I’m trying to come up with an analogy of dark energy, the best I can do is a bath tub full of water representing the dark energy. I drop a solution of permanganate of potash (that purple crystal – dye) into the bath (this represents matter and the big bang).
Diffusion of the purple colour represents the expansion of the universe.

Unfortunately unlike diffusion where the rate of expansion slows with time, the universe’s rate of expansion increases with time. If the analogy were accurate the purple dye would diffuse slowly at first then get faster the more diffuse it became.

Are there any real world analogies that better describe dark energy?

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“Life is not measured by the number of breaths we take, but by the moments that take our breath away”

Well, there is the biblical account of how some dude wanted to keep slaughtering his enemies, so he ordered the sun to stand still and thus make the day longer...

Seriously, you can't find good analogies because there is no energy budget for Dark Energy that is consistent with our laws of thermodynamics. Although Dark Energy is a widely accepted solution proposed to solve several cosmologically scaled problems, it is a vacuous concept.

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jwj

The Reluctant Cosmologist

Not sure I understand your energy budget remark, could you expand upon that please.

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“Life is not measured by the number of breaths we take, but by the moments that take our breath away”

It is common, when looking at a proposed mechanism or feature in space to bump the numbers against a reasonable thermodynamic model: Is there enough energy in the system/mechanism to explain the behavior? Dark Energy has no known thermodynamics - no known source of energy. When Dark Energy is proposed as a cosmic solution, there is no way to count calories.

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jwj

The Reluctant Cosmologist

I see, if I understand you correctly you are saying there is no ‘conventional’ way to balance the books. Yet, the observations point to the existences of some negative pressure accelerating the expansion of the universe.

Could the current situation not be considered analogous to observing the ebb and flow of the tide realising the moon has an effect but not understanding gravitational attraction.

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“Life is not measured by the number of breaths we take, but by the moments that take our breath away”

I think you could say if the universe is a balloon, the expansion would be slow as you start blowing it up, but one you get it going it get easier to push more air in so it expands quicker. But I think what Jerry is saying if Dark energy was our air we could not say where it is coming from.

t seems to me that there really is no good analog for datrk energy. I suggest that we merely visualize dark energy as what it seems to be -- an intrinsic energy density present in space itself? In other words, simply regard each small volume of space as containing within itself a certian density of energy that is always maintaining an internal pressure that causes that volume of space to tend to expand to keep that internal pressure constant? As that volume of space containing objects such as galaxies expands, these objects are carried further apart. It seems to me that that model should be sufficient for whatever anyone wants to do in visualizing how dark energy causes space to expnd without stretching objects imbedded inside that space.