Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated:
1
00:00:01,673 --> 00:00:04,775
[narrator] Scientists believ there is a hidden substance deep in space
2
00:00:04,777 --> 00:00:07,111
that keeps the cosmos runnin
3
00:00:08,180 --> 00:00:11,048
But is that substance real?
4
00:00:11,050 --> 00:00:14,385
We've never seen dark matter,
it's completely invisible,
5
00:00:14,387 --> 00:00:17,354
but we know
that it has to be there.
6
00:00:17,356 --> 00:00:22,459
Not only can you not see it,
you couldn't really touch it
or taste it, or smell it,
7
00:00:22,528 --> 00:00:25,662
and yet it is all around us it affects everything that we do.
8
00:00:25,731 --> 00:00:27,664
[narrator] After searching for decades,
9
00:00:27,733 --> 00:00:32,136
we still don't understand this inexplicable substance
10
00:00:32,138 --> 00:00:36,840
[de Rham] We know dark matte is there because we feel its strong gravitational pul
11
00:00:36,842 --> 00:00:39,676
but it just doesn't
want to talk to us.
12
00:00:39,678 --> 00:00:41,578
[narrator] There's evidence that dark matter
13
00:00:41,580 --> 00:00:45,582
makes up 85% of all the matter in the universe.
14
00:00:45,651 --> 00:00:49,153
We can see dark matter
holding galaxies together
15
00:00:49,188 --> 00:00:53,991
and ripping
other structures apart,
we even see it bending light.
16
00:00:53,993 --> 00:00:58,629
Dark matter itself has been
around since the beginning
of the universe.
17
00:00:58,631 --> 00:01:02,533
Without dark matter,
we wouldn't be here.
18
00:01:02,535 --> 00:01:04,701
[narrator] But if you can't see dark matter
19
00:01:04,703 --> 00:01:09,006
and if you can't touch it, does it really exist?
20
00:01:22,922 --> 00:01:25,489
[narrator] The Hyades star cluster.
21
00:01:26,859 --> 00:01:32,863
This family of 700 stars is 150 light years from Eart
22
00:01:32,865 --> 00:01:36,266
At the scale of the universe it's in our backyard.
23
00:01:37,002 --> 00:01:38,836
Hyades is actually
close enough to Earth
24
00:01:38,838 --> 00:01:39,970
that you could see it
with your naked eye.
25
00:01:39,972 --> 00:01:42,206
When you look up
at the night sky,
26
00:01:42,208 --> 00:01:45,943
Hyades is in that V-shape
in Taurus the Bull.
27
00:01:47,613 --> 00:01:50,948
[narrator] For most of its 650-million-year lifetime,
28
00:01:51,016 --> 00:01:54,685
the Hyades enjoyed a peaceful existence.
29
00:01:54,687 --> 00:01:58,055
But something is breaking the calm.
30
00:01:58,123 --> 00:02:01,625
The Hyades cluster
is one of the most
well-studied clusters of stars
31
00:02:01,627 --> 00:02:03,660
we have in the entire sky
and yet there's something
32
00:02:03,729 --> 00:02:06,330
very deeply mysterious
going on.
33
00:02:07,366 --> 00:02:11,068
[narrator] Two star tails extend from the cluster center,
34
00:02:11,103 --> 00:02:17,674
they should be roughly equal but one tail is hemorrhaging stars.
35
00:02:17,676 --> 00:02:20,677
Something is disrupting it,
there's something exerting
a force on it
36
00:02:20,679 --> 00:02:24,114
that's ripping stars
out of their orbits.
37
00:02:25,885 --> 00:02:28,752
[narrator] Something with immense gravitational pull
38
00:02:28,820 --> 00:02:30,454
has passed by the cluster
39
00:02:31,257 --> 00:02:33,590
and robbed it of stars.
40
00:02:33,592 --> 00:02:37,895
In order to be gravitationally
pulling stars out
of an object like Hyades,
41
00:02:37,897 --> 00:02:39,730
you need to have an incredibly
massive structure,
42
00:02:39,765 --> 00:02:43,000
as much as 10 million times the mass of the sun.
43
00:02:44,036 --> 00:02:48,005
[narrator] This monstrous cosmic mugger should still be visible,
44
00:02:48,507 --> 00:02:50,607
but when we point our telescopes
45
00:02:50,609 --> 00:02:55,078
to where it should be, that region is empty.
46
00:02:56,115 --> 00:03:00,217
There's nothing there
and I mean nothing.
47
00:03:00,219 --> 00:03:04,087
And not a little bit
or something dark,
or something small,
48
00:03:04,089 --> 00:03:06,223
but there's literally
nothing that we can see.
49
00:03:07,793 --> 00:03:12,763
[narrator] We know somethin is out there, invisible and powerful.
50
00:03:12,765 --> 00:03:15,899
And whenever we witness these unseen assaults,
51
00:03:15,935 --> 00:03:18,835
a prime suspect gets called in,
52
00:03:18,837 --> 00:03:20,304
a phantom of physics,
53
00:03:21,574 --> 00:03:23,307
dark matter.
54
00:03:24,777 --> 00:03:31,415
So what can we confidently s about this mysterious cosmic substance?
55
00:03:31,417 --> 00:03:37,087
It does not emit light,
it does not reflect light,
it does not absorb light.
56
00:03:37,089 --> 00:03:40,891
The only thing we know
about dark matter
is that it has gravity.
57
00:03:40,893 --> 00:03:42,526
We're not even really sure
it's matter at all.
58
00:03:42,528 --> 00:03:45,295
It's just that that's the only
thing we know,
that it has gravity.
59
00:03:45,364 --> 00:03:49,366
[narrator] We may not be abl to see or touch dark matter
60
00:03:49,368 --> 00:03:54,671
but we are very good at finding its fingerprints all over the universe.
61
00:03:54,740 --> 00:04:00,043
We can see dark matter's use of gravity to break and bind structures
62
00:04:00,112 --> 00:04:03,480
and we've been spotting its handiwork for decades.
63
00:04:04,850 --> 00:04:08,018
Let's rewind back to 1933.
64
00:04:09,488 --> 00:04:13,957
Swiss-American physicist, Fritz Zwicky tracks strange movements
65
00:04:13,959 --> 00:04:18,462
in a far off collection of galaxies called the Coma cluster.
66
00:04:18,464 --> 00:04:22,933
He knows he's not seeing the whole picture.
67
00:04:22,935 --> 00:04:28,772
Some galaxies are speeding around the cluster at inexplicably fast rates.
68
00:04:28,774 --> 00:04:30,674
[Bullock] Zwicky is looking at these galaxies
69
00:04:30,676 --> 00:04:34,544
and if the only mass
that was there were the other
galaxies you can see,
70
00:04:34,613 --> 00:04:38,315
you would expect
these galaxies to be moving
at about 50 miles a second,
71
00:04:38,317 --> 00:04:41,618
then they would stay bound
to each other
and not fly apart.
72
00:04:41,620 --> 00:04:45,289
Instead, he sees them moving
at 1,000 miles a second.
73
00:04:46,725 --> 00:04:48,492
[narrator]
At these velocities,
74
00:04:48,494 --> 00:04:53,230
galaxies should be flying of the cluster like sparks from fireworks.
75
00:04:54,933 --> 00:04:59,002
Zwicky realized there had to be extra stuff,
76
00:04:59,338 --> 00:05:03,106
in his words, Dunkle Materie
77
00:05:03,141 --> 00:05:04,908
Dark matter.
78
00:05:04,910 --> 00:05:05,308
Dark matter.
79
00:05:05,310 --> 00:05:07,377
Dark matter.
80
00:05:07,379 --> 00:05:13,817
[narrator] It becomes clear that Zwicky's Coma cluster isn't an isolated case.
81
00:05:13,885 --> 00:05:19,923
Astronomers begin seeing the same dynamics within galaxies themselves.
82
00:05:19,991 --> 00:05:23,126
In systems governed exclusively by gravity,
83
00:05:23,195 --> 00:05:25,295
objects farthest away from the center
84
00:05:25,364 --> 00:05:27,964
would take the longest to complete an orbit.
85
00:05:27,966 --> 00:05:32,502
But in many galaxies, stars on the outside are orbiting
86
00:05:32,504 --> 00:05:36,306
at almost the same rate as those in the core.
87
00:05:36,308 --> 00:05:37,807
[Thaller] It's almost like a photograph record.
88
00:05:37,809 --> 00:05:41,878
Every part of that record spins around like a solid disc.
89
00:05:41,880 --> 00:05:46,416
The stars are going too fast
to stay bound to the gravity
of the galaxy.
90
00:05:46,418 --> 00:05:49,019
They should just
fly right off into space.
91
00:05:49,521 --> 00:05:53,256
[narrator] Physicists come u with an explanation.
92
00:05:53,292 --> 00:05:59,763
Galaxies sit in a giant hal or ball of invisible dark matter.
93
00:05:59,765 --> 00:06:04,101
And it's that extra mass that allows the stars to turn fast
94
00:06:04,103 --> 00:06:06,937
all the way out to the galactic rim.
95
00:06:06,939 --> 00:06:08,638
[Thaller] Think about actual taking a disc of dough
96
00:06:08,640 --> 00:06:10,774
and spinning it
to make a pizza.
97
00:06:10,842 --> 00:06:15,479
The more you spin it,
the more those outer regions
go farther and farther away.
98
00:06:15,481 --> 00:06:17,748
Eventually, the dough
just goes flying everywhere,
99
00:06:17,816 --> 00:06:21,184
that's what would happen to a galaxy if it weren't for dark matter.
100
00:06:21,186 --> 00:06:24,054
Uh, as you spin pizza dough and you spin it faster and faster,
101
00:06:24,056 --> 00:06:25,889
it does hold itself together
102
00:06:25,891 --> 00:06:30,527
because there's all this yummy
gluten that's acting
as a glue.
103
00:06:30,595 --> 00:06:33,997
Dark matter is the gluten
of our universe.
104
00:06:34,733 --> 00:06:37,734
[narrator] By calculating the mass needed to bind
105
00:06:37,736 --> 00:06:40,871
those speeding outer stars to the galaxy,
106
00:06:40,939 --> 00:06:43,006
physicists are able to estimate
107
00:06:43,008 --> 00:06:47,177
how much visible matter there is compared to dark matter.
108
00:06:47,179 --> 00:06:49,813
The results are staggering.
109
00:06:49,881 --> 00:06:53,884
[Tegmark] All the stuff we thought existed was just maybe 15% of our universe.
110
00:06:53,886 --> 00:06:56,019
That's like if you go
to a restaurant
111
00:06:56,021 --> 00:07:00,624
and leave like the measly
15% tip, you know,
that's what we are.
112
00:07:00,626 --> 00:07:02,426
I mean, not even
the majority substance.
113
00:07:03,595 --> 00:07:05,495
[narrator] We may not be able to see it,
114
00:07:05,497 --> 00:07:10,066
but dark matter makes up some 85% of all matter.
115
00:07:10,101 --> 00:07:14,638
Wherever we look, we can se its gravity having effects.
116
00:07:14,640 --> 00:07:18,842
It glues galaxies like our Milky Way together
117
00:07:18,910 --> 00:07:25,081
And a close look reveals dark matter can also bend light itself.
118
00:07:26,752 --> 00:07:29,586
It's called gravitational lensing.
119
00:07:29,588 --> 00:07:32,722
A massive object
can bend space and time,
120
00:07:32,724 --> 00:07:38,728
and light must follow
the curves of that space
and time.
121
00:07:38,730 --> 00:07:43,834
[narrator] Gigantic clumps of any matter create a gravitational lens.
122
00:07:43,902 --> 00:07:48,605
Dark matter showed its space-warping power in a trick it played
123
00:07:48,607 --> 00:07:53,310
with a gigantic explosion in a far off galaxy cluster
124
00:07:54,980 --> 00:08:00,016
Supernova Refsdal was first detected in November of 2014
125
00:08:00,986 --> 00:08:04,988
Supernova Refsdal
is actually one of my favorite
recent results
126
00:08:04,990 --> 00:08:07,424
in all of the astronomical
literature.
127
00:08:07,426 --> 00:08:08,992
That result blew me away.
128
00:08:09,027 --> 00:08:12,863
So a star explodes,
light is emitted
in all directions,
129
00:08:12,865 --> 00:08:15,966
and some of it makes its way
towards the Earth.
130
00:08:15,968 --> 00:08:18,702
So far so good.
This is very standard.
131
00:08:18,770 --> 00:08:20,237
So the flash appears
132
00:08:20,973 --> 00:08:23,340
and then, another flash appears.
133
00:08:24,476 --> 00:08:28,945
We see it again,
and again, and again.
134
00:08:28,947 --> 00:08:32,883
[Mingarelli] We see the explosion go off in four parts of the sky.
135
00:08:32,885 --> 00:08:36,119
And then, a year later,
a fifth explosion goes off
136
00:08:36,187 --> 00:08:38,088
in a totally different part
of the sky.
137
00:08:38,090 --> 00:08:39,990
What's going on?
138
00:08:39,992 --> 00:08:45,662
[narrator] Analysis proves that these multiple explosio are the same supernova.
139
00:08:45,664 --> 00:08:50,133
-[explosion]
-But between this one dying star and our telescope
140
00:08:50,135 --> 00:08:53,403
sits a giant mass of dark matter,
141
00:08:53,405 --> 00:08:56,840
a huge gravitational lens.
142
00:08:56,842 --> 00:09:01,511
What that means is that some
of these rays of light
will take much longer,
143
00:09:01,580 --> 00:09:05,282
more complicated paths
through this region
of space time.
144
00:09:05,951 --> 00:09:09,519
[narrator] The dark matter lens turns one supernova
145
00:09:09,588 --> 00:09:14,224
into a fireworks display lasting an entire year.
146
00:09:15,494 --> 00:09:19,763
Dark matter affected
the trajectory of light
from this supernova so much
147
00:09:19,831 --> 00:09:21,865
that for some
of those trajectories,
148
00:09:21,900 --> 00:09:24,467
it added a whole light year,
149
00:09:24,536 --> 00:09:28,438
it took a whole extra year for light to reach us.
150
00:09:29,608 --> 00:09:32,842
[narrator] Something is ver definitely out there
151
00:09:32,911 --> 00:09:35,445
distorting our view of the cosmos.
152
00:09:36,682 --> 00:09:41,117
It's a potent clue that dark matter is real.
153
00:09:41,119 --> 00:09:47,090
Now, new evidence suggests that without it, we might not exist at all.
154
00:09:54,866 --> 00:09:58,268
[narrator] The cosmos is filled with an unseen substance,
155
00:09:58,503 --> 00:10:02,739
its mass even bends starligh
156
00:10:02,774 --> 00:10:09,212
Gravitational lensing sugges dark matter holds our entir universe together.
157
00:10:10,515 --> 00:10:14,651
For decades, this specter of space has haunted us.
158
00:10:14,719 --> 00:10:17,787
We've never been able to pin it down.
159
00:10:17,789 --> 00:10:23,927
In 2021, an international te ran a virtual experiment to try to predict
160
00:10:23,929 --> 00:10:27,631
where dark matter should be by letting computers
161
00:10:27,699 --> 00:10:30,400
map out where we think it lives.
162
00:10:30,468 --> 00:10:33,003
[Bullock] Because we think we know how it behaves,
163
00:10:33,071 --> 00:10:36,506
we can model what it should
be doing in supercomputer
simulations.
164
00:10:37,676 --> 00:10:42,946
[narrator] The team taught the computer how dark matte bends light,
165
00:10:42,948 --> 00:10:49,986
then applied computational power to 17,000 unexplored galaxies.
166
00:10:50,656 --> 00:10:55,558
The model created a dark matter map.
167
00:10:55,560 --> 00:10:58,728
I think a lot of people,
when they imagine the universe
on the larger scales,
168
00:10:58,730 --> 00:11:01,031
think it's sort of boring,
everything's uniform.
169
00:11:01,033 --> 00:11:03,500
But that's not what we see.
170
00:11:03,502 --> 00:11:06,436
What's amazing is that
on the larger scales
of the universe,
171
00:11:06,438 --> 00:11:09,105
we see a very
particular pattern.
172
00:11:09,107 --> 00:11:12,475
When we zoom out,
we see this magnificent
structure,
173
00:11:12,477 --> 00:11:15,378
this cosmic web
that's created by dark matter.
174
00:11:16,581 --> 00:11:19,282
[narrator]
The interweaving tendrils of dark matter stretch
175
00:11:19,284 --> 00:11:23,887
for thousands of light year across the cosmos.
176
00:11:23,922 --> 00:11:30,093
At the junctions where matte is concentrated, we find galaxies form,
177
00:11:30,095 --> 00:11:32,462
illuminating the dark scaffold.
178
00:11:34,066 --> 00:11:36,733
If dark matter exists, scientists believe
179
00:11:36,735 --> 00:11:40,937
it makes up 85% of the matte in the universe,
180
00:11:41,005 --> 00:11:45,575
and also controls the remaining 15% regular matter,
181
00:11:45,643 --> 00:11:49,179
like stars, planets, us.
182
00:11:50,482 --> 00:11:54,250
If they're right, dark matte played a critical role
183
00:11:54,252 --> 00:11:58,388
in actually building the universe we see today.
184
00:12:03,061 --> 00:12:04,494
2021.
185
00:12:04,496 --> 00:12:08,231
Astronomers using the SkyMapper observatory in Australia
186
00:12:08,233 --> 00:12:14,738
trains specialist optics on a dwarf galaxy called Tucana II.
187
00:12:14,740 --> 00:12:20,477
The SkyMapper's filters split up the starlight into a spectrum of wavelengt
188
00:12:20,479 --> 00:12:24,347
revealing some very ancient light.
189
00:12:25,751 --> 00:12:30,186
[Tremblay] One of the best clocks that we can put on the universe
190
00:12:30,255 --> 00:12:32,288
is the progress of chemistry.
191
00:12:32,390 --> 00:12:33,456
Right?
192
00:12:33,458 --> 00:12:37,527
The build-up of more complex
elements over time.
193
00:12:37,529 --> 00:12:41,898
Stars are nothing if not factories of chemical complexity.
194
00:12:41,900 --> 00:12:45,602
They slam, uh, particles
together and create
heavier elements,
195
00:12:45,670 --> 00:12:48,238
right, through a process
called fusion.
196
00:12:48,273 --> 00:12:52,475
The later the generation of star, the more chemicall complex it is.
197
00:12:52,477 --> 00:12:56,613
[narrator] Tucana II's spectral signature reveals its stars contain
198
00:12:56,681 --> 00:13:00,517
very few of these heavy complex elements.
199
00:13:00,519 --> 00:13:05,822
A clue that lets astrophysicists calculate the age of the galaxy.
200
00:13:05,890 --> 00:13:10,693
These are very, very old stars
from the very early days
of the universe
201
00:13:10,695 --> 00:13:15,265
when the gas
in the universe was not
that chemically complex.
202
00:13:15,967 --> 00:13:19,936
Tucana II might be one of the oldest known structur
203
00:13:20,004 --> 00:13:21,905
that we can see in our local universe.
204
00:13:21,973 --> 00:13:25,341
It could be as old
as 13 billion years.
205
00:13:25,343 --> 00:13:28,111
You know, almost as old
as the universe itself.
206
00:13:29,848 --> 00:13:33,283
[narrator] This grand old la of a galaxy is a tiny thing
207
00:13:33,318 --> 00:13:35,385
Barely 3,000 stars.
208
00:13:37,088 --> 00:13:39,589
And yet, way out on her galactic rim,
209
00:13:39,657 --> 00:13:43,993
stars hurdle around at breakneck speed.
210
00:13:43,995 --> 00:13:47,497
[Plait] When you look at the mass of this ultra-faint dwarf galaxy,
211
00:13:47,499 --> 00:13:50,700
it only has a few thousand
times the mass of the sun.
212
00:13:50,702 --> 00:13:52,268
That's really small.
213
00:13:52,270 --> 00:13:54,904
And at the speed it's moving,
it should fly apart.
214
00:13:54,906 --> 00:14:00,009
[narrator] Tucana II doesn' break up because it's glued together,
215
00:14:00,011 --> 00:14:04,581
apparently by an incredible amount of dark matter.
216
00:14:04,583 --> 00:14:06,649
When you look at a galaxy
like our Milky Way,
217
00:14:06,651 --> 00:14:10,053
it's about 85% dark matter,
which is a lot.
218
00:14:10,055 --> 00:14:14,090
But with Tucana II,
it's more like 99%.
219
00:14:14,092 --> 00:14:18,361
[narrator] Tucana II is old among the oldest galaxies in the universe
220
00:14:18,363 --> 00:14:22,365
and it is packed full of dark matter.
221
00:14:22,367 --> 00:14:27,437
Simulations suggest this dark matter played a ke role in shaping Tucana II
222
00:14:27,439 --> 00:14:31,574
and other very early galaxie right from the beginning,
223
00:14:31,576 --> 00:14:38,848
gathering regular matter into clumps and building the first galaxies.
224
00:14:38,850 --> 00:14:41,017
[Thaller] The importance of dark matter really can't be overstated.
225
00:14:41,019 --> 00:14:44,454
It has actually controlled
the way matter has evolved
226
00:14:44,522 --> 00:14:45,488
since the beginning of the universe.
227
00:14:45,556 --> 00:14:47,357
It brings matter together.
228
00:14:47,359 --> 00:14:53,096
You need this underlying structure of dark matter to make it all happen.
229
00:14:53,098 --> 00:14:58,468
[narrator] Scientists think that for billions of years as the early universe grew,
230
00:14:58,470 --> 00:15:00,670
dark matter called the shots
231
00:15:00,672 --> 00:15:06,109
Without its gravity, structures like the Milky Wa wouldn't have formed.
232
00:15:07,812 --> 00:15:11,147
We've seen dark matter's light-bending effects.
233
00:15:11,149 --> 00:15:14,450
We've even deduced where it should be.
234
00:15:14,452 --> 00:15:18,454
Dark matter really does appear to exist,
235
00:15:18,456 --> 00:15:22,292
but this evidence is indirect, circumstantial
236
00:15:23,161 --> 00:15:27,497
To get conclusive proof that dark matter exists,
237
00:15:27,499 --> 00:15:29,232
don't we need to find some?
238
00:15:29,668 --> 00:15:33,903
If we could find a lump
of dark matter [laughs],
239
00:15:33,972 --> 00:15:37,106
um, that would be one
of the greatest discoveries
in all of nature,
240
00:15:37,108 --> 00:15:38,541
in all of our history, right?
241
00:15:38,543 --> 00:15:40,042
Because we would understand
242
00:15:40,278 --> 00:15:44,280
one of the most fundamental
components for how
our universe works.
243
00:15:44,816 --> 00:15:47,016
Dropping the title,
they love that.
244
00:15:48,153 --> 00:15:52,221
[narrator] It's time to hun for dark matter itself.
245
00:15:52,223 --> 00:15:56,459
Could it be hiding in the darkest place of all
246
00:15:57,796 --> 00:15:59,429
Black holes.
247
00:16:09,574 --> 00:16:11,874
[narrator] Scientists believ an invisible substance
248
00:16:11,943 --> 00:16:15,878
is pulling the strings in our universe.
249
00:16:15,947 --> 00:16:19,882
But until we see it, sense i perhaps even touch it,
250
00:16:19,951 --> 00:16:22,452
dark matter is just a theory
251
00:16:23,855 --> 00:16:26,022
Sometimes though, ideas dreamed up
252
00:16:26,024 --> 00:16:28,324
by scientists come true
253
00:16:28,827 --> 00:16:31,961
like black holes.
254
00:16:31,963 --> 00:16:35,965
Once the stuff of science fiction and children's nightmares,
255
00:16:35,967 --> 00:16:40,770
black holes today are confirmed reality.
256
00:16:40,772 --> 00:16:43,940
So black holes
and dark matter have a ton
of similarities, right?
257
00:16:43,942 --> 00:16:46,476
You know,
an unseen collection of matter
258
00:16:46,478 --> 00:16:48,878
that creates an enormous
gravitational field, check.
259
00:16:48,913 --> 00:16:52,882
It bends light
and causes gravitational
lensing, check.
260
00:16:52,917 --> 00:16:56,352
Tests the boundaries
of known physics, check.
261
00:16:57,622 --> 00:16:59,956
[narrator] It seems crazy to even ask,
262
00:16:59,958 --> 00:17:01,858
but could our search for dark matter
263
00:17:01,860 --> 00:17:06,596
end in an idea more than 100 years old?
264
00:17:06,598 --> 00:17:10,099
Could dark matter be black holes?
265
00:17:11,669 --> 00:17:14,570
Black holes appear when stars explode.
266
00:17:14,572 --> 00:17:17,774
And their remaining mass crunches down into a sphere
267
00:17:17,842 --> 00:17:22,845
so dense even light can't escape its gravity.
268
00:17:22,847 --> 00:17:27,350
But that's where the black hole dark matter theory stumbles.
269
00:17:27,352 --> 00:17:29,619
We know
that black holes happen.
We know how they form.
270
00:17:29,687 --> 00:17:34,924
And we also know that there's
nowhere near enough of them
to be dark matter.
271
00:17:34,926 --> 00:17:38,728
[narrator] Not enough stars have lived and died in the history of the univer
272
00:17:38,730 --> 00:17:42,932
to create 85% of the matter in it.
273
00:17:42,967 --> 00:17:46,235
If dark matter is made up of black holes,
274
00:17:46,237 --> 00:17:50,673
they would have to be an entirely new type.
275
00:17:50,675 --> 00:17:55,678
It's possible that these black
holes are of a type
that we've never seen before.
276
00:17:55,746 --> 00:17:59,148
They could be
primordial black holes.
277
00:18:00,585 --> 00:18:03,686
[Hopkins] Primordial black holes are an idea.
278
00:18:03,688 --> 00:18:05,488
A theoretical concept at this point
279
00:18:05,490 --> 00:18:10,159
that we've never seen,
but they could exist.
280
00:18:10,194 --> 00:18:15,765
If primordial black holes
are real then the universe
is flooded with black holes.
281
00:18:15,767 --> 00:18:18,367
[Hopkins] The smallest coul have the mass of Mount Evere
282
00:18:18,402 --> 00:18:20,436
packed into the size of one atom.
283
00:18:20,438 --> 00:18:27,443
The biggest could be hundreds
of thousands or millions
of times the mass of the sun.
284
00:18:27,512 --> 00:18:30,780
[narrator] Stephen Hawking first suggested that primordial black holes
285
00:18:30,782 --> 00:18:35,718
could be dark matter back in the 1970s.
286
00:18:35,720 --> 00:18:40,389
The idea centers on what happened during that intangible momen
287
00:18:40,391 --> 00:18:45,895
13.8 billion years ago, the big-bang.
288
00:18:45,963 --> 00:18:50,466
Theory says
that primordial black holes
formed in the first fraction
289
00:18:50,468 --> 00:18:52,401
of a second
of the early universe.
290
00:18:52,403 --> 00:18:55,104
It's that time
between when the universe
291
00:18:55,106 --> 00:19:00,576
goes from a pinprick
to this giant inflating
ball of gas.
292
00:19:00,578 --> 00:19:03,746
[narrator] In these first moments of the universe's existence,
293
00:19:03,748 --> 00:19:07,150
matter is packed incredibly tightly.
294
00:19:07,185 --> 00:19:10,520
But it's not quite evenly spread.
295
00:19:10,522 --> 00:19:16,225
Even the tiniest fluctuation in density could trigger gravitational collapses.
296
00:19:17,495 --> 00:19:21,330
In other words, black holes would be forming everywhere,
297
00:19:21,866 --> 00:19:24,967
theoretically, in huge numbers.
298
00:19:25,737 --> 00:19:30,506
By the time one second
has passed in our universe,
299
00:19:30,508 --> 00:19:33,276
you're already making
black holes
300
00:19:33,344 --> 00:19:37,947
thousands, hundreds
of thousands of times
more massive than our sun.
301
00:19:37,949 --> 00:19:41,517
[narrator] The collective ma of these objects could be va
302
00:19:41,586 --> 00:19:46,622
but could they be 85% of the universe's matter?
303
00:19:46,624 --> 00:19:48,591
[Sutter] If primordial black holes really do exist
304
00:19:48,593 --> 00:19:53,663
there might be enough
to explain the dark matter.
305
00:19:53,731 --> 00:20:00,770
[narrator] It's a tantalizin possibility, but there's on pretty big problem.
306
00:20:00,772 --> 00:20:03,739
For most scientists, the physics of the very early universe
307
00:20:03,741 --> 00:20:06,876
is incomplete and hard to trust.
308
00:20:06,878 --> 00:20:11,681
Generations of physicists dismissed primordial black holes
309
00:20:11,749 --> 00:20:17,019
as myths, fantasies, astrophysical unicorns,
310
00:20:17,021 --> 00:20:21,224
until that is, an earthshaki crash in space.
311
00:20:21,793 --> 00:20:24,427
May, 2019.
312
00:20:24,462 --> 00:20:27,463
A violent cosmic event rocks the USA.
313
00:20:27,465 --> 00:20:29,198
How violent?
314
00:20:29,200 --> 00:20:33,236
Well, the physical distance between Louisiana and Washington state
315
00:20:33,271 --> 00:20:39,575
is stretched by nearly the width of an atom which is bigger than it sounds.
316
00:20:39,577 --> 00:20:42,578
The Laser Interferometer Gravitational-Wave Observato
317
00:20:42,580 --> 00:20:45,982
detects this wobble in space time.
318
00:20:46,484 --> 00:20:51,587
This is the biggest
gravitational wave event
that LIGO has seen.
319
00:20:51,589 --> 00:20:56,559
[narrator] This cosmic disturbance seems to come from colliding black holes
320
00:20:56,561 --> 00:21:02,198
but crucially not the ordina dead star type.
321
00:21:02,233 --> 00:21:06,836
In this LIGO detection,
one of the black holes
is 85 solar masses.
322
00:21:06,838 --> 00:21:12,375
There's no way that a star
could've made that black hole.
323
00:21:12,377 --> 00:21:15,411
[narrator] Physicists believ there's a range of masses
324
00:21:15,413 --> 00:21:20,883
where dying stars can't collapse into black holes.
325
00:21:20,885 --> 00:21:26,822
Instead, stars in this zone become insanely hot and rip themselves apart
326
00:21:26,824 --> 00:21:31,294
leaving nothing to crunch do into a black hole.
327
00:21:32,664 --> 00:21:35,731
Eighty-five solar masses sits right in the middle
328
00:21:35,800 --> 00:21:39,902
of this so called forbidden mass range.
329
00:21:39,904 --> 00:21:43,472
The black hole that LIGO detected can't be a dead star,
330
00:21:43,474 --> 00:21:47,643
but in theory it could be primordial.
331
00:21:47,645 --> 00:21:52,481
Could this discarded theory of dark matter be back in fashion?
332
00:21:52,483 --> 00:21:55,217
The LIGO detections come up
and everyone says,
333
00:21:55,286 --> 00:21:57,753
"Oh, right,
primordial black holes.
334
00:21:57,755 --> 00:22:00,623
Maybe we should pay
more attention to that."
335
00:22:00,691 --> 00:22:03,059
Primordial black holes can
be really appealing
336
00:22:03,061 --> 00:22:05,961
because they would solve the dark matter problem.
337
00:22:06,531 --> 00:22:09,699
But unfortunately,
it's not that simple.
338
00:22:09,767 --> 00:22:13,803
The thing with flooding
the universe with primordial
black holes
339
00:22:13,805 --> 00:22:16,339
is that you expect
a lot of collisions.
340
00:22:16,341 --> 00:22:18,641
And so LIGO shouldn't
have seen one,
341
00:22:18,709 --> 00:22:23,045
it should have seen a thousand
of these collisions
and we don't.
342
00:22:24,115 --> 00:22:29,318
[narrator] Many scientists doubt what LIGO saw was a primordial black hole
343
00:22:30,288 --> 00:22:34,457
To them, these beasts remai fairytales of physics,
344
00:22:34,459 --> 00:22:38,494
red herrings in the quest for solid evidence of dark matter.
345
00:22:41,833 --> 00:22:43,866
Does dark matter exist?
346
00:22:43,868 --> 00:22:46,635
Or are we chasing shadows?
347
00:22:46,637 --> 00:22:49,472
Some scientists think it's not only real,
348
00:22:49,474 --> 00:22:52,775
but the dark matter is within our grasp,
349
00:22:52,777 --> 00:22:57,279
and that it's flying through our bodies right now
350
00:23:07,125 --> 00:23:11,394
[narrator] We think 85% of the universe's matter is dark.
351
00:23:12,563 --> 00:23:15,698
And yet, we've never found a speck of it.
352
00:23:15,700 --> 00:23:19,802
We can't prove dark matter exists.
353
00:23:19,837 --> 00:23:25,040
Regular matter is made up of everyday particles, like electrons and protons.
354
00:23:26,477 --> 00:23:31,414
Scientists wonder if dark matter is also a type of particle.
355
00:23:32,517 --> 00:23:34,717
One of the leading candidates
for dark matter
356
00:23:34,719 --> 00:23:38,454
are these things called
Weakly Interacting
Massive Particles.
357
00:23:38,522 --> 00:23:41,657
They're massive particles
like protons and electrons
and things like that.
358
00:23:41,725 --> 00:23:44,927
But they don't interact well
with normal matters,
so they're weakly interacting.
359
00:23:44,929 --> 00:23:48,097
And they just have this name
because it's awesome
to call them WIMPs.
360
00:23:49,600 --> 00:23:51,967
[narrator] For decades, scientists have struggled
361
00:23:51,969 --> 00:23:55,971
to find these shy theoretical particles.
362
00:23:55,973 --> 00:23:59,074
[Oluseyi] The very first physics research I ever did in my life
363
00:23:59,076 --> 00:24:04,480
was about actually
measuring directly
dark matter particles,
364
00:24:04,482 --> 00:24:06,148
these so called WIMPs.
365
00:24:06,150 --> 00:24:10,686
And if they exist,
then there will be a flux
of millions of them
366
00:24:10,688 --> 00:24:13,856
through my hand right now,
just by holding out
right here.
367
00:24:13,858 --> 00:24:17,460
If dark matter is actually
made of WIMPs,
if these particles exist,
368
00:24:17,462 --> 00:24:21,530
then we're actually living
basically in a sea of them.
369
00:24:21,532 --> 00:24:25,501
It surrounds and penetrates us and it bin the galaxy together.
370
00:24:26,737 --> 00:24:30,773
[narrator] WIMPs don't play by our rules.
371
00:24:30,775 --> 00:24:33,809
They barely interact with the world of regular matter,
372
00:24:33,811 --> 00:24:36,011
so they're hard to detect.
373
00:24:36,514 --> 00:24:38,781
But when they play with each other,
374
00:24:38,849 --> 00:24:45,221
sparks fly, intense flashes that we just might be able to see.
375
00:24:45,957 --> 00:24:49,892
[Plait] As the theory goes, WIMPs will self-annihilate.
376
00:24:49,894 --> 00:24:53,028
WIMP A and WIMP B
get too close together, poof,
377
00:24:53,030 --> 00:24:55,331
they explode
and they create gamma rays.
378
00:24:56,367 --> 00:25:01,103
[narrator] Gamma rays are high energy light, making them easy to spot.
379
00:25:03,541 --> 00:25:07,710
Scientists point their detectors at the cente of the Milky Way,
380
00:25:07,712 --> 00:25:12,948
where they believe the WIMP collision rate should be especially high.
381
00:25:13,017 --> 00:25:15,217
[Plait] We have a 4 million solar mass black hole there
382
00:25:15,219 --> 00:25:16,485
There are billions of stars there.
383
00:25:16,553 --> 00:25:20,756
That's where most of the mass
of the galaxies is densest.
384
00:25:20,824 --> 00:25:24,460
So any WIMPs orbiting the galaxy will feel this natural attraction
385
00:25:24,462 --> 00:25:26,896
towards the center and fall toward it.
386
00:25:26,898 --> 00:25:29,798
[narrator] The Fermi Large Area Telescope scoured
387
00:25:29,867 --> 00:25:33,269
the center of our galaxy for more than 10 years.
388
00:25:33,671 --> 00:25:36,338
It detected lots of gamma rays,
389
00:25:36,340 --> 00:25:41,410
but scientists couldn't tel if they came from colliding WIMPs.
390
00:25:41,412 --> 00:25:45,014
The Galactic Center is a mess.
It's like downtown
of a city, right?
391
00:25:45,016 --> 00:25:47,483
That's where everything is,
where all the hustle
and bustle is.
392
00:25:47,485 --> 00:25:49,451
There are stars exploding there,
393
00:25:49,520 --> 00:25:51,887
just tons of stars, gas,
magnetic fields, a black hole,
394
00:25:51,889 --> 00:25:53,656
a lot of sources
of gamma rays,
395
00:25:53,658 --> 00:25:56,458
so it's very difficult
to tease out the signal.
396
00:25:56,460 --> 00:25:59,061
[narrator] Downtown Milky Wa was a washout.
397
00:25:59,063 --> 00:26:01,730
So the scientists turned their attention to planets
398
00:26:01,799 --> 00:26:03,866
living in less noisy ZIP codes,
399
00:26:03,868 --> 00:26:07,970
where WIMP collisions should be easier to spot.
400
00:26:07,972 --> 00:26:10,639
One place where you might see
evidence for WIMP collisions
401
00:26:10,641 --> 00:26:12,908
is actually the cores
of exoplanets.
402
00:26:12,910 --> 00:26:19,148
Turns out exoplanets might
be the best dark matter
detector we have.
403
00:26:20,017 --> 00:26:22,885
You can use giant planets
orbiting distant stars
404
00:26:22,887 --> 00:26:26,155
as laboratories
to understand dark matter.
405
00:26:26,891 --> 00:26:30,526
[narrator] We know gravity should attract WIMPs.
406
00:26:30,594 --> 00:26:35,764
The more gravity, the more dark matter particl come together.
407
00:26:35,766 --> 00:26:39,969
Scientists suggest that WIMP congregate inside the cores
408
00:26:40,037 --> 00:26:42,805
of the Milky Way's largest gas planets.
409
00:26:42,807 --> 00:26:45,674
In these super-sized gas giants,
410
00:26:45,676 --> 00:26:51,413
WIMPs could collide, annihilate, and release gamma rays.
411
00:26:51,415 --> 00:26:53,482
If there are these WIMPs
that are collecting
the centers
412
00:26:53,484 --> 00:26:56,018
of mass of exoplanets,
the annihilation
of that dark matter
413
00:26:56,020 --> 00:26:57,886
can heat those exoplanets up.
414
00:26:57,888 --> 00:27:02,291
If you have a WIMP-heated
exoplanet, and that's just fun
to say,
415
00:27:02,359 --> 00:27:03,859
this thing is going
to be warm,
416
00:27:03,861 --> 00:27:06,829
it's gonna be warmer
than the heat of space,
which is very cold.
417
00:27:06,831 --> 00:27:09,164
So what you need
is an infrared telescope,
418
00:27:09,166 --> 00:27:11,700
something that sees
an infrared light
and is sensitive enough
419
00:27:11,702 --> 00:27:14,803
to be able to measure
the temperatures
of these things.
420
00:27:14,872 --> 00:27:20,042
[narrator] But a dedicated telescope like this won't launch until 2028.
421
00:27:21,746 --> 00:27:25,547
For some dark matter hunters that's too long to wait.
422
00:27:25,549 --> 00:27:29,485
They argue that WIMPs do have one characteristic
423
00:27:29,487 --> 00:27:33,155
that should allow us to detect them right here on Earth.
424
00:27:33,891 --> 00:27:37,826
The key to detecting WIMPs
is in their name,
it's the W-I.
425
00:27:37,828 --> 00:27:40,829
They're weakly interacting.
They're not not interacting.
426
00:27:40,831 --> 00:27:43,599
They do interact,
it's just very weak
with matter.
427
00:27:43,634 --> 00:27:46,502
And that means that
there are the rare occasions
428
00:27:46,504 --> 00:27:48,771
where it will smack
into a particle
of normal matter
429
00:27:48,839 --> 00:27:51,273
and then there are effects
that we can observe.
430
00:27:52,777 --> 00:27:58,414
[narrator] Scientists in Gran Sasso in Central Italy watch for a spark of energy
431
00:27:58,449 --> 00:28:02,685
generated when a WIMP hits an atom of regular matter.
432
00:28:02,720 --> 00:28:06,522
Their detector, a tank of super cooled xenon
433
00:28:06,524 --> 00:28:11,493
built thousands of feet beneath the Earth's surface
434
00:28:11,495 --> 00:28:14,997
The beauty of putting
this detector under a mountain
is that you've got all of this
435
00:28:14,999 --> 00:28:16,732
rock and soil
and everything else
436
00:28:16,734 --> 00:28:18,801
which is blocking
a lot of background noise.
437
00:28:18,836 --> 00:28:20,936
When you're looking
for a WIMP interaction,
438
00:28:20,938 --> 00:28:24,573
you're looking for something
that's very rare
and something very subtle,
439
00:28:24,575 --> 00:28:27,009
so you don't want
other things going on.
440
00:28:27,044 --> 00:28:29,411
You don't want other particles
coming in and messing up
your experiment.
441
00:28:29,480 --> 00:28:33,849
These Weakly Interacting
Massive Particles will pass
right through that mountain,
442
00:28:33,917 --> 00:28:36,418
and then if they smack into a xenon atom, we can look at it and go,
443
00:28:36,420 --> 00:28:39,388
"Ah, that was a dark matter particle."
444
00:28:39,390 --> 00:28:44,927
[narrator] Detecting a WIMP could be definitive proof that dark matter exists.
445
00:28:44,995 --> 00:28:49,898
In 2020, the scientists spotted something in the results.
446
00:28:49,900 --> 00:28:52,301
But was it the elusive evidence
447
00:28:53,003 --> 00:28:56,205
or a ghost among the stars?
448
00:29:03,614 --> 00:29:06,749
[ambient music playing]
449
00:29:06,751 --> 00:29:09,284
[narrator] Scientists believ they can prove dark matter is real
450
00:29:09,320 --> 00:29:12,621
by detecting WIMPs.
451
00:29:12,623 --> 00:29:16,792
An experiment buried deep beneath an Italian mountain
452
00:29:16,794 --> 00:29:21,096
spotted unusual activity in a tank of regular matter
453
00:29:21,098 --> 00:29:22,898
pure liquid xenon.
454
00:29:22,900 --> 00:29:25,000
[popping]
455
00:29:26,470 --> 00:29:29,972
So a WIMP detector,
like the XENON1T,
456
00:29:30,007 --> 00:29:33,909
waits for a little WIMP,
tiny, tiny little particle
457
00:29:33,977 --> 00:29:36,745
to hit an atom
of normal matter,
458
00:29:36,747 --> 00:29:38,747
and that creates a vibration.
459
00:29:38,749 --> 00:29:42,718
And we can see this entire
block of xenon shake
460
00:29:42,786 --> 00:29:46,255
just a little bit
from that little,
subatomic collision.
461
00:29:47,458 --> 00:29:49,191
[narrator] The intensity of the vibration
462
00:29:49,193 --> 00:29:52,127
from the particle collision is critical.
463
00:29:52,129 --> 00:29:58,534
In theory, a WIMP striking a xenon atom should generat a powerful shock.
464
00:29:58,536 --> 00:30:03,405
The vibrations XENON1T detected were too weak.
465
00:30:05,042 --> 00:30:08,010
When a WIMP comes through,
it smashes into the atom.
466
00:30:08,012 --> 00:30:11,513
It seemed like here
something was just sort of
rattling the electrons
467
00:30:11,515 --> 00:30:13,248
on the outside of the atom.
468
00:30:13,283 --> 00:30:15,584
So whatever is causing
these detections was likely
469
00:30:15,586 --> 00:30:18,487
something much smaller
than a WIMP.
470
00:30:18,489 --> 00:30:21,290
[Sutter] Let's take these results at face value
471
00:30:21,358 --> 00:30:23,926
It... If they're correct,
it's telling us
472
00:30:23,994 --> 00:30:26,428
that the dark matter
isn't a WIMP,
473
00:30:26,463 --> 00:30:28,397
but something
much, much smaller
474
00:30:28,399 --> 00:30:30,332
and something
much, much lighter.
475
00:30:31,368 --> 00:30:34,469
[narrator] The results sugge that what hit the xenon
476
00:30:34,471 --> 00:30:40,776
was actually a much smaller theoretical particl called an axion.
477
00:30:40,844 --> 00:30:44,146
[Bullock] Axions are really weird particles, incredibly light.
478
00:30:44,148 --> 00:30:47,916
In fact, almost zero mass
is possible for an axion.
479
00:30:47,918 --> 00:30:50,519
An axion is no bigger
480
00:30:50,587 --> 00:30:55,457
than 150 billionth
the size of an electron.
481
00:30:55,459 --> 00:31:02,731
Compared to a WIMP,
an axion is like a soccer ball
compared to our sun.
482
00:31:02,733 --> 00:31:05,534
[narrator] The sheer tinines of axions makes them seem
483
00:31:05,536 --> 00:31:08,070
like an unlikely candidate for dark matter.
484
00:31:09,740 --> 00:31:14,977
If dark matter is real, it makes up 85% of the matte in the universe.
485
00:31:18,015 --> 00:31:24,152
To account for all that mass we would need an almost unfathomable number of axion
486
00:31:24,955 --> 00:31:28,590
142 trigintillion of them, in fact.
487
00:31:28,592 --> 00:31:32,027
That's 140 with 93 zeros after it.
488
00:31:33,364 --> 00:31:37,833
If axions exist, space must swimming with them.
489
00:31:37,835 --> 00:31:42,437
They must be packed into every corner of the cosmos.
490
00:31:42,506 --> 00:31:46,008
When regular matter clumps together, it forms stars.
491
00:31:46,644 --> 00:31:49,611
So, to prove dark matter exists,
492
00:31:49,613 --> 00:31:52,447
maybe we should be looking for dark stars.
493
00:31:53,984 --> 00:31:56,218
There's no reason they can't exist.
494
00:31:56,220 --> 00:31:58,053
There's even a name for them
495
00:31:58,923 --> 00:32:00,389
Ghost stars.
496
00:32:01,558 --> 00:32:03,825
[Bullock] They're very weird objects.
497
00:32:03,827 --> 00:32:07,930
These ghost stars are like
nothing we would ever see
in the night sky.
498
00:32:07,932 --> 00:32:09,431
[narrator] We've never seen a ghost star.
499
00:32:09,433 --> 00:32:14,870
They are theoretical object made of hypothetical axions
500
00:32:14,872 --> 00:32:20,208
But in theory, ghost stars should form like any other star,
501
00:32:20,243 --> 00:32:22,544
pulled together by gravity.
502
00:32:22,546 --> 00:32:28,417
They would be gigantic, super dense objects floating through space.
503
00:32:28,419 --> 00:32:32,321
They could reach the mass of tens of millions of suns
504
00:32:32,823 --> 00:32:35,891
But because they are made of dark matter,
505
00:32:35,926 --> 00:32:40,696
ghost stars would produce no energy and emit no light
506
00:32:40,698 --> 00:32:45,667
They would be transparent to both light and matter.
507
00:32:45,669 --> 00:32:48,870
If you were right next to it,
you wouldn't
even notice it, right?
508
00:32:48,905 --> 00:32:52,474
If we sent a probe through it,
it'd sail right through it
509
00:32:52,476 --> 00:32:55,911
uh, and once it passed
through, it would be
pulled back by its gravity.
510
00:32:55,946 --> 00:33:02,584
[narrator] 85% of the matte in our universe could consis of transparent orbs
511
00:33:02,586 --> 00:33:07,322
made of infinitesimally small, dark matter particles
512
00:33:08,058 --> 00:33:11,226
But do these invisible stars exist?
513
00:33:11,294 --> 00:33:13,462
The evidence is thin, but..
514
00:33:13,464 --> 00:33:14,763
[tape rewinding]
515
00:33:14,765 --> 00:33:18,433
[narrator] Rewind back to th LIGO detection in 2019.
516
00:33:21,905 --> 00:33:25,173
The gravitational wave detector picked up the signa
517
00:33:25,175 --> 00:33:28,377
of two massive objects colliding.
518
00:33:28,946 --> 00:33:30,379
[pulsating explosion]
519
00:33:31,382 --> 00:33:34,983
We call the event GW190521.
520
00:33:34,985 --> 00:33:38,854
Most scientists agree this w a black hole collision.
521
00:33:38,856 --> 00:33:43,058
But could it have been clashing ghost stars?
522
00:33:43,794 --> 00:33:45,994
[Plait] If there are ghost stars out there
523
00:33:45,996 --> 00:33:47,729
and they can interact with
each other gravitationally,
524
00:33:47,731 --> 00:33:49,898
they may collide.
525
00:33:49,900 --> 00:33:51,833
And when they do,
they would emit
gravitational waves
526
00:33:51,869 --> 00:33:54,936
and it would look
a lot like
two black holes colliding.
527
00:33:54,938 --> 00:34:00,342
In fact, it would look
theoretically very much
like GW190521.
528
00:34:01,678 --> 00:34:04,346
[narrator] One collision, two explanations.
529
00:34:05,916 --> 00:34:09,384
Primordial black holes or ghost stars,
530
00:34:10,821 --> 00:34:13,488
LIGO can't tell them apart.
531
00:34:13,490 --> 00:34:18,994
Do these ideas bring us closer to proving the existence of dark matter
532
00:34:18,996 --> 00:34:25,133
Or are we just hurtling further down a weird physics rabbit hole
533
00:34:25,135 --> 00:34:29,571
[Chiara Mingarelli]
Primordial black holes, ghost stars, axions,
534
00:34:29,639 --> 00:34:32,140
this is all very
exotic physics.
535
00:34:32,176 --> 00:34:36,745
We can't take for granted
that any of this is real
or that it's not real.
536
00:34:36,747 --> 00:34:37,612
We just don't know.
537
00:34:37,614 --> 00:34:40,549
Dark matter is irritating.
538
00:34:40,551 --> 00:34:43,752
[groans] We know
it's out there.
We see its effects, right?
539
00:34:43,787 --> 00:34:48,924
But we can't see
the dark matter
and that's frustrating.
540
00:34:48,992 --> 00:34:51,893
And it's like a lot
of young fields in astronomy.
541
00:34:51,929 --> 00:34:56,264
We have way more ideas
than we do hard observations.
542
00:34:57,468 --> 00:35:00,402
[narrator] We have ideas, we have theories,
543
00:35:00,404 --> 00:35:05,440
but without direct observations, we just can't back them up with solid proo
544
00:35:06,844 --> 00:35:11,313
The more we look, the harder it is to find dark matter.
545
00:35:12,549 --> 00:35:16,818
Maybe it's primordial black holes from the early universe.
546
00:35:16,820 --> 00:35:22,290
Maybe it's a sea of particle that flow right through us every day.
547
00:35:22,626 --> 00:35:28,630
Or maybe it's gigantic, transparent ghost stars.
548
00:35:28,632 --> 00:35:34,202
Perhaps it's the combined ma of Santa's sleigh and the Easter Bunny's baske
549
00:35:34,204 --> 00:35:39,441
Or maybe all our physics is based on questionable mat
550
00:35:49,553 --> 00:35:54,856
[narrator] 85% of the stuff in the universe is missing in action.
551
00:35:54,858 --> 00:35:58,226
The search for this dark matter looks hopeless.
552
00:35:59,696 --> 00:36:03,064
This problem of dark matter
is really a tough one.
553
00:36:03,066 --> 00:36:04,165
Everything that
we've predicted
554
00:36:04,167 --> 00:36:07,169
and then gone and looked for,
we're not finding.
555
00:36:07,171 --> 00:36:09,704
It's starting to become
a huge embarrassment.
556
00:36:09,706 --> 00:36:11,907
Surely something
so fundamental
557
00:36:11,909 --> 00:36:13,808
to our cosmology
should be detectable.
558
00:36:13,810 --> 00:36:15,577
And yet, it remains elusive.
559
00:36:17,981 --> 00:36:22,584
[narrator] We're stumbling blindly around the limits of our understanding.
560
00:36:22,586 --> 00:36:26,288
As of right now, there are zero direct observations.
561
00:36:27,624 --> 00:36:31,059
Maybe dark matter doesn't exist after all.
562
00:36:31,061 --> 00:36:33,895
Instead of searching for an invisible substance
563
00:36:33,897 --> 00:36:36,765
affecting the universe with its gravity,
564
00:36:36,767 --> 00:36:41,736
maybe it's gravity we don't quite understand.
565
00:36:41,738 --> 00:36:45,941
If you're looking in a galaxy
and it's spinning
way too quickly,
566
00:36:45,943 --> 00:36:50,045
either there's a new
ingredient in the galaxy,
567
00:36:50,047 --> 00:36:52,581
like dark matter,
that holds it all together.
568
00:36:52,583 --> 00:36:56,818
Or you're misunderstanding
the laws of physics.
569
00:36:56,820 --> 00:36:58,720
[narrator] To describe the effects of gravity,
570
00:36:58,722 --> 00:37:04,326
we use the nearly 350-year-o math of Sir Isaac Newton.
571
00:37:05,929 --> 00:37:10,465
Maybe to explain the excess gravity we see in the universe,
572
00:37:10,467 --> 00:37:13,168
it's not extra matter we nee
573
00:37:13,470 --> 00:37:15,503
It's better math.
574
00:37:15,505 --> 00:37:17,606
Although we understand
very well how gravity works
575
00:37:17,608 --> 00:37:19,874
here on Earth
and in our Solar System,
576
00:37:19,876 --> 00:37:22,744
perhaps when you get up
to galactic scales,
577
00:37:22,746 --> 00:37:25,580
it actually behaves
just slightly differently.
578
00:37:25,582 --> 00:37:29,084
And if that were the case,
you can kind of
tweak that idea
579
00:37:29,086 --> 00:37:33,154
until it fits the data we see
of how galaxies
are spinning around
580
00:37:33,156 --> 00:37:36,024
without needing dark matter.
581
00:37:36,927 --> 00:37:38,393
[narrator] Questioning the math of a legend
582
00:37:38,395 --> 00:37:41,363
of physics might sound like sacrilege,
583
00:37:41,365 --> 00:37:45,600
but to solve the dark matter conundrum, it has been done.
584
00:37:45,602 --> 00:37:50,805
It's called Modified Newtonian Dynamics or MOND.
585
00:37:50,807 --> 00:37:56,311
Modeling galaxies with this math produces very different results.
586
00:37:57,748 --> 00:38:01,850
On its surface,
MOND is not a bad idea.
587
00:38:01,852 --> 00:38:04,753
In the same way that we would
normally program a computer
588
00:38:04,755 --> 00:38:07,589
to include dark matter
in our simulations,
589
00:38:07,591 --> 00:38:10,492
you can take that out,
and instead program it
590
00:38:10,494 --> 00:38:12,927
with a different law of gravity with MOND.
591
00:38:12,929 --> 00:38:16,831
And then, you can set up
a kind of spinning mass of gas
592
00:38:16,833 --> 00:38:19,567
and it does seem to be possible with MOND
593
00:38:19,569 --> 00:38:23,171
to get things settled down and look a bit like a real galaxy.
594
00:38:25,976 --> 00:38:29,477
[narrator] Changing the law of gravity accurately recreates
595
00:38:29,479 --> 00:38:34,015
the super-fast spin astronomers see through their telescopes.
596
00:38:34,017 --> 00:38:37,485
No need for dark matter. It doesn't exist.
597
00:38:37,921 --> 00:38:39,154
Case closed?
598
00:38:39,589 --> 00:38:40,889
Not by a long shot.
599
00:38:40,891 --> 00:38:43,458
With anything bigger than a galaxy,
600
00:38:43,460 --> 00:38:46,995
this artificial physics breaks down.
601
00:38:47,798 --> 00:38:50,999
MOND does really well
on galaxy scales,
602
00:38:51,001 --> 00:38:52,801
but when you zoom out
and you go to larger
603
00:38:52,803 --> 00:38:55,103
and larger structures
in our universe,
604
00:38:55,105 --> 00:38:59,174
like clusters of galaxies, big, big structure,
605
00:38:59,176 --> 00:39:03,278
you see that MOND by itself can't reproduce all of our observations.
606
00:39:03,280 --> 00:39:04,779
There's something missing.
607
00:39:04,781 --> 00:39:05,680
Dark matter.
608
00:39:05,949 --> 00:39:07,382
Dark matter,
dark matter, dark matter.
609
00:39:07,384 --> 00:39:09,017
Dark matter.
610
00:39:09,019 --> 00:39:13,355
In MOND, you still have
to invoke the existence
of material you can't see.
611
00:39:13,990 --> 00:39:15,657
[Andrew Pontzen]
It basically introduces
612
00:39:15,659 --> 00:39:17,859
some of its own dark matter as well,
613
00:39:17,861 --> 00:39:21,363
which kind of negates
the point of having MOND
in the first place.
614
00:39:24,434 --> 00:39:28,069
[narrator] MOND doesn't replace dark matter.
615
00:39:28,071 --> 00:39:31,940
The universe still needs something to hold it togethe
616
00:39:31,942 --> 00:39:33,842
We just don't know what it i
617
00:39:33,844 --> 00:39:37,245
But there are plenty of new ideas flying around.
618
00:39:38,515 --> 00:39:41,416
In my theory, the dark matter
is a super fluid.
619
00:39:42,853 --> 00:39:45,920
[narrator] It's a radical new theory of dark matter,
620
00:39:45,989 --> 00:39:48,790
particles not acting individually,
621
00:39:48,792 --> 00:39:54,028
but flowing as one invisibl mass around the galaxies.
622
00:39:54,731 --> 00:39:58,633
A super fluid is like
an ordinary fluid that flows,
623
00:39:58,635 --> 00:40:02,137
but in this case,
it flows without
any resistance or viscosity.
624
00:40:02,139 --> 00:40:05,440
If I pour honey, it will flow very slowly.
625
00:40:05,442 --> 00:40:06,741
It has high viscosity.
626
00:40:06,743 --> 00:40:10,745
A super fluid will just flo and never stop flowing.
627
00:40:10,747 --> 00:40:14,849
[narrator] As the super flui dark matter flows around the universe,
628
00:40:14,851 --> 00:40:21,122
eddies and waves form large enough to engulf entire galaxies.
629
00:40:21,124 --> 00:40:24,959
The gravity of the fluid holds the stars together.
630
00:40:25,996 --> 00:40:31,699
But like most theories on dark matter, there's no direct evidence.
631
00:40:31,701 --> 00:40:35,136
If these waves are on the size
of galaxies,
632
00:40:35,138 --> 00:40:39,774
then we have to find
detectors that can detect
those types of huge waves.
633
00:40:39,776 --> 00:40:41,976
They don't exist
at the moment.
634
00:40:42,913 --> 00:40:45,680
[narrator] Which brings us back to square one.
635
00:40:45,682 --> 00:40:48,616
We just can't prove that dark matter is real.
636
00:40:48,618 --> 00:40:51,719
Primordial black holes, ghost stars, WIMPs,
637
00:40:51,721 --> 00:40:55,990
a super fluid sloshing about the cosmos,
638
00:40:55,992 --> 00:40:59,060
or maybe we're just using the wrong math.
639
00:41:00,630 --> 00:41:02,864
What's your money on?
640
00:41:02,866 --> 00:41:07,368
If I had to wager $20
on what dark matter is.
641
00:41:07,704 --> 00:41:08,870
Hmm.
642
00:41:08,939 --> 00:41:12,707
I would never place money
on what dark matter is.
643
00:41:12,709 --> 00:41:14,442
I just think we have no idea.
644
00:41:15,178 --> 00:41:20,114
My money is on
dark matter itself is real,
645
00:41:20,116 --> 00:41:22,217
but it's not
the whole picture.
646
00:41:22,219 --> 00:41:26,254
I would say
left socks in dryers.
647
00:41:26,256 --> 00:41:30,725
I would say remote controls
that fall into sofa cushions
and disappear.
648
00:41:30,727 --> 00:41:32,093
I would love there to be
649
00:41:32,095 --> 00:41:35,797
dark matter,
ghost stars, planets,
even dark matter people.
650
00:41:35,799 --> 00:41:37,465
I'm going all black.
651
00:41:37,968 --> 00:41:43,037
I think no current
ideas are correct.
652
00:41:43,039 --> 00:41:47,342
I think dark matter
is something that
we haven't thought of yet.
653
00:41:48,979 --> 00:41:50,512
[narrator]
Does dark matter exist?
654
00:41:51,314 --> 00:41:52,947
Watch the space.
74109
Can't find what you're looking for?
Get subtitles in any language from opensubtitles.com, and translate them here.