Okay, we’re not quite there yet. But some very bright physicists are seriously considering how a mini-universe might be fashioned from a magnetic monopole and lots of energy
ONE of the good things about being God is that there’s not much competition. From time immemorial, no one else has boasted the skills necessary to create a Universe. Now that’s about to change.
“People are becoming more powerful,” says Andrei Linde, a cosmologist based at Stanford University in California. “Maybe it’s time we redefine God as something more sophisticated than just the creator of the Universe.”
Linde was prompted to make this wry observation by the news that a glittering prize is within physicists’ reach. For decades, particle accelerators have been racking up an impressive list of achievements, including creating antimatter and exotic particles never seen in Nature. The next generation of these giant colliders will provide the hunting ground for the elusive Higgs boson, thought to be the source of all mass. These machines might even create mini black holes.
Mighty as those discoveries and creations are, however, they pale into insignificance beside what Nobuyuki Sakai and his colleagues at Yamagata University in Japan have now put on the table. They have discovered how to use a particle accelerator to create a whole new universe.
The idea of creating another cosmos is not a new one; in fact, it has a long history. “The story really begins with the question of the origin of our own Universe,” says Eduardo Guendelman, a physicist at Ben Gurion University in Beer Sheva, Israel. As physicists began to research what kick-started our Universe, they realised that if it happened once, maybe it could happen again. The growing acceptance of the Big Bang model in particular, which suggested that spacetime burst forth in an explosion of energy concentrated in a tiny space, opened up a new set of tantalising possibilities.
“People immediately started to wonder what would happen if you put lots of energy in one space in the lab – shot lots of cannons together,” Linde says. “Could you concentrate enough energy to set off a mini Big Bang?”
For theoretical physicists, the initial answer was a resounding “no”. All of the particles that you would create in such a process would have their own gravity, pulling them together. So, instead of creating a baby universe in the lab, you would just create a black hole. The idea came back to life in 1981, however, when Alan Guth at the Massachusetts Institute of Technology proposed the theory of inflation, which suggests the Universe went through a period of rapid expansion just after the Big Bang.
Guth’s idea solves many cosmological puzzles, but no one really knew how or why it happened. So he and his colleagues set about trying to find out what might have made our Universe inflate – exactly the question that would help us create a new universe using our own tools.
Inflation theory, subsequently modified by Linde, relies on the fact that the “vacuum” of empty spacetime is not a boring, static place. Instead, it is subject to quantum fluctuations that cause strange bubbles to appear at random times. These bubbles of “false vacuum” contain spacetime with different – and very curious – properties.
According to our best understanding of physics, the Universe’s energy is stored in different kinds of fields. One of these is the Higgs field, which plays a vital role inside bubbles of false vacuum: it keeps the energy density within the bubbles constant.
That has two effects. First, it creates a repulsive gravitation within the bubble, which causes the bubble’s spacetime to swell. Although that might seem just what a budding creator requires, the effect doesn’t change the size of the bubble to an observer on the outside – the growth is only noticeable within the body of the false vacuum bubble. Nor are things improved by the second consequence of a constant energy density.
In 1987, Guth and Ed Farhi, also at MIT, demonstrated that bubbles which start out below a certain size collapse under the tension of the bubble walls before the space they enclose has a chance to expand. That happens because the pressure inside the bubble of false vacuum is always lower than the pressure of the true vacuum outside. In other words, if the bubble is too small, its walls will always have a tendency to collapse inwards.
Frustratingly, there’s even a problem with the larger bubbles. Although they could grow to cosmological scales in theory, they also need a kick-start before they will expand. In our early Universe, that kick was provided by the Big Bang, a point with infinite energy density. Reproducing one of those in the lab isn’t exactly plain sailing.
In 1989, however, Willy Fischler, a cosmologist at the University of Texas in Austin, and his colleagues found a way out. They showed that the same random quantum processes that create a false vacuum bubble would also allow it to spontaneously turn into a larger one. Their calculations showed that once this larger bubble had been burped out, it could inflate into a new universe without a kick-start from infinite energy.
Only one problem remained for the wannabe creators of a universe: a crippling time delay. The spontaneous transition from small bubble to large bubble can take a long time to occur, and the initial bubble tends to collapse under the tension of its walls before it can transform itself into a larger bubble.
Guendelman and his colleague Jacov Portnoy, also at Ben Gurion University, took matters into their own hands, and came up with some ways to prop the bubble walls apart. They factored in fields of energy known as “gauge fields” to the small bubble’s surface to keep its skin taut, holding it at a constant radius. “With that in place, all you need to do is sit there, watch the small bubble and wait for the large bubble to appear,” says Guendelman.
By this point, however, the home-made universe was starting to look rather cobbled together, to say the least. Though Guendelman and Portnoy’s trick was neat, no one knew how you might add these gauge fields into an experiment. Plenty of other obstacles remained, too. For a start, although Guth had calculated that the size of bubble needed was invitingly small – just 10-26 centimetres across – there still wasn’t any realistic way to create the bubble in the first place.
What’s more, one unfortunate consequence of quantum mechanics is that, even if you set up the right conditions for the process to occur and stop the bubble imploding, you still don’t know exactly when the inflation will happen. So even with a small bubble in place, and Guendelman and Portnoy’s theoretical fields doing their job, there was no guarantee it would turn into a baby universe any time soon. “You could be sitting and waiting from here to eternity,” says Guendelman.
For years, Guendelman and his colleagues sought to break through this impasse. What they needed was something that would create the bubble, then quickly blow it up into a universe.
And that is what Sakai has just found. The vital part of the new universe-creation tool kit is a magnetic monopole – a strange spherical particle that encapsulates an isolated north or south magnetic field. For would-be universe builders, the big attraction of a monopole is that it has a huge mass concentrated into a tiny volume, with an enormous energy density created by the Higgs field – just like false vacuum bubbles.
Sakai and his team realised that a seemingly stable monopole in our Universe is always teetering on the brink of expansion – needing just a nudge to start it inflating. Hurling mass on to the monopole – increasing its energy density – will push it over the edge, leading to runaway inflation. “Our calculations show that, given enough energy, the monopole will inflate eternally,” Sakai says.
This process could be triggered naturally. According to Sakai, if a monopole floating through spa
ce collided with another massive object, it would gain the mass needed to trigger inflation. One candidate is a cosmic string – a kind of high-energy rip in spacetime. Though we have yet to see one, cosmic strings may have been created as a by-product of the Big Bang.
But since we have no cosmic strings – and we’d like to remain in control of the project – Sakai suggests we might be able to trigger inflation by hurling particles on to a monopole in an accelerator. This would add mass, and thus energy, to the monopole, and make it blow up into an entirely new universe.
It would be an extraordinary achievement, of course, but what happens then? It’s one thing to create a universe, but quite another to know where to keep it. After all, an eternally inflating universe might be expected to take up quite a bit of space – the cupboard under the stairs simply won’t do.
Actually this wouldn’t be a problem, Sakai says. For a start, the process warps spacetime enormously, so that it is no longer the Euclidean space we are familiar with. This highly distorted space doesn’t have the same geometry as normal space, so it’s not as if the universe would blow up and engulf us.
Also, the baby universe has its own spacetime, and as this inflates, the pressure from the true vacuum outside its walls continues to constrain it. As these forces compete, the growing baby universe is forced to bubble out from our spacetime until its only connection to us is through a narrow spacetime tunnel called a wormhole.
In the end, spacetime becomes so distorted that even this umbilical cord is severed. The baby universe’s spacetime is left entirely divorced from our own. If you were sitting inside the monopole, you would see space expanding, rushing out in every direction – just as it did after the Big Bang in our Universe. The view from our Universe, outside the monopole looking in, would be rather less spectacular. “Once disconnected, the baby universe will be locked inside a microscopic black hole.”
Sakai’s calculations show that, once disconnected, the baby universe will be locked inside a microscopic black hole which will not appear to grow in size. This mini black hole will emit Hawking radiation and quickly evaporate from our Universe. It will continue to grow its own spacetime, but will leave behind little trace of its presence in our Universe. “We would make this tiny little thing and before we know it, it has flown away – escaped from our grasp,” says Linde.
In fact, it will disappear so fast it may even be difficult to tell if we’ve managed to create it at all, Sakai says. Plans are under way to detect mini black holes in the next generation of particle accelerators, such as the