Constancy of light speed

[kamil]

hi,

 

Is it true that when you move at speed 'v' time dilates in accordance with the lorentz factor so that light beams move at the same speed. I read a book on einstein by Michio Kaku and it had said that Einstein was thinking about this problem:

A police man is chasing a light beam, but no matter how fast he moves, the speed of light is always faster by 'c'. But an observer standing on earth sees the policeman almost catch the light beam. The observer and policeman are in contradiction.

Einsteins solution for this problem stated: Time beats at different rates for different observers. Michio Kaku said that that is the reason why they both see the speed of light moving at 'c'.

So if i tried to catch a light beam and i moved at 0.5c, then i would see the light beam still travel at 'c' because time beats differently for me. So wouldn't it beat by half as much, but it doesnt according to the lorentz equation.

[Qfwfq]

Einsteins solution for this problem stated: Time beats at different rates for different observers.

Minkowsy stated it even better: for different observers the space-time coordinates are different.

[UncleAl]

Physical reality is not Galilean transforms, it is Lorentzian transforms. A vector resultant can be arbitrarily decomposed into summed components. Get over it.

 

For any physics in which Lorentz symmetry is valid, all inertial observers see a unique finite lightspeed. That enforces causality. Lightspeed in this universe is set by observed values of the permeability and permittivity of vacuum. A photon's frame of reference is not inertial.

 

Given any achievable velocities V1 and V2 and any finite lightspeed, the bound on the relative velocities of V1 and V2 as viewed by any inertial observer cannot exceed

 

(V1 + V2)/[1 +(V1)(V2)/c^2]

 

This is transformation of velocities parallel to the direction of motion. For velocities at an arbitrary angle theta, Jackson gives

 

u_parallel = (u'_parallel + v)/(1+(v dot u')/c^2)

u_perp = u'_perp/(gamma_v(1+(v dot u')/c^2))

 

http://www.physics.umanitoba.ca/~souther/waves02/feb0402/sld011.htm

 

Observers with relative velocities will not observe a change in lightspeed, they will observe a Doppler shift of frequency,

 

http://www.mathpages.com/rr/s2-04/2-04.htm

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html

http://www.phys.ufl.edu/~rfield/PHY2061/images/chp39_2.pdf

 

If gravitation is involved we go from Special to to General Relativity, and causality is still maintained,

 

hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html

[Qfwfq]

Get over it.

Get over what? Quit being grumpy UA.

 

For any physics in which Lorentz symmetry is valid, all inertial observers see a unique finite lightspeed. That enforces causality.

Enforces what????

 

I'd say it leads to the limitation on causality. As usual, you're ever so Knowledgeable. :rolleyes:

[Tormod]

A police man is chasing a light beam, but no matter how fast he moves, the speed of light is always faster by 'c'.

 

Technically speaking, the speed of light is not "faster by" c, but it *is* c, regardless of the speed of the observer.

[FrankM]

The last time I looked it up, the only place the speed of light has been measured is in a vacuum on the surface of the Earth. There are some who have the gall to state a vacuum on the Earth's surface is equivalent to "freespace".

 

I notice the NIST constants pages refer to the values of speed of light, permittivity, permeability are those obtained in a vacuum, they aren't going out on a limb to equate them to freespace.

 

There are those that want to measure the "parameters" of freespace, way out in freespace. I consider freespace being well beyond the influence of the Sun's heliosphere, but I would compromise to have a measurement out near Plutos distance. Would you believe that there are individuals in high places of influence that think a true "freespace" measurement is unncessary. What do they have to fear?