# Gravitational acceleration VS the speed of light

• Accuser
In summary, three preconceptions were discussed in this conversation. First, it was suggested that gravity's effects propagate faster than the speed of light, but this is not the case. Second, it was noted that gravity increases proportionately to an object's mass. And third, it was mentioned that there is no functional limit to the distance over which gravity may have an effect, with the effect decreasing by the square of the distance. The conversation then moved on to a thought experiment involving two stationary objects in a universe with no matter, anti-matter, or energy. The question was posed whether these objects could reach near light speed due to the effects of gravity. It was clarified that the objects would indeed reach the same speed as the effect of
Accuser
Three preconceptions for our thought experiment:

1. Gravity's effects propagate at a rate faster than the speed of light. This is demonstrated by the fact that the Earth is not thrown out into space due to the constantly shifting position of the Sun and an 8.3 min delay of "gravity waves" pulling us toward the Sun's previous position.

2. Gravity increases proportionately to an object's mass.

3. There is no functional limit to the distance over which gravity may have an effect (the effect decreasing by the square of the distance, of course).

Imagine a Universe with physical laws identical to our own. Imagine it with no matter, anti-matter, energy, etc (excepting what I'll colloquially call "quantum turbulence"). Now imagine 2 very massive bodies which are stationary and extremely far from each other.

With only 2 bodies in this Universe, each would eventually experience the other's gravitational effects and begin to accelerate toward the other body. Assume the distance between them is sufficient that there is enough time in their transit to accelerate to near light speed. Relativity states that no body can achieve the speed of light due to the increase of mass and the slowing of local time with increased speed. However, wouldn't increased gravity exactly compensate for the increased mass of acceleration? Is there a reason that these two bodies would not achieve at least gravitational speed, given their initial position was far enough apart?

My apologies if this has been answered before, but I can't seem to find it elsewhere. Also, if you can provide an answer, I would deeply appreciate the use of layman's vocabulary ^_^

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I have removed the the URL, which violates Physics Forums rules, to which everyone agrees when they register.

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Accuser said:
Three preconceptions for our thought experiment:

1. Gravity's effects propagate at a rate faster than the speed of light. This is demonstrated by the fact that the Earth is not thrown out into space due to the constantly shifting position of the Sun and an 8.3 min delay of "gravity waves" pulling us toward the Sun's previous position.

The effects of gravity do not propagate faster than the speed of light. See

My apologies on the worthless link then. It wasn't "obviously 'crank' or 'crackpot' as I read it, but I'll chalk that up to a lack of thorough understanding of the topic.

But to get on to the question, what is it that would limit the speed of the objects?

EDIT:
To be more precise, why would they not reach the same speed as the effect of gravity?

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To be more precise, why would they not reach the same speed as the effect of gravity?
They would. That speed is the speed of light.

Ich said:
They would. That speed is the speed of light.

Fair enough, thanks for the fast and informative responses!

## 1. What is gravitational acceleration?

Gravitational acceleration is a measure of the rate at which an object falls towards the Earth's surface due to the force of gravity. It is typically denoted by the symbol "g" and has a constant value of approximately 9.8 meters per second squared near the Earth's surface.

## 2. What is the speed of light?

The speed of light is a fundamental physical constant that represents the maximum speed at which any object or information can travel in the universe. It is approximately 299,792,458 meters per second in a vacuum and is denoted by the symbol "c".

## 3. How does gravitational acceleration compare to the speed of light?

Gravitational acceleration and the speed of light are two different physical quantities that cannot be directly compared. While gravitational acceleration is a measure of an object's acceleration due to gravity, the speed of light is a measure of how fast an object can travel in the universe. However, in some cases, the effects of gravity can influence the speed of light, such as in the phenomenon of gravitational lensing.

## 4. Can anything travel faster than the speed of light?

According to the theory of relativity, it is not possible for anything to travel faster than the speed of light. The speed of light is often referred to as the "cosmic speed limit" and is a fundamental constant in the laws of physics. While there have been some theories and experiments that suggest faster-than-light travel may be possible, it has not been conclusively proven.

## 5. How does gravitational acceleration affect the speed of light in different environments?

The speed of light is affected by the presence of gravity, as seen in the phenomenon of gravitational time dilation. In environments with stronger gravitational acceleration, such as near massive objects like black holes, the speed of light appears to slow down from an outside observer's perspective. However, the actual speed of light remains constant, and it is the perception of time that changes due to the effects of gravity.

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