Specific Relativity/Light-Speed Question

[EWright]

That isn't true. There is no force required to move at a constant velocity. It would require no repulsive force at all. That is Newtonian physics.

 

 

 

That also is not true. Conservation of momentum holds in ANY inertial frame, not only in the sun's rest frame, as you claim.

-Will

Bull and Bull. In order for the particle to be stationary, the earth and sun have to be moving away from it. Something would have to put the earth and sun in motion relative to it, from the moment of its creation.

 

I am not only considering the inertial frame of the sun. Consider the inertial frames of all three objects as I expressed it and it can not be true that the sun is moving away from them both at the same time.

[Erasmus00]

Bull and Bull. In order for the particle to be stationary, the earth and sun have to be moving away from it. Something would have to put the earth and sun in motion relative to it, from the moment of its creation.

 

You are correct. The particle could measure its acceleration. However, it has no way to determine wether or not the sun was moving when the sun spit it out. And that acceleration defines only relative velocity to the sun. It does NOT define an absolute velocity. Consider this thought experiment: an astronaut leaves from Earth, and figures out his velocity relative to earth to be v. Another astronaut leaves from planet Y and accelerates to a velocity w. The two rockets meet, head on, and measure their relative velocity to be u=w-v. (since you think relativity is wrong, I'm falling back on Galilean relativity) They come to the conclusion that one of the planets, either the Earth or Planet Y must be moving with a speed u. Which planet is the one that is moving? How do you know?

 

I am not only considering the inertial frame of the sun. Consider the inertial frames of all three objects as I expressed it and it can not be true that the sun is moving away from them both at the same time.

 

You implied conservation of momentum forbid you to look at any one particle's frame. This simply is not true. That is mechancis. Also, before you try to rewrite modern physics, I suggest learning at least classical physics.

-Will

[EWright]

it has no way to determine wether or not the sun was moving when the sun spit it out.[/Quote]

 

This says to me that the sun sent it on its way and hence gave it the momentum. Furthermore, if you apply this to a photon spit out by the sun and make the photon stationary, it means that the sun is moving away at light speed. Not possible. If it is a particle spit out at .8c, and the particle is stationary, how the hell did the sun reach .8c and what does that do to the earth's orbit around it?

 

Consider this thought experiment: an astronaut leaves from Earth, and figures out his velocity relative to earth to be v. Another astronaut leaves from planet Y and accelerates to a velocity w. The two rockets meet, head on, and measure their relative velocity to be u=w-v. (since you think relativity is wrong, I'm falling back on Galilean relativity) They come to the conclusion that one of the planets, either the Earth or Planet Y must be moving with a speed u. Which planet is the one that is moving? How do you know?

[/Quote]

 

 

Because the second astronaut accelerated is has no implications on the speed of his planet. The question doesn't work. The speed of the motion of the planets is irrelevant and there are too many variables and not enough information given to determine the actual answer.

 

You implied conservation of momentum forbid you to look at any one particle's frame. This simply is not true. That is mechancis. Also, before you try to rewrite modern physics, I suggest learning at least classical physics.

-Will

 

No, I'm looking at the big picture rather than one PERSPECTIVE.

[Erasmus00]

This says to me that the sun sent it on its way and hence gave it the momentum. Furthermore, if you apply this to a photon spit out by the sun and make the photon stationary, it means that the sun is moving away at light speed. Not possible. If it is a particle spit out at .8c, and the particle is stationary, how the hell did the sun reach .8c and what does that do to the earth's orbit around it?

 

A photon is not an inertial frame. No Lorentz boost can connect a photon frame and a frame traveling at a lesser speed. Relativity only says all inertial frames are equivalent. Now, lets say two solar systems comes together and slam into each other. Each system will think the other is the moving one, which one is right?

 

Now, your problem with relativity seems to be that you think its possible to define absolute motion. (i.e., motion isn't a relative thing). How would you define your absolute frame?

 

No, I'm looking at the big picture rather than one PERSPECTIVE.

 

Relativity says all motion is relative, but quotes like this seem to indicate that there is an absolute frame, a "bigger picture." How would you define your absolute frame?

-Will

[EWright]

A photon is not an inertial frame. No Lorentz boost can connect a photon frame and a frame traveling at a lesser speed. Relativity only says all inertial frames are equivalent. [/Quote]

 

You're so predictable, hence I offered the particles at .8c in opposite directions relative to the sun scenario; but I see you skirted that example.

 

I also see you didn't defend your u=w-v example or whatever it was.

 

Now, lets say two solar systems comes together and slam into each other. Each system will think the other is the moving one, which one is right? [/Quote]

 

They are both right to a degree. And that degree would indeed depend on factors of a larger framework, which would be outide of my abilities to define definitively. I could generalize using my theory, however. But using current ideas as the basis, and if possible, it would be most relevant to relate the solar systems to their rotation around the center of the galaxy; presumably the black hole at that location. This is getting a bit 'out there,' but so is the line of questioning. However, if we have precise enough measurements and knew the positional history of both systems, it would be apparent, which was crashing into the other and to what degree.

 

Now, your problem with relativity seems to be that you think its possible to define absolute motion. (i.e., motion isn't a relative thing). How would you define your absolute frame?

 

Relativity says all motion is relative, but quotes like this seem to indicate that there is an absolute frame, a "bigger picture." How would you define your absolute frame?

-Will

 

Well there is always a bigger frame of reference, now isn't there?

[Qfwfq]

Cool it boys, cool it These boards are meant for reasonable discussion.

 

Erasmus, I have seen that you are quite competent but please avoid "this is right, that is wrong" type of arguments. It doesn't prove anything and doesn't help him where he doesn't understand.

 

EWright, there's no use calling your famous theory in cause when you never illustrate it or discuss it. You might as well say that you're a Jedi and that the Force is with you. Also, avoid losing your temper. I'll close the thread if necessary.

 

Well there is always a bigger frame of reference, now isn't there?

What does "a bigger frame of reference" mean?

[Erasmus00]

EWright, I want some clarification on your point of view. You claim a rocket fired from Earth knows its moving because it accelerated. Thats fine, that references your rocket to the Earth. So to know the rocket's speed, we must know the Earth's. So you say we measure the Earth's speed around the sun. But now we need to know the speed of the sun,etc,etc.

 

That process keeps referencing the motion of your rocket to larger and larger systems, but if at any point you can't determine the motion of your new system, the whole scheme falls apart. If you can't determine the motion of the sun, you can't determine the motion of the rocket.

 

Now, it seems to me that eventually you'll hit some "center of the universe" type point if you follow your chain all the way. Now, how would you determine if your center of the universe is sitting still or travelling at a constant velocity?

-Will

[EWright]

Cool it boys, cool it These boards are meant for reasonable discussion.

 

Erasmus, I have seen that you are quite competent but please avoid "this is right, that is wrong" type of arguments. It doesn't prove anything and doesn't help him where he doesn't understand.

 

EWright, there's no use calling your famous theory in cause when you never illustrate it or discuss it. You might as well say that you're a Jedi and that the Force is with you. Also, avoid losing your temper. I'll close the thread if necessary.

 

What does "a bigger frame of reference" mean?

 

Qfwfq, Relax. I don't think that either Erasmus or myself are losing our tempers or being rude. I certainly have not felt offended by him and I thirst for the constructive criticism and feedback. Let us not be overly sesitive please. And if I use the rant smilie, it's because I think he's humorous, not because I'm genuinely angry. I take more offense to your reference to my "famous" theory than I do E's posts, because it is obviously meant as a poke. E and I, on the other hand, are attempting to have a constructive and challenging conversation.

 

Thank you

[Qfwfq]

I take more offense to your reference to my "famous" theory than I do E's posts, because it is obviously meant as a poke.

It is only meant in the sense that you keep mentioning it, to no avail at all

 

E and I, on the other hand, are attempting to have a constructive and challenging conversation.

Where is it getting?

 

Like Erasmus, I can see where you misunderstand the principle of relativity. I don't call this a constructive and challenging conversation. Do you understand what is meant by inertial coordinate system?

[EWright]

EWright, I want some clarification on your point of view. You claim a rocket fired from Earth knows its moving because it accelerated. Thats fine, that references your rocket to the Earth. So to know the rocket's speed, we must know the Earth's. So you say we measure the Earth's speed around the sun. But now we need to know the speed of the sun,etc,etc.

 

That process keeps referencing the motion of your rocket to larger and larger systems, but if at any point you can't determine the motion of your new system, the whole scheme falls apart. If you can't determine the motion of the sun, you can't determine the motion of the rocket.

 

Now, it seems to me that eventually you'll hit some "center of the universe" type point if you follow your chain all the way. Now, how would you determine if your center of the universe is sitting still or travelling at a constant velocity?

-Will

 

I was saying that you can not measure which planet is moving at speed u in your example because of the acceleration factor. If the rocket can choose independantly whether it wants to accelerate to .2c, .7c, etc... then it's speed when it encounters the other rocket has no bearing on the speed the planet was moving at when it left. It has full control over its speed and thus has the ability to alter the perception the other ship has of its speed.

 

I have tried to answer your challenges when you propose them. I would still like a response to the two particles ejected from the sun in opposite directions problem that I proposed; one which includes all three reference frames yet shows each particle has the right to claim it is at rest. The other particle's frame must be included in the explanation, not just one particle relative to the sun please.

 

And in case you didn't read my above post to the moderator, I do appreciate your challenges and I am not offended by them. I hope you are not offended by mine either.

[Erasmus00]

With regards to the rocket relative motion problem I proposed, I think the question of determining the speed of the "center of the universe" point goes more to the heart of the matter. See my previous post.

 

I have tried to answer your challenges when you propose them. I would still like a response to the two particles ejected from the sun in opposite directions problem that I proposed; one which includes all three reference frames yet shows each particle has the right to claim it is at rest. The other particle's frame must be included in the explanation, not just one particle relative to the sun please.

 

Alright, I'm going to do an analysis assuming non-relativistic speeds (galilean relativity), only because it is easier for explanatory purposes. If you want a full-on relativisitc treatment, nearly everything is the same, just private message me.

 

Now, to quantify this (and to present a simple case), consider the case of a particle of mass M that explodes into two pieces of mass M/2. In the frame of the mass that exploded, the momentum before the explosion is 0, and the two pieces travel in opposite directions, at some speed v<<c (here again, I wish to use galilean relativity).

 

Now lets go into the frame of one of the pieces of the explosion. (either one, its symmetrical). This frame is moving with speed v relative to the original mass M (using galilean relativity). The total momentum before the explosion is then Mv. After the explosion, one piece is at rest, and the other traveling at a speed 2v. The total momentum is M/2*2v=Mv and we see momentum is conserved in this frame as well. Momentum is conserved in any inertial frame.

 

And in case you didn't read my above post to the moderator, I do appreciate your challenges and I am not offended by them. I hope you are not offended by mine either.

 

No worries, I take no offense at anything.

-Will

[EWright]

With regards to the rocket relative motion problem I proposed, I think the question of determining the speed of the "center of the universe" point goes more to the heart of the matter. See my previous post.

 

 

 

Alright, I'm going to do an analysis assuming non-relativistic speeds (galilean relativity), only because it is easier for explanatory purposes. If you want a full-on relativisitc treatment, nearly everything is the same, just private message me.

 

Now, to quantify this (and to present a simple case), consider the case of a particle of mass M that explodes into two pieces of mass M/2. In the frame of the mass that exploded, the momentum before the explosion is 0, and the two pieces travel in opposite directions, at some speed v<<c (here again, I wish to use galilean relativity).

 

Now lets go into the frame of one of the pieces of the explosion. (either one, its symmetrical). This frame is moving with speed v relative to the original mass M (using galilean relativity). The total momentum before the explosion is then Mv. After the explosion, one piece is at rest, and the other traveling at a speed 2v. The total momentum is M/2*2v=Mv and we see momentum is conserved in this frame as well. Momentum is conserved in any inertial frame.

 

 

 

No worries, I take no offense at anything.

-Will

 

While I do not speak calculus, it is apparent that you are only partially correct. In order for both frames to be "symmetrical" they must (should) be equivalent. Also, if for ever action there is an equal and opposite reaction, one should also consider that both symetrical pieces of debris were effected symmetrically by the explosion. Thus each is moving away from the other at equal speeds in opposite directions.

There is also no reason the moving piece, if only one was moving, would be moving at 2v relative to its initial speed. Its speed relative to the other piece will depend on the force of the explosion, which I do not see factored in. If both pieces are affected equally, as they should be for reasons I stated, I ASSUME the equation should be something more along the lines of Mv/2 + Mv/2 = Mv.

[EWright]

Well?

[Southtown]

Thus each is moving away from the other at equal speeds in opposite directions.

Each particle would be moving away from the mass at identical velocities (Pv) in opposite directions, yes, in the frame of the mass. But, if the mass is moving, the velocity of the mass (Mv) is added to both (all) particles.

 

1.) The particle ejected in the direction that the mass is moving will be moving at Pv + Mv.

2.) The particle ejected opposite the direction that the mass is moving will be moving at Pv - Mv.

 

To know that the mass is moving requires defining another (bigger) frame of reference. Example: You're at the center of our galaxy watching the Sun circle you. One particle is emitted in direction the Sun is travelling and another particle emitted in the opposite direction. If all velocities are equal, then particle a is moving twice as fast as the Sun, and the other is stopped.

 

So let's switch frames again, to a bigger picture, if you will. You're in the next galaxy (Andromeda) and you're watching the whole show (in the previous example) going on in the Milky Way while the whole group of them are zipping past you. In which case the velocity differences between the MW galaxy center, the Sun, and both particles are so miniscule that you can barely perceive them, because the enormous velocity of the MW (relative to Andromeda) was just added to all their velocities.

[EWright]

Each particle would be moving away from the mass at identical velocities (Pv) in opposite directions, yes, in the frame of the mass. But, if the mass is moving, the velocity of the mass (Mv) is added to both (all) particles.

 

1.) The particle ejected in the direction that the mass is moving will be moving at Pv + Mv.

2.) The particle ejected opposite the direction that the mass is moving will be moving at Pv - Mv.

 

To know that the mass is moving requires defining another (bigger) frame of reference. Example: You're at the center of our galaxy watching the Sun circle you. One particle is emitted in direction the Sun is travelling and another particle emitted in the opposite direction. If all velocities are equal, then particle a is moving twice as fast as the Sun, and the other is stopped.

 

So let's switch frames again, to a bigger picture, if you will. You're in the next galaxy (Andromeda) and you're watching the whole show (in the previous example) going on in the Milky Way while the whole group of them are zipping past you. In which case the velocity differences between the MW galaxy center, the Sun, and both particles are so miniscule that you can barely perceive them, because the enormous velocity of the MW (relative to Andromeda) was just added to all their velocities.

 

I'm sorry, but you are mistaken. Both particles would be moving away from the sun at the same rate only if they are moving at the speed of light, and it has been argued in this post that a photon is not an inertial frame of reference. If we are talking particles, the particle that is trailing the sun will have more speed RELATIVE to the sun than the particle that the sun is trailing. Thus, if we can determine the speed of all three bodies/

[EWright]

With regards to the rocket relative motion problem I proposed, I think the question of determining the speed of the "center of the universe" point goes more to the heart of the matter. See my previous post.

 

 

 

Alright, I'm going to do an analysis assuming non-relativistic speeds (galilean relativity), only because it is easier for explanatory purposes. If you want a full-on relativisitc treatment, nearly everything is the same, just private message me.

 

Now, to quantify this (and to present a simple case), consider the case of a particle of mass M that explodes into two pieces of mass M/2. In the frame of the mass that exploded, the momentum before the explosion is 0, and the two pieces travel in opposite directions, at some speed v<<c (here again, I wish to use galilean relativity).

 

Now lets go into the frame of one of the pieces of the explosion. (either one, its symmetrical). This frame is moving with speed v relative to the original mass M (using galilean relativity). The total momentum before the explosion is then Mv. After the explosion, one piece is at rest, and the other traveling at a speed 2v. The total momentum is M/2*2v=Mv and we see momentum is conserved in this frame as well. Momentum is conserved in any inertial frame.

 

 

 

No worries, I take no offense at anything.

-Will

 

While I do not speak calculus, it is apparent that you are only partially correct. In order for both frames to be "symmetrical" they must (should) be equivalent. Also, if for ever action there is an equal and opposite reaction, one should also consider that both symetrical pieces of debris were effected symmetrically by the explosion. Thus each is moving away from the other at equal speeds in opposite directions.

There is also no reason the moving piece, if only one was moving, would be moving at 2v relative to its initial speed. Its speed relative to the other piece will depend on the force of the explosion, which I do not see factored in. If both pieces are affected equally, as they should be for reasons I stated, I ASSUME the equation should be something more along the lines of Mv/2 + Mv/2 = Mv.[/Quote]

 

:) Several days and I'm still waiting on a response to this one... :)

[Southtown]

I'm sorry, but you are mistaken. Both particles would be moving away from the sun at the same rate only if they are moving at the speed of light, and it has been argued in this post that a photon is not an inertial frame of reference. If we are talking particles, the particle that is trailing the sun will have more speed RELATIVE to the sun than the particle that the sun is trailing. Thus, if we can determine the speed of all three bodies/

In the frame of the Sun, the Sun isn't moving. That's why it's called a rest frame. Then the particles are equal, at least until we add velocity to the Sun via another rest frame (galaxy center.)