https://youtu.be/e-P5IFTqB98
Transcript
1
00:00:00,000 –> 00:00:03,052
Black holes are one of the strangest things in existence.
2
00:00:03,007 –> 00:00:05,015
They don’t seem to make any sense at all.
3
00:00:05,078 –> 00:00:06,122
Where do they come from…
4
00:00:07,003 –> 00:00:09,011
…and what happens if you fall into one?
5
00:00:15,068 –> 00:00:18,160
Stars are incredibly massive collections of mostly hydrogen atoms
6
00:00:19,064 –> 00:00:21,162
that collapsed from enormous gas cloud under their own gravity.
7
00:00:23,014 –> 00:00:26,098
In their core, nuclear fusion crushes hydrogen atoms into helium
8
00:00:26,098 –> 00:00:28,100
releasing a tremendous amount of energy
9
00:00:29,004 –> 00:00:31,026
This energy, in the form of radiation,
10
00:00:31,062 –> 00:00:32,069
pushes against gravity,
11
00:00:33,032 –> 00:00:36,034
maintaining a delicate balance between the two forces.
12
00:00:36,092 –> 00:00:37,168
As long as there is fusion in the core,
13
00:00:38,068 –> 00:00:40,080
a star remains stable enough.
14
00:00:41,018 –> 00:00:43,100
But for stars with way more mass then our own sun
15
00:00:44,004 –> 00:00:47,011
the heat and pressure at the core allow them to fuse heavier elements
16
00:00:47,074 –> 00:00:49,080
until they reach iron.
17
00:00:50,003 –> 00:00:52,015
Unlike all the elements that went before,
18
00:00:52,042 –> 00:00:54,058
the fusion process that creates iron
19
00:00:54,058 –> 00:00:55,120
doesn’t generate any energy.
20
00:00:56,005 –> 00:00:58,005
Iron builds up at the center of the star
21
00:00:58,005 –> 00:01:00,005
until it reaches a critical amount
22
00:01:00,005 –> 00:01:03,049
and the balance between radiation and gravity is suddenly broken.
23
00:01:04,048 –> 00:01:05,102
The core collapses.
24
00:01:06,038 –> 00:01:07,106
Within a fraction of a second,
25
00:01:08,006 –> 00:01:09,048
the star implodes.
26
00:01:09,072 –> 00:01:11,072
Moving at about the quarter of the speed of light,
27
00:01:11,072 –> 00:01:13,073
feeding even more mass into the core.
28
00:01:14,038 –> 00:01:18,052
It’s at this very moment that all the heavier elements in the universe are created,
29
00:01:18,052 –> 00:01:21,060
as the star dies, in a super nova explosion.
30
00:01:22,002 –> 00:01:24,040
This produces either a neutron star,
31
00:01:24,044 –> 00:01:25,130
or if the star is massive enough,
32
00:01:26,003 –> 00:01:29,010
the entire mass of the core collapses into a black hole.
33
00:01:30,004 –> 00:01:31,060
If you looked at a black hole,
34
00:01:31,098 –> 00:01:33,180
what you’d really be seeing is the event horizon.
35
00:01:35,002 –> 00:01:37,014
Anything that crosses the event horizon
36
00:01:37,014 –> 00:01:40,042
needs to be travelling faster than the speed of light to escape.
37
00:01:40,044 –> 00:01:41,053
In other words, its impossible.
38
00:01:42,008 –> 00:01:43,106
So we just see a black sphere
39
00:01:44,078 –> 00:01:45,104
reflecting nothing.
40
00:01:46,048 –> 00:01:48,056
But if the event horizon is the black part,
41
00:01:49,028 –> 00:01:51,100
what is the “hole” part of the black hole?
42
00:01:52,003 –> 00:01:53,029
The singularity.
43
00:01:54,008 –> 00:01:56,032
We’re not sure what it is exactly.
44
00:01:56,004 –> 00:01:58,046
A singularity may be indefinitely dense,
45
00:01:58,082 –> 00:02:01,104
meaning all its mass is concentrated into a single point in space,
46
00:02:02,004 –> 00:02:03,088
with no surface or volume,
47
00:02:03,088 –> 00:02:04,182
or something completely different.
48
00:02:06,036 –> 00:02:08,036
Right now, we just don’t know.
49
00:02:08,036 –> 00:02:10,040
its like a “dividing by zero”error.
50
00:02:10,076 –> 00:02:13,138
By the way, black holes do not suck things up like a vacuum cleaner,
51
00:02:14,068 –> 00:02:16,154
If we were to swap the sun for an equally massive black hole,
52
00:02:17,054 –> 00:02:18,136
nothing much would change for earth,
53
00:02:19,036 –> 00:02:21,044
except that we would freeze to death, of course.
54
00:02:21,092 –> 00:02:24,096
what would happen to you if you fell into a black hole?
55
00:02:24,096 –> 00:02:27,100
The experience of time is different around black holes,
56
00:02:28,000 –> 00:02:29,008
from the outside,
57
00:02:29,008 –> 00:02:31,090
you seem to slow down as you approach the event horizon,
58
00:02:31,009 –> 00:02:33,009
so time passes slower for you.
59
00:02:33,009 –> 00:02:35,097
at some point, you would appear to freeze in time,
60
00:02:36,078 –> 00:02:37,090
slowly turn red,
61
00:02:37,009 –> 00:02:37,105
and disapear.
62
00:02:38,086 –> 00:02:39,172
While from your perspective,
63
00:02:40,072 –> 00:02:42,076
you can watch the rest of the universe in fast forward,
64
00:02:43,012 –> 00:02:44,088
kind of like seeing into the future.
65
00:02:45,042 –> 00:02:47,044
Right now, we don’t know what happens next,
66
00:02:47,044 –> 00:02:49,060
but we think it could be one of two things:
67
00:02:50,004 –> 00:02:52,008
One, you die a quick death.
68
00:02:52,042 –> 00:02:54,043
A black hole curves space so much,
69
00:02:54,052 –> 00:02:55,104
that once you cross the event horizon,
70
00:02:56,004 –> 00:02:58,022
there is only one possible direction.
71
00:02:58,022 –> 00:03:01,023
you can take this – literally – inside the event horizon,
72
00:03:01,004 –> 00:03:03,020
you can only go in one direction.
73
00:03:04,042 –> 00:03:07,126
Its like being in a really tight alley that closes behind you after each step.
74
00:03:08,076 –> 00:03:10,124
The mass of a black hole is so concentrated,
75
00:03:11,024 –> 00:03:14,040
at some point even tiny distances of a few centimeters,
76
00:03:14,004 –> 00:03:18,076
would means that gravity acts with millions of times more force on different parts of your body.
77
00:03:19,012 –> 00:03:20,088
Your cells get torn apart,
78
00:03:20,009 –> 00:03:22,011
as your body stretches more and more,
79
00:03:22,092 –> 00:03:24,092
until you are a hot stream of plasma,
80
00:03:24,092 –> 00:03:25,106
one atom wide.
81
00:03:26,056 –> 00:03:28,064
Two, you die a very quick death.
82
00:03:28,098 –> 00:03:30,112
Very soon after you cross the event horizon,
83
00:03:31,012 –> 00:03:33,096
you would hit a firewall and be terminated in an instant.
84
00:03:34,044 –> 00:03:36,128
Neither of these options are particularly pleasant.
85
00:03:37,088 –> 00:03:39,180
How soon you would die depends on the mass of the black hole.
86
00:03:41,016 –> 00:03:44,072
A smaller black hole would kill you before you even enter its event horizon,
87
00:03:44,072 –> 00:03:48,080
while you probably could travel inside a super size massive black hole for quite a while.
88
00:03:48,086 –> 00:03:49,088
As a rule of thumb,
89
00:03:50,006 –> 00:03:52,010
the further away from the singularity you are,
90
00:03:52,001 –> 00:03:53,027
the longer you live.
91
00:03:53,078 –> 00:03:55,094
Black holes come in different sizes.
92
00:03:55,094 –> 00:03:56,168
There are stellar mass black holes,
93
00:03:57,068 –> 00:03:58,164
with a few times the mass of sun,
94
00:03:59,064 –> 00:04:00,150
and the diameter of an asteroid.
95
00:04:01,005 –> 00:04:03,061
And then there are the super massive black holes,
96
00:04:04,006 –> 00:04:06,024
which are found at the heart of every galaxy,
97
00:04:06,024 –> 00:04:08,120
and have been feeding for billions of years.
98
00:04:09,002 –> 00:04:11,100
Currently, the largest super massive black hole known,
99
00:04:12,018 –> 00:04:14,116
is S5 0014+81.
100
00:04:15,028 –> 00:04:17,032
40 billion times the mass of our sun.
101
00:04:18,028 –> 00:04:22,028
It is 236.7 billion kilometers in diameter,
102
00:04:22,028 –> 00:04:25,072
which is 47 times the distance from the sun to Pluto.
103
00:04:25,072 –> 00:04:26,168
As powerful as black holes are,
104
00:04:27,007 –> 00:04:30,091
they will eventually evaporate through a process called Hawking radiation.
105
00:04:31,094 –> 00:04:32,100
To understand how this works,
106
00:04:33,054 –> 00:04:34,112
we have to look at empty space.
107
00:04:35,052 –> 00:04:36,150
Empty space is not really empty,
108
00:04:37,005 –> 00:04:39,063
but filled with virtual particles popping into existence
109
00:04:40,008 –> 00:04:41,076
and annihilating each other again.
110
00:04:41,076 –> 00:04:43,132
When this happens right on the edge of a black hole,
111
00:04:44,032 –> 00:04:46,118
one of the virtual particles will be drawn into the black hole,
112
00:04:47,018 –> 00:04:49,096
and the other will escape and become a real particle.
113
00:04:50,012 –> 00:04:52,044
So the black hole is losing energy.
114
00:04:52,009 –> 00:04:54,023
This happens incredibly slowly at first,
115
00:04:55,001 –> 00:04:57,013
and gets faster as the black hole becomes smaller.
116
00:04:58,002 –> 00:05:00,003
When it arrives at the mass of a large asteroid,
117
00:05:00,012 –> 00:05:01,060
its radiating at room temperature.
118
00:05:02,014 –> 00:05:03,021
When it has the mass of a mountain,
119
00:05:03,084 –> 00:05:04,092
it radiates with about the heat of our sun.
120
00:05:05,064 –> 00:05:06,148
and in the last second of its life,
121
00:05:07,005 –> 00:05:11,077
the black hole radiates away with the energy of billions of nuclear bombs in a huge explosion.
122
00:05:12,082 –> 00:05:13,174
But this process is incredibly slow,
123
00:05:14,074 –> 00:05:15,152
The biggest black holes we know,
124
00:05:16,052 –> 00:05:18,126
might take up a googol year to evaporate.
125
00:05:19,052 –> 00:05:22,055
This is so long that when the last black hole radiates away,
126
00:05:22,082 –> 00:05:24,086
nobody will be around to witness it.
127
00:05:25,022 –> 00:05:27,044
The universe will have become uninhabitable,
128
00:05:27,006 –> 00:05:28,008
long before then.
129
00:05:28,008 –> 00:05:29,090
This is not the end of our story,
130
00:05:30,062 –> 00:05:32,110
there are loads more interesting ideas about black holes,
131
00:05:33,048 –> 00:05:35,066
we’ll explore them in part 2.