"Gravity Waves"

[tmccort]

E = mc^2 doesn't care about rest mass... that's the whole point.<br /><br />If you are talking about invariant mass (the correct definition of mass) then E = mc^2 does not apply. Instead you would have to use a different equation.<br /><br />Here is another page from the same site that explains more: http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

 

[igorsboss]

I understand that mass refers to either gravitational mass or inertial mass, or both, depending on context. I also understand that mass generally refers to rest mass, but mass increases depending on the speed of the (massive) particle, and this additional mass is called relativistic mass. Also, photons do not have a rest state, and hence no rest mass. I understand that photons are considered massless; otherwise, they would not reach the speed of light.<br /><br />Now, consider the scenario of a star suddenly going "poof", converting all of its mass to energy. The energy, E, released will be equal to the (original rest gravitational) mass of the star, times c squared. (e=mc^2)<br /><br />This scenario is used as an example of a source of (elusive) gravitational waves; in particular, when mass is converted to energy, the gravity dissapears.<br /><br />I'm saying that's possibly a bunch of BS, and here's why...<br /><br />1) According to the law of conservation of mass and energy, the same quantity of energy that was released when the star went "poof" could later be construct a new star, according to m=Ec^-2. And, when that happens, the gravity suddenly switches back on again. Hmmm....: what happened to the gravity in the meantime???<br /><br />2) According to the law of conservation of momentum, if an object (ie. a firecracker) simply explodes, its center of mass remains the same. That is, the sum of the momenta (total momentum) remains the same.<br /><br />The same goes for a star: if it goes "poof", its total momentum must also remain the same... except in this case, some of the mass was converted to energy in the form of photons. Although photons are massless, they do have momentum (p=E/c).<br /><br />Well, if (massless energetic) photons carry away momentum, and the total momentum remains the same, then doesn't the center of gravity remain the same too? So, then, where is the gravitational wave coming from?<br /><br />So, here's my "jatslo moment" for the month: Perha

 

[nojocujo]

If you converted a star (poof) to energy would you not also create a gravitational wave (pressure wave) traveling at the same speed c as the energy emitted? When you say poof to what extent do you mean?? A complete energy conversion? Isn't e=mc^2 relative to the splitting of an atom (Proton/Neutron)? A complete conversion would be also splitting the protons and neutrons into quarks and subsets of same and does relativity address that mass energy conversion ratio? I think that supernova, grb and xrf's might demonstrate a fusion reaction (gluonic?) at that level of energy. The same wave traveling at the speed of light would be distorting spacetime (flattening spacetime), any energy created and constrained within this bubble or local spacetime distortion would appear redshifted due to the flattening of spacetime.

 

[tmccort]

<br />igorsboss, here is a nice video showing what would happen if the sun were to disappear. It's from a PBS string theory documentary called The Elegant Universe.<br /><br />http://www.pbs.org/wgbh/nova/elegant/media2/3012_q_03.html

 

[jatslo]

..."<font color="yellow">gravitational wave (pressure wave)</font>... <--- Now that sings the dynamic harmonic sound of sweetness to my ears, so keep plugging away, because I know you are onto something.

 

[igorsboss]

<font color="yellow">igorsboss, here is a nice video showing what would happen if the sun were to disappear. It's from a PBS string theory documentary called The Elegant Universe.</font><br /><br />Excellent! This video elegantly depicts exactly what I'm talking about.<br /><br />I'm saying this example is bogus, because no star can suddenly dissapear. This is what I meant by going "poof". Even a supernova must obey the conservation laws.<br /><br />Where does the gravity go when mass is converted to energy?<br /><br />Where does the gravity come from when energy is converted to mass?<br /><br />Since the gravity that goes away always equals the gravity that comes back later, does this suggest a law of conservation of gravity?<br /><br />Do photons warp space gravitationally according to their momenta, even though they have no rest mass? We know they are accelerated (bent) by large gravitational fields.<br /><br />It appears to me that gravitational waves are the result of the change in the <i>geometry</i> of the star. The wave is generated when there is a significant shift in how the mass (and energy) of the star is <i>distributed</i>. <br /><br />For example, the gravitational field of a large, diffuse dust cloud would be different than the gravitational field of a neutron star of the same mass, because the matter is distributed differently in the two cases.

 

[igorsboss]

...But here on SDC, stars just appear! What an ironic post!

 

[bobw]

I have read the whole thread and have been following LIGO for many years. Here's a blurb from their website.<br /><br />LIGO may be able to detect some or all of these astrophysical sources of general-relativistic gravity waves:<br /><br />Waves from the coalescence of massive objects such as neutron stars or black holes. <br /><br />Waves from rapidly-spinning compact objects that are asymmetric, perhaps a variety of neutron star.<br /><br />Waves from supernovae.<br /><br />Remnant gravitational radiation from the big bang.<br /><br />I don't know but I was thinking that since gravity waves are from the acceleration of mass if a star just disappeared then mass wouldn't accelerate so there wouldn't be gravity waves from that event. The curvature of space in the area would flatten and the flattening would propogate at the speed of light. <br /><br />Supernovae throw a lot of mass but the hypothetical total conversion to energy sounds to me to be a lot like disappearing. I'm voting no gravity waves for that one too. <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>I'm saying this example is bogus, because no star can suddenly dissapear. This is what I meant by going "poof". Even a supernova must obey the conservation laws. <p><hr /></p></p></blockquote><br /><br />Ah, I see the problem, igorsboss. You're taking this as if people are saying stars could suddenly disappear. They're not. It's just a thought experiment, famously proposed by Albert Einstein. Everybody knows a star couldn't suddenly disappear. But if it could, then where would its gravity go? It may seem like a pointless exercise, since of course it can't really happen, but it is a useful illustration of a fundamental question: does gravity propagate over time, like light, or does it have an instantaneous effect? <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Saiph]

right, the same question can be asked in a different manner: What do we see, gravity wise, if the star moves really fast? Does gravity always tell us exactly where the star is (I.e. information is transmitted instantaneously via gravity) or is there a time lag as there would be with light? <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[j_rankin]

The gravity emitted from the star would be greater, due to its velocity.

 

[nojocujo]

Gravity has always been construed to be like a pickup in a bar "always attractive never repulsive". Now this is my crazy thinking but I do think that gravitational waves can and do flatten spacetime and in so doing also serve to act in a repulsive manner accelerating matter relativistically. Using GRB, XRF (matter within the schwartzchild radius) and supernova(having matter extant to the schwartzchild radius) as an example where a local spacetime distortion would occur as a result of a relativistic collapse of the mass and and the resulting rebound of the gravitational wave... GRB and XRF allowing energy to escape the event horizon due to the brief cancelation of the schwartzchild radius as the wave passes. Supernova being a product of the wave and the radius being inside the star and the matter outside the radius being accelerated to relativistic speeds as a result of both the fission reactions and the wave itself. Since the light emitted will be behind the gravitational wave it should be redshifted and the incremental spacetime distortion will decrease on the the inverse square. More distant supernova would be redshifted incrementally on the inverse square as a result. I guess I should state that gravity which weakens on the inverse square going away from the mass also strenghtens on the square. It does not recognize Planck Length and stop there with gravity becoming the dominant force as spacetime becomes increasingly curved.

 

[jatslo]

"<font color="yellow">Gravity has always been construed to be like a pickup in a bar "always attractive never repulsive".</font><br /><br />There cannot only be one; however, I am confused about which one is which, because I tried dissecting a star last night, and I got very confused. The effect was kind of like losing your bearing of direction, as in getting lost. Anyway, it is a long story involving a helium core and cold fusion, in short, I found a very dense core that had both high and low pressure characteristics at the same time, and I don't understand why, yet.<br /><br />"<font color="yellow"> Now this is my crazy thinking but I do think that gravitational waves can and do flatten space-time and in so doing also serve to act in a repulsive manner accelerating matter relativistic ally.</font><br /><br />Yes, and no; there are quite a lot of variables that one must consider, and I do not think flat is a good word. Try radial flatness emanating from one point in space-time in infinite directions. If the sun's mass increases due gravity leakage over time, Earth's orbit should shift outward; however, the sun would not be as hot and we could freeze, as opposed to getting fried like some science fiction writers would have you believe. On the flip side, if we added fuel to the sun over time, the sun will shrink and become hotter; our orbit would shift inward to a tighter and a hot sun fries us. This is all relative to velocity, and it would be almost impossible to predict what would happen. A more sudden event could eject us, or suck us in.<br /><br />If I were executing research in this arena, I would measure the velocity of pressure waves that emanate from a nuclear detonation, and then multiple the velocities to the sun's equivalent. This should give you the speed of gravity waves; if, in fact, you can accurately measure the sun. It seems possible to state pretty accurately that the sun requires (X) amount of stuff to produce (Y) amount of energ

 

[paintwoik]

<blockquote><font class="small">In reply to:</font><hr /><p>Where does the gravity go when mass is converted to energy? <p><hr /></p></p></blockquote> In this particular instance the gravitational wave (waves) would collapse in an instantaneous fashion. The gravitational waves does not go poof, it just colapses to a photon, which is a gravitational wave of sorts.<br /><blockquote><font class="small">In reply to:</font><hr /><p>Where does the gravity come from when energy is converted to mass?<p><hr /></p></p></blockquote> Since the gravity is already there in the form of a photon we don't need to ask where it came from. It's rather a question of the manner of propagation. A photon moving in a straight line as opposed to a photon in orbit for instance, wherein one would interact much less than the other in terms of gravitational influence.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Do photons warp space gravitationally <p><hr /></p></p></blockquote> Warped seems like the wrong word here. I look at photons as geometrical constructs that are curved for reasons I don't wish to get into for lack of time.<br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>It appears to me that gravitational waves are the result of the change in geometry .<p><hr /></p></p></blockquote><br />I took out four words in your sentence here. This is the whole thing in a nutshell.<br /><br />