The Week in Space and Physics
The Week in Space and Physics
On the search for flaws in general relativity and quantum physics, cloudy brown dwarves and a rocket company that has no rockets
As early as 1859 scholars knew that something was wrong with Mercury. The planet, they found, was refusing to follow the established laws of physics; subtly shifting its orbit with every revolution. It was a small effect, but a significant one: adding up to an error that could easily be measured over the decades.
Eventually physicists realised the problem lay in the law of gravity itself; that the cherished theories of Newton were flawed. Resolving it would take more than a half a century, and the application of a mind as brilliant as that of Einstein. His Theory of General Relativity – a piece of work unrivalled in its sheer genius and beauty – perfectly accounted for the unexpected motion of the charred innermost world of our Solar System.
Later studies showed the same error had afflicted the motions of all the known planets. But only Mercury, so close to the Sun, had shown the effect clearly enough to be visible. Might modern day astronomers draw inspiration from this tale? Once again they are on the hunt for a new theory of gravity, one that can unify the laws of the small – subatomic particles and their ilk – with the laws of the big – black holes and neutron stars. And, once again, they are turning to objects of cosmic importance in search of a clue.
Unfortunately for them, observations of Mercury will not cut it. The planet perfectly obeys the laws of relativity; circling the Sun exactly – as far as anyone can tell – as Einstein predicted. Instead they are turning to somewhere even more extreme: to stars locked in a perilous orbit around the Milky Way’s supermassive black hole.
Astronomers know of a handful of stars that lie extraordinarily close to that black hole. All are fascinating objects: as they approach the black hole they reach speeds unseen anywhere else in the galaxy. One, named S0-2, was spotted travelling at over seven thousand kilometres per second – roughly three percent of the speed of light itself.
A recent paper announced the discovery of an even more extreme example. A star, which they call S4716, sits so close to the black hole that it completes one orbit every four Earth years, the shortest period known. At its closest the star is nearer to the black hole than the Voyager spacecraft are to Earth; an almost insignificant distance on cosmic scales.
Here, trapped in the intense field of the black hole, astronomers are hoping to spot something akin to the motion of Mercury. A subtle shift in the motion of S4716, or one of its companions, could reveal the first discrepancy between reality and general relativity. If it does, that would be a true breakthrough – and, for the first time in a century, an opportunity to probe a deeper theory of gravity.
Muons: Not So Mysterious After All?
In the fight between general relativity and quantum physics, most theorists believe quantum physics will one day win out. The two theories – both incredibly successful – paint opposing pictures of the universe. One, relativity, is based on an elegant interplay between space, time and matter. The other, quantum theory, speaks of individual particles emerging from a bubbling vacuum.
Together they span the range of known physics: neatly covering everything from the spin of the electron to the passage of light across the universe. Only in the extremes - in the heart of a black hole or the birth of the universe - do their incompatibilities become clear. Yet in these places the theories do break down, producing paradoxes as the equations are pushed too far.
Many physicists think a deeper theory must exist; one from which quantum theory and relativity would both emerge. This, ideally, would take the form of quantum gravity. That's to say, a theory that describes a quantum nature of gravity, much as has been done for the other known forces. Yet to uncover this theory physicists need experimental evidence. They need a discovery that contradicts the Standard Model, the deepest form of quantum theory yet known.
Last year physicists thought they were close to finding exactly that. Experiments on muons – a subatomic particle similar to an electron – found them to differ slightly from predictions. A property known as the magnetic moment, a measure of how the particle behaves in a magnetic field, was fractionally higher than expected.
Yet there was always another possibility: physicists had messed up. The laws governing muons are fiendishly complex. Problems with those calculations – a mistake, or a lack of detail – could explain the discrepancy physicists saw. The problem, in other words, may not be with the theory, but with the computer programs that implement it.
Physicists thus began an effort to recalculate the equations. And, with the results now in, the experimental measurements look rather less unexpected. Some difference still seems to linger – but the new calculations have closed, somewhat, the gap. Muons, it seems, may not hold the key to a new theory of physics after all.
Dusty Clouds on Distant Dwarves
Brown dwarves are odd things: a kind of halfway house between stars and planets. They probably form in a similar way to stars – via the sudden collapse of a cloud of gas – but lack the mass to trigger nuclear fusion in their cores. The resulting objects are warm, not hot, and glow only faintly.
They thus behave somewhat like giant planets; to such an extent that clouds may even float high in their atmospheres. These, however, are no Earth-like clouds sailing peacefully across the skies. The clouds on brown dwarves are made of searing hot molten sand. Heated to thousands of degrees, they rain grains of quartz and olivine on whatever lies below.
The Spitzer Space Telescope, an infra-red observatory, found traces of clouds on half a dozen brown dwarves around a decade ago. But when the telescope stopped working, in 2009, astronomers thought they would have to wait to find more. Yet now a new analysis of the telescope’s data has found several more cloudy brown dwarves – but also shown that not all are hot enough for clouds of sand to form.
Similar things may be happening around the bigger planets in our Solar System, especially Jupiter. The inner layers of the planet’s atmosphere should be hot, far hotter than its surface. At that point clouds of molten sand may start to form, though – thanks to the thick atmosphere above – these are invisible to our telescopes.
Further evidence should arrive soon. The James Webb Space Telescope, a far more powerful telescope than Spitzer, will be able to spot clouds on brown dwarves. That should confirm they really exist, what they are made of, and hint at what might lie below the surface of Jupiter.
The Rocket Industry Takes Off
The shakeup in the global rocket market continues apace. In the latest announcement, an American company said it had received orders of more than one billion dollars - without ever launching a rocket.
The company in question, Relativity Space, is regarded as one of the biggest potential competitors for SpaceX. It has thus received huge investments from venture capitalists: money that has let the company develop a series of rocket engines. That, of course, has been done by others – what makes Relativity different is their focus on 3D printing.
The company believes it can print a reusable rocket, thus cutting the costs involved dramatically. The space industry certainly seems convinced. More than twenty launches have already been ordered by five different customers. Yet rocketry is hard, and Relativity still has not proven they can fly. The first test should come this summer, with the launch of their smallest rocket, the Terran 1. It promises to be a much watched event.
General versus quantum: The more we find, the more we have to understand.
This is truly an exciting age of discoveries.
And what about the number of dimensions revealed by the hadron collider.