Is there something that is not affected by gravity?

[Polaris]

In other words, is there something that is not affected by the gravitational force, no matter how strong the latter is?

None that we know.

This is not surprising because our only really successful model for modeling and predicting elementary makeup of the universe - known as the standard model of particle physics - does not give a description of how gravity fit into the scheme of interaction between different constituents of the universe. As a result we don't have any theoretical foundation to say where we should even look,of we were to try to find something that is totally uneffected by gravity.

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http://science.nasa.gov/astrophysics/foc...rk-energy/

http://www.universetoday.com/84934/antig...expansion/

http://www.dailygalaxy.com/my_weblog/201...time-.html

Did you even read any of these?

Dark energy menifest itself as a negative pressure intrinsic to space. By relativity Gravity interacts with pressure just as it interacts with any energy such as mass. It is only because of this that Einstein had anything to say about "cosmological constant" and why we can say that dark energy excert its effect as "negative gravity" and propels the acceleration in the expansion of the universe.

If it weren't for the fact dark energy interacts with gravity, we would have absolutely nothing to say about it.

That's like saying a feather affects the wind and is responsible for the wind because it is showing wind exists. You are mistaking the effect for the cause.