Understanding Einstein's Discovery: The Constant Speed of Light

  • Thread starter Thread starter mjolnir80
  • Start date Start date
  • Tags Tags
    Light
mjolnir80
Messages
54
Reaction score
0
how exactly did Einstein come to the conclusion that light travels at the same speed regardless of the observers own speed?
 
Physics news on Phys.org
It's not really a concusion it'sthe starting point.
There is a much earlier principle of relativity that says the laws of physics are the same for any moving body - so your physics test doesn't give different answers in the summer and winter when we are moving in opposite directions around the sun.
But Maxwell's laws give a fixed speed for light.
This would destroy the earier principle, because we could use a measurement of light speed to say how we were moving.

Einstein said 'what would we have to do to make the first principle work?' = the speed of light would have to be the same for everyone.
From this postulate (=claim) all the effects of special relativity follow.
 
Also a number of experiments, in particular the Michaelson-Morely experiment, showed that light could NOT be used to determine an "absolute" speed.
 

Thread 'Describing the Big Bang'

I started reading a National Geographic article related to the Big Bang. It starts these statements: Gazing up at the stars at night, it’s easy to imagine that space goes on forever. But cosmologists know that the universe actually has limits. First, their best models indicate that space and time had a beginning, a subatomic point called a singularity. This point of intense heat and density rapidly ballooned outward. My first reaction was that this is a layman's approximation to...
View full post »
Thread 'Dirac's integral for the energy-momentum of the gravitational field'

Thread 'Dirac's integral for the energy-momentum of the gravitational field'

See Dirac's brief treatment of the energy-momentum pseudo-tensor in the attached picture. Dirac is presumably integrating eq. (31.2) over the 4D "hypercylinder" defined by ##T_1 \le x^0 \le T_2## and ##\mathbf{|x|} \le R##, where ##R## is sufficiently large to include all the matter-energy fields in the system. Then \begin{align} 0 &= \int_V \left[ ({t_\mu}^\nu + T_\mu^\nu)\sqrt{-g}\, \right]_{,\nu} d^4 x = \int_{\partial V} ({t_\mu}^\nu + T_\mu^\nu)\sqrt{-g} \, dS_\nu \nonumber\\ &= \left(...
View full post »

Thread 'A sufficient condition for integrability of equation ##\nabla g=0##'

In Philippe G. Ciarlet's book 'An introduction to differential geometry', He gives the integrability conditions of the differential equations like this: $$ \partial_{i} F_{lj}=L^p_{ij} F_{lp},\,\,\,F_{ij}(x_0)=F^0_{ij}. $$ The integrability conditions for the existence of a global solution ##F_{lj}## is: $$ R^i_{jkl}\equiv\partial_k L^i_{jl}-\partial_l L^i_{jk}+L^h_{jl} L^i_{hk}-L^h_{jk} L^i_{hl}=0 $$ Then from the equation: $$\nabla_b e_a= \Gamma^c_{ab} e_c$$ Using cartesian basis ## e_I...
View full post »

Similar threads

I The invariance of the speed of light is not only a hypothesis?
2
Replies
57
Views
5K
I Conventionality of the One-Way Speed of Light
Replies
5
Views
357
B Speed of Light in Free Space - Einstein's Second Principle
Replies
8
Views
2K
B How does Einstein's equation work? Why do we need to square c?
Replies
18
Views
1K
B Speed of Light Reflection: Einstein's Train & Mirrors
Replies
38
Views
4K
B One-Way Speed of Light
2
Replies
93
Views
5K
B c^2 in Einstein‘s theory of relativity
Replies
10
Views
1K
B Problem about postulate of the invariance of the speed of light
Replies
33
Views
3K
A Electrodynamics of moving bodies - §2: On the relativity of... (again)
Replies
35
Views
4K
I Light speed independent of source
Replies
22
Views
2K

Hot Threads

Recent Insights

Back
Top