Tag: Mulitiverse

[/caption]The multiverse theory is famous for its striking imagery. Just imagine our own Universe, drifting among a veritable sea of spontaneously inflating “bubble universes”, each a self-contained and causally separate pocket of higher-dimensional spacetime. It’s quite an arresting picture. However, the theory is also famous for being one of the most criticized in all of cosmology. Why? For one, the idea is remarkably difficult, if not downright impossible, to test experimentally. But now, a team of British and Canadian scientists believe they may have found a way.

Attempts to prove the multiverse theory have historically relied upon examination of the CMB radiation, relic light from the Big Bang that satellites like NASA’s Wilkinson Microwave Anisotropy Probe, or WMAP, have probed with incredible accuracy. The CMB has already allowed astronomers to map the network of large-scale structure in today’s Universe from tiny fluctuations detected by WMAP. In a similar manner, some cosmologists have hoped to comb the CMB for disk-shaped patterns that would serve as evidence of collisions with other bubble universes.

Now, physicists at University College London, Imperial College London and the Perimeter Institute for Theoretical Physics have designed a computer algorithm that actually examines the WMAP data for these telltale signatures. After determining what the WMAP results would look like both with and without cosmic collisions, the team uses the algorithm to determine which scenario fits best with the actual WMAP data. Once the results are in, the team’s algorithm performs a statistical analysis to ensure that any signatures that are detected are in fact due to collisions with other universes, and are unlikely to be due to chance. As an added bonus, the algorithm also puts an upper limit on the number of collision signatures astronomers are likely to find.

While their method may sound fairly straightforward, the researchers are quick to acknowledge the difficulty of the task at hand. As UCL researcher and co-author of the paper Dr. Hiranya Peiris put it, “It’s a very hard statistical and computational problem to search for all possible radii of the collision imprints at any possible place in the sky. But,” she adds, “that’s what pricked my curiosity.”

The results of this ground-breaking project are not yet conclusive enough to determine whether we live in a multiverse or not; however, the scientists remain optimistic about the rigor of their method. The team hopes to continue its research as the CMB is probed more deeply by the Planck satellite, which began its fifth all-sky survey on July 29. The research is published in Physical Review Letters and Physical Review D.

Source: UCL

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Theoretical physics has brought us the notion that our single universe is not necessarily the only game in town. Satellite data from WMAP, along with string theory and its 11- dimensional hyperspace idea has produced the concept of the multiverse, where the Big Bang could have produced many different universes instead of a single uniform universe. The idea has gained popularity recently, so it was only a matter of time until someone asked the question of how many multiverses could possibly exist. The number, according to two physicists, could be “humongous.”

Andrei Linde and Vitaly Vanchurin at Stanford University in California, did a few back-of- the- envelope calculations, starting with the idea that the Big Bang was essentially a quantum process which generated quantum fluctuations in the state of the early universe. The universe then underwent a period of rapid growth called inflation during which these perturbations were “frozen,” creating different initial classical conditions in different parts of the cosmos. Since each of these regions would have a different set of laws of low energy physics, they can be thought of as different universes.

Linde and Vanchurin then estimated how many different universes could have appeared as a result of this effect. Their answer is that this number must be proportional to the effect that caused the perturbations in the first place, a process called slow roll inflation, — the solution Linde came up with previously to answer the problem of the bubbles of universes colliding in the early inflation period. In this model, inflation occurred from a scalar field rolling down a potential energy hill. When the field rolls very slowly compared to the expansion of the universe, inflation occurs and collisions end up being rare.

Using all of this (and more – see their paper here) Linde and Vanchurin calculate that the number of universes in the multiverse and could be at least 10^10^10^7, a number which is definitely “humungous,” as they described it.

The next question, then, is how many universes could we actually see? Linde and Vanchurin say they had to invoke the Bekenstein limit, where the properties of the observer become an important factor because of a limit to the amount of information that can be contained within any given volume of space, and by the limits of the human brain.

The total amount of information that can be absorbed by one individual during a lifetime is about 10^16 bits. So a typical human brain can have 10^10^16 configurations and so could never distinguish more than that number of different universes.

“So, the total number of possibilities accessible to any given observer is limited not only by the entropy of perturbations of metric produced by inflation and by the size of the cosmological horizon, but also by the number of degrees of freedom of an observer,” the physicists write.

“We have found that the strongest limit on the number of different locally distinguishable geometries is determined mostly by our abilities to distinguish between different universes and to remember our results,” wrote Linde and Vanchurin. “Potentially it may become very important that when we analyze the probability of existencse of a universe of a given type, we should be talking about a consistent pair: the universe and an observer who makes the rest of the universe “alive” and the wave function of the rest of the universe time-dependant.”

So their conclusion is that the limit does not depend on the properties of the multiverse itself, but on the properties of the observer.

They hope to further study this concept to see if this probability if proportional to the observable entropy of inflation.

Sources: ArXiv, Technology Review Blog