On the left, a box with a divider in the middle has cold gas on one side and hot gas on the other on the right, the divider is opened and the entire box has gas of the same temperature. WIKIMEDIA COMMONS USERS HTKYM AND DHOLLMĬonsider the two systems above, for example. If the particles are allowed to mix, there are more ways to arrange twice as many particles at the same equilibrium temperature than there are to arrange half of those particles, each, at two different temperatures. the door remains closed than if the door is opened. What entropy actually measures, rather than some nebulous characteristic like disorder, is this: the number of possible arrangements of the quantum state of your entire system.Ī system set up in the initial conditions on the left and let to evolve will have less entropy if. Instead, what we should be thinking about is - for all the particles, antiparticles, etc., that are present in the system - what the quantum state of each particle is, or what quantum states are allowed, given the energies and energy distributions at play. While these examples all correctly identify the higher-entropy versus the lower-entropy state, it isn’t precisely “order” or “disorder” that allows us to quantify entropy. RHIC COLLABORATION, BROOKHAVENīut what does entropy actually mean? We commonly talk about it as though it’s a measure of disorder: a broken egg on the floor has more entropy than an unbroken egg on the countertop a cold dollop of cream and a hot cup of coffee have less entropy than the well-mixed combination of the two a chaotic pile of clothes has a higher entropy than a neat set of dresser drawers with all the clothes folded and put away in an organized fashion. This primordial soup consisted of particles, antiparticles, and radiation, and although was in a lower entropy state than our modern Universe, there was still plenty of entropy. gluons present didn't form into individual protons and neutrons, but remained in a quark-gluon plasma. The early Universe was full of matter and radiation, and was so hot and dense that the quarks and. But what if we go all the way back to the earliest times of all: to the very first moments of the Big Bang? If entropy has always increased, does that mean that the Big Bang’s entropy was zero? That’s what Vratislav Houdek wants to know, asking: If you look at the Universe today and compare it to the Universe at any earlier point in time, you’ll find that the entropy has always risen and continues to rise, with no exceptions, throughout all of our cosmic history. This is true not only of a closed system within our Universe, but of the entire Universe itself. One of the most inviolable laws in the Universe is the second law of thermodynamics: that in any physical system, where nothing is exchanged with the outside environment, entropy always increases. In fact, the entropy was finite and quite large, with the entropy density being even higher than it is today. has always increased from any moment to the next, but that doesn't mean that the Big Bang began with zero entropy. Looking back a variety of distances corresponds to a variety of times since the Big Bang.
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