Is gravity faster than the speed of light?

Question

Consider the Earth orbits the Sun by constantly being attracted to it, yet it takes light from the Sun 8 minutes to get to Earth.

Consider also that if a galaxy is 100,000 light years across it would take 100,000 years for light to get across it. Now consider that gravity is holding the galaxy together therefore making me conclude that gravity is instantaneously holding the galaxy together across the entire 100,000 light years of distance.

So is gravity faster than the speed of light?

Answer 1

no, the first person is wrong. Gravity's effect is instantaneous, light has a speed limit. Sorry first dude, but you ARE wrong.

Answer 2

No, gravity has been proven to work at exactly the speed of light as well.

The Sun is eight light minutes from Earth. If the Sun were to somehow vanish, the Earth would continue to orbit the spot where the Sun was for eight more minutes. The light and the gravity from the Sun would appear to vanish at the same time from our viewpoint.

Your assumption that the galaxy is being held instantaneously has no basis in fact.

EDIT: From 'The Fabric of the Cosmos', by Brian Greene:

"Since general relativity specifies the detailed mechanism by which gravity works, it provides a mathematical framework for determining how fast it transmits its influence. The speed of transmission comes down to the question of how fast the shape of space can change in time. That is, how quickly can warps and ripples - ripples like those on the surface of a pond caused by a plunging pebble - race from place to place through space? Einstein was able to work this out, and the answer he came to was enormously gratifying. He found  that warps and ripples - gravity, that is - do not travel from place to place instantaneously, as they do in Newtonian calculations of gravity. Instead they travel at exactly the speed of light. Not a bit faster or slower, fully in keeping with the speed limit set by special relativity. If aliens plucked the moon from its orbit, the tides would recede a second and a half later, at the exact same moment we'd see the moon had vanished. Where Newton's theory failed, Einstein's general relativity prevailed." (pgs. 71-72)

That should be the end of it.

Answer 3

gravity travels at the speed of light, and is not instantaneous.

Answer 4

There are good reasons to believe that gravity moves at exactly the speed of light.  It's very hard to measure the speed of gravity because it's such a weak force.  However, measurements have been made, and the speed comes out to very close, and well within experimental error of the speed of light in a vacuum.

Let's go closer to home.  It takes light 8 minutes or so to get from the Sun to the Earth.  In that time, the Earth has moved.  So if gravity moves at that speed, then the Earth should feel the force from the Sun not where it is, but where it was 8 minutes ago.  So you'd expect a drag force, and over the life of the Earth it should noticeably fall into the Sun.  That clearly hasn't happened.  What's the deal?

What's happened is that mass creates a field everywhere.  Think of the field as the shape of a rubber sheet where a heavy ball is in the center.  The shape is smooth, and no matter where you are on it, it points towards the center. The Earth feels this field, and the direction of force is exactly towards the Sun.

So it's only if you change the gravity suddenly - like you have a pair of neutron stars orbiting each other very closely, or a supernova explosion, that gravity changes quickly, and you get gravity waves that move out at the speed of light.

Answer 5

gravity, it is name "THE BINDING FORCES", but remember this, THE BINDING FORCES HAD ALOT OF BINDING STAGES, and each stages bind differences particles, well iam not telling more about this, 'cause they would steal information from me then said that they discover by themself. THESE PEOPLE NOW A DAY ARE SO BADLY.

Answer 6

Gravity is more powerful than light.

Once a "Black Hole" developes, the gravity is so powerful that not even light can escape from the planet.This is why black holes cannot be seen even with the most powerful telescopes. Their position can only be established by studying the effect of their gravitational pull.

Answer 7

Gravity is an instantaneous force, so it has no velocity.

Answer 8

could b who really knows?

Answer 9

This question is not as simple as it appears. Gravity is an interaction between mass and space, not directly between mass and other mass. When the mass distribution in space changes, the gravitational effects of those changes propagate through space at the speed of light.

To understand why there's a difference in how a physical system would behave, between the case in which gravity were an interaction between mass and other mass (which is false) and the case in which gravity were an interaction between mass and space (which is true), consider a planet in a heliocentric circular orbit of radius r.

If gravity were an interaction between the sun and the planet, then the planet would respond to the gravitons from the sun as they arrived. However, the planet is moving in a direction perpendicular to the sun at a speed

v = sqrt(GM/r)

and the time required for the gravitons to travel from the sun to the planet is

dt = r/c

In time dt, the planet moves a distance

dr = v dt

Which means that gravitons arriving at the planet were emitted by the sun from an apparent position that leads the true position by an angle,

Q = Arctan (dr / r)

Which is as much as saying...

Q = Arctan ( v / c )

Or, to put it back together,

Q = Arctan { sqrt[ GM / ( r c^2) ] }

And, after combining the constants,

Q = Arctan { sqrt[ 1476.625 meters / r ] }

The above expression assumes that M is the mass of the sun.

If r = 1 au = 1.49597870691E+11 meters, then Q = 20.5 arcsec.

In other words, we see the sun 20.5" ahead of where it really is because of Earth's orbital motion. If gravity were constantly tugging us toward a position ahead of where the sun really is, there would be a torque on our planet's orbit that, eventually, would toss us out of the solar system, not to mention the fact that it would violate the conservation of energy.

So, necessarily, gravity is an interaction between mass and space. Mass establishes changes in the space around it, and other mass responds to those changes. That indirect relationship is reciprocal, of course.

Answer 10

The only particle that is currently know to travel faster than the speed of light is the tachyon!

Answer 11

Gravity is a tricky one, and I'm not sure we have a full understanding of what it is and how it works.

It's the commonly accepted idea's of gravity that have led us into more bizarre beliefs, the existence of dark matter for instance.

So until we know exactly what were dealing with your question is unanswerable.

Answer 12

Uh oh!  It looks like I have to step in! :P

In experiments that have been conducted (see the link), gravity has been found to propagate many times faster than the speed of light, but its very difficult to determine the exact speed.

Unfortunately, your analogy of the galaxy being "instantaneously" held together isn't valid.  Think of gravity not as some sort of a force or a particle which moves from one spot to another and affects something.  Gravity affects space itself, bending it, and that causes objects to 'fall' into this gravity well.

Imagine a trampoline.  In the middle of the trampoline put a 10 pound bowling ball.  Now roll some marbles around the trampoline.  The trampoline bends and stretches in order to hold the bowling ball and it makes a 'well'.  Now, when the marbles roll around, they seem to be attracted to the bowling ball.

In this way, it doesn't particularly matter how long the gravity takes to move across the galaxy, because the moving objects are all moving slowly enough that the gravity of all of the billions of stars sort of balances out to make a gravity disk the size of the galaxy.  The movement of a single star doesn't have the power to make a big difference on the orbit of another star in the galaxy, gravity is far too weak for that.  But the combined gravitational force of ALL of the stars is enough to keep them all orbiting the center of the galaxy.

Answer 13

The equations of general relativity treat gravity as if it were propagated instantaneously, but Einstein insisted that gravity is a warping of 4D space and not a force that propagates at any speed.

If gravity were to propagate at the speed of light, then Earth would be pulled toward the direction where the sun was eight minutes ago. That would result in dragging the Earth into a higher and higher orbit. There would be no planetary systems in the universe.

It has been calculated that gravity cannot propagate at any speed less than 20 billion times the speed of light without flinging planets away from their stars. That means gravity is at least as much faster than light as light is faster than a snail.  

Answer 14

Both light and gravity propagate at the speed of light.

Answer 15

our sun has a greater mass as compared to planets of our solar system so it  has a influence over solar system by means of its gravitational force of attraction derived from its immense mass .

so we can conclude that greater the mass of a body greater will be its gra.....al force of atr.......on.

but contrary to that light from a a bulb of 1 watt  & 1000 watt travel with  the same speed.



it is hypothicated that [ and probably all of us are well versed with this age old information , {unfortunately there is no update in this regard since long} ] even light rays are unable to escape the gravitational pull of BLACK HOLES.

what i mean to say more massive a BLACK HOLE is greater will be its force of attraction.May be there is certain limit for a BLACKHOLE to accumulate a certain mass.AND THAT IS EXACTLY WILL BE THE MAXIMUM HYPOTHICATED SPEED OF GRAVITATIONAL FORCE OF ATTRACTION.

so i think it is this optimum gravitational  force of attraction which causes even massless light rays to deviate from there path.

so definitely the force which causes this action travels faster than light.

Answer 16

consider a boat speeding at a velocity greater than that of the water it is moving on,

the water body it is on is 10000m in length and the boat take 50sec to get through the course...

now take a light beam as the boat,travelling in a gravitational field of field particles with velocities less than it,the field is 100 000 light years across,that is,light takes 100 000 light years to get through it...

dont u see that the distance the light is travelling does not matter,neither does the time the light takes to get through it,but what maters is the comparison of the 2 speeds....

HOPE U ARE ANSWERED...

Answer 17

same speed as the speed of light... (186,000 miles a second)

Answer 18

Gravity does not have speed. It can slow the speed of light down to zero, so it is stronger than the speed of light in a sense. To speak of the speed of gravity, we must find a graviton, which we have not. Though we do predict it. Until then the question is unanswerable.

Answer 19

What you leave out of your equation for gravity is "time."  Everything (the laws) in the universe as we currently understand it occurred at the moment after the big-bang.  Gravity was likely the first of the 4, maybe 5, forces of nature to break symmetry. When it did break away from the first unified force, it very likely fell under the universal speed limit of light at that time.  The other 3 forces broke symmetry later and then fell under the speed limit of light. Thus, perhaps the 4 forces when they were one unified force did behave at speeds beyond that of light, but certainly not awards.

So, as the universe expand and cooled, the laws of nature were already established; thus, the speed limit of light and of gravity, every where, in the universe were the same.  Now, it doesn't make any difference how far apart two bodies are in the universe, the speed limit was already established everywhere from the beginning.

Just my thoughts on the matter.