How do scientists know that dark energy is speeding up the expansion of the universe?

One of the great conundrums in astronomy is the nature of something called dark energy, a kind of anti-gravitational force that appears to be pushing the accelerator pedal of the universe. It has been known since long that the universe was born about 13.7 billion years ago and has been expanding ever since. Yet until quite recently scientists thought that the rate of expansion was slowing down. In the mid-1990s, they found to their amazement that they were utterly wrong. The universe was speeding up and still continues to expand at an accelerated rate.

The discovery was made quite accidentally. Two teams of astronomers were measuring the brightness of very distinct Type 1a supernovae. These stellar explosions are among the brightest events in the universe, which makes them an ideal tool for determining their distances. The light from a Type 1a supernova follows a predictable path, always peaking at the same level of brightness. The light itself has a specific attribute. Its intensity varies inversely (oppositely) with the square of the distance between the source such as a supernova and the surface such as a telescope’s mirror.

In other words, if the distance increases, the illumination decreases by the square of the distance. To cite an example, if a surface that receives 1 lux of light at a distance of 1 meter from the source is moved 2 meters from the source, that surface will receive 1/4 lux of light. Astronomers, who were using supernovae as ‘standard candles’ discovered that every remote Type 1a supernovae were significantly fainter than they should have been, based on their distances estimated using other techniques. This meant that these supernovae were farther away than originally thought, so the implication was that the rate of expansion of the universe must be accelerating.

We don’t know that exactly is the repulsive force that is causing the universe to expand, so it has been called dark energy, and yet astronomers are totally in the dark about its physical nature.

Prominent research institutions such as NASA and National Geographic are continually researching Dark matter to find out about something that is known but yet unknown at the same time. They have come to find out that the entire universe is 68% dark energy. The Dark Matter constitutes 27%.

Scientists and researches all across the globe have been making use of several theories, including Albert Einstien’s, but most of the time, they have got it wrong. However, Albert Einstein’s explanation regarding Dark Energy has somehow kept the researchers and scientists going. Since the Dark Matter does not interact with anything or cause anything, it is difficult to find out what it is.

Additionally, astronomers have been able to observe the light from distant supernovae, which has led them to the observation of supernovae’s host galaxies distancing away from each other by flying at an increasing speed, proving the speeding expansion rate of the universe. However, this is still observation, and marrying such observations to theories is the biggest challenge faced by researchers.

Dark Matter and Dark Energy: The Hidden 95% of the Universe by Brian Clegg

As the term suggests itself, Dark Matter and Dark Energy have kept everyone in the dark to this day. However, some people, such as Brian Clegg, are curious to find out what it is. The quest to find the answer lead him to this book, which makes the overall concept much easier to understand for a layman as well.

Dark Energy: Theory and Observations by Luca Amendola

Luca Amendola, in his book Dark Energy: Theory and Observations, has reviewed a combination of theories and observations to try explaining Dark Energy the best way he can. From the cosmic microwave background to baryon acoustic oscillations, the book aims to highlight every problem and provides solutions along the way. This not only makes it a book but a step-by-step guide as well.

Matter, Dark Matter, and Anti-Matter: In Search of the Hidden Universe by Alain Mazure and Vincent Le Brun

Authors Alain Mazure and Vincent Le Brun take a different approach to explain the concept of Dark Matter. The book starts with mentioning the concepts behind this revolution in addition to the measurements and phenomenon that has given rise to this relatively new view. By using color photographs, splendid illustrations, and line diagrams, the book can be said to be successful in its aim.

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Dark Matter and Dark Energy: The Hidden 95% of the Universe by Brian Clegg
Dark Energy: Theory and Observations by Luca Amendola
Matter, Dark Matter, and Anti-Matter: In Search of the Hidden Universe by Alain Mazure and Vincent Le Brun