Mass is not the cause of gravity?

In summary, the equation Fg = Gm1m2/r^2 is a good approximation for predicting the effects of gravity on "normal" objects where the mass energy is the only significant non-zero component of the stress energy tensor. However, it may not accurately predict the effects of gravity in situations involving relativistic flybys, light deflection, or black holes, where other components of the stress energy tensor become important. This does not mean the equation is fundamentally flawed, but rather that it has its limitations and should not be applied in all scenarios.
  • #1
Brady Campbell
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If the effects of gravity are relative to an objects stress-energy-momentum tensor, is the equation:
Fg = Gm1m2/r^2
fundamentally flawed since it is based off the mass of the two objects? Ignoring the "gravity isn't a force" (I understand that it is what is observed due to curves in spacetime) argument if at all possible. Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?
 
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  • #2
It is accurate enough for rockets, satellites, and all sorts of other purposes. It is a good approximation for many things where the mass energy is the only significant non zero component of the stress energy tensor.
 
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  • #3
Brady Campbell said:
If the effects of gravity are relative to an objects stress-energy-momentum tensor, is the equation:
Fg = Gm1m2/r^2
fundamentally flawed since it is based off the mass of the two objects? Ignoring the "gravity isn't a force" (I understand that it is what is observed due to curves in spacetime) argument if at all possible. Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?

As others have mentioned, it's a good approxiation, but don't expect it to work for relativistic flybys and/or light deflection (where the momentum components become important), or black holes (where the pressure terms become important, even dominant).
 
  • #4
Brady Campbell said:
Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?

Neither. Take a look at http://chem.tufts.edu/AnswersInScience/RelativityofWrong.htm to see why this isn't an either/or thing where one of the alternatives is "it's just wrong".
 
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  • #5


I would like to clarify that the statement "mass is not the cause of gravity" is not entirely accurate. While it is true that gravity is not a force in the traditional sense, it is still a fundamental force of nature that is caused by the presence of mass and energy in the universe.

The equation Fg = Gm1m2/r^2, also known as Newton's law of universal gravitation, is a simplified version of the more complex equations used in general relativity to describe gravity. It is based on the assumption that mass is the only factor affecting the strength of the gravitational force between two objects.

However, the effects of gravity are not solely determined by an object's mass. As mentioned in the content, the stress-energy-momentum tensor, which takes into account an object's energy, momentum, and pressure, also plays a role in the curvature of spacetime and thus the strength of gravity.

Therefore, while the equation may accurately predict the gravitational force between "normal" objects, it is not a complete representation of how gravity works. In order to fully understand and predict the effects of gravity, we must consider the more complex equations of general relativity and take into account all factors, including mass, energy, and momentum.
 

1. What is the cause of gravity if mass is not the cause?

The cause of gravity is the curvature of space-time, which is a result of the presence of mass and energy. Mass is not the cause of gravity, but rather it is a property of matter that interacts with the curvature of space-time.

2. How do we know that mass is not the cause of gravity?

Scientists have observed that objects with different masses fall at the same rate in a vacuum, which contradicts the idea that mass is the cause of gravity. Additionally, the theory of general relativity explains gravity as a result of the curvature of space-time, rather than the presence of mass.

3. Does this mean that objects without mass (such as light) are not affected by gravity?

No, even though light does not have mass, it still follows the curvature of space-time and is affected by gravity. This is because energy, which light possesses, also contributes to the curvature of space-time.

4. Is mass completely irrelevant to gravity?

No, mass still plays a role in the strength of gravitational attraction between objects. The greater the mass of an object, the greater its influence on the curvature of space-time and the stronger its gravitational pull.

5. How does the concept of mass not causing gravity affect our understanding of the universe?

The understanding that mass is not the cause of gravity has greatly impacted our understanding of the universe. It has led to the development of the theory of general relativity, which has revolutionized our understanding of gravity and its effects on the universe.

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