Robittybob1 Posted March 22, 2016 Posted March 22, 2016 "gravitational spiral wave" put those words into Google search and look at the many images of gravitational waves. Which one gives the best description and why? I'm thinking the two masses orbiting each other for a billion plus years has produced 2 waves that have traveled like 2 spirals if looked at on a plane extending from the orbital plane. Or a sinusoidal line if you look at the effect at a point. What is the shape in the 3D space? http://www.dam.brown.edu/people/sandsted/APMA1940R.php The middle picture is a single spiral wave looked at from a plane and a line but I couldn't find a 3D image that I could relate to. Does anyone have an idea of the description of a 3D gravitational wave at a distance from the binary? https://en.wikipedia.org/wiki/Plane_wave#/media/File:Plane_wave_wavefronts_3D.svg https://books.google.co.nz/books?id=Tna0Va-iRygC&pg=PA447&lpg=PA447&dq=h%2B+and+hx+polarization&source=bl&ots=FvhUfLtR0U&sig=mhJIIuVgdZsH1MSsClk8t6Zuess&hl=en&sa=X&ved=0ahUKEwjV2Myt6NPLAhXk4KYKHeDBDHIQ6AEIJTAE#v=onepage&q=h%2B%20and%20hx%20polarization&f=false Says the waves are "plane fronted waves" so that is like the wave fronts in the first link. So my thought they are like a section of onion. Shells make the onion spherical but if you cut an onion into slices and the cut the slices into strips you could get pieces that are like plane fronted waves.
ajb Posted March 22, 2016 Posted March 22, 2016 With any graphical representation you need to take care with what it is depicting. You should read whatever description comes with the image very carefully. As to what is best, well this will depend on what you are trying to see using the image. In relation to pp-waves, these are an important class of exact solution to the Einstein field equations, and what most mathematically minded people would think of as a gravitational wave. Though astrophysically important waves are going to be more complicated than that.
Robittybob1 Posted March 22, 2016 Author Posted March 22, 2016 (edited) With any graphical representation you need to take care with what it is depicting. You should read whatever description comes with the image very carefully. As to what is best, well this will depend on what you are trying to see using the image. In relation to pp-waves, these are an important class of exact solution to the Einstein field equations, and what most mathematically minded people would think of as a gravitational wave. Though astrophysically important waves are going to be more complicated than that. I wanted to understand the spread throughout space. Like if they are plane fronted waves at any distant point that suggests to me shell like structure going outward at the speed of light. But each shell is connected to the one following with a spiral action. What shape are pp-waves? https://en.wikipedia.org/wiki/Pp-wave_spacetime#Physical_interpretation In other words, pp-waves model various kinds of classical and massless radiation traveling at the local speed of light. This radiation can be gravitational, electromagnetic, Weyl fermions, or some hypothetical kind of massless radiation other than these three, or any combination of these. All this radiation is traveling in the same direction, .So that sounds like spheres within spheres with the plane fronts moving outward at the speed of light. Small sections of the surface at any point all the radiation is traveling in "same direction". Edited March 22, 2016 by Robittybob1
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 This article starts to explain in terms I'm more familiar with: Could Gravitational Waves Ever Be Strong Enough To Feel? http://www.forbes.com/sites/briankoberlein/2016/02/13/could-gravitational-waves-ever-be-strong-enough-to-feel/#16d47c14aac3 The amount of shift caused by a gravitational wave is due to its amplitude, not its energy. While the energy of gravitational waves follow the inverse square relation, the amplitude of gravitational waves follows the inverse distance relation. In other words, if we were half as far away from the merger we’d have seen four times the energy, but only twice the shift. As long as we aren’t too close to the merger where things become complicated and nonlinear, this relation will give us a good idea of just how strongly the gravitational waves will affect us. Energy falls off by the inverse square relationship, but the amplitude by the inverse relationship. The wavelength and frequency is determined by the orbital parameters, but as the wave travels those two components do not vary, but the energy and amplitude decline with distance as per the discussed relationships.
EdEarl Posted March 25, 2016 Posted March 25, 2016 (edited) Light waves are photons traveling through space. Ocean waves move water up and down as the wave moves horizontally, sound waves compress and decompress air or other matter. Are gravity waves the movement of gravitons or Higgs bosons, space-time being compressed and decompressed, Higgs field perturbations, or something else? Edited March 25, 2016 by EdEarl
Strange Posted March 25, 2016 Posted March 25, 2016 Space-time being stretched and squeezed is the closest description. (As always, the devil is in the detail of the directions in which these take place.) Nothing to do with Higgs field/bosons which have nothing to do with gravity (other than being a cause of a small part of the mass of matter). We don't currently have a theory of gravitons and gravity.
EdEarl Posted March 25, 2016 Posted March 25, 2016 Space-time being stretched and squeezed is the closest description. (As always, the devil is in the detail of the directions in which these take place.) Nothing to do with Higgs field/bosons which have nothing to do with gravity (other than being a cause of a small part of the mass of matter). We don't currently have a theory of gravitons and gravity. That sounds like gravity waves traveling through space-time is analogous to sound traveling through air. Space-time is filled with virtual particles; do gravity waves move by compressing and decompressing virtual particles? I suspect the answer is no; although, they would move with space-time.
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 Light waves are photons traveling through space. Ocean waves move water up and down as the wave moves horizontally, sound waves compress and decompress air or other matter. Are gravity waves the movement of gravitons or Higgs bosons, space-time being compressed and decompressed, Higgs field perturbations, or something else? That sounds like gravity waves traveling through space-time is analogous to sound traveling through air. Space-time is filled with virtual particles; do gravity waves move by compressing and decompressing virtual particles? I suspect the answer is no; although, they would move with space-time. As long as you can think of it in 3D. It is the 3D nature of the GW I trying comprehend in this thread. There are animations showing ripples in ponds and others with tubes and others with wavy lines. But I want to develop how to think of the total effect radiating out from the source in a 3D fashion so we can understand how we can detect the wave wherever you are. Case: ripples in ponds - you would have to on that surface and others with tubes - you would have to be in the region and others with wavy lines - you would have to be on that line. 3D wave - anywhere in space you can detect the GW
Strange Posted March 25, 2016 Posted March 25, 2016 That sounds like gravity waves traveling through space-time is analogous to sound traveling through air. Space-time is filled with virtual particles; do gravity waves move by compressing and decompressing virtual particles? It is similar. The difference is that sound waves are changes in compression in the direction of travel (z). While gravitational waves have an effect in x, y and t but not z. I suspect the answer is no; although, they would move with space-time. Correct: no and yes. As long as you can think of it in 3D. It is the 3D nature of the GW I trying comprehend in this thread. 4D. Space-time, remember. ripples in ponds - you would have to on that surface And these are different again in that they are transverse waves in just one directional orthogonal to the direction of travel.
EdEarl Posted March 25, 2016 Posted March 25, 2016 As long as you can think of it in 3D. It is the 3D nature of the GW I trying comprehend in this thread. There are animations showing ripples in ponds and others with tubes and others with wavy lines. But I want to develop how to think of the total effect radiating out from the source in a 3D fashion so we can understand how we can detect the wave wherever you are. Case: ripples in ponds - you would have to on that surface and others with tubes - you would have to be in the region and others with wavy lines - you would have to be on that line. 3D wave - anywhere in space you can detect the GW Pictures characterize gravity waves somewhat like ripples in ponds because they are 2D trying to represent 3D; thus, misleading. I can't imagine a video that would be authentic, but maybe someone can. It seems we are left to our imagination. It is similar. The difference is that sound waves are changes in compression in the direction of travel (z). While gravitational waves have an effect in x, y and t but not z. Not z! That destroys my notion of how they propagate and seems to violate locality. How can they be so limited?
Strange Posted March 25, 2016 Posted March 25, 2016 Not z! That destroys my notion of how they propagate and seems to violate locality. How can they be so limited? They travel in all directions, but any point in space, they will cause distortions in the directions orthogonal to the direction of travel.
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 It is similar. The difference is that sound waves are changes in compression in the direction of travel (z). While gravitational waves have an effect in x, y and t but not z. Correct: no and yes. 4D. Space-time, remember. ..... No one can think in 4D spacetime, so I've been told, so stick to the 3D image first please. So what happens in z dimension? The 3D image is going to use all the dimensions x,y,and z. You must be looking at a local wavefront. Can we leave that aspect to another thread please, another discussion. They travel in all directions, but any point in space, they will cause distortions in the directions orthogonal to the direction of travel. As I said, let's leave that till later. It is the 3D image we are trying to build here. Pictures characterize gravity waves somewhat like ripples in ponds because they are 2D trying to represent 3D; thus, misleading. I can't imagine a video that would be authentic, but maybe someone can. It seems we are left to our imagination. Not z! That destroys my notion of how they propagate and seems to violate locality. How can they be so limited? We can pick up GWs from all directions in space so there must be the 3D structure. Is it like what I have proposed, a 3D spiral? It took me a while to see how the whole wave grows with time, so I don't really know if that is seeing the 4th dimension, but it would be more like seeing a car go down the road with time, which is more like seeing it move in a space coordinate at different times. If you have objects traveling in all 3 space coordinates at different speeds can you then introduce time? You can in the GW case as the wavefronts are moving away at the speed of light, they are all traveling at the same speed. Maybe that is the "z axis" Strange mentioned, the local "z" is always moving at the speed of light.
Strange Posted March 25, 2016 Posted March 25, 2016 No one can think in 4D spacetime, so I've been told, so stick to the 3D image first please. So what happens in z dimension? Z is the direction of propagation. There is no compression or stretching in that direction. As I said, let's leave that till later. It is the 3D image we are trying to build here. I didn't mention time, so that was just a description of what happens in the 3 spatial coordinates.
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 Z is the direction of propagation. There is no compression or stretching in that direction. I didn't mention time, so that was just a description of what happens in the 3 spatial coordinates. "Z is the direction of propagation" of a local wavefront (a small section of the total structure). Z is the direction of propagation. There is no compression or stretching in that direction. I didn't mention time, so that was just a description of what happens in the 3 spatial coordinates. You said "4D spacetime", which is time as well as the 3 space coordinates in #9. We do need to think how it grows in time but is that the same as "4D spacetime"? Our kids are 3 dimensional structure growing in time but that is not thinking in terms of "4D spacetime" surely? I definitely want to picture the 3D gravity wave growing with time.
Strange Posted March 25, 2016 Posted March 25, 2016 "Z is the direction of propagation" of a local wavefront (a small section of the total structure). Correct. I definitely want to picture the 3D gravity wave growing with time. A sphere.
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 (edited) Correct. A sphere. Serial wavefronts within a sphere? I don't accept that image as then there had to be moments when the GW stops and restarts, like the wavefront of a pulsing light. To me it is more like a garden sprinkler but the water drops never falling, but in 3D as well. Here is a possible image a 3D rotating water sprinkler in space. So the fronts aren't shells but growing spirals. The whole GW structure is one wave with many wavefronts when looked at locally, but to imagine the whole structure is what we are trying to do here. Edited March 25, 2016 by Robittybob1
Strange Posted March 25, 2016 Posted March 25, 2016 Serial wavefronts within a sphere? I don't accept that image as then there had to be moments when the GW stops and restarts, like the wavefront of a pulsing light. Gravitational waves propagate at the speed of light. Therefore, the wavefront will be a sphere.
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 Gravitational waves propagate at the speed of light. Therefore, the wavefront will be a sphere. From a point source it might, so that all distances (radii) were the same, but here we have a turning source that has an orbital plane. @Strange - How do you get successive wave fronts from your sphere concept? OK you make an initial sphere. How do you get another, to get the wave fronts?
Strange Posted March 25, 2016 Posted March 25, 2016 (edited) From a point source it might, so that all distances (radii) were the same, but here we have a turning source that has an orbital plane. At some point that will be insignificant. How do you get successive wave fronts from your sphere concept? OK you make an initial sphere. How do you get another, to get the wave fronts? They would be a series of (concentric) spheres. Edited March 25, 2016 by Strange
Robittybob1 Posted March 25, 2016 Author Posted March 25, 2016 At some point that will be insignificant. They would be a series of (concentric) spheres. It never loses its significance as once the orbital distance decreases the frequency increases so at the very time it should be insignificant because of overall distance (1.3 billion ly) the GW effects are maximized (GW150914). Never will they become concentric spheres. For how to you get from one sphere to the next? You can't with continuous GW production, so it is always a spiral, a 3D spiral.
imatfaal Posted March 26, 2016 Posted March 26, 2016 It never loses its significance as once the orbital distance decreases the frequency increases so at the very time it should be insignificant because of overall distance (1.3 billion ly) the GW effects are maximized (GW150914). Never will they become concentric spheres. For how to you get from one sphere to the next? You can't with continuous GW production, so it is always a spiral, a 3D spiral. Do you really not understand the notion of waves? What about an observer who is not 1.3 billion LY away? There is nothing special about our position. The waves propagate spherically - very close in (ie where tidal effects and simple gravity is still massively important) then you cannot ignore the fact that things are not spherically symmetrical but at cosmological distances they are. 1
Robittybob1 Posted March 26, 2016 Author Posted March 26, 2016 Do you really not understand the notion of waves? What about an observer who is not 1.3 billion LY away? There is nothing special about our position. The waves propagate spherically - very close in (ie where tidal effects and simple gravity is still massively important) then you cannot ignore the fact that things are not spherically symmetrical but at cosmological distances they are. I do understand the notion of these gravity waves. The waves are not always going to come from binary orbiting masses 1.3 billion LY away. "There is nothing special about our position." That is why I wanted to know the 3D shape of the wave. How is it that the wave can be detected in any direction? It has a 3D nature, and that 3D nature was not being described by anyone. "The waves propagate spherically - very close in (ie where tidal effects and simple gravity is still massively important) then you cannot ignore the fact that things are not spherically symmetrical but at cosmological distances they are." That sentence shorter version "The waves propagate spherically .... at cosmological distances." Well I had agreed that at large distances the wavefronts would "look" spherical. Do the extreme reaches of a spiral look circular? On closer examination you can follow it back and find it is not quite circular. At a distance it approximates a sphere. So when you do the maths on it one can treat it as a sphere, but I'm looking at the structure of the whole wave. If it was spherical the center point of the GW spheres from one moment of time to the next is changing location. You would then have to consider where the center point is in relation to the binary bodies. The center point of the orbit is the barycenter, but the central point of a gravity wave??? That has never been defined. If it was defined to get the 3D structure I am proposing there would need to be two points that are moving around the barycenter for there are two wavefronts produced per orbit. [From logic these two points would become the centers of mass of the two binary bodies but that is another thread.]
Robittybob1 Posted March 26, 2016 Author Posted March 26, 2016 (edited) .... They would be a series of (concentric) spheres. Are you still standing on that statement? How are you going to get 2 wavefronts per orbit as well as having concentric spheres? Quote RB We can pick up GWs from all directions in space so there must be the 3D structure. Is it like what I have proposed, a 3D spiral? Hypothesis: Binary orbiting masses produce gravitational waves that have a 3D structure. It is hypothesized this is a 3D spiral with the wavefronts moving outward at the speed of light. [it is right to have this hypothesis at the end of the thread for we started off with the concept of finding the 3D structure, and now I have formed an idea that fits in with the facts I have made the hypothesis.] Edited March 26, 2016 by Robittybob1
Strange Posted March 26, 2016 Posted March 26, 2016 How is it that the wave can be detected in any direction? It has a 3D nature, and that 3D nature was not being described by anyone. This has been covered in several threads already. The strength of the waves is not completely isotropic (they are slightly stronger in the orbital plane than in the orthogonal axis) but they travel at the speed of light and so will be spherical (once you are far enough away to ignore the slight asymmetry of the source; i.e. a few radii away).
swansont Posted March 26, 2016 Posted March 26, 2016 Hypothesis: Binary orbiting masses produce gravitational waves that have a 3D structure. It is hypothesized this is a 3D spiral with the wavefronts moving outward at the speed of light. What does this mean? What is spiralling? We already know they are 3D and move at c.
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