source of earth's gravity...

[mak10]

i think its more like F = Gm1m2/r^2 where G = 6.67^-11

 

-mak10

[Severian]

According to this, might it be possible (hypothetically) for two bodies who are in the process of exchanging gravitons, to be so far apart that they run out of gravitons to exchange before they collide? Suppose their masses were incredibly different from each other so that the larger one emits gravitons at such a high rate that, even though the smaller one is trying to compensate by exchanging gravitons at as high a rate as it possibly can, it could not possibly keep supplying the larger one with the gravitons it needs to replenish its stock. Is it possible that the larger one could actually run out?

 

Its actually weirder than that because of the non-local nature of quantum field theory. The two bodies wouldn't exchange a single force carrier - they would only do it if they can excahnge 2 at once in order to 'balance the books'. Since they would br borrowing energy from the uncertainty principle, they have to give it back pretty quickly, so the exchange can only happen if there is a compensating exchange.

 

But again, since T=0 is impossible, this is all speculation.

[gib65]

And another thing: How does Einsteins general theory of relativity fit into all this? It seems to me that gravitons and the warping of space-time are not quite the same theory. Are they simply different expressions for the same idea, are they mutually exclusive, or are they different theories but capable of coexisting as valid explanations for gravity?

[Severian]

They are just different ways of trying to describe the same thing - one classical and one quantum. GR can be reformulated to look almost exactly like Maxwell's theory of classical electromagnetism (which was written down in completely covariant form before special relativity!). It is only when one tries to quantize the theory of gravity that problems arise, whereas electromagnetism nicely quantizes into QED with photons.

[gib65]

That's interesting stuff. I'd really like to understand better. How exactly is GR and the theory of gravitons equivalent? Does it require extensive mathematics to understand? Is there a relatively simple way to explain it?

[Severian]

That's interesting stuff. I'd really like to understand better. How exactly is GR and the theory of gravitons equivalent? Does it require extensive mathematics to understand? Is there a relatively simple way to explain it?

 

That is not what I said. GR and a theory of gravitons are not equivalent. GR is a classical theory whereas a theory of gravitons would be a quantum theory. I was pointing out that one did not need to think of GR as bending space-time - one can write down GR as a classical theory in the same manner as classical electromagnetism (as written down by Maxwell), with gravitational waves playing a similar role to light.

 

The concept of a photon only occurs when one quantizes electromagnetism. The photon is a 'quanta' of light. Unfortunately no-one has been able to quantize gravity sucessfully, but the assumption is that its quantization will be similar to that of electromagnetism and a 'quanta' of the gravitational wave would be called a 'graviton'.

 

PS: Reading my previous post I see how you could have picked that up wrongly. Entirely my fault. I have edited the post to make it clearer.

[Severian]

That's interesting stuff. I'd really like to understand better. How exactly is GR and the theory of gravitons equivalent? Does it require extensive mathematics to understand? Is there a relatively simple way to explain it?

 

That is not what I said. GR and a theory of gravitons are not equivalent. GR is a classical theory whereas a theory of gravitons would be a quantum theory. I was pointing out that one did not need to think of GR as bending space-time - one can write down GR as a classical theory in the same manner as classical electromagnetism (as written down by Maxwell), with gravitational waves playing a similar role to light.

 

The concept of a photon only occurs when one quantizes electromagnetism. The photon is a 'quanta' of light. Unfortunately no-one has been able to quantize gravity sucessfully, but the assumption is that its quantization will be similar to that of electromagnetism and a 'quanta' of the gravitational wave would be called a 'graviton'.

 

PS: Reading my previous post I see how you could have picked that up wrongly. Entirely my fault. I have edited the post to make it clearer.

[Spazzy-kins]

To: Mak10

 

You want a simple answer to a reletively simple question, yes? Well, here you go.

 

Step one: Scientists don't know. This is why they speak of things such as "gravitons" (some unknown object that does some unknown act to produce a well-known result).

 

Step two: I'm not sure either. I've got a theory (a simple one that fits everything I think), but I don't really know. Keep searching and find experiments to test your theories. This will be the next step in understanding the physics involved in the world around us.

 

Now we begin. My personal theory involves what I like to call "energy particles" (much similar to light waves -- I think the only difference would be frequency). Assuming my theory to be correct, there are millions upon billions (rough guestimate) of these particles traveling through space at intense speeds. Presumably, they travel at light-speed. They are smaller than atoms (probably much smaller), and numerous to fill the emensity of space (for all intents and purposes). These energy particles collide with atoms constantly. Due to the weak force each particle exerts on the objects and the overwhelming abundance of them, net force can be taken to be 0 for each object. When two objects are put near each other, they shield each other from some of the energy particles. this causes a change in the net force. Thus Gravity.

 

I can't prove it, but I can't disprove it either. And it makes sense. Also, if you'd like proof of the exsistance of these "energy particles" check out "crystal radios." Go ahead and build one yourself; get it working, etc. Now, turn from your favorite station. Pass the country stations. That's right, keep going... Stop! There it is: static. Not enough, eh? Take out the speaker, and plug in a voltometer. Now you've got it: enough energy to light a tiny bulb. Not enough for practical use, but it's there. Not a broadcast; it just exsists. I'm not sure where it comes from, but it's out there.

 

Hope it helps. Oh, and remember...

"look for what is... not what you think should be." -direct quote from an inquisitive mind.

 

enjoy.

[JaKiri]

Step two: I'm not sure either. I've got a theory

 

Conjecture

 

I can't prove it, but I can't disprove it either. And it makes sense. Also, if you'd like proof of the exsistance of these "energy particles" check out "crystal radios." Go ahead and build one yourself; get it working, etc. Now, turn from your favorite station. Pass the country stations. That's right, keep going... Stop! There it is: static. Not enough, eh? Take out the speaker, and plug in a voltometer. Now you've got it: enough energy to light a tiny bulb. Not enough for practical use, but it's there. Not a broadcast; it just exsists. I'm not sure where it comes from, but it's out there.

 

If you don't know how to test it, then the conjecture is worthless.

 

Furethermore, we know where static somes from. Static is just the background E-M radiation, and if you're saying that light can transmit energy, then whoopdidoo. If gravitons existed, they could do that too (you'd need a different method of capturing them, obviously, as only EM particles work for the photo-electric effect).

[Spazzy-kins]

Conjecture...

Ok, that works. I have a conjecture.

 

If you don't know how to test it, then the conjecture is worthless.

 

*cough* String Theory *cough*

 

 

 

Sooo... These "gravitons"...

 

What are they? What exactly do they do? And why does this cause gravity? So much for your conjecture, eh?

 

The biggest difference is that your beloved scientists whom you revere so much thought of gravitons before energy particles. They aren't prophets you know. These scientists that you regard so highly are bright men to be sure, but they are guessing just as sure as any of us. Only those who don't know what they're talking about aren't questioning. Some focus on one conjecture rather than another, but they don't know if it's right.

[Spazzy-kins]

Oh, and couldn't "gravitons" be pushing instead of pulling? ie. energy particle=graviton?

[Sayonara]

Oh, this should be good.

[Gilded]

"Oh, this should be good."

 

Perhaps, but I'm afraid it's not going to be suitable for Christmas. ) (Hope swansont and the others are spending quality time with their families or something, a seizure would be quite an awful Christmas present )

[swansont]

The biggest difference is that your beloved scientists whom you revere so much thought of gravitons before energy particles. They aren't prophets you know. These scientists that you regard so highly are bright men to be sure, but they are guessing just as sure as any of us. Only those who don't know what they're talking about aren't questioning. Some focus on one conjecture rather than another, but they don't know if it's right.

 

Ah, yes, the old "it's all guesswork, so my guess is as good as anybody's" canard. Haven't heard that one in a little while. It's so nice to reminisce around Christmas and New Year's day.

[Gilded]

You know, it makes me and probably even the forest animals cry when physicists have to deal with this even at Christmas.

[coquina]

Your original question was about Earth's gravity - so I am giving you some information about it and how geologists measure and use it to derive subsurface information about the earth.

 

Here is a gravity map of the earth:

http://antwrp.gsfc.nasa.gov/apod/ap011113.html

 

Does it surprise you that Earth's gravity is not exactly the same all over? The main overall source of the earth's gravity, but materials that lie between the core and the surface, the altitude, and the gravitational effects of the moon all play a part in causing "gravity anomalies".

 

USGS explanation of measuring earth's gravity:

http://geopubs.wr.usgs.gov/open-file/of02-353/method.html

 

FS–239–95 OCTOBER 1997

Introduction to Potential Fields: Gravity

Introduction

 

Gravity and magnetic exploration, also referred to as “potential fields” exploration, is used to give geoscientists an indirect way to “see” beneath the Earth’s surface by sensing different physical properties of rocks (density and magnetization, respectively). Gravity and magnetic exploration can help locate faults, mineral or petroleum resources, and ground-water reservoirs.

Potential-field surveys are relatively inexpensive and can quickly cover large areas of ground.

 

What is gravity?

Gravitation is the force of attraction between two bodies, such as the Earth and our body. The strength of this attraction depends on the mass of the two bodies and the distance between them. A mass falls to the ground with increasing velocity, and the rate of increase is called gravitational

acceleration, g, or gravity. The unit of gravity is the Gal (in honor of Galileo). One Gal equals 1 cm/sec2. Gravity is not the same everywhere on Earth,

but changes with many known and measurable factors, such as tidal forces. Gravity surveys exploit the very small changes in gravity from place to place

that are caused by changes in subsurface rock density. Higher gravity values are found over rocks that are more dense, and lower gravity values are found

over rocks that are less dense.

 

How do scientists measure gravity?

 

Scientists measure the gravitational acceleration, g, using one of two kinds of gravity meters. An absolute gravimeter measures the actual value of g

by measuring the speed of a falling mass using a laser beam. Although this meter achieves precisions of 0.01 to 0.001 mGal (milliGals, or 1/1000 Gal),

they are expensive, heavy, and bulky.

 

A second type of gravity meter measures relative changes in g between two locations. This instrument uses a mass on the end of a spring that stretches where g is stronger. This kind of meter can measure g with a precision of 0.01 mGal in about 5 minutes. A relative gravity measurement is also made at the nearest absolute gravity station, one of a network of worldwide gravity base stations. The relative gravity measurements are thereby tied to the

absolute gravity network.

 

What is a gravity anomaly?

 

Gravity meters measure all effects that make up the Earth’s gravity field. Many of these effects are caused by known sources, such as the Earth’s rotation, distance from the Earth’s center, topographic relief, and tidal variation. Gravity caused by these sources can be calculated using realistic Earth models and removed from the measured data, leaving gravity anomalies caused by unknown sources. To the geologist, the most important unknown source is the effect of the irregular underground distribution of rocks having different densities. A sequence of gravity corrections are applied to the original gravity reading and result in various named gravity anomalies. The observed gravity anomaly has been corrected for Earth rotation, latitude,

tidal effects, and gravity meter fluctuations.

 

The free air gravity anomaly has been corrected for the gravity effect caused by the elevation difference between the station and sea level (a correction for distance) and is a standard for oceanic gravity interpretation.

 

The Bouguer (pronounced Boo-gay´) gravity anomaly has been further corrected for the mass that may exist between sea level and the observer (a correction for mass) and is a standard used in geologic interpretation on land. A simple-Bouguer anomaly has undergone a simplified removal of topographic

effects, which suffices in relatively flat areas. A complete- Bouguer anomaly contains a terrain correction that uses a more complete representation of the local topography, which is necessary for accurate gravity values in mountainous areas. The isostatic (pronounced iso-stat´-ic) gravity anomaly is calculated by subtracting the gravitational effect of low-density

mountain roots below areas of high topography. Although these roots have never been seen, their isostatic effect has been measured and models calculated using topography. Isostasy is typified by floating icebergs

that have 90% of their mass of ice below water that supports a smaller mass of ice projecting above water.

 

What is a gravity map?

A gravity map is made using numerous gravity measurements across the area of interest. Gravity surveying by aircraft is still a new science, so most gravity

measurements are made on the ground at discrete stations. Because access is often a problem, gravity stations may be randomly spaced, although detailed surveys are usually made at regular intervals. Gravity measurements are often processed to a complete-Bouguer or isostatic gravity anomaly. These data are then gridded, so that the randomly spaced data are converted to a representation of the gravity field at equally spaced locations. The distance chosen between grid points depends on the average distance between gravity stations. Too large a grid interval would not use all the information from the original data set, whereas too small a grid interval fragments the continuity of anomalies across a region—either result is a

poor representation of the true gravity field.

 

Gravity anomaly maps can be shown as color figures— with warm colors (reds and oranges) showing areas of higher gravity values and cool colors (blues

and greens) showing lower values—or as contour line maps, where each contour line follows a constant gravity value.

 

What is rock density?

 

Density is a rock property described by the ratio of mass to volume. Rock densities commonly range between 2.0 and 4.0 grams per cubic centimeter

(g/cm3). Pure water, by comparison, has a density of 1 g/cm3. Each rock type can have a range of density values, and tables in the scientific literature show the general range of densities for various rock types.

Often, the geoscientist will collect samples of exposed rocks in the study area and measure their densities to estimate the actual density of the rock unit where it is buried. Various rock types within a study area often

contrast enough in density to cause gravity anomalies. For example, sedimentary rocks that fill basins almost always have low densities and are characterized by gravity lows on anomaly maps. Mafic rocks, which contain high-density minerals, often are associated with gravity highs. The scientist can use these differences to map large regions where rocks are inaccessible or concealed, to look for faults that juxtapose rocks of different densities, or

to infer structures such as basins, arches, and buried intrusions.

 

What is a derivative gravity map?

 

A gravity anomaly map contains information about rock density, and depth and distribution of anomaly source rocks. Maps can be derived from the original gravity anomaly grid by using mathematical tools to enhance parts of the gravity field. Derivative maps can show, for example, anomalies that have been mathematically filtered for size and that show deeper or shallower sources. Other derivative techniques can magnify gravity gradients, places where the gravity field changes from high to low—these places often mark edges of rock units or faults, or they can mimic a geologic map by converting (or “terracing”) the gravity anomalies into discrete, bounded units representing rock units. All of these maps can be used together to make a geologic interpretation.

 

Additional information

U.S. Geological Survey Open-File Report 95–77 lists many USGS computer programs and databases used to create gravity maps, and it is available on the web site listed below. Information on gravity base stations and availability

of gravity maps and data in specific areas can be obtained from:

 

Pat Hill

U.S. Geological Survey

Box 25046, MS 964

Denver Federal Center

Denver, CO 80225

(303) 236-1343

pathill@musette.cr.usgs.gov

Viki Bankey (same address)

(303) 236-1348

viki@musette.cr.usgs.gov

Vicki Langenheim

U.S. Geological Survey

345 Middlefield Road, MS 939

Menlo Park, CA 94025

(415) 329-5313

zulanger@mojave.wr.usgs.gov

web site: http://minerals.er.usgs.gov

˘

[JaKiri]

*cough* String Theory[/size'] *cough*

 

What exactly are you expecting? That because String Theory is the current vogue conjecture, that I come out all guns blazing in support of it? Physics is NOT DOGMATIC. Currently, String Theory and its variants are utterly worthless to us because they do not actually do anything. I have stated this many times, on this site and elsewhere, and to think that such an obvious contradiction would have escaped my attention is rather naive.

 

Sooo... These "gravitons"...

 

What are they? What exactly do they do? And why does this cause gravity? So much for your conjecture' date=' eh?[/quote']

 

They are a conjectured force exchange particle, to match up gravity with the other 3 fundamental forces that we KNOW have force exchange particles. It is conjectured that it operates in the same way as the other exchange particles of force.

 

There is no problem with the mechanics of the graviton; finding it wouldn't be a paradigm shift in the same way as finding the Higgs Boson would be, it would merely act to further confirm other theories we have made.

 

For example, it is heavily suspected, if not proved (I cannot recall), that beyond a certain energy level, the four fundamental forces combine into one. This is old news. However, this operation becomes infinitely more complicated if there isn't symmetry between the forces, and this includes having exchange particles.

 

There is a very large body of evidence to suggest that the graviton exists; however, as is the nature of science, it is NOT STATED to DEFINITELY exist until it can be proved to exist beyond ALL REASONABLE DOUBT.

 

The biggest difference is that your beloved scientists whom you revere so much thought of gravitons before energy particles. They aren't prophets you know.

 

The biggest difference, as I have said, is that there is a substantial body of evidence and mathematical framework that suggests the existance of gravitons. You also continue with the suggestion that science, and physics in particular, is dogmatic; new conjectures ignored as the researchers are blinded by the wisdom from the past. This could not be further from the truth; do you know how many distinct variations have existed, and been discarded as incorrect, in even the vogue conjecture, String Theory? Do you realise that, as soon as evidence (usually in the form of a repeatable experiment or measurement, as to reduce the chance for a freak occurance) contradicting a previously held scientific theory has been found, the hunt is on for something better, to replace the discarded legacy of former peers? The entire point of String Theory is to find something better to replace the Standard Model of Quantum Mechanics and the General Theory of Relativity, things developed by such small names as Einstein, Schroedinger and Bohr. Physics. Is. Not. Dogmatic.

 

These scientists that you regard so highly are bright men to be sure, but they are guessing just as sure as any of us. Only those who don't know what they're talking about aren't questioning. Some focus on one conjecture rather than another, but they don't know if it's right.

 

They are not guessing; all conjectures are based around the need for new theory to explain the deviations of results with old theory. Einstein didn't pick the basis for Special Relativity out of the air; he was building on the work of Michaelson, Morley and Lorentz, to name but three. A 'scientist' in isolation doesn't know more than the rest of us, but this is never the case; science is based upon the foundations of hundreds of years of experiment, conjecture and change. And, whilst it is true that some do focus on one conjecture at the expense of another, what problem does this create? Discarding an invalid model is 'good science', because it involves creating new or improved experiments to test the validity of the new conjecture. They don't know if they're right, but they know that the only way to know for sure is to test it: for this is the basis of the sciences.

[Ophiolite]

Sayonara, you were right. Pretty good so far.

[Gilded]

"Sayonara, you were right. Pretty good so far."

 

Hmm... Should I watch Bottom (the comedy-show-thingie) or this thread... Hmmmm...

 

And seriously, when talking about this type of theories and "guesses", Ockham's razor is something that should come to mind...

[Spazzy-kins]

Well then. Without getting to far swept away, let me respond a little. First the pleasantries.

 

Sorry Jakira. I guess I'm not quite sure how this forum works so I don't know if it's dogmatic. But, if the week or so I've been here says anything... Anyway, I'm glad to see that you aren't set on string theory. I'm actualy glad you don't accept my views without proof either, but my idea is a possibility.

 

As for string theory being more than a guess: Yes it explains things. So does my idea.

 

I don't expect you (any of you) to accept my idea as anything more than that: an idea. But for having a non-dogmatic point of view you sure haven't given it much contemplation. None of you have given any science to go off of. And yet, you claim science as your only support. I don't mind adopting a better idea, but show me that it's better first.

 

Well, Merry post-Christmas!

[Spazzy-kins]

Ok. I think I've just accomplished what you were trying to do. I'm not so sure it would stand the test of a black hole. I suppose I'll have to think about it, do some research and see where it takes me. Thanks for the input though; more is always welcome.

[Spazzy-kins]

Nope. Never mind about the last post. Still works fine so far. Let the experimenting begin! (that is as soon as I can get some spare money in... oh... a few years or so) meh.

[swansont]

As for string theory being more than a guess: Yes it explains things. So does my idea.

 

Scientific theories have to do more than explain - they have to predict.

 

I can explain just about everything with invisible pink fairies, and you can't disprove their existence. But it's useless as a theory, as there is no predictive power, and nothing that is explained that isn't already.

 

(feel free to substitute the deity of your choice into that)

 

It's hypothesis for the moment, and to promote it as anything more, as JaKiri implied - is dogma.

[JaKiri]

I guess I'm not quite sure how this forum works so I don't know if it's dogmatic.

 

Who gives a flying dog about how this forum works?

 

It's how science works.

 

As for string theory being more than a guess: Yes it explains things. So does my idea.

 

Your idea explains nothing. String Theory also explains nothing (at the current point in time), but, if it is to come anywhere close to acceptance, has to predict things as well.

 

Furthermore, you're understimating the need for mathematics. Qualitatively, String Theory is fine. Great. Wonderful.

 

The reason it's not accepted as theory is that it has no mathematical backing, and that is the problem that is being worked on.

 

But for having a non-dogmatic point of view you sure haven't given it much contemplation.

 

Until there's some kind of mathematics involved, there's no need to; furthermore, you yourself said that there's no way to test it, and so the scientific method dictates that it is, by definition, not worth consideration.

 

The scientific method goes something like this.

 

1. You start off with established theory. Science being what it is, this is assumed to be false.

2. To test the established theory, you develop new conjectures, and new experiments with which you can compare the new conjectures and established theory (sometimes the experiments come before the conjecture).

3. If the conjecture successfully predicts something that the established theory does not, and is not shown to be lacking by the existing body of evidence for the established theory, the conjecture replaces the established theory as the established theory.

4. Repeat.

 

Your 'idea' cannot perform step 3, therefore it cannot ever become a scientific theory.

 

None of you have given any science to go off of. And yet, you claim science as your only support. I don't mind adopting a better idea, but show me that it's better first.

 

If you like, I (we) can explain all you like about General Relativity and the Standard Model of Quantum Mechanics. However, this was not asked for initially; it is assumed (wow!) that people who wish to be a constructive member of a scientific community, such as this, will fall into one of two groups:

 

1. People who know established theory, and can debate its merits or shortcomings.

2. People who do not decry established theory until they know what it is.

 

If you do not know how the current theory acts, how can you possibly construct a valid argument against it?

[Guest paragonis]

I am very interested in gravity and what gravity is. Is it possible that, like other forces, Gravity has a particle associated with it. I have read some material to do with this and believe such a particle would be a Graviton. Does anybody have anything to add to this?