Theory of relativity

[bommy261]

For one of my graduate classes I am investigating the properties of light travel within a fiber optic cable. The speed of light is completely constant no matter your frame of reference. So.... if I was traveling at half the speed of light and decided to get my trusty ole Maglight out and shine it in the distance i was traveling.... what would I see?

Since I was traveling at half the speed of light, would the output of the Maglight be visible light? Or would it be a wave traveling at (1.5E8 m/s - half the speed of light) with the same frequency from my moving reference.

From a stationary reference, you would see light I imagine, at 3E8.

Thoughts?

 

[Puppies04]

Read. Learn. Win. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970102c.html

 

[bommy261]

Thanks

 

[Paul98]

For one of my graduate classes I am investigating the properties of light travel within a fiber optic cable. The speed of light is completely constant no matter your frame of reference. So.... if I was traveling at half the speed of light and decided to get my trusty ole Maglight out and shine it in the distance i was traveling.... what would I see?

Since I was traveling at half the speed of light, would the output of the Maglight be visible light? Or would it be a wave traveling at (1.5E8 m/s - half the speed of light) with the same frequency from my moving reference.

From a stationary reference, you would see light I imagine, at 3E8.

Thoughts?

Half the speed of light with respect to what? There is no absolute rest frame, the only way to get speed is from another frame of reference. Lets say your in a space ship moving away from earth at half the speed of light. You can also say that the earth is moving away from you at half the speed of light. In the ships frame of reference it's not moving at the earth is moving at half the speed of light. From the earths frame of reference the earth isn't moving and the ship is moving at half the speed of light.

Now lets look at light, the speed of light is the same in all frames of reference. So lets say you shoot a beam of light from earth to the ship. From the earths frame of reference light moves away from it at the speed of light and it's approaching the ship at half the speed of light. From the ships frame of reference the beam of light that is shot from earth is moving towards the ship at the speed of light and it's moving away from the earth at 1.5x the speed of light.

Now you may say hey, how can something move away from earth at 1.5x the speed of light. Note that that's only from the ships frame an d nothing in the ships frame is moving away from the ship at faster than the speed of light. Same with the earth's frame.

Now look at two ships going in different directions away from earth at close to the speed of light. From the earth's frame of reference they will be moving away from each other at close to twice the speed of light. But from ether ship's frame of reference they will be moving away from the other ship at slightly under the speed of light. If you want to calculate how much you can use the formula that is here http://en.wikipedia.org/wiki/Velocity-addition_formula

 

[Farmer]

So.... if I was traveling at half the speed of light and decided to get my trusty ole Maglight out and shine it in the distance i was traveling.... what would I see?

Since I was traveling at half the speed of light, would the output of the Maglight be visible light? Or would it be a wave traveling at (1.5E8 m/s - half the speed of light) with the same frequency from my moving reference.

From a stationary reference, you would see light I imagine, at 3E8.

Thoughts?

So let me get the set up. You are traveling at 0.5c with respect to some inertial frame (call it the lab frame). In your frame, also inertial, you shine a light at visible frequency. Are you asking what frequency an observer in the lab frame will see?

It depends if he is standing behind you or in front of you. If behind, it will be redshifted. If in front, it will be blueshifted. See relativistic doppler shift.

You mention light as a wave. Then I have to ask you, what do you mean by "speed of light"? Obviously frequency is not frame independent. So what is meant by "the speed of light is the same in all inertial frames," or "the speed of light is invariant through Lorentz transformation"? At the end of it all, the phase velocity remains at c, while the group velocity can actually be anything, even greater than c (this is the wave explanation of dielectric phenomenon, like prisms).

Now lets look at light, the speed of light is the same in all frames of reference. So lets say you shoot a beam of light from earth to the ship. From the earths frame of reference light moves away from it at the speed of light and it's approaching the ship at half the speed of light. From the ships frame of reference the beam of light that is shot from earth is moving towards the ship at the speed of light and it's moving away from the earth at 1.5x the speed of light.

Now you may say hey, how can something move away from earth at 1.5x the speed of light. Note that that's only from the ships frame an d nothing in the ships frame is moving away from the ship at faster than the speed of light. Same with the earth's frame.

This is extremely confusing. In no frame does an object move faster than the speed of light, ever.

 

[Paul98]

So let me get the set up. You are traveling at 0.5c with respect to some inertial frame (call it the lab frame). In your frame, also inertial, you shine a light at visible frequency. Are you asking what frequency an observer in the lab frame will see?

It depends if he is standing behind you or in front of you. If behind, it will be redshifted. If in front, it will be blueshifted. See relativistic doppler shift.

You mention light as a wave. Then I have to ask you, what do you mean by "speed of light"? Obviously frequency is not frame independent. So what is meant by "the speed of light is the same in all inertial frames," or "the speed of light is invariant through Lorentz transformation"? At the end of it all, the phase velocity remains at c, while the group velocity can actually be anything, even greater than c (this is the wave explanation of dielectric phenomenon, like prisms).



This is extremely confusing. In no frame does an object move faster than the speed of light, ever.

This is true, what I am talking about is that in some frame of reference two things may be moving away from each other at greater than the speed of light. But with respect to the frame of reference nothing is actually moving faster than the speed of light.

Such as having two spaceships both moving in opposite directions away from earth. In the earths frame of reference both are moving at .6c in opposite directions. From the earths frame of reference, the ships are moving away from each other at 1.2c. Yet in each of the spaceships frame the other spaceship is moving away from it at .882c.

So what I was trying to get at earlier is that nothing may be moving faster than the speed of light to it's frame of reference. But with two things going in different directions from a third frame of reference from the third frame of reference they may be moving away from each other at greater than c. But nothing is moving faster than c with respect to which ever frame of reference you chose.

 

[Sunny129]

For one of my graduate classes I am investigating the properties of light travel within a fiber optic cable. The speed of light is completely constant no matter your frame of reference. So.... if I was traveling at half the speed of light and decided to get my trusty ole Maglight out and shine it in the distance i was traveling.... what would I see?

Since I was traveling at half the speed of light, would the output of the Maglight be visible light? Or would it be a wave traveling at (1.5E8 m/s - half the speed of light) with the same frequency from my moving reference.

From a stationary reference, you would see light I imagine, at 3E8.

Thoughts?

you would see a beam of light leaving your flashlight at c, regardless of the fact that you, the source, are moving at 0.5c with respect to some other frame of reference. let's substantiate this other frame of reference by calling it earth, and suppose your flashlight is now the headlights on your spaceship as you fly by earth at 0.5c. the light coming from the headlights on your ship appear to travel at c from both your own reference frame AND the earth's reference frame. in the NASA link provided by Puppies04, it is noted that distances shorten and time slows down as one's relative velocity increasingly approaches c. and so the real difference between the earth's frame and your frame on the spaceship boils down to where and when...that is to say, if you were flying in your ship at 0.5c toward earth (though not directly toward it, thus avoiding crashing into it) with no headlights on, and then turned them on the instant you pass by earth, you would disagree with an earth-based observer as to exactly when and where the lights came on. these discrepancies will only grow in disparity as the relative velocity between two observers approaches c.

to you, your flashlight (or the headlights on your spaceship) would still be visible light - it would not be shifted to shorter wavelengths despite your intuition. it is when a light source is moving relative to you that it is red-shifted or blue-shifted. while earthbound observers would still measure the source of light to be traveling at c, its wavelength would be shifted. specifically, it would be blue-shifted as your ship (and thus the light source) approached the earth, not shifted at all as your ship passes by the earth, and red-shifted as your ship recedes from the earth.

 

[wuliheron]

Perhaps the best analogy to the speed of light I've come across is a horizon. It may look like the horizon is a fixed point and represents some sort of absolute reference, but that is just an illusion caused by the curvature of the earth. From orbit or even further away the illusion breaks down completely and we can see the cause of the illusion.

Likewise, no matter how fast or in what direction we go the speed of light follows us like the horizon never getting closer or further away. How fast is the light really moving? Is it really moving at all or a complete illusion like the horizon? We can't just go outside the universe and see what is causing the illusion to settle the matter once and for all. For now at least, all we can do is measure how fast we are going relative to other objects, and the speed of light is the limit to how fast we can measure such differences.

 

[QuantumPion]

Perhaps the best analogy to the speed of light I've come across is a horizon. It may look like the horizon is a fixed point and represents some sort of absolute reference, but that is just an illusion caused by the curvature of the earth. From orbit or even further away the illusion breaks down completely and we can see the cause of the illusion.

Likewise, no matter how fast or in what direction we go the speed of light follows us like the horizon never getting closer or further away. How fast is the light really moving? Is it really moving at all or a complete illusion like the horizon? We can't just go outside the universe and see what is causing the illusion to settle the matter once and for all. For now at least, all we can do is measure how fast we are going relative to other objects, and the speed of light is the limit to how fast we can measure such differences.

Nope, no illusion. Light is a wave. It really does move. There is no absolute reference frame.

 

[wuliheron]

Nope, no illusion. Light is a wave. It really does move. There is no absolute reference frame.

So, you have proven wave-particle duality is an illusion and photons are really waves after all. We can I read about this momentous achievement? The World Weekly News?

 

[lefenzy]

So, you have proven wave-particle duality is an illusion and photons are really waves after all. We can I read about this momentous achievement? The World Weekly News?

All QuantumPion saying is that light is a wave that propagates. Where did QuantumPion say that light does not have particle-like properties?

In fact, I don't understand what your post meant at all.

 

[wuliheron]

All QuantumPion saying is that light is a wave that propagates. Where did QuantumPion say that light does not have particle-like properties?

In fact, I don't understand what your post meant at all.

In general I think it best to let people speak for themselves instead of attempting to interpret their meaning for them.

Light is demonstrably both a wave and a particle. We have one theory that describes light as a perturbation of the electromagnetic field and it is certainly a useful theory, but it doesn't resolve the issue of wave-particle duality.

In this case, QuantumPion asserted that:

Nope, no illusion. Light is a wave. It really does move. There is no absolute reference frame.

My contention is that:

Light is demonstrably both a particle and a wave and it is of dubious value to make metaphysical assertions. Whether or not light or anything else for that matter "really moves" is a metaphysical question that physics simply cannot answer by definition.

 

[silverpig]

Nope, no illusion. Light is a wave. It really does move. There is no absolute reference frame.

There actually is an absolute reference frame. It is the one where the CMB dipole is zero.

This doesn't violate anything though. Just because there is a single reference frame that all observers can agree on, it doesn't mess up relativity. Einstein only said that there is no SPECIAL reference frame where physics was different and you could figure it out by doing some experiment.

 

[KrAzYaZnFLiP808]

Just reading a couple of articles in the links you posted. I have come to a conclusion, its exactly like me holding gun, that fires at a velocity of 600 ft/sec, and me traveling in a car @ 600 Ft/sec. The bullet will not stall, and will fire at the speed I am traveling at, or frame of reference. If I shoot the bullet forward, I should add 600 plus 600 so total of 1200 ft/sec from a outside frame of reference. From me it still be 600. It goes for the light. Even if your traveling at the speed of light, and grab your mag lite, and shine it in front of you, it will travel at the speed of light from your reference, so you will be able to see it. But from a outside reference, I am not sure what you are going to see becuase its light upon light. And No mass can travel at the speed of light. So to answer this question, It is not possible to travel at the speed of light, or NO MASS is able to travel at the speed of light!

Now black holes is a different story. Supposedly the gravitational field or whatever it is, unexplainable, no light can escape, especially the supposedly comet annunuki and the end of the world in 2012. I need to make a thread for that. Lol

 

[Farmer]

I am not sure what you are going to see becuase its light upon light

From your frame, you see light at speed c. From outside reference frame, you also see light at speed c. The only frame-dependent quantity is the frequency of the light. The phase velocity remains at c regardless of frame.

That is what it means, light has no absolute rest frame. Your example is confusing just like half the posts in this thread. The velocity addition you described is Galilean relativity, not Einstein relativity.

Black holes are covered in the general theory, which handles acceleration/gravity. It can't be dealt with just with what we're talking about here.

 

[KIAman]

From your frame, you see light at speed c. From outside reference frame, you also see light at speed c. The only frame-dependent quantity is the frequency of the light. The phase velocity remains at c regardless of frame.

That is what it means, light has no absolute rest frame. Your example is confusing just like half the posts in this thread. The velocity addition you described is Galilean relativity, not Einstein relativity.

Black holes are covered in the general theory, which handles acceleration/gravity. It can't be dealt with just with what we're talking about here.

^ This. Doesn't matter if you are traveling at .99999c and shine a light forward. You will still measure the outgoing light at c. A person standing still from your reference frame will see you going at .99999c but the light coming from your flashlight is still c.

Now some might suggest it is impossible for anything to be faster than c and that is wrong. As long as you don't violate causality and special relativity, a phenomena can go faster than c because they don't send information or energy.

Paul98 is alluding to is called proper speed and he would be correct if he referenced it as such.

 

[QuantumPion]

So, you have proven wave-particle duality is an illusion and photons are really waves after all. We can I read about this momentous achievement? The World Weekly News?

I'm not sure how you went from reference frames to wave-particle duality but I'll bite.

There is no confusion over the so-called wave-particle duality. Light is made up of photons, which are particles. The behavior of these particles are governed by the rules of quantum mechanics, which means that they have a probability distribution described by a wave function. It just turns out that the probability distribution of the photons is mathematically equivalent to Maxwell's equations, which treat light as a wave.

I suggest watching this clip, he explains it way better than I can.

http://youtu.be/_7OEzyEfzgg

 

[wuliheron]

I'm not sure how you went from reference frames to wave-particle duality but I'll bite.

There is no confusion over the so-called wave-particle duality. Light is made up of photons, which are particles. The behavior of these particles are governed by the rules of quantum mechanics, which means that they have a probability distribution described by a wave function. It just turns out that the probability distribution of the photons is mathematically equivalent to Maxwell's equations, which treat light as a wave.

I suggest watching this clip, he explains it way better than I can.

http://youtu.be/_7OEzyEfzgg

Photons display both particle-like and wave-like properties and Maxwell's equations most certainly have not reconciled this in favor of some Bohmian vision of quantum mechanics.

 

[QuantumPion]

Photons display both particle-like and wave-like properties and Maxwell's equations most certainly have not reconciled this in favor of some Bohmian vision of quantum mechanics.

So do electrons. Or any other particle for that matter. I suggest you watch the video rather than stubbornly stick to your preconceived notions. It's unwise to argue about nuclear physics with a nuclear physicist.

 

[QuantumPion]

There actually is an absolute reference frame. It is the one where the CMB dipole is zero.

This doesn't violate anything though. Just because there is a single reference frame that all observers can agree on, it doesn't mess up relativity. Einstein only said that there is no SPECIAL reference frame where physics was different and you could figure it out by doing some experiment.

I may be wrong here, since I'm not a cosmologist, but I do not think there can be such a reference frame where the CMB dipole is zero for all observers.

 

[iCyborg]

What do you mean by this? Two observers standing still relative to each other can get different values for CMB rest frame measured at their respective locations?

 

[wuliheron]

So do electrons. Or any other particle for that matter. I suggest you watch the video rather than stubbornly stick to your preconceived notions. It's unwise to argue about nuclear physics with a nuclear physicist.

You're arguing metaphysics, not physics. If you prefer I can even link you to a moderated website dedicated to all things physics that has a special philosophy section where other physicists can help you to learn the distinction.

I've been talking and arguing metaphysics with physicists for decades, so I must be foolish. Most I've met simply have no clue what the distinction is because it is just not part of their job anymore then an auto mechanic's job is to be a race car driver or expert in thermodynamics. You can quote endless theories, scribble magical formulas, etc. and it proves nothing.

If quanta were proven to be merely particles or waves it would be the biggest news of the century. Strictly speaking they don't even display classic particle or wave behavior, but are said to have "particle-like" and "wave-like" behavior. Anyone, physicist or not, who says otherwise is spouting nonsense.

 

[QuantumPion]

You're arguing metaphysics, not physics. If you prefer I can even link you to a moderated website dedicated to all things physics that has a special philosophy section where other physicists can help you to learn the distinction.

I've been talking and arguing metaphysics with physicists for decades, so I must be foolish. Most I've met simply have no clue what the distinction is because it is just not part of their job anymore then an auto mechanic's job is to be a race car driver or expert in thermodynamics. You can quote endless theories, scribble magical formulas, etc. and it proves nothing.

If quanta were proven to be merely particles or waves it would be the biggest news of the century. Strictly speaking they don't even display classic particle or wave behavior, but are said to have "particle-like" and "wave-like" behavior. Anyone, physicist or not, who says otherwise is spouting nonsense.

You keep using that word. I do not think it means what you think it means. I am not arguing "metaphysics". I am trying to describe to you in laymen's terms the basics of quantum mechanics. Precisely the opposite of metaphysics - essentially what you would find in chapter 1 of introductory quantum mechanics textbook.

Claiming you have been arguing metaphysics with physicists leads me to believe you are some sort of kook. Like someone who claims to have invented a perpetual motion machine arguing with a thermodynamics professor as to why the laws of thermodynamics are wrong. Stop being a stubborn crank who has heard a bunch of physics terminology and thinks he knows physics better than a physicist.

Watch. The. Linked. Video. It is the words straight out of the mouth of one of the guys that invented the entire field. http://youtu.be/_7OEzyEfzgg

Oh, and if by moderated dicussion forum you are referring to physicsforums.com, I am a contributing member there. Here's a good thread for your reference: http://www.physicsforums.com/showthread.php?t=388969&highlight=duality#3

 

[wuliheron]

You keep using that word. I do not think it means what you think it means. I am not arguing "metaphysics". I am trying to describe to you in laymen's terms the basics of quantum mechanics. Precisely the opposite of metaphysics - essentially what you would find in chapter 1 of introductory quantum mechanics textbook.

What rubbish. You have been arguing QED which is merely one theory in quantum mechanics and does not constitute the "basics". Indeterminacy is the foundation of quantum mechanics which otherwise is an ad hoc collection of theories.

Claiming you have been arguing metaphysics with physicists leads me to believe you are some sort of kook. Like someone who claims to have invented a perpetual motion machine arguing with a thermodynamics professor as to why the laws of thermodynamics are wrong. Stop being a stubborn crank who has heard a bunch of physics terminology and thinks he knows physics better than a physicist.

Shall I bring up a list of all the kooks in history who were physicists?

Watch. The. Linked. Video. It is the words straight out of the mouth of one of the guys that invented the entire field. http://youtu.be/_7OEzyEfzgg

Oh, and if by moderated dicussion forum you are referring to physicsforums.com, I am a contributing member there. Here's a good thread for your reference: http://www.physicsforums.com/showthread.php?t=388969&highlight=duality#3

I've seen Feynman lectures before thank you very much and he most certainly did not "invent the field". He was a brilliant scientist who made major contributions. Nothing more and nothing less.

You certainly don't have to take my word for it that you are making metaphysical assertions. If you are a member of the physics forums then I suggest you post to the philosophy bulletin board there and ask other physicists who have studied the distinction. Otherwise I shall just assume you are another kook who happens to have a degree in physics. There are an endless supply of them including some so-called "New Age" philosophers I can introduce you to if you want.

 

[QuantumPion]

...Wow. Ok, So we're done here, then? Great.