by Paul Davies
The mysterious Cold Spot of Eridanus is just one feature in a collection of anomalies in the CMB that has left cosmologists scratching their heads. There is evidence that the overall power of the afterglow is lopsided between the hemispheres. Even stranger is that this asymmetry seems to align with the plane of the solar system, a finding so bizarre and heretical it has been dubbed the Axis of Evil. It’s almost as if the entire universe is being squeezed by a giant vice. What is going on? Is something outside the visible universe assaulting it? Could the cold spot be a sort of giant porthole into ‘pre-creation’, a cosmic epoch that preceded the big bang, very different from the cosmos we know? Might there be other portholes providing glimpses of this veiled ante-world? Windows into the wider multiverse? Or will all the puzzling anomalies turn out to be just statistical flukes? Watch this space . . .
Although the cosmic cataclysms outlined here are the stuff of nightmares, content yourself with the fact that the universe has endured for many billions of years without mishap so far. Of all the things to worry about, the possibility that our universe might be eaten by another should be low down on your list. But from the scientific point of view, hints that the cosmos might be blemished and wonky – that it is not quite perfect – raises an interesting and profound question: might it be flawed in other ways too?
24. Is the Universe Actually a Botched Job?
The idea that our universe is in some way special goes back to Isaac Newton’s continental rival, the seventeenth-century philosopher Gottfried Leibniz, who claimed that ours is actually the best of all possible worlds. He based this on theological grounds, reasoning that a perfect Divine Being wouldn’t make a flawed or ugly universe. Leibniz attracted much derision for his rosy view of the world, famously being lampooned as ‘Dr Pangloss’ in Voltaire’s 1759 novel Candide.
Is there any sense in which our universe would in fact come out top in a cosmic beauty contest? Imagine playing God and consider giving the universe a makeover. Could it be improved? It’s easy to think of simple things – one more bottle of champagne, prettier sunsets, fewer wars. However, these aren’t the sort of things that scientists normally have in mind when considering optimization problems.
If the universe were to get an upgrade to something better, we need to have a clear idea of what ‘better’ means. An obvious definition has to do with the existence of life. Life would seem to be a good thing (where would we be without it?), so a universe with more life might be an improvement. As I have explained, our universe is good at life, but could it be better? Could the laws of physics be tweaked so as to generate more habitable real estate?
The astronomer Fred Adams thinks the answer is yes. ‘The universe is not fully optimized for the emergence of life,’ he says. ‘One can readily envision more favourable universes.’ Adams bases his conclusion on an exhaustive study of the consequences for life if many of the unexplained constants of nature were different. By ‘constants of nature’ I am referring to seemingly fixed but unexplained quantities, such as the charge on the electron or the mass of the proton.
To make this analysis vivid, imagine a Designer Machine with knobs to adjust the various constants one by one. If you take the Standard Model of particle physics, and standard cosmology, there are thirty-something knobs determining such things as the strengths of forces, the masses of particles and the density of dark energy. Turn this knob and make all neutrinos a bit heavier; turn that one and make the weak force weaker. And so on. What happens to the universe?
Adams twiddled the knobs (metaphorically speaking) and found numerous cases where the upshot would be a more bio-friendly universe than ours. For example, if the strong force were stronger, the nuclear pathway to synthesizing carbon would be much more efficient. Also, stars could live much longer and sustain habitable planets for trillions of years. He looked at many features like this. His overall conclusion: the Great Cosmic Creator botched the numbers and he, Fred Adams, could do a better job if only he could get his hands on the Creation Machine. Given that neither Adams nor anyone else has access to a Creation Machine, we can at least try to determine by observation just how life-friendly our universe is. The anthropic principle only requires someone to inhabit the universe and observe it; it says nothing about the total population. Did life just squeak home, a marginal happy accident on a handful of planets in a universe that permits life without encouraging it? Or is the universe teeming with life?
25. Are We Alone?
I often give public lectures on astrobiology with the title: ‘Are we alone in the universe?’ From time to time somebody will raise a hand during the Q&A and announce that they know the answer, because they have met, or have even been abducted by, aliens. I don’t believe them, but I try not to be too dismissive. Occasionally my sense of mischief gets the better of me, though, and if I am asked whether I know anything about secret US government facilities with alien bodies, or crashed flying saucers, I reply by saying that I do know something, but I’m afraid I’m not at liberty to disclose it. That either causes uproar or brings the lecture to a convenient close.
Much as I would love to think we are not alone, I accept that there is still no sound scientific evidence for any life whatsoever beyond Earth, let alone intelligent life. The search for alien beings is another of those pendulum stories. Early scientists had little problem with the possibility of extra-terrestrial life, once it became established that the planets were other worlds. The seventeenth-century astronomer Johannes Kepler, for example, believed that Jupiter – and even the moon – were inhabited. But arguments for or against the existence of extra-terrestrials rested more on the arcana of Christian dogma than scientific inquiry. Interestingly, the person who gave us the word ‘scientist’, William Whewell, master of Trinity College, Cambridge, chose to reject the notion of alien beings on religious grounds, as being inconsistent with Christian salvation and the uniqueness of the Incarnation.
The scientific arguments against life elsewhere in the solar system began to strengthen with better telescopes, although the possibility of life on Mars persisted into the twentieth century (I’ve already mentioned Percival Lowell’s belief in Martians). It took the advent of the space age and a succession of Mars fly-bys, followed by orbiters and landers, to finally put paid to speculation about Martians. While it’s possible that Mars may have hosted primitive life in the far past – and there remains a faint hope it may still do so today – recent attention has focused on the icy moons of the outer solar system, such as Europa and Enceladus. Beneath their thick ice crusts they have liquid water, which just might provide suitable conditions for biology. However, nobody supposes that these bodies would harbour more than microbial life.
In the last decade, astronomers have discovered many extra-solar planets, a fraction of which will surely resemble Earth. Some estimates suggest a billion earth-like planets in the Milky Way alone. A major challenge is to find ‘bio-signatures’, detectable from Earth, that might indicate the presence of some form of life on these distant worlds. For example, oxygen in the atmosphere would be a positive (though not definitive) sign, because on Earth oxygen is a product of photosynthesis.
While it’s promising to know there are plenty of habitable planets out there, there is a huge difference between habitable and inhabited. For a habitable planet to spawn life, somehow a mish-mash of chemicals has to turn into something living. During my career, opinion has shifted from deep scepticism that life would readily arise in a chemical soup, to the currently fashionable view that the universe is seething with life. Contrast Francis Crick’s 1973 statement that ‘life seems almost a miracle’, so many are the conditions necessary for it to get going, with Christian de Duve’s 1995 opinion that the emergence of life is ‘a cosmic imperative’.
In the absence of hard facts there is plenty of scope for disagreement. At the heart of the problem is an almost complete ignorance of the process that turned non-life into life. Because scientists have only scrappy ideas of what that process was, they are
unable to reliably estimate the odds of it happening. The answer could lie anywhere on a spectrum from complete fluke to almost inevitable. If you believe the universe is rigged in favour of life, you would opt for the latter. Just a single data point – just one instance of a second sample of life – would clinch the matter.
26. Is ET in Our Backyard?
When most people refer to extra-terrestrial life, they usually have in mind not microbes but intelligent aliens. The search for extra-terrestrial intelligence – SETI – is a small but growing branch of science. It began in earnest in 1960 when a few optimistic astronomers, led by Frank Drake, began sweeping the skies with radio telescopes in the hope of coming across a message from an alien civilization. In my student days, I was a strong fan of SETI – I still am – but in the 1960s the idea of searching for aliens was regarded as decidedly crackpot. One might as well have professed an interest in looking for fairies. The prevailing scientific opinion was well captured in a 1964 article by the distinguished biologist George Simpson, entitled ‘The non-prevalence of humanoids’. The quest for them was utterly futile, wrote Simpson, so heavily are the odds stacked against it.
In this climate of scepticism, SETI limped along on a shoestring budget. NASA first supported it, but pulled out in 1993, and the whole project was obliged to rely on private donations, most notably by Paul Allen, co-founder of Microsoft. Then came a dramatic reversal of fortunes. In July 2015 the business magnate Yuri Milner, founder of the Breakthrough Prizes, announced a commitment of a hundred million US dollars to boost SETI research, with more to follow.*
In spite of the extra cash, traditional radio SETI remains hampered by a fundamental scientific obstacle. Our biggest satellite dishes lack the power to pick up an alien broadcast unless it is beamed directly at Earth. But why would an alien civilization deliberately send us radio messages unless they could be sure that our planet hosted a civilization with radio technology? They would of course know this by detecting our own radio transmissions. But these have scarcely penetrated a hundred light years into space, so unless there are aliens extremely close, by astronomical standards, we can’t expect anyone to be purposefully signalling us.
Still, we don’t need to pick up a customized radio message to discover that we are not alone in the universe. All it needs is convincing evidence for non-human technology – a ‘technosignature’ to use the buzzword. Earth abounds with technosignatures: ecosystems modified by agriculture, the Great Wall of China, CFCs in the atmosphere, night-time illumination . . . Given the millions of earth-like planets in the galaxy, there are plenty of potential targets to search for such telltale signs. Unfortunately, detection of any technology restricted to a planetary scale is way beyond our current capabilities, so researchers have focused their deliberations on two other avenues: megastructures and probes. An advanced alien civilization could have extended its technological footprint beyond the home planet and modified its astronomical environment in some conspicuous way. An early suggestion, made by the physicist and futurist Freeman Dyson in 1960, is that an energy-hungry supercivilization might build an enclosure round its host star to trap all its light – a solar energy project on a grand scale. Such a ‘Dyson sphere’ would show up as a strange infrared stellar-mass object.
Nothing quite like that has been found, but in 2015 there was a flurry of excitement when Tabetha Boyajian of Georgia State University identified a star – popularly called Tabby’s star – that keeps changing its brightness in erratic ways. Is it being partially eclipsed by some sort of artificial orbiting megastructure? Although graphic artists had a field day with this concept, most astronomers think there is a natural explanation. Another weird object is named after the Polish-Australian astronomer Antoni Przybylski. The spectrum of Przybylski’s star suggests the presence of a host of radioactive elements, including thorium, uranium, plutonium and einsteinium. How they got there remains a mystery. Is this some sort of extra-terrestrial nuclear waste dump?
A civilization able to build a megastructure would presumably also have the know-how to send probes to other star systems. So, could there be an alien technosignature in our cosmic backyard? If there were, where should we look? A few years ago, with the help of a resourceful undergraduate, I tested the feasibility of finding an alien artefact on the moon. The lunar surface is relatively unchanging, and a moderate-sized object might remain exposed for many millions of years. The Lunar Reconnaissance Orbiter (LRO) spacecraft operated by NASA, with help from Arizona State University, is photographing the moon to half-metre resolution. The LRO pictures clearly show technosignatures. To date, however, they are all of human origin.
But the moon isn’t our only close astronomical companion. There are also a few small asteroids stalking our planet. Physicist James Benford has suggested that these co-orbital rocks would be handy places for a probe to lurk for a few thousand years if it was designed to monitor Earth. (Jim is, by the way, the twin brother of Greg Benford, of Timescape fame – see p. 78.) For longer-term parking, a good location would be one of the so-called Lagrange points – regions of space where the gravitational forces of the Earth and sun are in balance, thus obviating the need for orbital corrections. If a dormant alien probe were to ‘wake up’ and start communicating, the job of SETI scientists would be easy. However, finding a defunct or dormant probe somewhere in the solar system would be like looking for a needle in a haystack – even more so when you consider not only the vastness of space, but the immensity of time. At 4.6 billion years old, the solar system is only about one-third of the age of the universe: there may have been inhabited planets around before Earth even existed. If interstellar missions are feasible, an alien probe could have arrived at any time in our planetary history.
When it comes to probes, my guess is that we are more likely to encounter robotic surrogates than biological organisms. On Earth, designed intelligence – usually called artificial intelligence or AI – is already penetrating many areas of human activity; it can do mathematics better than we can, and, increasingly, make decisions about complex systems. It is easy to imagine that in a few decades most of the intellectual heavy lifting on Earth will be done by AI that will likely far outstrip the human brain in capability. Besides, machines can be built to go almost anywhere, tolerating conditions well outside the comfort zone of living organisms. If we ever do detect extra-terrestrial intelligence, it will almost certainly be of this super-advanced post-biological variety.
This conclusion carries the depressing implication that whatever intellectual prizes might be stored in an artificial mega-brain, they would lie well beyond our realm of understanding anyway. Nevertheless, merely to know of the existence of this god-like entity – thereby confirming that we are not alone – would have enormous implications for our view of ourselves and our place in the universe.
27. Why Am I Living Now?
My parents were married in London on the first day of the Blitz, with dog-fights over the church, shrapnel falling and the taxi driver blaring his horn in panic. If one of the Luftwaffe pilots had sneezed, he might have dropped a bomb on the church, instead of the next street over, and I would not be writing these words now.
I remember being shocked as a child to learn that if my parents had never met, I wouldn’t exist. Even weirder, if a different sperm had made it ahead of the actual winner, I would be someone else! I began to fret: why am I me? This existential angst kept me awake at night, until a related question began to bother me even more: why am I living now – say, 1956 – rather than in 1066, or 2176? Many years later I found that there might actually be a rough-and-ready answer to this conundrum, on a cosmic timescale at least. Let me explain. First, when precisely is ‘now’? In cosmic terms, it is something like year 13,775,248,929 since the beginning of the universe (I just made up the last eight digits for purposes of illustration). So, there is a lot of time in the past when I might have existed, but didn’t. (And quite likely even more time in the future.) Which makes me living now seem even more baffling a
nd special. But hold on, could a sentient being have lived a billion years ago? Ten billion years ago? Maybe, maybe not.
In 1936, the physicist Paul Dirac noted something odd about ‘now’, that is, about the cosmic date corresponding to 1936. The terrestrial year is of course just an arbitrary unit. But physics, noted Dirac, supplies a fundamental unit of time, good for anywhere in the universe. It is the duration it takes for light to cross the nucleus of an atom, which is about a ten-trillionth of a second. Expressed in that atomic unit, the age of the universe is roughly 1040, which is one followed by forty zeros. It occurred to Dirac that he’d come across that enormous number before. It is about the same as the ratio of the electric to the gravitational attraction in a hydrogen atom, the combined force between the proton and its orbiting electron. Was this just a coincidence?
Generally speaking, scientists hate coincidences – or ‘Big Fixes’ – as explanations, as I have stressed on several occasions. That two huge numbers, arising in totally different contexts, should be even approximately the same, hinted at a deep link of some sort. Now, the thing about the age of the universe is that it’s not a fixed number. In the past, when the universe was younger, that number was smaller. At one hundred years after the big bang, it was only about 1033, which is ten million times smaller than the ratio of forces in the hydrogen atom as measured today, throwing the coincidence out of whack. But what if, conjectured Dirac, gravity was ten million times stronger then (i.e. a hundred years after the big bang) than it is today? The two numbers would then have matched at both epochs. So Dirac proposed that gravity slowly weakens over time in order to keep the two big numbers always in lockstep.
