A universe that is fine-tuned is a universe that is designed well-enough to support life. Life as we know it would be impossible if certain things in physics were slightly different. Our universe is fine-tuned for life, and this is seen as not likely. This is because many things have to come together in a certain way. One explanation for this is the anthropic principle. This means that the universe supports life because we wouldn't be here to wonder that if it didn't. This usage of the anthropic principle is tautological. This means that it is true because it is true.
Another explanation for this is the teleological argument. It is also known as argument from design. This means that an intelligent creator created the universe. It is still unknown if the universe created itself or if it was created by someone or something else.
Martin Rees had six of these examples. Some of these are:
- When four protons become helium, 0.7% of their mass is changed into energy. If it was 0.6%, only hydrogen could exist. If it was more than 0.8%, no hydrogen would exist because it would have all been fused shortly after the Big Bang. Some other physicists disagree with this.
- There are 3 dimensions in spacetime. If there were 2 or 4, life could not exist. If there was more than 1 time dimension, life could not exist either.