| Topic: |
Science > Physics |
| User: |
"Tom Lopata" |
| Date: |
03 Jul 2004 01:18:04 AM |
| Object: |
Speed of gravity? |
Scientists who are trying to determine the speed of gravity equate it
to being the same as the speed of light according to Einstein's theory
of relativity. Does that necessarily mean that gravity has to be
measured in miles or kilometers? Gravity isn't an accelerated photon
such as light therefore can it be measured in the same manner? I know
the moon and the sun have a direct impact on the ocean tides, if it
were a total eclipse, then would the tides go down canceling out the
gravitational pull of the sun. If not, then is the only way of
measuring gravity constant to the earth's gravity?
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Speed of gravity? |
04 Jul 2004 07:47:16 AM |
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Tom Gravity is never blocked. If the sun should just vanish it would
take the Earth 8 minutes to get the message. Bert
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| User: "Tom Lopata" |
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| Title: Re: Speed of gravity? |
06 Jul 2004 11:41:13 PM |
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(G=EMC^2 Glazier) wrote in message news:<24439-40E7FC54-534@storefull-3171.bay.webtv.net>...
Tom Gravity is never blocked. If the sun should just vanish it would
take the Earth 8 minutes to get the message. Bert
Thanks for responding to my questions about gravity. I apologize if
my terminology is off a bit because this is out of my reach (HS
junior)... Anyways, light (correct me if I'm wrong) is matter and can
be weighed etc. How does gravity (being invisible) travel?
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| User: "Bill Linares" |
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| Title: Re: Speed of gravity? |
07 Jul 2004 08:04:12 AM |
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junior)... Anyways, light (correct me if I'm wrong) is matter and can
be weighed etc. How does gravity (being invisible) travel?
Gravity being invisible has nothing to do with it. If explanations on
subjects such as light and gravity seem difficult to grasp, it is because we
do not have analogous models in our everyday experience.
Gravity can be descrived as a field. If you put mass within this field it is
affected by the field in very definite ways. It is the extension of the
field that travels.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Speed of gravity? |
07 Jul 2004 07:44:10 AM |
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Hi Tom Gravity going with QM is a massless particle called a graviton.
Gravitons like photons have waves. Sad part is we have yet to detect a
gravity wave. Light is not considered to be matter,and yet high energy
photons(gamma) can kick electrons around. 6 trillion photons
can sit on the tip of a pin. The sun loses 10 million tons of
mass each second,and it is from emitting photons. Still the photon is
massless. Go figure Bert
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| User: "greywolf42" |
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| Title: Re: Speed of gravity? |
03 Jul 2004 02:25:45 PM |
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Tom Lopata <tom1l21@aol.com> wrote in message
news:5c47ab7d.0407022218.1f1d03b0@posting.google.com...
Scientists who are trying to determine the speed of gravity equate it
to being the same as the speed of light according to Einstein's theory
of relativity.
Not quite. Einstein did assume that the speed of gravity equals the speed
of light (in his 1916 development of General Relativity). However, when
working the equations for GR in actual orbital dynamic calculations, one
uses instantaneous transmission (infinite speed) equations. You'll find
most people (on this newsgroup) agree that gravity moves at the speed of
light *in GR*. However simple a question this may be, you'll find the
answers are quite complex.
And the fact that Einstein assumed that gravity moved at the speed of light
does not necessarily mean that gravity actually does this in the real
universe.
Does that necessarily mean that gravity has to be
measured in miles or kilometers?
No. The units used for the speed of light are irrelvant. Speed is units of
distance per unit of time. It doesn't matter whether you have 186,000 miles
per second, 3.0E8 meters per second, or 1 light speed unit. It's all the
same speed -- even if the numbers used are different.
Gravity isn't an accelerated photon
such as light therefore can it be measured in the same manner?
You are correct, in that gravity cannot be measured in the same manner as
light. The main problem is that gravity is a very weak force (relative to
electromagnetism). Therefore, we can't easily set up laboratory experiments
to measure the speed of gravity. So we make do with astronomical
observations. This can be a problem, because we have to invoke dynamic
theories of astronomical motion in order to 'measure' the effect of a given
speed of gravity. And if we set up the problem wrong, or ignore a competing
effect (which is easy to do with such a weak force), then we get the wrong
answer.
I know
the moon and the sun have a direct impact on the ocean tides, if it
were a total eclipse, then would the tides go down canceling out the
gravitational pull of the sun.
Actually, this does not happen. The tides are a massive, dynamic system.
The Sun and the Moon both contine 'pulling' on the ocean tides, even if the
Sun is behind the Moon.
If not, then is the only way of
measuring gravity constant to the earth's gravity?
There are two basic methods of measuring the speed of gravity -- from
secondary effects.
ORBITAL STABILITY ARGUMENT:
The oldest one is the 'orbital stability' calculation. This method is based
upon the effect of gravitational aberration. When two bodies orbit each
other, the force of gravity reaching one body will not point directly to the
other body *when the force reaches the first body*. The force vector will
point to a position just a little bit to one side. This non-central force
will tend to increase the orbital radius of the second body. Hence, the
system is deemed 'unstable.' The degree of offset is proportional to the
speed of gravity. Hence, the slower the speed of gravity, the more unstable
the system. One then uses an estimate of the amount of time a body (such as
the Earth) is known to have been in orbit. One then back calculates a
minimum speed of gravity, based on keeping the Earth in orbit. For a
gravity speed equal to light speed, this comes to a factor of about 1
billion years to double the orbital size. (You'll often see a quote of
1,000 orbits to double the orbital size, but this value results from
improper application of the aberration formula for masses of equal size --
which the Sun and the Earth aren't.)
Even more venerable (older) than aberration is the 'drag' argument. This
version is applied only when the theory in use is an aether theory. In this
case, gravity results from the absorption of gravitational 'corpuscles'.
Hence, any body moving through the 'aether' will experience a drag, due to
the impact of these corpuscles. The amount of impact can be determined to
be a function of the average speed of the corpuscles -- which is also the
speed of gravity. As it turns out the 'drag' force is inversely
proportional to the speed of the corpuscles/gravity. Using the same
argument as above (from aberration), one can infer a lower bound to the
speed of gravity.
The problem arises in that your 'measured' speed of gravity is dependent
upon the fundamental theory that you are using to make the estimate. Hence,
you will have a different 'measured' speed of gravity for every theory that
you are evaluating.
ARGUMENT FROM NON-NEWTONIAN ADVANCE OF ORBITAL NODES:
In an orbital system, the 'nodes' of an orbit -- such as the perihelion of
Mercury -- will shift slightly in response to any nonspherical matter
distribution in the system. The most famous of these is the Non-Newtonian
Perihelion Advance (NNPA) of Mercury. A purely newtonian orbital force
(effectively infinite speed) will result in an orbit that does not shift
over time. (In the real solar system, all orbits shift as a result of
gravitational forces from other planets, as well.) But there is another
effect that results directly from a finite speed of gravity. The perihelion
shifts a little bit, in a value that is proportional to the speed of
gravity. (This is most famously attributed to Einstein, but was first
performed by a fellow named Paul Gerber, 17 years earlier.) Gerber used the
reported NNPA of Mercury (43 arcseconds per Earth century) to calculate a
speed of gravity equal to the speed of light. Einstein assumed that the
speed of gravity was equal to the speed of light, and calculated the NNPA of
Mercury.
Hence the NNPA method is more reliable inidicator of the speed of gravity.
Because drag and stability questions do not affect the result.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
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| User: "Nicolaas Vroom" |
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| Title: Re: Speed of gravity? |
04 Jul 2004 10:03:23 AM |
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"greywolf42" <mingstb@marssim-ss.com> schreef in bericht
news:10ee3i6kl0a2qd0@corp.supernews.com...
ORBITAL STABILITY ARGUMENT:
The oldest one is the 'orbital stability' calculation. This method is
based
upon the effect of gravitational aberration. When two bodies orbit each
other, the force of gravity reaching one body will not point directly to
the
other body *when the force reaches the first body*. The force vector will
point to a position just a little bit to one side. This non-central force
will tend to increase the orbital radius of the second body. Hence, the
system is deemed 'unstable.' The degree of offset is proportional to the
speed of gravity. Hence, the slower the speed of gravity, the more
unstable
the system. One then uses an estimate of the amount of time a body (such
as
the Earth) is known to have been in orbit. One then back calculates a
minimum speed of gravity, based on keeping the Earth in orbit. For a
gravity speed equal to light speed, this comes to a factor of about 1
billion years to double the orbital size.
Let us be more practical.
Suppose that the average distance Earth Sun increases with 1 km every
year are we able to detect that ?
I do not know over what period the Earth Sun distance is known, but is there
any information available between for Example 200 Years ago and Now ?
And what about the last 50 years ?
Is there any information available based on actual observations that
Earth Sun distance is actual increasing?
IMO to do any calculation based on the last 1 billion years is very tricky
because we know that for example the orbits of the outer planets are
not 100% stable just because of infalling asteroids (i.e. they wander).
and comets.
We have recently observed that by means of the planet Jupiter.
That means to do any sort of "speed of gravity" calculation over such
long periods is pure guess work.
In the book "Pierre Simon Laplace 1749-1827 A Life in exact Science"
By Charles Coulston Gillispie In chapter 4 Universal Gravitation
this same subject is discussed.
At page 30 is written:
3. The force of gravity is propagated instantaneously.
At page 34 there is an equation (13) for r, which changes as a function
of t. The velocity is difined as: Theta divided by alpha times T
There is written:
"Laplace turned to the observations and particularly to the lunar tables,
knowing that ancient and modern records of eclipses showed that the
earth's satellite has been increasing its mean speed of revolution"
At page 34 is written: Laplace found that the velocity of gravitational
corpuscule is 7680000 times as great as the velocity of light.
That means that Laplace made his calculation based on lunar
observations and not on Earth/Sun based observations.
It will be interesting to know what the current opinion is of the
methodes used by Laplace.
Are we currently better equiped to validate equation 13 ?
Nicolaas Vroom
http://users.pandora.be/nicvroom/
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| User: "greywolf42" |
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| Title: Re: Speed of gravity? |
04 Jul 2004 10:52:24 AM |
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Nicolaas Vroom <nicolaas.vroom@pandora.be> wrote in message
news:%_UFc.174351$dO3.8639599@phobos.telenet-ops.be...
"greywolf42" <mingstb@marssim-ss.com> schreef in bericht
news:10ee3i6kl0a2qd0@corp.supernews.com...
ORBITAL STABILITY ARGUMENT:
The oldest one is the 'orbital stability' calculation. This method is
based upon the effect of gravitational aberration. When two bodies
orbit each other, the force of gravity reaching one body will not
point directly to the other body *when the force reaches the first
body*. The force vector will point to a position just a little bit to
one side. This non-central force will tend to increase the orbital
radius of the second body. Hence, the system is deemed 'unstable.'
The degree of offset is proportional to the speed of gravity.
Hence, the slower the speed of gravity, the more unstable
the system. One then uses an estimate of the amount of time a body
(such as the Earth) is known to have been in orbit. One then back
calculates a minimum speed of gravity, based on keeping the
Earth in orbit. For a gravity speed equal to light speed, this comes
to a factor of about 1 billion years to double the orbital size.
Let us be more practical.
Suppose that the average distance Earth Sun increases with 1 km every
year are we able to detect that ?
I'm not sure. But how is this more practical? Astronomical dynamics is a
'wobbly' business over short time frames.
I do not know over what period the Earth Sun distance is known, but is
there any information available between for Example 200 Years ago
and Now ? And what about the last 50 years ?
Is there any information available based on actual observations that
Earth Sun distance is actual increasing?
Take a look at J.D. Anderson et al., Acta Astronautica 5 (1978) 43, for a
good reality check. The solar system is a
messy place.
IMO to do any calculation based on the last 1 billion years is very tricky
because we know that for example the orbits of the outer planets are
not 100% stable just because of infalling asteroids (i.e. they wander).
and comets.
Of course it's tricky. That's one of the reasons that I listed as
preferring the NNPA method (which you snipped) over the older 'instability'
argument.
We have recently observed that by means of the planet Jupiter.
That means to do any sort of "speed of gravity" calculation over such
long periods is pure guess work.
Pretty close. But that's what standard academia uses.
In the book "Pierre Simon Laplace 1749-1827 A Life in exact Science"
By Charles Coulston Gillispie In chapter 4 Universal Gravitation
this same subject is discussed.
At page 30 is written:
3. The force of gravity is propagated instantaneously.
At page 34 there is an equation (13) for r, which changes as a function
of t. The velocity is difined as: Theta divided by alpha times T
There is written:
"Laplace turned to the observations and particularly to the lunar tables,
knowing that ancient and modern records of eclipses showed that the
earth's satellite has been increasing its mean speed of revolution"
At page 34 is written: Laplace found that the velocity of gravitational
corpuscule is 7680000 times as great as the velocity of light.
That means that Laplace made his calculation based on lunar
observations and not on Earth/Sun based observations.
True. My apologies for simplifying the story.
It will be interesting to know what the current opinion is of the
methodes used by Laplace.
Are we currently better equiped to validate equation 13 ?
No, we are not. The drawbacks to the 'stability' argument are fundamental.
Not technological.
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
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| User: "Uncle Al" |
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| Title: Re: Speed of gravity? |
03 Jul 2004 09:45:05 AM |
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Tom Lopata wrote:
Scientists who are trying to determine the speed of gravity equate it
to being the same as the speed of light according to Einstein's theory
of relativity.
Idiot alert.
Does that necessarily mean that gravity has to be
measured in miles or kilometers? Gravity isn't an accelerated photon
such as light therefore can it be measured in the same manner?
Idiot alert confirmed.
I know
the moon and the sun have a direct impact on the ocean tides, if it
were a total eclipse, then would the tides go down canceling out the
gravitational pull of the sun. If not, then is the only way of
measuring gravity constant to the earth's gravity?
Drooling idiot needs chin wiped - with a guillotine.
http://arXiv.org/abs/gr-qc/0212121
Sergei Kopeikin
http://arXiv.org/abs/astro-ph/0301145
Clifford Will
http://arXiv.org/abs/astro-ph/0302294
Kopeikin's results
http://arXiv.org/abs/astro-ph/0302462
Kopeikin's analysis of results
http://arxiv.org/abs/astro-ph/0303346
Faber's dissent re parameterized post-Newtonian (PPN) model
http://arxiv.org/abs/astro-ph/0304006
Stuart Samuel's invalid analysis of Kopeikin
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
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| User: "Sam Wormley" |
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| Title: Re: Speed of gravity? |
07 Jul 2004 01:11:43 PM |
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Tom Lopata wrote:
Scientists who are trying to determine the speed of gravity equate it
to being the same as the speed of light according to Einstein's theory
of relativity. Does that necessarily mean that gravity has to be
measured in miles or kilometers? Gravity isn't an accelerated photon
such as light therefore can it be measured in the same manner? I know
the moon and the sun have a direct impact on the ocean tides, if it
were a total eclipse, then would the tides go down canceling out the
gravitational pull of the sun. If not, then is the only way of
measuring gravity constant to the earth's gravity?
Tom some basic background information about gravity.
Ref: Hartle, "Gravity: An Introduction to Einstein's General Relativity", Addison
Wesley (2003)
"A few properties of the gravitational interaction that help explain when
gravity is important can already be seen from the gravitational force law
F_grav = G m_1 m_2 / r_12^2
o Gravity is a universal interaction in Newtonian theory between all mass, and,
since E = mc^2, in relativistic gravity between all forms of energy.
o Gravity is unscreened. There are no negative gravitational charges to cancel
positive ones, and therefore it is not possible to shield (screen) the gravitational
interaction. Gravity is always attractive.
o Gravity is a long-range interaction. The Newtonian force law ia a 1/r^2
interaction. There is no length scale that sets a range for gravitational
interactions as there is for the strong and weak interactions.
o Gravity is the weakest of the four fundamental interactions acting between
individual elementary particles at accessible energy scales. The ratio of
the gravitational attraction to the electromagnetic repulsion between two
protons separated by a distance r is
F_grav G m_p^2 / r^2 G m_p^2
-------- = -------------------- = ------------- ~ 10^-36
F_elec e^2 / (4 pi e_0 r^2) (e^2/4pi e_0)
where m_p is the mass of the proton and e is its charge.
These four facts explain a great deal about the role gravity plays in physical
phenomena. They explain, for example, why, although it is the weakest force,
gravity governs the organization of the universe on the largest distance
scales of astrophysics and cosmology. These distance scales are far beyond
the subatomic ranges of the strong and the weak interactions. Electromagnetic
interactions COULD be long range were there any large-scale objects with net
electric charge. But the universe is electrically neutral, and electromagnetic
forces are so much stronger than gravitational forces that any large-scale net
charge is quickly neutralized. Gravity is left to govern the structure of the
universe on the largest scales.
Background:
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
http://scienceworld.wolfram.com/physics/Gravity.html
http://scienceworld.wolfram.com/biography/Newton.html
The theory of general relativity describes the phenomenon of gravity very differently:
http://scienceworld.wolfram.com/physics/GeneralRelativity.html
Crank Information
http://www.crank.net/usenet.html
http://users.pandora.be/vdmoortel/dirk/Physics/ImmortalFumbles.html
http://edu-observatory.org/cranks.html
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| User: "MorituriMax" |
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| Title: Re: Speed of gravity? |
03 Jul 2004 02:01:19 AM |
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Tom Lopata wrote:
Scientists who are trying to determine the speed of gravity equate it
to being the same as the speed of light according to Einstein's theory
of relativity. Does that necessarily mean that gravity has to be
measured in miles or kilometers? Gravity isn't an accelerated photon
such as light therefore can it be measured in the same manner? I know
Accelerated photon? Are you on drugs?
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