Is it possible for dark matter to have negative (but negligible) pressure? How small should it be to fit with observations? Dark matter pressure is actually known and measured?
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1$\begingroup$ Dark energy is already something that has negative pressure, there isn't any need for dark matter to also have negative pressure $\endgroup$– TriatticusCommented May 27, 2023 at 21:49
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$\begingroup$ The question regards if it is actually possible, having both a negarive pressure, and what would be the maximum possible pressure for dark matter for it to be consistent wirh current data. $\endgroup$– AntoniouCommented May 27, 2023 at 22:24
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$\begingroup$ Have you found any reputable references to dark matter possibly having negative pressure? If not, this seems to be an off-topic personal theory. $\endgroup$– GhosterCommented May 28, 2023 at 0:17
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1$\begingroup$ The reigning Lambda-CDM model assumes that the pressure of dark matter is zero. $\endgroup$– GhosterCommented May 28, 2023 at 0:23
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1$\begingroup$ It will be good if downvoters at least mention reasons for possible downvoting before downvoting so OP can modify the question. This is especially valid since this question has answers too. This will help build a better community. $\endgroup$– Duke WilliamCommented Jun 4, 2023 at 9:02
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2 Answers
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No, this wouldn't support our observations.
Here's the approximate breakdown of our universe's current composition:
- Dark Energy: $\sim69.1\%$
- Dark Matter: $\sim25.9\%$
- Baryonic Matter: $\sim4.9\%$
- Radiation: $\sim0.1\%$
We also know that as the universe expands,the density of each of these components changes at different rates. Specifically, dark energy's density doesn't change at all, but dark matter and Baryonic matter have their densities decreases at equal rates, and radiation has its density drop even faster (since it also gets redshifted).
With all of this information and observational data that tells us how the universe has expanded in the past, we can determine which components impart a positive pressure, which impart a negative pressure, and which impart no pressure. As significant as dark matter's contribution is even now, we would be able to tell if it had a negative pressure. Only dark energy imparts a negative pressure.
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Search for "dark matter with negative pressure" and you will find several proposals of this kind. The most sophisticated appears to be "Fluid Interpretation of Cardassian Expansion" from 2002.
answered Jun 4, 2023 at 7:10