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Thursday
Oct142010

Frying Brains…  

 

This post is intended to take you all the way to the edge of sanity; so dim the lights, put on some good new age music, and brace yourself… String Theory starts with the premise that the building blocks of matter and energy are not necessarily particles - that is point-like packets of energy. The theory proposes that of the three pillars of modern physics - gravitation, quantum mechanics, and relativity - the first is really not formulated properly, but the last two are right on target. The implication is that this is the cause of the difficulty of putting gravity and quantum mechanics together: basically, blame it on gravity! The theory also proposes that all physical observables should be computable from scratch; there are no magic numbers floating around in Nature, we should be able to understand every bit of observation. The principles I just listed, while frugal and rather general, are extremely powerful. I can argue that this is all that is  needed to develop the entire field of String Theory. The idea is that anything logically consistent within this framework is fair game and is to be allowed…

After a couple of decades of hard work by a group of several hundred overworked string theorists, we now have a remarkably detailed picture of what this String Theory thing is - but the full picture is still incomplete. We are able to show that quantum mechanics can be married successfully with the gravitational force. And many outstanding puzzles of theoretical physics get very interesting resolutions, from strange black hole physics to particle physics botany. But the full narrative is still being written with research in progress, and we cannot tell yet whether this theory - in its current incarnation - is to survive the ultimate tribunal: experiments and measurements. However, given the successes of the theory, it is now highly likely that some of the new revolutionary ideas the theory has introduced into discussion are to survive within the ultimate future framework of fundamental physics.

As a result of all this, String Theory requires that the world has ten space dimensions… see my previous post about compactification to see an alternative mechanism - to the one I will discuss in this post - through which this setup can still lead to the observation of only three space dimensions. Since the building blocks of the theory are not necessarily point-like, one finds that these can be in the form of tiny strings; or even in the shape of membranes… in the full 10 dimensions, you can even have a three-brane or brane for short… that is an object like a membrane but extended in three dimensions instead of two. You won't be able to visualize this (I hope), but you can view a cartoon depiction of a two dimensional membrane: it is now a good time to play the first video attached to this post to make things a bit less abstract…

And here comes the big punchline: in the context of this theory, our universe can be a three-brane… we are living in the fabric of the brane that is flopping around in a higher dimensional space. Imagine the first video of this post with a population of insects living on the membrane that is flopping around. That is us; except its a brane extended in three space dimensions instead of two, and hence we perceive the world in 3D! We are confined and welded to the three brane. In fact, we are made of the stuff of the three brane: the ripples on the brane represent nothing but the matter in our universe, including ourselves! We can show from string theory that the way these ripples behave, scatter off each other, and evolve, is indeed in tune with all the stuff around us: electrons, atoms, all the forces of Nature that we have measured… This is simply shocking; that a picture of a brane flopping around in a higher dimensional space appears from the perspective of things living on the brane as the universe we actually see today… But it gets more interesting…

If we are a three brane flying and rippling through some higher dimensional space, there may very well be other branes floating around nearby: other universes. Check out my post on the Multiverse picture for more about this topic. Let's get all the way to the edge now. Imagine a gas of universes: instead of molecules making up this gas, it's branes all over! Each brane is a universe with miserable beings living in it. As is typical in a gas, constituents of the gas will frequently collide. So, imagine another brane, our evil twins, on a collision course with our brane, our universe. Time to play the second video clip attached to this post. What would we then see from the perspective of our universe during this collision process? String Theory tells us that we would observe a violent exponential expansion of our universe… well, that's what we actually observe today (see post on inflation)… the endpoint of the collision in the second video corresponds to what I referred to as "graceful exit" in the previous post; the collision itself: the Inflationary Epoch.

A reference article: James M. Cline (2007). Braneworld Cosmology PoSstringsLHC:011,2006 arXiv: 0704.2198v1

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