Jasmine Thomson The Parallel Universe Theory The Parallel Universe theory has been expanded on by lots of scientists over many years. There are many different theories related to it. The ones that I am going to cover in this essay are the multiverse, the many interacting worlds theory and the bubble universe. The bubble universe and the many interacting worlds theory are both slight deviations from the multiverse theory with their own twist. The multiverse theory is the idea that there is more than just our universe in the cosmos; there are lots of separate universes all that do their own things but on the grand scale of things our universe isn’t really significant (Ellis, 2011). The multiverse theory is levels one to four, all are slightly different. Level one of the multiverse theory states that everything that is possible e.g. “configurations of particles” will have happened in one universe or another because the multiverse is “virtually infinite”. By using this theory that means that somewhere out their planets like earth must exist but because they are so far away we may never be able to find them. The reason that we are unable to see these other universes is due to the extent of our cosmic vision and because this has a limit called the speed of light we are unable to see it. (Zimmerman-Jones & Robbins, n.d.) Level two is very similar to level one except that it uses the eternal inflation theory or the expansion theory. The expansion theory has evidence that supports it, known as red shift. Red shift supports the expansion theory because as planets move away we see longer wavelengths from them, meaning that the light we receive from them is shifted into the red end of the spectrum. The majority of the galaxies we can see are red shifted and the size of their red shift is directly proportional to their distance away from us, again supporting the theory. The reason that the expansion theory works, and the universe doesn’t go from the big bang to the big crunch – this is where the universe will collapse in on itself, is because the universe is expanding fast enough, at the “critical rate”, it can actually overcome the force of gravity and will continue to expand forever (Hawking, A Brief History of Time, 2011). Level two of the theory states we will never be able to see, or contact, these universes because the universe is still expanding so they are moving further away from us. We will never be able to see them because they are moving away faster than the speed of light (Zimmerman-Jones & Robbins, n.d.). Level three is also known as the many interacting worlds theory so will be covered later on. Level four of the multiverse theory is that each different universe has different mathematical laws. This idea is based on the Mathematical Democracy Principle which is; “Any universe that is mathematically possible has an equal possibility of actually existing” Jasmine Thomson (Zimmerman-Jones & Robbins, n.d.). This means that every single universe will be immensely different, with very different life forms and environments, some may not even be able to host life. Level one, two and four are closely related to String Theory. String Theory is the first theory in physics to ever try and explain everything, with no exceptions. If they were to prove string theory it would be one step closer to proving parallel universe theory because string theory involves other universes and even higher dimensions than we already have (Bernatowicz, 2011). The reason a string is used is because everything is being explained as a moment in time and space (Hawking, A Brief History of Time, 2011). Due to the fact that the Standard Model doesn’t actually explain gravity, string theory is trying to explain a “consistent description of the fundamental structure of our universe”. It describes all particles as being a loop in a string. Each loop has a different oscillation and for each different oscillation it is a different particle. However, there is no experimental evidence for string theory (Güijosa, 2004). Level three, also known as the many interacting worlds theory, is the least to do with string theory. The many interacting worlds theory is the idea that there is an infinite number of worlds that are very similar to ours. The worlds constantly interact with each other, which is where this theory differs from level one, two and three. The reason the worlds interact is because they share the same space and time as one another. Due to the fact there is an infinite number of worlds like ours, it also means that there is an infinite number of you in each world, this is because that every decision you make results in you splitting off into many different versions of yourself in the different worlds depending on which decision they made. Although it is a relatively new theory it is being used to help reproduce lots of well- known quantum phenomena (Reyes, 2014). The other thing about the many interacting worlds theory is that for the theory to work, the wave function is a metaphorical thing rather than a literal thing. This is because they think the reason that the world splits off into multiple different ones is because the wave function collapses. Every single time it collapses it splits off again, but once they split off into their separate worlds, interaction between them is extremely rare. However, this theory helps to explain things that we, at the moment, are unable to explain. An example of this is the question what stops electrons in molecules not collapsing into the nucleus of the molecule? A hypothesis for this question is that because the other worlds share the same space and time as us, the pressure of the other worlds pushing in on our world prevents the electrons from collapsing into the nucleus of the molecule. It is, a very controversial theory because it contradicts Schrödinger’s theory because Schrödinger’s theory only works if there is an infinite number of universes, whereas in this theory there is a finite number of worlds, which makes all the equations from that theory approximate not dead on. The reason that they believe there is a finite number of worlds is because they can produce quantum effects when there is a finite number of worlds. For example, if there was forty one worlds, the effects of the double slit can be reproduced by using the idea that the “phantom photons” cause repelling Jasmine Thomson forces against one another, pushing them all in very slightly different directions. The idea of “phantom photons” is that they are particles from each of the different worlds, they are exactly the same with the exception of one or two minor things. When these particles collide they cause quantum effects (Slezak, 2014). The last theory I am going to talk about is the bubble universe theory. This idea uses inflation theory, stating that in some places in the universe it is still expanding and creating world’s like our own. When the worlds are created it all happens very quickly and they are pushed apart so that there is room for more world’s to be created. This is happening all the time. Figure 1 illustrates this point. This is one of the multiverse theories that believes in the infinite universe theory, and string theory supports it fairly strongly. The main difference between the bubble universe theory and the multiverse theory is that in the bubble universe theory, not every universe has to support life. The constants for things like gravity are different in each universe and some are just not suitable for life. Each of the separate bubbles are different universes so although we unable to do experimental tests, it is possible to do some observational tests. There are a couple of things we can do to test this theory. One is to do with statistical tests and one is to do with measuring cosmic background radiation (Vilenkin & Tegmark, 2011). Figure 1: White bubble being created, the rest expanding. The way that the cosmic background radiation work is by the reasoning that sometimes the bubbles are going to collide and if they were to collide there would be a change in the cosmic background radiation at a specific point. The collisions would cause a point of either higher or lower cosmic background radiation. If we were to observe this it would provide direct evidence of these bubble universes but we can’t guarantee that a collision will occur with our universe, or if it will occur in our time. However, scientists are on the look-out for these points of radiation just in case it does occur (Vilenkin & Tegmark, 2011). Statistical models can be used to help prove this by trying to predict different constants in various bubbles. We can then work from these and try and predict constants in our own bubble and see if they come out similar; if they do then it is more than likely that the other bubbles exist. They have already tried this technique for dark energy, about how fast it expands when the dark energy is denser and the prediction that has been made about dark energy in our universe is near enough the same as the actual values we have; this shows promise in this prediction (Vilenkin & Tegmark, 2011). In conclusion, the parallel universe theory is relatively new and is still being worked upon but I feel that it is plausible.