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

[Delta1212]

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.

Well, yes, each person is only ever in their own frame of reference, but if everyone is in their own frame, that's hardly one global frame.

[ajb]

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.

So I sit at some location in space-time. I then place three rules on my head at right angles to each other and have a clock in hand. I have a local coordinate system centered on myself. Surely any construction like this is local as we have space-time geometry to consider? I might be able to pick different coordinate systems, but unless we have very nice geometry picking global coordinates is not possible.

 

(Locally we can always pick coordinates that reduce the non-gravitational physics to special relativity.)

 

I suspect this is done to avoid giving students the idea that relativity is illusion, but that's another topic.

I have a feeling that whatever argument you have here could apply to all of physics. If the theory makes measurable predictions that agree well with nature then in what sense is in an illusion or not?

 

Statements such as "the universe is expanding" make me wonder about those who voice them.

This is based on observations being compared to models of cosmology. In fact from very few assumptions you realise that in the framework of general relativity or even Newtonian cosmologies that a static universe is unstable.

 

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.

This is standard cosmology of the large scale structure of the Universe. The interactions of individual stars in galaxies makes no difference to the large scale dynamics. In fact in cosmology it is normal to take clusters of galaxies to be points. Again the local interaction of the galaxies in the clusters can safely be ignored.

 

In the case of everything in the universe I buy into the idea that one size does fit all.

In principal we all agree with this, but in practice we need to make simplifying assumptions and take certain limits to get at the physics we wish to describe. This is particularly true of very large ensembles of objects.

 

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.

Sure, but we have very good effective theories that work well. You are right, we should in principal be able to calculate the properties of a given pizza from the standard model. But with so many particles and the fact we really want to know macroscopic properties we shift away from a fundamental individual particle description to a simpler phenomenological description. In this case we should consult a food scientist for details.

 

There are lots of folks out there who believe that math and geometry were discovered, not invented.

I think that is a very different and philosophical question.

[Fred Champion]

So I sit at some location in space-time. I then place three rules on my head at right angles to each other and have a clock in hand. I have a local coordinate system centered on myself. Surely any construction like this is local as we have space-time geometry to consider? I might be able to pick different coordinate systems, but unless we have very nice geometry picking global coordinates is not possible.

 

...

 

We are "inside" the universe and cannot isolate ourselves from it. We cannot look at it, or any part of it, from any point of viewing other than our own. We cannot isolate any part of the universe from the whole. Every coordinate system we might choose other than our own is imaginary. The only "real" coordinate system we have is the one where we "sit at some location in space-time". There is no other location where we may sit in space-time. This location is the origin of our one and only real universal global prefered frame of reference.

 

We may not sit at the center of mass of the universe, or at the location occupied by the singularity prior to the "beginning", or at the center of the limits of the universe (if there are limits) but I don't see why that would matter. The Earth does not sit at the center of the solar system, but we were able to discern the real configuration of the solar system. I don't know whether or not we have been able to discern the true configuration of the universe yet, but I expect that there is a true configuration.

 

Today it seems that the speed of light prevents us from knowing what "is". My objection to people saying the universe "is" expanding is that they also say the evidence they have of that expansion is several billion years old. My understanding is that the galaxies closest to us are getting closer. It seems to me that this observation might imply that a contraction has already begun. Better to say that the universe "was" expanding several billion years ago and might even be contracting today.

[ajb]

We are "inside" the universe and cannot isolate ourselves from it. We cannot look at it, or any part of it, from any point of viewing other than our own.

Because of the way the laws of physics work, I can make prediction here in my office as to what Swansont will measure in his lab. We can compare these and see that we agree. Even more, based on Swansont's lab results I know how that experiment will act in my lab (if I had one).

 

There is no reason why I can only have an understanding of physics exactly at my location.

 

We cannot isolate any part of the universe from the whole.

True, but if objects far away have practically no effect on my experiment then I can effectively isolate the experiment from the rest of the Universe. For example if I want to study how the period of a pendulum in my office varies with changing the length of the cord, then I don't really need to worry about how the motion of Jupiter effects this.

 

Every coordinate system we might choose other than our own is imaginary.

All coordinate systems are imaginary in the sense that they are an abstraction of nature that allows us to compare lengths and durations.

 

The only "real" coordinate system we have is the one where we "sit at some location in space-time".

Okay, as I can set up many local coordinate systems centered on me.

 

There is no other location where we may sit in space-time.

Okay, but as I said, I do know what is going on in Swansont's lab and can make predictions here in my office as to what he will see. I am able to change the reference frames so that Swantsont and I can compare physics.

 

This location is the origin of our one and only real universal global prefered frame of reference.

Not preferred in any sense as we usually mean it and global I doubt. GR tells us, due to the presence of singularites really, that global coordinate systems are not usually allowed.

 

We may not sit at the center of mass of the universe, or at the location occupied by the singularity prior to the "beginning", or at the center of the limits of the universe (if there are limits) but I don't see why that would matter.

But if we have sensible coordinate systems that we can patch together covering all the space-time in question (let us cut out singularites) then I know how to describe physics across all of that space-time.

 

Really this is the power of differential geometry in classical physics. With a little care it just does not matter what coordinate system I use. I can change coordinates and "patch" the local physics across all space-time.

 

The Earth does not sit at the center of the solar system, but we were able to discern the real configuration of the solar system.

We are at liberty to pick a coordinate system for which the Earth is stationary and consider the Sun, Moon and planets as going around the Earth. The trouble is the physics is messy. It is better to pick a coordinate system that respects the natural symmetry here, i.e. pick the center of mass frame of the solar system. This places the center of the Sun as just about the center of the solar system.

 

 

I don't know whether or not we have been able to discern the true configuration of the universe yet, but I expect that there is a true configuration.

I don't know what you mean by true configuration, but we have a good idea now of the history of the Universe.

 

Today it seems that the speed of light prevents us from knowing what "is". My objection to people saying the universe "is" expanding is that they also say the evidence they have of that expansion is several billion years old. My understanding is that the galaxies closest to us are getting closer. It seems to me that this observation might imply that a contraction has already begun. Better to say that the universe "was" expanding several billion years ago and might even be contracting today.

Your misconception here is common. The important thing is that the expansion of the Universe is only on the very large scale. We only see it when we think of clusters of galaxies as being "point-like objects". The local gravitational attraction keeping the galaxies in bound clusters is more than enough to overcome the global tenancy for expansion, at least the expansion today.

[swansont]

We are "inside" the universe and cannot isolate ourselves from it.

Nobody has claimed otherwise.

 

We cannot look at it, or any part of it, from any point of viewing other than our own.

False. Cameras exist. Detectors exist.

 

We cannot isolate any part of the universe from the whole. Every coordinate system we might choose other than our own is imaginary.

 

So? Why is this relevant?

 

The only "real" coordinate system we have is the one where we "sit at some location in space-time". There is no other location where we may sit in space-time. This location is the origin of our one and only real universal global prefered frame of reference.

Not preferred in the sense used by physics. It's difficult conversing when you are using a different definition of the word.

 

We may not sit at the center of mass of the universe, or at the location occupied by the singularity prior to the "beginning", or at the center of the limits of the universe (if there are limits) but I don't see why that would matter. The Earth does not sit at the center of the solar system, but we were able to discern the real configuration of the solar system. I don't know whether or not we have been able to discern the true configuration of the universe yet, but I expect that there is a true configuration.

Until you can figure a way to show this, you can't lay claim to the notion of a preferred frame.

 

[Lazarus]

Fred Champion said:

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.

 

 

Just for fun, here is an example of measuring hypersonic speed with sound.

 

Position yourself with a stopwatch equidistant from 2 mountan peaks a known distance apart..

Have a F16 buzz over the 2 peaks at a couple thousand MPH and fire off a noisy missile as

it passes each peak. The time difference of the 2 sounds lets you calculate the F16's speed.

[Fred Champion]

Fred Champion said:

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.

 

 

Just for fun, here is an example of measuring hypersonic speed with sound.

 

Position yourself with a stopwatch equidistant from 2 mountan peaks a known distance apart..

Have a F16 buzz over the 2 peaks at a couple thousand MPH and fire off a noisy missile as

it passes each peak. The time difference of the 2 sounds lets you calculate the F16's speed.

In your example you are cheating. You are using light to determine that the jet travels over the peaks.

 

You may hear two booms two seconds apart but you cannot determine where they were generated nor what generated them unless you look. Unless your pilot is also cheating by looking or using radar how does he know when to fire the missles?

 

You cannot set up and run the experiment with any degree of certainty without using light.

[Lazarus]

Fred Champion said:

You cannot set up and run the experiment with any degree of certainty without using light.

 

It seems even a blind man could perform this experiment. Put a computer in charge of the F16 and the pilot could be blind, too.

Or, just do it in the dark.

 

Cheers

[Fred Champion]

Fred Champion said:

You cannot set up and run the experiment with any degree of certainty without using light.

 

It seems even a blind man could perform this experiment. Put a computer in charge of the F16 and the pilot could be blind, too.

Or, just do it in the dark.

 

Cheers

And so the computer would know when to fire the missles? How, using radar (EMR)? And you would know that the noise (maybe both) was not from another source? How? You could not tell that the aircraft was even flying until it had passed, so when did the experiment begin? You could not tell that any of the conditions of the experiment were met using only sound. How would you know the aircraft was on the correct flight path, the missles were fired exactly on time, flew at exactly the correct speed, in exactly the right direction and exploded exactly on time without using light or radar? Your blind man cannot tell the difference between a sonic boom, an explosion and a clap of thunder.

 

Using touch, and not sound or light (EMR), we can measure velocity up to the point where we lose contact with the moving object. Adding sound frees us from the restrictions of touch and we can measure velocity up to the point where the object reaches Mach 1. Adding light (theorectically) allows us to measure velocity up to close to the speed of light. And if an object were moving faster than the speed of light, our instruments would need some other source of input faster than the speed of light to detect it.

 

The point is simply that the speed of the input to the instrument is the maximum velocity that can be detected.

[Delta1212]

And so the computer would know when to fire the missles? How, using radar (EMR)? And you would know that the noise (maybe both) was not from another source? How? You could not tell that the aircraft was even flying until it had passed, so when did the experiment begin? You could not tell that any of the conditions of the experiment were met using only sound. How would you know the aircraft was on the correct flight path, the missles were fired exactly on time, flew at exactly the correct speed, in exactly the right direction and exploded exactly on time without using light or radar? Your blind man cannot tell the difference between a sonic boom, an explosion and a clap of thunder.

 

Using touch, and not sound or light (EMR), we can measure velocity up to the point where we lose contact with the moving object. Adding sound frees us from the restrictions of touch and we can measure velocity up to the point where the object reaches Mach 1. Adding light (theorectically) allows us to measure velocity up to close to the speed of light. And if an object were moving faster than the speed of light, our instruments would need some other source of input faster than the speed of light to detect it.

 

The point is simply that the speed of the input to the instrument is the maximum velocity that can be detected.

So how would you measure speeds below that of sound using sound without using light?

[Sensei]

One cannot measure (...) nor super-light speeds using light.

 

I think so it's possible, but there must be meet couple requirements:

- faster than light object must be approaching us (not perfectly directly), not receding.

- faster than light object must be reflecting light.

 

Suppose so faster than light object is flying with v = 2c to Earth, at t = 0 it's 100*c distance from us.

We're sending photons in that direction (without knowing about object - similar like active radar is working), and photons are reflected from it somewhere around 33-34 seconds later, and then going back to us after 66-68 seconds after sending them.

 

In the mean time object is long time gone. So we cannot perform yet another test.

 

If we would be sending photons continuously in the all directions, we could see that object to be receding from us (photons send later by us, would return quicker, after reflection, than those send earlier!).

 

[Kramer]

 

Sensey

I don’t know a law, even in physic, that suma of two sides of a triangle to be less that the third. Am I wrong? Or I misunderstand your idea in your post?

[Sensei]

Sensey

I don’t know a law, even in physic, that suma of two sides of a triangle to be less that the third. Am I wrong?

They don't have to match..

 

Horizontal axis is time. Vertical axis is distance from us in c unit (1=~300,000 km)

 

Or I misunderstand your idea in your post?

I think so.

 

It's purely theoretical.

 

Imagine that mirror is approaching at v=2c. We have laser and sending beam of photons at that mirror. Mirror is reflecting laser to us and we measure delay between sending, and receiving.

 

After 33-34 second that red line should be going back to bottom. I was just interested in intersection time.

Edited June 22, 2014 by Sensei