The Week in Space and Physics #11
The future of science, Albert Michelson once said, must be looked for in the sixth decimal place. He was wrong, of course. Yet in 1894, the year in which he spoke, physicists were feeling confident. They had, after much effort, tamed the laws of gravity, magnetism and electricity, explained much of the natural world and found little to contradict their theories. Nothing of significance, they believed, remained to be discovered.
Nonetheless, deep cracks lay hidden under the surface. Within a decade the old theories of nature would be swept away, shattered under the weight of relativity and quantum physics. Science found an entirely new, deeper and previously unimagined view of the universe. Michelson was proven embarrassingly wrong.
Today, however, Michelson’s quote might once again be applied to physics. The theories of the twentieth century have proven remarkably resilient, predicting every experimental result with ease. The standard model – our deepest understanding of nature – foresaw the Higgs Boson, the top quark and the tau neutrino long before they were found.
Indeed, the model is so successful that no clear contradicting evidence has ever been found. Only the most extreme places in the cosmos – black holes and big bangs – are beyond its grasp. Only on the very largest scales – of galaxies and superclusters – does nature seem to deviate from its rules. That, however, is largely the fault of gravity, a force that so far eludes the grip of the standard model.
Yet the standard model is ugly; a hacked-together theory lacking the elegance sought by physicists. Deep cracks probably lie under its surface too. It can say nothing about the problems of dark matter and dark energy; nor explain why there seems to be a fundamental imbalance between matter and antimatter. And gravity, better explained by Einstein’s relativity, still frustrates scientists hunting a unified model.
Physicists once had dozens of ambitious theories ready to explain these mysteries. Ideas with names like string theory, supersymmetry and loop quantum gravity all claimed to offer a theory of everything; an ultimate theory of physics that would settle all the questions. Over time, however, these theories have faded away through lack of evidence. Physicists now seem rather empty handed in the search for something new.
That has led them to take up Michelson’s advice once more: running experiments with ever greater precision in the hopes of finding something new in the sixth decimal place. A handful of such claims have already been made – the magnetic moment of the muon, for example, seems slightly different from theoretical predictions. But no certain evidence has yet come to light.
Earlier this month physicists reported the surest evidence yet of a discrepancy. Measurements of a particle known as the W boson show it to be 0.1% heavier than expected. Those behind the experiment, done at Fermilab in Chicago, are confident in the accuracy of their experiments. Yet other, earlier, experiments found a lower mass, more in line with predicted numbers.
Even if the measurements from Fermilab are correct, they don’t yet tell us something new. Physicists will need to dream up theories to explain the result, fund new experiments to gather evidence and then piece together a new theory of reality. Still, if they can do that, Michelson may finally be proven right.
What Lies Beneath
In 1971 the US military drilled a mile into the Earth’s crust, placed a five megaton atomic bomb at the bottom of the resulting hole, and lit the fuse. All this was highly controversial – the site, in the remote Aleutian Islands off Alaska, was prone to earthquakes and volcanoes. The bomb, protestors feared, could trigger a disaster.
When the bomb detonated, a powerful earthquake shattered the test site. The hole itself collapsed, the force of the explosion leaving a radioactive crater on the surface. Shockwaves rippled through the planet, penetrating deep enough to bounce off the solid iron core of the planet.
The test, indeed, was powerful enough to allow geologists to study the inner planet; to shine a light on the deepest depths of the Earth. Of particular interest was the mysterious heart of our planet: the solid core that lies thousands of miles under our feet.
Roughly the size of Pluto, the inner core is a ball of solid iron both extremely hot and under enormous pressure. It is surrounded by a sphere of molten metal stretching almost half way to the surface. As measurements showed, however, the inner core does not rotate with the rest of the planet. Instead it seems to spin slightly slower or faster, an effect that may explain odd wobbles seen in the way the rest of the planet spins.
It may also explain why the Earth’s magnetic field – created by iron swirling around the core - seems to occasionally weaken, or even change direction completely. Over time the planet is slowly cooling, and as it does the inner core is growing. Subtle shifts in its shape may alter the way it spins, and, perhaps, change the way the outer core moves around it. That, in theory at least, could alter the magnetic field around us.
This formation of this core, as Paul Voosen explains in a fascinating article in Science, may have changed the course of history on our planet. Some five hundred million years ago the Earth’s magnetic field drastically weakened and then strengthened again, an event that some geologists link to the moment the core began to solidify. Shortly afterwards the Cambrian Explosion took place: the moment in which complex lifeforms first appeared and began to spread across the planet. Coincidence? Perhaps not.
Exploring the Ice Giants
In January 1986, Voyager 2 passed just fifty thousand miles from the surface of Uranus. It beamed back a handful of pictures, discovered ten moons and a magnetic field and then flew onwards, heading for Neptune and interstellar space. And that was it – the story of our exploration of Uranus begins and ends with Voyager.
Now, however, planetary scientists are calling for a return to the distant planet. Uranus is an ice giant: a type of cold and massive planet that may be widespread across the galaxy. That makes it especially interesting to study and – since it has so often been passed over in the past – scientists are hopeful of stumbling across something unexpected.
Some surprises are almost guaranteed. Science knows little about what makes Uranus tick, about what it is made of, what lies beneath its serene blue surface and about its many moons. We do know that Uranus spins on its side – an odd feature seen nowhere else in the Solar System, and perhaps the result of a long ago collision that knocked it over. But whether any evidence of that impact lingers, and what effects that unusual spin has, remain a mystery.
We will certainly have to wait a while for answers. Even if a probe is launched in the early 2030s – the earliest date suggested in the report – crossing the solar system will take around a decade. Answers, then, are unlikely to come before the 2040s.
To Catch a Falling Rocket
SpaceX land and reuse orbital rockets so frequently they almost make it look easy. Even so, no other company has yet managed to do the same. Might that soon change? Next week New Zealand-based Rocket Lab will make a serious attempt at catching a falling rocket – and, if all works out, at launching it again.
The company has been launching small rockets for a while now, typically carrying a handful of microsats and cubesats into orbit. After each launch the rocket has been lost, either falling into the Pacific or burning up in the atmosphere. That’s a shame, because reusing rockets is an essential part of lowering the cost of spaceflight.
Rocket Lab has gradually been preparing its Electron rocket for reusability. In recent launches the company has managed to guide the rocket back through the atmosphere towards a target area of the ocean. This time the company hopes to catch the rocket before it hits the water, using helicopters to pluck the falling rocket from the air.