Image credit: 'First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results'
The green and blue shapes are new to physics, the orange and red shapes had already been discovered. The orange shape is the WMAP Cold Spot, a giant void.
Fenney et al. will soon be able to study these regions further by applying their algorithm to data compiled by the European Space Agency's Planck satellite, WMAPs successor which was launched in 2009. The Planck satellite is ten times more sensitive than WMAP and it has three times the resolution although its data is not due to be released until 2013.
A Multitude of Multiverses
The theory of eternal inflation is not the only theory that predicts a multiverse. There are at least seven types of multiverse predicted by modern physics and they are all compatible. Swedish-American physicist Max Tegmark states that "the key question is not whether the multiverse exists but rather how many levels it has".
Multiverse Level #1
Space is extremely large and matter can only take a limited number of forms before things start to repeat.
The Star Garden
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Image credit: Eikongraphia
Earlier this month physicists working in the UK and Canada provided evidence that there may be universes beyond our own. Their research - co authored by Stephen Feeney, Matthew Johnson, Daniel Mortlock and Hiranya Peiris - is to be published in the journal Physical Review D but can be read for free here.
Fenney et al. have found a way to search for evidence of the multiverse predicted by eternal inflation theory. Eternal inflation refers to the inflationary epoch of the big bang, a period when spacetime expanded faster than the speed of light. This idea was first proposed by American physicist Alan Guth in 1980. Whereas standard inflation has a beginning and an end, eternal inflation does not necessarily have a beginning and continues forever. This is because inflation can end in one region of spacetime, forming a 'bubble universe' like our own, but continue in other regions, creating an infinite amount of other 'bubble universes'.
Eternal inflation is a consequence of a number of modern theories including string theory which predicts that some of these universes will have different physical constraints to our own. This means there could be universes with more or less dimensions or a higher gravitational constant than ours. By 2007, Guth stated that "essentially all inflationary models are eternal...if it starts anywhere, at any time in all of eternity, it produces an infinite number of pocket universes." Although these 'pocket universes' may have once been close enough to collide, no one could travel between them, even if they travelled at the speed of light forever. This is because the space between universes is expanding even faster than that.
Eternal inflation theory predicts that collisions between universes leaves distinct patterns in the temperature distribution of the cosmic microwave background radiation - light that was created shortly after the big bang. NASAs WMAP spacecraft has been measuring these changes since its launch in 2001 and Fenney et al. have created a computer algorithm which can identify the predicted effects of a collision from amongst this data. Although they do not yet have enough evidence to show that eternal inflation theory is correct, they have found four regions which are not consistent with the standard theory of inflation. These are shown at the bottom right of the picture below.
This idea is based on the assumption that space is indeed this large, and that matter is distributed in a roughly even manner. Both of these assumptions can be tested by measuring the temperature distribution of the cosmic microwave background radiation and data from WMAP suggests that this is the case. This is perhaps the least controversial theory that predicts a multiverse.
Multiverse Level #2
The theory of eternal inflation predicts that Multiverse #1 is one of many 'bubble multiverses'.
All theories of eternal inflation predict that there are other 'bubble universes' and string theory predicts that some of these will have different physical constraints to our own. This is the multiverse that Fenney et al. are searching for.
Multiverse Level #3
String theory and black hole thermodynamics suggest that Multiverses #1 and 2 are holographic.
The holographic principle uses string theory and black hole thermodynamics to show that the three dimensions we experience are actually projected from a two dimensional surface. This means that there are identical copies of Multiverses #1 and 2. String theory was devised to reconcile quantum mechanics and general relativity. It is not yet proven but provides unique predictions that we will one day be able to test for.
Multiverse Levels #4
String theory predicts that Multiverses #1, 2 and 3 could all exist on one 'brane' amongst many.
String theory states that subatomic particles can be modelled as one dimensional objects known as strings. All subatomic particles are modelled by different strings oscillating in different ways. Strings of larger dimensions are known as branes. String theory predicts that universes take the form of D-branes which are formed when p-branes collide. p-branes may be colliding all of the time, creating multiple big bangs.
Multiverse Level #5
Quantum mechanics implies that there are an infinite amount of #1, 2, 3 and 4 Multiverses, many of which exist in the same spacetime as our own, we are simply unaware of them.
The Everett, or many worlds, approach to quantum mechanics predicts that everything, even Multiverses #1, 2, 3 and 4, obey the laws of quantum mechanics. This means everything that's physically possible actually happens. Although this multiverse theory is often considered the most controversial, some argue that we have more evidence for the Everett approach than any of the other multiverse theories. I have written extensively about the Everett approach here.
Multiverse Level #6
Physicists predict that some of the intelligent beings in Multiverses #1, 2, 3, 4 and 5 will be able to create artificial realities inside of computers that will be nearly identical to our own.
A number of physicists and mathematicians have argued that we will one day be able to use quantum computers in order to create virtue reality environments that are indistinguishable from real life. We may even be able to create virtual copies of people that think and feel like 'real' people. This makes it possible that we are currently living in one of these simulations. I have written more about this here.
Multiverse Level #7
Beyond Multiverses #1, 2, 3, 4, 5 and 6, the ultimate multiverse is composed of nothing but mathematics and so multiverses of every conceivable shape exist.
As our understanding of the world has developed, mathematical models have become increasingly accurate. This has led some to argue that a complete mathematical description of the universe would be a perfect description. The idea that the universe is really a mathematical object is attributed to Ancient Greek philosopher Plato and is echoed in the intuitive idea that mathematical laws are discovered rather than invented.
Tegmark argues that if the universe is mathematical then "complete mathematical symmetry" suggests that universes of every possible shape must exist. This multiverse theory suggests that there are other universes that obey different physical laws to our own. Some may not obey the laws of quantum mechanics, relativity or string theory. Some universes are simply empty two dimensional triangles and some are shaped like cups of tea.
What does all this mean?
The idea that there are other universes may seem far-fetched, but all of these theories are either based on widely accepted physical theories such as relativity and quantum mechanics, or on theories that make unique predictions which we will one day be able to test.
The fact that people find the concept of a multiverse so bizarre does not make it any less likely to be true. We only have an intuition for the physics we needed to survive during the period in which we first evolved. Every time that we have looked at things which are larger, smaller, faster or more massive than that we have had to confront long accepted assumptions about the world. The concept of the multiverse is perhaps no less strange to us than the concept of a moving Earth was to people in the 1500s. If we are going to use science to confront the true nature of reality, then history has taught us that we should not expect mundane answers.
Related articles; Socrates, Plato and Aristotle, Einstein's theory of General Relativity, The Big Bang, Quantum Mechanics, Everett's Many Worlds Approach, Evidence of Parallel Worlds, Quantum Computers and Artificial Reality, Freewill and Parallel-selves and Should we trust Science?
References
Feeney, S., Johnson, M., Mortlock, D. and Peiris, H., 2011, 'First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results', Physical Review D, Vol.84
Feeney, S., Johnson, M., Mortlock, D. and Peiris, H., 2011, 'First Observational Tests of Eternal Inflation', Physical Review Letters, Vol.107
Guth, A., 1981, 'Inflationary Universe: A possible solution to the horizon and flatness problems', Physical Review D, Vol.23
Guth, A., 2007, 'Eternal Inflation and its Implications', Journal of Physics A: Mathematical and Theoretical, Vol.40
Tegmark, M., May 2003, 'Parallel Universes', Scientific American, pp.40-51
13th August 2011 0 Comments