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Q & A: surface tension of space?

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Most recent answer: 01/05/2013
Q:
I thought that perhaps space had a measurable surface tension; like water, if so then it would emit a faint sound as it expanded or at least give off a temperature variation where it was expanding. Thank you for your answer
- EDWARD CARREON (age 54)
United States
A:
Surface tension is a positive free energy per area of the 2-D surface between two different types of material, e.g. oil and water. Our space doesn't seem to have that sort of surfaces, so surface tension itself probably isn't exactly what you're interested in. (Here I'm assuming that interesting event horizons are not relevant.)

There is an analog, however. Our 3-D space can have positive energy per unit volume, providing a sort of "volume tension". This effect goes by the name "cosmological constant". It's what drives the acceleration of the rate of expansion of space. We know very little about what causes this effect. So far as we know currently it has no entropy (and hence no temperature) associated with it and also no dynamics that would support waves. However, the rest of the universe does have temperatures and sound waves, and these are affected by the cosmological constant. In fact, one of the key measurements in determining the cosmological constant looks at how spread out background ripples in the temperature of the cosmic microwave background are. Some of the features in this distribution correspond to various sound waves in the early universe.

So there is that indirect connection between the volume tension and temperature and sound ripples.

Mike W.

(published on 01/05/2013)

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