Gravitational Waves: Mass Interaction Questions Answered

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Discussion Overview

The discussion revolves around the behavior of gravitational waves in relation to mass, particularly focusing on their intensity as they escape gravitational fields and the concept of absorption by massive objects like black holes. Participants explore theoretical implications and analogies with electromagnetic waves.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the intensity of gravitational waves decreases as they escape from mass, suggesting a potential analogy to light waves and redshift.
  • Another participant argues that gravitational waves cannot be "completely absorbed" by mass, drawing parallels to electromagnetic waves and energy conversion into heat.
  • A participant raises the scenario of gravitational waves interacting with black holes, asking if they would be partially absorbed or converted to Hawking radiation.
  • Responses clarify that black holes behave differently from ordinary objects, indicating that gravitational waves do not re-emit in the same manner as other masses.

Areas of Agreement / Disagreement

Participants express differing views on the absorption and re-emission of gravitational waves by massive objects, particularly black holes. The discussion remains unresolved regarding the specifics of these interactions.

Contextual Notes

Participants rely on analogies with electromagnetic waves, which may not fully capture the complexities of gravitational wave interactions. The implications of Hawking radiation in this context are also not fully explored.

NotASmurf
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Hey all. Since gravitational waves travel at the speed of light, when they are "escaping" from mass, doe's their intensity lower? If so what mass would be needed to completely absorb a gravitational wave given the wave's properties? Any help appreciated.
 
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NotASmurf said:
Since gravitational waves travel at the speed of light, when they are "escaping" from mass, doe's their intensity lower?

In other words, do they behave like light waves and "redshift" as they climb out of a gravity well? I believe the answer is yes, but I have not seen any detailed treatments of this.

NotASmurf said:
what mass would be needed to completely absorb a gravitational wave

A wave can't really be "completely absorbed". Consider the analogy with electromagnetism: an object absorbs EM waves if it can take their energy and turn it into heat--i.e., into vibrations of its atoms (or molecules). But that heat will gradually get transferred, and at least part of it will go into EM radiation again--for example, objects at room temperature emit (mainly) infrared radiation, i.e., EM waves. So the original EM waves didn't get "completely absorbed"; they just got converted into other EM waves.

Similarly, a mass might convert the energy of incoming gravitational waves into heat, but that heat will get radiated away again, and some of it (at least in principle) will be radiated as gravitational waves again. So the gravitational waves won't get "completely absorbed".
 
So even if a gravitational wave from an external source hits a black hole, it will be partially absorbed, but will still be re-emitted? or would it all be converted to hawking radiation?
 
NotASmurf said:
even if a gravitational wave from an external source hits a black hole, it will be partially absorbed, but will still be re-emitted?

Black holes are not ordinary objects, so no, not the way you mean.

NotASmurf said:
or would it all be converted to hawking radiation?

Yes. Technically that counts as "re-emitted", but you distinguished it from other possible ways of being re-emitted, none of which are possible for a black hole.
 

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