All posts tagged white dwarf

The Last Three Minutes by Paul Davies (1994)

The telescope is also a timescope. (p.127)

Davies (b.1946) is an English physicist, writer and broadcaster. He’s written some 25 books, and hosted radio and TV series popularising science, especially in the areas of cosmology and particle physics, with a particular interest in the links between modern scientific theory and religion – hence his books God and the New Physics and The Mind of God.

The Last Three Minutes was his sixteenth book and part of the Science Masters series, short, clear primers written by experts across all areas of science. The advantage of The Last Three Minutes is that it is a clear explication of all the theories in this area; the drawback is that it is now precisely 25 years out of date, a long time in a fast-moving field like cosmology.

On the plus side, although the book might not capture the very latest discoveries and thinking, many of its basic facts remain unchanged, and many of those facts are enough to make the layman gawp in wonder before Davies even begins describing the wild and diverse cosmological theories.

1. Doomsday

The nearest star, Proxima Centauri, is 4.24 light years – twenty-four trillion years – away. Our galaxy is named the Milky Way. Until the 1920s astronomers thought all the stars in the universe were in the Milky Way. The observations of Edwin Hubble proved that the Milky Way is only one among billions of galaxies in the universe. The Milky Way is estimated to be somewhere around 200 light-years across. It might contain anything between 100 and 400 billion stars.

Our solar system is located about 26,000 light-years from the Galactic Centre on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The Milky Way is rotating. The sun and its retinue of planets take about 200 million years to rotate around the Galactic Centre.

The Earth could be destroyed by impact with any of the following:

  • asteroids, which are usually confined to a belt between Mars and Jupiter, but can be toppled out by passage of Jupiter’s mass
  • comets, believed to originate in an invisible cloud about a light year from the sun
  • giant clouds of gas won’t affect us directly but might affect the heat flow from the sun, with disastrous consequences
  • the Death Star some astronomers believe our sun may be part of a double-star system, with a remote twin star which may never be visible from Earth, but perturb elements in the system, such as our own orbit, or asteroids or comets

2. The Dying Universe

In 1856 the German physicist Hermann von Helmholtz proposed that the universe is dying because the heat in it will eventually become so evenly distributed that no heat passes from one area to another, no chemical reactions are possible, the universe reaches ‘thermodynamic equilibrium’ and is dead. In English this became known as the ‘heat death’ theory. In 1865 physicist Rudolf Clausius coined the term ‘entropy’ meaning ‘the unavailability of a system’s thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system’. The heat death idea became widely accepted.

Davies points out that it’s odd that so many brainy people didn’t draw the obvious conclusion from the heat death idea, for if a) the universe is winding down towards a heat death and b) it has existed forever, then c) it would have died already. The fact that the universe is still full of wildly uneven distributions of energy and heat shows that it must have had a beginning.

Moreover, calculation of the mass of the universe should have indicated that a static universe would collapse in upon itself, clumps of matter slowly attracting each other, becoming larger and heavier, until all the matter in the universe is in one enormous ball.

The fact that the universe still has huge variations in heat indicates that it has not been around forever, i.e. it had a beginning. And the fact that it hasn’t collapsed suggests that a force equal or greater to gravity is working to drive the matter apart.

He explains Heisenberg’s Uncertainty Principle according to which ‘quantum particles do not possess sharply defined values for all their attributes’, and one of the odder consequences of  this, which is the existence of ‘quantum vacuums’ which are in fact full of incredibly short-lived ‘virtual’ particles popping in and out of existence.

3. The First Three Minutes

Davies recapitulates the familiar story that Edwin Hubble in the 1920s detected the red-shift in light which indicated that distant galaxies are moving away from us, and the further way they are, the faster they’re moving – overthrowing millenia of dogma by showing that the universe is moving, dynamic, changing.

Presumably, if it is moving outwards and expanding, it once had an origin. In 1965 astronomers detected the uniform background radiation which clinched the theory that there had, at some point in the distant past, been an explosion of inconceivable violence and intensity. The so-called cosmic microwave background (MCB) radiation is the remnant.

Further observation showed that it is uniform in every direction – isotropic – as theory predicts. But how did the universe get so lumpy? Astrophysicists speculated this must be because in initial conditions the explosion was not in fact uniform, but contained minute differentials.

This speculation was confirmed in 1992 when the Cosmic Background Explorer satellite detected ripples or unevenness in the MCB.

Complicated calculations predicted the likely ratios of key elements in the universe and these, also have been proved to be correct.

Taken together the expansion of the universe, the cosmic background radiation, and the relative abundance of the chemical elements strongly support the theory of a big bang.

Davies then explains modern theories of ‘inflation’ i.e. that the bang didn’t lead to a steady (if fast) rate of expansion of the early universe but, within milliseconds, experienced a short inconceivable process of ‘inflation’, in which anti-gravity pushed the exploding singularity into hyper-expansion.

The theory of inflation is called for because it solves problems about the existence and relative abundance of certain sub-atomic particles (magnetic monopoles), and also helps explain the unevenness of the resultant universe.

4. Stardoom

In February 1987 Canadian scientists based at an observatory in Chile noticed a supernova. This chapter explains how stars work (the fusion of hydrogen into helium releasing enormous amounts of energy) but that this outwards radiation of energy is always fighting off the force of gravity created by its dense core and that, sooner or later, all stars die, becoming supernovas, red dwarfs, red giants, white dwarfs, and so on, with colourful descriptions of each process.

Our sun is about half way through its expected life of 10 billion years. No need to panic yet.

He explains gravitational-wave emission.

5. Nightfall

Beginning with the commonplace observation that, eventually, every star in every galaxy will die, this chapter then goes on to describe some abstruse aspects of black holes, how they’re made, and unexpected and freakish aspects of their condition as stars which have collapsed under the weight of their own gravity.

John Wheeler coined the term ‘black hole’.

6. Weighing the Universe

If we all accept that the universe began in a cataclysmic Big Bang, the question is: Will it carry on expanding forever? Or will the gravity exerted by its mass eventually counteract the explosive force, slow the expansion to a halt, and then cause the universe to slowly but surely contract, retreating back towards a Big Crunch

Davies tells us more about neutrinos (one hundred billion billion of which are penetrating your body every second), as well as Weakly Interacting Massive Particles, or WIMPs.

The basic problem is that all the suns and other objects in the observable universe get nowhere near the mass required to explain the relatively slow expansion of the universe. There must be a huge amount of matter which we can’t see: either because it is sub-atomic, or hidden in black holes, or for some other reason.

Hence the talk over the last thirty years of more of the search for ‘dark matter’ which astrophysicists estimate must outweigh the visible matter in the universe by anything from ten to one to a hundred to one. Anyway,

Given our present state of knowledge, we cannot say whether the universe will expand forever or not. (p.79)

7. Forever Is A Long Time

Consideration of the nature of infinity turns into a description of the Hawking effect, Stephen Hawking’s theory that black holes might not trap everything, but might in fact emit a low level of radiation due to the presence of virtual vacuums in which quantum particles pop into existence in pairs on the event horizon of the hole, one particle getting sucked inside and producing a little flash of energy, the other escaping, and using that burst of energy to convert from being a temporary virtual particle into a real, lasting one.

This is one aspect of the likely fate of black holes which is to collapse evermore on themselves until they expire in a burst of radiation. Maybe.

He moves on to consider the periodicity of proton decay, the experiment set up in a tank of water deep underground in Cleveland Ohio which failed to measure a single proton decay. Why?

If protons do decay after an immense duration, the consequences for the far future of the universe are profound. All matter would be unstable, and would eventually disappear. (p.96)

He paints a picture of the universe in an inconceivably distant future, vast beyond imagining and full of ‘an inconceivably dilute soup of photons, neutrinos, and a dwindling number of electrons and positrons, all slowly moving farther and farther apart’ (p.98).

8. Life In the Slow Lane

Davies undermines his credibility by speculating on the chances of humanity’s survival in a universe winding down. Maybe we can colonise the galaxy one star system at a time. If we can build spaceships which travel at only 1% the speed of light, it would only take a few centuries to travel to the nearest star. The ships could be self-contained mini-worlds. Or people could be put into hibernation. Better still a few engineers would take along hundreds of thousands of fertilised embryos to be grown on arrival. Or we could genetically engineer ourselves to survive different atmospheres and gravities. Or we could create entities which are half organic matter, half silicon-based intelligence.

He writes as if his book needs to address what he takes to be a widespread fear or anxiety that mankind will eventually – eventually – go extinct. Doesn’t bother me.

Davies describes the work done by some physicists (Don Page and Randall McKee) to calculate the rate at which the black holes which are predicted to become steadily more common – this is tens of billions of years in the future – a) decay and b) coalesce. It is predicted that black holes might fall into each other. Since they give off a certain amount of Hawking radiation, the bigger the black hole, the cooler at the surface and the more Hawking radiation it will give off and, Davies assures us, some technologically advanced descendant of humanity may, tens of billions of years in the future, just may be able to tap this radiation as an energy source to keep on surviving and thinking.

Apparently John Barrow and Frank Tipler have speculated on how we could send nuclear warheads to perturbate the orbits of asteroids, sending them to detonate in the sun, which would fractionally alter its course. Given enough it could be steered towards other stars. In time new constellations of stars – maybe entire galaxies – could be manipulated in order to suit our purposes, to create new effects of gravity or heat which we could use.

Meanwhile, back in reality, we can’t even leave the EU let alone the solar system.

9. Life In the Fast Lane

The preceding discussions have been based on the notion of infinite expansion of a universe which degenerates to complete heat death. But what if it reaches an utmost expansion and… starts to contract. In, say, a hundred billion years’ time.

There follows a vivid science fiction-ish account of the at-first slowly contracting universe, which then shrinks faster and faster as the temperature of the background radiation relentlessly rises until it is hundreds of degrees Kelvin, stripping away planetary atmospheres, cooking all life forms, galaxies crushing into each other, black holes coalescing, the sky turning red, then yellow, then fierce white. Smaller and hotter till is it millions of degrees Kelvin and the nuclei of atoms fry and explode into a plasma of sub-atomic particles.

Davies speculates that an advanced superbeing may have created communications networks the breadth of the universe which allow for an extraordinary amount of information processing. If it is true that the subjective experience of time is related to the amount of information we process, then a superbeing which process an almost infinite amount of information, would slow down subjective time. In fact it might cheat death altogether by processing so much information / thought, that it slows time down almost to a standstill, and lives on in the creation of vast virtual universes.

10. Sudden Death – and rebirth

If the preceding chapter seems full of absurdly fanciful speculation, recall that Davies is being paid to work through all possible versions of the Last Three Minutes. The book is sub-titled conjectures about the ultimate fate of the universe.

So far he has described:

  1. eternal expansion and the cooling of the universe into a soup of sub-atomic particles: in which case there is no last three minutes
  2. the preceding chapter discusses what a Big Crunch would be like, the physical processes which would degrade the universe and he has clearly taken as part of his brief trying to speculate about how any sentient life forms would cope

In this chapter he discusses a genuinely unnerving scenario proposed by physicists Sidney Coleman and Frank de Luccia in 1980. Davies has already explained what a virtual vacuum is, a vacuum seething with quantum particles popping in and out of existence. We know therefore that there are different levels of ‘vacuum’, and we know that all thermodynamic systems seek the lowest sustainable level of energy.

What if our entire universe is in an artificially raised, false vacuum? What if a lower, truer form of genuinely empty vacuum spontaneously erupts somewhere and then spreads like a plague at the speed of light across the universe? It would create a bow wave in which matter would be stripped down to sub-atomic particles i.e. everything would be destroyed, and a new value of gravity which would crunch everything together instantaneously. The Big Crunch would come instantaneously with no warning.

Astronomer Royal Martin Rees spooked the cosmology community by pointing out that the experiments in sub-atomic particles currently being carried out by physicists might trigger just such a cataclysm.

Conversely, Japanese physicists in 1981 floated the possibility of creating a new universe by creating a small bubble of false vacuum. The prediction was that the bubble of false vacuum would expand very quickly but – here’s the bit that’s hard to visualise – without affecting our universe. Alan Guth, the man who developed the inflation theory of the early universe, worked on it with colleagues and predicted that, although an entirely new universe might appear and hugely expand in milliseconds, it would do so into a new space, creating a new universe, and have little or no impact on our one.

Maybe that’s how our universe began, as a baby budding off from an existing universe. Maybe there is an endless proliferation of universes going on all the time, everywhere. Maybe they can be created. Maybe our universe was created by intelligent beings in its parent universe, and deliberately endowed with the laws of chemistry and physics which encourage the development of intelligent life. Or maybe there is a Darwinian process at work, and each baby universe carries the best traits of its parents onwards and upwards.

For me, the flaw of all this type of thinking is that it all starts from the axiom that human intelligence is somehow paramount, exceptional, correct, privileged and of immense transcendent importance.

In my opinion it isn’t. Human beings and human intelligence are obviously an accident which came into being to deal with certain conditions and will pass away when conditions change. Humanity is a transient accident, made up of billions of transient entities.

11. Worlds Without End?

A trot through alternative versions of The End. As early as the 1930s, Richard Tolman speculated that after each big crunch the universe is born again in another big bang, creating a sequence or rebirths. Unfortunately, a number of factors militate against complete regularity; the contraction period would create unique problems to do with the conversion of mass into radiation which would mean the starting point of the next singularity would be different – more degraded, less energy – than the one before.

In 1983 the Russian physicist Andre Linde speculated that the quantum state of the early universe might have varied from region to region, and so different regions might have experienced Alan Guth’s hyper-inflationary growth at different rates.

There might be millions of bubble universes all expanding at different rates, maybe with different fundamental qualities. A kind of bubble bath of multiple universes. We find ourselves in one of them but way off, beyond the limit of our vision, there may be an infinity of alternatives.

There is no end to the manufacture of these baby universe, and maybe no beginning.

Lastly, Davies re-examines the ‘steady state’ version of the universe propounded by Hermann Bondi and and Thomas Gold in the 1950s. They conceded the universe is expanding but said it always has. They invented ‘the creation field’ which produced a steady stream of new matter to ensure the expanding universe was always filled with the same amount of matter, and therefore gravity, to keep it stable. Their theory is another way of dispensing of an ‘end’ of the universe, as of a ‘beginning’, but it suffers from logical problems and, for most cosmologists, was disproved by the discovery of the microwave background radiation in 1965.

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by Simon on April 9, 2019  •  Permalink
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Posted by Simon on April 9, 2019

https://astrofella.wordpress.com/2019/04/09/the-last-three-minutes-paul-davies/