October 6, 2009 weblog

# Cosmic entropy could be 100 times greater than previously thought

(PhysOrg.com) -- A new analysis of supermassive black holes has discovered the entropy of the universe is much greater than previously thought, which means it may also be very slightly closer to ultimate heat death.

The study, analyzing measurements of the supermassive black hole mass function, was carried out by two Australian cosmologists: Chas A. Egan from the Australian National University in Canberra, and Charles H. Lineweaver from the University of NSW in Sydney. Their results indicated the entropy at the current cosmic event horizon is much greater than the entropy of the interior of the universe, and the total cosmic entropy is about 100 times greater than previous calculations.

Entropy increases as the number of ways the system can be arranged microscopically without changing the external appearance increases. Egan used the example of hot water being poured into a cold bath. Before the hot and cold water meet they are separate and orderly and the system has low entropy. When the hot and cold water are well mixed, the entropy is high and no heat flow between the two is possible.

Egan and Lineweaver found the collective entropy of the supermassive black holes was around 100 times higher than expected. Since these black holes contribute more to the entropy in the universe than anything else, the results imply that the entire cosmic entropy is also a 100 times greater than earlier estimates.

Previous calculations of the cosmic entropy assumed the presence of a 10 million solar-mass black hole at the center of each galaxy, and the entropy was calculated using an estimated average mass. Egan and Lineweaver had access to more recent data that gave them the range of supermassive black hole masses rather than an average. Egan said the study revealed a smaller number of larger supermassive black holes contribute much more to the entropy than previously believed.

The universe has much lower entropy than is theoretically possible, and this is still true, even with the new calculations. This is just as well because the entropy of the universe must be below the maximum theoretical value or life and other complex phenomena will cease to exist. As the entropy gradually increases it will eventually approach the theoretical maximum, a state many physicists have called the heat death of the universe. The new calculation takes the universe a little closer, but it is still only a billionth of a billionth of the maximum.

Not every scientist agrees that the higher entropy takes the universe closer to heat death. Ned Wright of the University of California in Los Angeles, for example, suggests the entropy is locked inside the supermassive black holes, and so the rest of the universe has lower entropy and is therefore further away from heat death.

__More information:__ The paper was published online at arXiv.org.

via Sciencenews.org

*© 2009 PhysOrg.com*

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**Citation**: Cosmic entropy could be 100 times greater than previously thought (2009, October 6) retrieved 16 September 2019 from https://phys.org/news/2009-10-cosmic-entropy-greater-previously-thought.html

## User comments

MorganWAlexaphyspuppykasenSo what's the external appearance of the universe? For thermodynamics to be applied to a system, doesn't it need to be limited? What are the limits of the universe, then?

lomedAdditionally, what is being discussed in the article is the entropy within the cosmic horizon, i.e. the entropy within the volume of space from which light has been able to reach us.

AlexakasenSo that would be the limit of the system, as we treat it. But what about the light that couldn't, or hasn't reached us?

I know it's not practical to ask such questions, but the thing is, cosmology isn't really much of a practical science. I think there are too many assumptions and approximations based on practicality and technological limitations.

Since there are currently few, if any, applications for this field, the focus should be on being as unequivocal as possible.

ProfessorRichbrentrobotHow can you possibly "measure" that?

Or are they saying that the black holes are larger than expected?

How can a black hole have entropy unless something is falling into it, or evaporating out of it? Isn't a black hole literally frozen in time? This article is very confusing.

jsa09This area is a great deal smaller than the "known" size of the universe depending on the complete interpretation of that phrase.

The expanding universe has much of what we have observed (i.e. distant galaxies) being now forever outside the volume of space where any light from those sources produced today could ever reach us.

Let us not forget that current measurements have the universe expanding at many times the speed of light.

So the entropy measured would be the either the entropy in our current region which includes heat from the distant past or it is the entropy from the measured "known" universe which is younger the further away the light was when it started.

It is just that are we calculating the entropy as it is now everywhere or as we measure it from sources that may have originated at or near the birth of the universe, and would therefore have barely started towards entropy.

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