1
00:00:02,040 --> 00:00:07,080
Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,

2
00:00:07,120 --> 00:00:11,479
Speaker 1: Lauren voc obam here. Days before his death. On March fourteen, eighteen,

3
00:00:11,840 --> 00:00:16,240
Speaker 1: famed theoretical physicist and cosmologist Stephen Hawking completed what would

4
00:00:16,239 --> 00:00:19,520
Speaker 1: be his final research paper. It has since passed peer

5
00:00:19,520 --> 00:00:21,919
Speaker 1: review and was published online in the Journal of High

6
00:00:21,960 --> 00:00:26,759
Speaker 1: Energy Physics on April. Written with co author Thomas Hertog,

7
00:00:26,960 --> 00:00:30,560
Speaker 1: a theoretical physicist at the University of louisn Belgium, the

8
00:00:30,640 --> 00:00:34,159
Speaker 1: paper adds another facet to our understanding of this universe

9
00:00:34,200 --> 00:00:37,600
Speaker 1: that we live in, and needless to say, it's complicated.

10
00:00:38,159 --> 00:00:42,600
Speaker 1: Titled a Smooth Exit from Eternal Inflation, the publication discusses

11
00:00:42,640 --> 00:00:46,960
Speaker 1: an enigmatic problem facing cosmologists. But before we delve into

12
00:00:47,040 --> 00:00:49,199
Speaker 1: the crux of the study, let's go back to when

13
00:00:49,200 --> 00:00:52,440
Speaker 1: our universe was a baby, some thirteen point eight billion

14
00:00:52,520 --> 00:00:56,520
Speaker 1: years ago. A lot of evidence suggests that our universe

15
00:00:56,520 --> 00:01:00,520
Speaker 1: originated from a singularity, an infinitely dense point from which

16
00:01:00,560 --> 00:01:03,240
Speaker 1: all the universe as we know it was born. We

17
00:01:03,400 --> 00:01:06,920
Speaker 1: call that event the Big Bang. But how the singularity

18
00:01:06,959 --> 00:01:09,479
Speaker 1: came to be and why the Big Bang happened isn't

19
00:01:09,480 --> 00:01:12,759
Speaker 1: of concern right now. We're interested in what happened immediately

20
00:01:12,880 --> 00:01:16,520
Speaker 1: after our universe was spawned, a period known as inflation.

21
00:01:17,160 --> 00:01:21,400
Speaker 1: Cosmologists predict that inflation occurred over a vanishingly small period

22
00:01:21,600 --> 00:01:24,839
Speaker 1: right after the Big Bang, during our universe's very first

23
00:01:24,959 --> 00:01:29,200
Speaker 1: ten to thirty two seconds. During inflation, the universe expanded

24
00:01:29,240 --> 00:01:32,840
Speaker 1: exponentially and much faster than the speed of light. After

25
00:01:32,880 --> 00:01:37,000
Speaker 1: only a second, the energy from this inconceivably gargantuan explosion

26
00:01:37,280 --> 00:01:41,319
Speaker 1: condensed to form sub atomic particles that, over millions of years,

27
00:01:41,600 --> 00:01:45,960
Speaker 1: created the stars, galaxies, planets, and, after another few billion years,

28
00:01:46,200 --> 00:01:50,120
Speaker 1: a life as we know it. Once this inflationary period ended,

29
00:01:50,280 --> 00:01:53,520
Speaker 1: the universe's rate of expansion slowed, but it continues to

30
00:01:53,560 --> 00:01:57,400
Speaker 1: expand to this day. Because inflation powered a faster than

31
00:01:57,520 --> 00:02:00,800
Speaker 1: light speed expansion, The observable uni verse that we see

32
00:02:00,800 --> 00:02:05,480
Speaker 1: today is not the entire universe. Rather, we exist inside

33
00:02:05,480 --> 00:02:08,239
Speaker 1: a region of the cosmos that light has had time

34
00:02:08,280 --> 00:02:11,280
Speaker 1: to reach. It's like dropping a pebble into a calm

35
00:02:11,320 --> 00:02:14,600
Speaker 1: swimming pool. The first circular ripple to propagate from the

36
00:02:14,639 --> 00:02:17,680
Speaker 1: splash travels at a fixed speed across the surface of

37
00:02:17,680 --> 00:02:20,280
Speaker 1: the pool. If we imagine that the limit of our

38
00:02:20,280 --> 00:02:23,960
Speaker 1: observable universe is that ripple traveling across the pool at

39
00:02:23,960 --> 00:02:26,960
Speaker 1: the speed of light. It's not that nothing exists beyond

40
00:02:27,040 --> 00:02:30,680
Speaker 1: that ripple. There's more pool or universe beyond it. We

41
00:02:30,800 --> 00:02:34,640
Speaker 1: just can't see it yet. So the consequence of inflation

42
00:02:34,760 --> 00:02:37,200
Speaker 1: is that there should be a lot more universe beyond

43
00:02:37,240 --> 00:02:40,120
Speaker 1: what we can see, even with our most powerful telescopes,

44
00:02:40,960 --> 00:02:43,919
Speaker 1: and cosmologists have been grappling with the possibility that our

45
00:02:44,040 --> 00:02:47,520
Speaker 1: universe is not the only universe. In fact, we could

46
00:02:47,520 --> 00:02:50,240
Speaker 1: be nothing more than a single bubble in an infinite

47
00:02:50,320 --> 00:02:54,280
Speaker 1: froth the ocean, a concept known as the multiverse. The

48
00:02:54,400 --> 00:02:58,400
Speaker 1: idea here is that inflation didn't happen once, It's always

49
00:02:58,400 --> 00:03:03,480
Speaker 1: happening via some infinitely vast chain reaction known as eternal inflation.

50
00:03:04,240 --> 00:03:07,440
Speaker 1: One universe will appear, and inflation will take over, expanding

51
00:03:07,440 --> 00:03:10,560
Speaker 1: that universe, and that universe will have its own quantum

52
00:03:10,600 --> 00:03:13,560
Speaker 1: instabilities that will spawn more singularities that go on to

53
00:03:13,680 --> 00:03:17,799
Speaker 1: create more universes. It's like blowing up a party balloon

54
00:03:17,880 --> 00:03:20,960
Speaker 1: that itself spawns many other party balloons that are rupped

55
00:03:20,960 --> 00:03:24,440
Speaker 1: from its rubbery surface seemingly at random. If this situation

56
00:03:24,520 --> 00:03:28,880
Speaker 1: sounds chaotic, it is. Proponents of this hypothesis think that

57
00:03:29,000 --> 00:03:34,960
Speaker 1: eternal inflation is unstoppable, vastly complex, and continually generating new universes,

58
00:03:35,560 --> 00:03:38,720
Speaker 1: and the math of this situation suggests that the multiverse

59
00:03:38,760 --> 00:03:42,280
Speaker 1: acts like a fractal, fractals being sets of data that

60
00:03:42,360 --> 00:03:46,640
Speaker 1: contain repeating patterns at every scale. Visually, this means that

61
00:03:46,720 --> 00:03:49,360
Speaker 1: complex shapes look pretty much the same at a wide

62
00:03:49,440 --> 00:03:51,960
Speaker 1: range of scales, like a small piece of it looks

63
00:03:51,960 --> 00:03:54,440
Speaker 1: pretty similar to the whole structure. Think of a head

64
00:03:54,440 --> 00:03:57,840
Speaker 1: of cauliflower. Any given segment will resemble the whole head,

65
00:03:58,160 --> 00:04:00,320
Speaker 1: and if you zoom in further, each clus store of

66
00:04:00,360 --> 00:04:04,600
Speaker 1: buds resembles the larger segments. It's worth noting that in

67
00:04:04,600 --> 00:04:08,240
Speaker 1: this theory, each successive universe and the multiverse doesn't likely

68
00:04:08,360 --> 00:04:11,920
Speaker 1: share the same physics as our universe. One universe might

69
00:04:11,960 --> 00:04:14,920
Speaker 1: not have gravity, another may not support the forces that

70
00:04:15,080 --> 00:04:18,320
Speaker 1: hold matter together. There would be a lot of stillborn

71
00:04:18,400 --> 00:04:21,800
Speaker 1: universes that just don't amount too much. We humans are

72
00:04:21,839 --> 00:04:23,919
Speaker 1: simply lucky to have a universe that has the right

73
00:04:24,040 --> 00:04:27,560
Speaker 1: environment to create what we see. A philosophical argument known

74
00:04:27,600 --> 00:04:31,839
Speaker 1: as the anthropic principle. The problem with eternal inflation is

75
00:04:31,839 --> 00:04:35,080
Speaker 1: that it's messy and infinite, and that the hypothesis is

76
00:04:35,360 --> 00:04:40,239
Speaker 1: ultimately untestable. So what does Hawking and her tog's research

77
00:04:40,440 --> 00:04:44,960
Speaker 1: have to do with this unrelenting multiverse In the multiverse.

78
00:04:45,000 --> 00:04:49,000
Speaker 1: Our universe is merely a pocket universe where inflation has ended,

79
00:04:49,279 --> 00:04:52,479
Speaker 1: and despite the odds, it found enough calm to create

80
00:04:52,480 --> 00:04:55,000
Speaker 1: a bounty of stars and galaxies and a bunch of

81
00:04:55,080 --> 00:04:58,679
Speaker 1: humans living on some random rock pondering the cosmos. What's

82
00:04:58,680 --> 00:05:02,400
Speaker 1: going on beyond our pocket of calm is, however, somewhat different,

83
00:05:03,320 --> 00:05:07,039
Speaker 1: Hawking said in an interview in Tween. The usual theory

84
00:05:07,080 --> 00:05:10,640
Speaker 1: of eternal inflation predicts that globally, our universe is like

85
00:05:10,760 --> 00:05:14,480
Speaker 1: an infinite fractal with a mosaic of different pocket universes

86
00:05:14,680 --> 00:05:18,320
Speaker 1: separated by an inflating ocean. The local laws of physics

87
00:05:18,320 --> 00:05:21,120
Speaker 1: and chemistry can differ from one pocket universe to another,

88
00:05:21,440 --> 00:05:24,640
Speaker 1: which together would form a multiverse. But I have never

89
00:05:24,680 --> 00:05:27,159
Speaker 1: been a fan of the multiverse. If the scale of

90
00:05:27,160 --> 00:05:30,560
Speaker 1: different universes in the multiverse is large or infinite, then

91
00:05:30,600 --> 00:05:34,200
Speaker 1: the theory can't be tested. The problem, according to Hawking

92
00:05:34,200 --> 00:05:38,120
Speaker 1: in Her Dog, allies with the incompatibility of Einstein's general

93
00:05:38,160 --> 00:05:41,760
Speaker 1: relativity that governs the evolution of the universe and quantum

94
00:05:41,839 --> 00:05:46,200
Speaker 1: mechanics that seeds the creation of new universes through quantum fluctuations.

95
00:05:46,880 --> 00:05:49,840
Speaker 1: The eternal inflation model of the multiverse, as her Dog

96
00:05:49,920 --> 00:05:53,440
Speaker 1: said in a press release quote, wipes out separation between

97
00:05:53,480 --> 00:05:57,760
Speaker 1: classical and quantum physics. As a consequence, Einstein's theory breaks

98
00:05:57,800 --> 00:06:01,479
Speaker 1: down in eternal inflation. Their study doesn't go as far

99
00:06:01,520 --> 00:06:05,440
Speaker 1: as reconciling general relativity with quantum physics, a quest that

100
00:06:05,520 --> 00:06:08,800
Speaker 1: has so far been unsuccessful, but they use the math

101
00:06:08,880 --> 00:06:12,600
Speaker 1: of string theory to help simplify the multiverse model. A

102
00:06:12,680 --> 00:06:16,279
Speaker 1: quick recap. String theory predicts that all subtomic particles in

103
00:06:16,279 --> 00:06:19,640
Speaker 1: our universe are in fact composed of one dimensional strings

104
00:06:19,680 --> 00:06:23,440
Speaker 1: that propagate through space. The vibrational state of these strings

105
00:06:23,480 --> 00:06:27,320
Speaker 1: is what gives these particles their quantum state such as charge, spin,

106
00:06:27,480 --> 00:06:31,359
Speaker 1: and mass. But string theory also predicts the existence of

107
00:06:31,400 --> 00:06:35,440
Speaker 1: the hypothetical graviton, a quantum particle that carries the force

108
00:06:35,480 --> 00:06:39,000
Speaker 1: of gravity. The math that suggests that gravitons exist is solid,

109
00:06:39,279 --> 00:06:41,440
Speaker 1: but no one's been able to point to one yet.

110
00:06:41,960 --> 00:06:45,560
Speaker 1: String theory would therefore provide an explanation of how Einstein's

111
00:06:45,600 --> 00:06:51,480
Speaker 1: general relativity gravity jibes with quantum physics using the mathematical

112
00:06:51,520 --> 00:06:55,200
Speaker 1: framework of string theory. This final study from Hawking simplifies

113
00:06:55,240 --> 00:06:58,679
Speaker 1: the multiverse. Hawking and her dog used the string theory

114
00:06:58,720 --> 00:07:02,320
Speaker 1: concept of holography, who reduce our three dimensional universe down

115
00:07:02,320 --> 00:07:05,680
Speaker 1: to a two dimensional surface from which the universe we

116
00:07:05,720 --> 00:07:08,760
Speaker 1: know and love is projected. By doing this, they were

117
00:07:08,760 --> 00:07:13,560
Speaker 1: able to describe eternal inflation without general relativity, creating a

118
00:07:13,600 --> 00:07:17,480
Speaker 1: timeless state. Her dog explained this move in a statement.

119
00:07:17,960 --> 00:07:20,800
Speaker 1: When we trace the evolution of our universe backwards in time,

120
00:07:21,200 --> 00:07:24,160
Speaker 1: at some point we arrive at the threshold of eternal inflation,

121
00:07:24,480 --> 00:07:27,880
Speaker 1: where our familiar notion of time ceases to have any meaning.

122
00:07:29,080 --> 00:07:32,160
Speaker 1: The math is complex, but the result is interesting. The

123
00:07:32,200 --> 00:07:35,600
Speaker 1: calculations have the effect of turning the infinite and fractal

124
00:07:35,680 --> 00:07:40,040
Speaker 1: multiverse into a far simpler and finite situation that eternal

125
00:07:40,040 --> 00:07:44,480
Speaker 1: inflation does predict. Hawking said this about it. We are

126
00:07:44,560 --> 00:07:47,920
Speaker 1: not down to a single unique universe, but our findings

127
00:07:47,920 --> 00:07:51,200
Speaker 1: imply a significant reduction of the multiverse to a much

128
00:07:51,240 --> 00:07:55,280
Speaker 1: smaller range of possible universes. To put it in perspective,

129
00:07:55,560 --> 00:07:59,120
Speaker 1: Hawking's final paper doesn't revolutionize our understanding of how the

130
00:07:59,240 --> 00:08:02,720
Speaker 1: universe and indeed the multiverse works, but it is a

131
00:08:02,840 --> 00:08:07,280
Speaker 1: valuable addition to a huge field of theoretical work. Specifically,

132
00:08:07,320 --> 00:08:09,679
Speaker 1: her TG hopes that this study may help us search

133
00:08:09,720 --> 00:08:13,360
Speaker 1: for ancient gravitational waves that were generated by eternal inflation.

134
00:08:14,040 --> 00:08:16,760
Speaker 1: These ripples in space time are far too weak for

135
00:08:16,960 --> 00:08:21,200
Speaker 1: current gravitational wave detectors to detect. However, we need to

136
00:08:21,240 --> 00:08:25,240
Speaker 1: wait until advanced space based observatories such as the European

137
00:08:25,320 --> 00:08:30,120
Speaker 1: Space Agencies planned LIESA mission are launched. Regardless of whether

138
00:08:30,160 --> 00:08:33,240
Speaker 1: the study leads to groundbreaking discoveries about the cosmos that

139
00:08:33,280 --> 00:08:36,040
Speaker 1: we live in, it's a testament to a great scientist

140
00:08:36,040 --> 00:08:39,120
Speaker 1: who worked tirelessly his entire life to answer some of

141
00:08:39,160 --> 00:08:43,280
Speaker 1: the biggest questions that humanity has pondered, and on Hawking's shoulders,

142
00:08:43,480 --> 00:08:46,120
Speaker 1: other great minds will build on this work to hopefully

143
00:08:46,160 --> 00:08:49,160
Speaker 1: decipher whether our universe is unique or if it's just

144
00:08:49,240 --> 00:08:52,600
Speaker 1: one bubble chaotically floating in the ocean of the multiverse.

145
00:08:57,760 --> 00:09:00,440
Speaker 1: Today's episode was written by Ian O'Neill and produced by

146
00:09:00,440 --> 00:09:04,080
Speaker 1: Tyler Clang with kind engineering assistance from Ramsay Yount. For

147
00:09:04,160 --> 00:09:07,400
Speaker 1: more on this and lots of other eternally expanding topics.

148
00:09:07,640 --> 00:09:21,559
Speaker 1: Visit our home planet, how staff Works dot com