# Mass = gravity?

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http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GravWaves.html

Eddington was not the only skeptic. Many physicists thought the waves predicted by the theory were simply a mathematical artifact. Yet others continued to further develop and test the concept. By the 1960s, theorists had showed that if an object emits gravitational waves, its mass should decrease. Then, in the mid 1970s, American researchers observed a binary pulsar system (named PSR1913+16) that was thought to consist of two neutron stars orbiting each other closely and rapidly. Radio pulses from one of the stars showed that its orbital period decreases by 75 microseconds per year. In other words, the stars are spiralling in towards each other -- and by just the amount predicted if the system were losing energy by radiating gravity waves.
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my understandig is that gravity is a curvature of spacetime
so how does spacetime "radiate" away?
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quote,if object EMITS gravitational WAVES its MASS should decrease?
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so mass converted to gravity??

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## Answers and Replies

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Originally posted by wolram
http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GravWaves.html

Eddington was not the only skeptic. Many physicists thought the waves predicted by the theory were simply a mathematical artifact. Yet others continued to further develop and test the concept. By the 1960s, theorists had showed that if an object emits gravitational waves, its mass should decrease. Then, in the mid 1970s, American researchers observed a binary pulsar system (named PSR1913+16) that was thought to consist of two neutron stars orbiting each other closely and rapidly. Radio pulses from one of the stars showed that its orbital period decreases by 75 microseconds per year. In other words, the stars are spiralling in towards each other -- and by just the amount predicted if the system were losing energy by radiating gravity waves.
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my understandig is that gravity is a curvature of spacetime
so how does spacetime "radiate" away?
---------------------------------------------------------------------
quote,if object EMITS gravitational WAVES its MASS should decrease?
---------------------------------------------------------------------
so mass converted to gravity??

Sure, as the quote says, gravity waves carry away energy. And if there is no other energy to carry away, mass energy will have to be depleted (a big if there). That is a completely classical computation of course: non-quantum.

The answer to "what is waving" is, "whatever is curving". If youi don't like to think of a space time fabric, you can have variation of geometry: angles of triangles add up to 180.001o over here, but 179.999o over there.

Mr. Robin Parsons

Originally posted by selfAdjoint
Sure, as the quote says, gravity waves carry away energy. And if there is no other energy to carry away, mass energy will have to be depleted (a big if there). That is a completely classical computation of course: non-quantum.
The answer to "what is waving" is, "whatever is curving". If youi don't like to think of a space time fabric, you can have variation of geometry: angles of triangles add up to 180.001o over here, but 179.999o over there.
Quantum Gravity predicts Quantum foam, at this link https://www.physicsforums.com/showthread.php?threadid=4396&perpage=&pagenumber=2" there is a reference (9th & 10th posts) to a reading that tells of the recent evidential proof, concerning the latest discoveries, relative to "Quantum Foam".

(It isn't there, so that theoretical aspect of Quantum theory appears "Now" as invalid)

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Wolram your headline asks a question "mass = gravity?"

It seems to me that is the wrong way to put it. May be better to say that mass is one of the things that CAUSES spacetime curvature or that causes gravity.

Sometimes it can help to be confronted with a totally unintuitive fact. If you put a cannonball in the oven and heat it up, the cannonball acquires some additional mass and becomes slightly more attractive gravitationally.

Any way you can pump energy into a system will increase its mass.

The changes are mostly unmeasurably small but folks are very confident about this because the theory is so well established (goes back to a 1905 paper of Einstein and has been well and truly tested over the years)

A system of two stars circling each other has some potential energy you can calculate from how far apart they are----if you could twirl them a bit faster so they swung wider apart this would pump energy into the system.

as they orbit they send out a changing pull-signal---a wave--that could drive something else in their neighborhood and even run a delicate little machine---so this signal carries energy away from them

so they have to spiral in closer together because energy is being bled out of the system

and also the mass of the system gets less (like the mass of a cooling cannonball gets less as it cools)

it would be difficult to measure the mass of two dense stars tightly orbiting each other except as a combined system

(it would be tough to yank them completely away from each other and measure their masses separately-----everything would be disrupted and the numbers would not even work out very well----mass depends on situation to some extent---it is a property of the whole system and you have to be careful about "assigning" it to separate parts which arent in reality separate)

in the combined system of the two stars, the energy of their interaction, their orbit, is actually a part of the combined system's mass!

and as orbit energy is bled off by causing ripples in the grav field,
the system's mass decreases

mass does not equal gravity, but mass is one of the things that causes curvature and causes gravity

there is a major equation that says

curvature = (some constant times) density of energy and also pressure

and the pressure part of that is usually negligible and
the energy-density part includes mass

so if one casually throws away stuff that is usuall neglible the
major (Einst. 1915) equation says

curvature = (some constant times) mass

but remember that is a simplification you got by throwing away stuff that usually is comparatively small

so mass, and more generally the concentration of energy in a region, causes gravity but is not quite the same as gravity

I'm responding here as best I can to these 3 comments of yours
hope these thoughts useful and not too disorderly
Originally posted by wolram

--------------------------------------------------------------------
my understandig is that gravity is a curvature of spacetime
so how does spacetime "radiate" away?
---------------------------------------------------------------------
quote,if object EMITS gravitational WAVES its MASS should decrease?
---------------------------------------------------------------------
so mass converted to gravity??

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Originally posted by Mr. Robin Parsons
...there is a reference (9th & 10th posts) to a reading that tells of the recent evidential proof, concerning the latest discoveries, relative to "Quantum Foam".

Mr. RP could you please post the names of the authors
of that article you referenced

You said:
"What I read was in the Aug 29 issue of the Journal "Science", (The A.A.A.S.) Vol 301 #5637 on Pg; 1169"

But my subscription ran out and I don't have a copy handy.

If you tell me the authors (and title would help but is less important) then I can very likely find the preprint online.

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thankyou MARCUS the penny has droped, i find it enjoyable
when one can VISULISE a system, the vertical hold slips
on mine sometimes but it is stabalizeing.

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Originally posted by wolram
thankyou MARCUS the penny has droped, i find it enjoyable
when one can VISULISE a system, the vertical hold slips
on mine sometimes but it is stabalizeing.

LOL, really like the analogy

better to have VH problems than screen full of snow

you and me both, like to keep adjusting screen to get better picture

Mr. Robin Parsons

Originally posted by marcus
Mr. RP could you please post the names of the authors
of that article you referenced
You said: "What I read was in the Aug 29 issue of the Journal "Science", (The A.A.A.S.) Vol 301 #5637 on Pg; 1169"
But my subscription ran out and I don't have a copy handy.
If you tell me the authors (and title would help but is less important) then I can very likely find the preprint online.
God willing I will make the effort to acquire all of the relevant names of all of the relevant Authors...TBC...

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Originally posted by Mr. Robin Parsons
God willing I will make the effort to acquire all of the relevant names of all of the relevant Authors...TBC...

If you don't have the information handy (dont want to put you to a lot of trouble) wait a bit. I might be able to find it online
even without an authorname or title

feeling guilty thinking of you riding your bicycle to the library
on some dark night pursued by wolves and so on----sit tight
and I or someone will get the reference

Mr. Robin Parsons

Originally posted by marcus
If you don't have the information handy (dont want to put you to a lot of trouble) wait a bit. I might be able to find it online
even without an authorname or title
feeling guilty thinking of you riding your bicycle to the library
on some dark night pursued by wolves and so on----sit tight
and I or someone will get the reference
Thanks for the concern, the reward? here's you goes...

So Marcus it's "Adrian Cho" who was the writer of the article, that I read, citing works either published, (by now) or To be Published, (TBP) as comming from #1) Floyd Stecker Of NASA Goddard in Md relating to Observational evidence (TBP) in The Journal of Astroparticle Physics and the second #2) A Ted Jacobsen of the U of M Pub in Nature and coorelated to the expressed opinion of one Lee Smolin of the Perimeter Inst. For Theoretical Physics who makes the 'case' of Hypotheis V Experimental Evidence hence the clear Victor in that one being "Observational Evidence" thus resulting in an expressed 'Validation' of Einstein's understandings of "Universal workings".

O.K.?

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Originally posted by Mr. Robin Parsons

So Marcus it's "Adrian Cho" who was the writer of the article, that I read, ...
O.K.?

Very much ok, thanks

With Adrian Cho's name I can almost surely find a preprint in the arxiv!

Mr. Robin Parsons
There is one more person whom I have neglected to mention, sadly, as that is the person who formulated the postulate that was followed as to seek the verification of the theory.

God Willing I will go, and find that name, and post it, as well, as clearly that person deserves Accreditation for the work that they clearly did. They have/had demonstrated a depth of understanding of the current knowledge, and the pathway of testing from available obsevation, as to understand how to extract from the "Universal Flashlight" the needed reading.

Mr. Robin Parsons
If I am reading it properly, then One Giovanni Amelino-Camelia, a Theoretical Physicist @ "The University of Rome, La Sapienza", was the postulator of the method of search. (what I have previously called "The Precept"...no, I am not the first to do that!)

As per the Article, This is the person who suggested in 1998 that "Scutinizing Gamma Ray Burts" would be a method of revealling if Lorentz Invariance Held, or was Violated.

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Originally posted by Mr. Robin Parsons
If I am reading it properly, then One Giovanni Amelino-Camelia, a Theoretical Physicist @ "The University of Rome, La Sapienza", was the postulator of the method of search. (what I have previously called "The Precept"...no, I am not the first to do that!)

As per the Article, This is the person who suggested in 1998 that "Scutinizing Gamma Ray Burts" would be a method of revealling if Lorentz Invariance Held, or was Violated.

Thanks RP for your efforts and good offices here
In fact I know a little of Giovanni A-C's work which
has been referred to by several PF posters over the past few
months. I did a search and came up with Tom and Thermonuclear
though I seem to remember other references (maybe in attachments or pages linked-to) He seems to be a very prominent guy and might even be worth going to Rome to chat with.
As it happens yesterday I was reading an article of Giovanni A-C,
called "Quantum Symmetry, the Cosmological Constant and Planck Scale Phenomenology"
http://arxiv.org/hep-th/0306134 [Broken]
This paper argues that if the cosmo constant Lambda is not zero (astronomers suggest it may be positive based on their observations) then the energy-momentum relation of special relativity is not quite right---but must be modified very slightly
in a non-linear way.

The observational evidence (which has now seemingly become famous frontpage stuff) is still very far from being conclusive so
people are loudly arguing this way and that about observations
of "gammaray bursts" and "crabnebula synchrotronradiation". It certainly has attracted a lot of attention and real interest on the part of astronomers! And old Roman Giovanni at "La Sapienza" is at the root of all this ruckus.

I guess you may know some Italian (with a name like Parsons you are bound to) and Sapienza is their word for Wisdom which given the state of the scientific endeavor could strike you as ironical.

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Mr. Robin Parsons
Originally posted by Marcus
(SNIP) I guess you may know some Italian (with a name like Parsons you are bound to) and Sapienza is their word for Wisdom which given the state of the scientific endeavor could strike you as ironical. (SNoP)
So Sorry, but I am adopted, so my last name reflects little. But, I had known that Spaienza should have meaning like wisdom, from "Homos Sapiens"/"Wise man".

But "Thanks!", just the same.

Canum
Any way you can pump energy into a system will increase its mass.

The changes are mostly unmeasurably small but folks are very confident about this because the theory is so well established (goes back to a 1905 paper of Einstein and has been well and truly tested over the years)

A system of two stars circling each other has some potential energy you can calculate from how far apart they are----if you could twirl them a bit faster so they swung wider apart this would pump energy into the system.

as they orbit they send out a changing pull-signal---a wave--that could drive something else in their neighborhood and even run a delicate little machine---so this signal carries energy away from them

so they have to spiral in closer together because energy is being bled out of the system

and also the mass of the system gets less (like the mass of a cooling cannonball gets less as it cools)

it would be difficult to measure the mass of two dense stars tightly orbiting each other except as a combined system

(it would be tough to yank them completely away from each other and measure their masses separately-----everything would be disrupted and the numbers would not even work out very well----mass depends on situation to some extent---it is a property of the whole system and you have to be careful about "assigning" it to separate parts which arent in reality separate)

in the combined system of the two stars, the energy of their interaction, their orbit, is actually a part of the combined system's mass!

and as orbit energy is bled off by causing ripples in the grav field,
the system's mass decreases

mass does not equal gravity, but mass is one of the things that causes curvature and causes gravity

there is a major equation that says

curvature = (some constant times) density of energy and also pressure

and the pressure part of that is usually negligible and
the energy-density part includes mass

so if one casually throws away stuff that is usuall neglible the
major (Einst. 1915) equation says

curvature = (some constant times) mass

but remember that is a simplification you got by throwing away stuff that usually is comparatively small

so mass, and more generally the concentration of energy in a region, causes gravity but is not quite the same as gravity

I don't know why, but I've never thought about this before.
Does this mean that any existing object with mass is losing its mass to gravity?