A Theory Of Everything
A Theory Of Everything
The aim of string theory is to get a theory which can describe everything in the universe and explain why this is the case. Even questions as fundamental as why we live in 3 spacial dimensions, why are there 4 forces, why time goes forward etc... should have answers if we ever do reach a theory of everything.
There may be a limit to how much we can hope to know however. For example, if you are doing a mechanics problem, you need to know the initial conditions of the system, such as starting speed, forces involved and starting location, so you can do calculations to predict the future. In the case of our universe, we may have a theory that can explain things from the big bang, but what about initial conditions before the big bang? Logically it makes sense that something caused the big bang? For example, the journey of Calabi-Yau shapes as they underwent many transitions initially may be very dependent on how that journey started. If we can never know how the journey started then a theory of everything may be impossible to reach.
Another problem is that we do not even know what kind of concepts and ideas were allowed in the early universe. General relativity says that it started from infinite energy as an infinitely small point. This goes against our intuition however because infinity in physics usually means something is wrong. But we must ask if we can even rely on our intuition when describing the birth of the universe. Maybe the idea of infinite energy could somehow be allowed?
Another possible theory is that we live in a multiverse. The main point here is that as long as the other universes are far enough that light from those universes doesn't reach ours, the laws of physics can differ in any way. In those other universes there could be 1 dimension, 99 dimensions, inverse gravity etc....
Formulating a theory of everything really should be able to work for the entire multiverse but a goal like this seems well beyond the reaches of humanity. Verifying that we live in a multiverse in the first place seems like an impossible task.
The Anthropic Principle
A way to explain why we see the laws of physics we see may be down to a very simple argument. If we look at most universes in the multiverse, most won't be able to support life (or life as we know it). This means the reason why we see the laws of physics we see is because they allow intelligent life to thrive. If the laws of physics were any different, we simply would not be here to see them.Another proposal comes from the fact the conditions around a black hole and the early universe seem very similar. Some suggest that black holes are seeds for new universes. The universe that arises from entering a black hole then has similar, but not identical, properties.
The small change in the laws of physics leads to a small change in black hole optimization. This leads to a natural selection type thing. Universes that are optimal for black holes give birth to more universes that are optimal for black holes, universes that are not optimal end up not giving birth to many universes. The multiverse then becomes dominated by universes with laws of physics that optimize black hole production. It is then very very very likely that we were put in a universe that optimizes black hole production since these fill the multiverse.
This argument says that we see the laws of physics that we see simply because they optimize the production of black holes.
At the moment physicists cannot confirm any of these theories but the hope is that solving the problem of quantum gravity will shed new light on if we will reach a theory of everything and how we can get there.
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Cosmology And String Theory
Thank you for such helpful content. I’m just starting my blog and your insight is greatly appreciated.
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