Strong Equivalence Principle

In summary, the blue shift in the appearance of a photon from observer A to observer B is due to the relativistic doppler shift equation and is due to the fact that the photons are moving faster in the rear of the spacecraft. The significance of this blue shift is that it shows that the strong equivalence principle is valid, as the photons are being emitted at a higher potential than when they are emitted from the front.
  • #1
latentcorpse
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Ok so I was answering a question about a spacecraft accelerating through deep space with observer A in the front and observer B in the rear. I was asked to explain why a phton sent from A to B would appear blue shifted to B - simple enough I just plugged in a positive velocity to the relativistic doppler shift equation. I was then asked to explain the significance of the blue shift in terms of the strong equivalence principle and, well frankly, I can't see the connection. any ideas? also an explanation of the use of the strong EP would be really helpful!
thanks for any help
latentcorpse
 
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  • #2
Pound-Rebka?
 
  • #3
Do you understand why the rear is moving faster than the front? If not, I suggest you read up on Born rigidity, e.g. by checking out what I've been saying about it in this forum the last few months: https://www.physicsforums.com/search.php?searchid=1377913 [Broken]
 
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  • #4
latentcorpse said:
I was then asked to explain the significance of the blue shift in terms of the strong equivalence principle and, well frankly, I can't see the connection. any ideas?

What is the Strong Equivalence Principle?
 
  • #5
Fredrik said:
Do you understand why the rear is moving faster than the front? If not, I suggest you read up on Born rigidity, e.g. by checking out what I've been saying about it in this forum the last few months: https://www.physicsforums.com/search.php?searchid=1377913 [Broken]


Hey that link you posted doesn't seem to be working - it just says "sorry no matches were found". erm..i amen't really sure about why the rear is moving faster than the front? could u post the link again
 
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  • #6
It was a link to the results of a search I just made. I guess it was a bit optimistic of me to expect that the link would work long enough to be useful. (It worked when I previewed). Click "search" at the top of this window. Choose "advanced search" (under "search forums", not under "search blogs"). Type "fredrik" in the user name field. Type "born rigid" in the "keyword(s)" field. Change "find posts from" to "3 months ago" (and newer). Highlight "special & general relativity" in the "search in forum(s)" field. Change "show results as" from "threads" to "posts". Then click "search now".
 
  • #8
There are two basic ways to look at this case.

Firstly, the spaceship is accelerating, so by the time the photon from the front reaches the back, it is moving faster, so relativistic doppler shift applies, as already mentioned.

Secondly, by the Strong Equivalence Principle, you can consider the environment inside the spaceship to be equivalent to a static situation in a gravitational field, so the photon is being emitted at a higher potential and hence apparently has a higher frequency when it reaches the bottom, as in the Pound-Rebka experiment (previously mentioned by atyy). As this sounds like a homework question, I'll leave the trivial calculation of the result and the check that it matches the other view to the student.
 

1. What is the Strong Equivalence Principle?

The Strong Equivalence Principle is a fundamental principle in physics that states that the effects of gravity are indistinguishable from the effects of acceleration. In other words, an observer cannot tell the difference between standing on a stationary planet and being in a rocket accelerating through space.

2. How is the Strong Equivalence Principle different from the Weak Equivalence Principle?

The Strong Equivalence Principle is a more strict version of the Weak Equivalence Principle. While the Weak Equivalence Principle only applies to small regions of spacetime, the Strong Equivalence Principle applies to all regions, regardless of their size or curvature.

3. Why is the Strong Equivalence Principle important in physics?

The Strong Equivalence Principle is important because it is a fundamental principle that helps us understand the behavior of gravity and its effects on objects in the universe. It has been a cornerstone of Einstein's theory of general relativity and has been tested and confirmed through numerous experiments.

4. How is the Strong Equivalence Principle related to the concept of inertia?

The Strong Equivalence Principle is closely related to the concept of inertia. Inertia is the tendency of an object to resist changes in its motion, and the Strong Equivalence Principle states that this resistance to change is equivalent to the effects of gravity. This means that the mass of an object is directly related to its ability to resist changes in motion.

5. Are there any exceptions to the Strong Equivalence Principle?

While the Strong Equivalence Principle has been tested and confirmed in many situations, there are some exceptions. For example, in extreme cases such as near the event horizon of a black hole or during the Big Bang, the effects of gravity and acceleration may not be equivalent. However, in most everyday situations, the Strong Equivalence Principle holds true.

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