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When we have a sound-wave it means air-pressure changes along the peaks and troughs of the wave. When we have a gravitational wave what measurable quantity cha

When we have a sound-wave it means air-pressure changes along the peaks and troughs of the wave. When we have a gravitational wave what measurable quantity changes?

mrkramer 5y ago
Ask a physicist but as far as I understood gravitational waves are dents in spacetime[0] and as they travel their energy, momentum, and angular momentum change over time because of interaction and collision with other "stuff" in space. Idk how you can measure any of that. [0]https://www.esa.int/Science_Exploration/Space_Science/Gravitational_waves_dents_in_spacetime https://www.esa.int/Science_Exploration/Space_Science/Gravit...
- galaxyLogic 5y ago
  Is there a simple way to explain what a "dent in spacetime" means? How can it be measured. I don't doubt that science and you all are right, I'm only asking questions in the hope that there is a simple explanation that would make a light-bulb go off in my head.
jjk166 5y ago
Gravitational waves change the definition of length and time. If you have some baseline pressure in a room, a pressure wave causes a small region to be briefly higher or lower pressure. If you have a meterstick and a stopwatch, a gravitational wave causes the meter to grow bigger or smaller and the stopwatch to run fast or slow. It's as if you are briefly closer to some immense object like a black hole which causes time dilation - indeed that's exactly what it is. No matter how ridiculously far away they are, as two celestial objects orbit each other they are continually moving closer and then further away from you, and while gravity drops off with distance it never goes to zero. You are feeling the gravitational pull of that celestial object on the other side of the universe getting infinitesimally stronger and weaker as the distance between you and it shrinks and grows, or more accurately as the distance between you and where it was all those millions of years ago when the waves were first emitted shrinks and grows.
- galaxyLogic 5y ago
  So you're saying that measuring gravitational waves means we measure how much a given distant mass pulls us towards it and the value of that pull-force goes up and down like a wave? Can we measure the "pull" of a specific distant mass? Or do we measure something else like the change in distance between two points?
  - jjk166 5y ago
    Well the pull of gravity is really just the warping of spacetime. A gravitational wave communicates the change in the gravitational field caused by an accelerating mass. We measure this by shooting lasers along two paths and comparing how long it takes light to traverse the paths, the warping of spacetime causes this value to change. You could use this value to directly calculate how much the pull of the distant object upon us varied. But we can only see the variation, not the absolute pull, of these distant objects; and even then only for extreme cases like black hole and neutron star pairs moments before they collide.
    - galaxyLogic 5y ago
      Good explanation thanks. // we can only see the variation Can we also see the direction from which the wave is coming from ?

When we have a sound-wave it means air-pressure changes along the peaks and troughs of the wave. When we have a gravitational wave what measurable quantity changes?

mrkramer 5y ago

Ask a physicist but as far as I understood gravitational waves are dents in spacetime[0] and as they travel their energy, momentum, and angular momentum change over time because of interaction and collision with other "stuff" in space. Idk how you can measure any of that. [0]https://www.esa.int/Science_Exploration/Space_Science/Gravitational_waves_dents_in_spacetime https://www.esa.int/Science_Exploration/Space_Science/Gravit...

galaxyLogic 5y ago
Is there a simple way to explain what a "dent in spacetime" means? How can it be measured. I don't doubt that science and you all are right, I'm only asking questions in the hope that there is a simple explanation that would make a light-bulb go off in my head.

jjk166 5y ago

Gravitational waves change the definition of length and time. If you have some baseline pressure in a room, a pressure wave causes a small region to be briefly higher or lower pressure. If you have a meterstick and a stopwatch, a gravitational wave causes the meter to grow bigger or smaller and the stopwatch to run fast or slow. It's as if you are briefly closer to some immense object like a black hole which causes time dilation - indeed that's exactly what it is. No matter how ridiculously far away they are, as two celestial objects orbit each other they are continually moving closer and then further away from you, and while gravity drops off with distance it never goes to zero. You are feeling the gravitational pull of that celestial object on the other side of the universe getting infinitesimally stronger and weaker as the distance between you and it shrinks and grows, or more accurately as the distance between you and where it was all those millions of years ago when the waves were first emitted shrinks and grows.

galaxyLogic 5y ago
So you're saying that measuring gravitational waves means we measure how much a given distant mass pulls us towards it and the value of that pull-force goes up and down like a wave? Can we measure the "pull" of a specific distant mass? Or do we measure something else like the change in distance between two points?
- jjk166 5y ago
  Well the pull of gravity is really just the warping of spacetime. A gravitational wave communicates the change in the gravitational field caused by an accelerating mass. We measure this by shooting lasers along two paths and comparing how long it takes light to traverse the paths, the warping of spacetime causes this value to change. You could use this value to directly calculate how much the pull of the distant object upon us varied. But we can only see the variation, not the absolute pull, of these distant objects; and even then only for extreme cases like black hole and neutron star pairs moments before they collide.
  - galaxyLogic 5y ago
    Good explanation thanks. // we can only see the variation Can we also see the direction from which the wave is coming from ?