Why Einstein (Probably) Isn't Wrong
Scientists have found a way to map the invisible Universe. What they see is helping to prove Einstein mostly right.
Several stories came out last week claiming scientists had once again proven Einstein wrong. They haven’t, of course, though they might have found a bit more evidence that one day leads to a new theory of physics. More interesting than the headlines are the details of the study itself and how they managed to map something we can’t see or detect: dark matter.
The trigger for these stories was the latest data release from the Dark Energy Survey, a project to map millions of galaxies, supernova and other cosmic structures. In doing so, the researchers hope they will uncover traces of dark energy, a mysterious force that seems to be driving the expansion of the universe.
That data seemed to hint that something was slightly wrong with our cosmological models. Matter is more evenly spread out — smoother — than it should be, at least according to predictions. That points to a flaw in the models and, perhaps, in Einstein’s equations.
The model in question is known as the Lambda Cold Dark Matter(ΛCDM) model. It assumes a few things — notably the accuracy of Einstein’s theory of relativity, the existence of dark matter and dark energy, and a Big Bang to kick things off. As cosmological models go, it is simple and effective, and therefore widely accepted among cosmologists.
Researchers have built computer simulations of the universe, starting from the Big Bang and running up to the present day. The simulations based on the ΛCDM model work well. They predict a universe that looks much like the one we see through telescopes, with galaxies and stars strung out in a vast cosmic web.
The problem, though, is that key building blocks — dark energy and dark matter — remain mysterious. Both were conjured up by astronomers to explain discrepancies between observation and theory — dark matter to explain the spin of galaxies, dark energy to explain the accelerating expansion of the universe. Neither has yet been directly detected.
The Dark Energy Survey does not aim to find either dark matter or dark energy. Instead it seeks to better understand them by accurately measuring their impact on the universe. That should help to eliminate some theories and hopefully strengthen others, helping us narrow down the possibilities.
To learn more about dark energy, specifically, the researchers needed to know how the largest structures in the universe have changed over time. That turns out to be difficult, however, as most of the matter in those large structures is dark, and therefore invisible. To find what they wanted, then, the researchers needed a way to make the invisible visible.
Fortunately, and, given the claims, somewhat ironically, Einstein provided a way. According to his theories, large objects distort space and time around them. As movies like Interstellar have explored, these distortions can have strange effects. Most importantly, for this study at least, is the effect they have on light rays.
Normally these travel in straight lines across the universe, but close to a massive object they curve. The result is an apparent shift when a large object passes in front of a faraway one. To give an example, when the Sun moves in front of distant stars, the position of those stars seems to shift slightly in the sky.
This effect varies depending on the positions of the objects. Sometimes the light is distorted, creating an arc, or if the alignment is exactly right, a ring — an example of which is shown in the image above. They are nice to look at, but the implications are more powerful: we can look for massive objects, even invisible ones, by looking for these kinds of distortions in the night sky.
That is exactly what the Dark Energy Survey has done. By looking at galaxies that appeared stretched or distorted in some way, they were able to locate the biggest objects around us. The result is a map of unprecedented detail, showing not just the visible things — the stars and galaxies — but all the invisible things too.
The result, by the way, seems to largely confirm the accuracy of the ΛCDM model. That adds evidence to support the established theories of cosmology — from Einstein to dark matter. There are some things in the results that suggest not everything with the model is quite right — which means that at least some of the assumptions need adjusting. But it doesn’t yet mean that Einstein was wrong.
The European Space Agency, ESA, is funding studies of future satellite networks around the Moon. The effort forms part of the Moonlight initiative, a project to look at the infrastructure needed to allow more permanent missions to the lunar surface.
ESA is interested in two key areas: navigation and communications. The first could see some kind of GPS network put in place around the Moon, allowing rovers or explorers to know exactly where they are. The second — a primitive lunar internet — would ease exploration of the far side of the Moon, an area permanently hidden from the Earth.
Such infrastructure would enable far more advanced missions on the Moon than have been attempted so far. Some exciting possibilities could open up, including moon bases and sophisticated telescopes placed on the dark side of the Moon.
Like the far side of the Moon, the centre of our galaxy is a mysterious and mostly unseen region. Clouds of dust and gas in the galactic core have so far blocked much of our view. Now astronomers have managed to take an x-ray of the core, revealing beautiful images of the heart of our galaxy. The images show intriguing details about the black hole believed to lie there and the magnetic field around it.
So much reporting around health, science and space exploration is unrealistic, hyperbolic and misleading. These are complicated topics, and there are often no easy or straight forward answers. Instead what is needed is analysis, discussion and an exploration of the possible ways forward.
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