[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.88,0:00:10.45,Default,,0000,0000,0000,,There's a concept that's crucial\Nto chemistry and physics.
Dialogue: 0,0:00:10.45,0:00:15.29,Default,,0000,0000,0000,,It helps explain why physical processes\Ngo one way and not the other-
Dialogue: 0,0:00:15.29,0:00:16.85,Default,,0000,0000,0000,,why ice melts,
Dialogue: 0,0:00:16.85,0:00:19.28,Default,,0000,0000,0000,,why cream spreads in coffee,
Dialogue: 0,0:00:19.28,0:00:22.53,Default,,0000,0000,0000,,why air leaks out of a punctured tire.
Dialogue: 0,0:00:22.53,0:00:27.04,Default,,0000,0000,0000,,It's entropy, and it's notoriously\Ndifficult to wrap our heads around.
Dialogue: 0,0:00:27.04,0:00:31.88,Default,,0000,0000,0000,,Entropy is often described as\Na measurement of disorder.
Dialogue: 0,0:00:31.88,0:00:35.74,Default,,0000,0000,0000,,That's a convenient image,\Nbut it's unfortunately misleading.
Dialogue: 0,0:00:35.74,0:00:38.51,Default,,0000,0000,0000,,For example, which is more disordered -
Dialogue: 0,0:00:38.51,0:00:43.47,Default,,0000,0000,0000,,a cup of crushed ice or a glass\Nof room temperature water?
Dialogue: 0,0:00:43.47,0:00:45.37,Default,,0000,0000,0000,,Most people would say the ice,
Dialogue: 0,0:00:45.37,0:00:49.07,Default,,0000,0000,0000,,but that actually has lower entropy.
Dialogue: 0,0:00:49.07,0:00:52.90,Default,,0000,0000,0000,,So here's another way of thinking\Nabout it through probability.
Dialogue: 0,0:00:52.90,0:00:57.29,Default,,0000,0000,0000,,This may be trickier to understand,\Nbut take the time to internalize it
Dialogue: 0,0:00:57.29,0:01:01.26,Default,,0000,0000,0000,,and you'll have a much better \Nunderstanding of entropy.
Dialogue: 0,0:01:01.26,0:01:03.66,Default,,0000,0000,0000,,Consider two small solids
Dialogue: 0,0:01:03.66,0:01:07.54,Default,,0000,0000,0000,,which are comprised \Nof six atomic bonds each.
Dialogue: 0,0:01:07.54,0:01:12.78,Default,,0000,0000,0000,,In this model, the energy in each solid\Nis stored in the bonds.
Dialogue: 0,0:01:12.78,0:01:15.29,Default,,0000,0000,0000,,Those can be thought of \Nas simple containers,
Dialogue: 0,0:01:15.29,0:01:20.07,Default,,0000,0000,0000,,which can hold indivisible units of energy\Nknown as quanta.
Dialogue: 0,0:01:20.07,0:01:24.60,Default,,0000,0000,0000,,The more energy a solid has,\Nthe hotter it is.
Dialogue: 0,0:01:24.60,0:01:29.04,Default,,0000,0000,0000,,It turns out that there are numerous\Nways that the energy can be distributed
Dialogue: 0,0:01:29.04,0:01:30.55,Default,,0000,0000,0000,,in the two solids
Dialogue: 0,0:01:30.55,0:01:34.59,Default,,0000,0000,0000,,and still have the same \Ntotal energy in each.
Dialogue: 0,0:01:34.59,0:01:38.50,Default,,0000,0000,0000,,Each of these options \Nis called a microstate.
Dialogue: 0,0:01:38.50,0:01:43.34,Default,,0000,0000,0000,,For six quanta of energy in Solid A\Nand two in Solid B,
Dialogue: 0,0:01:43.34,0:01:47.83,Default,,0000,0000,0000,,there are 9,702 microstates.
Dialogue: 0,0:01:47.83,0:01:52.86,Default,,0000,0000,0000,,Of course, there are other ways our eight\Nquanta of energy can be arranged.
Dialogue: 0,0:01:52.86,0:01:57.83,Default,,0000,0000,0000,,For example, all of the energy\Ncould be in Solid A and none in B,
Dialogue: 0,0:01:57.83,0:02:00.87,Default,,0000,0000,0000,,or half in A and half in B.
Dialogue: 0,0:02:00.87,0:02:04.15,Default,,0000,0000,0000,,If we assume that each microstate\Nis equally likely,
Dialogue: 0,0:02:04.15,0:02:06.79,Default,,0000,0000,0000,,we can see that some of the energy\Nconfigurations
Dialogue: 0,0:02:06.79,0:02:10.54,Default,,0000,0000,0000,,have a higher probability of occurring\Nthan others.
Dialogue: 0,0:02:10.54,0:02:14.18,Default,,0000,0000,0000,,That's due to their greater number\Nof microstates.
Dialogue: 0,0:02:14.18,0:02:20.14,Default,,0000,0000,0000,,Entropy is a direct measure of each\Nenergy configuration's probability.
Dialogue: 0,0:02:20.14,0:02:23.19,Default,,0000,0000,0000,,What we see is that the energy\Nconfiguration
Dialogue: 0,0:02:23.19,0:02:26.84,Default,,0000,0000,0000,,in which the energy\Nis most spread out between the solids
Dialogue: 0,0:02:26.84,0:02:28.92,Default,,0000,0000,0000,,has the highest entropy.
Dialogue: 0,0:02:28.92,0:02:30.47,Default,,0000,0000,0000,,So in a general sense,
Dialogue: 0,0:02:30.47,0:02:34.85,Default,,0000,0000,0000,,entropy can though of as a measurement\Nof this energy spread.
Dialogue: 0,0:02:34.85,0:02:37.89,Default,,0000,0000,0000,,Low entropy means \Nthe energy is concentrated.
Dialogue: 0,0:02:37.89,0:02:41.62,Default,,0000,0000,0000,,High entropy means it's spread out.
Dialogue: 0,0:02:41.62,0:02:45.76,Default,,0000,0000,0000,,To see why entropy is useful for\Nexplaining spontaneous processes,
Dialogue: 0,0:02:45.76,0:02:48.08,Default,,0000,0000,0000,,like hot objects cooling down,
Dialogue: 0,0:02:48.08,0:02:52.43,Default,,0000,0000,0000,,we need to look at a dynamic system\Nwhere the energy moves.
Dialogue: 0,0:02:52.43,0:02:54.94,Default,,0000,0000,0000,,In reality, energy doesn't stay put.
Dialogue: 0,0:02:54.94,0:02:58.06,Default,,0000,0000,0000,,It continuously moves between \Nneighboring bonds.
Dialogue: 0,0:02:58.06,0:03:00.21,Default,,0000,0000,0000,,As the energy moves,
Dialogue: 0,0:03:00.21,0:03:02.96,Default,,0000,0000,0000,,the energy configuration can change.
Dialogue: 0,0:03:02.96,0:03:05.08,Default,,0000,0000,0000,,Because of the distribution \Nof microstates,
Dialogue: 0,0:03:05.08,0:03:09.84,Default,,0000,0000,0000,,there's 21% chance that the system\Nwill later be in the configuration
Dialogue: 0,0:03:09.84,0:03:13.60,Default,,0000,0000,0000,,in which the energy is maximally \Nspread out,
Dialogue: 0,0:03:13.60,0:03:17.36,Default,,0000,0000,0000,,there's a 13% chance that it will\Nreturn to its starting point,
Dialogue: 0,0:03:17.36,0:03:22.86,Default,,0000,0000,0000,,and an 8% chance that A will actually\Ngain energy.
Dialogue: 0,0:03:22.86,0:03:26.94,Default,,0000,0000,0000,,Again, we see that because there are\Nmore ways to have dispersed energy
Dialogue: 0,0:03:26.94,0:03:30.03,Default,,0000,0000,0000,,and high entropy than concentrated energy,
Dialogue: 0,0:03:30.03,0:03:32.56,Default,,0000,0000,0000,,the energy tends to spread out.
Dialogue: 0,0:03:32.56,0:03:35.51,Default,,0000,0000,0000,,That's why if you put a hot object\Nnext to a cold one,
Dialogue: 0,0:03:35.51,0:03:40.42,Default,,0000,0000,0000,,the cold one will warm up\Nand the hot one will cool down.
Dialogue: 0,0:03:40.42,0:03:41.87,Default,,0000,0000,0000,,But even in that example,
Dialogue: 0,0:03:41.87,0:03:47.12,Default,,0000,0000,0000,,there is an 8% chance that the hot object\Nwould get hotter.
Dialogue: 0,0:03:47.12,0:03:50.31,Default,,0000,0000,0000,,Why doesn't this ever happen\Nin real life?
Dialogue: 0,0:03:50.31,0:03:54.18,Default,,0000,0000,0000,,It's all about the size of the system.
Dialogue: 0,0:03:54.18,0:03:58.06,Default,,0000,0000,0000,,Our hypothetical solids only had\Nsix bonds each.
Dialogue: 0,0:03:58.06,0:04:03.94,Default,,0000,0000,0000,,Let's scale the solids up to 6,000 bonds\Nand 8,000 units of energy,
Dialogue: 0,0:04:03.94,0:04:07.53,Default,,0000,0000,0000,,and again start the system with\Nthree-quarters of the energy in A
Dialogue: 0,0:04:07.53,0:04:10.13,Default,,0000,0000,0000,,and one-quarter in B.
Dialogue: 0,0:04:10.13,0:04:14.34,Default,,0000,0000,0000,,Now we find that chance of A\Nspontaneously acquiring more energy
Dialogue: 0,0:04:14.34,0:04:17.25,Default,,0000,0000,0000,,is this tiny number.
Dialogue: 0,0:04:17.25,0:04:22.31,Default,,0000,0000,0000,,Familiar, everyday objects have many, many\Ntimes more particles than this.
Dialogue: 0,0:04:22.31,0:04:25.92,Default,,0000,0000,0000,,The chance of a hot object \Nin the real world getting hotter
Dialogue: 0,0:04:25.92,0:04:28.01,Default,,0000,0000,0000,,is so absurdly small,
Dialogue: 0,0:04:28.01,0:04:30.41,Default,,0000,0000,0000,,it just never happens.
Dialogue: 0,0:04:30.41,0:04:31.53,Default,,0000,0000,0000,,Ice melts,
Dialogue: 0,0:04:31.53,0:04:32.92,Default,,0000,0000,0000,,cream mixes in,
Dialogue: 0,0:04:32.92,0:04:34.68,Default,,0000,0000,0000,,and tires deflate
Dialogue: 0,0:04:34.68,0:04:39.94,Default,,0000,0000,0000,,because these states have more\Ndispersed energy than the originals.
Dialogue: 0,0:04:39.94,0:04:43.63,Default,,0000,0000,0000,,There's no mysterious force\Nnudging the system towards higher entropy.
Dialogue: 0,0:04:43.63,0:04:48.93,Default,,0000,0000,0000,,It's just that higher entropy is always\Nstatistically more likely.
Dialogue: 0,0:04:48.93,0:04:52.48,Default,,0000,0000,0000,,That's why entropy has been called\Ntime's arrow.
Dialogue: 0,0:04:52.48,0:04:56.74,Default,,0000,0000,0000,,If energy has the opportunity\Nto spread out, it will.