Gravity-like Force: Is Another Force Weaker Than Gravity?

[accdd]

Is it true that if there was another force similar to gravity (dependent on the stress-energy tensor) then it would have to be weaker than gravity? If so, why?

 

[anuttarasammyak]

Because we have not observed such a force which should supplement gravity.

 

[Nugatory]

If so, why?

We have not observed any such thing,so if it exists it must be weaker than what we are able to observe, and we do observe gravitational effects.
(There are also some good theoretical reasons to be skeptical of the possibility).

 

[Vanadium 50]

If it couples to the stress-energy tensor just as gravity does, how could you ever tell?