Equivalence Principle: Photon Fall Near Earth's Surface

In summary, the photon travels 3 km horizontally before 'falling' according to the equivalence principle.
  • #1
k3r0
15
0

Homework Statement


A photon near the surface of the Earth travels a horizontal distance of 3 km. How far (in meters) does the photon 'fall' in this time? (Hint: think equivalence principle).

Homework Equations


N/A


The Attempt at a Solution


My understanding of the equivalence principle is that experiments carried out in a 'free fall' frame will have the same results as an experiment done floating in space (far from a large body). I'm confused because the photon near the surface of Earth is in neither of these situations -- so would the answer be that it doesn't 'fall' at all? I would expect it to travel horizontally only.

Thanks.
 
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  • #2
k3r0 said:

Homework Statement


A photon near the surface of the Earth travels a horizontal distance of 3 km. How far (in meters) does the photon 'fall' in this time? (Hint: think equivalence principle).

Homework Equations


N/A


The Attempt at a Solution


My understanding of the equivalence principle is that experiments carried out in a 'free fall' frame will have the same results as an experiment done floating in space (far from a large body). I'm confused because the photon near the surface of Earth is in neither of these situations -- so would the answer be that it doesn't 'fall' at all? I would expect it to travel horizontally only.

Thanks.

The usual picture is to imagine an experiment carried out in an elevator (3km wide), where you shoot a beam of photons straight across the elevator. If you carry this out in space it will travel straight across. If you are in the same elevator at the Earth's surface in free fall, accelerating towards the center of the earth, from the view point of someone in the elevator it will also travel straight across. You are supposed to think of how it looks from the view point of someone who is not in the elevator and standing on the Earth's surface.
 
  • #3
Thanks, I've got it now!
 

Related to Equivalence Principle: Photon Fall Near Earth's Surface

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 uniformly accelerating reference frame would experience the same physical laws as an observer in a stationary reference frame in a gravitational field.

2. How does the Equivalence Principle apply to photons near Earth's surface?

According to the Equivalence Principle, the path of a photon near Earth's surface will be affected by gravity in the same way as the path of a massive object. This means that a photon, which has no mass, will also follow a curved trajectory in the presence of a gravitational field, just like a massive object would.

3. Why is the Equivalence Principle important in understanding gravity?

The Equivalence Principle helps us to understand the fundamental nature of gravity and its relationship to acceleration. It also allows us to make predictions about the behavior of objects and particles in a gravitational field, including the paths of photons near Earth's surface.

4. How does the Equivalence Principle relate to Einstein's theory of General Relativity?

Einstein's theory of General Relativity is based on the Equivalence Principle, which he used to develop his theory of gravity. In General Relativity, gravity is explained as the curvature of space-time caused by the presence of massive objects, and the Equivalence Principle helps to explain how this curvature affects the paths of objects and particles.

5. Are there any exceptions to the Equivalence Principle?

While the Equivalence Principle holds true in most cases, there are some situations where it does not apply. For example, at a quantum level, the effects of gravity and acceleration can be distinguished. Also, in extremely strong gravitational fields, such as those near black holes, the Equivalence Principle breaks down due to the extreme curvature of space-time.

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