Tech UPTechnologyThe inflation that saved the universe

The inflation that saved the universe

It was time for the midnight foray into the world of cosmology. By eleven o’clock his son Larry and his wife Susan were in bed. He headed for his office in the guest room of his ranch house, located so close to the Linear Accelerator in Stanford, California, that he could bike to work. The rent was beyond their means, but they were only going to live there for a while: then they would go back to Cornell.

He sat. There was silence; It was the best time of day to work. He opened his notebook and wrote in small letters at the top of the page: “EVOLUTION OF THE UNIVERSE. I’d like to consider the effects of (1) a cosmological constant, and (2) freezing of degrees of freedom on the evolution of the universe.” Underneath he wrote the standard equations for an expanding universe. Around one in the morning, and after three pages of calculations, he found a surprise: almost as soon as he was born, the entire universe went haywire. Within 10-32 seconds of birth (one hundred millionth of a trillionth of a trillionth of a second) the universe had doubled in size almost 1000 times . What he had found that night of December 6, 1979, was of such magnitude that if the same thing happened to the flu virus, in a snap of the fingers it would become much larger than the current visible universe. Its discoverer, Alan Guth, called this exponential doubling process inflation.

Thanks to this strange idea Guth was able to explain one of the mysteries that brings cosmologists upside down, why the universe is so flat . To understand what this means, let’s keep in mind that the future of the universe is determined by the amount of matter in it. In essence, everything can end in two ways: in an eternal expansion or with a tremendous implosion, a Big Crunch . It is like being on the shore of a lake or in it. However, there is a very special case, which is when we are right on the edge that separates the water from the sand. To be there we have to refine our position a lot. The same goes for the universe. There is a special case that separates both destinations and corresponds to a very specific value for the amount of matter in the universe that receives the name of critical density . Well, one of the most incredible surprises that the universe has given us is that its density is exactly critical. To achieve it, it would be enough for there to be a brick of one kilo for each cube of 500 million kilometers on a side . Nothing more, but nothing less. That the universe is so well adjusted was something that had no convincing explanation… until inflation came along. Through this process of super-accelerated expansion, practically all the inhomogeneities that could have arisen with the initial explosion were erased: inflation “smoothed out” any type of curvature that existed in the universe.

Starting from this idea, other cosmologists, such as the Russian Andrei Linde, have explored other possibilities. For example, why did there only have to be one inflationary epoch that affected the entire universe? This is how the so-called eternal or chaotic inflation is born.

To understand it Linde proposes to consider the following analogy: imagine a soccer ball, with the hexagons and pentagons painted a certain color. The inflation process affects the entire universe as a whole, but differently in different regions (the hexagons and pentagons of the ball). Each of these regions grows in size, as indicated by inflation, exponentially and with no causal connection to any other polygon: everyone living in a brown pentagon will believe the universe to be brown, and everyone living in the yellow hexagon They’ll think it’s that color. Transferred to cosmology, each polygon/universe is inside the ball/multiverse and its color is the physical laws that govern that particular polygon/universe: in some they will be very simple and will not have formed stars or galaxies, in others they may not allow appearance of life while in many others, like ours, they can be truly prolific: it all depends on the type of laws that have appeared. In this way Linde and his colleague, the Russian theoretical physicist Alexander Vilenkin, give an answer to another of the great questions of cosmology: why are the values of the universal physical constants such that they allow the appearance of life? According to chaotic inflation, the answer is simple: among the entire panoply of universes born from eternal inflation, it is the one that has been assigned the values that allow the existence of life .

This is the part of cosmology that studies what happened in the first babble of the universe: a pure theoretical exercise, a search with paper and pen. We will never be able to get any direct proof of what happened; It is a time that will always be closed to us . It is certainly shocking: the largest known waste of energy is shrouded in a veil of total darkness.


Guth, A. (1997). The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Perseus Books
Linde, A. (2004) “Inflation, Quantum Cosmology and the Anthropic Principle” en John Barrow, Paul C W Davies, and C L Harper, eds., Science and Ultimate Reality: From Quantum to Cosmos, Cambridge University Press

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