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Author Topic: How to calculate speed of light on surface of the Sun relatively coordinates o?  (Read 6055 times)

Offline simplified

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simplified asked the Naked Scientists:

How to calculate speed of light on surface of the Sun relatively coordinates of a far observer?
I can calculate speed of light slowed by time:
T=T_0/√(1-2GM/Rc˛)
T=1.000002123658*T_0
then speed of light=299791821 m/s
But i think this slowing is insufficient.
« Last Edit: 29/05/2011 15:17:08 by simplified »


 

Offline Phractality

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There is no calculation to be done. By definition, the speed of light in a vacuum is 299,792,458 metres per second, everywhere, for all observers. Time is dilated, and distance is contracted, but the speed of light is constant.
 

Offline simplified

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There is no calculation to be done. By definition, the speed of light in a vacuum is 299,792,458 metres per second, everywhere, for all observers. Time is dilated, and distance is contracted, but the speed of light is constant.
Let's allow you are right.Dilated time makes factor of delay 1,000002123658(on surface of Sun). Does contracted distance make such factor of delay?
 

Offline Phractality

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There is no calculation to be done. By definition, the speed of light in a vacuum is 299,792,458 metres per second, everywhere, for all observers. Time is dilated, and distance is contracted, but the speed of light is constant.
Let's allow you are right.Dilated time makes factor of delay 1,000002123658(on surface of Sun). Does contracted distance make such factor of delay?

To an observer on the sun's surface, there is no time dialation or length contraction, so the speed of light is what it is defined to be. An observer outside the sun's gravity sees a photon on the sun's surface passing length-contracted meter sticks 1,000002123658 times faster than non-contracted meter sticks. (Assuming you are using the correct figure) But time-dilated clocks attached to those meter sticks exactly compensate for the length contraction; so the photon passes 299,792,458 length-contracted metre sticks per time-dilated second.
 

Offline simplified

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And so speed of light on surface of Sun to solar observer = 299792458 short meters/long second.
 1 meter of far observer=1.00000213658 m of solar observer
 1 second of solar observer=1.00000213658 s of far observer
Let's put data:
 299792458*0.99999787635 m of far observer/1.00000213658 s of far observer=299791181 m/s
This is speed of light on surface of Sun relatively of far observer! :P
 

Offline simplified

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 "The time the light takes to traverse the path is recorded on the remote bookkeepers clock. I'll give you an example. I'll use light emitted at the surface of the Sun and received on Earth. For conveniece we can say the path of the light is the shortest distance between emission and reception.

The remote radial coordinate speed of light

dr/dt = (1-2M/r)

You can integrate this over the path and build a formula for predicting the Shapiro delay. For our case

dt = [r_earth orbit - r_sun] + 2M_sun ln[r_earth orbit/r_sun]

The 1st component is the distance between where the light is emitted and received and the 2nd component is the predicted Shapiro delay due to a path through curved spacetime.

I'll solve it for our case

r_earth orbit = 1 AU = 1.495978E11 m

r_sun = 6.9598E8 m

M_sun = 1477 m [using geometric units]

dt_bkkp = [ 1.495978E11m - 6.9598E8m] + 2954m ln[1.495978E11m/6.9598E8m]

= 1.4890182E11m + 15854.11645m = 1.489018359E11m

15854.11645m is the delay time in geometric units. dt_meter.

To convert this to seconds divide by c.

dt_second = 15854.11645m/2.99792458E8m/s

= .00005288367752 second

~ 53 microsecond

That is the extra time due to the path through curved spacetime." brucep on Phys Forum posted this,see link:http://www.physforum.com/index.php?showtopic=29175&st=240

      I can not use such calculations because I don't know geometric units.
Phractality, do you deny this calculation?
« Last Edit: 01/06/2011 19:00:23 by simplified »
 

Offline imatfaal

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Simplified - you really cannot cut and paste posts by another person on a different forum.  If you know the physics then enter into the debate and post your logic, if you don't then work to learn it.  Please do not cut and paste like this again.
 

Offline simplified

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 What, told by me, is wrong?
 

Offline yor_on

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Simplified. This is one of the clearest explanations I know of. The guy is very clear, and easy to read. It's worth rereading it until you think you see how he thinks. Because, if you want to disprove relativity, you will benefit from understanding how it is defined.

Just one page, about rods and light, but so good.
 

Offline rosy

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Quote
What, told by me, is wrong?

If you wish to refer to information elsewhere on the internet, whether that's another forum, or wikipedia, or whatever, you should quote, selectively, and reference your source (for example.. "brucep on PhysForum posted this, see link: http://linkgoeshere").

Large, unattributed copy-and-paste posts, are effectively plagiarism even if not intended as such... forum or blog posts are by default protected by copyright (belonging to the author). This is not widely understood, but as forum moderators we are obliged to act where it comes to our notice.

Please go back and modify your post so that it does not simply consist of a copy of a post existing elsewhere, and to include proper attribution and a link. If this doesn't appear in 24 hours I'll remove the post.
 

Offline yor_on

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As for how Einstein thought of it. He started with questioning what he would see if he was traveling at 'c' looking at his mirror image in the direction of his motion. Doing so he found that if the light only could move at 'c' then there should be no mirror reflection. That result stood against all reasoning about uniform motion, since Galilee. In Galilee's principle of relativity (created from defining uniform motion on a boat) there was no way of defining a speed or direction, inside a room at that boat, moving uniformly. Either his thought experiment was wrong or Galilee was wrong. (because no mirror image did define a 'speed')

So that started him on Maxwell to see if the definitions of light always being at 'c' would hold. What differs special relativity from the general are two things, general relativity is about gravity foremost, meaning that in a acceleration you always will know whom it is 'moving', at least in a non-uniform accleration. So acceleration and the possibility to always define a motion as belonging one specific object. In special relativity motion is 'relative', it will depend on whom is observing whom, and so will the 'time durations' be.

That's also why people want to use distant 'fixed' stars for defining that motion. The real truth though, is that all uniform motions are prefaced by an acceleration, at least as I know and so there will always be a 'kingpin' for it as long as you know its origin. Without that 'origin' it becomes trickier. Still, even if knowing that the rocket came from Mars you will only be able to define its speed relative Mars. And what speed Mars have you will then need to define arbitrarily. So you better forget that argument. In the end all uniform motions becomes indefinable. I should have remembered that :)

There is also the definition of inertial frames belonging to SR. That is best understood as any object in a geodesic, 'weightless' (e.g astronaut in space) and uniformly moving. Although when it comes to mass, you do have to consider the 'gravitational acceleration' created by its invariant mass. But for all practical purposes we can call Earth a 'inertial frame', as I understands it.
« Last Edit: 01/06/2011 17:59:13 by yor_on »
 

Offline Geezer

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That result stood against all reasoning about uniform motion, since Galilee. In Galilee's principle of relativity (created from defining uniform motion on a boat) there was no way of defining a speed or direction, inside a room at that boat, moving uniformly. Either his thought experiment was wrong or Galilee was wrong.


Well, he was pretty good on the old telescope, so it's hardly suprising they called him the "See of Galilee"  ;D
 

Offline imatfaal

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Well as far as I can see brucep's formulation is definitely correct in magnitude - although try as I might I get an extra factor of 2 in the numerator of the log

setting c=G=1

Δt ≈ X + 2Mlog(2X/R)

solar mass -->(2x10^30)*G/c^2 =1485metres
X = distance = Surface of sun to earth = 1 AU - Radius of sun = 1.489028707×10^11 metres
R  = radius of Sun = 695,500,000 metres

The Shapiro delay is the second half of the equation (the first X is the expected time in flat space)

the time delay thus equals 17996.91003 metres.  which in more conventional units is 6*10^-5seconds  . That's with my extra 2 in the numerator of the log expression, otherwise Bruce is correct.

The Shapiro delay has been tested by bouncing radar off satellites and other planets, and sending the beam skimming past the Sun - it is shown to be correct with amazing precision.  It is a composite of both the temporal and spatial coefficients in the metric. Far from being a problem for einstein's relativity - it is often shown as one of the concrete proofs.  the Wikipedia page on the shapiro delay has a line from Einstein
Quote
We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light).
 

Offline yor_on

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Yep, all experiments involving moving clocks, measuring, in a accelerated frame (rocket ship) will have to involve, and compensate for, gravity. There you can find that light do have 'two speeds'. But only if ignoring gravity.
 

Offline simplified

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Well as far as I can see brucep's formulation is definitely correct in magnitude - although try as I might I get an extra factor of 2 in the numerator of the log

setting c=G=1

Δt ≈ X + 2Mlog(2X/R)

solar mass -->(2x10^30)*G/c^2 =1485metres
X = distance = Surface of sun to earth = 1 AU - Radius of sun = 1.489028707×10^11 metres
R  = radius of Sun = 695,500,000 metres

The Shapiro delay is the second half of the equation (the first X is the expected time in flat space)

the time delay thus equals 17996.91003 metres.  which in more conventional units is 6*10^-5seconds  . That's with my extra 2 in the numerator of the log expression, otherwise Bruce is correct.

The Shapiro delay has been tested by bouncing radar off satellites and other planets, and sending the beam skimming past the Sun - it is shown to be correct with amazing precision.  It is a composite of both the temporal and spatial coefficients in the metric. Far from being a problem for einstein's relativity - it is often shown as one of the concrete proofs.  the Wikipedia page on the shapiro delay has a line from Einstein
Quote
We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light).

Thank you for useful answer.
 

Offline simplified

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Simplified. This is one of the clearest explanations I know of. The guy is very clear, and easy to read. It's worth rereading it until you think you see how he thinks. Because, if you want to disprove relativity, you will benefit from understanding how it is defined.


Dear.My calculation of speed of light relatively of far observer is part of relativity.Only you don't know relativity.
Δt ≈ X + 2Mlog(2X/R) Where does this formula  come from?
« Last Edit: 03/06/2011 03:19:59 by simplified »
 

Offline yor_on

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Did you read it?

And what do you think you prove by the math?
==
And you better read up on your English my friend :)
I'm not your 'dear' ::))
« Last Edit: 03/06/2011 02:29:36 by yor_on »
 

Offline yor_on

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The Shapiro delay describes the lights path 'bending' due to gravity. I might have been wrong in steering you to SR there but gravity is a simple phenomena, although very strange. What wasn't simple was how to relate it to motion and Space & Time. Still, after Einstein succeeded most found it quite natural.

According to his views gravity is space, you won't have a space without gravity, at least not one containing a metric (distance). I like the way you educate yourself Simplistic, and develops your mathematic understanding. I wasn't attacking you, just trying to show you what I thought was good sources of relativity, easy to test with a good description.

One of the most stupid things I know is the saying that it is hard to understand relativity. Once Einstein had laid the groundwork it wasn't that hard. What was missing before was his understanding of how it all hung together. What he didn't do was to explain those facts he built on, like lights 'propagation' in a vacuum. But then again, neither has anyone else. You might come across some saying that it is a direct effect of the Lorentz transformations but that's a circular proof to me.

I wonder how many that never try to understand it reading that only 'three people' can understand it etc etc? And how many that just look for some crumble to question without trying to see the magnificent construction he erected. Both of those views I think is a direct result of a unspoken assumption that it isn't any idea to try to take it all in as it will take a 'lifetime', if it now is worth it.

The link is very good.

 

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