Testing Einstein's Theory: Examining Light Deviation by Gravity

In summary, Simon He meant that Newton's law of gravity can be 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 h\nu=mc^2. If you use Newton's law of gravity with this mass, you get the wrong result by a factor of two.
  • #1
SimonB
8
0
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
 
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  • #2
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
Fredrik said:
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.

You don't have to assign any mass to light to predict its Newtonian acceleration; you just assume that light in a beam accelerates in the same way as anything else.

Einstein's theory introduces an extra factor of (1+v2/c2) 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
Thank you, very clear (now!)
 
  • #5
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
Jonathan Scott said:
You don't have to assign any mass to light to predict its Newtonian acceleration; you just assume that light in a beam accelerates in the same way as anything else.
I actually forgot that that when we're dealing with gravity we can eliminate the mass simply by dividing both sides of F=ma with m. But we can't divide with m when m=0, so we have have to assume either that m>0 or that there's a law of gravity for massless particles that works in this particular way.
 
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1. What is Einstein's Theory of General Relativity?

Einstein's Theory of General Relativity is a theory of gravitation that explains the force of gravity as a curvature of spacetime caused by the presence of mass and energy. It is considered one of the most important theories in physics and has been extensively tested and confirmed.

2. How does gravity affect light according to Einstein's Theory?

According to Einstein's Theory, gravity bends the path of light as it travels through spacetime, causing it to deviate from a straight line. This phenomenon is known as gravitational lensing and has been observed and confirmed through various experiments and observations.

3. How is light deviation by gravity tested?

One commonly used method for testing light deviation by gravity is through astronomical observations of stars and galaxies behind massive objects, such as galaxies or galaxy clusters. The light from these background objects is bent by the gravitational pull of the foreground object, causing it to appear distorted or duplicated.

4. What are the implications of confirming light deviation by gravity?

Confirming light deviation by gravity would provide further evidence for the validity of Einstein's Theory of General Relativity and our understanding of the nature of gravity. It could also have practical applications in fields such as astrophysics, where gravitational lensing can be used to study distant objects and dark matter.

5. Have there been any experiments that have confirmed light deviation by gravity?

Yes, there have been several experiments and observations that have confirmed light deviation by gravity, including the famous Eddington experiment in 1919 and more recent observations by the Hubble Space Telescope. These confirmations have further strengthened our understanding of gravity and the validity of Einstein's Theory.

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