Why do we Need a Unified Theory?

[dimensionless]

Main Question or Discussion Point

I've been reading about string theory and extra dimensions that have been compactified. ..Anyway, why is there a desire to unify the various forces?

 

[Nabeshin]

Our current theory (standard model) makes no sense at high enough energies. Therefore we seek to expand the scope of our physics by creating this unified theory, which will not break down until a higher energy (or at all, perhaps). Practically, this allows us to look farther back into the earliest moments of the universe. Unifying the forces is an interesting thing for a physicist in and of itself, but it also should prove to be very useful in exploring this high energy realm.

 

[Chronos]

It's what we do. Understanding the universe is all about science.

 

[Chimps]

Exactly as Chronos says, it is scientific endeavor to find out how our universe works. We have already managed to unify some of the fundamental forces so why not all the rest?

What is the alternative? Should we just draw a line and say God did it?

 

[Chalnoth]

The progress of physics has always been a progress of unification: showing that apparently very different phenomena are just different parts of the same whole. Newton showed, for instance, that it is the very same thing (gravity) that makes rocks fall and keeps the Moon in orbit. Later, Maxwell showed that the forces that previously people thought were different things, electricity and magnetism, were but different aspects of the same thing.

Now we believe that all of physics stems from one single mathematical structure. Basically, it has to, because a mathematical structure is nothing more and nothing less than a fully self-consistent system. So unless you want to entertain the possibility that our universe contradicts itself, there must be some mathematical structure that describes our universe, and our preference tends to be towards simpler structures as being more likely.

Perhaps a bit more telling is that if you look at our two main prevailing theories: the standard model of particle physics, which governs the strong, electromagnetic, and weak forces, and General Relativity, which governs gravity, are fundamentally incompatible. That is, we can talk about the strong, electromagnetic, and weak forces in the same language. But when we try to talk about GR in the same way, we get inconsistencies. Similarly, if we try to talk about the three quantum forces in the language of GR, we get different inconsistencies. So we expect that there is one consistent picture that let's us talk about both gravity and the three quantum forces in one language, we just don't know what that picture is yet (though Loop Quantum Gravity and String Theory are attempts to do just that).

 

[dimensionless]

I just get the sense that this is potentially something much more complicated (or maybe even much more simple) than we realize. The fact that we are unable to find 90% of the mass in the universe implies to me that our entire understanding of the workings of the universe is massively deficient.

The introduction of compactified dimensions seems to make the model more complicated, as it raises the question of why some dimensions are compactified and others are not. I'm in no way an expert in this area, so feel free to fill me in.

 

[Chalnoth]

I just get the sense that this is potentially something much more complicated (or maybe even much more simple) than we realize. The fact that we are unable to find 90% of the mass in the universe implies to me that our entire understanding of the workings of the universe is massively deficient.

Don't be fooled by the amount of stuff. The baryonic part has physics that is vastly, vastly more complicated than the rest, so as far as the physics is concerned, we know a heck of a lot more than this simple counting of energy densities implies.

The introduction of compactified dimensions seems to make the model more complicated, as it raises the question of why some dimensions are compactified and others are not. I'm in no way an expert in this area, so feel free to fill me in.

Well, string theory requires a specific number of dimensions, and that number is more than the dimensions we observe. So this necessitates that those dimensions be difficult to observe. There are two known ways to do this:

1. The extra dimensions could be small. If the extra dimensions are small enough, we wouldn't yet have observed them.

2. We could be stuck on a brane, unable to move off of it. The other dimensions could well be quite large, but we still might not be able to detect them if we can't move off of our 3+1 dimensional brane.

Also, a combination of the above two options is possible.

Where string theory is concerned, I think we generally expect that lots of stuff is allowed to happen in string theory (work remains to be done on the implications of string theory: it's not an easy thing), but we end up with 3+1 apparent dimensions because it is only when things turn out in that way that life is possible.

 

[really]

I think we will find a very elegant and very simple answer once people accept that some of the things we are taught are not true. They are just theories after all but it seems that we accept them as laws. This is preventing us from finding the true answers. We will have to question all things we think we know to come up with a theory of everything. The key is to get less complicated in the answer not more complicated.

 

[Chalnoth]

I think we will find a very elegant and very simple answer once people accept that some of the things we are taught are not true. They are just theories after all but it seems that we accept them as laws. This is preventing us from finding the true answers. We will have to question all things we think we know to come up with a theory of everything. The key is to get less complicated in the answer not more complicated.

There is a tendency to think that knowledge can be a crutch. It isn't. It's a staggeringly-powerful tool. The truth of the matter is that if you don't know about what people have learned before, about what they have discovered works and doesn't, your chance of coming to something even remotely accurate is slim to none.

But perhaps more importantly, learning about what people have thought of before you is actually a fantastic way to generate new ideas. Knowledge really isn't a crutch or a limiting thing at all, but rather fuel for creativity.

And if you think that the things we know today are incorrect, you first need to point out what is incorrect, present convincing evidence or argument that it is incorrect, and, perhaps even more importantly, show where it breaks down. Because the fact is that we know that all of our current physical theories are correct in that they are good approximations to the behavior of our world. We know they must be wrong somewhere, but the trick is finding out precisely where reality starts to deviate from our current theories.

 

[inflector]

I think we will find a very elegant and very simple answer once people accept that some of the things we are taught are not true. They are just theories after all but it seems that we accept them as laws. This is preventing us from finding the true answers. We will have to question all things we think we know to come up with a theory of everything. The key is to get less complicated in the answer not more complicated.

Do you have some suspicions where the current theories break down? Or some idea of a simpler theory that works? Any papers you think look promising?