Even since more than a hundred years ago, after the observations of the great American astronomer Edwin Hubble, humanity knows that the Universe is constantly expanding. That expansion process started even since the Big Bang kicked in. In fact, the ‘bang’ wasn’t an explosion, despite the common belief, but only the start of the expansion process itself.
What exactly could have triggered the Big Bang so that the Universe will start expanding? Is there ever an end or objective purpose for the expansion? While humanity still needs time to answer such huge and primordial questions, first of all, we have to understand exactly how fast the Universe is expanding. According to a new study that InterestingEngineering.com tells us about, we may finally have a definitive answer.
The standard model is correct
To understand how fast our Universe is expanding, the scientists used two different methods and also found two slightly different answers. Therefore, the “Hubble tension” managed to divide astrophysicists into two groups: some that believe the difference is pretty much meaningless, and those who think that we need new scientific explanations to explain the difference, as it shouldn’t be neglected. But the new study claims that the difference may not be that different after all.
The rate at which the Universe is expanding is scientifically known as the Hubble constant. In one of the methods used by astrophysicists, they analyzed the cosmic microwave background radiation, meaning the leftover from the Big Bang itself. Therefore, the scientists concluded that the Hubble constant is 67.4 kilometres per second per megaparsec (km/s/mpc).
By using the second method about 20 years ago, such as looking at Cepheid stars using the Hubble Space Telescope and measuring how fast they’re moving away from us, scientists discovered that the Hubble constant is a bit higher: 72km/s/mpc. The same scientists decided to cross-check the method in 2019 by taking a look at red giant stars. They measured the actual peak brightness, and were thus able to determine the distance to the space objects. By further using four different measurement methods for various stars and galaxies, they were accurate with one percent error. By using red giant stars to find the Hubble constant, its value was found to be 69.8 km/s/mpc, meaning much closer to the value obtained after measuring the cosmic microwave background radiation.
Scientist Wendy Freedman explained as cited by InterestingEngineering.com:
The Cepheid stars have always been a little noisier and a little more complicated to fully understand; they are young stars in the active star-forming regions of galaxies, and that means there’s potential for things like dust or contamination from other stars to throw off your measurements.
Freedman also added as cited by the same publication:
There is still some room for new physics, but even if there isn’t, it would show that the standard model we have is basically correct, which is also a profound conclusion.
The new study will be published in Astrophysical Journal.