Specific Relativity/Light-Speed Question

[EWright]

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.)

 

Respectfully, you are still mistaken. You can make the sun the rest frame, but it will then find that one of the particles is moving at a different rate of speed than it is. This is because you are just 'calling' the sun the rest frame. Relative to whatever larger frame, if the sun has motion, it still has motion. It just "sees" itself as still, but it is not factually still. Therefore it will encounter a perplexing problem in wondering why the two particles are moving away from it at different speeds. (this assumes one in front of and one behind, in its course of direction... even though it doesn't know its moving.)

 

A metaphore I proposed before was one of a person driving a stickshift car, who is stopped on a hill waiting for the light to change. He looks to his right and sees the car next to him advancing forward, even though the light is still red. SR says he can assume he's the one at rest after all, right? But when he smacks into the truck behind him, only then does he realize that the other car was stationary and he was actually rolling backwards. For any visual measurements taken between the two's line of sight, SR holds true. But when you smack into the truck behind you, REALITY tells you they are NOT equivalent and both drivers do NOT have the right to assume they are the one at rest. The reality is that only one of them (in this particular case) was moving. The inability to be able to tell which is moving due to deliberately narrowing the playing field, does not nullify the overall reality of the situation.

[Southtown]

Respectfully, you are still mistaken. You can make the sun the rest frame, but it will then find that one of the particles is moving at a different rate of speed than it is.

Why is that? Weren't the particles simultaneously ejected at equal velocities in opposing directions? What happened to alter them?

 

This is because you are just 'calling' the sun the rest frame. Relative to whatever larger frame, if the sun has motion, it still has motion. It just "sees" itself as still, but it is not factually still.

Agreed. All frames of reference are assumed.

 

Therefore it will encounter a perplexing problem in wondering why the two particles are moving away from it at different speeds. (this assumes one in front of and one behind, in its course of direction... even though it doesn't know its moving.)

Disagree, unless the Sun changed velocity, or the particles changed velocity (via wind resistance or whatever) the Sun will notice no such thing because the particles will inherit the velocity of the Sun (unless they are photons.)

 

A metaphore I proposed before was one of a person driving a stickshift car, who is stopped on a hill waiting for the light to change. He looks to his right and sees the car next to him advancing forward, even though the light is still red. SR says he can assume he's the one at rest after all, right? But when he smacks into the truck behind him, only then does he realize that the other car was stationary and he was actually rolling backwards. For any visual measurements taken between the two's line of sight, SR holds true. But when you smack into the truck behind you, REALITY tells you they are NOT equivalent and both drivers do NOT have the right to assume they are the one at rest. The reality is that only one of them (in this particular case) was moving. The inability to be able to tell which is moving due to deliberately narrowing the playing field, does not nullify the overall reality of the situation.

"Reality" is relative, meaning velocity depends on the frame of reference. When the frame was an adjacent car, Mr. Mojo was motionless, but when the frame changed to the truck, Mr. Mojo's motion changed, too. Of course this is all relative. If the cars were facing North, Mr. Mojo would actually be travelling southeasterly because of the rotation of the earth (bigger frame/greater reality defined.)

 

Point is, there is no "real" velocity. Velocity can only be measured against a frame of reference. You keep alluding to a "greater" frame of reference called "reality" without defining it. Imagine flying through space, except there are no stars, planets, quasars, nothing. Just you and cold, black vaccuum. How would you know if you were moving?

 

You wouldn't. Even if a single star flew past you, was it moving or were you? It depends completely on the frame of reference.

[EWright]

Why is that? Weren't the particles simultaneously ejected at equal velocities in opposing directions? What happened to alter them?

 

 

Agreed. All frames of reference are assumed.

 

 

Disagree, unless the Sun changed velocity, or the particles changed velocity (via wind resistance or whatever) the Sun will notice no such thing because the particles will inherit the velocity of the Sun (unless they are photons.)[/Quote]

 

I do thank you for helping me to understand this, but I still disagree strongly. Nothing had to alter the particles' velocities. We are discussing the situation with all bodies in motion. The particles are on opposite sides of the sun, in front and rear of its direction. If the sun were still, you would be correct. But the fact that we are stating that the sun is in motion, automatically references it to a larger frame. ie, What is in motion relative to? If ur driving down the road and from the front of your car you launch a tennis ball in front of and behind you, they will not adapt the car's motion as they would inside the vehicle because they're now outisde of the car's reference frame. If the sun is in motion and ejects the particles at equal speeds, the relative forward motion of the forward ejected particle will be reduced by the speed of the sun in its direction. Just the opposite will hold true for the other particle.

 

"Reality" is relative, meaning velocity depends on the frame of reference. When the frame was an adjacent car, Mr. Mojo was motionless, but when the frame changed to the truck, Mr. Mojo's motion changed, too. Of course this is all relative. If the cars were facing North, Mr. Mojo would actually be travelling southeasterly because of the rotation of the earth (bigger frame/greater reality defined.)[/Quote]

 

Nothing to do with directions here... they're on a hill... gravity is all that matters. The visual frame of reference never has to change to the truck. Mr. Mojo realizes he was the one moving upon impact. SR told him he had an equal right to say he was the one at rest. But then how did he smack into that truck if the truck wasn't moving?

 

Point is, there is no "real" velocity. Velocity can only be measured against a frame of reference. You keep alluding to a "greater" frame of reference called "reality" without defining it. Imagine flying through space, except there are no stars, planets, quasars, nothing. Just you and cold, black vaccuum. How would you know if you were moving?

 

You wouldn't. Even if a single star flew past you, was it moving or were you? It depends completely on the frame of reference.

 

It seems you are trapped inside of Enstein's box as well. I must again ask why SR must always remove all external reference points to make itself work. This is because it is demonstrating a means of measuring TWO things relative to one another. It does not encompass the larger reality fully.

[Guest loarevalo]

I have a question also:

 

Someone X leaves earth and travels at the speed of light, then returns to earth, and finds out that 100 years have passed on earth, yet X's watch marks that 0 time has passed.

 

Was that at least theoretically acurate?

 

If so, then in X's reference frame X was traveling at infinite speed ( traveled some distance under 0 time). Is that correct?

[EWright]

I have a question also:

 

Someone X leaves earth and travels at the speed of light, then returns to earth, and finds out that 100 years have passed on earth, yet X's watch marks that 0 time has passed.

 

Was that at least theoretically acurate?

 

If so, then in X's reference frame X was traveling at infinite speed ( traveled some distance under 0 time). Is that correct?

 

Due to the mistaken perceptions of SR, yes, that is basically correct... but not possible. However, relativists avoid this paradox by throwing in that you inertial reference frames do not apply to light. Scientifically, why is this exactly?

[Southtown]

If ur driving down the road and from the front of your car you launch a tennis ball in front of and behind you, they will not adapt the car's motion as they would inside the vehicle because they're now outisde of the car's reference frame. If the sun is in motion and ejects the particles at equal speeds, the relative forward motion of the forward ejected particle will be reduced by the speed of the sun in its direction. Just the opposite will hold true for the other particle.

In the car example, wind resistance and gravity will slow the balls because they aren't countering that resistance with a gas guzzling v8. In space, the particles will retain their exact ejection velocity plus the Sun's velocity. The particles will even gravitate back to the Sun at the same time.

 

The Sun will not catch up to one and leave the other behind as if wind resistance were involved. Velocity is inherited. So much so that if you are moving in space and throw a ball 90 degrees perpendicular to your path at velocity equal to yours, it will forever travel at 45 degrees to your path, and not 90.

 

If you throw a ball out the driver window while driving north, will the ball be travelling immediately due west? Or will it appear to hover out the window for a short time and travel slowly away from the car? Until wind resistance decreases its northward velocity and gravity takes it down?

 

Nothing to do with directions here... they're on a hill... gravity is all that matters. The visual frame of reference never has to change to the truck. Mr. Mojo realizes he was the one moving upon impact. SR told him he had an equal right to say he was the one at rest. But then how did he smack into that truck if the truck wasn't moving?

How did Mr. Mojo know the truck did not hit him from the rear until he referenced the ground, buildings, etc.? As far as he knew, looking at an adjacent car and feeling a rear impact, the other two vehicles could have seemed to both be moving forward. I'm not saying that was the case, I'm just saying he needed to define his greater frame of reference in order to get the right measurements.

 

It seems you are trapped inside of Enstein's box as well. I must again ask why SR must always remove all external reference points to make itself work. This is because it is demonstrating a means of measuring TWO things relative to one another. It does not encompass the larger reality fully.

I don't even understand relativity, but removing some references makes math simpler. If you want to factor in external forces then you have to define them. And I'm definitely not trapped in Einstein's box. (HAHA) I do NOT think that reality is subject to the math used to describe it. Atomic time isn't even consistent with orbital time according to Tom Van Flandern. (http://www.metaresearch.org)

[EWright]

In the car example, wind resistance and gravity will slow the balls because they aren't countering that resistance with a gas guzzling v8. In space, the particles will retain their exact ejection velocity plus the Sun's velocity. The particles will even gravitate back to the Sun at the same time.

 

The Sun will not catch up to one and leave the other behind as if wind resistance were involved. Velocity is inherited. So much so that if you are moving in space and throw a ball 90 degrees perpendicular to your path at velocity equal to yours, it will forever travel at 45 degrees to your path, and not 90.

 

If you throw a ball out the driver window while driving north, will the ball be travelling immediately due west? Or will it appear to hover out the window for a short time and travel slowly away from the car? Until wind resistance decreases its northward velocity and gravity takes it down?

 

 

How did Mr. Mojo know the truck did not hit him from the rear until he referenced the ground, buildings, etc.? As far as he knew, looking at an adjacent car and feeling a rear impact, the other two vehicles could have seemed to both be moving forward. I'm not saying that was the case, I'm just saying he needed to define his greater frame of reference in order to get the right measurements.

 

 

I don't even understand relativity, but removing some references makes math simpler. If you want to factor in external forces then you have to define them. And I'm definitely not trapped in Einstein's box. (HAHA) I do NOT think that reality is subject to the math used to describe it. Atomic time isn't even consistent orbital time according to Tom Van Flandern. (http://www.metaresearch.org)

 

I did consider the dynamics of wind and gravity and thought you might present the argument that you did regarding that particular comparison. And I admit, i threw that out there as a 'rough' comparison/example and that there may be fault with it... it was more intended to demonstrate the 'general idea'.

 

Still, if we say that the sun ejected the particles at .8c (for example) and seems to me that their velocity is sufficient enough to overcome the gravitational influence of the sun. Thus the rear projected particle will be traveling AWAY from the sun at .8c (deduct .0001c if yo u like for the suns gravity... no matter). The two particles must be departing in opposite directions from the sun at this speed. Thus, the particles MUST be distancing themselves from the sun and each other. Their relative speed from each other should be greater than it is for either of them relative to the sun. The way you descrive it, the particles could not actually BE ejected because they'd continue to travel with the sun like a baloon INSIDE of a moving car as opposed to outside the car. Yes, wind resistance would cause it to fall behind; but in the case of the particles, the fact that they are EJECTED (not just sluffed off) at .8c is the equivalent of the wind factor (a force acting upon them in either case). Thus, the three bodies can lay claim to moving at different rates of speed through space. Even without any external reference points, they can claim the sun has no motion (relatively speaking) and that they each have motoin of .8c relative to it because there's no way either of them could have ejected the sun and the other particle. It seems to me this is similar to your reasoning for the ball forever traveling at 45 degrees to you... though that makes even less sense to me because I don't see the force that caused it to lose its paralell motion to you (i'm not arguing against it though).

 

As for Mr. Mojo... that's my point. He was IGNORANT (him, not you... I have to put that disclaimer in or Tormod will get all bent out of shape because they must not have freedom of speach rules in Greece. That or he's just really sensitive or doesn't know when people are joshing with each other when they do poke fun.) of the circumstances of his larger surroundings because he was using SR. SR told him he had the right to say he was at rest and the other car was moving NO MATTER WHAT.

 

So OK, if he doesn't look at his surroundings forever, can he just claim that he was the one at rest all along? Can he drive off with is eyes closed and then open them after crossing the intersection and not look back and expect the other guy's insurance company (and the police) won't come calling because he has "the right" to claim he was at rest, so any thud he felt HAD to be the other person's fault and thus the police should be off looking for that other vehicle who must have been guilty of running a red light?

 

As you say, he had to expand his frame of reference for the right MEASUREMENTS... SR is measurement based... NOT reality based. His correct measurements has NOTHING to do with who hit who. There's not "uncertainty principle" at work here, in which only his viewing the circumstances make them so!

[Southtown]

Thus, the particles MUST be distancing themselves from the sun and each other. Their relative speed from each other should be greater than it is for either of them relative to the sun.

Ya, agreed.

 

The way you descrive it, the particles could not actually BE ejected because they'd continue to travel with the sun like a baloon INSIDE of a moving car as opposed to outside the car.

Oh no, nuh-uh. I'm saying the particles will continue to move away from the Sun at an equal rate, regardless of the Sun's (constant) motion.

 

His correct measurements has NOTHING to do with who hit who. There's not "uncertainty principle" at work here, in which only his viewing the circumstances make them so!

Ya, I'm with you, dude. Reality is reality, and math is only relevant in the context of reality. I don't know much about relativity, so I'll just stop here. LOL

[EWright]

Disagree, unless the Sun changed velocity, or the particles changed velocity (via wind resistance or whatever) the Sun will notice no such thing because the particles will inherit the velocity of the Sun (unless they are photons.) [/Quote]

 

Oh no, nuh-uh. I'm saying the particles will continue to move away from the Sun at an equal rate, regardless of the Sun's (constant) motion.[/Quote]

 

So you're saying if the particles are photons, they will not have equals speeds relative to the sun's motion!? You can not make the same argument for both .8c particles and photons here, which is it?

[Tormod]

I have a question also:

 

Someone X leaves earth and travels at the speed of light, then returns to earth, and finds out that 100 years have passed on earth, yet X's watch marks that 0 time has passed.

 

Was that at least theoretically acurate?

 

If so, then in X's reference frame X was traveling at infinite speed ( traveled some distance under 0 time). Is that correct?

 

No, it is not correct. nothing can travel at "under 0 time", since that implies travel backwards in time.

 

You also need to factor in that nothing can leave the Earth at the speed of light (except light itself) and as such it is not even theoretically accurate.

 

Since the laws of physics are the same for everyone, a someone traveling at the speed of light must also perceive time to be ticking. So if you theoretically could travel at the speed of light for any amount of time, your clock would show how long you have been subjectively away. The clocks on Earth show how long you have been away from Earth.

 

There really is no paradox in this. I still fail to understand why it is even necessary to *assume* there is a paradox. Time is relative to the observer, and time always flows at different rates for observers in different frames of motion.

[EWright]

No, it is not correct. nothing can travel at "under 0 time", since that implies travel backwards in time.

 

You also need to factor in that nothing can leave the Earth at the speed of light (except light itself) and as such it is not even theoretically accurate.

 

Since the laws of physics are the same for everyone, a someone traveling at the speed of light must also perceive time to be ticking. So if you theoretically could travel at the speed of light for any amount of time, your clock would show how long you have been subjectively away. The clocks on Earth show how long you have been away from Earth.

 

There really is no paradox in this. I still fail to understand why it is even necessary to *assume* there is a paradox. Time is relative to the observer, and time always flows at different rates for observers in different frames of motion.

 

Ugh. With all due respect Tormod, you are mistaken even within the context of SR. While traveling *hypothetically* (not theoretically) at light speed, your own watch, according to relativity would register NO TIME. SR dictates that TIME STOPS for a photon, or a photon experiences NO TIME and thus does not age.

 

And where does this idea stem from that traveling faster than c will cause you to travel backwards in time, which based on this post, you believe!? This most certainly would not be the case and if relativity predicts it, it will prove to be a fatal flaw.

[Tormod]

Ugh. With all due respect Tormod, you are mistaken even within the context of SR. While traveling *hypothetically* (not theoretically) at light speed, your own watch, according to relativity would register NO TIME. SR dictates that TIME STOPS for a photon, or a photon experiences NO TIME and thus does not age.

 

And where does this idea stem from that traveling faster than c will cause you to travel backwards in time, which based on this post, you believe!? This most certainly would not be the case and if relativity predicts it, it will prove to be a fatal flaw.

 

Breathe out. First of all, he wrote "traveled under 0 time" which implies a negative passing of time. But assuming he meant "zero time" - we have actually discussed instant travel somewhere here before, where I pointed out that if a spaceship could move from A to B in no time, then an observer at B could theoretically see the spaceship leave A after it arrives B - which for all practical purposes violates the requirement that movement takes time.

 

Even the spaceship pilot himself would be able to turn his (extraordinarily good) telescope around and watch himself leave. Thus instantaneous travel is equal to travel backwards in time *as seen from B* - no paradox involved.

 

Secondly, according to SR my watch would no longer exist at c because all matter would have been turned into energy.

 

The thing is of course that this kind of travel is impossible (*theoretically*) because only energy can travel at the speed of light. So I argue that if *hypothetically* someone could travel at the speed of light they would see time pass, because they would be observers in a specific frame of motion. This would however be a violation of relativity...which will be necessary in order to perform travel at c or FTL.

 

I can recommend an excellent FTL FAQ here:

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

[EWright]

Breathe out. [/Quote]

 

This is what I'm talking about. Tormod can mix it up without getting bent out of shape. You've put a smile on my face.

 

First of all, he wrote "traveled under 0 time" which implies a negative passing of time. But assuming he meant "zero time" - we have actually discussed instant travel somewhere here before, where I pointed out that if a spaceship could move from A to B in no time, then an observer at B could theoretically see the spaceship leave A after it arrives B - which for all practical purposes violates the requirement that movement takes time.

 

Even the spaceship pilot himself would be able to turn his (extraordinarily good) telescope around and watch himself leave. Thus instantaneous travel is equal to travel backwards in time *as seen from B* - no paradox involved.

[/Quote]

False. If the traveler moved with zero time, he would be stretched across time and frozen in motion. Thus he couln't turn around. If he could, he would see his tail end where he left, but he won't see his entire self leave. To do this he would have to travels faster than the speed of light. This does not mean he travels into the past. It means the light has to then catch up to him before he can view it. He's seeing his IMAGE as he was... NOT seeing himself in any 'present' way.

 

 

Secondly, according to SR my watch would no longer exist at c because all matter would have been turned into energy.

 

The thing is of course that this kind of travel is impossible (*theoretically*) because only energy can travel at the speed of light. So I argue that if *hypothetically* someone could travel at the speed of light they would see time pass, because they would be observers in a specific frame of motion. This would however be a violation of relativity...which will be necessary in order to perform travel at c or FTL.[/Quote]

 

So you're saying energy violates the conditions of relativity? because it does travel at this speed. And according to relativity it experiences no time. Oh wait, we don't apply inertial fields to EM energy. Why? In order to avoid this paradox. Face it, what is happening is that R BREAKS DOWN at light speed just like at a singularity. And I suspect GR breaks down at a singularity for the same reason.

 

I can recommend an excellent FTL FAQ here:

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

[Erasmus00]

And where does this idea stem from that traveling faster than c will cause you to travel backwards in time, which based on this post, you believe!? This most certainly would not be the case and if relativity predicts it, it will prove to be a fatal flaw.

 

I'm going to do some math for you, but do not freak out, its just algebra. I'll even try to motivate it a little.

 

In 3D space, we can define the distance between two points by a line segment. The line segment can be thought of has having three different "components" i.e., you can measure a length along an x direction, a length along the y direction, and a length along the z direction, using standard cartesian coordinate deffinitions. Using dx for the x distance, dy for the y distance and dz for the z distance, we can say the length of the line segment dL can be written:

 

dL^2=dx^2+dy^2+dz^2.

 

Now, for different frames of references, dx, dy,dz will differ, because the choice of coordinates effects these lengths. However, dL is always the same.

 

Now, in SR we have 4D space. We can something akin to length in 3D space. This is often called the interval(which I shall call dT), or proper time. Proper time is the time the object experiences in its own frame. The formula for the interval is

 

dT^2= dt^2 -1/c^2 (dx^2+dy^2+dz^2)

 

Here dx, dz and dy are the distance the object travels in a time interval dt. Now, lets use this formula to evaluate the two situations being talked about. The first, a photon. Lets say we picked our coords. such that travels on our x axis. So now, dy=0, dz=0. Now, in a time interval dt, our object travels a distance of c*dt, so dx=c*dt and our formula for dT becomse

 

dT^2=dt^2-dt^2 = 0.

 

dT=0. So our photon doesn't experiences any proper time.

 

Now consider something traveling faster then light. For this, using a similar analysis,

 

dT^2< 0.

 

This means dT is a complex number. In other words, our concept of time doesn't seem to extend very well to objects faster then light.

-Will

[Erasmus00]

So you're saying energy violates the conditions of relativity? because it does travel at this speed. And according to relativity it experiences no time. Oh wait, we don't apply inertial fields to EM energy. Why? In order to avoid this paradox.

 

In relativity, its perfectly acceptable for objects with 0 rest mass to travel at light speed. (in fact, in relativity, objects with no rest mass MUST travel at light speed).

 

Now, by inertial fields, I assume you mean inertial frame. And you are right, we don't apply inertial frames to EM, as EM isn't in an inertial field. Why not? Because you can move from any inertial frame to any other inertial frame by accelerating, but you can never accelerate into (or out of) light speed. You also don't apply inertial frames to accelerating observers (because they are moving through several frames, and no one frame can apply).

-Will

[EWright]

I'm going to do some math for you, but do not freak out, its just algebra. I'll even try to motivate it a little.

 

In 3D space, we can define the distance between two points by a line segment. The line segment can be thought of has having three different "components" i.e., you can measure a length along an x direction, a length along the y direction, and a length along the z direction, using standard cartesian coordinate deffinitions. Using dx for the x distance, dy for the y distance and dz for the z distance, we can say the length of the line segment dL can be written:

 

dL^2=dx^2+dy^2+dz^2.

 

Now, for different frames of references, dx, dy,dz will differ, because the choice of coordinates effects these lengths. However, dL is always the same.

 

Now, in SR we have 4D space. We can something akin to length in 3D space. This is often called the interval(which I shall call dT), or proper time. Proper time is the time the object experiences in its own frame. The formula for the interval is

 

dT^2= dt^2 -1/c (dx^2+dy^2+dz^2)

 

Here dx, dz and dy are the distance the object travels in a time interval dt. Now, lets use this formula to evaluate the two situations being talked about. The first, a photon. Lets say we picked our coords. such that travels on our x axis. So now, dy=0, dz=0. Now, in a time interval dt, our object travels a distance of c*dt, so dx=c*dt and our formula for dT becomse

 

dT^2=dt^2-dt^2 = 0.

 

dT=0. So our photon doesn't experiences any proper time.

 

Now consider something traveling faster then light. For this, using a similar analysis,

 

dT^2< 0.

 

This means dT is a complex number. In other words, our concept of time doesn't seem to extend very well to objects faster then light.

-Will

 

I feel very close to being able to see where the differences lie in this, relative to my ideas; but I don't fully understand it or how to express my own idea. I get the first linear distant part. Can you explain please the different between T and t and specifically why c was added to the equation when talking about SR.

[Erasmus00]

I feel very close to being able to see where the differences lie in this, relative to my ideas; but I don't fully understand it or how to express my own idea. I get the first linear distant part. Can you explain please the different between T and t and specifically why c was added to the equation when talking about SR.

 

Why we need to add c is pretty simple. Time and space are measured in different units, and c is the factor that converts between them. In units where c = 1 (time measured in meters) the proper time interval looks a bit nicer:

 

dT^2=dt^2-dx^2-dy^2-dz^2.

 

The different sign between space and time dimensions is also interesting, and shows the different nature of the space and time dimensions.

 

T is what your watch measures. t is the dilated time interval seen by an observer watching you. Note that in your own frame, you aren't moving, so dx=dy=dz=0, and dT=dt.

 

From the formula for the interval, it is actually pretty easy to get the formula for time dilation. Consider an observer moving only in the x direction:

 

dT^2=dt^2-(1/c^2)dx^2. (dy=dz=0)

 

dT=dt*sqrt(1-(1/c)^2(dx/dt)^2). Here I took the square root and pulled out dt.

 

Now, we consider a constant velocity, so dx/dt = v, and normally in we solve for the dilated time t, so.

 

dt = dT/sqrt(1-v^2/c^2)

-Will