- #1
Gerenuk
- 1,034
- 5
Why is it that to derive general relativity you use the equivalence principle on gravity and not electromagnetism for example?
Equivalence principle to other forces?
- Thread starter Gerenuk
- Start date
In summary: So the equivalence principle wouldn't be applicable to electromagnetism.In summary, the equivalence principle is used in deriving general relativity because gravitational mass and inertial mass are equivalent, while this is not the case for electromagnetism. The principle applies to gravity because it is a force and acceleration exhibits a force, but this is not the case for electromagnetism as it can be easily detected by local experiments. The principle is based on the equivalence of reference frames, not forces, and is not applicable to electromagnetism due to the dependence of acceleration on charge-to-mass ratio.
- #2
Al68
Because the equivalence principle would be obviously false if applied to electromagnetism instead of gravity.Gerenuk said:
- #3
Gerenuk
- 1,034
- 5
That's a "Becauso so." answer 
Electromagnetism is a force and acceleration exhibits a force. So at least from the basic ideas that I heard it doesn't make a difference.
Electromagnetism is a force and acceleration exhibits a force. So at least from the basic ideas that I heard it doesn't make a difference.
- #4
Nabeshin
Science Advisor
- 2,207
- 16
Gravitational mass and inertial mass are the same.
What equivalent statement could you possibly make about any of the other forces?
What equivalent statement could you possibly make about any of the other forces?
- #5
Gerenuk
- 1,034
- 5
I see. I was thinking about the force argument only. I have the feeling that's a good answer.
And I cannot apply the same concept to electric charge? (converting the units appropriately)
And I cannot apply the same concept to electric charge? (converting the units appropriately)
- #6
Al68
I don't know what a "Becauso so." answer is, but the "force" of electromagnetism isn't equivalent to a pseudoforce in accelerated reference frames the way gravitational "force" is.Gerenuk said:That's a "Becauso so." answer
Electromagnetism is a force and acceleration exhibits a force. So at least from the basic ideas that I heard it doesn't make a difference.
The "basic idea" of the equivalence principle isn't about forces being equivalent, they generally aren't. It's about the equivalence of reference frames. Two accelerated reference frames are equivalent if the only difference between them is the presence of a gravitational field. No local experiment can even detect the presence of the gravitational field. In both cases a ball thrown "up" will "fall", for example. The ball "falls" because of the acceleration of the reference frame, not because of a real force.
An electromagnetic field can easily be detected by local experiments, so the equivalence principle is not valid for electromagnetism.
- #7
DrGreg
Science Advisor
Gold Member
- 2,462
- 1,954
I think you've more or less worked this out now. In Newtonian terminology, the "acceleration due to gravity" of a particle does not depend on the particle's mass (or any other property of the particle). The "acceleration due to electromagnetism" depends on the particle's charge-to-mass ratio.Gerenuk said:
1. What is the Equivalence Principle?
The Equivalence Principle is a fundamental concept in physics that states that the effects of gravity are indistinguishable from the effects of acceleration. This means that an observer in a gravitational field cannot tell the difference between being at rest in that field and being in a uniformly accelerating reference frame.
2. How does the Equivalence Principle relate to other forces?
The Equivalence Principle applies specifically to the force of gravity, but it has implications for other forces as well. It suggests that other forces, such as electromagnetism and the strong and weak nuclear forces, may also have an equivalent acceleration effect on objects within their respective fields.
3. What is the difference between the Strong and Weak Equivalence Principles?
The Strong Equivalence Principle is a more strict version of the Equivalence Principle that states that not only are the effects of gravity and acceleration indistinguishable, but all physical laws and experiments must be the same in a gravitational field and an equivalent non-inertial reference frame. The Weak Equivalence Principle, on the other hand, only applies to the motion of objects under the influence of gravity.
4. How was the Equivalence Principle first tested?
The Equivalence Principle was first experimentally tested by Galileo in the 16th century. He dropped objects of different masses from the Leaning Tower of Pisa and observed that they fell at the same rate, regardless of their mass. This demonstrated that the acceleration due to gravity is independent of an object's mass, supporting the concept of equivalence between gravity and acceleration.
5. What are the implications of the Equivalence Principle for gravitational theories?
The Equivalence Principle has significant implications for gravitational theories, such as Einstein's theory of General Relativity. It suggests that gravity is not a force between masses, but rather a curvature of spacetime caused by the presence of mass and energy. This concept has been confirmed by numerous experiments and is now a fundamental part of our understanding of gravity.
Similar threads
-
Special and General Relativity
-
Special and General Relativity
-
Special and General Relativity
-
Special and General Relativity
-
Special and General Relativity
-
Special and General Relativity
-
Special and General Relativity