Thread: Does gravity travel? how fast?

Does it take time for the sun's gravity to reach the earth, just like it takes light time to get here? I would assume that it would travel at the speed of light. Is it conceivably possible to measure the speed of gravity?

In the general theory of relativity, gravity propagates at the speed of light in a vacuum (300,000 km/s).

Here is the Wikipedia page on the topic. Short version: ^what he said^

Originally Posted by John Partika

In the general theory of relativity, gravity propagates at the speed of light in a vacuum (300,000 km/s).

In Quantum Theory and Newtonian physics it follows that quantized gravity could travel. Then light speed would be indicated. But General Theory portrays gravity as the curvature of space and could only travel as space expands, at the rate that space expands. Gravity would curve more rapidly (smaller radius) at speeds closer to light speed and curve less rapidly (no discernible radius) at rest. Gravity as a characteristic of space then can only move as space moves.

Newton still reigns supreme in subatomic physics and Quantum Mechanics. Relativity rules in astrophysics. Unless you specify which field that you are considering you may be comparing apples and oranges, so to speak.

To quantify gravity is to quantify space. The question then becomes is space composed of tiny packets of space or does it flow smoothly, which begs the question does space flow? We can ask the same question of time. We say time flows, but does it really. Quantum theorists wish to quantify both time and space giving them the status of a "dual nature". I think that they give themselves away when they say "acts like". An electron is always an electron whether it acts like a wave or a particle it is still an electron. The language is more confusing with light and gravity. When it acts like light it is said that it is a wave, when it acts like a particle it is called a photon or a graviton.

In objective reality there are no particles or waves. These are artifices that help us order our thoughts and advance our understanding. They work up to a point then they begin to hinder further advancement. It is too difficult to envision them as both or something different encompassing both so we switch back and forth like we think they do. Until this glitch is overcome it will be impossible to reconcile Quantum Mechanics with Relativity. Einstein may have summed this up when he said. "God would not play dice with the universe." . Although I am usually inclined to think that he meant something else, I am willing to give him the benefit of the doubt.

Heres a fun little bit of sudoscience i thought up at work.( i have a boring job) tell me what cha think.
assuming that a "graviton" is a particle that is responsible for gravity
and according to the book of Newton....

If gravity were to propagate at the speed of light that would mean that Gravitons do not decay,like photons.
This would allow someone like me to come to the conclusion that celestial body X's gravitational pull is just as strong 10 lightyears away as it is ten miles away.
clearly this is not the case, at least i dont think it is.
please, fix my logic.

Originally Posted by Joe McCarron

...
This would allow someone like me to come to the conclusion that celestial body X's gravitational pull is just as strong 10 lightyears away as it is ten miles away.
clearly this is not the case, at least i dont think it is.
please, fix my logic.

Your conclusion is incorrect. Keeping in mind that there is no quantum theory of gravitation, the strength of the gravitational force is not determined by a single graviton acting alone. The force due to the exchange of a single graviton or a single photon, for that matter, is a quantum fluctuation. The strength of the force is determined by number of photons or gravitons exchanged. A static object's gravitons and photons propagate uniformly in all directions. They diverge from their source, which drops the field strength by the square of the distance. Just to pick a number: if an object exchanges 100 photons or gravitons with a source object that is 1 lightyear away, then it will exchange only 25 gravitons or photons when the object is 2 lightyears from the source.

I read that gravity propagates at the speed of light. Experiments are hard to come by. Imagine creating a mass big enough to count (stars are pretty heavy and hard to create quickly) and having gravity detectors measuring the time it takes the signal to reach them. Who'd fund that? ... There might be some work around neutron stars in close orbits, that kind of thing, with big masses moving around, maybe yielding some measurements to confirm the idea.

It is not at all true that experiments are hard to come by. LIGO is the most famous set of gravity wave experiments. There are others. The problem is that gravity is nature's weakest force. Also and unique among nature's forces, gravity is unmitigated. This makes data analysis extremely difficult because all gravitational events have some non-zero effect on the instrumentation. This is why gravity wave experiments are usually conducted using at least two synchronized detectors that are separated by great distance.

Gravity, unlike light, has a decay factor. That being said it cannot travel at the speed of light because the speed of light is a constant. Unless of course all heavenly bodies are effected by each others gravity at some point in time. Since all objects in the universe are traveling away from the center (assuming you agree with the big bang ) then what is that effect on the decay.

Originally Posted by Dr. Ken

Gravity, unlike light, has a decay factor. That being said it cannot travel at the speed of light because the speed of light is a constant. Unless of course all heavenly bodies are effected by each others gravity at some point in time. Since all objects in the universe are traveling away from the center (assuming you agree with the big bang ) then what is that effect on the decay.

The decay factor is on intensity not on speed. Gravitational waves propagate at the speed of light. The gravitational waves are changes in the topology do to movements of mass.