Almost all the ground-breaking ideas look ridiculous at the start, same thing happened with concept of Multiverse. A recently published research paper by a team of physicists revolves around the same idea. Alexander Vilenkin, co-author of the paer, professor of physics and director of the Institute of Cosmology at Tufts University said: “Fifteen years ago, when you talked about the multiverse, the attitude of many physicists was just ridicule, but there has been a great change in attitude.”
The concept of a multiverse is debatable and, at times, argumentative. Today, many scientists are understandably doubtful about this concept. A few even reject the notion completely. But for others like Vilenkin, the arguments for the multiverse are so persuasive, they inspire others to think about it. Vilenkin, who introduced the idea of quantum creation of the universe from a quantum vacuum believes that there could be infinite universes jam-packed with the different versions of ourselves.
Another idea is also famous among physicists that the Big Bang might not be the singular creation of all space and time. There may have been other circumstances creating other universes: a multiverse. Same as almost 100 years ago there was the concept that Milky Way is the whole universe, then it was discovered that many other galaxies exist outside the limits of our home galaxy. Vahe Petrosian, a Stanford professor of physics and of applied physics said “What lies beyond the visible bounds of our universe? When I teach elementary courses, I usually say the universe is everything that there is, If you go to the edge of it and there is still some more, that is part of the universe, too”.
In late 2015, Vilenkin and his colleagues proposed another way to determine if the multiverse exists: black holes. Vilenkin says that there is a fair possibility that bubble universes were shaped inside of the visible universe during the Big Bang. Many of these universes warped up and made black holes. If the black holes are big enough, they may have expanding universes inside of them, and these expanding universes would be connected to the visible universe by wormholes.
About 13.8 billion years ago Big Bang happened, a really hot, compact phase when the universe started expanding. But there is also a universe that is restricted by what people can see: the visible universe. Everything in the visible universe has to be younger than that. But, hypothetically, researchers are uncertain that the universe seen with telescopes, what we see may not the all that is there.
Petrosian said “You say this is the beginning, and then you ask, ‘What was before that?’ If you go to some edge, there is always the question, ‘Is there something beyond that edge? Say, what are the possibilities, what happens if these bubbles interact, what sort of information it will give us, once a reasonable idea comes, you can never say it’s wrong. This is not too crazy. We will probably never have answers to these questions, but it is important to ask them. So we do ask, and sometimes we are successful.”
Inflation would thus leave behind a population of black holes with a telltale range of masses. In principle, by measuring the ripples in space and time produced in black hole collisions—like the gravitational waves discovered by LIGO last year astronomers can take a census of black hole masses and see if they were created by inflation, which would imply the multiverse.
But there is also a universe that is limited by what people can see: the visible universe. Around 13.8 billion years ago there was a Big Bang, a really hot, dense phase when the universe started expanding. Everything in the visible universe has to be younger than that. But, theoretically, people suspect that the universe seen with telescopes – what we see within the horizon of the Big Bang may not be all there is.
Petrosian said “You say this is the beginning, and then you ask, ‘What was before that?’ If you go to some edge, there is always the question, ‘Is there something beyond that edge?” The theory of eternal inflation, proposed in part by Vilenkin, could begin to answer these questions. Eternal inflation says that space is always expanding overall, but some pockets of space will expand and create universes while others stop expanding. The universes that form are called “bubble universes” because they bubble up where energy is being concentrated.
“We used to think that beyond the visible universe there was simply more of the same,” said Vilenkin. “More planets and stars and galaxies. But other universes may have different physical laws.” Not all bubble universes are created equally. If the mass of a proton or electron were tweaked, the universe might not have stars, planets or life. Some of the universes expand, contract and collapse in a very short time before forming everything. Some universes are like ours.
It’s possible that sometimes these bubbles interact, and that one will interact with our bubble and produce observational evidence. “Say, what are the possibilities, what happens if these bubbles interact, what sort of information will it give us,” says Petrosian. Despite the similarities between Vilenkin’s theory and the film Interstellar, many scientists have hope for the multiverse theory. “Once a reasonable idea comes, you can never say it’s wrong,” affirms Petrosian. “And this is not too crazy. We will probably never have answers to these questions, but it is important to ask them. So we do ask, and sometimes we are successful.”
Source: Stanford University and NPR Science Friday
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