Have you ever wondered how the universe would end? Speculations can be made, but how would an actual physicist describe the end of the universe as? Well, search no further, for Brian Greene, theoretical physicist and an inspiration for pursuing physics, gave a lecture at Arizona State University on his book titled “Until the End of Time”, in which I gained insights on how a physicist actually thinks. Dr. Greene explored questions about our existence using the concept of the three Es: Evolution, Entropy, and Eternity. The depth of control physics has over the world is absolutely flabbergasting - it is perplexing to just think about how our species has reached this point of time that we can push boundaries of something we were never supposed to. We evolved our brains for survival in the wild and we are at the point where we are finding things about the universe that would not help in our survival in our day-to-day life. For example, figuring out how the big bang happened is not going to save us from a lion waiting to pounce. We are way out of our league, and this fact fills me with pride and joy.
Let's go over the three Es, beginning with evolution. When we hear the word "evolution," many of us think about Charles Darwin’s theory of evolution. However, that’s not all there is to it. We tend to think about evolution as if it is only for living systems, when in fact, it has occurred for everything in existence.
This process can be traced all the way back to atoms. Consider a scenario at the dawn of the universe where a unique molecule, composed of four distinct types of atoms, exists. Assume that these molecules catalyze the other atoms to build identical molecules. However, the rate of their multiplication is pretty slow. Now, suppose that there is a disturbance, due to any reason, and instead of the four atoms making the molecule, one of the atoms gets replaced by a different atom. The rate of multiplication of these new molecules is faster than the older molecule. As a result, these molecules will start taking over and dominate the older molecule. Hence, complex structures evolve through this process.
The next term, Entropy, is a particularly interesting concept. Entropy, in a nutshell, can be stated as the "order of chaos." This is not the whole explanation of entropy, of course, but it is the simplest way to make sense of it.
Let's do a thought experiment: suppose there is a very messy room with books, toys, etc., spread around the room. If I rearrange the room and change the position of one or two of the books (without organizing them) and some toys, you will not notice the difference. It will still be a messy room to you. The number of ways I can rearrange the room while it still looks messy can be called Entropy.
Entropy is a very important phenomenon in physics and chemistry. According to the laws of thermodynamics, entropy always wants to increase. Why? Because the number of ways a gas (or any system) can be messy is way more than the number of ways it can look ordered, a system always tends towards a higher entropy.
So, there’s this tug of war between Entropy and Evolution, where entropy leads us to a more disordered system and evolution leads us to a more refined system. This steers us to the third E, Eternity. Humanity still does not know what the end of the cosmos will bring us, how the universe will end, if it does at all. Dr. Greene believes that the universe will end in a big freeze (or heat death, which ends up being the same concept). When the universe, at its end, stabilizes the temperatures, it is the same temperature across the whole universe, and this is called the heat death. But since the temperature would tend to be very low, it is also pretty much what the big freeze would do.
However, since the end is so far away, we would definitely not be around to witness it. To help us comprehend how distant it is, Dr. Greene uses the analogy of the Empire State Building.
Imagine that every floor of the Empire State Building represents time in years, and as you ascend, the time in years increases by a factor of 10. For example, the first floor would represent 10 years from the Big Bang, the second would represent 102 years, the third floor would represent 103 years, and so on. Currently, we are on the tenth floor of the Empire State Building, which is to say, we are around 1010 years after the Big Bang. Even if we ascend to the 100th floor of the Empire State Building, the time is just a mere blink of an eye on the scale of the universe.
So, what is left in the universe at the very end? Well, black holes will definitely not be there, because according to Stephen Hawking’s theory of black hole decay, particles will escape them through certain quantum processes, and these bodies will eventually evaporate. By the time we reach the 100th floor, these black holes would have evaporated. The only things remaining by then will be the most stable particles. They will be floating through dark space, and there will be quantum fluctuations which will allow small energetic fluctuations to appear and disappear. Sometimes, these fluctuations can be large - rare things can happen. Rare fluctuations where energetic collections momentarily form, stick around for a certain amount of time, and then dissipate can happen en route to eternity. Now, these collections have a relatively finite number of configurations in the cosmos, and so, even though this is extremely rare, these configurations might repeat - and if that happens, the universe as we know it repeats itself.
In fact, there is this concept called a Boltzmann brain, which is absolutely fascinating, and somewhat terrifying. A Boltzmann brain is a brain formed out there in the universe which has exactly the memories I have, and thinks it is me. After all, what are memories? What are thoughts? They are made up of configurations in your brain which tell you exactly what memories you have, and what you're thinking. These configurations, at the end of time, can be attained by particles floating in the vastness of space. A Boltzmann brain can form arbitrarily many times, and so, it will form arbitrarily many times, en route to eternity. It could be literally me wondering how I arrived at the place.
Physicists try to eliminate the concept of a Boltzmann brain, because if it exists, that means that the fact that you are reading this on your device, the concepts you have learned up till now, are all false. They are all just configurations of particles in your brain, making you think that it is true, when in reality, this never happened. So, although physicists are trying to eliminate this concept to restore our confidence, we are not there yet.
This remarkable lecture fundamentally shifted my perspective on our origins. Dr. Greene’s exploration of evolution, which I had never truly considered before, opened up an entirely new world of understanding. The concept of the Boltzmann brain, discussed in the lecture hall, sent shivers down my spine. It sparked so many questions, like what would happen if two Boltzmann brains meet? Would they annihilate each other, like shown in movies, or would something different happen? If a Boltzmann brain can literally be me, there must be a Boltzmann brain out there, much much smarter than any human can even think of, and if so, is there an upper limit on the intelligence for this brain? And if our thoughts are just configurations of particles in our brains, is there something like "space" in reality, or is that also just a configuration of particles making me think that it exists? Is there an actual truth, or is truth just a fallacy, something humans jumped on to satisfy our need for validity?
The longer I think about it, the more questions I have! Quantum physics, a beautiful idea, beckons us to unravel its mysteries—it is a realm yet to be fully explored.
