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Existence: Why is the universe just right for us?
• 20 July 2011 by Marcus Chown
IT HAS been called the Goldilocks paradox. If the strong nuclear force which glues atomic nuclei together were only a few per cent stronger than it is, stars like the sun would exhaust their hydrogen fuel in less than a second. Our sun would have exploded long ago and there would be no life on Earth. If the weak nuclear force were a few per cent weaker, the heavy elements that make up most of our world wouldn't be here, and neither would you.
If gravity were a little weaker than it is, it would never have been able to crush the core of the sun sufficiently to ignite the nuclear reactions that create sunlight; a little stronger and, again, the sun would have burned all of its fuel billions of years ago. Once again, we could never have arisen.
Such instances of the fine-tuning of the laws of physics seem to abound. Many of the essential parameters of nature - the strengths of fundamental forces and the masses of fundamental particles - seem fixed at values that are "just right" for life to emerge. A whisker either way and we would not be here. It is as if the universe was made for us.
What are we to make of this? One possibility is that the universe was fine-tuned by a supreme being - God. Although many people like this explanation, scientists see no evidence that a supernatural entity is orchestrating the cosmos. The known laws of physics can explain the existence of the universe that we observe. To paraphrase astronomer Pierre-Simon Laplace when asked by Napoleon why his book Mécanique Céleste did not mention the creator: we have no need of that hypothesis.
Another possibility is that it simply couldn't be any other way. We find ourselves in a universe ruled by laws compatible with life because, well, how could we not?
This could seem to imply that our existence is an incredible slice of luck - of all the universes that could have existed, we got one capable of supporting intelligent life. But most physicists don't see it that way.
The most likely explanation for fine-tuning is possibly even more mind-expanding: that our universe is merely one of a vast ensemble of universes, each with different laws of physics. We find ourselves in one with laws suitable for life because, again, how could it be any other way?
The multiverse idea is not without theoretical backing. String theory, our best attempt yet at a theory of everything, predicts at least 10500 universes, each with different laws of physics. To put that number into perspective, there are an estimated 1025 grains of sand in the Sahara desert.
Fine-tuned fallacy
Another possibility is that there is nothing to explain. Some argue that the whole idea of fine-tuning is wrong. One vocal critic is Victor Stenger of the University of Colorado in Boulder, author of The Fallacy of Fine-tuning. His exhibit A concerns one of the pre-eminent examples of fine-tuning, the unlikeliness of the existence of anything other than hydrogen, helium and lithium.
All the heavy elements in your body, including carbon, nitrogen, oxygen and iron, were forged inside distant stars. In 1952, cosmologist Fred Hoyle argued that the existence of these elements depends on a huge cosmic coincidence. One of the key steps to their formation is the "triple alpha" process in which three helium nuclei fuse together to form a carbon-12 nucleus. For this reaction to occur, Hoyle proposed that the energy of the carbon-12 nucleus must be precisely equal to the combined energy of three helium nuclei at the typical temperature inside a red giant star. And so it is.
However, Stenger points out that in 1989 a team at the Technion-Israel Institute of Technology in Haifa showed that, actually, the carbon-12 energy level could have been significantly different and still resulted in the heavy elements required for life.
There are other problems with the fine-tuning argument. One is the fact that examples of fine-tuning are found by taking a single parameter - a force of nature, say, or a subatomic particle mass - and varying it while keeping everything else constant. This seems very unrealistic. The theory of everything, which alas we do not yet possess, is likely to show intimate connections between physical parameters. The effect of varying one may very well be compensated for by variations in another.
Then there is the fact that we only have one example of life to go on, so how can we be so sure that different laws could not give rise to some other living system capable of pondering its own existence?One example of fine-tuning, however, remains difficult to dismiss: the accelerating expansion of the universe by dark energy. Quantum theory predicts that the strength of this mysterious force should be about 10120 times larger than the value we observe.
This discrepancy seems extraordinarily fortuitous. According to Nobel prizewinner Steven Weinberg, if dark energy were not so tiny, galaxies could never have formed and we would not be here. The explanation Weinberg grudgingly accepts is that we must live in a universe with a "just right" value for dark energy. "The dark energy is still the only quantity that appears to require a multiverse explanation," admits Weinberg. "I don't see much evidence of fine-tuning of any other physical constants."
Existence: Am I a zombie?
• 01 August 2011 by Michael Brooks
IN A nutshell, you don't know.
Philosopher René Descartes hit the nail on the head when he wrote "cogito ergo sum". The only evidence you have that you exist as a self-aware being is your conscious experience of thinking about your existence. Beyond that you're on your own. You cannot access anyone else's conscious thoughts, so you will never know if they are self-aware.
That was in 1644 and little progress has been made since. If anything, we are even less sure about the reality of our own existence.
It is not so long ago that computers became powerful enough to let us create alternative worlds. We have countless games and simulations that are, effectively, worlds within our world. As technology improves, these simulated worlds will become ever more sophisticated. The "original" universe will eventually be populated by a near-infinite number of advanced, virtual civilisations. It is hard to imagine that they will not contain autonomous, conscious beings. Beings like you and me.
According to Nick Bostrom, a philosopher at the University of Oxford who first made this argument, this simple fact makes it entirely plausible that our reality is in fact a simulation run by entities from a more advanced civilisation.
How would we know? Bostrom points out that the only way we could be sure is if a message popped up in front of our eyes saying: "You are living in a computer simulation." Or, he says, if the operators transported you to their reality (which, of course, may itself be a simulation).
Although we are unlikely to get proof, we might find some hints about our reality. "I think it might be feasible to get evidence that would at least give weak clues," says Bostrom.
Economist Robin Hanson of George Mason University in Fairfax, Virginia, is not so sure. If we did find anything out, the operators could just rewind everything back to a point where the clue could be erased. "We won't ever notice if they don't want us to," Hanson says. Anyway, seeking the truth might even be asking for trouble. We could be accused of ruining our creators' fun and cause them to pull the plug.
Zombie invasion
Hanson has a slightly different take on the argument. "Small simulations should be far more numerous than large ones," he says. That's why he thinks it is far more likely that he lives in a simulation where he is the only conscious, interesting being. In other words, everyone else is an extra: a zombie, if you will. However, he would have no way of knowing, which brings us back to Descartes.
Of course, we do have access to a technology that would have looked like sorcery in Descartes's day: the ability to peer inside someone's head and read their thoughts. Unfortunately, that doesn't take us any nearer to knowing whether they are sentient. "Even if you measure brainwaves, you can never know exactly what experience they represent," says psychologist Bruce Hood at the University of Bristol, UK.
If anything, brain scanning has undermined Descartes's maxim. You, too, might be a zombie. "I happen to be one myself," says Stanford University philosopher Paul Skokowski. "And so, even if you don't realise it, are you."
Skokowski's assertion is based on the belief, particularly common among neuroscientists who study brain scans, that we do not have free will. There is no ghost in the machine; our actions are driven by brain states that lie entirely beyond our control. "I think, therefore I am" might be an illusion.
So, it may well be that you live in a computer simulation in which you are the only self-aware creature. I could well be a zombie and so could you. Have an interesting day.