The universe is not going to continue to expand into infinity, writes Michael Brooks, but only until it falls apart – in about 15- billion years
Is there such a thing as eternal life? Of all the questions mankind has wrestled with over the millennia, this one has been a consistent source of concern.
Well, fret no more, because physicist Lawrence Krauss has the answer, and it’s an emphatic no. Life in the universe is hurtling towards oblivion – it cannot possibly continue forever.
The result, Krauss says, is a shock; it directly contradicts the last major study of this subject.
The astronomy professor from Case Western Reserve University (CWRU) in Cleveland, Ohio, used to deal with relatively trivial topics – he brought us The Physics of Star Trek, for instance – but Krauss has now decided to turn his hand to weightier issues.
After considering all the available data on the expansion of the universe, the role of energy in providing us with life and information, the nature of consciousness, and, er, the unreliability of alarm clocks, he has concluded that civilisation in the cosmos is doomed.
In a relatively short time – maybe 15-billion years – the stars will start disappearing. The universe is able to expand at speeds greater than the speed of light (space itself is not restricted by the law that says nothing can travel faster than light), and so within a few billion years, most of the stars will be moving away from our galaxy so rapidly that their light can’t ever reach us.
According to Krauss’s calculations, distant galaxies and stars are going to blink out of existence very soon.
“The surprising fact is not so much that energy is disappearing, but that it’s going to happen so quickly,” he says. “Within 100- billion years, everything but our own cluster of galaxies will be invisible.”
Since the energy that comes from the stars is necessary for life, the universe’s expansion will strip us of the one thing we need for continued existence. The universe, however, is eternal: it will keep on going, leaving us to fade quietly away.
So the end of the world is relatively nigh. What’s the plan?
Krauss and his co-author from CWRU, Glenn Starkman, have considered a number of options. The first is to build some kind of energy-mining machine to harvest all the currently available energy before it disappears over the horizon. Black holes seem to offer the best possibility; they are remarkably good at absorbing energy.
“The trouble is,” says Krauss, “it’s hard to get energy out of them.” Whatever the imaginary machines Krauss and Starkman considered, they seemed impossible to build, difficult to use, or used more energy than they collected. Time for plan B: hibernation.
Back in 1979, the Princeton physicist Freeman Dyson first raised the possibility of a limited amount of energy in the universe. He was optimistic: with the data available to him then, it seemed that there wasn’t too much of a problem, and that life could go on forever in these conditions.
He suggested lowering the metabolism of biological life, so that it used energy at a minimal rate. Occasional forays into the active world, combined with energy-saving hibernation periods, would ensure eternal life.
Krauss and Starkman have two arguments against Dyson’s plan. The first is that his complex quantum mechanical calculations were wrong: the perpetual use of energy, no matter how slowly, is impossible. The second objection is more simple: who’s going to wake us up?
“Alarm clocks aren’t reliable,” Krauss says. “Everyone who goes to work knows that.”
Even an infinitely reliable alarm clock, that would, without fail, awaken civilisations after millennia of hibernation, has a fatal flaw. Any alarm clock, Krauss points out, uses energy. “Even if one could manage to expend energy only to wake up the hibernator, and not run the alarm clock in the interim, the alarm clock would still eventually exhaust the entire store of energy.”
Dyson, Krauss and Starkman are in discussions about the paper at the moment – the CRWU researchers posted their ideas on the Internet only last month – and, so far, Dyson doesn’t entirely agree with their evaluation.
“Krauss and Starkman say my calculations are wrong, and I still say they are right,” he says. He believes their disagreement arises from different ways of thinking about information.
Krauss believes that a scientific view of the energy requirements of biological life has to centre on the problem of consciousness. That, he says, must have something to do with computing, which uses energy to process information.
“We don’t know the nature of consciousness, but the most reasonable assumption is that it involves computations.”
Dyson shares this view, but offers a different type of computation. “In thinking about information and memory, they think digital and I think analogue,” he says.
In Krauss and Starkman’s view of life, information is carried in discrete states, like the zeroes and ones used to encode binary data. In normal life that data is kept stable by contact with our environment, which acts like a shock absorber, suppressing the potentially disastrous random quantum fluctuations that occur in the universe.
In hibernation, they argue, we will be detached from the environment in order to conserve energy. That will leave us vulnerable, our data too easily disturbed by the random fluctuations. Eventually they will cause us to jump out of one discrete state into another, so that we become “disorganised” and lose consciousness. The end.
Dyson, on the other hand, has everything operating in analogue fashion: little dust grains, for example, floating freely in space and communicating with each other by electric and magnetic fields.
“It is easy to calculate that in this situation quantum fluctuations are unimportant,” says Dyson. “The disasters described by Krauss and Starkman don’t happen.”
Of course, many would argue computing is a very poor reflection of consciousness. Krauss admits it’s a bit of a leap from information processing to the understanding of life, but he can’t find a better way to approach the issue scientifically.
“There are always going to be people who say there’s something that goes beyond the laws of physics, that consciousness is some spiritual thing. Once people start talking like that I can’t argue with them.”
And that’s what he wants to do. Having laid out the physics of doomsday, he hopes that fellow researchers will be provoked into thinking up solutions to mankind’s not-so- imminent extinction.
“We have a lot of time left to figure a way out,” he says. “It isn’t exactly a pressing problem.”
So far, the reaction from the cosmology community has been slow but encouraging. Once people stop shrugging their shoulders and muttering “so what?”, they then start to think about the challenges.
Krauss says he understands their initial reluctance to get involved. He had his own doubts about the validity of the research for a while. Now, he is convinced – and amazed – that physics can address these issues.
In general, researchers aren’t exactly falling over themselves to get involved in end-time predictions. The beginning of the universe is fashionable; the end is not.
“Occasionally people spend some time thinking about it, but there’s no ongoing research effort,” says John Barrow, professor of astronomy at the University of Sussex. In a 1986 book, The Anthropic Principle, Barrow examined, among other things, what might happen if the universe was found to be expanding more rapidly than was then supposed. His conclusion accords with Krauss.
Perhaps the dearth of research interest can be put down to the depressing nature of the subject. When University of Texas professor Steven Weinberg published his book The First Three Minutes, describing the origins of the universe, he summed up his view of the universe’s future rather glumly: “The more the universe seems comprehensible, the more it also seems pointless.”
Krauss prefers to see the bright side. “You could see it as depressing. On the other hand, you could argue that, since life can’t be eternal in the universe, it’s remarkable how fortunate one is to be around during the time that life exists.”
Krauss could, of course, be wrong (although he thinks it unlikely). His forecast depends on the energy in the universe being largely composed of a ghostly entity known as the cosmological constant, which defines the energy contained in “empty” space.
Albert Einstein first introduced the cosmological constant to his theory of general relativity as a simple fudge factor. Its addition made the universe into the static and stable place he assumed it to be. This approach didn’t really fit the evidence, so eventually he abandoned it.
A few years later, physicists realised that empty space is not actually empty: “virtual” particles are continually popping in and out of existence. The cosmological constant, they realised, could be linked to the energy of these particles.
Until recently, the astronomical evidence was all consistent with a zero cosmological constant. That would mean that the universe’s expansion is regulated by the gravitational attraction of all the matter within it. In this scenario, the universe would either keep expanding (but at a steady speed that allowed life to continue forever) or that it would gradually slow down and begin to contract into a reverse of the big bang.
But new data, some of it collected by the Hubble telescope, suggests that the universe is actually expanding at an ever-increasing speed. Cosmologists infer from these measurements that the universe’s empty space holds twice as much energy as is held in the universe’s matter; so the cosmological constant is positive, not zero, and its energy produces a repulsive force in empty space.
That makes the universe expand and hurtle away from us, taking all the necessities of life with it.
Although the evidence for a positive constant is strong, Krauss admits that things are “still tentative”. Until cosmologists are sure about the value of the cosmological constant, no one can be sure about the doomsday problem.
Finding out the energy associated with “empty” space is therefore a vital piece of the cosmology puzzle: in the end, it seems, nothing matters. And it matters a great deal.