Science

Cosmology

by Duncan Lunan

Over these last three articles, on the Milky Way and on galaxies (Galaxies Part 1,Galaxies Part 2) in general, inevitably we’ve had to cover much of the ground normally assigned to cosmology – the study of the nature and form of the Universe.  But it’s not over yet:  we still have to look at the origin of the Universe, and the different ways in which it may end.

Expansion-of-the-universe

It has been recognised since the 1920s that the Universe is expanding:  the more distant that galaxies are from us, the more the radiation from them is ‘red-shifted’ by the Doppler effect of increasing velocity.  Also, because the speed of light is finite, the further away we look, the further back we see into time;  and the further back we go, the more tightly the galaxies are clustered in space.  So space itself is expanding;  and running that expansion backwards brings us to an origin for the entire Universe, approximately 13.8 billion years ago.  The discovery of the Cosmic Microwave Background, at just the right temperature for the residual radiation of the Big Bang, settled the main question as far back as the 1960s.  Foreground ripples in it show the beginnings of the organisation of matter into the Universe we know.  But that’s not quite the whole of the story.

Hubble Deep Field, 1995

The famous Hubble Deep Field observation, compiled in 1995, was followed by the Deep Field South in 1998, the Ultra Deep Field in 2004, and in 2012 by the Extreme Deep Field, compiled from 10 years of observations at the centre of the original Deep Field.  Six more years on, the Hubble Legacy Field recorded 265,000 galaxies in 7,500 images.  Optically and in the infrared, the current limit of observation with the Hubble Space Telescope is about 13.2 billion light-years, so we’re seeing galaxies formed ‘only’ 600 billion years after the Big Bang, and they look very different from today’s, as previously noted.  To begin with, their cores are blue, because they’re dominated by new giant stars, rather than the reds and yellows of old giants in galactic cores today.   But we can glimpse some objects further back.  Gravitational lensing, where the light of distant objects gets bent around nearer ones, can form ‘Einstein rings’, arcs and multiple images of the distant ones, allowing us to obtain spectra or even to reconstruct blurred images.  The James Webb Telescope will be able to look at those more distant objects directly, out to 13.4 billion light-years at least, with much higher resolution than the HST due to its larger mirrors.  In other wavelengths,  the Chandra orbiting x-ray telescope has imaged galaxies apparently at only 300 million years after the Bang, which is getting near to the very furthest we can see, close to the epoch of reionisation when the Universe first became transparent. 

Hubble improvements and JWST
This new Hubble image shows galaxy cluster Abell 1689. It combines both visible and infrared data from Hubble’s Advanced Camera for Surveys (ACS) with a combined exposure time of over 34 hours (image on left over 13 hours, image on right over 20 hours) to reveal this patch of sky in greater and striking detail than in previous observations. This image is peppered with glowing golden clumps, bright stars, and distant, ethereal spiral galaxies. Material from some of these galaxies is being stripped away, giving the impression that the galaxy is dripping, or bleeding, into the surrounding space. Also visible are a number of electric blue streaks, circling and arcing around the fuzzy galaxies in the centre. These streaks are the telltale signs of a cosmic phenomenon known as gravitational lensing. Abell 1689 is so massive that it bends and warps the space around it, affecting how light from objects behind the cluster travels through space. These streaks are the distorted forms of galaxies that lie behind the cluster.

When we look in opposite directions, however, problems start to arise.  Already, we can see objects so distant that no light or any other information can ever have been exchanged between them.  Yet they demonstrably obey the same physical laws – gravity and electrodynamics are the same, the processes we’re observing can be understood.  One way round that is Inflation Theory, the idea that the Universe underwent a brief, very rapid expansion after those laws had gained universal hold.  Recently it’s been suggested that some, perhaps most of the Cosmic Microwave Background came from energy released at the end of the Inflation episode, rather than from the Big Bang itself.  But attempts to pin down the details are starting to turn up worrying conflicts.  There are indications that Inflation may have had different values in different parts of the Universe, which rather defeats the object of the exercise;  there are suggestions that there may have been several inflationary episodes in the history of the Universe, some of them perhaps not universal.  Trying to pin down the Hubble Constant, which governs the overall rate of expansion, again produce discrepancies and even suggestions that different parts of the Universe may expand at different rates, or have done in the past.  Being able to see further back may resolve many of those apparent difficulties.

For a long time, the ultimate fate of the Universe was in doubt.  The rate of expansion seemed to be precisely on the dividing line between expanding forever, or collapsing due to gravitational attraction.  I was in negotiation for a time with a publisher who wanted an overview of cosmology, and one of my chapter titles was to be ‘the impossibly balanced Universe’.  I felt sure that it had to be a purely theoretical possibility, like a parabolic orbit  (possible in theory, but always an eclipse of a hyperbola in real life.)  Sure enough, the evidence began to stack up for the open Universe. 

Accelerated Expansion of the Universe

It wasn’t entirely a cheerful prospect.  As expansion continued the galaxies would continue to recede from one another, until first each Cluster, then each Group, and finally each individual galaxy would be completely isolated, with everything else beyond the Red Limit.  Meanwhile, all the stars would die, and their remains would be absorbed into black holes.  Those in turn would succumb to Hawking Radiation, eventually becoming unstable and finally exploding in bursts of gamma rays, to be added to as even the fundamental particles decayed.  Protons would be last to go, after unimaginable stretches of time, and in September 1981 Isaac Asimov wrote an article about the ultimate end which he titled, ‘After many a summer dies the proton’.  

Out of the featureless sea of radiation which would be left, in theory, quantum fluctuations could give rise to a new Big Bang and a new Universe.  It would be meaningless to ask, ‘How soon?’, because in that uniform, infinite radiation sea nothing else could ever happen.  Highly theoretical concepts such as String Theory arose to suggest how nevertheless it might happen – but then the discovery of Dark Energy changed everything.  Roughly 7.5 to 5 billion years ago, seemingly, this previously unknown expansive force gained the upper hand over gravitational attraction and the expansion of the Universe began to accelerate.  Within the previously stable lifetime of the Sun, quite possibly the Universe would end in a ‘Big Rip’ as first galactic clusters, then galaxies, then solar systems and ultimately all matter would be torn apart.  

Big Bang to Big Rip

However, a news article in the February 2009 issue of Astronomy Now, ‘Dark Energy Makes its Presence Felt’, describes how the Chandra X-ray orbiting observatory had studied galaxies in the Abell 85 cluster and produced a much more precise value for the extent to which dark energy affects the cosmological constant governing the expansion of the Universe.  Apparently Dark Energy has just the right value to push the galactic clusters apart, ultimately becoming invisible to one another at the Red Limit where they’re receding at the speed of light, but isn’t powerful enough to disrupt the clusters themselves.  Other researchers have since confirmed the finding in other areas of space.   (Nancy Atkinson, ‘Astronomers Closing in on Dark Energy with Refined Hubble Constant’, Universe Today, May 7th, 2009).

Dark energy red expansion

It’s been known for a long time that the values of the fundamental constants of nature are ‘just right’ for the evolution of sunlike stars, earthlike planets and life.   It leads to the Anthropic Argument, that the Universe is as it is so that we and perhaps other forms of intelligence can come to understand it.   (See Alan Longstaff, ‘Why Is the Universe the Way It is?’ on pp. 30-34 of the same issue.)   Strong forms of the argument are used to back up the case for Intelligent Design, and no doubt the new values for dark energy will be marshalled to strengthen the case;  but they give the argument a new twist.

At the end of Profiles of the Future  (Gollancz, 1962), the late Sir Arthur C. Clarke wrote, “Our galaxy is now in the brief springtime of its life – a springtime made glorious by such brilliant blue-white stars as Vega and Sirius, and, on a more humble scale, our own Sun.   Not until all these have flamed through their incandescent youth, in a few fleeting billions of years, will the real history of the universe begin.

“It will be a history illuminated only the reds and infra-reds of dully glowing stars that would be almost invisible to our eyes;  yet the sombre hues of that all-but-invisible universe may be full of colour and beauty to whatever strange beings have adapted to it.  They will know that before them lie, not the millions of years in which we measure the eras of geology, nor the billions of years which span the lifetimes of the stars, but years to be counted literally in trillions.

“They will have time enough in those endless aeons, to attempt all things, and to gather all knowledge.  They will not be like gods, because no gods imagined by our minds have ever possessed the powers they will command.   But for all that, they may envy us, basking in the bright afterglow of Creation;  for we knew the Universe when it was young.”

I was saddened when I heard of the possible ‘Big Rip’, because it could have occurred within the lifetime of the Sun and long before that ‘real history’ took shape.  But now that it seems it may come to pass, the apparent ‘fine tuning’ of dark energy means that the Anthropic Argument may not apply to our kind of life at all, but to those ‘strange beings’ which we might not even recognise as living.  We would be just a brief accident on the way to them.  To quote David Lindsay’s Voyage to Arcturus, it may be that ‘the music was not playing for you, my friend’.

I tried to get a comment on that in March 2009, when I had dinner with Brother Guy Consolmagno of the Vatican Observatory, just after the Space Shuttle had docked with the International Space Station  (the staff of Glasgow’s Panjea restaurant joined us outside to see them go over).  All he would say was that he didn’t accept the Anthropic Argument in the first place – an interesting reply in itself.

In a further complication, Prof. Roger Penrose and his colleagues believe they have identified concentric ripples in the microwave background of the Universe, the remnant radiation of the Big Bang, which reveal that our Universe was born out of the collapse of a previous one.  In the 1960s the idea that the Universe oscillated, from Big Bang to collapse, to be reborn from a ‘Cosmic Egg’ or ‘Primeval Atom’, was a major contender in cosmology along with the Steady State theory and the Big Bang itself.   (Ernst J. Öpik, The Oscillating Universe, Mentor, 1960.)   My own ‘Interface’ stories, published in Galaxy and If in the early 1970s and reprinted in my collections From the Moon to the Stars  (2019)  and The Other Side of the Interface  (2021), were set within a larger framework of an oscillating universe.  In Poul Anderson’s novel Tau Zero  (1970), an interstellar ramscoop with its drive jammed on comes so close to the speed of light that due to time dilation, the occupants see the Universe collapse around them, slingshot around the Primeval Atom and emerge into a new Universe where they can match velocities with a newborn galaxy. I was politely disbelieving until I read Prof. John Wheeler’s paper ‘Our Universe:  the Known and the Unknown’  (American Scientist, Vol. 56 No. 1, pp. 1-20, Spring 1968)  in which he argues that information and even matter could bypass the moment of collapse – a bit like the theory of flight in The Hitch-Hiker’s Guide, where ‘you throw yourself at the Earth and miss’.  Even so, being able to see the Primeval Atom as you pass it in a different reality is pretty major poetic license.    

Poul Anderson Tau Zero, 1970

In the 1970s, the first discovery of a pulsar which was slowing down too slowly for the rate to be measured, led to the suggestion that it might be older than our Universe and have ‘fallen through’ from a previous one.  By 1982, however, other observations of pulsars with very slow decay rates had let it be calculated that a rate too small to be measured indicated an age of ‘only’ 100,000-plus years.  (New Scientist, 2nd December 1982, p.562.)  Opponents of Big Bang theory tell me that there are galaxies older than the apparent age of the Universe, and if true, that could support both Wheeler and Penrose.  But if so, it would imply either that the evidence from dark energy for an indefinite future is wrong, or that after an unknown number of prior Universes, ours is the first in which the dark energy constant is high enough to prevent a future collapse.

In the words of W.E. Geil, an American missionary who walked the length of the Great Wall of China at the end of the 19th century, “after such inscriptions, all others seem tame”.  Yet amazingly enough, Wheeler’s vision and Poul Anderson’s open up still more possibilities.

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