“MY GOAL is simple,” Stephen Hawking once said. “It is a complete understanding of the universe, why it is as it is and why it exists at all.” That, in a nutshell, is the scientific manifesto – ambitious, maybe, but at least in theory possible.
But what if it isn’t?
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There’s no shortage of indications that there might be limits to how far we can penetrate with science. String theory, for example, regarded by many physicists as our best bet for a unified theory of reality, proposes between 10 and 26 space-time dimensions, many of them wrapped so up tightly as to be virtually inaccessible. That could slam the door on answering mysteries such as why gravity is so weak, or how mysterious dark energy is apparently accelerating our universe’s expansion.
The rebooted Large Hadron Collider at CERN near Geneva, Switzerland, is one place hints of hidden dimensions. Does it matter if we occupy the cheap seats in the cosmic theatre? at Queen Mary University of London is relaxed about the idea. “In some sense, science has always been about approximating reality,” he says.
“We thought we were at the centre of the universe, but ever since Copernicus it has all been downhill”
More perplexing, perhaps, is that our universe may be just one of countless others. Space-time’s headlong expansion might have led individual patches to become so far detached as to be independent. Some part of such a vast “multiverse” would be bound to have the life-friendly laws of our own universe – and so our physics could be entirely unrepresentative of the whole.
We can’t yet conceive how we might access other parts of the multiverse, but proof it exists might not be beyond us, says of Tufts University in Medford, Massachusetts. Budding universes bumping into each other as they expand might leave marks visible from Earth, perhaps in the cosmic microwave background, the ancient radiation that suffuses our sky. That would be just the latest reassessment of our place in the cosmos. “Long ago, humans thought they were at the centre of the universe, but ever since Copernicus, it was all downhill. We had better get used to it.”
With the quantum multiverse, things are even more unsettling. The strange consequences of quantum theory – like cats being dead and alive at the same time – are explained away by the many-worlds interpretation, which says the universe splits every time we look at it. That creates a new universe for every possible outcome of our observation.
But what does it mean for morality if there are countless universes out there, all containing near-identical copies of us? Are we responsible for them all? That depends, says , a philosopher at King’s College London. On the one hand, if you got away with something here, don’t think that you did elsewhere. “If your behaviour really made nasty results likely, then there are many other branches of reality on which people have been injured and maimed because of your recklessness.” At the same time, if sensible behaviour backfires in this world, take heart that most other yous are probably better off.
Such questions may seem like idle speculation at the moment – but they might not always be, says Berman. Perhaps one day, we will travel to another universe or visit worlds in another dimension, and judge things for ourselves. “There’s an enormous arrogance associated with people who put limits on what we might one day be able to see,” he says. “Why should the human lifetime be a natural unit for studying the progress of science?”
This article appeared in print under the headline “What if … Most of reality is hidden?”
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