“Heat death” of the cosmos

Submitted by AWL on 30 October, 2019 - 9:18 Author: Misha Zubrowski
carina nebula

Paul Vernadsky (Solidarity 520) wrote a valuable article on Marx and the environment, and a review of a book on the same topic. I want to pick up on one point.

“Similarly, Engels is sometimes accused of rejecting the second law of thermodynamics in the course of an argument with scientists over the heat death hypothesis. William Thomson (later Lord Kelvin) had supported the latter claim to justify the role of God in the universe. Engels rejected the role of a deity on materialist grounds, while accepting that entropy was a feature of the universe. Latter day scientists agree with Engels: energy dissipation continues but the universe expands at a faster rate, meaning the universe is getting further away from thermal equilibrium.” (emphasis added)

Not so.

The heat death hypothesis is a theory about the ultimate fate – or one possible fate — of the universe. On this theory, the universe will asymptotically evolve to a state of thermal equilibrium; entropy reaches a maximum, so entropy-increasing processes are ceased; there is no thermodynamic free energy.

Suppose I have a bath, with a divider: X molecules of scalding hot liquid on one side, and another X molecules of the same liquid, but cold, on the other; 2X altogether. I then remove the divider.

At this point, the liquid not in thermal equilibrium: one half is at a considerably higher temperature than the other. As a result, thermal energy — heat — is flowing from the hotter to the colder side; through conduction, through mixing and convection, and to some extent through radiation. Through this process it is moving closer towards all the fluid being the same tepid temperature, towards thermal equilibration.

Entropy can be taken as an expression of the number of different microscopic configurations that are consistent with a given macroscopic configuration.

Compare a single macroscopic configuration of liquid at the beginning, half-hot, half-cold; to a macroscopic configuration of the liquid when it has become constant temperature. In the first situation there are a lower number of possible microscopic configurations. Any of the (approximately) X molecules with an amount of kinetic energy which means it is very hot could be (approximately) anywhere within one half of the bath; and conversely for the other (approximately) X molecules.

At the end, when constant temperature, any of the 2X molecules could be anywhere within the bath; a higher number of possible microscopic configurations.

At this point no net thermal energy flows. The system has reached maximum entropy, and this liquid is in thermal equilibrium.

Suppose this bath-liquid system was isolated, was the whole universe. It would, at this tepid end state, have undergone “heat death” (it need not be cooled down to the temperature “absolute zero”). Entropy never decreases. An isolated uniformly tepid bath never separates into a bath of two halves, regressing to our lower-entropy beginning state. So this liquid universe, after this “heat death”, remains unchanged. Nothing interesting ever occurs.

If you leave most human-scale closed systems for a long enough time you expect them to reach thermal equilibrium. On the scale of the universe, however, gravity, and the universe’s expansion complicate matters a lot – to name just two factors.

Gravitational bound systems do not tend towards simple thermal equilibrium. Unlike our liquid universe, something like our solar system, where gravity is a major factor, doesn’t tend towards being evenly distributed. It naturally “clumps” into the sun and planets, which orbit the sun. This cuts against thermal equilibrium.

However, the expansion of the universe cuts in the opposite direction. How exactly the universe will evolve in that respect is dependent on features currently unknown: its curvature (open, flat, or closed), and the exact proportion of “dark energy”. Dark energy can fuel the expansion — indeed accelerated expansion — of the universe. Current evidence suggests that our universe is accelerating in its expansion, and will continue to, rather than slowing down and re-collapsing to a “Big Crunch”.

If this is indeed the case, a “heat death” may be expected to occur as the universe is spread more and more thinly, and energy continues to dissipate.

The expansion of the universe is bringing it towards thermal equilibrium faster than it would otherwise — not the reverse. Expansion leads to cooling. It also means that matter and energy being radiated – in the end, probably, the evaporation of black holes via Hawking radiation – will interact again at a lower rate.

With this, comes less of the interesting stuff – stars and the like – which make up our current universe, and which cut against thermal equilibration.

It is true that a different ultimate fate, currently on the table, is a “Big Rip”. In this scenario, the universe will still progress towards thermal equilibrium. However, the universe’s expansion at some point will tear apart even space-time itself.

There are other mechanisms and factors, such as spontaneous quantum fluctuations creating “zero-point energy”, which complicate the picture further.

Nonetheless, heat death of some form is still on the table.

Much of this, of course, couldn’t be known at the time of Engels. He died before the big bang and the universe’s expansion were theorised, let alone its acceleration, most of modern cosmology, or quantum physics.
In a non-expanding universe of his day, the heat death hypothesis held a lot less water.

Engel’s scepticism is certainly not a reason for suggesting — as some critics have, through selective misreading — that Engels didn’t believe in entropy, or that his science is not valid.

In many ways, the heat deaths discussed in Engels’ time and today are actually different propositions. Indeed, it could reasonably be argued that the term “heat death” oversimplifies and obscures the details more than it clarifies.

One interpretation, likely the best, and certainly the most favourable, is that Engels’ was arguing less against the heat death hypothesis and more against theological concerns which were justifying or prompting this hypothesis.

These theological concerns were for a “first cause” of the universe, an external impetus — by god — and a “final cause”, “telos”, or “purpose”, which the universe is inexorably progressing towards. A heat death fitted these concerns. Engels was, of course, right to reject these theological impetuses or justifications for scientific conclusions. Nowadays, thankfully, a materialist approach to natural science is ubiquitous.

Foster (2008) argues that Engels aimed for a dialectic approach to natural philosophy, akin to that of the ancient “Greek philosophers [for whom] the world was essentially something that had emerged from chaos, something that had developed, that had come into being.” (Engels) Engels contrasted this to his contemporary Newtonian mechanism which “everywhere... sought and found its ultimate cause in an impulse from outside [God] that was not to be explained from nature itself.”

Some fringe contemporary Marxists, influenced by Ted Grant and Alan Woods, take what they understand as a dialectical approach too far, and reject the big bang. I doubt Engels would have been that dogmatic, or that stupid.

Unlike Engels’ general approach, they see calling into question of this scientific near-consensus akin to challenging “the modern equivalent of the old religious dogma of the creation of the world from nothing.”

As Foster (2008) notes, when considering entropy:

“Marx and Engels kept abreast of the natural–scientific literature and did not dispute the conclusions of natural — scientific research where there was an actual scientific consensus — although they did raise questions about what appeared to be incomplete, inconclusive, partial, and contradictory results.”

This perspective is even more vital today. Scientific understanding and research has been undergoing a continuous exponential explosion since Engels’ time and before. With the field of cosmology maturing, the depth and breadth of an individual needs to become familiar with before they can engage critically and usefully with the cutting edge on these questions is probably greater.

The big bang theory does not preclude discussion of what caused the big bang, and indeed theories have been postulated. It certainly does not attempt to shoe-horn in religious concerns, acts by god, into the beginning or end of our universe.

I would not suggest that the big bang theory is infallible. Likely, in the not too distant future, most of our contemporary cosmology, and physics more broadly, will be considered false. The big bang theory may be replaced, or subsumed within more comprehensive models. And details of it are and should certainly be questioned, such as the models used for the first fraction of a nanosecond after the big bang itself.

Natural science is constantly evolving. We should engage with it and critically engage with it. Sometimes it does, or should, mean rethinking, renewing, remaking our world-view or our approach to natural philosophy; rather than the other way around.

Add new comment

This website uses cookies, you can find out more and set your preferences here.
By continuing to use this website, you agree to our Privacy Policy and Terms & Conditions.