By Raunak Haldipur
All of us have heard from various astrophysicists that the Universe is endless and keeps expanding. As humans, we have always had the curiosity to explore and learn more about the universe. Billions of dollars have been spent on building telescopes for this purpose. However, almost all of the universe is utterly invisible. All the stars, planets, and galaxies that can be seen today make up just 5% of the universe. The other 95% is made up of objects the astronomers cannot see, detect or even comprehend. About 95% of the cosmos cannot be seen because it is made of the mysterious “dark matter” and “dark energy” that does not interact with light. Astronomers infer their existence based on their gravitational influence on what little bits of the universe can be seen but dark matter and energy themselves continue to elude all detection.
Dark matter: Genesis and implications
Some of the first hints astronomers had that there might be more mass in the universe than what we can see were observed in the 1960s and 1970s. An astronomer called Vera Rubin was observing the speed of stars at various locations in galaxies. Newtonian physics states that the stars on the outskirts of a galaxy would orbit more slowly than stars at the centre. Yet Rubin’s observations found no drop-off at all in the stars’ velocities further out in a galaxy. Instead, she found that all stars in a galaxy seem to circle the centre at roughly the same speed.
Ultimately, based on observations and computer calculations, scientists concluded that there must be much more matter in galaxies than what is obvious to us. If the stars and gas that we can see inside galaxies are only a small portion of their total mass, then the velocities make sense. Thus, astronomers nicknamed this extra unseen mass as “dark matter.”
Yet, until today, researchers still haven’t been able to figure out what dark matter is made of. A popular hypothesis is that dark matter is formed by exotic particles that don’t interact with regular matter, even light, and are hence invisible. Yet, their mass exerts a gravitational pull, just like normal matter, which is why they affect the velocities of stars and other phenomena in the universe. However, scientists have yet to detect any of these particles, even with tests designed specifically to target their predicted properties. Still, many hold out hope that they are getting closer and that experiments such as the newly built Large Hadron Collider particle accelerator in Geneva may finally solve the puzzle.
Unravelling old mysteries with dark energy
Dark energy is possibly even more baffling than dark matter. It’s a relatively more recent discovery, and it’s one that scientists have even less of a chance of understanding anytime soon. It all started in the mid-1990s when two teams of researchers were trying to figure out how fast the universe was expanding, in order to predict whether it would keep spreading out forever, or if it would eventually crumble back in on itself in a “Big Crunch”.
To do this, scientists used special tricks to determine the distances of many exploded stars called supernovas throughout the universe. They then measured their velocities to determine how fast they were moving away from us.
When we view very distant stars, we are viewing an earlier time in the history of the universe because the light of those stars has taken millions and billions of light-years to travel to us. In order to understand this with a hypothetical example, we can say that living beings in a distant galaxy when they look at Earth will probably see Dinosaurs roaming the Earth. Thus, looking at the speeds of stars at various distances tells us how fast the universe was expanding at various points in its lifetime.
Decoding the dark energy concept
Astronomers predicted two possibilities—either the universe has been expanding at roughly the same rate throughout time, or that the universe has been slowing in its expansion as it gets older. Surprisingly, the researchers observed neither possibility. Instead, the universe appeared to be accelerating in its expansion. This fact could not be explained based on what we knew of the universe at that time. All the gravity of all the mass in the cosmos should have been pulling the universe back inward, just as gravity pulls a ball back down to Earth after it’s been thrown into the air.
Richard Panek, a science writer explained that there is some other force out there or something on a cosmic scale that is counteracting the force of gravity. People didn’t believe this at first because it’s such a weird result. Scientists named this mysterious force “dark energy”. Though no one has a good idea of what dark energy is, or why it exists, it is the force that appears to be counteracting gravity and causing the universe to accelerate in its expansion. The lack of a good explanation for dark energy hasn’t seemed to lower scientist’s enthusiasm for it. Overall, dark energy is thought to contribute 73% of all the mass and energy in the universe. Another 23 percent is dark matter, which leaves only 4% of the universe composed of regular matter, such as stars, planets and people. This gives an idea as to how we all are so tiny in the entire universe.
A telescope hunting for the invisible?
The European Space Agency (ESA) is hoping to launch the Euclid Space Mission which will go into orbit, trying to sniff out the nature of dark matter and dark energy. Now NASA has also formally joined the Euclid Project, funding 43 US-based scientists to work with their international counterparts. In order to hunt for the invisible, they plan to use a technique called ‘weak lensing’, says Jason Rhodes, of the Jet Propulsion Laboratory, the research leader of the NASA contingent. The idea is based on Einstein’s General Theory of Relativity which states that a massive foreground object warps space-time, distorting the images of objects in the background. To map out the dark matter in a nearby cluster of galaxies, one should look at the distortions of thousands of other galaxies behind it. The pattern of distortions tells us the size and shape of the dark matter cloud that must have caused it. Euclid would probably not be able to solve the mystery revolving around dark matter and dark energy, but it surely is a start considering 40 years of very little progress.
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