Category Archives: energy science

More on white dwarfs and existentialism

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Image by Sarah

Image by Sarah

When I was writing about cosmic heat death a couple of weeks ago [see ‘Will it all be over soon?’ posted on November 2nd, 2016], I implied that our sun would expire on a shorter timescale of about 4 to 5 billion years but without mentioning what we expect to happen.  The gravitational field associated with every piece of matter is proportional to the mass of the piece of matter and inversely proportional to distance from its centre.  The size of the sun implies it should collapse under its own gravitational forces, except that the fusion of hydrogen in its core causes an outwards heat transfer, which prevents this from happening. The sun remains a sphere of hot gases with diameter of about 864,000 miles by ‘burning’ hydrogen.  When the hydrogen runs out, the gravitational field will take over and the sun is expected to collapse to a 30,000 mile diameter ball of atoms and free electrons, or a white dwarf.

These are all spontaneous processes and so the total entropy must increase although there are some local reductions.  The heat dissipated following the fusion of two hydrogen nuclei generates more entropy in the surroundings than the local reduction caused by the fusion.  The collapse to white dwarf would appear to represent a substantial reduction of entropy of the sun because the atomic particles are crushed together. However, this is countered by the release of photons to the surroundings which ensures that the entropy of the surroundings increases sufficiently to satisfy the second law of thermodynamics.

Source:

Isaac Asimov, The roving mind: a panoramic view of fringe science, technology, and the society of the future, London: Oxford University Press, 1987.

An extract is available in John Carey (editor), The Faber Book of Science, London: Faber & Faber, 2005.

Will it all be over soon?

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milkywayNASAAs you may have gathered from last week’s post [Man, the Rubbish-Maker on October 26th, 2016], I have been reading Italo Calvino’s Complete Cosmicomics.  In one story, ‘World Memory’ the director of a project to document the entire world memory in the ‘expectation of the imminent disappearance of life on Earth’ is explaining to his successor that ‘we have all been aware for some time that the Sun is halfway through its lifespan: however well things went, in four or five billion years everything would be over’.  The latter is one of the scientific conclusions around which Calvino weaves these short stories and this one put into perspective the concerns expressed by some of my students on both my undergraduate course and MOOC in thermodynamics the prospect of a cosmic heat death resulting from the inevitable consequences of the second law of thermodynamics [see my post ‘Cosmic Heat Death‘ on February 18th, 2015].  The second law requires ‘entropy of the universe to increase in all spontaneous processes’.   Entropy was defined by Rudolf Clausius about 160 years ago as the heat dissipated in a process divided by the temperature of the process.  The dissipated heat flows into random motion of molecules from which it is never recovered.  So, as William Thomson observed, this must eventually create a universe of uniform temperature – an equilibrium state corresponding to maximum entropy where nothing happens and life cannot exist.   Entropy has been increasing since the Big Bang about 13.5 billion years ago.  And as Calvino writes, the sun is about halfway through its life – it is expected to collapse into a white dwarf in 4 to 5 billion years when its supply of hydrogen runs out.  These are enormous timescales: the first human cultures appeared about 70,000 years ago [see my post ‘And then we discovered thermodynamics‘ on February 3rd, 2016]  and history would suggest that our civilization will disappear long before the sun expires or cosmic heat death occurs.  A more immediate existential threat is that our local production of entropy on Earth destroys the delicate balance of conditions that allows us to thrive on Earth.  See my post on Free Riders on April 6th, 2016 for thoughts on avoiding this threat.

Sources:

Italo Calvino, The Complete Cosmicomics, London: Penguin Books, 2002.

 

Revisiting closed systems in nature

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milkywayNASA

It is the beginning of the academic year and once again I am teaching introductory thermodynamics to engineering undergraduate students and my MOOC entitled ‘Energy: Thermodynamics in Everyday Life‘ is running in parallel.  Last week after my lecture on thermodynamic systems, a student approached me to ask whether the universe is a closed and isolated system.  It’s an interesting question and the answer is depends on the definition of universe.   In thermodynamics, we usually define a boundary to delineate the system of interest as everything inside the boundary and everything else are the surroundings.  The system and surroundings taken together are the universe (see my post ‘No beginning or end‘ on February 24th, 2016).  If the universe is defined as the system then there are no surroundings; hence the system cannot exchange energy or matter with anything which is the definition of a closed and isolated system.

Physicists often refer to the observable universe, or define the universe as everything we can observe.  We are aware that we cannot observe everything.  Hence, it is reasonable to suppose that the observable universe exchanges energy and matter with the unobservable space beyond it, in which case the observable universe is an open system.  We could also consider the concept that we are part of multiverse and our universe is only one of many, in which case it seems likely that is not isolated, i.e. it can exchange energy, and perhaps it is open, i.e. it can exchange both energy and matter with other parts of the multiverse.

This is not really thermodynamics in everyday life.  However, the occurrence of closed systems in nature appears to interest a lot of people to judge from the visits to my previous posts on this topic.  See ‘Closed Systems in Nature?‘ on  December 12th, 2012; Is Earth a closed system? Does it matter? on December 10th, 2014; and ‘No Closed Systems in Nature‘ on August 12th, 2015. For more about system boundaries, see my post entitled ‘Drawing Boundaries‘ on December 19th, 2012.

More uncertainty about matter and energy

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woodlandvalley

When I wrote about wave-particle duality and an electron possessing the characteristics of both matter and energy [see my post entitled ‘Electron uncertainty’ on July 27th, 2016], I dodged the issue of what are matter and energy.  As an engineer, I think of matter as being the solids, liquids and gases that are both manufactured and occur in nature.  We should probably add plasmas to this list, as they are created in an increasing number of engineering processes, including power generation using nuclear fission.  But maybe plasmas should be classified as energy, since they are clouds of unbounded charged particles, often electrons.   Matter is constructed from atoms and atoms from sub-atomic particles, such as electrons that can behave as particles or waves of energy.  So clearly, the boundary between matter and energy is blurred or fuzzy.  And, Einstein’s famous equation describes how energy and matter can be equated, i.e. energy is equal to mass times the speed of light squared.

Engineers tend to define energy as the capacity to do work, which is fine for manufactured or generated energy, but is inadequate when thinking about the energy of sub-atomic particles, which probably is why Feynman said we don’t really know what energy is.  Most of us think about energy as the stuff that comes down an electricity cable or that we get from eating a banana.  However, Evelyn Pielou points out in her book, The Nature of Energy, that energy in nature surrounds us all of the time, not just in the atmosphere or water flowing in rivers and oceans but locked into the structure of plants and rocks.

Matter and energy are human constructs and nature does not do rigid classifications, so perhaps we should think about a plant as a highly-organised localised zone of high density energy [see my post entitled ‘Fields of flowers‘ on July 8th, 2015].  We will always be uncertain about some things and as our ability to probe the world around us improves we will find that we are no longer certain about things we thought we understood.  For instance, research has shown that Bucky balls, which are spherical fullerene molecules containing sixty carbon atoms with a mass of 720 atomic mass units, and so seem to be quite substantial bits of matter, exhibit wave-particle duality in certain conditions.

We need to learn to accept uncertainty and appreciate the opportunities it presents to us rather than seek unattainable certainty.

Note: an atomic mass unit is also known as a Dalton and is equivalent to 1.66×10-27kg

Sources:

Pielou EC, The Energy of Nature, Chicago: The University of Chicago Press, 2001.

Arndt M, Nairz O, Vos-Andreae J, Keller C, van der Zouw G & Zeilinger A, Wave-particle duality of C60 molecules, Nature 401, 680-682 (14 October 1999).