Alan Guth and the Multiverse

Feature Photo: The Atlantic

The content from this article was produced by Mathilde Papillon.

On the evening of January 18, 2018, Alan Guth, a famous American theoretical physicist and cosmologist, visited McGill University to deliver a talk entitled “Inflationary Cosmology: Is our Universe Part of a Multiverse”. Over the course of his career, Guth has won several prestigious awards in physics. He currently works as a professor at MIT, and is recognized as the inventor of the Inflation Theory. Across the scientific community, it is largely agreed that the Inflation Theory is humanity’s best guess to date of how to universe came to be.

The talk took place in McGill University’s biggest Lecture hall: Leacock 132. Notably, the room was packed, and organizers had to send dozens of people home due to a lack of seating space. This talk was part of Anna I. McPherson Lectures in Physics, a series of lectures regarding hot topics in physics that McGill has taken part of for twenty years now.

Guth’s talk addressed three main subjects: The theory of inflation, evidence for such, and the resulting possibility of a multiverse. He began by making the distinction between the conventional Big Bang theory, a concept that only addresses the aftermath of the “bang”, and inflation. Inflation describes what happened during the bang. By the laws of general relativity, gravitational repulsion is theoretically possible. In this, gravity works in an opposite way to what we are all used to.

The Inflation theory states that in the beginning, matter was comprised of tiny patches of negative pressure – on the order of 10E-28 cm large – that continued to exponential expansion. The phenomena is driven by repulsive gravity.

The “second miracle of physics”, and the other main idea that is at the heart of the theory of Inflation, is negative energy. This simply states that there exists negative energy, allowing the total amount of energy in the universe to the 0. All the energy that people are “familiar with”, are counterbalanced by negative energy. It is theorized that in the beginning of time, there was an exponential expansion of both positive and negative energies.

Photo: Mathilde Papillon

Next, Guth presented evidence for inflation. He asked a series of questions that are left unanswered by the conventional Big Bang theory, and proceeded to show how Inflation can resolve or explain these gaps in the knowledge.

  1. In a macroscopic sense, why is the universe so uniform? Inflation suggests that the universe is stretched out in each region in order to accommodate specific density.
  2. Why is the universe flat? If we define Ω to be the ratio between the universe’s measured mass density and the critical mass density for flatness, we find that Ω is equal to 1 to 16 significant digits. Inflation’s gravitational repulsion drives Ω to 1, making the universe’s mass density closer to the mass density required for flatness.
  3. On a small scale, why is the universe so non-uniform? Inflation uses a quantum mechanical approach that is based on probability. Therefore, in the beginning of the universe, there is a very high chance that there were improbably, tiny fluctuations caused by gravity. These regions would be a little more dense, and have a gravitational pull that is a little stronger. This phenomenon is known as quantum fluctuations. There is evidence for quantum fluctuations in the universe’s cosmic radiation background.

After addressing these questions, Guth described the possibility of a multiverse as suggested by inflation. Assuming that inflation is correct, since the universe has started to inflate, it should inflate forever. Physicists have determined that the basis for inflation, the material with negative pressure, has a half-life, and decays. However, the rate of inflation is so high, by the time one half-life has gone by, the remaining half that is still ‘active’ has grown to be beginning than the lost half. Therefore, it is possible for the universe to inflate forever.

In the process of inflation, it is possible for pieces of inflating material to break off, creating “pocket universes” on their own. From this, it is possible that our universe is one of these pockets.

Guth kept the large audience engaged for the hour he spoke for, receiving a few rounds of applause. He closed off his talk with a question period, in which an audience member asked him what his thoughts were on the religious and philosophical beliefs that humanity holds. Guth believes that his work shows us how small and insignificant humanity is, but that humanity is important to ourselves. As such, it is important to keep building a civilization that we wish to keep living in.

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