A question about dark energy and the expansion/acceleration of the Universe.

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The universe is currently accelerating in its expansion, primarily due to dark energy, which exerts a "repulsive force" counteracting gravity on large scales. This acceleration has been measured using Type IA supernovae, whose brightness diminishes with redshift if the universe is accelerating. The presence of dark energy, characterized by negative pressure, is essential in explaining this acceleration. Observations confirm that the universe's expansion is not only ongoing but also increasing over time. Understanding dark energy is crucial to grasping the dynamics of the universe's expansion.
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I was curious about whether or not the Universe was accelerating or decelerating and how we could know one way or another.

I read an article I found online http://curious.astro.cornell.edu/question.php?number=63" and it said that, among other things, that the universe is accelerating partly due to dark energy and its "repulsive force of empty space that counteracts gravity on large scales." I had never heard of anything actually "repulsive" to gravity and was wondering if this was right or wrong.
 
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It is correct that the expansion of the universe is accelerating. The way this has been typically measured is to look at things, typically Type IA supernovae, which we know how bright they should be. If the universe is accelerating then they'll look less bright as a function of redshift than they would if the universe wasn't accelerating.

It can indeed be shown that a term with negative pressure, like dark energy, causes the expansion of the universe to accelerate.
 

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