Is dark energy something we have known for a long time now?

Centrifugal force is a fallacy, a fictitious force. In a centrifuge, there is no force pushing outward. What's actually happening is the contents of the centrifuge are trying to fly off at a tangent to the circular track, but the centrifuge is in the way.

No. Hardly; from 75 years (I don't think that it is a long time) as a Mathematical proposition made by Einstein. It remains a Mathematical proposition as there is no evidence of dark energy unless you take the proposition as proof itself.

Is it possible that the whole universe is rotating creating huge centrifugal force we call the dark energy? : Before you utter the word "rotate" you must spell the reference against which it rotates.

nearly everything in the universe rotates so might the whole universe as well rotate its not so unlikely is it? : [same as above; define your reference frame]

It was believed earlier that the universe has enough energy density to stop expanding and thereby re collapsing under the effect of gravity.However Hubble Space Telescope showed that the universe is still accelerating.Eventually theorists came up with an explanation that maybe there was some strange kind of energy-fluid that filled space. Maybe there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. Theorists still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.

However,we don't know for sure that the proposed conjecture is correct but however this does sit well with the current rate of expansion of the universe.

No, sorry. Though an interesting concept, that would not work as a solution.

A rotating universe would expand far more rapidly in the direction of the rotation. There would be no force causing expansion perpendicular to the rotation.

The universe appears to be expanding at the same rate in each direction that we look.

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What would the Universe be rotating relative to? Rotation by definition has to have a center of rotation, or at least an axis, and if the Big Bang theory is true, there is no such center. I'm no cosmologist, though, but I have to believe that people who get paid to think about things like this all day have probably thought about anything likely to occur to me or you.

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No, it's something that was invented when cosmologists got it in their heads that the universe was expanding at an accelerating rate. The universe isn't actually expanding at all though. The idea that it does comes from misinterpreting galactic redshifts as a doppler effect when they are actually a forward scattering effect. The galaxies are not generally receding from each other at all. Their light simply loses energy through it's interaction with the intergalactic medium... http://www.newtonphysics.on.ca/universe/

If the doppler effect was responsible for cosmological redshifts, as well as stretching out the wavelengths of light, it would also stretch out the light curves of quasars (their oscillation in luminance), but we find this is not the case: http://phys.org/news190027752.html

This documentary may enlighten you:

http://www.youtube.com/watch?v=1yTfRy0LTD0&playnex...

Dark energy may have its background as far back as when "Einstein reportedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder". But Dark Energy was only coined by Michael Turner in 1998 and the first direct evidence for dark energy came from supernova observations of accelerated expansion. This consequently resulted in the Lambda-CDM model, which as of 2006 is consistent with a series of increasingly rigorous cosmological observations, the latest being the 2005 Supernova Legacy Survey.

we don't know since we can't observe the entire universe

sorry for the boring answer

No, you need to go back to your physics books!