h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

One idea, that is rarely discussed is 'what is the speed of Gravity' ?
Apparently, the speed of gravity is much FASTER than light.

But what does it mean to say 'the speed of gravity' ?

If you look at the sun (not a good idea in practice, you would blind
yourself!) then you see where it was 8 minutes ago. (Taking Earth as
our frame of reference.) The light has taken 8 minutes to get from
the sun to Earth. However, the gravitation pull on the Earth is not
in the same direction as the light. Apparently, the pull of gravity
from the Sun is in the direction of where the Sun is "NOW"...

Strange eh?

Or is it ??

Apparently Einstein reckons the speed of gravity to be equal to the speed of light, but an experiment is planned to find out for sure...

Yes.

Assuming, say an asteroid is falling towards the moon. Wouldn't it be traveling at the speed of gravity. If so than gravity cannot be equal to light.

Well usually I close my eyes, or at least squint when I look at the sun. Sometimes I have my shades on.
But, isnt light a waveform and gravity a force. The force can be with you much sooner than the wave. Ask a surfer.

Jigga What?

> Assuming, say an asteroid is falling towards the
> moon. Wouldn't it be traveling at the speed of
> gravity. If so than gravity cannot be equal to
> light.

No, it doesn't travel at the speed of gravity. Gravitation simply accelerates it. The gravitational field is there, and the asteroid cruises through it.

> But, isnt light a waveform and gravity a
> force.

Light consists of electromagnetic forces only.

> The force can be with you much sooner than the
> wave. Ask a surfer.

No, it can't. As long as light or gravitation haven't arrived, they can't cause action.

Gravity propagates at the speed of light in current physical model.

Got it. Until the

>Gravity propagates at the speed of light

Wouldn't that mean that gravity is traveling at the speed of light?

Yes, this is what I wanted to say!

O.k. I think I got it now.

The graviational force travels at the speed of light, but it depends on the mass of the object exerting that force, i.e. the moon, that decides the speed of the object moving towrds it. If you two large mass objects, stars, they would move towards each other much faster than two lesser mass objects. What i'm trying to say is that the force travels to the object at the speed of light, but the object travels towards the force at a speed depending on the mass of the initial object.

And what about inertia?

Gravity is just a warping of 4D space time. You can think of space-time as like a trampoline, any object dents space-time. The effect of gravity is just any object falling into this "valley". Rather than being pulled towards the sun the Earth is "rolling" around the rim of this valley. Therefore the effect of gravity is always being felt because it doesn't have to travel anywhere. Also the acceleration due to gravity depends on the mass of the object "excerting" the force

Hi researcher 247536

Welcome to h2g2,

You need to do is activate your personal space (that’s your ‘homepage’) and you can do this by using the 'edit page' button on the rhs of the page or by clicking on this shortcut >> <./>UserEdit?masthead=1</.>. Just type anything – even just hello to start off will do, and click update. Once that is done a friendly ACE, like myself will drop by your page and leave a welcome message with some tips and hints to get you started!

Mort

Let's back up here people:
Post 1: the speed of gravity is much faster than the speed of light
Post 7: gravity propagates at the speed of light
Can we make up our minds here?

224872-One of the variables of the speed of an object accelerated by gravity include the mass and not just the gravity produced thereof. Meaning that two objects with large mass will travel towards eachother at the same speed as two smaller objects that are perportional.

Researcher 247536: Please forget the image with the trampoline. I know that it's very popular, but is is equally misguiding.

b9nr515: See http://www.astronomy.net/forums/blackholes/messages/4156.shtml for a clear statement which I can only underline. You can google for more.

O.k. then, we'll go with gravity travels at the speed of light, no more no less.

Gravity does not travel at the speed of light because it does not travel at all.Gravity is the effect of the fourth dimension.

The present theory is that gravity effects time, not time gravity and I do have a tendency to agree.

> Gravity does not travel at the speed of light
> because it does not travel at all.Gravity is the
> effect of the fourth dimension.


Well, if you define it this way, there is no travelling in this universe at all. The point is this:

If, somewhere in spacetime, a new, fresh mass came into existence (the how is insignificant here), then it will have effect (=force) on another mass which is one lightyear away after one year.

Gavitational waves (disturbances of the spacetime continuum) propagates at light speed, too.