Would Gravity Waves Show Doppler Shift?

In summary, the conversation discusses the relationship between gravity waves and their frequency, as well as how they are affected by an object's movement. The experts explain that the frequency of a gravity wave indicates the rotation rate of the object emitting it and that it does not affect its strength. They also mention that the source of gravity waves is due to the changing relationships between multiple objects and not emitted by individual objects. They also clarify that the concept of "rotation" in the context of gravity waves refers to a changing relationship between objects, rather than an actual rotation. Overall, the experts agree that the frequency of gravity waves does not significantly impact their strength.
  • #1
peter0302
876
3
Random question that I thought of while trying to fall asleep last night. :)

We all know that galaxies moving very fast away from us exhibit visual redshift.

If gravity waves / gravitons are real, they must then have a frequency of some kind. Does the frequency of a gravity wave affect its strength? (i.e. does a more massive object emit higher frequency gravity waves?) If so, would an object moving away from us be "red shifted" to have a weaker gravitational effect than if it were the same distance away, but moving towad us?
 
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  • #2
The frequency of the wave indicates the rotation rate of the object emitting it.

And yes, they would exhibit a Doppler shift. Doppler shift happens for any periodic emission with a finite propagation speed. Light, sound, and gravity waves all have this property.
 
  • #3
Ah, I see. So the frequency of the gravity wave would not affect its strength?

I was wondering if gravity waves would behave like photons, i.e., the frequency - not amplitude - would determine the force it exerted on a particle.
 
  • #4
Frequency would determine the energy of individual gravitons.

However, in practice the field of a gravitational wave would contain many gravitons. The amplitude of the field would determine the force exerted on a mass.

Similarly, it is the electric field amplitude that determines the force that a laser beam exerts on, say, an electron.
 
  • #5
Redbelly98 said:
The frequency of the wave indicates the rotation rate of the object emitting it.

By "rotation", do you mean about an axis through the object's center of gravity, something akin to an orbit, or both?

Regards,

Bill
 
  • #6
Redbelly98 said:
The frequency of the wave indicates the rotation rate of the object emitting it.
I think in GR it is incorrect to think that gravitational waves are emitted by objects. Gravitational waves exist due to the changing relationships between multiple objects.
 
  • #7
MeJennifer said:
Gravitational waves exist due to the changing relationships between multiple objects.

I think that is sufficiently vague to cover what I was alluding to. :smile:

Regards,

Bill
 
  • #8
Antenna and MeJen,

I should probably have used the word "system" rather than object. At any rate, I was making a general comment to answer the op's question about the meaning of frequency.

As to the source of gravity waves that people are trying to detect, I'll defer to somebody more knowledgeable than I:
https://www.physicsforums.com/showpost.php?p=1696992&postcount=5

Regards,

Mark
 
  • #9
Well, what I (the op :)) was getting at was would an object moving very fast either toward or away from us exert a different instantaneous force than if it were stationary, due to doppler shift of the gravity waves?

If I understand Redbelly correctly, the answer is no.
 
  • #10
Redbelly98 said:
As to the source of gravity waves that people are trying to detect, I'll defer to somebody more knowledgeable than I:
https://www.physicsforums.com/showpost.php?p=1696992&postcount=5

The "mountain range" on a spinning object is a pretty good example of what I was thinking of when I said "akin to an orbit". I might even wager that such an oscillation would yield the highest frequency waves.

Regards,

Bill
 
  • #11
peter0302 said:
Well, what I (the op :)) was getting at was would an object moving very fast either toward or away from us exert a different instantaneous force than if it were stationary, due to doppler shift of the gravity waves?

If I understand Redbelly correctly, the answer is no.

I think E=hf still holds (which would imply the opposite), but I'll defer to someone more knowledgeable than myself.

Regards,

Bill
 

1. What are gravity waves?

Gravity waves are ripples in the fabric of space-time caused by massive objects moving through the universe. They were first predicted by Albert Einstein's theory of general relativity.

2. How are gravity waves different from electromagnetic waves?

Gravity waves are different from electromagnetic waves in that they are not a type of radiation and do not carry energy. Instead, they are distortions in the fabric of space-time itself.

3. How would gravity waves show Doppler shift?

Gravity waves would show Doppler shift because, as they travel through space, their wavelength would change depending on the velocity of the source and the observer. This change in wavelength is known as the Doppler effect.

4. What evidence do we have for the existence of gravity waves?

The existence of gravity waves was first indirectly detected in 1974 through observations of a binary pulsar system. In 2015, the first direct detection of gravity waves was made by the Laser Interferometer Gravitational-Wave Observatory (LIGO).

5. How would the detection of gravity waves with Doppler shift impact our understanding of the universe?

The detection of gravity waves with Doppler shift would provide valuable information about the motion and properties of massive objects in the universe, such as black holes and neutron stars. It would also confirm the validity of Einstein's theory of general relativity and open up new avenues for studying the universe.

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