In this reading of The Fabric of the Cosmos, Greene goes even deeper into the concept of entropy. He starts off the chapter by giving an example of an ice cube meting to explain entropy. If you watched an ice cube melt, you would know that it began as a fully formed cube and slowly melted and transformed into water over time. Entropy would say that as sure that you are that the cube was fully formed in the past, it was actually less formed because of entropy in the past and future. When I think about entropy in terms of the universe, disorder will be more likely in the future and the past of any given moment. The conclusion that the book came to is that the universe was in the ultimate low entropy state before the big bang and moves toward higher entropy in the future. This concept makes more sense to me, but does not agree with the Second Law of Thermodynamics.
In this reading of the fabric of the Cosmos, Entropy is introduced. High entropy is defined as something that can happen in many different ways while low entropy is the opposite. But how does this relate to our physics class? The answer is that it is involved in the arrow of time and the second law of thermodynamics. The Second Law of Thermodynamics states that physical systems tend to evolve towards a state of higher entropy. This can be involved in time because as we move into the future, there is higher entropy throughout the universe. Because of time reversal symmetry, the Second Law of Thermodynamics can also be applied to the past. Therefore, now is always the moment of least entropy. This is a weird thought and one that is not easily comprehended. Something I wonder about the movement of entropy in time is what the higher number of possibilities is moving towards.
In this reading of The Fabric of the Cosmos, Greene asks the question “Does time have a direction?” We expect and experience certain things happening in a specific way, but does it have to happen that way? Is it possible for it to happen another way? For example, if i dropped an egg on the floor, would it be possible for the egg to reform and come back to my hand? It would seem like that would be impossible, but according to the time-reversal symmetry nothing says that it can not happen. The time reversal symmetry says that if something happening in the present occurs, then the opposite of that thing can also happen. An easy way to imagine the time reversal symmetry is to imagine watching a film on a projector, stopping that film, and then reversing the direction of that film. I think that the concept of time reversal symmetry makes sense, but I do not understand what would be needed for the direction of time to be reversed.
Chapter five of Greene’s Fabric of the Cosmos deals with the flow of time. The book asks the question “Does time really flow?” It certainly seems like times flow from the human perspective, but the book says that there is no compelling evidence to prove that time does flow. The concept of a “now moment” is talked about consistently throughout the chapter. A now moment is everything that happens at exactly this moment. A good question regarding the past is does the past actually exist. If the past does not exist, the chance of time travel in the future is likely impossible. We have learned about the reference to time being a loaf which is cut diagonally at every moment. What would a parallel slice of the loaf then become? Something would have to be constant for the slice to be parallel but I can’t seem to wrap my mind around what that is.
In this reading of the Fabric of the Cosmos, we first learn of the results of Bell’s experiment. Instead of the results being five-ninths which would have proved that the particles had a pre-determined spin, the results were almost exactly fifty percent, proving that the spin on the particles were actually random. I find it easier to agree with Einstein’s idea of having some unknown factor and that the particles do have predetermined spin, but Bell’s experiment proves that the particles do have random spin. Another question that I have about the quantum view is how can just observing one particle affect another? I understand that two particles can have opposite spins, but how can the observation of one f those particles change another? The book gives no explanation, saying that after 70 years, we still have no explanation as to why the observation of one particle can affect another. The whole idea of entanglement of particles throughout space opens the door to plenty of opportunities if we can fully understand it. For example, could instant transportation or time travel be possible through entanglement? Perhaps.
In this reading of the Fabric of the Cosmos, the question relating to whether or not the uncertainty principle also relates to reality is asked. It does not make much sense to me that the uncertainty principle could relate to, for example, the speed of a baseball. The book later on explains this by saying that while particle qualities are not definite, relationships between particles can be definite. After this explanation of the uncertainty principle in reality, I am even more confused about the uncertainty principle. It just does not logically make sense to me. Later in the chapter, John Bell is introduced. He said that if there are more than two qualities that fall under the uncertainty principle, then none of those qualities can be definitively known. The hidden variables in the uncertainty principle enable me to understand the uncertainty principle better. It makes sense that something new still needs to be learned in this whole idea of uncertainty.
In this reading, I learned that it is impossible to pinpoint the location of even a single particle in the universe. This concept is because all particles in the universe have wave like qualities. While we can not ever pinpoint the exact location of a particle, we can mathematically predict the location at which that particle will be. I think it is very interesting that we can never know the location of a particle. According to Einstein, a particle does not ever have a definitive location. I also find this interesting because even though we do not know the location a particle is at, I would still think the particle has a location. Another important concept in this reading involves the uncertainty principle. The uncertainty principle says that if we know some quality about a particle, we can not know another similar particle of that same particle. While this explanation explains why we can not pinpoint a particle, it just does not logically make sense to me.