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Subject:
Speed of Propagation of Gravity
Category: Science > Physics Asked by: bazuul-ga List Price: $10.00 |
Posted:
29 Jul 2004 17:44 PDT
Expires: 29 Jul 2004 23:09 PDT Question ID: 381053 |
Since I was a kid, I've wondered what would happen to the orbit of the Earth if the Sun suddenly ceased to exist. Would the Earth continue to orbit around "nothing" for the 8 minutes or so that it would take light to travel from the Sun to the Earth? Intuitively, I have a hard time picturing the Earth orbiting around nothing. I would think that it would instantly fly off into space. But that would violate the law that information can not travel faster than light. I've tried researching this on my own but get conflicting data. Here are two links, one from space.com that says the speed of gravity is near the speed of light, and another that says that it is much faster. http://www.space.com/scienceastronomy/gravity_speed_030107.html http://www.metaresearch.org/cosmology/gravity/speed_limit.asp My specific question is this: If the Sun were made to vanish, would the Earth continue to rotate around the spot where the Sun was until the last rays of light from the Sun hit it? |
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There is no answer at this time. |
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Subject:
Re: Speed of Propagation of Gravity
From: crythias-ga on 29 Jul 2004 18:24 PDT |
All this is stuff even the experts don't agree on. :) You expect someone (with all due respect to the wonderful researchers here) to provide a more clear cut answer than that? :) A 20% margin of error to boot :) |
Subject:
Re: Speed of Propagation of Gravity
From: bazuul-ga on 29 Jul 2004 18:33 PDT |
Thanks for the comment, Crythias. I'm hoping that there is a generally accepted answer in the physics community that not everybody is already clued to. I wouldn't have asked the question if I didn't think it hasn't already been answered. If mankind simply doesn't know what will happen in this scenario yet, then I forget about it because the answer isn't out there. A lot of people in my generation still think Australia is a continent. :) |
Subject:
Re: Speed of Propagation of Gravity
From: case1234-ga on 29 Jul 2004 20:45 PDT |
Hi bazuul-ga, Good question. This was a topic that Einstein mulled over for quite some time. The end result was his theory of special relativity. In this, he calculated that the gravitational waves of which you speak, travel at EXACTLY the speed of light. Interesting eh? If you'd like to learn more about Newtonian physics, relativity, quantum mechanics, and string theory, simply check out the NOVA website on the PBS homepage. (http://www.pbs.org/wgbh/nova/elegant/program.html). They did a show not to long ago called the "Elegant Universe". The entire episode is available in streaming video at this website, and you can watch it for free. They address your particular question (with some cool computer animations) in Chapter three of hour 1 ("A New Picture of Gravity"). The entire video is explained in laymans terms, so it's pretty easy to understand. Enjoy! |
Subject:
Re: Speed of Propagation of Gravity
From: case1234-ga on 29 Jul 2004 20:49 PDT |
Just noticed a mistake.... Einstein talked about this in his GENERAL theory of relativity, not his thoery of special relativity. FYI |
Subject:
Re: Speed of Propagation of Gravity
From: bazuul-ga on 29 Jul 2004 20:50 PDT |
Thanks Case1234, much appreciated. I'll give it a go. |
Subject:
Re: Speed of Propagation of Gravity
From: neilzero-ga on 29 Jul 2004 21:53 PDT |
I think the mainstream opinion is that space is warped by gravity, and it would unwarp instantly or at the speed of light if the source of gravity was removed instantly. Some experiments have led to one conclusion, and others to the other conclusion. None of the experiments have been compelling. If a compact star passes though our Solar System at 0.999 c (with respect to Earth) next year, we may have compelling data for persons who servive. It is generally thought, the probability is very close to zero for a nearby compact star to have a velocity of even 1% of light speed, which may not br fast enough to produce compeling data reguarding the speed of gravity. Neil |
Subject:
Re: Speed of Propagation of Gravity
From: purkinje-ga on 29 Jul 2004 22:06 PDT |
The second website you provide is hardly a reputable source since it is a metaphysical/cosmology website. However, much of the info on there is pretty good, but I noticed a few incongruencies and propagandish type material. If gravity is a particle (the gravitron), then it would be impossible to go faster than light, even if it had zero rest-mass (unless it were like the theoretical tachyon, which cannot go below the speed of light). But what in physics anymore is *just* a particle? haha. I thought of a question similar to what you are asking, and it may give another perspective on the subject. Imagine a long rod or bar. If you push it, doesn't the other end also instantaneously accelerate (assuming there is no compression of the material)? This is because all the atoms have electrical forces (which are field forces, like gravity) that repel each other, or the bonds themselves keep the conformation of the rod (as in carbon fiber rods). So by pushing one end of the bar, does that mean that force was instantaneously transferred to the other end of the bar? This is a similar question to yours, except instead of attractive forces it involves repulsive forces or the forces of molecular bonds. (I realize that there will always be some compression of the material though-- but could this compression travel through the bar faster than light, since it is not an actual object? What about sheering forces that travel faster than the natural speed of wave propagation in a material? I'm almost sure the answer is that the propagations still cannot travel faster than light, since the reason for things not being able to travel faster than light is not just that mass increases with velocity requiring infinite energy, but also the component of time slowing for something moving through space. It seems that to fully answer the question, we'd have to know the mechanism of how gravity works-- is gravity a particle, a wave, both, or is it an actual effect of mass on space and time. (e.g., mass could just instrinsically slow down time in space-- then, as an object enters regions of more slowing of time, it loses rest mass, and gains kinetic energy to maintain the total energy, thus creating the gravity's force. This requires no particles at all, but it still requires "info" to be carried through space....) It remains to be seen how field forces work. In quantum mechanics, if a particle randomly appears and then quickly disappears, as sometimes happens, does it instantaneously exert effects on surrounding particles? My guess is yes, just by its nature of coming into existence, the other particles instantly respond to the loss of energy in the system and the addition of mass into the system. How that happens, I have no idea. |
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