Absolute frame of reference (split from does relativity even exist)

[Fred Champion]

Edgard, you are right about at least one thing; there is one absolute frame of reference. It is the space in which light propagates. If one accepts that the speed of light is constant in all frames of reference, then one must accept that no reference frame is isolated from any other reference frame.

 

Your notion of birds carrying information may be correct, but it makes my brain hurt.

 

I believe what you are actually questioning is how we measure without touching. Unless you accept a defined frame of reference and a means of communication moving at a defined velocity within that frame of reference (and all other frames), you have no basis for consistent measuring without touching. This is what we have with space and light, an absolute frame and a constant velocity means of communication.

 

I'm sure you will recognize that, for any object, the maximum velocity that can be measured is less than (or possibly just equal to) the velocity of the means of communication. One cannot measure supersonic speeds using only sound, nor super-light speeds using light.

[Delta1212]

Edgard, you are right about at least one thing; there is one absolute frame of reference. It is the space in which light propagates. If one accepts that the speed of light is constant in all frames of reference, then one must accept that no reference frame is isolated from any other reference frame.

 

Your notion of birds carrying information may be correct, but it makes my brain hurt.

 

I believe what you are actually questioning is how we measure without touching. Unless you accept a defined frame of reference and a means of communication moving at a defined velocity within that frame of reference (and all other frames), you have no basis for consistent measuring without touching. This is what we have with space and light, an absolute frame and a constant velocity means of communication.

 

I'm sure you will recognize that, for any object, the maximum velocity that can be measured is less than (or possibly just equal to) the velocity of the means of communication. One cannot measure supersonic speeds using only sound, nor super-light speeds using light.

You do realize that the constant velocity of light means that if I see a beam of light shining away from me, I will measure it as moving at 186,000 miles per second. If I accelerate in the direction of the light so that I'm moving 100mph, I will measure the light moving 186,000 miles per second faster than me, and if I accelerate in the direction of the light until I'm moving at 185,000 miles per second, I will see the light moving 186,000 miles per second faster than me.

 

That's what light's constant velocity means. There is no preferred frame through which it moves at 186,000 miles per second. It moves trough every frame at 186,000 miles per second relative to that frame.

[Fred Champion]

You do realize that the constant velocity of light means that if I see a beam of light shining away from me, I will measure it as moving at 186,000 miles per second. If I accelerate in the direction of the light so that I'm moving 100mph, I will measure the light moving 186,000 miles per second faster than me, and if I accelerate in the direction of the light until I'm moving at 185,000 miles per second, I will see the light moving 186,000 miles per second faster than me.

 

That's what light's constant velocity means. There is no preferred frame through which it moves at 186,000 miles per second. It moves trough every frame at 186,000 miles per second relative to that frame.

I believe you do not understand that "constant" means everwhere and that there is only one "real" or preferred frame of reference. An imaginary frame of reference we construct will not be isolated from the one real frame except in our imagination. Light will not change speed as it enters and then exits our spaceship. (I like to travel with the windows open.)

 

The notion that what will be measured in any given imaginary frame actually reveals what "is" is not correct. What will be revealed is what appears to be, not necessarily what is.

 

Note that there is no such thing as a "beam" of light; there will be a succession of wave crests (or however you wish to describe what we determine as frequency). The fact that light propagates at a constant speed and we may move at variable speeds is what gives us the component of the doppler shift due to the motion of the observer. Of course the other component of the doppler shift is due to the motion of the light source.

 

Note that the speed of light does not change because we are moving, even light from a source moving with us. If we travel at half the speed of light in the same direction as the light is propagating, the wave crests will pass us at one-half light speed. If we travel at half the speed of light in the opposite direction as the light is propagating, the wave crests will pass us at one and one-half light speed. If lt did not happen this way we would see no doppler shift.

 

Convince yourself that light acts this way by imagining we are on a moving spaceship. We shoot a bullet straight up at a target on the ceiling. The bullet will appear to us to go straight up and hit the target. Now we shine a light straight up toward the ceiling. The light will not illuminate the target, it will illuminate a position some distance to the rear of the target, depending on the speed of the spaceship and the distance to the ceiling.

 

There is no "beam" of light that bends. Each wave crest propagates from the place in space (the one real frame of reference) where it originated and will continue straight up untill it reaches the ceiling. Each successive wave crest will be originated at a place a bit further in the direction of travel than the previous one and will also continue straight up until it too reaches the ceiling. Note that even though the target was directly above the point of origin for each wave crest, the target moves away in the direction of travel before that wave crest can reach the ceiling.

 

The bullet attains a velocity component from the motion of the ship, but the light does not. The velocity of light is constant everywhere and is independent of the motion of the source. This tells us that there is one real, preferred, "everywhere" frame of reference.

[MigL]

Your thought experiment is wrong.

You are using this 'bending' of light as a way to measure and detect absolute speed or velocity and from that, implying that there must be an absolute frame.

 

There is no preferred or absolute frame. There is no absolute speed or velocity, only relative speed or velocity.

And light within an inertial frame doen't 'bend' as it does within an accelerating or gravitational frame.

[Fred Champion]

Your thought experiment is wrong.

You are using this 'bending' of light as a way to measure and detect absolute speed or velocity and from that, implying that there must be an absolute frame.

 

There is no preferred or absolute frame. There is no absolute speed or velocity, only relative speed or velocity.

And light within an inertial frame doen't 'bend' as it does within an accelerating or gravitational frame.

The thought experiment is correct.

 

I did not use the "bending" of light in any way. In fact I denied that there is a beam of light which might be described as bending.

 

Each "wave" of light is emitted from a point in space. (If you don't like the term wave, substitute whatever you use to describe the cause of the effect we call frequency.) Each wave is emitted separately. What we call a "beam" is just a succession of individual waves emitted from the same source. Each individual wave propagates out from its point of origin. If the source of the light is moving, each wave will be emitted from a different point in space.

 

If you accept that the speed of light (in space) is constant everywhere, then you must accept that light waves propagate at a constant speed everywhere. This speed of light is unchangeable, fixed, not modifiable, in other words, absolute.

 

Space (our universe) is the frame of reference that light moves through. This is our one and only real, true, absolute frame of reference. No part of the universe may be isolated from any other part. Every other frame of reference you may construct is imaginary, not real.

 

The speed of light, the propagation of light, the rate of propagation of light waves, is not relative to anything except space. Space is absolute. The speed of light in space is absolute. If you do not accept this, you cannot accept any notion or calculation in all of relativity. The absoluteness of space and light is fundamental to relativity.

 

As to your last statement, light doesn't bend at all, anywhere. Accelleration may produce the appearance of distortions and gravity may result in distortions. If we cannot accept that space is absolute, how can we accept that gravity produces a distortion in it?

[swansont]

In introductory physics, a frame of reference refers to a choice of a coordinate system. Inertial frames move at constant velocity with respect to others. Non-inertial ones accelerate. In GR, freefall in a uniform gravitational field is an inertial frame.

 

"The universe" is not a single frame of reference, since an infinite number choices for inertial frames are possible.

[Dekan]

In introductory physics, a frame of reference refers to a choice of a coordinate system. Inertial frames move at constant velocity with respect to others. Non-inertial ones accelerate. In GR, freefall in a uniform gravitational field is an inertial frame.

 

"The universe" is not a single frame of reference, since an infinite number choices for inertial frames are possible.

 

I suppose an infinite number of choices would be possible. If the Universe were infinite, extending endlessly in all directions. Then it wouldn't have any "background". It would just go on forever, without limit.

But nowadays we know that the Universe isn't unlimited. It has a definite size, about 13.5 billion light-years. This has been proved by the discovery of the Cosmic Background Radiation.

 

The background radiation can be mapped, Some maps have been published in recent years. They show the background isn't smooth and featureless. It shows irregularities.

Such irregularities seem to provide Universal reference points .

 

Couldn't they be used to measure absolute speed within the Universe?

Edited May 26, 2014 by Dekan

[ajb]

If one accepts that the speed of light is constant in all frames of reference, then one must accept that no reference frame is isolated from any other reference frame.

Light speed is constant only in inertial frames of reference. In a general frame the speed of light will almost never be constant. What do you mean by the "no frame is isolated" statement? We have inertial frames that are not connected by a Lorentz transformation.

Couldn't they be used to measure absolute speed within the Universe?

The CMBR does provide a useful frame to describe cosmology, but this is not a true absolute frame.

[swansont]

I suppose an infinite number of choices would be possible. If the Universe were infinite, extending endlessly in all directions.

 

It would happen in a finite universe as well. There are an infinite number of velocities you can have relative to me. Each one represents an inertial frame.

[Fred Champion]

In introductory physics, a frame of reference refers to a choice of a coordinate system. Inertial frames move at constant velocity with respect to others. Non-inertial ones accelerate. In GR, freefall in a uniform gravitational field is an inertial frame.

 

"The universe" is not a single frame of reference, since an infinite number choices for inertial frames are possible.

There are many different types of coordinate systems. Of course we may choose a particular type from among them. It should be obvious that choosing the type of coordinate system is only the first step in setting up a frame of reference.

 

The next step is picking a point of origin. A point of origin must be somewhere. In order to pick one place we must have a choice of places. In order for there to be multiple places to choose from, we must posit a volume to contain those places. That volume may be imaginary or real.

 

If it is real, the volume is the universe. If the volume posited is imaginary, we will find utility in physics for our imagined frame only if we can translate from it into the universe.

 

A frame of reference is not just a coordinate system; it must include a volume. Our universe is the only real volume we have; within it the point of origin for any coordinate type chosen will be a real place.

 

I suggest that the type of coordinate system and the point of origin is trivial for any application to the universe. This means that every possible application is essentially the same and will refer to the universe and what happens here. Thus the universe is our one and only real frame of reference.

Light speed is constant only in inertial frames of reference. In a general frame the speed of light will almost never be constant. What do you mean by the "no frame is isolated" statement? We have inertial frames that are not connected by a Lorentz transformation.

 

The CMBR does provide a useful frame to describe cosmology, but this is not a true absolute frame.

We may posit unconnected imaginary frames if we wish, but their utility in physics will be nil. Without a transformation into the universe there is no connection to the universe and thus no utility.

 

Any coordinate system imposed on any part of the universe is imposed on the entire universe. We cannot separate (isolate) any part of the universe from any other part. I have seen no one claim that the universe is anything other than a contiguous whole.

[swansont]

There are many different types of coordinate systems. Of course we may choose a particular type from among them. It should be obvious that choosing the type of coordinate system is only the first step in setting up a frame of reference.

 

The next step is picking a point of origin. A point of origin must be somewhere. In order to pick one place we must have a choice of places. In order for there to be multiple places to choose from, we must posit a volume to contain those places. That volume may be imaginary or real.

No (the extent of x, y and z can be undetermined) but that's not really an issue here.

 

 

If it is real, the volume is the universe. If the volume posited is imaginary, we will find utility in physics for our imagined frame only if we can translate from it into the universe.

 

A frame of reference is not just a coordinate system; it must include a volume. Our universe is the only real volume we have; within it the point of origin for any coordinate type chosen will be a real place.

Even within this artificial constraint I can still choose any of the infinite points within the universe as my origin, and infinite number of velocities to define different inertial systems. Thus, there are an infinite number of frames.

[ajb]

We may posit unconnected imaginary frames if we wish, but their utility in physics will be nil. Without a transformation into the universe there is no connection to the universe and thus no utility.

Inertial frames that are not connected by a Lorentz transformation are really at the heart of the causal structure of special relativity.

[Fred Champion]

Light speed is constant only in inertial frames of reference. In a general frame the speed of light will almost never be constant. ...

On this side of the looking glass, "c" is taken to be constant. If one wants to define space as being distorted, one first has to establish what it means to be not distorted. Measuring non-distortion in a distorted environment is above my pay grade.

[swansont]

On this side of the looking glass, "c" is taken to be constant. If one wants to define space as being distorted, one first has to establish what it means to be not distorted. Measuring non-distortion in a distorted environment is above my pay grade.

You can measure changes or differences fairly precisely.

[Fred Champion]

No (the extent of x, y and z can be undetermined) but that's not really an issue here.

 

 

Even within this artificial constraint I can still choose any of the infinite points within the universe as my origin, and infinite number of velocities to define different inertial systems. Thus, there are an infinite number of frames.

Well, I'm not ready to accept an infinite number of real points in the universe. It seems much more likely that space is granular; thus a smallest unit of place, a smallest volume. If I were to attempt a GUT, I would start with a unit volume and build from there, but that's another topic.

 

I will go back to my original claim that the universe is our only real frame of reference. The only real point of origin for each individual is the location of that individual's identity. Each of us has only one real frame of reference. We may choose a point other than our location to use as a mathematical or geometric origin, and as you point out there are a very large number of possible points.

 

Any conditions, other than the real conditions at your location or at a location directly translated from your location, that you may impose at a chosen origin are imaginary. The point to keep in mind is that experiments done at such locations can only be "thought experiments" and the results should be applied to a real location with real conditions only if they are properly translated from the imaginary frame into the real frame. I'm sure you know all this. I say it only as a reminder for those who may try to apply results from thought experiments to the real world. Peace.

[swansont]

Well, I'm not ready to accept an infinite number of real points in the universe.

 

Again we're back to how you define "real". What is a "real" point?

 

But this is an artificial constraint you've placed on the problem. If we are discussing this in the context of physics that means we take these issues as given. If you aren't going to start there, then it's a different discussion.

[Delta1212]

Well, I'm not ready to accept an infinite number of real points in the universe. It seems much more likely that space is granular; thus a smallest unit of place, a smallest volume. If I were to attempt a GUT, I would start with a unit volume and build from there, but that's another topic.

 

I will go back to my original claim that the universe is our only real frame of reference. The only real point of origin for each individual is the location of that individual's identity. Each of us has only one real frame of reference. We may choose a point other than our location to use as a mathematical or geometric origin, and as you point out there are a very large number of possible points.

 

Any conditions, other than the real conditions at your location or at a location directly translated from your location, that you may impose at a chosen origin are imaginary. The point to keep in mind is that experiments done at such locations can only be "thought experiments" and the results should be applied to a real location with real conditions only if they are properly translated from the imaginary frame into the real frame. I'm sure you know all this. I say it only as a reminder for those who may try to apply results from thought experiments to the real world. Peace.

You seem to be using the word frame in a very, very different context than is used in physics. A frame of reference is not a location. It could more accurately be compared to a velocity.

[ajb]

You seem to be using the word frame in a very, very different context than is used in physics. A frame of reference is not a location. It could more accurately be compared to a velocity.

The usual meaning in physics is just a local coordinate system on space-time, or sometimes on other manifolds depending what we are talking about. By local coordinates we mean a coordinate system in the neighborhood of some specified point. The location could be understood as this point, or more simply as the origin of the coordinate system employed.

[Delta1212]

The usual meaning in physics is just a local coordinate system on space-time, or sometimes on other manifolds depending what we are talking about. By local coordinates we mean a coordinate system in the neighborhood of some specified point. The location could be understood as this point, or more simply as the origin of the coordinate system employed.

I do realize this, but the impression I'm getting from Fred is that, the way he's using frame, he means a volume of space surrounding each of our individual origin points, this making "the universe" a universal frame because it is the volume of space that encompasses everything.

 

What I was trying to get across (perhaps not as well as I'd hoped?) is that the distinguishing factor between frames isn't really the area of the location they occupy so much as the velocity at which they are traveling. I realize that isn't strictly the definition of a frame, but I've found it helpful for visualizing what is going on to remember that frames are separated by the way they move moreso than by distance between them.

[swansont]

I think we have a situation of "if we redefine a word, it has a different meaning" which is kind of a pointless discussion.

[ajb]

What I was trying to get across (perhaps not as well as I'd hoped?) is that the distinguishing factor between frames isn't really the area of the location they occupy so much as the velocity at which they are traveling. I realize that isn't strictly the definition of a frame, but I've found it helpful for visualizing what is going on to remember that frames are separated by the way they move moreso than by distance between them.

 

This sounds like you are talking about moving frames which are of course very important notions in general relativity.

[Fred Champion]

The usual meaning in physics is just a local coordinate system on space-time, or sometimes on other manifolds depending what we are talking about. By local coordinates we mean a coordinate system in the neighborhood of some specified point. The location could be understood as this point, or more simply as the origin of the coordinate system employed.

 

 

I do realize this, but the impression I'm getting from Fred is that, the way he's using frame, he means a volume of space surrounding each of our individual origin points, this making "the universe" a universal frame because it is the volume of space that encompasses everything.

 

What I was trying to get across (perhaps not as well as I'd hoped?) is that the distinguishing factor between frames isn't really the area of the location they occupy so much as the velocity at which they are traveling. I realize that isn't strictly the definition of a frame, but I've found it helpful for visualizing what is going on to remember that frames are separated by the way they move moreso than by distance between them.

I think you both are pretty much correct. I accept that in order for a frame of reference to have any utitily it must include a volume within which things will be described, a point of origin within that volume and a coordinate type imposed with a zero point at the point of origin.

 

If the volume chosen is the universe and if the point of origin chosen is the location of the identity doing the choosing, I accept that the frame thus constructed is real. For each individual, there can be only one such frame. To me, the choice of a different volume, a different point of origin or different conditions makes the frame imaginary. In either case the coordinate type chosen is imaginary.

 

If any imaginary frame is to have any utility, that is to say that anything discovered or results achieved within it are to have any application in the real frame, there must be a translation into the real frame such that discoveries or results in the imaginary frame are consistent with those in the real frame; the "laws of physics" in an imaginary frame must be consistent, with translation, with the "laws of physics" in the real frame. My experience is that some do not seem to understand this as well as they might, thus causing some degree of confusion and so I feel it necessary for us to bring the point to the fore.

[ajb]

If the volume chosen is the universe and if the point of origin chosen is the location of the identity doing the choosing, I accept that the frame thus constructed is real.

So you want to set up a global coordinate system. Generally you cannot do this, but it maybe okay for the observable Universe using the CMBR for example, I will have to check this. Anyway you should note that this assumes that the galaxies are point like and are interested in the large scale structure. When dealing smaller scale phenomena it may not be possible at all to set up global coordinates.

[swansont]

If the volume chosen is the universe and if the point of origin chosen is the location of the identity doing the choosing, I accept that the frame thus constructed is real. For each individual, there can be only one such frame. To me, the choice of a different volume, a different point of origin or different conditions makes the frame imaginary. In either case the coordinate type chosen is imaginary.

Such a distinction between real and imaginary frames is not made within the normal study of physics. There are just frames.

 

 

If any imaginary frame is to have any utility, that is to say that anything discovered or results achieved within it are to have any application in the real frame, there must be a translation into the real frame such that discoveries or results in the imaginary frame are consistent with those in the real frame; the "laws of physics" in an imaginary frame must be consistent, with translation, with the "laws of physics" in the real frame. My experience is that some do not seem to understand this as well as they might, thus causing some degree of confusion and so I feel it necessary for us to bring the point to the fore.

That's one of the postulates of special relativity, and as it happens all of the time anyway, it's pretty much moot. Unless you think there is someone who is going to stand inside of a vacuum system where the physics is taking place at CERN or in my lab, or anywhere else. You are making a point that everyone in physics takes as given and obvious, AFAIK.

[Fred Champion]

So you want to set up a global coordinate system. Generally you cannot do this, but it maybe okay for the observable Universe using the CMBR for example, I will have to check this. Anyway you should note that this assumes that the galaxies are point like and are interested in the large scale structure. When dealing smaller scale phenomena it may not be possible at all to set up global coordinates.

No, I do not want to set up a global coordinate system. I only point out that such a system already exists for each individual. It happens when one recognizes one's identity. The reason I felt a need to respond in this thread was because it seems there are so many who have bought into the idea that setting up a frame of reference somehow produces a real environment which is somehow isolated from the real universe. We can see that in any number of posts in the Relativity threads. The first part of swansont's post (#24) confirms that the distinction is not generally driven home to students. I suspect this is done to avoid giving students the idea that relativity is illusion, but that's another topic.

 

As for our view of the observable universe and the notion of expansion, inflation or whatever is the latest, it seems like speculation to me. I do have one problem with explanations of the cosmic background radiation, inflation, expansion and all the rest and that problem is when the word "is" is used. I really do wish those reporting or commenting would remember that what we observe is not current but history; at least that's what we're told. Statements such as "the universe is expanding" make me wonder about those who voice them.

 

I don't know about treating galaxies as point like, but I am not willing to accept that the "laws of physics" are different for objects of different size. In the case of everything in the universe I buy into the idea that one size does fit all. Now I'm not saying that we should describe a pizza or the process of baking one in terms of the quarks that make up the dough and cheese, just that whatever is happening at every scale is directly connected and is part of the same system. But, this is a different topic, too.

Such a distinction between real and imaginary frames is not made within the normal study of physics. There are just frames.

 

 

That's one of the postulates of special relativity, and as it happens all of the time anyway, it's pretty much moot. Unless you think there is someone who is going to stand inside of a vacuum system where the physics is taking place at CERN or in my lab, or anywhere else. You are making a point that everyone in physics takes as given and obvious, AFAIK.

You are correct of course. I think the fact that the distinction is not made and is not driven home to students has caused confusion. There are lots of folks out there who believe that math and geometry were discovered, not invented. Old hands see the forest, new ones may see only the trees.