The mysterious Speed of Gravity

How fast does gravity travel? When I was young I thought “instantly” while once I had some univeristy-level physics I thought: “at the speed of light” (like everything does, it seems sometimes). It’s actual speed has never yet been definitively measured by science.

If the gravity force was instant then if we were clever we could devise a machine to sense the gravity waves given off by a distant moving object, a gravitational radio. With one, we could send information faster than light (FTL), and from there its a slippery slope to full FTL travel.

I was recently startled to learn of some scientifically uncontested observations that naively suggest that gravity is instant, or near enough.

We live 8 light minutes from the Sun. So when you look up into the sky each day, the sunlight you see is 8 minutes old. And, because we move relative to the sun, its observed position slightly differes from its actual (supposed) position “right now”.

The startling thing is that when they measure the direction of the gravity coming from the sun, it’s coming from where the Sun is right now! Not where it was 8 minutes ago. Implying an instant speed for gravity. Seriously. Its been measured and there is little dispute of the observations.

Gravitational Abberation

Of course, there’s still debate on the Hows and Whys. The mystery goes under the name “Gravitational Abberation”, and it yields another puzzle: Analyses show that if the gravity did come from where the sun was 8 minutes ago, that all the solar system’s orbits would not be anything like what they are today. Their current stable configuration implies an instant speed for gravity.

Despite this, mainstream physics still seems to think gravity waves move at c. The explanation is yet to be clearly articulated, but seems to involve some miraculous cancellation caused by “velocity dependent interactions“. Another exotic concept Gravitomagnetism also seems to implicated. My takeout was that if one tried to ever make use of gravity to send a message, equal and exactly opposite forces will leak out of the walls of reality and into the equations to frustrate you.

In 1910 or 1920, the predictions of relativity (ie warping of time and space) must have seemed either crazy or impossibly abstract. Since then ,we have a hundred year to come up with analogies and mental tools to handle the stuff, so that “time warps” are now covered in in every uni level physics textbook. I suspect for Gravitational Abberation, we are waiting for a smart communicator to formulate an explanation for us masses to consume.

3 Comments

  1. Walter Hecker said,

    December 30, 2007 at 8:43 pm

    Hi Ben:

    A few years before Albert Einstein appeared on the map a Prussian school teacher by the name of Paul Gerber wondered if the part of mercury’s perihelion shift left unexplained by the influence of the other planets could be due to some finite speed of gravity. So he set out to calculate what that speed would have to be and came up with 302000 km/sec which is roughly 1% more than the speed of light.

    For details I suggest you google for “Paul Gerber” and “perihelion” or some such. Please note that Gerber’s derivation makes portions of General Relativity superfluous and is, therefore, widely attacked by proponents of GR.

    Enjoy,

    Walter

  2. Richard Alsenz said,

    February 22, 2008 at 1:58 pm

    You may want to review this site.
    http://www.mathpages.com/home/kmath451/kmath451.htm
    Measuring the Speed of Gravity

    If Gerber is right a wave would have to exist which traveled at the speed of gravity.

    hope this helps.

  3. stefjourdan said,

    January 22, 2014 at 1:15 pm

    You can switch on a light source somewhere and the light it emits will start to travel away but you cannot switch on a mass somewhere, you have to carry it there. When carrying it you will be puling its gravity field at the same time, because the existence of this mass of matter and the gravity field surrounding it are the same thing. So when the sun travels, it means the sun AND his gravity field travel. You cannot start by taking just the sun and then suppose it emits a gravity field, and then wonder at what speed its gravity field will travel…This is how I see this question.

    I don’t need this experience you’re refering to of “where does come the gravity of sun from” to know it comes from the center of where the sun IS, not from the center the sun I see (and WAS):

    If gravity was traveling at the speed of light, Newtonian trajectories would not be followed by astronomical objects because this theory is based upon the fact that objects are attracted in the direction where the center of gravity of other objects IS, not by the place where other objects were some time ago.


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