8
   

A speed beyond light question ^^

 
 
edgarblythe
 
  1  
Reply Sun 28 Dec, 2008 12:02 pm
You say, that if gravity didn't propagate instantaneously, our solar system would fly apart. Please show your calculations for me to check. - quote

That's hilarious to me this mid day.
gungasnake
 
  1  
Reply Sun 28 Dec, 2008 06:24 pm
@Brandon9000,
The Kopeikin study has been debunked. I'd suggest you read that page on Metarresearch:

http://www.metaresearch.org/cosmology/speed_of_gravity.asp
Brandon9000
 
  1  
Reply Sun 28 Dec, 2008 06:38 pm
@gungasnake,
gungasnake wrote:

The Kopeikin study has been debunked. I'd suggest you read that page on Metarresearch:

http://www.metaresearch.org/cosmology/speed_of_gravity.asp

I asked you to support your contention that if gravity weren't instantanous, then the solar system would fly apart by showing the calculation. Ignoring the question won't confuse me. Show your calculation.
gungasnake
 
  1  
Reply Sun 28 Dec, 2008 10:40 pm
@Brandon9000,
I've never done the calculations myself but it is common knowledge that they have been done by first rate mathematicians and physicists and, generally, the example used is not planetary systems but binary pulsars, since the use of such an extreme example eliminates every other possible theoretical quibble anybody might have. If gravity propagated at C, there would be no such thing as a binary pulsar.
0 Replies
 
gungasnake
 
  1  
Reply Sun 28 Dec, 2008 10:43 pm
@Brandon9000,
I mean, you don't need to be Albert Einstein to see how the thing works. Just draw a circle, a point on the circle, a force vector going from the point to the center ( instantaneous gravity like in real life), and then a vector from the point in the same direction as a vector would have had from the point to the center five or ten degrees back on the circle....
Brandon9000
 
  1  
Reply Sun 28 Dec, 2008 11:22 pm
@gungasnake,
gungasnake wrote:

I mean, you don't need to be Albert Einstein to see how the thing works. Just draw a circle, a point on the circle, a force vector going from the point to the center ( instantaneous gravity like in real life), and then a vector from the point in the same direction as a vector would have had from the point to the center five or ten degrees back on the circle....

And how exactly does this high school physics prove that if gravity weren't instantaneous, but only propagated at the speed of light, the solar system would fly apart?
High Seas
 
  1  
Reply Thu 1 Jan, 2009 09:32 am
@Brandon9000,
Brandon9000 wrote:

gungasnake wrote:

I mean, you don't need to be Albert Einstein to see how the thing works. Just draw a circle, a point on the circle, a force vector going from the point to the center ( instantaneous gravity like in real life), and then a vector from the point in the same direction as a vector would have had from the point to the center five or ten degrees back on the circle....

And how exactly does this high school physics prove that if gravity weren't instantaneous, but only propagated at the speed of light, the solar system would fly apart?


Brandon - Gunga is actually correct in that statement. High-school physics is mostly Newtonian physics, and Newton's gravitational equations unquestionably show the transmission of gravity to be instantaneous.

This was never doubted by anyone since Newton, btw. Subsequent confusion arose because relativity equations for gravity (mathematically speaking, which is the only approach I'm qualified to discuss, being a mathematician and not a physicist) permit both a "geometric" and a "field" interpretation.

I took a seminar with the late, great, Dick Feynman, on mathematical applications of the laws of physics (applications frequently found in apparently completely unrelated fields, like the pricing of options and warrants in financial markets, for which another teacher, Bob Merton, got a Nobel prize, as of course did Feynman) and I posted earlier on this thread a link to his theory of gravity, where he confirms this.

I'll see if I can find the excerpt on the web - BRB. Happy 2009 to y'all, btw!
High Seas
 
  1  
Reply Thu 1 Jan, 2009 09:41 am
@edgarblythe,
Edgar - these aren't necessarily "Gunga's calculations": they're the standard equations valid in both field and geometric interpretations of Lorentz transformations for gravity.

The mathematical equations are not in dispute: light from the sun's last rays (if our sun were to collapse) would still reach us with the usual delay - but we wouldn't be at our previous orbit to see it.

All planets in our solar system would have continued to follow their outwards motions (same as our own artificial satellite orbits work), but now unrestrained by our sun's gravity field, and be flung far into the outer darkness - all of them from Mercury to Sedna and other trans-Uranian objects. Earth and other planets' satellites, including our moon and man-mad objects, should presumably stick around, but wouldn't do us much good!

As promised, will be right back with the Feynman summary.
0 Replies
 
High Seas
 
  1  
Reply Thu 1 Jan, 2009 09:53 am
@gungasnake,
Gunga - at least Dick Feynman agreed with you, even if Brandon and Edgar don't.

Quote:
"It is one of the peculiar aspects of the theory of gravitation, that it has both a field interpretation and a geometrical interpretation. ... the fact is that a spin-two field has this geometrical interpretation: this is not something readily explainable -- it is just marvelous. The geometrical interpretation is not really necessary or essential to physics.


I typed this text in from a printed book, not available online, but this is the book, available in any university or other scientific library:

R.P. Feynman, Feynman Lectures on Gravitation, Addison-Wesley, New York (1995) p. 113
Brandon9000
 
  1  
Reply Thu 1 Jan, 2009 10:29 am
@High Seas,
High Seas wrote:

Brandon9000 wrote:

gungasnake wrote:

I mean, you don't need to be Albert Einstein to see how the thing works. Just draw a circle, a point on the circle, a force vector going from the point to the center ( instantaneous gravity like in real life), and then a vector from the point in the same direction as a vector would have had from the point to the center five or ten degrees back on the circle....

And how exactly does this high school physics prove that if gravity weren't instantaneous, but only propagated at the speed of light, the solar system would fly apart?


Brandon - Gunga is actually correct in that statement. High-school physics is mostly Newtonian physics, and Newton's gravitational equations unquestionably show the transmission of gravity to be instantaneous.

This was never doubted by anyone since Newton, btw. Subsequent confusion arose because relativity equations for gravity (mathematically speaking, which is the only approach I'm qualified to discuss, being a mathematician and not a physicist) permit both a "geometric" and a "field" interpretation.

I took a seminar with the late, great, Dick Feynman, on mathematical applications of the laws of physics (applications frequently found in apparently completely unrelated fields, like the pricing of options and warrants in financial markets, for which another teacher, Bob Merton, got a Nobel prize, as of course did Feynman) and I posted earlier on this thread a link to his theory of gravity, where he confirms this.

I'll see if I can find the excerpt on the web - BRB. Happy 2009 to y'all, btw!

First of all, you're not correct, because Newton's equations make no statement whatsoever about the speed of propagation of gravity. Secondly, Gunga is not correct because both General Relativity and experiment show a speed of light propagation. Furthermore, he is not correct because his ludicrous high school description of a free body diagram does not, as he asserts, prove that the solar system would fly apart if gravity propogation were at the speed of light and not instantaneous.
Brandon9000
 
  1  
Reply Thu 1 Jan, 2009 10:32 am
@High Seas,
High Seas wrote:

Gunga - at least Dick Feynman agreed with you, even if Brandon and Edgar don't.

Quote:
"It is one of the peculiar aspects of the theory of gravitation, that it has both a field interpretation and a geometrical interpretation. ... the fact is that a spin-two field has this geometrical interpretation: this is not something readily explainable -- it is just marvelous. The geometrical interpretation is not really necessary or essential to physics.


I typed this text in from a printed book, not available online, but this is the book, available in any university or other scientific library:

R.P. Feynman, Feynman Lectures on Gravitation, Addison-Wesley, New York (1995) p. 113

Please explain how this quotation implies an instantaneous propagation for gravity. Please give an actual quotation in which Feynman asserts instantaneous propagation. You sound suspiciously like someone who knows nothing at all about physics.
Fountofwisdom
 
  1  
Reply Thu 1 Jan, 2009 11:03 am
Having actually read the general theory it is quite simple in principle: one of its tenets is that the universe is non-Euclidean. For the non-Mathematicians amongst you this means that "common sense" assumptions about space don't apply.
The geometry is key to the understanding of Einstein.
0 Replies
 
High Seas
 
  0  
Reply Thu 1 Jan, 2009 11:36 am
@Brandon9000,
Brandon9000 wrote:

................
First of all, you're not correct, because Newton's equations make no statement whatsoever about the speed of propagation of gravity. .......


LOL Brandon - you don't even know grade school physics if you never heard of Newton's equations; high-school or higher are sadly beyond you, if that's the case, but I rather think your apparent crass ignorance is due to late partying, so here's an easy-to-understand version of Newtonian physics:

Quote:
Given two bodies attracting each other, the question then arises as to the speed of propagation of the force itself. Newton demonstrated that unless the force was instantaneous, relative motion would lead to the non-conservation of angular momentum. This he could observe as not being true, in fact the conservation of momentum was one of the observations that led to his theory of gravitation in the first place. He therefore concluded that gravity was instantaneous. In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ...


http://www.nationmaster.com/encyclopedia/Speed-of-gravity
High Seas
 
  0  
Reply Thu 1 Jan, 2009 11:41 am
@Brandon9000,
Read the damn book, Brandon, exact reference was posted above. Sober up enough to learn basic Newtonian gravity (infinite GRAVITY propagation speed MUST apply IF angular momentum is to be conserved, and the conservation of angular momentum wasn't doubted by Newton!) first, though.

I really don't see where you add value to this discussion if you can't even grasp complete BASICS. Sorry I'm not going to waste any more time until you start showing at least SOME grasp of basic concepts, never mind relativistic gravity field equations.
Brandon9000
 
  1  
Reply Thu 1 Jan, 2009 12:00 pm
@High Seas,
High Seas wrote:

Brandon9000 wrote:

................
First of all, you're not correct, because Newton's equations make no statement whatsoever about the speed of propagation of gravity. .......


LOL Brandon - you don't even know grade school physics if you never heard of Newton's equations; high-school or higher are sadly beyond you, if that's the case, but I rather think your apparent crass ignorance is due to late partying, so here's an easy-to-understand version of Newtonian physics:

Quote:
Given two bodies attracting each other, the question then arises as to the speed of propagation of the force itself. Newton demonstrated that unless the force was instantaneous, relative motion would lead to the non-conservation of angular momentum. This he could observe as not being true, in fact the conservation of momentum was one of the observations that led to his theory of gravitation in the first place. He therefore concluded that gravity was instantaneous. In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ...


http://www.nationmaster.com/encyclopedia/Speed-of-gravity

Newton lived centuries ago, and his equations are now believed to be only approximately correct . The actual equation written by Newton giving the gravitational force between objects was:

F = GM1M2/r^2

where F is force, G is Cavendish's gravitational constant, M1 and M2 are the masses of the two objects, and r is their separation.

Gunga asserted that gravity does, in actual reality, propagate instantaneously. General Relativity predicts that gravity propagates at the speed of light, and, from the quantum electrodynamic point of view, gravitons would propagate at the speed of light. Virtually every physicist believes in speed of light propagation for gravity. So, from what point of view is he correct?

Gunga specifically asserted that if gravity propagated only at the speed of light, the solar system would fly apart, yet when asked to show his calculations, only described the rudiments of a free body force diagram, which shows nothing of the sort. So, from what point of view is he correct?
0 Replies
 
DrewDad
 
  1  
Reply Thu 1 Jan, 2009 03:42 pm
@High Seas,
Are you seriously arguing that Newton's theory trumps experimental evidence?

Newton's theory is based on what was known in the 18th century.
0 Replies
 
Brandon9000
 
  1  
Reply Thu 1 Jan, 2009 05:27 pm
@High Seas,
High Seas wrote:

Read the damn book, Brandon, exact reference was posted above. Sober up enough to learn basic Newtonian gravity (infinite GRAVITY propagation speed MUST apply IF angular momentum is to be conserved, and the conservation of angular momentum wasn't doubted by Newton!) first, though.

I really don't see where you add value to this discussion if you can't even grasp complete BASICS. Sorry I'm not going to waste any more time until you start showing at least SOME grasp of basic concepts, never mind relativistic gravity field equations.

Although Newtonian mechanics has been superseded by relativistic mechanics, and, therefore, is not relevant here, I am willing to respond to this post of yours. Neither of us can add value unless he understands the basics. With two physics degrees, I think I do. Do you? I'll ask you an elementary question about gravity and circular motion in Newtonian mechanics, which anyone who completed a high school physics class with good grades could work out in 10 or 15 minutes. If you can answer, we can continue the discussion. If not, I'll give the solution in detail, and you can stop talking about physics.

Your post was number 3519687. I'll use that number. A satellite has a circular orbit around the Earth at a height of 3519 miles. What is its speed and kinetic energy? Give your units, and show your work.
0 Replies
 
Brandon9000
 
  1  
Reply Thu 1 Jan, 2009 05:57 pm
For the kinetic energy question, you can assume that the satellite weighs 10 pounds, or else keep your equations in symbolic form.
High Seas
 
  2  
Reply Sat 3 Jan, 2009 03:36 am
@Brandon9000,
Brandon - for reasons unrelated to this discussion, my only work with satellites has centered on Molniya orbits. The speed of satellites in such orbits varies considerably, as I assume you know. As to the field vs geometrical interpretations of gravity, I don't think I can improve on Feynman's analysis.

Some background info for those unfamiliar, though it's a digression from the topic of gravity:
Quote:
The satellite swings low and fast over the southern hemisphere and then slows as it rises toward its apogee in the northern hemisphere, making it appear to "hover" in the sky over northern territories for long periods of time.

http://www.centennialofflight.gov/essay/Dictionary/MOLNIYA/DI166.htm

P.S. to Brandon: it's ironic that you, a physicist, are taking the position usually adopted by mathematicians (geometrical) on gravity, whereas I, trained in mathematics, see the field equations for gravity propagation as blindly obvious! But as Feynman observed, both interpretations are valid - and FYI, neither has been "superseded" yet - check the Lorentz transformations, they're perfectly consistent with relativity, and show the speed of gravity to be as close to infinity as we can measure.
Brandon9000
 
  1  
Reply Sat 3 Jan, 2009 09:58 am
@High Seas,
High Seas wrote:

Brandon - for reasons unrelated to this discussion, my only work with satellites has centered on Molniya orbits. The speed of satellites in such orbits varies considerably, as I assume you know. As to the field vs geometrical interpretations of gravity, I don't think I can improve on Feynman's analysis.

Some background info for those unfamiliar, though it's a digression from the topic of gravity:
Quote:
The satellite swings low and fast over the southern hemisphere and then slows as it rises toward its apogee in the northern hemisphere, making it appear to "hover" in the sky over northern territories for long periods of time.

http://www.centennialofflight.gov/essay/Dictionary/MOLNIYA/DI166.htm

P.S. to Brandon: it's ironic that you, a physicist, are taking the position usually adopted by mathematicians (geometrical) on gravity, whereas I, trained in mathematics, see the field equations for gravity propagation as blindly obvious! But as Feynman observed, both interpretations are valid - and FYI, neither has been "superseded" yet - check the Lorentz transformations, they're perfectly consistent with relativity, and show the speed of gravity to be as close to infinity as we can measure.


I appreciate the reduced tone of your letter, but I still get the feeling that you're pretending a familiarity with physics that you don't have, and am going to have to request again that you demonstrate the knowledge you are claiming by solving the quick, high school physics problem I outlined above.
 

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