1 00:00:00,000 --> 00:00:18,000 Why are general relativity and quantum physics incompatible? 2 00:00:18,000 --> 00:00:24,000 How is it that macroworld and microworld work according to different rules? 3 00:00:24,000 --> 00:00:29,000 Since we are also made of atoms, what does this say about us? 4 00:00:29,000 --> 00:00:34,000 Yeah, this is one of the great problems of modern physics, 5 00:00:34,000 --> 00:00:36,000 is putting gravity and quantum mechanics together. 6 00:00:36,000 --> 00:00:40,000 So, I don't think anyone would say it's impossible to put them together, 7 00:00:40,000 --> 00:00:42,000 but no one has succeeded yet. 8 00:00:42,000 --> 00:00:46,000 And part of it, it just is different length scales, 9 00:00:46,000 --> 00:00:51,000 that general relativity, the effects normally we would only see 10 00:00:51,000 --> 00:00:55,000 on very, very large scales of the distance of stars. 11 00:00:55,000 --> 00:01:00,000 Although, if you want to get extremely accurate, 12 00:01:00,000 --> 00:01:03,000 then you actually do need to pay attention to general relativity. 13 00:01:03,000 --> 00:01:06,000 The GPS satellite system that we all use, 14 00:01:06,000 --> 00:01:09,000 actually uses general relativity in the calculations, 15 00:01:09,000 --> 00:01:13,000 and that's because they want to get extremely accurate to many decimal places. 16 00:01:13,000 --> 00:01:15,000 On the other hand, quantum mechanics, 17 00:01:15,000 --> 00:01:19,000 typically the effects are even much smaller scale than us, 18 00:01:19,000 --> 00:01:22,000 down at the atomic level. 19 00:01:22,000 --> 00:01:25,000 And so, part of it is just the mismatch between those. 20 00:01:25,000 --> 00:01:28,000 Now, a lot of the normal physics that we experience 21 00:01:28,000 --> 00:01:33,000 is averaged over many, many particles. 22 00:01:33,000 --> 00:01:36,000 And so, even in one gram of material, 23 00:01:36,000 --> 00:01:39,000 you might have 10 to the 23rd atoms, 24 00:01:39,000 --> 00:01:42,000 which is one with 23 zeros, 25 00:01:42,000 --> 00:01:44,000 and just an enormous number of atoms. 26 00:01:44,000 --> 00:01:47,000 And so, almost always at the level that we live at, 27 00:01:47,000 --> 00:01:49,000 which we call the macroscopic, 28 00:01:49,000 --> 00:01:52,000 we're seeing average behavior of a lot of things. 29 00:01:52,000 --> 00:01:56,000 And so, we don't see these tiny quantum mechanical effects. 30 00:01:56,000 --> 00:01:58,000 Now, that's not always true, actually. 31 00:01:58,000 --> 00:02:01,000 You can, I study things called Bose condensates, 32 00:02:01,000 --> 00:02:05,000 and you can have a Bose condensate or a superconductor 33 00:02:05,000 --> 00:02:09,000 which show quantum mechanical effects even in large scale systems. 34 00:02:09,000 --> 00:02:12,000 And so, it's not quite accurate to say that quantum mechanics 35 00:02:12,000 --> 00:02:14,000 is always only at the small scale, 36 00:02:14,000 --> 00:02:15,000 but typically it is. 37 00:02:15,000 --> 00:02:18,000 And so, we typically don't worry about it. 38 00:02:18,000 --> 00:02:20,000 But the other thing I would say is, 39 00:02:20,000 --> 00:02:23,000 special relativity and general relativity 40 00:02:23,000 --> 00:02:26,000 are considered by most scientists 41 00:02:26,000 --> 00:02:29,000 to be very well understood, 42 00:02:29,000 --> 00:02:32,000 in some sense, classical theories. 43 00:02:32,000 --> 00:02:35,000 That they don't involve anything 44 00:02:35,000 --> 00:02:38,000 that's really conceptually hard for us philosophically. 45 00:02:38,000 --> 00:02:41,000 Now, we have to change our concept of time, 46 00:02:41,000 --> 00:02:44,000 but if you can do that, 47 00:02:44,000 --> 00:02:46,000 then actually special relativity and general relativity 48 00:02:46,000 --> 00:02:48,000 are not that problematic. 49 00:02:48,000 --> 00:02:50,000 Quantum mechanics, on the other hand, 50 00:02:50,000 --> 00:02:51,000 people still argue about. 51 00:02:51,000 --> 00:02:53,000 I was just at a meeting a couple of weeks ago 52 00:02:53,000 --> 00:02:56,000 where we were five Christian scientists 53 00:02:56,000 --> 00:02:58,000 debating about the meaning of quantum mechanics 54 00:02:58,000 --> 00:03:00,000 and didn't agree between ourselves. 55 00:03:00,000 --> 00:03:03,000 Because quantum mechanics is still not considered 56 00:03:03,000 --> 00:03:05,000 to be a fully understood theory. 57 00:03:05,000 --> 00:03:08,000 So, we can do a lot of things with it, 58 00:03:08,000 --> 00:03:10,000 calculate things extremely accurately, 59 00:03:10,000 --> 00:03:12,000 and yet still debate about what it all means 60 00:03:12,000 --> 00:03:14,000 and what's really going on with it. 61 00:03:14,000 --> 00:03:16,000 So, part of the reason why putting gravity 62 00:03:16,000 --> 00:03:18,000 and quantum mechanics together is hard 63 00:03:18,000 --> 00:03:20,000 is because we still don't entirely understand 64 00:03:20,000 --> 00:03:22,000 quantum mechanics in some ways 65 00:03:22,000 --> 00:03:24,000 as to what's really going on at the basic level.