| Topic: |
Science > Physics |
| User: |
"Gerhard W. Gruber" |
| Date: |
22 Apr 2006 04:11:07 PM |
| Object: |
Realtivity vs. Quantumphysics on gravity |
Hi,
I'm not a physicist or related to the fields, but I'm interested in physics as
a hobby and I try to learn a bit about it, so I hope my questions don't seem
to dumb. :)
First question that I was wondering about (though there will be more :) ), is
about realtivity vs. quantumphysics. Special relativity says that mass will
distort space and time, which is ok for me, and understandable. From this it
followed is, that any object moving through space in free fall, is actually
following the geometry of this distorted space, which was proven with that
experiment where light was bent while an eclipse.
Now when I look at it from the quantumphysical point of view, the literature
says that we have a lot of particles doing this or that. Especially scientists
expect to find a graviton that should be responsable for transferring the
power of gravity. Following string theory, it even seems to predict a particle
that would have the characteristics of that graviton.
This is what I don't really understand. If realtivity is right, and gravity is
in truth an effect of distorated space, then why do we need a particle that is
supposed to transmit that "power"? I would assume that, if it is really a
characteristic of distorted space, than it wouldn't need a particle to do
something, because what would that particle do?
Speaking of which, what exactly does it mean, when scientists say there is a
particle that transfers the power of X? How does such a particle work? It is a
bit hard for me to nvision a particle that transfers something like gravity,
because how do you have to imagine this? I can understand that particles can
collide with each other, and this will have some effects, but I don't see
where gravity would fit in, in terms of particles effects.
.
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| User: "" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
22 Apr 2006 05:20:08 PM |
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Gerhard W. Gruber wrote:
Hi,
Hi!
I'm not a physicist or related to the fields, but I'm interested in physics as
a hobby and I try to learn a bit about it, so I hope my questions don't seem
to dumb. :)
We'll see. :P
First question that I was wondering about (though there will be more :) ), is
about realtivity vs. quantumphysics. Special relativity says that mass will
distort space and time, which is ok for me, and understandable.
That's general relativity.
From this it
followed is, that any object moving through space in free fall, is actually
following the geometry of this distorted space, which was proven with that
experiment where light was bent while an eclipse.
That's still general relativity.
Now when I look at it from the quantumphysical point of view, the literature
says that we have a lot of particles doing this or that. Especially scientists
expect to find a graviton that should be responsable for transferring the
power of gravity. Following string theory, it even seems to predict a particle
that would have the characteristics of that graviton.
If you want to see why SR and acceleration are REALLY incompatible,
look at
http://math.ucr.edu/home/baez/physics/Relativity/SR/rigid_disk.html
which tells us that curved spacetime is the ONLY method that works.
This is what I don't really understand. If realtivity is right, and gravity is
in truth an effect of distorated space, then why do we need a particle that is
supposed to transmit that "power"? I would assume that, if it is really a
characteristic of distorted space, than it wouldn't need a particle to do
something, because what would that particle do?
The ideas that you can quantize gravity separate from quantizing
spacetime is in fact flawed.
Speaking of which, what exactly does it mean, when scientists say there is a
particle that transfers the power of X? How does such a particle work? It is a
bit hard for me to nvision a particle that transfers something like gravity,
because how do you have to imagine this? I can understand that particles can
collide with each other, and this will have some effects, but I don't see
where gravity would fit in, in terms of particles effects.
It doesn't. Unless you can conceive of some particle made OUT of
spacetime itself. Even then, to have a wave we need both positive
energy and negative energy, such that from higher energy fields it
looks like negative energy and from lower energy fields it looks like
positive energy.
(...Starblade Riven Darksquall...)
.
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| User: "Edward Green" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
27 Apr 2006 04:52:57 PM |
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wrote:
If you want to see why SR and acceleration are REALLY incompatible,
look at
http://math.ucr.edu/home/baez/physics/Relativity/SR/rigid_disk.html
which tells us that curved spacetime is the ONLY method that works.
Curved spacetime has nothing to do with it.
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| User: "Gerhard W. Gruber" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
23 Apr 2006 02:56:34 AM |
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On 22 Apr 2006 15:20:08 -0700 wrote in sci.physics with
<1145744408.486560.312270@t31g2000cwb.googlegroups.com>
If you want to see why SR and acceleration are REALLY incompatible,
look at
http://math.ucr.edu/home/baez/physics/Relativity/SR/rigid_disk.html
which tells us that curved spacetime is the ONLY method that works.
Thx for the link. It will take some time until I can comprehend it, because
looking at it, I will have a hard time understanding it, a tmy current level.
:)
The ideas that you can quantize gravity separate from quantizing
spacetime is in fact flawed.
That's what I thought as well.
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| User: "Gregory L. Hansen" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
23 Apr 2006 08:47:04 AM |
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In article <um6l42hdaenblvfap4gh3ib3rr5t44h84q@4ax.com>,
Gerhard W. Gruber <sparhawk@gmx.at> wrote:
Hi,
I'm not a physicist or related to the fields, but I'm interested in physics as
a hobby and I try to learn a bit about it, so I hope my questions don't seem
to dumb. :)
First question that I was wondering about (though there will be more :) ), is
about realtivity vs. quantumphysics. Special relativity says that mass will
distort space and time, which is ok for me, and understandable. From this it
followed is, that any object moving through space in free fall, is actually
General relativity. But go on.
following the geometry of this distorted space, which was proven with that
experiment where light was bent while an eclipse.
Now when I look at it from the quantumphysical point of view, the literature
says that we have a lot of particles doing this or that. Especially scientists
expect to find a graviton that should be responsable for transferring the
power of gravity. Following string theory, it even seems to predict a particle
that would have the characteristics of that graviton.
That's not unique to string theory, but a reuirement of a quantized field
theory.
This is what I don't really understand. If realtivity is right, and gravity is
in truth an effect of distorated space, then why do we need a particle that is
supposed to transmit that "power"? I would assume that, if it is really a
characteristic of distorted space, than it wouldn't need a particle to do
something, because what would that particle do?
Speaking of which, what exactly does it mean, when scientists say there is a
particle that transfers the power of X? How does such a particle work? It is a
bit hard for me to nvision a particle that transfers something like gravity,
because how do you have to imagine this? I can understand that particles can
collide with each other, and this will have some effects, but I don't see
where gravity would fit in, in terms of particles effects.
In this context, the most important postulate of quantum mechanics is
DeBroglie's relation, which relates the momentum of a particle to a
wavelength,
p = h/lambda
where h is Planck's constant. It also relates the wavelength of a field
to a momentum. Suppose you had an electron in an electromagnetic field
with some wavelength lambda-- then the momentum that can be transferred to
the particle is h/lambda, no more and no less. (It might get two or three
or more momentum transfers, and after each one the effective wavelength
can be different due to Doppler shifting, but that's unnecessary
complication at this level.) It's this sudden and finite transfer of
momentum that makes the field act as if a particle knocked into the
electron. It also relates to the sensible question "How can an exchange
of particles create an attractive force?" Because the particles in
question aren't little billiard balls-- they're a representation of the
field, and so they do what the field does.
They suppose that gravitational fields must also obey DeBroglie's
relation.
--
"Pain is temporary, quitting lasts forever" -- Lance Armstrong
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| User: "Gerhard W. Gruber" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
24 Apr 2006 01:11:50 PM |
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On Sun, 23 Apr 2006 13:47:04 +0000 (UTC) wrote
(Gregory L. Hansen) in sci.physics with
<e2g0go$50v$4@rainier.uits.indiana.edu>
complication at this level.) It's this sudden and finite transfer of
momentum that makes the field act as if a particle knocked into the
electron. It also relates to the sensible question "How can an exchange
of particles create an attractive force?" Because the particles in
question aren't little billiard balls-- they're a representation of the
field, and so they do what the field does.
I have to think about this, as I read it now several times, but I can't relate
to it right now. I have the feeling that this makes sense though. :)
They suppose that gravitational fields must also obey DeBroglie's
relation.
If an attractive force can be created in the way you described above, then it
would make sense.
.
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| User: "Henning Makholm" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
22 Apr 2006 06:04:49 PM |
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Scripsit Gerhard W. Gruber <sparhawk@gmx.at>
Now when I look at it from the quantumphysical point of view, the literature
says that we have a lot of particles doing this or that. Especially
scientists expect to find a graviton that should be responsable for
transferring the power of gravity. Following string theory, it even
seems to predict a particle that would have the characteristics of
that graviton.
This is what I don't really understand. If realtivity is right, and
gravity is in truth an effect of distorated space, then why do we
need a particle that is supposed to transmit that "power"?
As far as I understand, the holy grail of the QG research is to find a
way to get gravitons PLUS flat space to reproduce the experimental
effects that we have henceforth needed curved spacetime to explain,
at least within the experimental precision.
It would be OK for QG to depart from the GR predictions in situations
that we have no observation for - for example, if the average energy
density approaches a significant fraction of one Planck mass per cubic
Planck length. Something like that might save us from having
singularities within black holes.
Speaking of which, what exactly does it mean, when scientists say
there is a particle that transfers the power of X? How does such a
particle work?
In mysterious ways. I usually have a vague feeling of understanding
after rereading the discussion of the hydrogen molecular ion in volue
3 of the Feynman lectures, but it seldom lasts. I think one really
needs to learn quantum field theory and do the math in order to get a
real feel for this question.
I can understand that particles can collide with each other, and
this will have some effects, but I don't see where gravity would fit
in, in terms of particles effects.
One thing that is certain is that collisions between particles is not
the right mental image for understanding particle-mediated forces. The
effect is not one of individual interactions, but an interference-like
collective effect of various different ways a particle exchange
_could_ have happened at the quantum levels.
--
Henning Makholm "Den nyttige hjemmedatamat er og forbliver en myte.
Generelt kan der ikke peges på databehandlingsopgaver af
en sådan størrelsesorden og af en karaktér, som berettiger
forestillingerne om den nye hjemme- og husholdningsteknologi."
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| User: "Gerhard W. Gruber" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
23 Apr 2006 02:50:39 AM |
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On Sun, 23 Apr 2006 01:04:49 +0200 wrote Henning Makholm <henning@makholm.net>
in sci.physics with <87hd4lyzxq.fsf@kreon.lan.henning.makholm.net>
In mysterious ways. I usually have a vague feeling of understanding
after rereading the discussion of the hydrogen molecular ion in volue
3 of the Feynman lectures, but it seldom lasts. I think one really
needs to learn quantum field theory and do the math in order to get a
real feel for this question.
That's what I'm trying to do. :) I ordered the Feynmann lectures and started
to read the first volume, which is quite interesting to read, and I already
learned some details from it. :) I thought it would be better to start at the
beginning, then going right to the heavy stuff.
One thing that is certain is that collisions between particles is not
the right mental image for understanding particle-mediated forces. The
effect is not one of individual interactions, but an interference-like
collective effect of various different ways a particle exchange
_could_ have happened at the quantum levels.
Thx. I'm not so convinced of that particle idea anyway, because from what I
have read, it seems better to assume that "everything is a wave" and explain
particles in terms of waves. Fortunately I have a collegue at work (I'm a
programmer) who was before that job a scientists working on some project for
neutrino detection and he knows a lot about this, obviously. :) When I asked
him about that wave approach, he said this is basically the same idea as the
Feynmann pathintegration method.
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| User: "Henning Makholm" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
23 Apr 2006 04:13:38 AM |
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Scripsit Gerhard W. Gruber <sparhawk@gmx.at>
On Sun, 23 Apr 2006 01:04:49 +0200 wrote Henning Makholm
<henning@makholm.net>
In mysterious ways. I usually have a vague feeling of understanding
after rereading the discussion of the hydrogen molecular ion in volue
3 of the Feynman lectures, but it seldom lasts. I think one really
needs to learn quantum field theory and do the math in order to get a
real feel for this question.
That's what I'm trying to do. :) I ordered the Feynmann lectures and
started to read the first volume, which is quite interesting to
read, and I already learned some details from it. :) I thought it
would be better to start at the beginning, then going right to the
heavy stuff.
Excellent plan, I hope. I did the same thing. But beware that the
three-volume set goes nowhere near quantum _field_ theory.
Thx. I'm not so convinced of that particle idea anyway, because from what I
have read, it seems better to assume that "everything is a wave" and explain
particles in terms of waves.
Perhaps. Up to a certain point. Then along come Feynman diagrams and
purport to explain the waves in terms of particles. Except a bit later
nonpertubative field theory shows up and says that Feynman diagrams
are not telling the full story after all, except without them one
immediately hits a wall of computational intractabilty. And so forth ...
--
Henning Makholm "Jeg forstår mig på at anvende sådanne midler på
folks legemer, at jeg kan varme eller afkøle dem,
som jeg vil, og få dem til at kaste op, hvis det er det,
jeg vil, eller give afføring og meget andet af den slags."
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| User: "Gerhard W. Gruber" |
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| Title: Re: Realtivity vs. Quantumphysics on gravity |
24 Apr 2006 01:06:42 PM |
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On Sun, 23 Apr 2006 11:13:38 +0200 wrote Henning Makholm <henning@makholm.net>
in sci.physics with <87mzec8xj1.fsf@kreon.lan.henning.makholm.net>
Excellent plan, I hope. I did the same thing. But beware that the
three-volume set goes nowhere near quantum _field_ theory.
That's not really a problem. Since this book is rather old, I expect to get
other books as well, if I ever manage to work through them AND understand
them. For my current level, they should at least give me a good starting. :)
Perhaps. Up to a certain point. Then along come Feynman diagrams and
purport to explain the waves in terms of particles. Except a bit later
That's ok. After all, if I can claim that a particle can be explained in terms
of waves, then the other should also be true. After all, IMO that we talk
about particles is just a usefull analgoy, just like we can treat the sun as
dimensionless point of mass for some calculations.
Funnily enough, the conlusion that particles are just waves, I came up with
myself, after reading of particles and waves, and I tried to get to terms with
it. Now when I started to read the Feynman lectures Volum one, there is a
table which shows several different wavelengths and how we perceive them, and
above a certain wavelength it says "Particles". :) This is quite motivating,
because it means that my conclusions, even though I lack the formal training,
are not always wrong. :)
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