Tufts Institute of Cosmology’s research points to the possibility of multiverse

Professor of Physics and Astronomy Alexander Vilenkin in his office on Jan. 20. Professor Vilenkin is involved in ongoing research on multiverse theory. Sofie Hecht / The Tufts Daily

It may sound like something from a science fiction movie, but recent research from the Tufts Institute of Cosmology confirms the possibility that multiple universes could exist within black holes.

Last December, physics and astronomy professor Alexander Vilenkin, also the director of the Institute of Cosmology, published a paper with his colleagues verifying the possible existence of the multiverse theory.

The theory is controversial, according to Cosmology graduate student and co-author of the paper Jun Zhang. However, he explained that this scientific skepticism makes research on multiverse theory that much more important.

“Multiverse has always been a very interesting but also controversial concept,” Zhang told the Daily in an email. “It provides an anthropic approach to some fundamental questions, like why does our universe have a such small vacuum energy. But not all the physicists buy it. Physicists who believe in multiverse try very hard to find the evidence of multiverse.”

The theory behind the possibility of multiverses existing within black holes is also known as the theory of cosmic inflation. According to Vilenkin, who is also the Leonard and Jane Holmes Bernstein Professor in Evolutionary Science, inflation is the theory of extremely rapid acceleration and expansion. The research paper he co-authored on this topic describes how during inflation, small quantum fluctuations in the universe create bubbles. Vilenkin explained that when inflation continues, these bubbles expand. Once inflation ends, however, these bubbles stop contracting, collapse and form black holes.

According to Zhanginflation theory also accounts for the creation of our galaxy.

[Inflation theory] solves many projects like the big bang theory,” Zhang said. “And an amazing thing is, it gives us a reason why we have such structures on very large scales. Because if you start from a homogenous universe, you cannot have galaxies – you cannot have this life. So you need to know where these structures come from, and inflation provides a framework.”

Vilenkin described these black holes as “fossils” of the bubbles — a cosmologist’s way of observing the bubbles in today’s observable universe. While cosmologists can only observe the black hole, expansion continues within it, forming what could be another universe. Vilenkin illustrated this process using a balloon as a metaphor.

“So you can imagine that our exterior space is like a flat surface,” Vilenkin said. “Then, you have a balloon, and the balloon grows, and the balloon is connected to this flat surface by a little – we call it a wormhole – tube. And this balloon keeps growing forever, right? But if you look at it from outside, you see a black hole.”

According to a Jan. 6 article in the New Scientist, this research also helps solve the mystery of how supermassive black holes achieved their current size. The research describes how bubbles formed later in inflation period would collapse and form smaller black holes, but bubbles created earlier in inflation period would become larger black holes with an inflating universe existing within them.

Zhang said that the next part of the research process will be finding the mass distribution of black holes.

“We want to find the black hole spectrum,” Zhang said. “So given a bubble, you want to find out the mass of the black hole because you have many different kinds of bubbles because bubbles nuclearize at different time.”

According to Zhang, he and another graduate student are coding a program to run numerical simulations of these different black holes. 

Jaume Garriga, a visiting professor from the University of Barcelona and co-author of the research paper with Vilenkin and Zhang, said that this is only the beginning of a long-term project. Garriga explained that there are many different types of black holes and different scenarios that the team must simulate mathematically to obtain more accurate conclusions. Garriga said that one of these specific cases meriting further examination is vacuum bubbles, which have more complicated dynamics than those studied previously by the team. He also stated that the research team should study the effects of radiation on black hole mass.

“To obtain an accurate determination of black hole mass, we have to simulate this process numerically,” Garriga said. “So there are a lot of odds and ends, and ramifications. There are also issues having to do with how to detect these black holes, [and] what other constraints can we impose on this model.”

While Garriga and his colleagues have their work lined up for them now, Garriga recognizes an interest in cosmology that did not exist in his earlier years of study. 

“I grew up in a time when there was not much public interest in science or in cosmology in particular,” Garriga said. “People thought, ‘this is useless.’ But these days, if you go to some social event, there’s always somebody who will ask you questions. I think probably thanks to articles, television, the ‘Big Bang Theory’ (2006 – present), all these movies [involving] black holes. People are interested; it’s part of our 21st century culture, I suppose.”

Vilenkin had a similar experience, as he also dealt with the lack of public interest in cosmology before. In a Nov. 12, 2007 Tufts Now storyVilenkin described how difficult it was to get a job in cosmology. After writing his Ph.D. on the physics of biopolymers, such as DNA, and working as a condensed matter physicist at Tufts for one year. He made a risky move applying to be a professor in cosmology. He got the job, however, and his new research puts him at the forefront of his field.

Now, Vilenkin is surprised at the growing public interest in cosmology.

“I don’t think they should be interested, but they are,” he said. “Cosmology just fascinates people. All cultures developed creation myths; everyone wanted to know where things came from [and] how the universe originated. There is a tremendous interest in cosmology, and it’s not because it is a practical value in the sense that it proves our culture of life, but it certainly satisfies our curiosity.”


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