relative velocity. That's SR time dilation. For GR time dilation, you arrange one parallel-mirror light clock above the other like so:

View attachment 161

See how the lower clock goes slower? It can only do that if the light goes slower. Of course you'll find a way to dismiss that too. And it will probably involve some abuse.

Let me ask you this, and please note I think I understand the concept that your gif is intended to convey. Lower clocks measure time to pass more slowly. I'm sure that is true. But that same concept could be equally depicted if you made the lower mirrors closer together, so that the photon covered the shorter distance between the mirrors in the same amount of time as it took the photon in the higher clock to cover the greater distance. Am I right? Why not show it both ways.

You could still say the clocks were identical, and represent the gif as depicting the different distance that light would travel in the identical amount of time. This clarifies the concept that what we observe is not really a different rate of time passing, but a different rate at which identical clocks measure.

 

[OnlyMe]

Let me ask you this, and please note I think I understand the concept that your gif is intended to convey. Lower clocks measure time to pass more slowly. I'm sure that is true. But that same concept could be equally depicted if you made the lower mirrors closer together, so that the photon covered the shorter distance between the mirrors in the same amount of time as it took the photon in the higher clock to cover the greater distance. Am I right?

You could still say the clocks were identical, and represent the gif as depicting the different distance that light would travel in the identical amount of time. This clarifies the concept that what we observe is not really a different rate of time passing, but a different rate at which clocks measure.

For Farsight, it is a speed of light issue. The problem is that when using any accurate clock the speed of light in vacuum is always measured to be the same... Unlike what he is trying to say with his pong gif.

 

[PhysBang]

Thanks. It is interesting to think that a person could confuse his particular relative motion so much as to really believe the entire universe was moving while he was fixed in place. No one is that detached from their surroundings and from cause and effect. You are saying that we can't tell, but are you saying we could be fixed and the universe is revolving around us; rhoterical question to make my point. Humans can misinterpret local observation and sensation, but only to a reasonable degree, lol.

Writing as you do, I imagine that you think that, when you look like you are sitting still, then you believe that you are really spinning around the Earth, which is really spinning around the Sun, which it really spinning around the center of the Milky Way.

So you can imagine a scenario where you jump up, expending energy to move, but during the duration of that jump you happen to cancel out all the movement associated with that rotation. So you would have done motion, seemed to the ignorant eye as if you were moving, but in fact you didn't move.

The difference between you and a serious physicist is that they take these ideas seriously and wonder what relative motion really means and requires for a theory of physics and you do not.

 

[Aqueous Id]

The pong gif is a fraud. It purports to warp time but not space which is absurd.

Also Farsight is years away from understanding the difference between longitudinal and transverse dilation/contraction.

And yes Farsight can talk about feeling thrust but no space agency will let him near a spacecraft. But the real folks who make the grade can feel thrust yet will not be moving toward the star until they exceed the recession velocity.

 

[quantum_wave]

Writing as you do, I imagine that you think that, when you look like you are sitting still, then you believe that you are really spinning around the Earth, which is really spinning around the Sun, which it really spinning around the center of the Milky Way.

So you can imagine a scenario where you jump up, expending energy to move, but during the duration of that jump you happen to cancel out all the movement associated with that rotation. So you would have done motion, seemed to the ignorant eye as if you were moving, but in fact you didn't move.

The difference between you and a serious physicist is that they take these ideas seriously and wonder what relative motion really means and requires for a theory of physics and you do not.

Understood, and point taken. You can't acknowledge my point though, can you.

 

[quantum_wave]

For Farsight, it is a speed of light issue. The problem is that when using any accurate clock the speed of light in vacuum is always measured to be the same... Unlike what he is trying to say with his pong gif.

Maybe so. I just look at the gif as depicting the rate that clocks at different altitudes measure time. I asked him in another thread to clarify the cause; still waiting.

 

[PhysBang]

Understood, and point taken. You can't acknowledge my point though, can you.

Well, yes and no.

It requires a lot of thinking to understand that what seems so obvious to us is superfluous to a better understanding of the phenomena we care about. I don't like the idea that taking the time to work carefully through a situation makes one obtuse.

 

[quantum_wave]

Well, yes and no.

It requires a lot of thinking to understand that what seems so obvious to us is superfluous to a better understanding of the phenomena we care about. I don't like the idea that taking the time to work carefully through a situation makes one obtuse.

I'll take that as a tentative acknowledgement of my point. What you say is scientifically true, but I don't think it takes a lot of thinking to understand, once you understand the physics. Everyone loves to imply others are ignorant, but often they are not. The potential of the human brain to sort out cause and effect is not part of GR, but it is part of reality as I see reality.

 

[Farsight]

Let me ask you this, and please note I think I understand the concept that your gif is intended to convey. Lower clocks measure time to pass more slowly. I'm sure that is true. But that same concept could be equally depicted if you made the lower mirrors closer together, so that the photon covered the shorter distance between the mirrors in the same amount of time as it took the photon in the higher clock to cover the greater distance. Am I right?

No. Because the lower clock goes slower, so the greater distance would be between the lower pair of mirrors. And because gravitational length contraction is radial, not horizontal. Only if it was horizontal, it would be making the distance between the lower pair of mirror shorter. The lower clock would run faster, not slower. It just doesn't work.

You could still say the clocks were identical, and represent the gif as depicting the different distance that light would travel in the identical amount of time. This clarifies the concept that what we observe is not really a different rate of time passing, but a different rate at which identical clocks measure.

It just doesn't work. And it doesn't tally with what Einstein said.

NB: this notion of us being fixed and the universe revolving around us is specious woo. We know we're rotating. We know that all those distant galaxies aren't orbiting us at trillions and zillions of light years per second.

We always measure the local speed of light to be 299,792,458 m/s because we use the motion of light to define the second and the metre. It's a tautology. See http://arxiv.org/abs/0705.4507:

"Following Ellis [1], let us first consider c as the speed of the photon. Can c vary? Could such a variation be measured? As correctly pointed out by Ellis, within the current protocol for measuring time and space the answer is no. The unit of time is defined by an oscillating system or the frequency of an atomic transition, and the unit of space is defined in terms of the distance travelled by light in the unit of time. We therefore have a situation akin to saying that the speed of light is “one light-year per year”, i.e. its constancy has become a tautology or a definition."

 

[Farsight]

Maybe so. I just look at the gif as depicting the rate that clocks at different altitudes measure time. I asked him in another thread to clarify the cause; still waiting.

I didn't know there was anything outstanding about this. A concentration of energy in the guise of a massive star "conditions" the surrounding space. It alters it. As a result the speed of light is reduced, the effect diminishing with distance. As a result of that, light curves. In mechanics a shear wave travels at a speed determined by the stiffness and density of the medium: v = √(G/ρ). You might think space is nothing like that, but there's a shear-stress term in the stress-energy-momentum tensor. It is like that. And in electrodynamics the expression is somewhat similar: c = √(1/ε0μ0) where ε0 is electric permittivity and μ0 is magnetic permeability. See Gravity Works Like This and see this bit:

"I don’t know if you know, but there’s another couple of problems with the rubber-sheet picture. One is that it depicts tension instead of pressure. Einstein’s stress-energy tensor has an energy-pressure diagonal, and to envisage pressure you need to step up from a rubber sheet to three-dimensional space. Imagine it’s like some gin-clear ghostly elastic jelly, then you insert a hypodermic needle and inject more jelly to represent the mass-energy of the Earth. The surrounding jelly is pressed outwards rather than being pulled inwards."

The energy-density of space is greater near the star than far from the star. If it wasn't, light wouldn't curve and things wouldn't fall down. IMHO the interesting thing to note is that the gin-clear ghostly elastic jelly represents space, and you inject more jelly to represent energy. So in a way space and energy are the same thing.

 

[OnlyMe]

Maybe so. I just look at the gif as depicting the rate that clocks at different altitudes measure time. I asked him in another thread to clarify the cause; still waiting.

Farsight has answered that question so many times, it has become cliché.

His answer is that clocks go slower closer to the ground (or when they are lower), because the speed of light is slower. In Farsight's world the speed of light is not a constant. The problem is he has never provided any proof to support that belief, that does not depend on his belief, misinterpretation and/or misunderstanding.., of historical quotes, experimental evidence and reality.​

To be clear, I do not know (with any certainty) if the speed of light is truely a universal constant, because I have seen no direct evidence where the speed of light has been accurately measured anywhere other than our local frame of reference.., where it is always measured to be uniformly constant, in vacuum... But.., at the same time, all of our observations of the distant universe, are currently interpreted with the understanding that the speed of light, c is uniform and constant, and those same observations make sense, when the speed of light is constant... Where if the speed of light were not constant, everything we think we know about the distant universe would not make sense!

IOW If the speed of light varies with location in a gravitational field, looking with any detail at the night sky (distant objects even in our own Galaxy) would be like trying to understand the room you are in, reflected in a carnival mirror. What we see does not seem to be distorted in any way that a variable speed of light would suggest it should be.., given the constantally changing spacetime it would have traveled through to reach us.

Is any of that proof? No! But until otherwise proven false, what we see of the world and universe around us makes most sense, when we assume that the speed of light IS uniformly constant.

So to restate the obvious. We know with certainty that locally the speed of light in vacuum is constant.., and what we see of the distant universe makes most sense when we interpret what we see, within the context that what we measure locally, is universally true.

 

[quantum_wave]

No. Because the lower clock goes slower, so the greater distance would be between the lower pair of mirrors. And because gravitational length contraction is radial, not horizontal. Only if it was horizontal, it would be making the distance between the lower pair of mirror shorter. The lower clock would run faster, not slower. It just doesn't work.

It just doesn't work. And it doesn't tally with what Einstein said.

NB: this notion of us being fixed and the universe revolving around us is specious woo. We know we're rotating. We know that all those distant galaxies aren't orbiting us at trillions and zillions of light years per second.

We always measure the local speed of light to be 299,792,458 m/s because we use the motion of light to define the second and the metre. It's a tautology. See http://arxiv.org/abs/0705.4507:

"Following Ellis [1], let us first consider c as the speed of the photon. Can c vary? Could such a variation be measured? As correctly pointed out by Ellis, within the current protocol for measuring time and space the answer is no. The unit of time is defined by an oscillating system or the frequency of an atomic transition, and the unit of space is defined in terms of the distance travelled by light in the unit of time. We therefore have a situation akin to saying that the speed of light is “one light-year per year”, i.e. its constancy has become a tautology or a definition."

Thanks. One point. If the clocks are identical, and light travels slower in the lower clock, changing the separation of the mirrors in the lower clock in the gif would then convey the concept equally as well, as long as you explain the clocks are identical. The lower mirrors would have to be closer if the length of time it takes to traverse the distance between mirrors was the same, because light goes slower in the lower clock.

Edit note: I hadn't read Farsight's most recent post prior to this response. I stand corrected.

 

[PhysBang]

I'll take that as a tentative acknowledgement of my point. What you say is scientifically true, but I don't think it takes a lot of thinking to understand, once you understand the physics. Everyone loves to imply others are ignorant, but often they are not. The potential of the human brain to sort out cause and effect is not part of GR, but it is part of reality as I see reality.

GR is very much about cause and effect. It puts hard constraints on what event can be a cause of another event.

The problem here is one of what motion is being caused to happen. If we are going to say that a certain motion is being caused to happen, then we have to identify the movement relative to some standard.

 

[PhysBang]

I didn't know there was anything outstanding about this. A concentration of energy in the guise of a massive star "conditions" the surrounding space. It alters it. As a result the speed of light is reduced, the effect diminishing with distance. As a result of that, light curves. In mechanics a shear wave travels at a speed determined by the stiffness and density of the medium: v = √(G/ρ). You might think space is nothing like that, but there's a shear-stress term in the stress-energy-momentum tensor. It is like that. And in electrodynamics the expression is somewhat similar: c = √(1/ε0μ0) where ε0 is electric permittivity and μ0 is magnetic permeability. See Gravity Works Like This and see this bit:

"I don’t know if you know, but there’s another couple of problems with the rubber-sheet picture. One is that it depicts tension instead of pressure. Einstein’s stress-energy tensor has an energy-pressure diagonal, and to envisage pressure you need to step up from a rubber sheet to three-dimensional space. Imagine it’s like some gin-clear ghostly elastic jelly, then you insert a hypodermic needle and inject more jelly to represent the mass-energy of the Earth. The surrounding jelly is pressed outwards rather than being pulled inwards."

The energy-density of space is greater near the star than far from the star. If it wasn't, light wouldn't curve and things wouldn't fall down. IMHO the interesting thing to note is that the gin-clear ghostly elastic jelly represents space, and you inject more jelly to represent energy. So in a way space and energy are the same thing.

This is not an explanation that we can test.

Please, Farsight, show us how to predict the time dilation of a clock based on your ideas.

 

[Farsight]

Please, Farsight, show us how to predict the time dilation of a clock based on your ideas.

No. Because they aren't my ideas. They're Einstein's ideas. And it was Einstein who said this:

"Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields."

if the speed of light varies with location in a gravitational field, looking with any detail at the night sky (distant objects even in our own Galaxy) would be like trying to understand the room you are in, reflected in a carnival mirror. What we see does not seem to be distorted in any way that a variable speed of light would suggest it should be...

It's called gravitational lensing.

Is any of that proof? No! But until otherwise proven false, what we see of the world and universe around us makes most sense, when we assume that the speed of light IS uniformly constant.

Well it isn't.

So to restate the obvious. We know with certainty that locally the speed of light in vacuum is constant...

Oh no you don't.

 

[quantum_wave]

Farsight has answered that question so many times, it has become cliché.

His answer is that clocks go slower closer to the ground (or when they are lower), because the speed of light is slower. In Farsight's world the speed of light is not a constant. The problem is he has never provided any proof to support that belief, that does not depend on his belief, misinterpretation and/or misunderstanding.., of historical quotes, experimental evidence and reality.​

I know, and you are saying that the path of the light in the lower clock is longer because spacetime is more curved.

What I'm trying to understand is how Farsight deals with the longer path, or is he saying that the path is not longer due to the curvature of spacetime, but instead, light is traveling slower. I think he is saying light is traveling slower along a straight path. I'm wondering about the cause for light to move along a straight path at a slower velocity.

Edit note: I hadn't seen Farsight's recent post with the explanation. I stand corrected.

 

[quantum_wave]

GR is very much about cause and effect. It puts hard constraints on what event can be a cause of another event.

The problem here is one of what motion is being caused to happen. If we are going to say that a certain motion is being caused to happen, then we have to identify the movement relative to some standard.

I think I get that. If you kick someone in the butt, they move faster, lol. But to a perceptive human, the question of cause and effect between the events of kicking, and going faster is clear, and the theory of GR doesn't need to be stated or consulted in order to get the right answer. So in my example, a human brain can take a shortcut through the applicable science and get the right answer, within the limits of perception.