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Worm hunter
2004-Oct-01, 02:33 AM
Ok, im not sure if this is the right forum for this post, but its about string theory so im pretty sure it is.

I have just finished watching the three hour NOVA program, "The Elegant Universe" and have several questions and issues.

I would like to point out that i have no background in mathematics but mearly an interest, and although the mathmatics that drives string theory described to me at this point is beyond me, the program was very understandable even to a layperson like myself. In this regard I liked the program. However there were several issues that I just couldnt let alone.

At the begining of the program they mention that while string theory is just that, a theory, it is an untestable theory with no chance of being falsified. To me this was an important point and one that i thought wasnt made clear enough for those who might not understand the importance of a theory proposing the ways in which it could be shown wrong.

The gravity issues i have with the program involved the mechanisms described about how gravity works. According to the program gravity is a force particle that bounces back and forth between two objects. The more particles that are shared the more apparent the force between those objects are. This is ok to me. Though i understand that we have yet to discover a particle that could be responsible for gravity, how it was proposed that it works makes sense to me and for the sake of sticking with the programs information I will use that description for this post. The problem came in near the end of the program where the host says that gravity seems to be weaker then the electromagnetic force. In the example he asks the question if gravity is so strong why can he overcome the force so simply by for example picking an object up even with the entire mass of the earth pulling it down. (the object was an apple) Now given the original description this didnt seem to contradict the laws of gravity to me. An apple has very little mass compared to the earth and gravity is combined effect of mass between two objects. The force particles that can bounce between an apple and the earth are very little given the total mass of the apple. (if I am missunderstanding this at this point let me know) He went further to use theoretical solultions to this problem using string theory. According to string theory there are two type of strings: open ended, and closed. The open ended strings are anchored to the membrane that we perceive as our universe and thus appear strong, while the closed strings are able to float from membrane to membrane dilluding the strength of gravity. To me this seems wrong. They ignore their original description of how gravity works to support and propose a new mechanism which supports their theory.

Another issue I have is how they unified GR and Quantum Mechanics. They showed how when we model big things such as solar systems the fabric of space is smooth, and when we do the same on the attomic level it is chaotic. Now, to me this doesnt seem complicated. From outterspace the earth looks smooth, the hight of mountains are not dicernable from the level of the oceans, yet when we take a vantage point on the top of a mountain we can clearly see that the earth seems quite bumpy and chaotic. Furthermore if you were to accelerate our clocks not only is the earth a bumpy place but changes quite chaotically. Now to me instead of proposing something like string theory, could it simply be our vantage point that when look at the incredibly tiny that is making our view seem chaotic and bumpy. This issue is less of a problem then the first i mentioned more of an idea i had while watching that im quite currious about the answer too.

One more problem I had with the program is that again in the begining of the program they assert that string theory is not observable and makes no predictions, and is unobservable, yet by the end they assert over and over that it does make predictions. To me it makes no difference either way, but it is very dishonest to assert two opposing views like that. Also when they did mention that it is both unobservable and makes no predictions they seemed to skim past it and hit you with some other major information that makes it hard to remember that string theory is more of a philosophy then it is a science.

I hope that people with more knowledge on this subject can explain to me if I am just missinterpreting this or if im on to something and perhaps direct me in the right path to get to the bottom of this. Again I am not a mathematician, I did teach myself algebra several years ago but do to lack of study have lost most of that knowledge.

Thanks for any replies,
Worm

(p.s. I am probably forgeting several of the points I wanted to make at this point, though as the discussion picks up I will attempt to lay them out as I can recall them)

Normandy6644
2004-Oct-01, 04:00 AM
At the begining of the program they mention that while string theory is just that, a theory, it is an untestable theory with no chance of being falsified. To me this was an important point and one that i thought wasnt made clear enough for those who might not understand the importance of a theory proposing the ways in which it could be shown wrong.

It's not as simple as that really. The energies that string theory deal with are at present unattainable, but that doesn't mean it never will. Also, it does make predictions that can be falsified, albeit in an indirect way.

The gravity issues i have with the program involved the mechanisms described about how gravity works. According to the program gravity is a force particle that bounces back and forth between two objects. The more particles that are shared the more apparent the force between those objects are. This is ok to me. Though i understand that we have yet to discover a particle that could be responsible for gravity, how it was proposed that it works makes sense to me and for the sake of sticking with the programs information I will use that description for this post. The problem came in near the end of the program where the host says that gravity seems to be weaker then the electromagnetic force. In the example he asks the question if gravity is so strong why can he overcome the force so simply by for example picking an object up even with the entire mass of the earth pulling it down. (the object was an apple) Now given the original description this didnt seem to contradict the laws of gravity to me. An apple has very little mass compared to the earth and gravity is combined effect of mass between two objects. The force particles that can bounce between an apple and the earth are very little given the total mass of the apple. (if I am missunderstanding this at this point let me know) He went further to use theoretical solultions to this problem using string theory. According to string theory there are two type of strings: open ended, and closed. The open ended strings are anchored to the membrane that we perceive as our universe and thus appear strong, while the closed strings are able to float from membrane to membrane dilluding the strength of gravity. To me this seems wrong. They ignore their original description of how gravity works to support and propose a new mechanism which supports their theory.

Not entirely, since particles would be made up of strings. In this case the gravity particle (graviton) is composed of open ended strings and thus not anchored to a particular membrane.

Another issue I have is how they unified GR and Quantum Mechanics. They showed how when we model big things such as solar systems the fabric of space is smooth, and when we do the same on the attomic level it is chaotic. Now, to me this doesnt seem complicated. From outterspace the earth looks smooth, the hight of mountains are not dicernable from the level of the oceans, yet when we take a vantage point on the top of a mountain we can clearly see that the earth seems quite bumpy and chaotic. Furthermore if you were to accelerate our clocks not only is the earth a bumpy place but changes quite chaotically. Now to me instead of proposing something like string theory, could it simply be our vantage point that when look at the incredibly tiny that is making our view seem chaotic and bumpy. This issue is less of a problem then the first i mentioned more of an idea i had while watching that im quite currious about the answer too.

It's more of an issue with quantum mechanics. Basically, the smaller area you look at, the more chaotic it has to be based on the quantum uncertainty principle, and this chaos becomes overwhelming for a singular point, since technically you have specified the exact position and (presumably) velocity, which you can't do. This means that the "quantum jitters" must be overwhelming. String theory smooths this all out by proposing an actual limit to how small things can get. Thus the smoothness required by GR as achieved. (It's more complicated than that, but that's the idea)

One more problem I had with the program is that again in the begining of the program they assert that string theory is not observable and makes no predictions, and is unobservable, yet by the end they assert over and over that it does make predictions. To me it makes no difference either way, but it is very dishonest to assert two opposing views like that. Also when they did mention that it is both unobservable and makes no predictions they seemed to skim past it and hit you with some other major information that makes it hard to remember that string theory is more of a philosophy then it is a science.

That's all debatable. I was skeptical at first, but it certainly does make real predictions, even though at the moment they are more abstract. Supersymmetry is one of them (every particle has an identical twin with opposite spin). The idea of membranes makes the scale of the strings much larger than previously thought, and some weird ideas with strings and inflation predict that some strings could be strewn across the sky large enough to cover the length of the universe. Just because direct experiments are out of out of our reach now does not mean it will always be so.

Worm hunter
2004-Oct-01, 04:19 AM
Normandy6644,

Im not sure what you mean in your second answer. Or atleast not sure how it answers my question entirely. I underrstand that particles would be made of strings and that the particle that would govern gravity would the graviton. but lets just assume that string theory is wrong, but that there is still a force particle that is a graviton. Wouldnt the fact that givin the small size of an apple only very few gravitons could bounce back and forth between the apple and the earth be very few. Hence the small weight of the apple. To further expand the example lets just say that the earth and mars orbited eachother at a distance of five feet, ignoring all the atomospheric problems. the gravitational forces between those two objects would be so high that i couldnt possibly move mars. Which makes sense since mars is so big and the earth is so big that there would be more of these gravitons bouncing back and forth increasing the force of gravity between the two.

I just dont see why string theory is required to explain why gravity appears weaker then em in some cases and stronger in others. One more question regarding cases where gr is a stronger force then em. If em is stronger then why doesnt it regulate the orbits of planets not gravity? I would assume it is because of the simple explanation I have of how gravity works. So why is string theory really needed for all this?

Worm hunter
2004-Oct-01, 04:36 AM
Before I forget to comment,

First, if you took a could take a video of atoms interacting on the quantum level, which you couldnt do I know. But if you did then blew it up to be the size of the universe. According to the show if one atom was the size of the solar system one string in that atom would be the size of a tree. Would the jitters still be apparent. or if you took the universe and shrunk it down to the size of an atom. would the fluctations in the fabric of space jitter like that of the quantum level, without needing to introduce strings. I ask this because as we look at things jittering is very dependent on vantatge point.

Normandy6644
2004-Oct-01, 05:21 AM
Normandy6644,

Im not sure what you mean in your second answer. Or atleast not sure how it answers my question entirely. I underrstand that particles would be made of strings and that the particle that would govern gravity would the graviton. but lets just assume that string theory is wrong, but that there is still a force particle that is a graviton. Wouldnt the fact that givin the small size of an apple only very few gravitons could bounce back and forth between the apple and the earth be very few. Hence the small weight of the apple. To further expand the example lets just say that the earth and mars orbited eachother at a distance of five feet, ignoring all the atomospheric problems. the gravitational forces between those two objects would be so high that i couldnt possibly move mars. Which makes sense since mars is so big and the earth is so big that there would be more of these gravitons bouncing back and forth increasing the force of gravity between the two.

Right, that's fine. I was just explaining what M-theory (string theory's generalization) has to say about why gravity is weaker than the other forces.

I just dont see why string theory is required to explain why gravity appears weaker then em in some cases and stronger in others. One more question regarding cases where gr is a stronger force then em. If em is stronger then why doesnt it regulate the orbits of planets not gravity? I would assume it is because of the simple explanation I have of how gravity works. So why is string theory really needed for all this?

Gravity is never stronger than EM. Ever. String theory explains potentially why gravity is so much weaker than the other forces, and that is because of the open/closed strings. The example he used in the NOVA special was showing why EM was much stronger than gravity, and how easy it is to overcome the gravitational force. I think you might have misunderstood something.

First, if you took a could take a video of atoms interacting on the quantum level, which you couldnt do I know. But if you did then blew it up to be the size of the universe. According to the show if one atom was the size of the solar system one string in that atom would be the size of a tree. Would the jitters still be apparent. or if you took the universe and shrunk it down to the size of an atom. would the fluctations in the fabric of space jitter like that of the quantum level, without needing to introduce strings. I ask this because as we look at things jittering is very dependent on vantatge point.

I think I understand what you mean. Basically the quantum jitters arise when you try to confine your space. If you took the atomic level and enlarged it (which is exactly what the universe is) you would see no jitters. Shrinking the universe to a single point would do the opposite. What strings do is smooth out the jitters by imposing a minimum length limit, above which the jitters don't happen.

Worm hunter
2004-Oct-01, 05:40 AM
Im not sure i missunderstood. I still dont see why gravity is explaned as weaker in the example. An apple can only pass so many gravitons back to to the earth, hence causing a low weight for the apple. The bigger the object the bigger the weight because more gravitons get passed between the two objects. If em is stronger then gravity then doesnt the magnetism of the earth and the sun determine the orbit of the earth around the sun rather then gravity? How in the case of planets can gravity be weaker then em?

gzhpcu
2004-Oct-01, 06:20 AM
Earth's magnetic field may be more of a product of its orbit around the Sun as it cuts through the Sun's gravitational pull than from interior flows of molten material. In any case, the gravitational field of the earth is certainly stronger than its magnetical field.

As to string theory:

First we had zero dimensional points. This broke down at the Planck length. Some up we come with one dimensional strings.

There are some problems with string theory. First of all, it requires 10 dimensions for the strings to vibrate in as opposed to 4.

Another problem with string theory is that there are 5 different formulations of it.

This is why there is now the M-theory (murky theory?) M-theory encompasses all flavors of string theory. M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories.

The proposed M-theory would instead be a theory that took place in 11 dimensions. This theory is somewhat nebulous in nature and has not been pinned down yet.

Also the orders of magnitude between the Planck length and the distances our accelerators can investigate are enormous (at least 10 to the minus 16 smaller...) Imagine the energy you need to investigate such small distances! Forget it...

Normandy6644
2004-Oct-01, 12:57 PM
If em is stronger then gravity then doesnt the magnetism of the earth and the sun determine the orbit of the earth around the sun rather then gravity? How in the case of planets can gravity be weaker then em?

That's what I'm saying you're misunderstanding. Gravity is always weaker than EM. The EM force is so many orders of magnitude larger gravity pales in comparison. In SI units, the gravitational constant is on the order of 10^-11 (if I remember right), whereas the EM constant is 9x10^9. That's twenty orders of magnitude! EM is absolutely never weaker than gravity.

Jim
2004-Oct-01, 01:21 PM
If em is stronger then gravity then doesnt the magnetism of the earth and the sun determine the orbit of the earth around the sun rather then gravity? How in the case of planets can gravity be weaker then em?

That's what I'm saying you're misunderstanding. Gravity is always weaker than EM. The EM force is so many orders of magnitude larger gravity pales in comparison. In SI units, the gravitational constant is on the order of 10^-11 (if I remember right), whereas the EM constant is 9x10^9. That's twenty orders of magnitude! EM is absolutely never weaker than gravity.

Don't overlook the effect distance has on the forces. Gravity is much weaker than EM, but acts over a virtually infinite distance. EM is much stronger, but acts over a much shorter distance.

worzel
2004-Oct-01, 01:28 PM
If em is stronger then gravity then doesnt the magnetism of the earth and the sun determine the orbit of the earth around the sun rather then gravity? How in the case of planets can gravity be weaker then em?

That's what I'm saying you're misunderstanding. Gravity is always weaker than EM. The EM force is so many orders of magnitude larger gravity pales in comparison. In SI units, the gravitational constant is on the order of 10^-11 (if I remember right), whereas the EM constant is 9x10^9. That's twenty orders of magnitude! EM is absolutely never weaker than gravity.
I read a good description of this somewhere, along the lines of: all the gravitional force of the earth is pulling you down put you can easily resist it, if all the EMF of the world were directed in one direction it would be astronomical, but as it is it mostly cancels out.

Normandy6644
2004-Oct-01, 01:50 PM
If em is stronger then gravity then doesnt the magnetism of the earth and the sun determine the orbit of the earth around the sun rather then gravity? How in the case of planets can gravity be weaker then em?

That's what I'm saying you're misunderstanding. Gravity is always weaker than EM. The EM force is so many orders of magnitude larger gravity pales in comparison. In SI units, the gravitational constant is on the order of 10^-11 (if I remember right), whereas the EM constant is 9x10^9. That's twenty orders of magnitude! EM is absolutely never weaker than gravity.

Don't overlook the effect distance has on the forces. Gravity is much weaker than EM, but acts over a virtually infinite distance. EM is much stronger, but acts over a much shorter distance.

Yeah I think I see what the problem is here. We're talking about fields, not just forces. It's not that EM acts over any shorter distance than gravity, it's that as a whole, matter is neutral. Stars don't have lightning (or the equivalent) between them because there isn't a big enough potential difference, whereas gravity works on neutral matter in general. Think of it this way. You have a relatively strong magnet and hold it above a table. The magnet can't pull up the table because the gravity field at that point is much stronger than the EM field generated by the magnet. However, place a paperclip on the table and it will fly up to the magnet (depending on strength and distance). How can it do that? Well, the material that makes up the paperclip is made of up certain compounds where electrons can move relatively easily through the clip. In general, it is neutral, but place it in a magnetic field and you generate movement in the electrons. The resulting for is so much stronger that it can overcome the gravitational pull of the entire earth.

The difference is all in the fields. On the scale of the solar system, the objects are sufficiently neutral that the gravitational field is the only force that has any real affect on planetary motion. The same principle can be generalized to star clusters, galaxies, and galactic clusters. I think the misunderstanding here was the difference between forces and fields though.

Eta C
2004-Oct-01, 01:57 PM
A couple of quick comments on the relative strengths of EM and gravity. Yes, EM is the stronger force, and also has an infinite range, just as gravity does. A difference, however is that the attractive force of EM acts only between opposite charges, gravity is always attractive ( 8) ).

Anyway, the consequence of this is that bulk matter is electrically neutral, so that any EM interactions between two planets are minimal. So gravity dominates at long ranges (fringe claims by electric universe types notwithstanding).

As an exercise, try calculating the charge the earth and sun would have to carry (of opposite signs mind you) for EM to generate the necessary centripital force that keeps the earth in orbit. It comes out to a whopping 2.7x10^17 Coulombs. This would generate an electric field of about 1.2x10^5 V/m at the earth's surface. I think we'd have noticed a field that large by now.

Ut
2004-Oct-01, 02:02 PM
Just condensing some of what has been said:

Gravity is weak. It's really, really weak. It's so weak, you can uncouple an object and the earth with your bare hands. In fact, it's so weak, objects have to be kilometres across for you to really notice its effects.

Meanwhile, try pulling two speaker magnets apart.

The reason the EM force doesn't dominate the universe is because it's dipolar. There are positive and negative particles, and north and south poles. When you bring a positive and negative particle together, on the large scale their fields seem to cancel. They no longer feel forces from other EM fields. Meanwhile, gravity, to the best of our knowledge, has only monopoles. Everything attracts everything else, and on larger and larger scales, the field never appears neutral. You can't shield things from gravity.

TravisM
2004-Oct-01, 02:32 PM
And the number of dimensions string theory or M-Theory (Mother of all string theories) would have to account for somehow.
That the zero-th dimension, Time, we can't "see" is no problem for people to grasp. It's a direction we're headed at a costant velocity with no current hope of steering... Time...
Then the three spatial dimensions, 1-2-3, familiar, easy to grasp, if you've played a 3D game like Doom you'll know what I'm talkin about... :-? wait, real life is 3D... There are rules for the relationships between these dimensions, those rules are called geometry... Space...
When you get time jiving with the 3 spatial dimensions, you get Dynamics, the rules governing the relationship between objects in three dimensions over or through time... Dynamics...
Then gravity, if we think of it as a dimension, curves the other three due to the presence of energy. Guv=8piTuv, Guv=Ruv-1/2guvR - SpaceTimeDynamics...
Then if we add something to measure, like, the spin of an electron or photon, then we need another dimension. Also, there's matter and anti-matter, out of phase in a particular dimension. Then there's charge, another dimension, positive, negative....
It ends up that each state of matter/energy can have a state-vector composed of a myrid of indicies on a huge array, like, g{a,b,c,d,e,f,g,h,i,j,k}... Very handy for mathmatic formulations...
All string theory does is attempt to establish geometric relationships between the various dimensions that yield a reflection of observations we've made here...
The assumption is that these dimensions have curled up all tiny as the universe expanded, they shrank to plank length, and that we've been callin' them quarks... But, then again, I don't think it matters if there really are these dimensions as long as the theory works to show what's happening across all distance scales. If there's some prediction that would say, on dimension such-n-such we could 'twist' a quark like so, and presto: __________ Then there might be a need to know exactly what these dimensions represent...

Jeeze, I've gotta lotta ... in there!

Trav[/i]

ExpErdMann
2004-Oct-01, 04:24 PM
The gravity issues i have with the program involved the mechanisms described about how gravity works. According to the program gravity is a force particle that bounces back and forth between two objects. The more particles that are shared the more apparent the force between those objects are. This is ok to me.

There seems to be a discrepancy here. On one hand, the gravitational force is considered proportional to the number of gravitons being exchanged between bodies. Gravitons are considered to transfer 'negative momentum'. But in discussions of GR (eg this current BABB thread (http://www.badastronomy.com/phpBB/viewtopic.php?t=16019&amp;start=50) p. 3), when two binary stars emit gravitational waves their orbits decay.

Now if gravitational waves are comprised of gravitons, and gravitons carry negative momentum, should the emission of gravitational waves not tend to boost the binaries in their mutual orbit?

Normandy6644
2004-Oct-01, 04:48 PM
The gravity issues i have with the program involved the mechanisms described about how gravity works. According to the program gravity is a force particle that bounces back and forth between two objects. The more particles that are shared the more apparent the force between those objects are. This is ok to me.

There seems to be a discrepancy here. On one hand, the gravitational force is considered proportional to the number of gravitons being exchanged between bodies. Gravitons are considered to transfer 'negative momentum'. But in discussions of GR (eg this current BABB thread (http://www.badastronomy.com/phpBB/viewtopic.php?t=16019&amp;start=50) p. 3), when two binary stars emit gravitational waves their orbits decay.

Now if gravitational waves are comprised of gravitons, and gravitons carry negative momentum, should the emission of gravitational waves not tend to boost the binaries in their mutual orbit?

No, because it's a loss of energy essentially. The numbers are really small, but for binary pulsars or something the effect would be noticeable.

ExpErdMann
2004-Oct-01, 05:13 PM
Yes, I can see that's how they must be picturing it. But it's wrong, isn't it? How can we be talking about energy associated with negative momentum at one instant and then energy with positive momentum the next.

electromagneticpulse
2004-Oct-01, 09:26 PM
The gravity issues i have with the program involved the mechanisms described about how gravity works. According to the program gravity is a force particle that bounces back and forth between two objects.

The Force particle is called a graviton, as i understand it well its kind of like a photon. As two electrons move closer together photons are exchanged between them which causes them to repel. In gravitons the opposite effect happens, the gravitons "pull" on the reciever and the closer they get the more gravitons are exchanged.

Thats how i understand it in laymans terms anyway. I think its actualy something to do with gluons and their half-life.

Normandy6644
2004-Oct-01, 10:06 PM
Yes, I can see that's how they must be picturing it. But it's wrong, isn't it? How can we be talking about energy associated with negative momentum at one instant and then energy with positive momentum the next.

To be honest, I'm not sure. The way I understood it was (for example) a binary pulsar system very close together. They will emit gravitational radiation, which in turn contributes to a slight loss of momentum (energy) of the orbits of the pulsars, causing their orbits to decay. This would be reasonably noticeable over time, i think. I'll have to do some more reading about it all.

Worm hunter
2004-Oct-02, 07:03 PM
Thanks for all of the replies, they have been helpful.

But I still have a problem with the example used in the program I watched.

The Force particle is called a graviton, as i understand it well its kind of like a photon. As two electrons move closer together photons are exchanged between them which causes them to repel. In gravitons the opposite effect happens, the gravitons "pull" on the reciever and the closer they get the more gravitons are exchanged.

Thats how i understand it in laymans terms anyway. I think its actualy something to do with gluons and their half-life.

Ok, if that is so then why do we expect a small object to be bound to the earth so much that we cant pick it up? A small object cant reflect as many gravitons back to the earth to make the force very large.

I guess I am not expressing myself very well here but I appreciate the answers so far. I am just not sure how to go about asking my questions about this. Something with the whole way they described gravity doesnt seem right to me. I can see that gravity is weaker then em now. But for some reason the example of being able to pick up an apple with my hands, or a paperclip with a magnet doesnt seem like an example of how gravity is weak using the programs own description of how gravity works.

gzhpcu
2004-Oct-03, 05:16 AM
Correct me if I am wrong, but GR breaks down at the micro level, and QM breaks down at the marco level. When describing massive objects, you can not use QM. GR says that gravity is not a force, just a distortion of space. You can not speak of gravitons in attemptling to explain planetary physics IMO.

worzel
2004-Oct-03, 10:37 AM
WH: Are you saying that an apple sould only be able to exchange so many gravitons due to its mass and, although the attraction may increase with reduced distance because of the increased rata of exchanges, how can the attraction be greater without limit due to the other mass?

Normandy6644
2004-Oct-03, 02:43 PM
Correct me if I am wrong, but GR breaks down at the micro level, and QM breaks down at the marco level. When describing massive objects, you can not use QM. GR says that gravity is not a force, just a distortion of space. You can not speak of gravitons in attemptling to explain planetary physics IMO.

While GR does break down at the micro level, QM doesn't really "break down" at the macro level. it's still just as valid, it's just the the effects are much less noticeable, if at all.

I'm not exactly sure how the GR description and gravitons work together to be honest. I haven't read enough about it. It's possible that they combine to say that the gravitons will follow the curved space in order to make an attractive "force," though I'm not even sure if the idea of a gravitational force makes sense in GR. Time to read some more...

gzhpcu
2004-Oct-03, 03:40 PM
Correct me if I am wrong, but GR breaks down at the micro level, and QM breaks down at the marco level. When describing massive objects, you can not use QM. GR says that gravity is not a force, just a distortion of space. You can not speak of gravitons in attemptling to explain planetary physics IMO.

While GR does break down at the micro level, QM doesn't really "break down" at the macro level. it's still just as valid, it's just the the effects are much less noticeable, if at all.

I'm not exactly sure how the GR description and gravitons work together to be honest. I haven't read enough about it. It's possible that they combine to say that the gravitons will follow the curved space in order to make an attractive "force," though I'm not even sure if the idea of a gravitational force makes sense in GR. Time to read some more...

As far as I know, GR does not encompass gravitons. There are many different superstring theories and each has a different model for the graviton. In some the graviton is a closed string, in others it is an open string. In some it has no amplitude, in others a small amplitude.

electromagneticpulse
2004-Oct-03, 11:13 PM
Ok, if that is so then why do we expect a small object to be bound to the earth so much that we cant pick it up? A small object cant reflect as many gravitons back to the earth to make the force very large.

I guess I am not expressing myself very well here but I appreciate the answers so far. I am just not sure how to go about asking my questions about this. Something with the whole way they described gravity doesnt seem right to me. I can see that gravity is weaker then em now. But for some reason the example of being able to pick up an apple with my hands, or a paperclip with a magnet doesnt seem like an example of how gravity is weak using the programs own description of how gravity works.

Well EM is "Tubed" through the material. The Photons are emited from the north pole (for example i dont know enough to say which end for sure or if they even come from an end but this is how i get it) and go around to the south pole and are reabsorbed, the larger the distance the less energy the photon has so the less "pull" or "push" it has. Say a bar magnet has 1000 atoms in and each emits one photon, this means it has 1000 photons which are coming out of the north pole and going to the south pole.
Gravity as far as we know can't be aligned like EM so the 1000 gravitons emited just grip the atoms around it so while gravity is still strong say only 100 of the gravitons actualy get out to grip anything else (this isn't the proper explination i've not read up properly on gravitons yet but when i get the internet back on my computer i'll check it out.).

Gravity is concentrated at the centre of an object, while EM is normaly just disipated in objects as all the atoms are all in a jumble but in ferrite materials they can be arranged and this gives a powerful magnetic force. One thing that is armageddon the film did happen with it being a ferrite asteroid if it had passed relatively close to jupiter we would have noticed it when there was a big bang as jupiter has the largest magnetic field in the whole of our solar system from its liquid hydrogen streams.

Anyway i think i've talked enough i'll get back to kicking things made in taiwan :lol:

ExpErdMann
2004-Oct-04, 03:19 PM
Correct me if I am wrong, but GR breaks down at the micro level, and QM breaks down at the marco level. When describing massive objects, you can not use QM. GR says that gravity is not a force, just a distortion of space. You can not speak of gravitons in attemptling to explain planetary physics IMO.
Why does GR fail at the micro level? Two atoms attract each other gravitationally, so there should be no problem.

Would it be fair to say that the people who talk about gravitons are merely trying to 'make sense' out of GR? Distortion of space may not appeal to everyone.

BTW, anyone know what Einstein said about gravitons, their existence, etc?

TravisM
2004-Oct-04, 03:21 PM
Einstein, about quantum mechanics in general said, "I am convinced that the Old One [God] does not play dice..." Refering to QM's probabilistic nature...

ExpErdMann
2004-Oct-04, 03:54 PM
Yes, but he also invented the photon and the graviton is just its cousin, right? Einstein favoured a field interpretation of GR (not a geometrical interpretation) so I'd suppose gravitons would be fine by him. Yet from the present discussion one gets the impression that GR and gravitons are almost two separate theories.

TravisM
2004-Oct-04, 04:01 PM
They are seperate theories. Gravitons are supposed to exist in QM but are not defined at all in GR.
QM and GR are not compatable. QM being composed of point particles and GR having, as you said, an infinite field. The incombatibility lies in the fact that at zero distance (i.e.: a point particle) GR equations break down and give nonsensical answers.
This is how I understand it at least...

ExpErdMann
2004-Oct-04, 04:12 PM
So when physicists talk about gravitational waves, the waves are not necessarily comprised of gravitons? What are they made up of then?

TravisM
2004-Oct-04, 06:34 PM
When using magnetic field equations what "magnetic" particles are we talking of? The magnetron? NO! The geometric description of GR given by Minkowski is the most elegant to me, which states that, space and time are inter-mingled, that gravity is a bend in a direction we can't see, a down-hill-toward graivty slope... The fabric itself is bent, or warped, like around a black hole, but much less extreeme...
There are only particles in QM (wich are actually wave-packets, as close as QM can get to a standard particle) and there are only fields in GR. So the two are totally seperate and don't have 1 variable in common, except maybe c &amp; PI...
Mmmmmmm, pie...

gzhpcu
2004-Oct-04, 07:25 PM
Correct me if I am wrong, but GR breaks down at the micro level, and QM breaks down at the marco level. When describing massive objects, you can not use QM. GR says that gravity is not a force, just a distortion of space. You can not speak of gravitons in attemptling to explain planetary physics IMO.
Why does GR fail at the micro level? Two atoms attract each other gravitationally, so there should be no problem.

Would it be fair to say that the people who talk about gravitons are merely trying to 'make sense' out of GR? Distortion of space may not appeal to everyone.

BTW, anyone know what Einstein said about gravitons, their existence, etc?

No, the two theories are completely different. The problem is that quantum mechanics is a theory that describes matter and energy in terms of discrete packets of energy, which move unhindered through space. General relativity says nothing about the structure of matter. It says nothing about how the gravitational field is generated by matter and energy. It is a 'global' theory of space-time, not a 'local' theory of space-time. The challenge is to find the right mathematics to bridge the conceptual gap between classical gravity and space-time on the one hand, and a quantum description of gravity and space-time on the other.

The uncertainty principle applies not just to particles but also to empty space. Over very short intervals virtual particles can appear. The shorter the time the more massive the particles can be. At very short intervals virtual particles will be massive enough to form black holes. One cannot extrapolate simultaneously both quantum mechanics and general relativity to minute distances. The theories explode or diverge.

gzhpcu
2004-Oct-04, 07:28 PM
Yes, but he also invented the photon and the graviton is just its cousin, right? Einstein favoured a field interpretation of GR (not a geometrical interpretation) so I'd suppose gravitons would be fine by him. Yet from the present discussion one gets the impression that GR and gravitons are almost two separate theories.

Not according to this source:

Einstein never had a good word for the relativity version of quantum mechanics known as quantum field theory. Its successes did not impress him. Once, in 1912, he said of the quantum theory the more successful it is the sillier it looks. When speaking of successful physical theories, he would, in his later years, quote the example of the old gravitational theory. Had Newton not been successful for more than two centuries? And had his theory not turned out to be incomplete.

source:
Page 24
Abraham Pais.
Subtle is the Lord.
Oxford University Press, New York, 1982.

gzhpcu
2004-Oct-04, 07:30 PM
So when physicists talk about gravitational waves, the waves are not necessarily comprised of gravitons? What are they made up of then?

Waves are not composed of particles. Waves are probability states. Particles result when the Schroedinger Wave Function collapses.

ExpErdMann
2004-Oct-04, 08:17 PM
Yes, but he also invented the photon and the graviton is just its cousin, right? Einstein favoured a field interpretation of GR (not a geometrical interpretation) so I'd suppose gravitons would be fine by him. Yet from the present discussion one gets the impression that GR and gravitons are almost two separate theories.

Not according to this source:

Einstein never had a good word for the relativity version of quantum mechanics known as quantum field theory. Its successes did not impress him. Once, in 1912, he said of the quantum theory the more successful it is the sillier it looks. When speaking of successful physical theories, he would, in his later years, quote the example of the old gravitational theory. Had Newton not been successful for more than two centuries? And had his theory not turned out to be incomplete.

He might not have liked QM even when dressed up with relativity, but that does not imply he liked the geometric, space-bending description of GR. Einstein supported the field theory interpretation, meaning gravity is a force propagated through space like other forces. From your description, I take it he would not have used the term graviton for the physical entities transmitting the force. Yet it seems most natural for Einstein to have done so, given his role in the photon theory. For sure he wouldn't have gone for the 'wave as probability wave' notion, as in your follow-up post.

electromagneticpulse
2004-Oct-04, 11:06 PM
The matter isn't that Einstein didn't like QM it's simply that he would accept things with proof and at that time there wasn't as much proof as there is now. He Accepted that QM worked but he thought that it was simply a part of a "bigger picture". If you gave Einstein all the info on string theory he might not have liked it but he would have accepted it as a posibility until it had proof.
If gravitons inface to work like photons in the QM sense then the "warp" in space time would be the exact same as the graviton forces. The more energy a particle has the more gravitons it produces so the bigger their range. A black hole infact has the most energy we know of afterall it is the collapse of a star that would have created a super massive supernova so it explains why it has enough energy to be able to stop anything escaping, or in GR "warp space".

Its not that different if you think about it, its just different ways of reading the same thing. Its like desert and desert, one is food and could be ice cream the other is a desert with no food or water, QM and GR are kind of the same thing their both physics but just a different way of reading it. :)

gzhpcu
2004-Oct-05, 02:11 AM
From what I read, I gathered that Einstein was a "neorealist": his view was not so different from Newton's, that reality consisted of force and particles. This despite his formulation of GR.

QM has led to a number of different models of reality. Which one is really true? Probably none, IMHO. The emphasis is to explain how things work, not why.

Yes, we are like the blind men touching an elephant: one touch's the trunk, the other the leg. Each makes his own description of the elephant (snakelike, treelike). They are all right, but all wrong in what the elephant really is.

TravisM
2004-Oct-05, 11:49 AM
I don't know...

The force model doesn't sit well with me, and particles 'invented' to carry a force doesn't sit well with me... I enjoy the idea that gravitational orbits are mearly bent space, that massive objects distort space so that things like planets and moons can, from their frame of reference, travel in a straight line preserving "...a body in motion tends to stay in motion..." notion. :) (you have no idea how long i've been waiting to work that into a convesation...)

I studied electronics in vocational school and electricity is a pretty powerful force. Yet, not so strong as CRT displays or vaccum tubes need just that, all the air pumped out of them to make electron propogation easier. Electricity is limited to the distance it travels by dielectric properties of the medium it is propogating in. Dry air is a dielectric as well as distilled water and a vaccum is even better. ( for more see here (http://whatis.techtarget.com/definition/0,,sid9_gci211945,00.html) ) not discounting the effects I've seen of lightning and industrial voltages. I've seen some enormous arcs in my day. But, at the distance of galaxies? Through an excellent dielectric? #-o

Observables. That's what it boils down to. How much are we allowed to know at what pace and time. It's taken us quite a while to get to where we are, to be able to study and ponder the things we do...
It's early, I need coffee or get rather coherent. :wink:

electromagneticpulse
2004-Oct-05, 02:48 PM
I don't know...

The force model doesn't sit well with me, and particles 'invented' to carry a force doesn't sit well with me... I enjoy the idea that gravitational orbits are mearly bent space, that massive objects distort space so that things like planets and moons can, from their frame of reference, travel in a straight line preserving "...a body in motion tends to stay in motion..." notion. :) (you have no idea how long i've been waiting to work that into a convesation...)

Well distortions in space don't sit well with me at all in fact it freaks me out (what i want to say would get me banned probably). A black hole is a "hole in space" well i wouldn't want a hole in a fish tank why in the heck would anyone in their right mind put one in space.
Simply a black hole is a singularity which means the scientists have screwed up. So they put an event horizon around it so they don't have to worry about it, i've still heard it claimed to be a hole in space after Hawking invented black hole radiation. How can it be a hole in space if things come out of it and it would be majorly destroying the whole point of conservation of energy if you could put the whole of the universe through one and it not be a little bit messed up.

As for moons orbiting planets etc, this would happen with gravitons anyway! They can do it with magnets you just need to give the "orbitor" enough energy and it won't fall out of orbit, thats how sattelites stay up.

I studied electronics in vocational school and electricity is a pretty powerful force. Yet, not so strong as CRT displays or vaccum tubes need just that, all the air pumped out of them to make electron propogation easier. Electricity is limited to the distance it travels by dielectric properties of the medium it is propogating in. Dry air is a dielectric as well as distilled water and a vaccum is even better. ( for more see here ) not discounting the effects I've seen of lightning and industrial voltages. I've seen some enormous arcs in my day. But, at the distance of galaxies? Through an excellent dielectric? #-o

Umm the Vaccum tube used in a TV works on QM principals, so do lasers and indeed everything that makes up your computer. It uses the "quantum cookbook". I can say that dialectrics have nothing in the slightest to do with this. The carrier of the EM field is a photon, light. If dielectric was involved i think we'd all be blind cause our eyes would have the least use ever as they have the energy of eV not V, IIRC the dielectric charge of dry air is 21 volts, its about 1400 volts for glass and i can see through glass so it certainly has nothing to do with electrons floating through space to be a form of EM field. Electromagnetics works on the process of photons being emitted from all electrons, these are then arranged in magnetic materials so they all propogate the same way increasing the force. Its based on the uncertanty principal as we can never know how much energy something has.

Okay let me explain how electrons behave (to the best of my understanding), as an electron travels through space it emits a photon which is then reabsorbed quickly so the energy isn't lost at all. Once reabsorbed it will spontaniously emit another and so on. Now it gets close to another electron their both emiting photons and reabsorbing, they move close enough so that the photons jump to the other electron, this causes a repulsion between the electrons and they move away from each other.
Using the uncertanty principal a photon could spontaniously make an electron leaving a positron behind, the electron can emit a proton, which can emit a pion which can turn into a neutron... same thing with the positron and hey presto they are gone again. Which ties into your last paragraph.

Observables. That's what it boils down to. How much are we allowed to know at what pace and time. It's taken us quite a while to get to where we are, to be able to study and ponder the things we do...

We can know as much about the place and time of an object as we are about the velocity and mass of a particle. Einstein came up with a thought experiment called "the clock in the box", Doesn't work. To measure it accurately everything is set on the uncertanty principal and fails drasticly. The more accurate get the more uncertanty there is in it so it falls flat on its face.

The most likely way we could do it is by entangeling to helium atoms for example and as they seperate one could be measured for mass and one for momentum, add it together and you should have half of the answer but in turn this can fail. I never read into how but there would be alot of hype over it if it didn't fail and theres been people trying to prove it since the day of Einstein so its safe to assume they failed.

gzhpcu
2004-Oct-05, 06:22 PM
I don't know...

The force model doesn't sit well with me, and particles 'invented' to carry a force doesn't sit well with me... I enjoy the idea that gravitational orbits are mearly bent space, that massive objects distort space so that things like planets and moons can, from their frame of reference, travel in a straight line preserving "...a body in motion tends to stay in motion..." notion. :) (you have no idea how long i've been waiting to work that into a convesation...)

Actually, I find both versions weird: the graviton particle and curved space. Curved space implies higher dimensions in which our three space dimension can be distorted (as in "Flatland" by Abbott).