Relativity acceleration paradox?

[Erasmus00]

You might want to stick to just two trains if you want to make this challenging. If you include three trains and they can see each other on paralell tracks, the answer seems obvious. For two trains, see my post above about the space ship scenarios.

 

No windows.

-Will

[Erasmus00]

Even without any reference points, the fact is that in your spaceship scenario, you can tell. The REALITY of the situation is that an amount of force was necessary to set one or both ships in motion.

 

Say the rocket ship starts on Earth. How fast is the Earth moving? Is the Earth moving? We can measure the Earth's velocity relative to the Sun, but is the Sun moving? If you are drugged, and wake up in a train on very smooth tracks how do you tell if its moving? Without the ability to define some absolute point, all motion must be relative.

-Will

[EWright]

Say the rocket ship starts on Earth. How fast is the Earth moving? Is the Earth moving? We can measure the Earth's velocity relative to the Sun, but is the Sun moving?[/Quote]

 

No earth. No sun. :)

[EWright]

If you are drugged, and wake up in a train on very smooth tracks how do you tell if its moving? Without the ability to define some absolute point, all motion must be relative. [/Quote]

 

Please tell me you see the flaw in this question.

[Erasmus00]

No earth. No sun. :)

 

Fine, if the whole universe is just those two rocket ships, how do they know they weren't moving before they accelerated? How do they know they didn't START with some motion?

-Will

[EWright]

Fine, if the whole universe is just those two rocket ships, how do they know they weren't moving before they accelerated? How do they know they didn't START with some motion?

-Will

 

Then what started their motion? There must be a force involved, thus I have already answered this question. If nothing else exists in the universe, then the only force that could cause the movement of the two ships is the gravitational attraction of the ships themselves. If both are equal in mass, then the rate of attraction would be equal between them and both would be moving and at the same speed. If they were not equal in mass, the ship with less mass would be moving faster as it is more strongly attracted by the heavier mass object. You can still argue the perspective matter based on relativity theories, but this is in fact what would ACTUALLY happen, not the perspective. If the two know the mass of their ships, they should be able to calculate who is accelerating relative to each other.

[Erasmus00]

Then what started their motion? There must be a force involved, thus I have already answered this question. If nothing else exists in the universe, then the only force that could cause the movement of the two ships is the gravitational attraction of the ships themselves. If both are equal in mass, then the rate of attraction would be equal between them and both would be moving and at the same speed. If they were not equal in mass, the ship with less mass would be moving faster as it is more strongly attracted by the heavier mass object. You can still argue the perspective matter based on relativity theories, but this is in fact what would ACTUALLY happen, not the perspective. If the two know the mass of their ships, they should be able to calculate who is accelerating relative to each other.

 

You assume they knew their initial state at the begininng of the universe. Imagine a universe, called into being by this very thought experiment. The universe consists of two very light space ships seperated by a very large distance (so much so that gravity can be neglected). One of the two ships was moving with a constant velocity v at time 0, right when the universe was called into being. How can each ship determine wether or not it is the one moving?

 

To be less absurd in our approach, an even simpler thought experiment, having to do with the universe we live in. How do you determine if the sun is moving, or sitting still? How about the Earth? If you woke up in a space ship, how could you tell if the space ship was moving with a constant velocity v, or standing still?

-Will

[EWright]

You assume they knew their initial state at the begininng of the universe. Imagine a universe, called into being by this very thought experiment. The universe consists of two very light space ships seperated by a very large distance (so much so that gravity can be neglected). One of the two ships was moving with a constant velocity v at time 0, right when the universe was called into being. How can each ship determine wether or not it is the one moving? [/Quote]

How much more metaphisical do we have to make this? How much more of the universe must we remove to make relativity work?

 

To be less absurd in our approach, an even simpler thought experiment, having to do with the universe we live in. How do you determine if the sun is moving, or sitting still? How about the Earth? If you woke up in a space ship, how could you tell if the space ship was moving with a constant velocity v, or standing still?

-Will

 

Huh? We do know that the earth moves around the sun and that the sun moves around the galactic center, and we even know where in the grand scheme of the milky way the sun is located and how it moves in relation to the rest of the galaxy. And if you include this knowledge in the scenario of waking up on the spaceship, it is easly solved. You can only make your argument if you take away all the matter in the universe except for two spaceships and I have already answered that scenario.

[Erasmus00]

Huh? We do know that the earth moves around the sun and that the sun moves around the galactic center, and we even know where in the grand scheme of the milky way the sun is located and how it moves in relation to the rest of the galaxy. And if you include this knowledge in the scenario of waking up on the spaceship, it is easly solved. You can only make your argument if you take away all the matter in the universe except for two spaceships and I have already answered that scenario.

 

All the arguments you have made, the Earth moves around the sun, the sun moves around the center of the galaxy, etc. describe motion in relation to another body. The galactic center in reference to other galaxies, etc. You are, in fact, confirming special relativity, which says all motion is relative. To disprove special relativity you need to figure out some absolute way to measure velocity, which you have yet to do.

-Will

[EWright]

All the arguments you have made, the Earth moves around the sun, the sun moves around the center of the galaxy, etc. describe motion in relation to another body. The galactic center in reference to other galaxies, etc. You are, in fact, confirming special relativity, which says all motion is relative. To disprove special relativity you need to figure out some absolute way to measure velocity, which you have yet to do.

-Will

I am certainly not disputing the relative relationships of movement between the earth, sun and galaxy as I have described it. What I argue is the fact that SR would say that it is equivalent to say that the earth revolves around the sun, or the sun and everything else revolves around the earth, relatively speaking.

[Erasmus00]

I am certainly not disputing the relative relationships of movement between the earth, sun and galaxy as I have described it. What I argue is the fact that SR would say that it is equivalent to say that the earth revolves around the sun, or the sun and everything else revolves around the earth, relatively speaking.

 

You need to learn a bit more relativity. SR would not say that the sun revolves around the Earth. You can do tests to figure out which body is accelerating.

 

However, if you have two objects traveling linearly, say two meteors coming head on, then a guy on meteor A could say "I'm standing still and meteor B is coming right at me" and a guy on meteor B could say "I'm standing still, and meteor A is coming right at me." Then there is no test that can be done to determine who is correct.

-Will

[EWright]

You need to learn a bit more relativity. SR would not say that the sun revolves around the Earth. You can do tests to figure out which body is accelerating.

 

However, if you have two objects traveling linearly, say two meteors coming head on, then a guy on meteor A could say "I'm standing still and meteor B is coming right at me" and a guy on meteor B could say "I'm standing still, and meteor A is coming right at me." Then there is no test that can be done to determine who is correct.

-Will

 

I am very much open to being informed about any mistakes I may make in my understanding; and in fact I very much welcome the constructive criticisms because I am currently striving to improve my understanding of SR, as you suggest I do. However, if the two are inertial reference frames (earth and sun), my understanding is that SR says their movement is relative and that either has the right to claim it is at rest in relation to the other.

 

Whether a test can be done concerning the two persons riding meteors that are approachign each other is irrelevant. The FACT is that each is moving according to the source that set it in motion and any factors that have affected its position or speed since that time. The apparent inability of modern physics to measure this does not change that fact.

[Erasmus00]

However, if the two are inertial reference frames (earth and sun), my understanding is that SR says their movement is relative and that either has the right to claim it is at rest in relation to the other.

 

Rotation is noninertial. Rotating bodies are constantly accelerating towards the center of rotation. This isn't SR, this is physics 101.

 

 

The apparent inability of modern physics to measure this does not change that fact.

 

You don't understand the point. The fact that no test can distinguish between standing still and moving with a constant velocity v means that all motion can only be described in relative terms. Unless you find a way to define some absolute way to measure velocity, then you haven't unearthed any problem in SR. You want to define motion based on the sources that started the motion. However, the sources might be in motion relative to each other. So you have to go find THEIR sources of motion, etc, etc. Its an infinite, unsolvable, regress. It cannot be done. Your solution doesn't work.

-Will

[EWright]

Rotation is noninertial. Rotating bodies are constantly accelerating towards the center of rotation. This isn't SR, this is physics 101.

 

 

 

 

You don't understand the point. The fact that no test can distinguish between standing still and moving with a constant velocity v means that all motion can only be described in relative terms. Unless you find a way to define some absolute way to measure velocity, then you haven't unearthed any problem in SR. You want to define motion based on the sources that started the motion. However, the sources might be in motion relative to each other. So you have to go find THEIR sources of motion, etc, etc. Its an infinite, unsolvable, regress. It cannot be done. Your solution doesn't work.

-Will

 

Again, the fact that you can not measure it, does not mean it isn't so, whether my solution works or not (which given the variables I mentioned, it does. Perhaps it does not under different circumstances.) If SR can not measure the speeds of an objects motion, than it is not a complete theory, now is it?

[Erasmus00]

If SR can not measure the speeds of an objects motion, than it is not a complete theory, now is it?

 

SR contends that there is no such thing as absolute motion. You can't measure what doesn't exist. Given that the relativity of motion is pretty much the starting point of the relativity theory, you must not have gotten very far in your study. To make corrections to a theory, you must first understand it. I'd highly recommend "An Introduction to Mechanics" By Kleppner and Kolenkow. It covers a bit of intro physics, and does a nice bit of special relativity at the end, though the 4-vector notation is a bit out dated.

-Will

[EWright]

SR contends that there is no such thing as absolute motion. You can't measure what doesn't exist. Given that the relativity of motion is pretty much the starting point of the relativity theory, you must not have gotten very far in your study. To make corrections to a theory, you must first understand it. I'd highly recommend "An Introduction to Mechanics" By Kleppner and Kolenkow. It covers a bit of intro physics, and does a nice bit of special relativity at the end, though the 4-vector notation is a bit out dated.

-Will

The relativity of motion is not the basis of my theory. It is something you and I got sidetracked on. As for your comments on motion, I am finding now that you are contradicting yourself.

[Erasmus00]

The relativity of motion is not the basis of my theory.

 

No, you won't discuss your theory. However, the relativity of motion is the basis of SR, which is actually what we were talking about.

-Will