Invariant speed of Light—second postulate of special

relativity

David

Lily

P

Proton,Photon,Pion,Physics,...

[ ] Ding

Light speed is...constant ？

Suppose ：A proton is running at 99% of the light speed. Its n

ame is Poppy

1

A beam of light passes by Pop

py

2

As observers, we see Poppy goes almost

as fast as light

3

However, Poppy feels

that light goes as fast as it used to be

4

P

Stellar Aberration

2 methods to approach

Michelson-Morley Experiment(1887)

Michelson-Morley

Experiment

Assumption: one fixed star emits two types of light with differe

nt speed----c and C (c>C)

Because c and C are both constant, observer can receive them

at the same time.

As a result, c and C didn't depart simultaneously from the star.

StellarAberration

If the difference is 13 m/s,

1

the star, which is 30 lower light yr far away, will exist at the same time BOTH at site A and B where the angular distance is 10'.

2

If the star light is changing constantly in the range C~c,

3

the star should look like a LINE which is 10' long.

4

But this line is never seen,

5

so...6

Conclusion

The speed of light seems to never change

RESULT

In fact, vacuum speed of light is constant----Maxwell Equation in 1861

Lorentz Transformation (1892-1904)

in order to explain the baffling outcome of the 1887 ether-wind experiment of Michelson and Morley. In 1892, Lorentz independently FitzGerald-Lorentz contraction hypothesis

☺POPPY → US

→

P P

WE → POPPY

→

How Lorentz Transformation worksInvariance of speed of light (Second Postulate of Special Relativity):

For two events A and B(x1,x2,x3,t) and (y1, y2, y3, s) on one inertial reference frame M, and (x1’, x2’, x3’, t’) and (y1’, y2’, y3’, s’) on another inertial reference frame N

---->space-time interval is invariant

Derivation

Mysteries and Further development

1. EPR paradox2. Gravity, General Relativity,

and Black Hole3. Relationship between light

and space&time

THANKS!