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Science fiction writers have always had a special place in their hearts for parallel universes. Also known as the Multiverse Theory, the idea is mind-boggling when taken to its extreme. It states that there are an infinite number of universes making up all of physical reality. Our world is one of many.
While some worlds will be virtually identical to ours, others will be unrecognizable – containing space, time and bizarre forms of exotic matter. In effect, the Multiverse caters for every possible outcome of every single event.
“Your idea is crazy,” the physicist Niels Bohr once said. “But is it crazy enough to be true?”
Today, scientists seem to think so.
This is possible due to the theory of quantum mechanics, which dictates that energy and matter can appear anywhere out of the space vacuum because of what is known as a quantum fluctuation. Cosmologists say that this is how the Big Bang came to be and that the same could have happened to form other universes as well.
Bubble Theory explains how these multiple universes exist and interact. It posits that each universe is an enormous membranous bubble, among an infinite number of other bubbles, rippling through the eleventh dimension. This fits well with the established idea of cosmic inflation.
Astonishingly, some quantum physicists believe that some of these bubbles exist less than a millimeter away from ours, in another dimension. Forget the search for alien planets – we may just be rubbing shoulders with infinite versions of ourselves in parallel worlds.
One major supporting factor for this is that gravity is a relatively weak force compared to other Earthly forces, and should be far stronger. Therefore, it is thought to be leaking through from these other dimensions.
In his article ‘How we could see another universe”, appearing in the June 2009 Astronomy Magazine, Steve Nadis examines in depth how it would be possible to detect other universe bubbles.
“Our universe may form one bubble of many in a vast multiverse. Cosmologists are now searching for signs of another bubble universe colliding with ours,” Steve Nadis says. If this were to happen it could be quite destructive, but if the collision happened far enough from the area of the Solar System, then it could be probable that scientists would be able to find evidence of it, Nadis further states.
The idea for bubble universes comes form cosmic inflation, the notion that an explosive brief growth during the Big Bang is what came to be the vast and expanding universe of today. Cosmologist and inflation theory pioneer Alexander Vilenkin of Tufts University says that there is a high-energy vacuum during inflation that drives the universe’s expansion.
This fast and vicious growth phase stops, but the bubbles retain the ability to continue their expansion at a slower pace. The inflation then never ends, it stops in one region and starts in another. This is possible because of the odd property that the material driving inflation decays, forming lower energy bubbles, more slowly than it expands.
This causes a never-ending expansion, which keeps spinning endless bubbles. These bubble universes will all have different energies and physical features, so they may not all hold the needed materials for life to form.
The mechanics behind inflation are not yet fully explained and it may take a theory of quantum mechanics and general relativity to fully understand it. But it is nonetheless a successful theory that is said to be one of the best ideas in cosmology to come for a long time.
Scientists believe that the CMB, cosmic microwave background, is the best bet for clues. The CMB was emitted some hundred thousand years after the Big Bang and it is pretty smooth and uniform throughout the universe. Thus, a collision with another universe bubble would definitely deviate the CMB signature in the locality of the crash site.
Physicist and cosmologist Anthony Aguirre at the University of California, Santa Cruz says that if such a deviation would be so apparent as having rings of different temperatures running around a symmetric part of the sky, it would be hard not to interpret that as another bubble universe colliding with ours.
Many scientists remain skeptical of such findings because they believe that inflation can actually work against these theories.
To make the explanations of the physics on this short, they believe that the number of observers that could detect a collision are infinite and infinite is also the number of observers that could not, Astronomy’s Steve Nadis concludes.
Further, the chance of seeing the effects of such a collision would be very small because they could remain hidden from possible observers due to the size of the universe.
However, scientists also have a more feasible probability that narrows down to three numbers. Some equations that involve the number given by the ratio of the vacuum energy multiplied by the rate at which the bubbles form could give the answer to how many, if any, bubble universes could be observed.
Unfortunately that product is very hard to attain because cosmologists don’t really know the exact numbers. At least the possibility remains and scientists will continue to check the CMB data for any telltale disks that will confirm a collision with another universe.
Much of modern physics is based on pure theory, making it very difficult to test these hypotheses in a real experiment.