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Robert
science forum beginner
Joined: 17 Nov 2005
Posts: 41
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 Posted: Sun Jun 11, 2006 6:42 pm Post subject:
Gravity - Caused by GR curvature or gravitons?
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As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone. No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is through
the interaction of gravitons that gravity is produced.
On the surface it seems as if these are two totally imcompatible world
views. One has go to go. Well, in discussions here and elsewhere we always
get the same result. Some people say "Yes, these two views are really
imcompatible" while another groups saus "No, you're crazy, they are totally
compatible."
Umm, both groups can't be correct. I would it appreciate it if people would
look through the various answers to this question, and let me know what they
think?
One very interesting answer is here. Thoughts?
http://www.lns.cornell.edu/spr/1999-02/msg0014781.html
Re: Gravity: Wave-Particle vs Space-Time Warpage
Subject: Re: Gravity: Wave-Particle vs Space-Time Warpage
From: baez@galaxy.ucr.edu (john baez)
Date: 14 Feb 1999 00:00:00 GMT
Other answers came from a discussion on www.physicsforums.com. Some people
there answered that GR's model of a curved space causing gravity is totally
at odds with the graviton model of gravity. For instance:
selfAdjoint states:
"The graviton is a theoretical particle predicted by string theory but not
yet demonstrated to exist. If it exists and is the cause of gravity it will
do away with spacetime curvature and produce gravity the way the photon
carries electromagnetism. Then gravity would be a (quantum) force in your
sense."
"At the present time however, our best theory of gravity is Einstein's 1915
General Theory of Relativity. One of the basic propositions of that theory
is the Principle of Equivalence: On a sufficiantly small scale, it is
impossible to tell the difference between an imposed force and a
gravitational one. Notice that the shape is the shape of spacetime, not just
of space. Therefore a curved geodesic goes through time as well as space,
and by curving, causes those travelling along it to experience an
acceleration. Anything that produces an acceleration deserves the name
force, no?"
Nenad writes:
"...because if the graviton is found, then there is no curvature of space
time, the reson there is gravity will be because of the graviton. You cant
have both explaining the same thing."
However, some people come to exact opposite conclusion! They hold that the
GR model is compatible with the graviton model of gravity. For instance:
jtolliver writes:
| Quote: | yes, if the graviton is found, General Relativity will be wrong.
|
"Not really. Any lorentz-invariant interaction that preserves causality can
be described in terms of particles. GR satisfies those conditions.
Gravitational waves have many properties traditionally associated with
particles (If you pretend spacetime is flat and you add gravitational forces
to compensate), such as energy-momentum. Using curved space-time(the
technique traditionally used in GR), and using flat space-time with an
additional force that makes it act exactly as though it were curved(this was
the technique used in classical mechanics, except that that force didn't
quite make it act exactly as curved space-time) are just different ways of
looking at the same thing. The first way is much more convient
mathematically, and the second way doesn't really explain why we have this
additional force. The graviton's only look like particles when we assume
spacetime is flat. If we assume spacetime is curved we see it is really only
an effect of the curvature of spacetime, even though it looks exactly like a
particle."
pmb_phy writes:
....It is not the curvature of spacetime that causes gravitational
acceleration. Spacetime curvature causes two particles moving under to have
a relative acceleration between them, i.e. spacetime curvature causes tidal
accelerations. But you can have a gravitational force in the absense of
spacetime curvature."
| Quote: | The graviton is a theoretical particle predicted by string theory
but not yet demonstrated to exist.
|
It doesn't come from string theory. It comes from quantum gravity/quantum
field theory.
| Quote: | If it exists and is the cause of gravity it will do away
with spacetime curvature ...
|
That is incorrect. The graviton is responsible for producing gravitational
forces, not just tidal forces. Therefore one should aslo be able to detect
gravitons in a gravitational field even when the spacetime is flat. The
graviton, if it exists, will have a relative existance in that sense.
| Quote: | yes, if the graviton is found, General Relativity will be wrong.
if the graviton is found, then there is no curvature of space time,
the reson there is gravity will be because of the graviton. You cant
have both explaining the same thing.
|
That is very much incorrect. You can most certainly have both. If the
graviton is detected then we will have the mechanism behind GR. Gravitons
are certainly not inconsistent with general relativity.
| Quote: | Couldnt you say the graviton cause the curvature of spacetime...lol
|
Absolutely. That is 100% correct.
Gravity is not like other forces like the electric of magnetic forces. The
gravitational force is an inertial force where the others aren't.
---
Ok, so which view is correct? (References to peer-reviewed lit, or books by
respected authors, would also be appreciated.)
Thanks,
Robert |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
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| Posted: Sun Jun 11, 2006 7:33 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Robert wrote:
snip
| Quote: |
Ok, so which view is correct? (References to peer-reviewed lit, or books by
respected authors, would also be appreciated.)
Thanks,
Robert
|
The concept of a photon does not help you understand the
propagation of light. It helps to understand atomic absorbtion
and emission.
http://nobelprize.org/physics/articles/ekspong/index.html
Likewise a gravi-photon would not help to understand gravity.
It can be quatified however:
http://www.esa.int/SPECIALS/GSP/SEM0L6OVGJE_0.html
The 'graviton', which high energy labs would like to find may
need to be reconsidered if Tajmar and de Matos's experiment
is repeated. IMHO the signal from LIGO has already forcast
the outcome of Gravity Probe B but the proof is in the puddin'.
http://einstein.stanford.edu/
Sue... |
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Igor
science forum Guru
Joined: 15 May 2005
Posts: 315
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| Posted: Sun Jun 11, 2006 7:36 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Robert wrote:
| Quote: | As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone. No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is through
the interaction of gravitons that gravity is produced.
|
A comprehensive theory of quantum gravity that actually works has never
been found. It's still elusive.
| Quote: | On the surface it seems as if these are two totally imcompatible world
views. One has go to go. Well, in discussions here and elsewhere we always
get the same result. Some people say "Yes, these two views are really
imcompatible" while another groups saus "No, you're crazy, they are totally
compatible."
|
Actually, they might not be as incompatible as they appear to be.
There's an already established example, in electrodynamics. We can
think of things in terms of electric and magnetic fields governed by
Maxwell's equations or we can say that interactions occur through the
exchange of virtual photons as described by quantum-electrodynamics.
The two are fully compatible.
| Quote: | Umm, both groups can't be correct. I would it appreciate it if people would
look through the various answers to this question, and let me know what they
think?
|
It's really quite hard to say. While it seems to work for
electrodynamics, it may not actually work for gravity. One of the
problems is that gravity is connected to the curvature of spacetime and
is not a force in the conventional sense. Also, gravitons would have
to be a quantization of gravitational waves, which are literally
propagating oscillations of spacetime. This has been one of the
biggest stumbling blocks for quantum gravity. |
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FrediFizzx
science forum Guru
Joined: 01 May 2005
Posts: 774
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| Posted: Sun Jun 11, 2006 8:46 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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"Igor" <thoovler@excite.com> wrote in message
news:1150054585.237900.222460@j55g2000cwa.googlegroups.com...
| Quote: |
Robert wrote:
As I understand it, Einstein's theory of General Relativity (GR)
seems to
describe gravity as being caused by curved space-time alone. No
gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is
through
the interaction of gravitons that gravity is produced.
A comprehensive theory of quantum gravity that actually works has
never
been found. It's still elusive.
On the surface it seems as if these are two totally imcompatible
world
views. One has go to go. Well, in discussions here and elsewhere we
always
get the same result. Some people say "Yes, these two views are
really
imcompatible" while another groups saus "No, you're crazy, they are
totally
compatible."
Actually, they might not be as incompatible as they appear to be.
There's an already established example, in electrodynamics. We can
think of things in terms of electric and magnetic fields governed by
Maxwell's equations or we can say that interactions occur through the
exchange of virtual photons as described by quantum-electrodynamics.
The two are fully compatible.
Umm, both groups can't be correct. I would it appreciate it if
people would
look through the various answers to this question, and let me know
what they
think?
It's really quite hard to say. While it seems to work for
electrodynamics, it may not actually work for gravity. One of the
problems is that gravity is connected to the curvature of spacetime
and
is not a force in the conventional sense. Also, gravitons would have
to be a quantization of gravitational waves, which are literally
propagating oscillations of spacetime. This has been one of the
biggest stumbling blocks for quantum gravity.
|
Taking the quantum "vacuum" as a relativistic medium, eliminates the
"stumbling block".
Volovik says it like it is very well in his book "The Universe in a
Helium Droplet" page 461 sect. 33 Conclusion;
"According to the modern view the elementary particles (electrons,
neutrinos, quarks, etc.) are excitations of some more fundamental medium
called the quantum vacuum. This is the new ether of the 21st century.
The electromagnetic and gravitational fields, as well as the fields
transferring the weak and the strong interactions, all represent
different types of collective motion of the quantum vacuum."
Paraphrasing, he goes on to say that the only thing that remains
fundamental in this viewpoint is hbar, Planck's reduced constant.
Everything else is seen to be emergent. So all that is left is to
figure out is what hbar is. ;-)
Whether or not the detection of a photon can be considered to be
evidence of the relativistic medium is purely interpretational. All
that is required is to take "vacuum" polarization to tree level. And
with the relativistic medium model, even EM can be seen as spacetime
curvature although somewhat different from gravitational.
FrediFizzx
Quantum Vacuum Charge papers;
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.pdf
or postscript
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.ps
http://www.arxiv.org/abs/physics/0601110
http://www.vacuum-physics.com |
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N:dlzc D:aol T:com (dlzc)
science forum Guru
Joined: 25 Mar 2005
Posts: 2835
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| Posted: Sun Jun 11, 2006 9:22 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Dear Robert:
"Robert" <rkscience100@NOSPAM.yahoo.REMOVECAPS.com> wrote in
message news:xuZig.245$2R.68@trndny02...
| Quote: | As I understand it, Einstein's theory of General Relativity
(GR) seems to describe gravity as being caused by
curved space-time alone.
|
Right. Spacetime is modeled as a continuum, much as Maxwell's
"aether" is a continuum.
| Quote: | No gravitons are necessary. However, quantum field
theory is said to predict
|
.... "require" ...
| Quote: | the existence of a graviton (which is massless, like
a photon) and it is through the interaction of
gravitons that gravity is produced.
|
Quantum theory deals with exchange particles. Any action
requires an exchange, and space and time are not players.
| Quote: | On the surface it seems as if these are two totally
imcompatible world views.
|
As are "wave" and "particle".
Not at all. Each has its strong points. And both are wrong.
Any construct of our imaginations is only as good as the
experiments it can describe. Nature decides which survive, and
where they survive.
| Quote: | Well, in discussions here and elsewhere we
always get the same result. Some people
say "Yes, these two views are really
imcompatible" while another groups saus "No,
you're crazy, they are totally compatible."
|
In some sense they are. They (attempt to) describe the same
behavior from two different points of view.
| Quote: | Umm, both groups can't be correct.
|
But they both can be right... in their own domain of
applicability.
| Quote: | I would it appreciate it if people would look
through the various answers to this question,
and let me know what they think?
|
Study more. It gets even stranger.
| Quote: | One very interesting answer is here. Thoughts?
....
Other answers came from a discussion on
www.physicsforums.com. Some people there
answered that GR's model of a curved space
causing gravity is totally at odds with the
graviton model of gravity.
....
However, some people come to exact opposite
conclusion! They hold that the GR model is
compatible with the graviton model of gravity.
....
Ok, so which view is correct?
|
Yes.
| Quote: | (References to peer-reviewed lit, or books by respected
authors, would also be appreciated.)
|
Wouldn't it?
Your quotations are from a "sewing circle". I suggest you go to
school for this, if it is interesting to you.
David A. Smith |
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Sue...
science forum Guru
Joined: 08 May 2005
Posts: 2684
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| Posted: Sun Jun 11, 2006 9:38 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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N:dlzc D:aol T:com (dlzc) wrote:
snip
| Quote: |
Your quotations are from a "sewing circle". I suggest you go to
school for this, if it is interesting to you.
|
Harumph!
Do you practice sewer analysis or sewer analysis ?
I happen to know a few sewers that aren't to shabby
when it comes to electromagnetism.
But some complain it is just the work for the sewer.
Suzysewnshow...  )
|
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Thomas Heger
science forum Guru Wannabe
Joined: 16 Nov 2005
Posts: 151
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| Posted: Sun Jun 11, 2006 10:16 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
|
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"Robert" <rkscience100@NOSPAM.yahoo.REMOVECAPS.com> schrieb im Newsbeitrag
news:xuZig.245$2R.68@trndny02...
| Quote: | As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone. No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is
through the interaction of gravitons that gravity is produced.
On the surface it seems as if these are two totally imcompatible world
views. One has go to go. Well, in discussions here and elsewhere we always
get the same result. Some people say "Yes, these two views are really
imcompatible" while another groups saus "No, you're crazy, they are
totally compatible."
Umm, both groups can't be correct. I would it appreciate it if people
would look through the various answers to this question, and let me know
what they think?
One very interesting answer is here. Thoughts?
http://www.lns.cornell.edu/spr/1999-02/msg0014781.html
Re: Gravity: Wave-Particle vs Space-Time Warpage
Subject: Re: Gravity: Wave-Particle vs Space-Time Warpage
From: baez@galaxy.ucr.edu (john baez)
Date: 14 Feb 1999 00:00:00 GMT
|
Hallo Robert
I read the article and liked it. To me, the idea of gravitons is 'very
suspect'. Last chrismas I started a thread and collected some (funny)
arguments against gravitons. These 'things' are still suspect to me, since I
think the approach of relativity is more valid.
BUT relativity is very strange too! I started to take the idea of spacetime
serious and tried to find out, how things would look like, if watched from
the perspective of spacetime. If you do this, the universe is (for
illustration purposes) reduced by one dimension, a sheet on the outside of a
hypersphaere, that expands with c.
A particle drags a sinus curve behind, same a swinging field.
If you try to think about spacetime as something real, than suddenly space
and time are something 'not real'. Those are observations of an other object
(the observer =us). Since geometry is something that belongs to space (not
to spacetime), geometry is something 'unreal' too. This is a very strange
idea. But somehow it works. The reason to think like this is gravitation.
Gravitation is a force that prevents us from floating away, so its an
obvious observation. But we are objects in the same kind of expanding
spacetime too, so we would observe spacetime as space and time. Since
gravitation is proportional to inertia, its obvious to think about timeflow
as equivalent to motion (as a real motion). But we are 'moving ' only in
spacetime. (Something like riding a bullet.)
Now it would be usefull to find a mechanism, that allow spacetime to expand,
host fields and particles and to propagate energy. Me idea to do this is a
bit strange. It goes like this: if you invert the relation between field and
space and build the inverse of the wavefunction, you have a function x,t=
phi'(S) (however that works) and can define space without knowing anything
about spacetime at all, except that it is able to swing like the em-field.
The advantage of this picture is, that fields wouldn't fill space. They
obviously do, but only to us (observers observing space). But even the
magnetic force in space is a really mysterious thing, same as gravity, and
not explained at all. If you invert this picture you get a lot of new
myteries, but those vanish.
Thomas Heger |
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N:dlzc D:aol T:com (dlzc)
science forum Guru
Joined: 25 Mar 2005
Posts: 2835
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| Posted: Sun Jun 11, 2006 10:40 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Dear Sue:
"Sue..." <suzysewnshow@yahoo.com.au> wrote in message
news:1150061885.168487.223030@u72g2000cwu.googlegroups.com...
| Quote: |
N:dlzc D:aol T:com (dlzc) wrote:
snip
Your quotations are from a "sewing circle". I
suggest you go to school for this, if it is
interesting to you.
Harumph!
Do you practice sewer analysis or sewer
analysis ? I happen to know a few sewers
that aren't to shabby when it comes to
electromagnetism.
But some complain it is just the work for the
sewer.
|
And your point is?
Do you think the OP is going to get nothing but the straight
scoop here? Or is he going to have to learn to separate wheat
from chaff AND something about physics?
David A. Smith |
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Bill Hobba
science forum Guru
Joined: 02 May 2005
Posts: 2138
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| Posted: Mon Jun 12, 2006 12:16 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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"Igor" <thoovler@excite.com> wrote in message
news:1150054585.237900.222460@j55g2000cwa.googlegroups.com...
| Quote: |
Robert wrote:
As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone. No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is
through
the interaction of gravitons that gravity is produced.
A comprehensive theory of quantum gravity that actually works has never
been found. It's still elusive.
|
Of course true. But the key word is comprehensive. Impose a cutoff at
about the plank scale and no problemo:
http://arxiv.org/abs/gr-qc/9512024
Thanks
Bill
| Quote: |
On the surface it seems as if these are two totally imcompatible world
views. One has go to go. Well, in discussions here and elsewhere we
always
get the same result. Some people say "Yes, these two views are really
imcompatible" while another groups saus "No, you're crazy, they are
totally
compatible."
Actually, they might not be as incompatible as they appear to be.
There's an already established example, in electrodynamics. We can
think of things in terms of electric and magnetic fields governed by
Maxwell's equations or we can say that interactions occur through the
exchange of virtual photons as described by quantum-electrodynamics.
The two are fully compatible.
Umm, both groups can't be correct. I would it appreciate it if people
would
look through the various answers to this question, and let me know what
they
think?
It's really quite hard to say. While it seems to work for
electrodynamics, it may not actually work for gravity. One of the
problems is that gravity is connected to the curvature of spacetime and
is not a force in the conventional sense. Also, gravitons would have
to be a quantization of gravitational waves, which are literally
propagating oscillations of spacetime. This has been one of the
biggest stumbling blocks for quantum gravity.
|
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| Back to top |
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tomgee
science forum Guru
Joined: 31 Jan 2006
Posts: 750
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| Posted: Mon Jun 12, 2006 12:53 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Robert wrote:
| Quote: | As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone. No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is through
the interaction of gravitons that gravity is produced.
Interesting topic, and I for one appreciate you having done |
some opinion-polling on it and posting it here for comparison.
First, it is not a fact yet that photons are massless and IMO it
will be seen in the end that they are not. That is not a topic
here, I know, but it has relevance to the issue at hand. It has
not yet been proven that light is massless, and my model of
the universe explains that in more detail. The evidence that
massless particles exist is based on conclusions made from
effects observed, and not on more reasonable explanations
than that. This is important when we talk of graviton particles.
The concept of curved space is really not a good explanation
at all, since it invariably causes more confusion than it dispells.
The ball-on-a-rubber-sheet only shows that massive objects
are heavy, and we already knew that. If space did curve around
massive objects, it would not be seen as a rubber sheet being
curved by the weight of a massive object. It would curve more
at the equator of the object if the object is spinning on an axis,
and less toward the poles. That could be seen as what we call
frame-dragging, which should be seen like that or, if the object
is not spinning, frame-dragging should occur behind the object
as it moves throught space.
If it is shown to occur, GRians will leap with joy at another
"exoneration" of the much-maligned GRT. However, just to
throw some cold water on that, that is not the only explanation
available from those effects. My model suggests that there
will be some frame-dragging observed, but that can also be
seen as a response to the gravitational force affecting the
Dark Matter that surrounds the object. DM is as invisible to
us as is space, and the experiments cannot distinguish one
from the other.
My model agrees with Gamow that space is filled with a sea
of Dirac's invisible negative-mass invisible particles, and those
more likely are what we will see as the dragging-around of
curved space. All the space of our universe is defined by the
existence of such particles, and my model explains how we
can have it as a mobile ether and also as a stationary one, to
satisfy both camps around the ether fires.
Gravitation surrounds massive objects, it does not lay at the
"bottom" of an object. The rubber-sheet silliness ignores that
fact, and the analogy does nothing to help understand what the
curvature of space around an object would look like. It is said
that empty space is curved and so massive objects can only
follow or move within its curves. This curved-space episode
will go down as AE's second greatest blunder, I'm afraid, once
we accept the better explanations that my model provides.
Finally, we get to the quantum graviton. As a "massless"
particle, it can only carry a "signal" of mass, but not the mass
itself. But since the effect is one of attraction between masses,
there must be something in it to produce such an effect. Yet,
invisible particles can have no positive mass, only negative
mass, meaning they can have no energy of their own that would
enable them to do anything. My model suggests that DM is the
real player in the gravitational interactions between visible and
invisible objects.
Both contain mass, but only positive mass can contain energy,
which satisfies E=mc^2 and the Principle of the Conservation of
Mass and Energy. For an object to be visible to us, it must have
energy, and to have that means it has temperature. Our visual
sense responds to light as opposed to darkness. We can see
through light, but not through the dark. Light brings the universe
to us one light wave at a time, but so rapidly that we can discern
a moving universe from the mosiac of pictures that light brings.
Suppose we know the location of a negative mass, and we shine
light at that place; yet we still cannot see it, why? Because our
eyes cannot see objects of negative mass other than in the same
way they see light - by seeing through it! And then, only when we
have light through which to see. Otherwise, without light, we
cannot see through DM, it is only darkness to us.
| Quote: |
On the surface it seems as if these are two totally imcompatible world
views. One has go to go. Well, in discussions here and elsewhere we always
get the same result. Some people say "Yes, these two views are really
imcompatible" while another groups saus "No, you're crazy, they are totally
compatible."
I submit that the basis of the confusion between the two groups |
lies in their thinking that there are no alternative explanations
other than just those two. I will read your citations and post some
more on this. |
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Tom Roberts
science forum Guru
Joined: 24 Mar 2005
Posts: 1399
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| Posted: Mon Jun 12, 2006 12:54 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Robert wrote:
| Quote: | As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone.
|
Not quite. Spacetime curvature is not a "cause" of gravity, it is a
_model_. GR, and modern physics in general, makes no attempt to discuss
"causes" (in the sense of naive causality as you used the word).
Related example: in classical electrodynamics does charge
"cause" the electric field. The answer is quite clearly: No.
But the Maxwell's equations describe a direct relationship
between them.
| Quote: | No gravitons
are necessary. However, quantum field theory is said to predict the
existence of a graviton (which is massless, like a photon) and it is through
the interaction of gravitons that gravity is produced.
|
Sort of. No complete theory of quantum gravity is known, but
semi-classical approximations indicate this. It is by no means clear
that gravitons are the whole story, because they are imagined as
perturbations on a flat background manifold, and it seems likely that QG
cannot be known via either perturbation theory or via a background
geometry of any sort.
| Quote: | [...]
Gravity is not like other forces like the electric of magnetic forces. The
gravitational force is an inertial force where the others aren't.
|
Inertial forces are fictitious, just like gravitation in GR (i.e. they
are mere artifacts of one's coordinates). It might be more accurate to
say that gravitation is not a force while the other "forces" are. But
there are lots of PUNs here, and the weak, strong, and electromagnetic
"forces" would be better called _interactions_ rather than "forces" (the
word "force" has been used in several different ways in this paragraph,
but that is the usual way to phrase this).
Tom Roberts |
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Bilge
science forum Guru
Joined: 30 Apr 2005
Posts: 2816
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| Posted: Mon Jun 12, 2006 6:07 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Robert:
| Quote: | As I understand it, Einstein's theory of General Relativity (GR) seems to
describe gravity as being caused by curved space-time alone.
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Actually, it would be more accurate to say that gravity is the name we
give to spacetime curavature.
| Quote: | No gravitons are necessary.
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That is because general relativity is a classical theory in the same
way that maxwell's theory is a classical theory of E&M. Maxwell's
equations do not require photons. Unlike E&M in which quantum effects
are easy to observe, such effects have not been experimentally observed
for gravitational phenomena. Since general relativity is a theory about
the _geometry_ of spacetime, there is the additional problem of under-
standing what it means to quantize geometry.
| Quote: | However, quantum field theory is said to predict the existence of a
graviton (which is massless, like a photon) and it is through the
interaction of gravitons that gravity is produced.
On the surface it seems as if these are two totally imcompatible world
views. One has go to go.
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That is somewhat oversimplified. If it really makes sense to quantize
general relativity, then the graviton carries the spacetime curvature
that we call gravity. This has to be the case because general relativity
does give the correct results at the classical level and any quantum
theory must reduce to general relativity in the classical limit. So,
gravitons and general relativity cannot be incompatible. The question
is whether or not it makes sense to quantize general relativity. Most
physicists seem to think that it should.
| Quote: | Umm, both groups can't be correct. I would it appreciate it if people would
look through the various answers to this question, and let me know what they
think?
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Anyone who believes that quantizing gravity is the correct approach has
to believe that general relativity is a limiting case of the quantized
theory. By definition, the quantum in the quantized theory is the graviton,
(although the graviton might not be the entire story as there are theories
which include additional particles called the dilaton and/or the axion).
On the other hand, if one believes that a quantum theory of gravity is
not the way to go, the reason would be that he does not believe that
quantizing gravity makes sense, and hence that gravitons are not compatible
with general relativity.
| Quote: | One very interesting answer is here. Thoughts?
http://www.lns.cornell.edu/spr/1999-02/msg0014781.html
Re: Gravity: Wave-Particle vs Space-Time Warpage
Subject: Re: Gravity: Wave-Particle vs Space-Time Warpage
From: baez@galaxy.ucr.edu (john baez)
Date: 14 Feb 1999 00:00:00 GMT
Other answers came from a discussion on www.physicsforums.com. Some people
there answered that GR's model of a curved space causing gravity is totally
at odds with the graviton model of gravity. For instance:
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But that is not really correct. If you look at the form of the
gauge covariant derivative in E&M and the generally covariant
derivative in general relativity, you will see a similarity.
The term eA^u is the electromagnetic connection represented by
the photon and the connection coefficients, C^a_uv play that
role for gravitons. The electromagnetic equivalent of the bianchi
identities are the homogeneous maxwell equations. The main difficulty
is understanding what it means to quantize spacetime. |
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FrediFizzx
science forum Guru
Joined: 01 May 2005
Posts: 774
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| Posted: Mon Jun 12, 2006 6:58 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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"Bilge" <dubious@radioactivex.lebesque-al.net> wrote in message
news:slrne8q52c.68.dubious@radioactivex.lebesque-al.net...
| Quote: | Robert:
As I understand it, Einstein's theory of General Relativity (GR)
seems to
describe gravity as being caused by curved space-time alone.
Actually, it would be more accurate to say that gravity is the name
we
give to spacetime curavature.
No gravitons are necessary.
That is because general relativity is a classical theory in the same
way that maxwell's theory is a classical theory of E&M. Maxwell's
equations do not require photons. Unlike E&M in which quantum effects
are easy to observe, such effects have not been experimentally
observed
for gravitational phenomena. Since general relativity is a theory
about
the _geometry_ of spacetime, there is the additional problem of under-
standing what it means to quantize geometry.
However, quantum field theory is said to predict the existence of a
graviton (which is massless, like a photon) and it is through the
interaction of gravitons that gravity is produced.
On the surface it seems as if these are two totally imcompatible
world
views. One has go to go.
That is somewhat oversimplified. If it really makes sense to
quantize
general relativity, then the graviton carries the spacetime curvature
that we call gravity. This has to be the case because general
relativity
does give the correct results at the classical level and any quantum
theory must reduce to general relativity in the classical limit. So,
gravitons and general relativity cannot be incompatible. The question
is whether or not it makes sense to quantize general relativity. Most
physicists seem to think that it should.
Umm, both groups can't be correct. I would it appreciate it if
people would
look through the various answers to this question, and let me know
what they
think?
Anyone who believes that quantizing gravity is the correct approach
has
to believe that general relativity is a limiting case of the quantized
theory. By definition, the quantum in the quantized theory is the
graviton,
(although the graviton might not be the entire story as there are
theories
which include additional particles called the dilaton and/or the
axion).
On the other hand, if one believes that a quantum theory of gravity is
not the way to go, the reason would be that he does not believe that
quantizing gravity makes sense, and hence that gravitons are not
compatible
with general relativity.
One very interesting answer is here. Thoughts?
http://www.lns.cornell.edu/spr/1999-02/msg0014781.html
Re: Gravity: Wave-Particle vs Space-Time Warpage
Subject: Re: Gravity: Wave-Particle vs Space-Time Warpage
From: baez@galaxy.ucr.edu (john baez)
Date: 14 Feb 1999 00:00:00 GMT
Other answers came from a discussion on www.physicsforums.com. Some
people
there answered that GR's model of a curved space causing gravity is
totally
at odds with the graviton model of gravity. For instance:
But that is not really correct. If you look at the form of the
gauge covariant derivative in E&M and the generally covariant
derivative in general relativity, you will see a similarity.
The term eA^u is the electromagnetic connection represented by
the photon and the connection coefficients, C^a_uv play that
role for gravitons. The electromagnetic equivalent of the bianchi
identities are the homogeneous maxwell equations. The main difficulty
is understanding what it means to quantize spacetime.
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Shouldn't be too difficult if spacetime is defined by quantum objects.
We probably just don't know what all the quantum objects are yet.
FrediFizzx
Quantum Vacuum Charge papers;
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.pdf
or postscript
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.ps
http://www.arxiv.org/abs/physics/0601110
http://www.vacuum-physics.com |
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Y.Porat
science forum Guru
Joined: 04 May 2005
Posts: 1809
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| Posted: Mon Jun 12, 2006 7:04 am Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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Sue... wrote:
| Quote: | Robert wrote:
snip
Ok, so which view is correct? (References to peer-reviewed lit, or books by
respected authors, would also be appreciated.)
Thanks,
Robert
The concept of a photon does not help you understand the
propagation of light. It helps to understand atomic absorbtion
and emission.
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-----------------------------------
the photon cannot cause any attraction force since it moves in straight
lines!!
it isself contardictory
if you will say that garvitins move matirally (repeat - naturally) in
curved closed path
than i will agree and suggest to call them Circlons !!
a much more indicative name toits nature of behaviour
and be tter unserstanding of any attraction force !!
ATB
Y.Porat
--------------------------------
> |
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Harry
science forum Guru
Joined: 08 May 2005
Posts: 1010
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| Posted: Mon Jun 12, 2006 2:42 pm Post subject:
Re: Gravity - Caused by GR curvature or gravitons?
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"Y.Porat" <maporat@012.net.il> wrote in message
news:1150095846.249933.294510@u72g2000cwu.googlegroups.com...
| Quote: |
Sue... wrote:
Robert wrote:
snip
Ok, so which view is correct? (References to peer-reviewed lit, or
books by
respected authors, would also be appreciated.)
Thanks,
Robert
The concept of a photon does not help you understand the
propagation of light. It helps to understand atomic absorbtion
and emission.
-----------------------------------
the photon cannot cause any attraction force since it moves in straight
lines!!
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Not so according to Einstein...
Harald
| Quote: | it isself contardictory
if you will say that garvitins move matirally (repeat - naturally) in
curved closed path
than i will agree and suggest to call them Circlons !!
a much more indicative name toits nature of behaviour
and be tter unserstanding of any attraction force !!
ATB
Y.Porat
--------------------------------
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