Register to reply 
Twice Newtonby SimonB
Tags: newton 
Share this thread: 
#1
Nov2308, 05:34 AM

P: 8

Hi
I am reading a popular physics book. It discusses the test of Einsteins theory by Eddington at the eclipse. "The deviation of the light was double that predicted by Newton's physics" Why does classical physics predict any deviation of light by gravity, did light have a mass in classical physics and if so how was it estimated (to allow for the deviation to be predicted)??? Many thanks in advance Simon 


#2
Nov2308, 05:49 AM

Emeritus
Sci Advisor
PF Gold
P: 9,414

He meant Newton's law of gravity combined with the idea that light consists of particles with energy equal to Plancks constant times the frequency, and that you can define a "mass" of such a particle by setting [itex]h\nu=mc^2[/itex]. If you use Newton's law of gravity with this mass, you get the wrong result by a factor of two.



#3
Nov2308, 06:08 AM

PF Gold
P: 1,159

Einstein's theory introduces an extra factor of (1+v^{2}/c^{2}) into the coordinate acceleration in this case, which means that the deflection is doubled for light and similarly increased for anything else moving at relativistic speeds. 


#4
Nov2308, 06:49 AM

P: 8

Twice Newton
Thank you, very clear (now!)



#5
Nov2308, 07:40 AM

P: 5,632

Another way to think about curvature of light: half is classical (per Newtons laws) and the other half is relativistic due to the curvature of space and time itself.
Had Eddington's experiment been conducted a few years earlier, Einstein's career might have suffered a major blow since he originally predicted the classical degree of curvature and only later when working general relativity discovered an additional amount. Dr Kaku just mentioned this on a 2 hour TV show now airing "EINSTEIN"....HISTORY CHANNEL I believe. 


#6
Nov2308, 03:53 PM

Emeritus
Sci Advisor
PF Gold
P: 9,414




Register to reply 
Related Discussions  
How did Newton come about with F=ma?  Classical Physics  18  
Newton`s Law  Introductory Physics Homework  2  
Newton 3  Introductory Physics Homework  9  
Newton first and second law  Introductory Physics Homework  2  
Newton first and second law  Introductory Physics Homework  4 