The apparent inability of physics' string theory to be proved right or wrong is one of the stickiest – and argument-generating – problems in modern science. But now researchers at the University of Illinois say they might have a way to test some of string theory's predictions.
Only problem? It'll be very, very expensive.
String theory is probably the most well-fleshed out candidate today for a so-called Theory of Everything. That means that it would integrate virtually everything we know about physics thus far, including the microscopic observations of the sub-atomic world and events that happen on a galaxy-wide scale, and follow the rules of Einstein's General Theory of Relativity. Those two scales – the micro and the macro – have proven difficult to reconcile on a mathematical level.
String theorists say they're on track to doing just this. But their answer requires mind-bogglingly complicated mathematics, and recourse to theories about the universe that some physicists find fanciful. The
"strings" involved are exquisitely tiny strings that bend and vibrate in ten- or 11-dimensional space, with different configurations leading to the different kinds of matter we see in our 4-D universe.
More advanced versions include the prospect of "branes," (think membrane, but in more dimensions), one of which might have our own universe embedded in it completely, and be floating around higher-dimensional space.
But because none of these descriptions of the universe offered any obvious way to be tested or proven, skeptics have called string theory
"not even wrong" – meaning that it doesn't fulfill the most basic requirement of a proper scientific theory, the ability to be be proven wrong.
Now Illinois cosmologist Benjamin Wandelt, along with graduate student
Rishi Khatri, say that some of these predictions can be tested, or at least addressed, by looking at remnants of conditions shortly after the
Big Bang.
About 400,000 years after the Big Bang, the universe was made up mostly of neutral hydrogen atoms – single protons, with a single electron –
along with the background radiation left over from the Big Bang,
Wandelt says.
At that time, string theorists believe that so-called cosmic strings also existed, essentially creating slight discontinuities in space, that would manifest as fluctuating densities in the gas around them.
These slight discontinuities could have imprinted themselves on the surrounding hydrogen atoms, which would have absorbed radiation at the specific wavelength of 21 centimeters, Wandelt and his co-author say.
Fast forward about 14 billion years. The universe has expanded dramatically, and the wavelength of the radiation absorbed and re-emitted by those original hydrogen atoms would have been stretched to nearly 21 meters before reaching Earth.
But build a radio telescope big enough to pick up that early radiation, and maybe we can see the echoes of those early cosmic string imprints, Wandelt says.
That won't be easy. It would require an array of telescopes with a collective area of more than 1000 kilometers (621 miles). That's not as insane as it sounds, since the telescopes don't have to be located next to each other (the Very Long Baseline Array radio telescope is made of ten antennae, scattered from Hawaii to the Virgin Islands, for example).
But it would, Wandelt says, be "prohibitively expensive."
Nevertheless, the idea offers hope of testing certain parameters of string theory, including string tension, which would help set parameters for other features, the researchers say.
Disclosure: I have no idea whether this makes sense. This summary is almost certainly doing some violence to the idea. I encourage interested parties to read the Illinois press release, or the pair's paper when it is published in Physical Review Letters. But I'd love to hear your thoughts.
Scientists propose test of string theory based on neutral hydrogen absorption [University of Illinois]
(Image: Part of the Very Large Array, a radio telescope facility in New Mexico. Credit: National Radio Astronomy Observatory)
