Can the Sun be weighed using General Relativity?

I'm stuck on:

"we should expect that a ray of light which is passing close to a heavenly body would be deviated towards the latter… It may be added that, according to the theory, half of this deflection is produced by the Newtonian field of attraction of the sun, ..."

as photons are massless and therefore should not be so influenced.

Generally speaking (_{OH ha ha haaaa}) I am mostly "wrong" when speaking sagely about Einstein's theories OR quantum dynamics: but that's my current opinion, nonetheless.

So my opinion is absolutely correct only in the local (relative) field.

Hi I)AVI),

You've got to remember it's Einstein speaking. If it was anybody else I might have written him off as a quack. I have the same problem as you, with no mass how does the theory predict it? The other half is the bending of space.

regards,

S

Your title of the post is wrong. It should be "Can the mass of the Sun....." Weight is the gravitational force on a mass. What gravity we should consider while weighing the Sun?

Hi gsuhas,

The two terms are used interchangeably. I said mass in the text. Everyone will know what I meant. Do you know how the mass has been determined up till now?

regards,

S

I promise, I will come back on the matter on Sunday/Monday. I need to make it simple, and correct.

The answer is yes. The mass influences "space" be it, the so called "dark matter" or what ever. Space it self is curved by the influence of the mass of the sun. If you can figure out the influence then you should be able to figure out its mass. I have not mentioned gravity until (oops just did) now, as gravity doesn't seem fit into the theory of relativity, because of the mass of the photon (0). But how does a gravitron influence itself on a photon both without....., but a wave no less. (?????)

Yes it is interesting, and I'm tempted to put in my two bobs worth. The point I'm wrestling with is time and space being distorted("curvature"), and trying to build up a mental picture of how that could possible work. As I have stated in other posts, I believe that space is infinite, and that means no edge and no centre, but has two features, an expanding force,(dark matter), and a contracting force, (gravity). And as space has no edge or centre then these forces are acting homogeneously three dimensionally. To visualise this more easily it is better thought of two dimensionally, as a scribed circle, with the centre point expanding to the circumference and the circumference contracting to the centre, and this is happening in phase with each other. Therefore at some point they will be the same size or circumference, and if the phase between them is slightly altered, one starts before the other, them the point of equilibrium where they are the same size shifts, either smaller or larger than the mid point.

So when one places a mass such as the sun into space then the point of equilibrium moves towards contraction and space around it bends? equilibrium moves towards the mass. So when a photon moves through space, I visualise it travelling at that point of equilibrium, a wave with no mass, a ripple in the equilibrium? And as such will follow the curvature of space. This is not a theory, just a mental aid for me to understand.

As for calculating the mass, I don't know, I vaguely remember something in the book by Dr Hawking's, I will see if I can find it, my grandson has it at the moment.

Regards JD.

If I remember correctly, as all scientists say.... Space in finite. It is not infinite.

Original question is simple... how the mass of sun is estimated by using bending of light etc.

Your biiiiig explanation may be for your understanding, but creating more confusion (at least in my mind)

I found this experiment on gravity and space quite helpful in helping me get some better understanding.

Thanks G,

Interesting link. There are some books in the reading section that have been recommended to me. There are introductory to advanced ones.

regards,

S

Hi qsuhas

Just a liiiiitle answer, thank you for your input, the word finite meaning, bounded, limited and exhaustible I find hard to live with, I prefer to think of space with out limit.

Not clearly stated in my answer, but I suppose that the further a sun's gravitational force extends into space the greater the cuvature of space, the stronger the field, the more light will be bent when passing, I believe this was how Einstein first calculated the speed of light? How much deflection to mass, I don' know.

Regards JD.

Hi jdretired,

I appreciate your comments. I asked those unrelated questions in my opening post so this thread could go in several directions. Personally, I think the universe is finite, not that it matters. I have trouble accepting that an infinite thing can expand. We all have our mental limits, I think. From Einstein's theories we learn that space and time are tied together. If the Big Bang theory is correct, then time is finite, therefore it follows that space (the universe) is finite. Of course the BB theory is just that. I saw a book at the library I intent to get next time. The title is The Big Bang Never Happened. Have you read it? It's not very recent, so I don't know if a newer version is available. I had trouble following your 'mental aid', but thanks just the same.

Regards,

S

Hi StandardsGuy

I was worried that I was taking your post in an unintentional direction, I was just trying to point out why a photon without mass could be used. No I have not read the book, still on a learning curve. Will keep it in mind. Yes perhaps my metal aid is a bit difficult to understand, if it is understandable? like a resent post by vermin, the problem is in the language when trying to convey one's concepts.

Regards JD.

I am not a physicist so stand to be corrected, but I think photons are only massless at rest. The mass of moving photon depends on its energy which depends on its wavelength.

Hi Chankley,

I think you have something there. So I think the kinetic energy is what the gravity attracts, but don't you need mass to get kinetic energy? Hmmm...

S

I suppose your original question was "How the mass of Sun is determined by theory of relativity, deflection of photons by Sun's gravity". This I will try to answer in next few days.

Code master's reply is other way of finding the mass, which is available at http://zebu... which I also saw, but didn't put as reply for above reason.

Hi gsuhas,

I did ask several questions, and he answered one, but not the main one. I will look forward to your reply.

regards,

S

Hello again StandardsGuy

If you're interested, I calculated the deflection of a photon by the Sun's gravity, using Newtonian mechs. Assuming the photon has mass due to its energy, it doesn't matter just how much mass, as it cancels, in the same way as any body falls at the same g on Earth.

For a photon that just misses the edge of the Sun, can work out the transverse g-force at any point of its travel, hence with a bit of integration the total deflection. Integrating between ± ∞ I make it just over 2*10^-6 radians. Integrating between ± distance to Earth makes negligible difference. Don't know whether that agrees with the "official" figure, if you know please post.

Also, the 2x factor predicted by Relativity over Newton, is that from Special or General Relativity, (or both) does anybody know? From the date 1919 it could be either. Though on 2^nd thoughts, if it's due to curved spacetime, it must be General, as I don't think spacetime is curved in Special.

Cheers.......Codey

Hi Codey,

Einstein's book says: "For a ray of light which passes the sun at a distance of Δ sun-radii from it's centre, the angle of deflection (a) should amount to a= 1.7 seconds of arc/Δ."

You asked "Also, the 2x factor predicted by Relativity over Newton, is that from Special or General Relativity, (or both) does anybody know?"

This is written in his book in appendix III titled "The experimental Confirmation of the General Theory of Relativity." I am assuming that the 2X effect was confirmed. Let me know if your calculations disagree.

Regards,

S

This was nor clear. Half of the above deflection should be caused by gravity and half by bending of space.

Hi StandardGuy

My calc was for Δ = 1 so Einstein's figure = 1.7 seconds. Converting my 2*10^-6 rad to seconds = 0.43. So need to x 4 to agree with the great man. x 2 no doubt due to the Relativity/Newton effect, so it looks like I'm out by the other x 2. I've checked the maths and can't see anything obvious. I'll have another look when I've a minute and try to post the calcs. Positive sign that it's out by an integer, suggests calcs are on the right track.

Cheers.....Codey

Hi StandardsGuy,

I came across this thread this morning, 02 April 2008. I am pleased to answer your questions.

Yes, the mass of the Sun can be determined. Yes, there is a single set of formulas. And Yes, Newton and later comers knew the value of the Gravity constant by the time Einstein set his value of the defection. The formulas will be in a forthcoming paper or book.

These formulas start with F=ma; today we know "m" the mass of the Sun [be patient with "m"]

By integration of "a" we get velocity; in this case the departing velocity of the stream of photons after passing through the limb of the Sun.

The angle between the departing stream from a straight-line continuation of the incoming photon stream is the deflection angle.

Now, if the mass of the Sun were not known but the deflection was known, all we have to do is a little bit of "reverse engineering" and voila! We calculate the mass, m, of the Sun.

Hmm-m? Well, well, where did we get the information to determine the "set of equations" in the first place? That is a very good question.

Mm-m-m. Let's see now. I used "photons" above -- Let's change that to a "ray" of starlight -- same thing in the different time - 2008 back to Eddington's trip, 1919, for fairly accurate measurement of the Einstein predicted deflection angle.

The speed of the ray of starlight was known -- Maxwell's electromagnetic equations gave us that. Everything was in place – including, from them, the determination of the deflection formulas, by 1902, no less!

By the way -- all of the "set of equations" are hard simple mathematical statements. Nothing theoretical anywhere.

soaralone1

Does not a photon move at the speed of light?

If so, then it's mass is either zero, or infinite, is it not?

It falls to reason, then, (although "reason"s conclusions are "suspect" in this arena..) that the mass is zero, by definition.

The "rest mass" of a photon is zero, but I defy you to find me one "at rest", as a corellary to Einstein's relativity theory is that any old photon you happen to "see" from any old frame of reference, is moving at (all together now) "the speed of light":

although there will be IN FACT a frequency shift. (LYman balmer Pachen brackett pfund..{now THERE's an old memory})

I am not one to second guess Einstein, if he's the one that stated that "Newtonian" physics gives rise to the bending,

but absent that, I would boldy proclaim that it's only the gravitational distortion of space/TIME itself that gives rise to the diffraction of a massless PHOTON in the vicinity of a large mass such as the sun.

It could be that the problem can be "solved" classically, as the gentleman above has demonstrated, but it imputes a quality to a photon (mass) which is not extant.

How can a photon be massless, and yet have momentum and energy?

Beats the crap outa me, but Planc's constant and wavelength are involved, if I recall.

In a way, this is an argument as to how the question is posed, and not to the question itself: but it is interesting in it's own right.

If anything has momentum, then it must have mass.

If anything has energy, it must have mass. Mass-energy equivalence is fundamental to Special Relativity hence e=mc².

You can't find a photon at rest as such because that would imply knowing both its position and momentum which is not possible on this scale due to Heisenberg's Uncertainty Principle.

A photon has no mass, It has energy, which can be expressed as a massequivalence using the formula you laid out. This is a construct of math relating to a "resting" frame of reference.

"You can't find a photon at rest as such because that would imply knowing both its position and momentum which is not possible on this scale due to Heisenberg's Uncertainty Principle"

Heisenburg's uncertainty principle is not the reason why you cannot find a photon at rest. The reason is even more fundamental than that.

The speed of light (in a vacuum) is a constant in any frame of reference.

This is getting into quantuum wierdness, in which the highest probability is that I am wrong, so I shall bow out before providing further proof that I am "out of my element.."

Hi I)AVI),

Thanks for your comments. As Codey pointed out, the mass falls out of the formula, so I guess it doesn't matter if a photon has mass to bent by gravity. The universe is so weird at the quantum level it puts us all out of our element.

S

Hi SG (BOOK > Big bang never happened)

Book available from Amazon, paper back around $14, should make interesting reading, same on order.

regards JD.

I have read that book. Don't remember much, except that the author said the universe behaved like a plasma.

http://www.geocities.com/sciliterature/RelativityDebates.htm