The Universe Has a Cold Spot (That Can't be Explained)
The temperature is the same throughout the universe – except from in one cold spot. Scientists thought that the spot was an optical illusion, but according to a new theory, it may be evidence of a collision.
In 2015, the Planck satellite mapped out a cold spot in the background radiation of the universe. The radiation, which was emitted by the young universe 380,000 years after the Big Bang, fills the entire universe. Originally, the radiation was very energetic (or hot), but the expansion of the universe has extended the rays into much cooler microwaves with a temperature of 2.73 degrees above absolute zero. Except for slight variations of a few millionths of a degree, the temperature of the universe is generally the same, and so, the cold spot fascinated astronomers. First, they thought that the spot had been caused by a huge void
between the spot and Earth. On the way through the void, the wavelength of light is stretched, getting colder than when light travels through space with a normal quantity of galaxies. However, new observations by English scientists show that this void does not exist and so, it cannot explain the cold area.
Right after the Big Bang, the young universe expanded from the size of an electron to the volume of a football. The inflation happened extremely fast, i.e. at a speed higher than that of light, and lasted a trillionth of a trillionth of a trillionth of a second. Subsequently, the expansion continued at a slower pace.
The process is known as inflation, and cosmology rests on this one, fundamental foundation stone. However, the inflation theory involves a major challenge to our understanding of how space is organised. It predicts that inflation did not only take place in the small area that grew into our universe. Instead, the process was more chaotic, taking place in a much larger space, in which myriads of universes popped up at the same time just like popcorn in a pot of hot oil. According to the theory, billions of universe bubbles exist around our own universe – we are living in a multiverse.
For decades, astronomers have debated whether the theory’s prediction of the multiverse can be true, and now, scientists have found the first possible evidence: the universe includes a mysterious cold spot, which could be a crater resulting from a collision with another universe.
Inflation explains the universe
The inflation theory was introduced into scientists’ model of the Big Bang in the 1980s to explain why galaxies are evenly distributed across the universe. If the expansion of the universe had happened at an even pace following the Big Bang, gravity would make galaxy clusters clump together to produce major differences in the distribution of mass. The rapid inflation distributed the mass evenly from the very beginning of the universe – like when air is evenly distributed in a balloon that is inflated.
Inflation als o explains why the temperature is almost the same throughout the universe. When our newborn universe was the size of an electron, all matter had the same temperature. During the inflation, the temperature averaged out to be more or less the same no matter which way we look.
The uniform temperature can be observed from the cosmic background radiation of the universe. The radiation was emitted in the young universe, 380,000 years after the Big Bang. Before, the universe was so hot that radiation was constantly converted into matter, so no light escaped. But when the universe had grown big and cold enough for the first hydrogen atoms to form, light escaped from the matter in a glimpse. Subsequently, the universe turned dark again, as the new, neutral hydrogen atoms do not emit any visible light. The light did not return, until the first galaxies formed hundreds of millions of years later.
Decades of observations of cosmic background radiation show that the temperature generally only varies a few millionths of a degree – except in one place. In 2004, astronomers discovered a particularly cold spot in the background radiation three billion light years from Earth. The spot covers an area of five degrees of the sky and is 0.00015 degrees colder than the general radiation temperature of 2.73 degrees above absolute zero.
Until recently, scientists thought that the cold area was due to a huge void extending 1.8 billion light years between us and the cold spot. When light waves from the background radiation travel through such a void, the light waves lose energy on their way into the void, regaining energy on their way out. Astronomers compare the phenomenon to a ball that loses energy on its way uphill, rolling faster down the other side. In a stagnant universe, the light would escape the void with the exact same energy with which the waves entered. But because the universe has expanded over the 1.8 billion years that the light took to travel through the super-void, the hill on the way out of the void will be less steep. So, the light will not regain all the energy, becoming slightly more long wave and colder. Hence, scientists thought that the cold spot was an optical illusion caused by the void.
Now, English astronomers from Durham University have rejected the original explanation by showing that the huge void does not exist. There are as many galaxies between Earth and the cold spot as between our world and all other places of the background radiation. So, astronomers tend to prefer another explanation: The spot is a crater caused by a collision between our universe and another one under inflation.