# The Naked Scientists Forum

### Author Topic: gravity  (Read 6119 times)

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##### gravity
« on: 09/04/2005 05:20:44 »
gravity is every where and every thing has it.
i was woundering how fast does gravity move???

#### Ultima

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##### Re: gravity
« Reply #1 on: 09/04/2005 11:32:55 »
If you mean how fast the effects of the force propagate through space, then no one is 100% sure. Like if the Sun just disappeared how long would we remain in orbit...? Would it be instantaneous or would we continue around for a little while.

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html
http://www.ldolphin.org/vanFlandern/gravityspeed.html

wOw the world spins?
« Last Edit: 09/04/2005 11:33:25 by Ultima »

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##### Re: gravity
« Reply #2 on: 09/04/2005 16:30:35 »
thank u ultima!!!!!!!!

#### DoctorBeaver

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##### Re: gravity
« Reply #3 on: 11/04/2005 15:02:07 »
It must be near-instantaneaous otherwise when you dropped something it would hover in the air for a while before falling to the ground

#### realmswalker

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##### Re: gravity
« Reply #4 on: 12/04/2005 00:59:00 »
i would think it was the speed of light (it obviously cannot be faster). Also doctorbeaver, when you are holding something and let go it is actually travelling much farther than it appears. The earth is in motion and rotating, so this basically throws the ball forwards with you. However it is all relative, you dont realise its being thrown forward as well as falling down because everything else observable to you is moving with it.

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##### Re: gravity
« Reply #5 on: 13/04/2005 03:37:21 »
it could possibly be faster then light

#### realmswalker

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##### Re: gravity
« Reply #6 on: 13/04/2005 06:55:41 »
o well i guess your right...
i got confused, i was thinking of things with matter...and i guess gravity is assumed to be something with the curving of reality sooooo...please forgive my statement...

#### DoctorBeaver

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##### Re: gravity
« Reply #7 on: 13/04/2005 13:28:27 »
realmswalker - I appreciate that the Earth is in motion, as are the solar system & our galaxy: but that doesn't detract from what I said. I'm also aware that physics postulates the possibility of Gravitons. In fact, are gravitons not essential if gravity is to be combined with the electroweak force in the theory of everything?

#### gsmollin

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##### Re: gravity
« Reply #8 on: 15/04/2005 16:47:59 »
quote:

gravity is every where and every thing has it.
i was woundering how fast does gravity move???

General relativity says gravitons travel at the speed of light. However, gravitons are only produced by a gravitational quadrupole, unlike electromagnetic phenomena, which can radiate photons from a dipole. So the sun radiates light, which takes 8 minutes to reach us here on earth. The earth also orbits around the sun due to the gravitational attraction. However, the center of earth's orbit is not where we see the sun, but slightly ahead (I forget the number, but it is an easily measurable angle). It's as if the gravity traveled to us at infinite speed, but the light went only at c. This is also true for all the other planets in the solar system.

The solution to this riddle is that gravity is not a force, but space curvature. The earth is following the space curvature to make its orbit. The space is curved ahead of the earth in its orbit, no gravitons are needed. Its like a road, it is already there for you to follow.

Things are not as simple where graviton radiation is happening. A rotating binary star system, similar to a rotating barbell, would produce gravitons because that is a quadrupole. The gravitons travel at light speed from such a radiator.

#### DoctorBeaver

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##### Re: gravity
« Reply #9 on: 15/04/2005 22:22:25 »
Thanks GSMolin, that's explained it a bit better for me. Strangely enough I managed to understand most of it.Just 1 point, though. Wouldn't a rotating binary system just be 2 dipoles rather than a quadrupole? Or are they the same thing?

#### DoctorBeaver

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##### Re: gravity
« Reply #10 on: 17/04/2005 00:57:01 »
ukmickey - ANY object will bend light to a certain extent but the less massive the object, the less the bending. The Earth's gravitational field would not bend light to any significant degree.
1 of Einstein's triumphs was predicting the observed change in Mercury's position in the sky as it passed behind the sun. The sun altered the path of the light between Mercury & the Earth and it fitted as near as dammit with his predictions.
Newtonian gravity works ok until you get really massive objects such as black holes. Then even relativity breaks down when you get close enough. In fact, I believe even quantum physics breaks down when you talk about black holes

#### gsmollin

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##### Re: gravity
« Reply #11 on: 19/04/2005 20:06:05 »
quote:
Originally posted by DoctorBeaver

Thanks GSMolin, that's explained it a bit better for me. Strangely enough I managed to understand most of it.Just 1 point, though. Wouldn't a rotating binary system just be 2 dipoles rather than a quadrupole? Or are they the same thing?

You are now asking a harder question. First off, yes, a quadrupole can be two dipoles. That's certainly the case with an electromagnetic quadrupole, made up of opposing dipoles. Gravity is always more difficult however. Here's a picture of a gravitational quadrupole:
http://www.theory.caltech.edu/people/patricia/exp3a.html
Gravity can't radiate from a dipole, and I think the reason is that there is not negative mass, unlike charge which comes in two polarities.

#### DoctorBeaver

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##### Re: gravity
« Reply #12 on: 24/04/2005 14:23:54 »