Yes, OK, four dimensions – time is a dimension too, albeit an oddly unidirectional one (see “Cosmic uncertainty: Does time go both ways?“). But we’ve long thought there might be more large-scale spatial dimensions than the up-down, left-right, in-out we are all used to.
In the late 19th century, British mathematician Charles Howard Hinton suggested that what we perceive as different objects moving in relation to one another could be thought of as passing through our three-dimensional universe. To get a sense of what that means, imagine what a spherical ball looks like observed as it passes through a two dimensional sheet – as a circle whose radius expands and then contracts in time (see “View from Flatland”).
Advertisement
Read more: Cosmic uncertainty: Five universal truths that might be wrong
In physics, things are as they are – until they’re not. Here are five cosmic impossibilities that just might turn out to be true
Adding extra dimensions to the universe is easy enough, on paper at least: you just need additional terms in your coordinate system. The question becomes how we perceive them. Einstein slipped in an additional space-like dimension to his equations of general relativity to explain how mass warps space-time. We don’t perceive this dimension directly, but experience it as an acceleration and explain it as the force of gravity.
Some physicists are adamant that more physical dimensions must exist beyond those we can see. In string theory – still most physicists’ chosen route to a unifying theory that combines gravity and the forces of the quantum world – the number of spatial dimensions is at least 10. This gives physicists enough wiggle room to try to explain all of the forces of nature together – but doesn’t explain where these extra dimensions are.
Extra dimensions have some odd consequences, too – implying, for example, a multiverse of distinct universes next to one another. Not everyone likes that. “I’m not a fan of the multiverse picture,” says physicist Erik Verlinde of the University of Amsterdam in the Netherlands. “Universes that we cannot communicate with are not that interesting to talk about. I think that we should be happy if we can explain the universe that we live in.”
Verlinde has been developing a quantum description of space and gravity to replace Einstein’s smooth space-time “continuum”. In his picture, minuscule building blocks made of quantum information become increasingly quantum entangled and create the seemingly continuous three dimensions of space.
But why three? That question remains open. “A lot of these ideas can be implemented in two, three, four or higher dimensions, so I don’t have an immediate reason why there should be three dimensions,” Verlinde says. And until someone can find one, tales of dimensions beyond those we can see might not be so wacky after all.
This article appeared in print under the headline “What if… there were more than three dimensions?”
