Problem caused by length contraction and relativity and personal expla

[Brucezhou]

The problem has been shown in the picture. Because of relativity, both the guys on the ground and on the vehicle would observe length contraction. So the destination of the guy on the vehicle---the galaxy, would be more closed to him. If the vehicle is replaced with the light, which means the distance between the photons and the galaxy would be 0 based on the formula of Lorentz's Transformation. But if this was possible, we can't measure the c=3000000000m/s, since the light can reach where we are immediately without time passes.Personal Explanation1:
To solve such problem, I think the key is that photons do not have mass. So when the they speed up to c, their mass is still 0. Based on General Theorem Of Relativity, the space will not warp and no time dilation will be observed.

 

[PAllen]

There is no such thing as the rest frame of light. See the FAQ at the top of this forum section on this:

https://www.physicsforums.com/showthread.php?t=511170

 

[Psychosmurf]

The problem has been shown in the picture. Because of relativity, both the guys on the ground and on the vehicle would observe length contraction. So the destination of the guy on the vehicle---the galaxy, would be more closed to him. If the vehicle is replaced with the light, which means the distance between the photons and the galaxy would be 0 based on the formula of Lorentz's Transformation. But if this was possible, we can't measure the c=3000000000m/s, since the light can reach where we are immediately without time passes.Personal Explanation1:
To solve such problem, I think the key is that photons do not have mass. So when the they speed up to c, their mass is still 0. Based on General Theorem Of Relativity, the space will not warp and no time dilation will be observed. View attachment 64204

Agreeing with the above poster, but to clear up another misconception, time dilation isn't due to the warping of spacetime but rather to the Lorentzian character of flat spacetime.

 

[Brucezhou]

Agreeing with the above poster, but to clear up another misconception, time dilation isn't due to the warping of spacetime but rather to the Lorentzian character of flat spacetime.

Ok, thanks

 

[jtbell]

I think the key is that photons do not have mass. So when the they speed up to c, their mass is still 0. Based on General Theorem Of Relativity, the space will not warp and no time dilation will be observed. View attachment 64204

In GR, spacetime curvature is "caused" by energy and momentum, via the stress-energy tensor. Mass is only one form of energy. Photons do not have mass, but they do have energy and momentum, therefore they can create spacetime curvature.

 

[Naty1]

Hi Bruce:

which means the distance between the photons and the galaxy would be 0 based on the formula of Lorentz's Transformation.

Any photons must travel at 'c' in the local frame. Also, the Lorentz transform only applies where relative speed between frames [observers] is less than 'c'. edit: in the absence of gravity...no curvature of spacetime...

since the light can reach where we are immediately without time passes.

the speed of light is always 'c'..never 'instantaneous'...

photons do not have mass.

as already posted, that is correct.

So when the they speed up to c...

photons always move at 'c' in free vacuum space...So, for example, a photon emitted from an electron orbital begins at speed 'c'...and stays that way.

 

[Brucezhou]

In GR, spacetime curvature is "caused" by energy and momentum, via the stress-energy tensor. Mass is only one form of energy. Photons do not have mass, but they do have energy and momentum, therefore they can create spacetime curvature.

But how to explain that phenomenon

 

[Naty1]

But how to explain that phenomenon

John Wheeler explains it this way:

Mass⁺ tells spacetime how to curve; spacetime tells mass how to move."

+ ...or energy or momentum

 

[Naty1]

time dilation isn't due to the warping of spacetime but rather to the Lorentzian character of flat spacetime.

careful here ...gravitational time dilation exists:

Two things affect the relative passage of time for different observers: relative speed as in special relativity [and associated length contraction] and in GR, relative gravitational potential.
So in GR, for example, a clock in the bottom a building ticks more slowly relative to a local clock in the top of the building.

http://en.wikipedia.org/wiki/Hafele–Keating_experiment#Gravitational_time_dilation

 

[Mentz114]

But how to explain that phenomenon

No scientific theory explains anything. GR is like a good map, it helps us move about in a terrain and predicts what we will see at different places. It is not trying to explain anything.

I could give you a good explanation of why water boils in terms of atoms, heat, and so on. But then you could ask me to explain 'atoms' and we're back to square one.