Object moving at speed of light as Reference frame.

In summary, we discussed the possibility of objects other than photons moving at the speed of light and concluded that only objects with zero rest mass, such as photons, can achieve this speed. We also explored the concept of using an object moving at the speed of light as a reference frame and found that it would not be possible due to the limitations of the observer's time and spatial axes at this speed. Finally, we touched on the idea of observing an object with respect to another object moving at the speed of light and determined that it would require three frames of reference to accurately measure the motion.
  • #1
aleemudasir
68
0
Is there any other object except photon which moves at the speed of light?
Why can't an object moving at the speed of light be taken as reference frame?
Can we use the equation m=m(0)/sqrt(1-v^2/c^2) for an object moving with speed of light?
 
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  • #2
aleemudasir said:
Is there any other object except photon which moves at the speed of light?
Why can't an object moving at the speed of light be taken as reference frame?
Can we use the equation m=m(0)/sqrt(1-v^2/c^2) for an object moving with speed of light?
Part of the answer directly follows from your questions: using your equation, you will find that only an object with zero rest mass can propagate at the speed of light; and such objects are called photons (it is assumed that photons have exactly zero rest mass). Note that as 0/0 is useless, for the "mass equivalent" of light you can use m=p/c.

And how would you use a photon as reference frame? A reference frame is a system for comparing (measuring) such things as time and distance. If a clock and ruler would be accelerated to light speed (although impossible), they would stop ticking and have zero length.
 
  • #4
So does that mean it is impossible for an object with non-zero rest mass to move with speed of light? And Why?
 
  • #5
aleemudasir said:
So does that mean it is impossible for an object with non-zero rest mass to move with speed of light? And Why?
Again, use your own equation! How much relativistic mass will it have at the speed of light? How much energy is needed to bring it to that speed?
 
  • #6
aleemudasir said:
Is there any other object except photon which moves at the speed of light?

Yes, other massless bosons.

aleemudasir said:
Why can't an object moving at the speed of light be taken as reference frame?

Your question has been answered quite well here. Also, you might consider the problem in the context of space-time diagrams (google it or find discussions of space-time diagrams in other posts). The sketches below show a sequence in which an observer (blue frames of reference) moves at ever greater relativistic velocities with respect to a rest frame (black perpendicular coordinates). One aspect of the photon (any massless boson) that makes it so special is that its worldline always bisects the angle between the time axis and the spatial axis for any observer, no matter what the observer's speed (thus, the speed of light is the same for all observers).

Notice in the sequence that the moving observer's X4 and X1 axes rotate toward each other, getting closer and closer to each other as the speed of light is approached. In the limit the X4 axis and the X1 axis overlay each other. So, if the observer were actually moving at the speed of light, both his time axis and his spatial axis would be colinear with the photon worldline. How would you define that as a coordinate system?

Approach_LightSpeed_B.jpg
 
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  • #7
bobc2 said:
Yes, other massless bosons.



Your question has been answered quite well here. Also, you might consider the problem in the context of space-time diagrams (google it or find discussions of space-time diagrams in other posts). The sketches below show a sequence in which an observer (blue frames of reference) moves at ever greater relativistic velocities with respect to a rest frame (black perpendicular coordinates). One aspect of the photon (any massless boson) that makes it so special is that its worldline always bisects the angle between the time axis and the spatial axis for any observer, no matter what the observer's speed (thus, the speed of light is the same for all observers).

Notice in the sequence that the moving observer's X4 and X1 axes rotate toward each other, getting closer and closer to each other as the speed of light is approached. In the limit the X4 axis and the X1 axes overlay each other. So, if the observer were actually moving at the speed of light, both his time axis and his spatial axis would be colinear with the photon worldline. How would you define that as a coordinate system?
I am not talking of an observer moving at the speed of light rather I am talking about an observer observing an object x w.r.t to an object y(moving at the speed of light).
Approach_LightSpeed_B.jpg
I didn't get well this graphical explanation, would you please elaborate.
 
  • #8
aleemudasir said:
I am not talking of an observer moving at the speed of light rather I am talking about an observer observing an object x w.r.t to an object y(moving at the speed of light).
Then you will have to explain what you mean by that. What do you mean by "observing x with respect to y"? Any observer see object with respect to himself, not with respect to any other frame of reference.
 
  • #9
HallsofIvy said:
Then you will have to explain what you mean by that. What do you mean by "observing x with respect to y"? Any observer see object with respect to himself, not with respect to any other frame of reference.

I don't think that is necessary, let's talk as an example about 3-Dimensinal co-ordinate system in which an observer observes the motion of any object w.r.t to the origin(0,0,0).
 
  • #10
aleemudasir said:
I don't think that is necessary, let's talk as an example about 3-Dimensinal co-ordinate system in which an observer observes the motion of any object w.r.t to the origin(0,0,0).

Ah, but is the observer moving with respect to that origin? If so, we have three frames (observer, object, and frame-with-origin-at-(0,0,0)) to transform between, not two. None of these frame can have a velocity greater than or equal to to the speed of light relative to any other of these frames.
 
  • #11
Nugatory said:
Ah, but is the observer moving with respect to that origin? If so, we have three frames (observer, object, and frame-with-origin-at-(0,0,0)) to transform between, not two. None of these frame can have a velocity greater than or equal to to the speed of light relative to any other of these frames.
The observer is at rest w.r.t origin.
 
  • #12
aleemudasir said:
So does that mean it is impossible for an object with non-zero rest mass to move with speed of light? And Why?
Yes, any object with non zero rest mass must move slower than c in any inertial frame.

As far as why, that is inherently a tricky question. What are you allowing to be assumed when answering? And what kind of answer are you looking for? If I were asking the question I would be looking for a geometric answer and I would allow the Minkowski metric to be assumed. Then the answer is that a massive object has a timelike four momentum by definition, and any timelike four momentum corresponds to a three velocity < c. If that doesn't answer the question then you will need to clarify what you want better.
 
  • #13
aleemudasir said:
I don't think that is necessary, let's talk as an example about 3-Dimensinal co-ordinate system in which an observer observes the motion of any object w.r.t to the origin(0,0,0).
The observer is at rest w.r.t origin.
OK, then my answer of post #5 applies. How much energy do you think is required?

If you did not manage to calculate that a division by zero is infinite, the answer is given in section 10 of http://www.fourmilab.ch/etexts/einstein/specrel/www/ :
Thus, when v=c, [kinetic energy] W becomes infinite
 

1. What is the concept of an object moving at the speed of light as a reference frame?

An object moving at the speed of light as a reference frame is a theoretical concept in physics in which an observer is travelling at the speed of light relative to another object. This means that the observer experiences time dilation and length contraction, and all other objects appear to be stationary.

2. Is it possible for an object to actually move at the speed of light as a reference frame?

No, it is not possible for an object to move at the speed of light as a reference frame. According to Einstein's theory of relativity, the speed of light is the maximum speed that can be attained in the universe. Therefore, an object cannot travel at the speed of light, let alone act as a reference frame.

3. How does the concept of an object moving at the speed of light as a reference frame impact our understanding of time and space?

The concept of an object moving at the speed of light as a reference frame challenges our understanding of time and space. It shows that time and space are relative and can be perceived differently by different observers. This concept has greatly contributed to our understanding of the universe and has revolutionized the field of physics.

4. Can the speed of light be used as a reference frame in practical applications?

No, the speed of light cannot be used as a reference frame in practical applications. As mentioned earlier, it is a theoretical concept and cannot be achieved in reality. In practical applications, the speed of light is used as a constant value for various calculations and is not considered a reference frame.

5. How does the concept of an object moving at the speed of light as a reference frame relate to the theory of relativity?

The concept of an object moving at the speed of light as a reference frame is a fundamental part of the theory of relativity. It is one of the key principles that led to the development of this theory and has been confirmed by numerous experiments and observations. Without this concept, our understanding of the universe and the laws of physics would be incomplete.

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